61115352 (1981-82)
65105041 (1980-81)
FinalReport
RADIONUCLIDE AND HEAVY METAL DISTRIBUTIONIN
RECENT SEDIMENTS
OF MAJOR
STREAMSI N THE GRANTSMINERAL BELT, N.M.
C
d
l
l
&?.
Carl J . Popp
‘
New Mexico Institute of Mining and Technology
Department of Chemistry
Socorro, New Mexico 87801
and
John
W
. Hawley
I
David W . Love
New Mexico Bureau of Mines and Mineral Resources
Socorro, New Mexico 87801
to
Branch of Mining and Mineral I n s t i t u t e s
Division of Research
Office of Surface Mining
United States Department of the Interior
Washington, D.C. 20204
March,1983
TABLE OF CONTENTS
Item
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I
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LISTOFFIGURES
LISTOFTABLES
SUMMARY
INTRODUCTION
A . Research Objectives
B . General Approach
C Overviewof Study Area . . . . . . . . . . . . . . . . . .
D
Radiometric Dating of Sediments
1 General
2 . Pb-210dating
3 Cs-137dating
E . FactorsAffectingRadioisotope
Uptake by Sediments
1 Uptake as a function of grainsize
2
Uptake as a function of time
F Other Radionuclides
G TraceMetals
H Geologic Setting . . . . . . . . . . . . . . . . . . . .
1 Drainagebasin
2 Geomorphology of the Rio Puerco and tributaries
3 Bedrock geology
4 Sources of radionuclides and heavy metals i n the
drainage basin
5 . Possible reworking of sedimentswithinthe
drainage basin
6 Hydrology of the Rio Puerco and i t s t r i b u t a r i e s
METHODS AND PROCEDURES
A
Selection of Sample S i t e s
B Age of Samples
C
Surveying Procedures
D . Estimationof Bank-Full Discharge a t Ungaged Locations
E . Examination of Sediments and Sampling Procedures i n
the f i e l d . . . . . . . . . . . . . . . . . . . . . .
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Sample Handling i n the Laboratory
Determination o f Pb.210.,
Cs.137.
and Other
Radionuclide Activities
1
H . Trace Metal Analysis
I
Neutron ActivationAnalysis
J
Determination of RelativeProperties o f S i l t and Clay
K
X-Ray Diffraction o f the Clay-SizeFraction
RESULTS AND DISCUSSION
A . GeologicDescription o f Sample Locations
1 Rio Puerco
a S i t e s 1, l A , 2. 2A
b Sites3, 3A, 4. 5
c Sites 6, 7. 7A
d
S i t e s8 a n d 9
e SiteslOand11
2 . Rio San Jose
a S i t e SJ-1
b . S i t e SJ-5
c . SitePAG-1
B
Sample Characterization .Physical and MineralogicalAspects
C . Dating the Sediments using Pb.210,
Cs.137.
andPb-214
D Pb.210, Pb.214. and Cs-137 Activities
E Correlation of Pb.210, Pb.214. andCs-137 Activities
w i t h Grain Size
F . Correlation of Pb.210. Pb.224, andCs-137 Activities
w i t h depth
G
Pb-210 Dating
H . Cs-137 Dating
1 S i t e 1A-Rio Puerco
2 S i t e 2A-Rio Puerco
3 S i t e 3A-Rio Puerco
4 . S i t e 5 - R i O Puerco
F
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ii
103
Item
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S i t e 6-Rio Puerco . . . . . . . . . . . . . . . . . . . . . . 103
S i t e s 7 and 7A-Rio Puerco . . . . . . . . . . . . . . . . . . 103
S i t e 9-Rio Puerco
. . . . . . . . . . . . . . . . . 104
S i t e 1-Rio San Jose
. . . . . . . . . . . . . . . . .104
Paguate Reservoir
104
I
RadionuclideOistrituion
.
105
1 General
105
2 . Pb-210 . . . . . . . . . .
105
3 Ra-226.Th-234
. . . . . . . . . . . . . . . . . 113
4 Ac-228 . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
J . Trace Metal Distribution . .
113
1. Tracemetalsinpostand pre-1950 oxbow sediments
118
2 . Trace metals i n surfacesediments .230- fraction . . . . . . 118
3 . Tracemetalsinactive
channelsedimentcore
samples .
230- fraction . . . . . . . . . . . . . . . . . . . . . . .
121
SUMMARY AND CONCLUSIONS
123
REFERENCES
CITED
125
ACKNOWLEDGEMENT
130
APPENDIXES
A . Core and P i t Descriptions
B
Selected X-ray Diffraction Data
C
Radionuclide ActivitiesforIndividual
Samples .
pCi/g Dry Weight
0 . Profiles of Normalized Cs-137 Activities of Samples
from S i t e s 1-7
E Histograms of RadionuclideDistributionin
Core Samples
Activity E Depth i n Core See Appendix C f o r Numbers .
F Trace Metal ConcentrationsforIndividual
Samples .
ppm Dry Weight
G
Neutron ActivationAnalysis of Clays
5
6
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iii
LIST OF FIGURES
PEE
1. Locationof mines and mills o f the Grants Mineral Belt. gaging s t a t i o n s
2
3
4
5
6
7
8
9
10
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11
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20
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23
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and sample s i t e s i n the Rio Puerco drainagebasin ..................
The
U-238
decay scheme
Jackpile-Paguate uranium minecomplex in center of picture.
Rio
Paguate drainage and PaguateReservoir i n lower r i g h t
Geomorphic features of Rio . Puerco Arroyo and adjacent valley floor
i n reach downstreamfrom s i t e 5
Features of theinner channel a t s i t e 6
Processes o f meander formation
Map showing uranium mines and radioactive occurrences i n the Rio
Puerco drainagebasin. New Mexico (modified from McLemore. 1982)
Average monthly flow for water year fo r f i v e gaging s t a t i o n s i n
the Rio Puerco drainagebasin
Annual flow (wateryear)fortheperiodorrecordfor
5gaging
s t a t i o n s i n the Rio Puerco drainagebasin
Rise and f a l l of daily average flows for flood of September 11.14.
1972. from gaging s t a t i o n s along theRio'Puerco and Arroyo Chico
Number of floods larger than baseflow a t f i v e gaging s t a t i o n s i n
the Rio Puerco drainagebasin
Oxbow and arroyowalls a t s i t e 2
Aerial photographsof the area including sites
1 and 2 taken i n
1954 (A) and
1979
(B)
Cross-sectionof Rio Puerco Arroyo a t sample s i t e s 1A and 2A
Profileacrossinner
channel of Rio Puerco nearSite 1 A
Sample s i t e 2A i n oxbow f i l l
P i t exposinglaminated s i l t and clay i n oxbow a t s i t e 2A
Laminatedand structureless s i l t and clay i n upper 1.1 m of oxbow
d e p o s i t sa ts i t e 2A
Aerial photographsof t h e reachincluding s i t e s 3. 4 and 5 taken
i n 1935 (A) and
1954
(B)
Cross p r o f i l e o f Rio Puerco Arroyo a t S i t e s 3A and 5
Profileacrossinner
channel of Rio Puerco near s i t e 5
A . Sample s i t e 3A i n oxbowand edge of tributary fan
Cross-laminated f i n e sand i n upper partofpit
3A
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iv
34
35
53
54
55
56
57
58
59
51
62
63
64
67
24.
25.
26.
27
28.
29.
30.
31.
32.
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34.
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35.
36.
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39.
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41.
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43.
44.
45.
46.
47.
48.
49.
50.
51 .
52.
53.
54.
55 .
Oxbow at sites 6and 7 in 1935 (A) and in 1954 (6) ................. 68
Profile across Rio Puerco Arroyo at sites 6 ..................
and 7
69
.....6 70
Profile acrossthe inner channel of the Rio Puerco near site
Sedimentary structures of
a channel-marginal bar at site 6......... 72
73
Stratigraphy of pit at site ......................................
7
Confluence o f Rio Puerco and Arroyo Chicoin 1935 (A) and 1954 (6) . 7 5
Cross profile ofRio Puerco Arroyoin vicinity of site9 ........... 76
Profiles across the inner channelthe
ofRio Puerco near site ....
9
77
Sample pit in oxbow at site9 ......................................
79
Cross profile of Arroyo Chico near sample sites
10 and 11
81
including site SJ-1in 1935 (A)
Aerial photographs showing the area
and 1954. (6) .......................................................
82
Profile across inner channel Rio
of San Jose near site SJ-1
84
Aerial photographs of the area including sample sitesandSJ-5
PAG-1 in 1935 (A) and 1954 (B)
85
Stratigraphy exposed in pit SJ-5 ...................................
87
Pb-2107Pb-214 activity ratios
in surface clay samples .............. 91
Pb-210/Pb-214 activity ratios
in surface sand and si1
t samples ..... 93
Cs-137 activityin surface clay samples
94
Cs-137 activityin surface sand and silt samples ................... 95
Cs-137 activity as a functiondepth.
of
. site 7.....................
99
Cs-137 activity as
a function ofdepth.. site 9
100
Cs-137 activity as
a function o f depth.. Paguate ....................
101
Pb-210 activity aasfunction ofdepth.. site 2. Rio Puerco 1 .... 106
Pb-210 activity as a function
depth..of site 3. Rio Puerco
......... 107
Pb-210 activity aasfunction ofdepth.. site 7, Rio Puerco......... 108
Pb-210 activity as a function
o f depth.. site 7A, Rio Puerco
109
Pb-210 activity as
a function ofdepth.. site 9, Rio Puerco......... 110
Pb-210 activity as
a function ofdepth.. site 1. Rio San Jose....... 111
Pb-210 activity as a function
depth.. ofPaguate Reservoir.......... 112
Ac-228 activity as
a function ofdepth.. Paguate Reservoir.......... 114
Ac-228 activity as
a function ofdepth.. site 2, Rio Puerco
115
Ac-228 activity as a function
depth..of site 7, Rio Puerco......... 116
Ac-228 activity as a function
depth..of site 1, Rio San Jose
....... 117
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V
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LIST OF TABLES
Table #
1
Item
.
Percentages of geologic units exposed in the
Rio Puerco drainage basin
Bank-full discharge
S e n s i t i v i t i e s for tracemetals
S i t e #'s/UTM coordinates
Normalization factor used i n Cs-137 dating
Tracemetals i n 230- ( < 6 3 ~ oxbow
)
coresediments
Pre- and post-1950 comparison
Tracemetals i n 230- (<63p)surfacesediments a t
oxbow s i t e s and Paguate Reservoir
Tracemetals i n active channel coresediments.
230- fraction
. . . . . . . . . . . . . . . . . 18
. . . . . . . . . . . . . . . . . . . . . 42
. . . . . . . . . . . . . . . 46
. . . . . . . . . . . . . . . . . . 52
. . . . . . . . . 96
7
a
.
. . . . . . . . . . . . . . .119
. . . . . . . . . . . . .120
. . . . . . . . . . . . . . . . . . . . . . . 122
vi
.
SUMMARY
In the absence of h i s t o r i c geochemical baseline data for
the Grants Mineral
Belt, environmentalchanges resulting from uranium mine-mill a c t i v i t i e s can only
be determined by indirect methods. A methodology f o r determining the ageof
recentsediments i n streamsdraining the regionhas been established based on
combined geomorphic, stratigraphic, and radiometric d a t i n g techniques. Because
clay-richsedimentsretainpossibleradionuclides
and heavy metalsderived from
mineralization and mined sources, sample sites which containfine-graineddeposits
t h a t b o t h predate and postdate mine-mill a c t i v i t y were located i n abandonedchannelsegments (oxbows) of major streamsdraining the easternGrants Mineral
Belt.Aerialphotographs
(and derivative maps) taken between 1935 and 1971
provided the historical and geomorphic
documentation of approximatedates o f
.
oxbow formation and a j e s of a l l u v i a l f i l l s i n the abandoned-channelsegments.
Pits were dug a t these oxbow sites t o determine stratigraphy and composition
of the deposits. Samples collected from p i t walls and auger'holes below the
p i t s were subjected t o radiometric analysis by gamma ray spectrometry f o r the
artifical radionuclide Cs-137and thenatural radionuclide Pb-210 as well as
other U-238 and Th-232 daughters. Because of the dynamic nature of the system,
absolute dating w i t h Cs-137 was not possible b u t samples could be dated as
either pre- or post-1950. The 1950 date i s importantbecause i t marked the
b e g i n n i n g of the uranium a c t i v i t y i n the region. The Pb-210 dating was n o t
possible because background Pb-210was very h i g h r e l a t i v e t o f a l l o u t Pb-210.
I t maybe possible to separate effects of uranium mining and m i l l i n g a c t i v i t y
by comparing U-238 daughteraccumulation to daughters in the Th-232 series.
Sediments dated by the correlative Cs-137, stratigraphic, and h i s t o r i c
techniques were thenanalyzed for radionuclides and trace metals whichwould
be associated w i t h uranium ores. The U-238 daughtersaregenerally high i n .
the region and l i t t l e difference was observed for their values between the
control s i t e and the sites in the uranium mining and millingregion except f o r
the PaguateReservoir s i t e . Recent sediments a t Paguate clearly show elevated
levels of U-238 daughters i n sediments unambiguously dated a f t e r the mid 1950's.
Sediments from the Jackpile uranium mine have been trapped i n the r e s e r v o i r f i l l .
Tracemetals were also analyzedin o l d and more recentsediments and As,
Se, Cd, Hg, and U show elevatedvalues on a regional basis b u t no correlation
w i t h age (i.e.pre-orpost-1950).
These elevatedtrace metal values may
simply be due t o their association w i t h the regionally mineralized material.
vi i
I.
INTRODUCTION
Research Objectives
has been t o determine
The major objective of thisresearchproposal
the extent t o which active uranium mining and milling operations i n the
Grants Mineral Belt of west-central New Mexico may be contributingexcess
tracemetals and radionuclides t o Rio Puerco and Rio San Josesediments.
Historicalbaselinedataforthe
regi'on i s n o t available. The Rio Puerco
andRio San Jose are ephemeral and intermittentstreams which drain the
active uranium mining areaeast of theContinentalDivide.Episodic
major
floods deliver large quantities
of sedimentsderived from the region of
uranium mineralization and mine-mill a c t i v i t y downstream to the BernardoElephantButtereach
of the Rio Grande. Sediment deliveryis very e f f i c i e n t
because flood flows are largely transmitted
through a regional systemof
channelsconfinedinarroyo-typevalleys.Availablehistoricaldata
on
Puerco-San Jose channel behaviorpermitsidentification
and sampling of
streamsediments t h a t b o t h predate and postdate onset of uranium mine-mill
operations which began about 1950 (Perkins1979).
In ordertodetermine
trace metal and radionuclide contributions from the uranium industry d u r i n g
the past thirty years, the processes
of sediment transport and the age of
sediments tested must be established.Therefore,subsidiaryobjectives
of
t h i s proposalinclude (1) determination of the modes ofsediment movements
in the San Jose-Rio Puerco drainagesystems and ( 2 ) determination of the
age o f depositsalong and adjacent to the modern drainagechannels.
Comparison of sedimentsdeposited w i t h i n thepast 30 years (1950-1980) with
e a r l i e r sediments from the same areawillestablish
man-induced contributions to sediments and willprovide long-term baselinedata on behavior of
the affected drainage system.
A.
B.
General Approach
Figure 1 shows thestudy area, including the Rio Puerco-Rio San Jose
watershed of thewest-central Rio Grande basin and relationships between
major streams and uranium mine-mill a c t i v i t y . Procedures used t o determine
theprocesses ofsediment transport and deposition,theages
of the sediments, and the tracemetal-radionuclidecontent
of thesedimentsinclude
-. Streoms draining oreas of uronium mine-mill
uranium mines in Morrison Formation
:-.
....., M a j o rwith
iorgc numberotmojorminer
........: Area
Uranium mi115 iapsroting and pionnod)
8
7,,
operotion,
See C h w m o n a n d Others (19791 for details on mine-mill activity
and w o i o g i c setting
Goging s t d i m
Somple site
Figure 1. Location o f mines and mills o f the Grants Mineral
Belt,gagingstations,
and sample s i t e s i n the Rio
Puerco drainage basin.
?
the followingcategories:
geomorphic evaluation of the fluvial transport and depositional
system from the uranium mines and mills in the headwatersthrough
the Rio San Jose-Rio Puerco drainagesystems, and evaluation of
loci of sediment depositionalongthedrainages;
historical documentation o f loci of depositiontoaidindetermining the age o f sediments;
f i e l d sampling and sediment characterizationalongthe
drainages;
laboratory characterization of grain size and grain mineralogy
of sediment samples;
laboratory determination of trace metals and radionuclide concent r a t i o n s i n sediments; and
laboratorydetermination of ages of sedimentsusingradioactive
Cesium-137 (Cs-137) and Lead-210 (Pb-210).
Categories ( 2 ) and ( 6 ) should corroborate each other i n establishingthe
age o f a particular sediment layer.
Overview ofStudy Area
Since 1948, New Mexico has supplied more than 40% of the nation's
uranium production, 99.8% ofwhich came from the Grants Mineral Belt
(Rautnan 1977). I t i s estimated t h a t New Mexico has 52% of the United
States reserves of U308 a t $ 50 per pound and 16% of the world's reserves
excluding Chinaand the U.S.S.R. (Perkins1979).
As of 1978, there were
35 active uranium mines inthe Grants Mineral Belt, as well as five mills
capable (by1977) of h a n d l i n g about 21,000 tons o f ore per day. Until
recently activity i n the area was increasingrapidly;nine
more mines
a r e under development (Perkins1979),
and a largemilltohandle
Gulf
Mineral Corporation's Mt. Taylor mine i s intheplanningstage
(Rautman
1977). The locations of a number of t h e s e f a c i l i t i e s are shown i n Figure 1.
In order t o assess the impactof mining operationsin the area, i t i s
important t o determine both the present and the past condition of the
r i v e r sediments.
A growing population attracted primarily
by the mining a c t i v i t y i s
located along the Rio San Jose from the Grantsarea t o Laguna (seeFigure 11,
with the bulk of thehabitationin
the streamvalley; i t i s important t o
C.
3
ensurethesafety
of t h i s population as well as the localIndianpopulation.
Also, the sediments from the San Jose enter the RioGrande system through
the Rio Puerco and areeventuallydepositedinElephant
Butte Reservoir.
I t has been estimated that the Rio Puerco contributes more t h a n 50% of
the sedimentload t o the RioGrande incentral New Mexico whilecarrying
l e s s than 16% of thewater(Waite
e t a l . 1972;'Popp and Laquer 1980).
Excess metalsassociatedwith
the sediments may be mobilizedinthereservoir due t o biological activity and theresultinganaerobicconditions
occurring on thereservoir bottom. Surface waters inthe RioSan Jose
show higher amounts of uranium, vanadium, molybdenum,and other trace
metals t h a n waters such as the Rio Grande (Brandvold e t a1 1981).
I t i s imperative t h a t regulatoryagencies such a s the New Mexico
Environmental Improvement Division have data of this nature f o r t h e i r
pond
assessments and evaluations. The impact of therecenttailings
s p i l l a t the United Nuclearmillnear
Churchrock, N.M. (July 1979) on
thewesternslope
may never be known because baselinedata of t h i s type
are not available.
.
D.
Radiometric Dating of the Sediments
1. General
Threetypes of radioactive isotopes are present in
the environment:
those of primordial,cosmic-ray,
and a r t i f i c i a lo r i g i n s .
Although those
of primordial origin are by f a r the most widely used inradiometricdating,
methods based on all three types
of radionuclidesarepresently
employed.
Examplesof d a t i n g methods based on primordialradionuclides, or on
the decay products of thesenuclides,include
K-Ar, U-Th, and Pb-210
dating. These methods, as well as methods usingisotopes of cosmic-ray
origin, are based on changesin the isotopic composition of the sample
with time. Such changes will begin tooccur, as a r e s u l t of radioactive
decay, once the sample i s closedto the nuclide(s)inquestion.
The time
elapsedsincethisevent
can then be determined from the i n i t i a l and final
isotopiccompositions.
Isotopes of a r t i f i c i a l o r i g i n , such a s Cs-137, Co-60, and Mn-54 have
also been used inradiometricdating.
In contrast t o theprevious methods,
4
however, most methods of this typeare based on the irregular rate
of
influx of theseisotopes, or on t h e i r absenceintheenvironmentbefore
1945 (Krishnaswami and La1 1978).
The use of radionuclideswithrelatively
short half-lives, such as
Pb-210andCs-137,
t o daterecentsediments
such asthoseinthisstudy
and establishanthropogenicinputs
of metals i s now well-established.
Thissubjecthas
been reviewed by Krishnaswamiand La1 (1978).
Robbins and Edgington (1975) .
have used b o t h Pb-210 and
Cs-137
t o establishanthropogenicinputs
of lead from coal and gasoline use t o
Lake Michigan sediments. Bennington (1978) has used Pb-210 t o determine
Long Island Sound, andSmithand
Wal t o n (1980) have used
lead fluxes in
Cs-137, as well aspollenassemblages,
t o determinethesedimentation
ratein a fjordinQuebec.Determination
of Pb-210 by d i r e c t gamma ray
spectrometry, by f a r the simplest method (and the method used in this
study)has been discussed by GXggeler e t a l . (1976) and Schery(1980).
A major concern indatingthesesedimentswill
be problems of mixing
and redeposition which may affect the distribution
of theradionuclides.
This i s due t o the dynamic nature of this system as opposed t o the normal
application t o areas such as lakes and estuaries which have a well-behaved
depositionalpattern.
Pb-210 d a t i n g
Pb-210 i s a naturally occurring isotope w i t h a h a l f - l i f e of approximately22.3years(Lederer1967).
Along with Ra-226, Rn-222, Pb-214,
and a number of otherisotopes, i t i s an intermediate i n the U-238 decay
series(seeFigure
2).
Because radon i s a gas a t room temperature, a fraction of the Rn-222
produced by the decay of Ra-226 i n the crust diffuses into the
atomosphere,
where i t i n turn decays (via a s e r i e s of very short-livedintermediates)
t o Pb-210. This isotope i s then removed from the atomosphere (over a
period of severaldays) by both wet and dry precipitation (Krishnaswami
Pb-210 i s verystrongly bound by sediments,virtually
and La1 1978).Since
a l l of this influxwill be trapped by the surfacelayer of the soil or
sediment.
2.
5
1
8.0 x 104 y
Rn
m
3.82 d
/
218 Po
218 At
85
2
4 /&
Po
S.l
3.05 m
214
83
214
Pb
82
1 4-f
210 T1
81
Figure 2.
The U-238 Decay Scheme.
138.4 d
206 Pb
82
In a d d i t i o n , a certain amount of Pb-210 i s being constantly
produced withinthe sediment i t s e l f by the decay of other nuclides
in the U-238 decay series. This Pb-210, termed supported Pb-210, will
be inradioactiveequilibriumwith
i t s precursors so long as the system
remains closed w i t h respect t o a l l of thespeciesinvolved(Jenne
and
Wahl berg 1968).
The a c t i v i t y of the supported Pb-210 in a sample may thus be determined directly by measuring the activity of Pb-214 or any other isotope i n
the decay series with which thesupported Pb-210 i s i n radioactive equilibrium. (Alternately, i t may beassumed t o be equal t o theactivity of a
similar b u t older sample,in which the unsupported Pb-210 has decayed
away). From theactivity of thesupported Pb-210and
the total Pb-210
a c t i v i t y , the unsupported (atmospheric) Pb-210canbe
calculated(Krishnaswami and La1 1978).
Sincethe i n f l u x of atmospheric Pb-210 t o the surface layer will
essentially end once t h i s l a y e r i s covered by additionalsediment,the
a c t i v i t y of unsupported Pb-210 in the layer will thereafter decline
exponentially with time. The age of thesediment - o r , more correctly,the
time since i t s burial
can therefore be calculatedusingtheradioactive
decay equation, A ( t ) = A(0)exp(-0.693 t/t+),where A(0) and A ( t ) are the
a c t i v i t i e s of thenuclide a t time zero and a t time t , respectively. In
many cases, the valueof A(0) canbe taken t o be equal t o thepresent
a c t i v i t y of unsupported Pb-210 a t the surface of the sediment (Krishnaswami
and La1 1978).
This method has been used i n recent years t o date a number of sediment
samples (as well asvarious non-sediment samples) u p t o 100 yearsinage.
The maximum age is limited by the initial concentration of Pb-210, by the
counting s t a t i s t i c s , and by the ratio of supported t o unsupported Pb-210.
I-
3.
Cs-137 dating
Cs-137 i s an artificial radioisotope formed by nuclear fission, and
has a h a l f - l i f e of approximately30.0years(Lederer1967).
I t has been
introducedintotheatmosphere,
i n irregularlyvarying amounts, since
aboveground nucleartesting began in 1945 (Krishnaswami and La1 1978;
Durham and Jashi1980).
7
As is the case with Pb-210, Cs-137 is strongly bound by sediments.
I t willtherefore become trapped by the uppermost layer of the sediment,
and as this layer is buried
by succeedingones, a sequence of sediment
layers having the same irregular variations i n Cs-137 concentrationwill
be b u i l t up. This should be t r u e , as pointed o u t by Ritchie, even inareas
where sheet or gullyerosionprocesses predominate (Alberts et al. 1979).
Dating of thesediment i s thuspossible by determination of the Cs-137
concentrationin each intervalinthe
sedimentsequence, and by correlaconcentrations w i t h the pattern of
tion of the resulting pattern ofCs-137
atmosphericlevelssince
1945 (Krishnaswami and La1 1978). The concentrat i o n ofCs-137 inthe atmosphere peaked sharply ( a t l e v e l s more than an
order o f magnitude higherthaninpreviousyears)in
1958-1959and 19621963,with a further peak in 1971 (Wise 1980).
As a r e s u l t , i t i s on these intervals, and on t h e f i r s t appearance of
detectable amounts of Cs-137 in the late 1940's
or early 1950's that a
correlation i s generally based.
This method has also beenused t o date a variety of sediment and
non-sedimentsamples.
Unlike Pb-210 dating, however, t h i s method generally
requires the analysis o f considerableportions o f thesedimentaryrecord,
and n o t merely individual samples. Only limiteddating may be possible,
therefore,inthosecases
where critical portions of thesedimentaryrecord
a r e n o t preserved.
E.
FactorsAffectingRadioisotope
Uptake by Sediments
Uptake a s a function of grainsize
I t has been shown by a number of authors t h a t Pb-210, (Robbins and
Edgington 1975; Goldberg e t a l . 1978) Cs-137 (Smith andWalton 1981;
Edgington and Robbins 1975) and various other radionuclides are significantly
enriched in the finest size fractions
a finding which i s inagreement w i t h
the greater surface area, cation
exchange capacity, and hydrous metal oxide
and organiccontents of thesefractions.
As a r e s u l t , the a c t i v i t i e s of
b o t h Pb-210 and Cs-137 may be significantly affected by the s i l t and clay
content o f the samples.
1.
-
8
Suchan e f f e c t (which has generally n o t been s i g n i f i c a n t a t s i t e s
chosen inpreviousstudies)
may be corrected for i n a variety of ways.
First, the concentration of stable lead or cesium adsorbed by each sample
can be determined, and the a c t i v i t i e s of the Pb-210 or Cs-137 normalized
t o thesevalues.Thisapproach,
however, i s based on the assumption t h a t
nearly all of theelementinquestion
i s presentasions
adsorbed o n t o
the surface of the particles, and not trappedwithinthe
framework of the
s i l i c a t e or metal oxide structures. Such an assumption,although i t may
be warranted f o r cesium on account of i t s large ionic radius, is
probably
not true for lead, which i s scavenged by the hydrousmetal oxide phase
(Lewis 1977).(Inaddition,
a portion of the leadwill be of anthropogenic
origin, and will n o t have been added a t a constant rate).
Alternately,several samples of identical age
such assurface samples
canbe analyzed f o r Pb-210 or 13-137, andan attempt made t o determine
an empiricalcorrelation between the a c t i v i t y of the isotope and the percentages of the different size fractions. Thisempirical
relationship can
then be used t o normalize the Pb-210 or Cs-137 a c t i v i t i e s of the remaining
samples.
Finally, samples canbe chosen which are a l l of similar lithology, or
whichcanbe
mechanicallyseparated t o remove certain of the size fractions.
Coarser sand f r a c t i o n s , f o r example,could be removed by passing the sample
through a screen or sieve o f appropriate size, while s i l t and claycould
beremoved manually if i t i s present as discrete, cohesive layers.
-
-
Uptake as a function of time
Although the annual flux of Pb-210 t o sedimentshas been shown t o remain
relatively constant from year to year, (Benninger1978; Krishnaswamiand La1
1978) the same i s n o t necessarily true over shorterperiods of time. The
atmosphericconcentrations of b o t h Pb-210 (Peirson e t a l , 1966) andCs-137
(Burton and Stewart1960) i n f a c t , have been shown t o fluctuate a t some
s i t e s by nearly an order of magnitude overperiods of severaldays, and also
from season t o season. Such behavior i s indeednotsurprising,asweather
conditions will clearly affect
the transport of nuclides such as Rn-222,
Pb-210,andCs-137
w i t h i n the atmosphere, a s well as the emanationof radon
from crust. By scavenging locallyavailable Pb-210 and Cs-137, rainfall
2.
9
can also be expected t o causetemporarilyincreased(andlaterdecreased)
fluxes of b o t h of theseisotopes (Krishnaswami and La1 1978).
As mentioned by Krishnaswami, t h i s e f f e c t has n o t been significant
in most previous studies because deposition has been continuous and individual samples have typically represented a year or more of such deposition.
In contrast, most samples i n the presentstudyappeartorepresentsingle
brief episodes of sediment deposition, probably lasting a few days t o a t
most a few weeks. I t seems inevitable,therefore,that
some of these
irregular variations will
be preservedinthefinalpattern
of Pb-210 and
Cs-137 a c t i v i t i e s of the samplesin this study.
Nevertheless, i t should be recognized t h a t drydeposition of these
isotopes willgenerallycontinue
even a f t e r sediment deposition has ceased.
Sincedryratherthan
wet deposition may i n f a c t be the major source of these
isotopesinaridareas(Turekian
e t a l . 1977)considerablysmaller random
variations i n a c t i v i t y may thereforeresult.
For the same reason, any
variations in Pb-210 and Cs-137 uptake due t o the differing lengths of
time which the samples spend i n contactwiththewater
d u r i n g deposition
(Smith andWalton 1980) will also be p a r t i a l l y masked.
Other Radionuclides
Iwaddition t o Pb-210andCs-137
which can be used for radiometric
d a t i n g , other radionuclides such a s Th-234,Ra-226,Pb-214,
and Bi-214
(as well as Pb-210) from the U-238 decay s e r i e s (see Figure 1) may be
mobilizedin uranium m i n i n g and milling activities.
The a c t i v i t i e s o f these
radionuclides should, ingeneral,parallel
the uranium concentrations i n
sediments. One
way of separatinggeneralradioactivity
from the uraniumrelated radioactivity i s t o examine isotopesinthe
Th-232 decay series.
Suchan isotope i n the Th-232 s e r i e s i s Ac-228 so i t i s possible t o compare
r e l a t i v e a c t i v i t i e s of Ac-228 and the U-238 daughters to attempt t o s o r t
o u t m i n i n g and milling contributions.
F.
Trace
Metals
A number of trace metals such a s As, Se, Mo, and V are often found
associated with uranium ores and may be mobilizedduring ore processing.
Such metals are often found in high concentrationsinmilltailingsin
G.
10
the Grantsarea(Gallaher
and Goad 1981) and depending on transport mechanism,
may accompany uranium and i t s daughtersinstreamwaters
and sediments.
Previous work by Brandvold e t a1 (1981) and Popp e t a l . (1981) inthe Rio
Puerco and Rio San Joseindicated Mo and V values were elevated in filtered
water from the Rio Puerco r e l a t i v e t o the Rio Grande. Also, suspended
sediments i n the Rio San Jose carried greater concentrations
of As, Cd,
Co, Hg, Mo, U, V , and Zn than found i n the Rio Puerco and Rio Grande.
H.
Geologic Setting
1. Drainagebasin characteristics
The Rio Puerco drainagebasin i s more than 200 km long, encompassing
approximately 18,892 km 2 A l t h o u g h most of thedrainagebasin
i s l e s s than
2,000 m above sea level, the headwaters l i e inthe Nacimiento Mountains
(up t o 3,176 m ) , the Z u n i Mountains (2,821 m ) , and Mount Taylor (3,345 m )
(seeFigure 1 ) . Two major subbasinsdrain the Grants Mineral Belt, Rio
San Jose, and Arroyo Chico. Smallerdrainages from the Marquez areadrain
the easternmostpart of the mineralizedbelt.
A particularlyimportant
'tributary t o Rio San Jose i s Rio Paguate, which is bisected by the extensive
open p i t and waste p i l e s of the Jackpile-Paguate uranium minecomplex
(see Figure 3 ) .
The drainage basin straddles. the boundaries between the Colorado
Plateau, Southern Rocky Mountains and Basin andRange physiographic provinces. The upper portions of the drainagebasinareunderlain
by thick
semi-consolidateddepositsinthe
Albuquerque structuralbasin.
.
Geomorphologyof the Rio Puerco and t r i b u t a r i e s
The landscapealong the Rio Puerco and i t s tributaries i s q u i t e
diverse.Pertinent
t o t h i s studyarethegeneralfeatures
of the stream
valleys. The valleysconsist o f (1) theslopingvalleymargins,
commonly
cut i n bedrock or insemiconsolidatedbasin
fill(seegeology),
( 2 ) the
valleyfloor,underlain
by thickalluvialdeposits,
and ( 3 ) the incised
axial stream channel (arroyo) and related features.
The valley side slopes are dissected
by tributaries which transport
sediment from the slopes t o the valleyfloor.
Some tributariesdeposit
sedimentinalluvialfansalongthemargins
of thevalleyfloor.
Others
2.
11
Figure 3 .
J a c k p i l e - P a g u a t eu r a n i u m
mine complex i n c e n t e r
o f p i c t u r e , R i oP a g u a t ed r a - i n a g ea n dP a a u a t e
R e s e r v o i r i n lower r i g h t .
P h o t o g r a p h by J.W.
Hawley, 1 9 7 7 .
12
have become integrated w i t h thearroyo system and contribute sediment t o
the axialstreamchannel.
The v a l l e y f l o o r i s r e l a t i v e l y f l a t , c o n s i s t i n g
ofsediment layers
when i t was notentrenched, and
b u i l t u p by flooding from theaxialstream
by deposition from the toes of alluvial fans alongthevalley
margins.
Valley floors presently are
undergoingerosion by l a t e r a l and vertical
cutting of surfacestreams(axialarroyos
and dendritic tributary arroyos)
and subsurfacetributariesinpipes(naturalcave-likepassages
through clayrichsediments).
Rio Puerco and major t r i b u t a r i e s have developed d i s t i n c t i v e geomorphic
features w i t h i n t h e i r confinedarroyowalls.
Rio Puerco Arroyo ranges from
145 t o 245 m widebetween walls 8 t o 13 m highinstudiedreaches.
Geomorphic features within and adjacent t o Rio Puerco Arroyo (seeFigure 4)
include ( A ) the inner channel, ( B ) pointbars a l o n g thechannel, (C) an
inner floodplain which may include oxbows, (D) w i t h sand plugs, ( E ) where
the channelhas been c u t o f f , ( F ) erosional and depositionalterraces above
the innerfloodplain, ( G ) verticalarroyowalls,
( H ) remnants of v a l l e y f i l l
w i t h i n the arroyo, ( I ) gently- t o steeply-sloping eroded slopes, ( J ) the
mouths and alluvialfans of soil pipes and t r i b u t a r i e s , and ( K ) uneroded
valley floor.
According t o Love e t a l . (1933), the pattern of the inner channel of
Rio Puerco Arroyo consists ofcomplex meanders, straight reaches, and
gentlearcuatereaches.
Some meanders areveryelongate,
b u t overall
sinuosity i s about 1 . 5 ( r a t i o of .stream length/straight line distance).
Geomorphological -sedimentologicalfeatures of theinner channel and
inner floodplain commonly include sand bars and ripple-markedsurfaces
along the f l o o r of the inner channel, slightly finer-grained
sand bars
along the margins of the inner channel (seeFigure 5 ) , naturalleveesalong
the outer margins of the inner channel, a relatively flat floodplain, and
coppicedunes.
Chutes across p o i n t bars or parallel t o the inner channel
produce r e l i e f on the innerfloodplain.Locally,adjacenttotheinner
channel, i s a subhorizontal zone where sheetflowoccursduringlargefloods
(Shepherd 1976). Tamarisks commonly arethe dominant vegetation, a1 though
willows and cottonwoods a r e common locally. In broad reaches of thearroyo,
tamarisksdieout away from the margins of the inner channel and chamisa
... .
Figure 4.
G e o m o r p h i cf e a t u r e so f
R i o PuercoArroyoand
a d j a c e n t * v a l l e y f l o o r i n reachdownstreamfrom
s i t e 5 . L e t t e r as r e x p l a i n e d
i n t e x tP. h o t o g r a p h
by K . Novo-Gradacand- A . G u t i e r r e z , J u n e , 1 9 8 2 .
14
Figure 5.
F e a t u r e s o f t h e i n n e r c h a n n e la ts i t e
by D . W . L o v e ,A p r i l ,1 9 8 1 .
15
6.
Photograph
and four-winged saltbrush dominate.
Sedimentsaccumulatealong
modern streamsinseveraldepositional
the
environments. Sediments aredeposited i n channel-marginalbars,along
margins of p o i n t bars,in low areasalongtheinnerfloodplain,
and in
cut-offchannels
(oxbows). Oxbows arelikely t o accumulate thethickest
and most fine-grained deposits, so they were sought for study.
Channel meanders can be cut off t o form oxbowsby two mechanisms.
One mechanism occurs as meanders shift l a t e r a l l y downstream, when one
meander l o o p overtakes the meander loop downstream, causing neck cutoff
(seeFigure 6A). Other meanders are cut off by formation of a secondary
channel across the enclosedpointbar,
forming a chutecutoff(see
Figure 66)
Once a meander loophas been c u t o f f , new channelmarginal sand barscalled
"sandplugs"buildacrossthe
mouths of the abandoned meander loop and the
resulting oxbow begins t o receivefine-grained overbank sediments when
floodsovertop the sand plugs or adjacentfloodplain.
As oxbows f i l l , they
become stable parts of the inner floodplain and receive less sediment a s
theyreachthetopographiclevel
of thefloodplain.
The f i l l i n g process
may take 15 t o 30 years i n the Rio Puerco.
Topographically above and adjacent t o the modern inner floodplain are
localerosionaland/ordepositionalterrace.s
a t one or more 1 eve1 s. Oepositional terraces retain the arcuate form and deposits of abandoned
channel and floodplain. (see Figure 4H). Other terracesare eroded scarps
and benches withoutdepositionalfeatures.Eolian
sand commonly covers the
surface of the terraces.
Tributaries commonly have steeper gradients and have l e s s well
developedchannel and innerfloodplainfeaturesthanthe
Rio Puerco.
Bedrock geology
The drainagebasin i s underlain by a variety of rocks and l e s s consolidated deposits (Table 1). Point-counts of 212 township and range l i n e
intersections i n the drainagebasin on the geologic map of New Mexico (Dane
and Bachman 1965), were used t o estimate the relative proportions of rocks
exposed. About 6 percent o f thedrainagebasin
has exposures of l a t e
Tertiary and Quaternaryunconsolidated t o semiconsolidatedsediments
3.
16
$
$
neck-
oxbow
B
A
Figure 6.
Oxbow$
P r o c e s s e s o f oxbow f o r m a t i o n , A . Neck c u t o f f
hy
meander
migration
downstream.
B.
C h u t ce u t o f f
b y s e c o n d a r yc h a n n e ld e v e l o p m e n ta c r o s sp o i n tb a r .
17
Unit
Thick Quaternarysediments (8 percent Holocene f i l l )
Upper Tertiary and Quaternarybasin f i l l
Upper Tertiary and Quaternary volcanics
Lowerand Middle Tertiarysediments and
volcaniclastics
Cretaceoussandstones,shale,
and mudstones
Jurassicsandstone, mudstone, limestone, and gypsum
Triassic mudstone and sandstone
Upper Paleozoic 1 imestone, mudstone, sandstone
Precambrian igneous and metamorphic rocks
Total
Table 1. Percentages of geologicunits
Rio Puerco drainagebasin.
Percent
9.4
6.1
17.0
6.6
40.6
4.7
5.7
7.5
2.4
100.0
exposed inthe
depositedwhile the Rio Puerco drainagebasin was developing. These
sediments are derived from sources which continue t o contribute sediments
t o the drainage. Thus, sediments reworked from relatively young basin
fill are similar to
sedimentspresently being shed from the headwater
areas. Another 8 percent of thedrainagebasin
i s underlain by thick
Holocene alluvium w i t h characteristics similar to 20th centuryalluvium.
About 17 percent of the drainagebasin i s underlain by Tertiary and
Quaternaryvolcanicrocks,primarilybasaltflows,
which c o n t r i b u t e l i t t l e
runoff or sediment topresentstreams.
Nearly 18 percent o f thedrainage
basin i s underlain by Paleozic t o Jurassicsandstone,limestone
and shale,
includingabout 3 percent T o d i l t o Limestone and MorrisonFormation, the
two major uranium host rocks of the Grants Mineral Belt (the amount of
mineralizedrocks a t the surface is estimated t o be much smaller than 1
percent of thedrainagebasinarea).
More than 6 percent of the rocks a r e
Chinle Formation .and Abo Formation,major contributors of red clays to the
basin f i l l and t o modern sediments. About40 percent of the drainagebasin
i s underlain by Cretaceoussandstones and shales. These relativelyerodable
rocks have as much as 600 m of r e l i e f and a r e major contributors of sediment
in modern channels and invalley f i l l s . Precambrian c r y s t a l l i n e and
18
metamorphic rocksaccount for about 2 percent of exposuresinthedrainage
basin, b u t c l a s t s of these hardrocks a r e common inbasin f i l l and younger
alluvium.
4.
,
Sources of radionuclides and heavy metals i n thedrainagebasin
As previouslymentioned,the
major surfaceoccurrence ofuranium-bearing
of the Jurassic, Todilto, and MorrisonFormations
rocks i s inoutcropareas
(<1% of drainagebasin).
Uranium prospects and mines in the easternpart
of the Grants Mineral Beltarediscussed
by
McLemore
(1982;Figure 7 ) . Most
surfaceoccurrences of uranium mineralization are sites of mines o r prospects.
Further discussion of uranium occurrencesin the Rio Puerco drainagebasin i s
given inHilpert(1969),
Rautman (1980),Perkins(1979),Hatchell
and Wentz
(1980), and McLemore (inpress).
Many of the mines and mineraloccurrences
a r e underground and have little surface expression other than
man-made disturbance. A survey of abandoned mines and prospects (Anderson 1981)revealed
t h a t few prospects had extensive surface disturbance with elevated
amounts
of radioactivity. With severalnotableexceptions,thereappearto
befew
surface sources for radionuclides and heavy metals from the Grants Mineral
Bel t.
Uranium i s a l s o found i n EoceneBaca Formation alongthesouthern
margin
of thedrainagebasin
(Chamberlin 1981). Uranium mineralizationislocalized
along the eastern margin of the Ladron Mountains (McLemore 1982) and in
CerroColorado,an
exhumed volcanic complex near the Rio Puerco west of
A1 buquerque (Hi1pert 1969).
Other rocks which may produce above-background trace elements or
radionuclideswithinthedrainagebasinincludesedimentarycopper
deposits
along the f r o n t of the Nacimiento Mountains (Kaufman e t a l . 1972), f l u o r i t e
(-sulfide)deposits i n the Zuni Mountains (Goddard 1966) and trace-metal
bearingcoal andhumate deposits of Cretaceousformations (Bachman e t a l .
1959; New Mexico
Bureau
Mines
of and
Mineral
Resources
unpublished
coal
d a t a f i l e s ; Siemers andWadell 1977).
Another possible source of radionuclides and tracemetalshas
been mine
dewatering.Discharges
t o the Rio Puercoabove i t s confluencewiththe
San Joseareapproximately 22.7 m 3/sec and t o t r i b u t a r i e s of the San Jose
a b o u t 13.2m3/sec (Perkins and Goad 1980). The New Mexico Environmental
19
02
Improvement Divisonhas measured concentrations of trace metals and
radionuclides i n mine discharges which exceed New Mexico groundwater
standards (New MexicoWater Quality Control Commission 1982). Thesame
report also indicates that mill tailings liquids
may be contaminating
aquifers. Any of thismaterialentering
the drainagesystems may
be
moved downstream. Total uranium production t o datein New Mexico has been
approximately 1.6 x 105 tons w i t h 99% from theGrants Mineral Belt
(McLemore, inpress).
The Jackpile-Paguate mine i s oneof the largest open
p i t uranium mines i n the world,coveringabout
10.7 km 2 . The Rio Paguate
runs through the p i t and drains into the Rio San Jose. The sum o f a c t i v i t y
related to uranium mining intheregioncouldconceivablymobilize
radionuclides and trace metals.
Possible reworking of sedimentswithinthedrainagebasin
may account
Recycling (retransporting)previouslydepositedsediments
f o r much of the dilution of sediments derived from primarysourcesinthe
drainagebasin.Recycling
of grains may occur on severalscales,including
(1) episodic transport and deposition of loose sedimentwithinthe
modern
channel, ( 2 ) recycling modern sediment by eroding 20th century bank and
floodplaindeposits, (3) recyclingearliervalleyfill
by lateralerosion
of arroyowalls, (4) r e c y c l i n g e a r l i e r v a l l e y f i l l
by vertical erosion a t
the baseof the modern channel, and ( 5 ) erosion of v a l l e y f i l l by tribut a r i e s . There are no data on episodic transport of sediment w i t h i n the
modern channel, b u t bars are deposited and are reworked by later floods.
The distanceindividualgrainsaretransportedprobably
i s r e l a t e d t o the
s i z e of the grains (whether they are part
of the bedload or suspended load)
Some marshy areas along the
and thestream power of individualfloods.
modern Rio San Jose above Laguna a c t a s normal sediment traps.
In order t o assessthe amount of lateral erosion of b o t h 2 0 t h century
deposits (floodplain) and e a r l i e r v a l l e y f i l l , a 10 km stretch of the
Rio Puerco between sites 1 and 5 was analyzed by determining the course of
the inner channel on 1:4,800 scale maps produced in 1979 by the Army Corps
of Engineers. About 77 percent of the length of the inner channel was
between banks which appeared t o be relatively stable (neither eroding
nor
receivingsediment).
About 9 percent of the l e n g t h of the channelappeared
5.
t o be i m p i n g i n g on 20th centurydepositsand,in
some cases,clearly
The inner channel impinged directly
cuttingintotheinnerfloodplain.
o n t o exposures of older valley fill a1 ong 14 percent of the channel.
Vertical cutting into older deposits is difficult to assess
because
commonly the channel f l o o r i s coveredwith loose sandy sediment or with
water. In e a r l y f a l l , 1982, however, a largeflood removed loose sediment
from some reaches of the Rio Puerco and i t was possible to see that
the
channel l o c a l l y r e s t s on oldervalley f i l l . Nonetheless i t i s notyet
possible t o estimate what proportion of the channel length i s eroding
older valley fill.
Pipes and small incised tributaries contribute reworked v a l l e y f i l l
directlyonto the innerfloodplain and t o the innerchannel.Largertributaries recycle sediments from the valley margins a s well a s v a l l e y f i l l
directly i n t o theinnerchannel.
Hydrology of the Rio Puerco and i t s t r i b u t a r i e s
The Rio Puerco i s an ephemeral streamthroughout much of i t s length,
flowingonly i n response toprecipitation.
Water discharge and sediment
transport data from f i v e United States Geological Survey gaging stations
w i t h long-termrecordswithin
the Rio Puerco drainagebasin were analyzed
t o determine the size and frequency of floods and the generalbehavior of
the Rio Puerco. The stationsincluded Bernard0(1940-1982), Rio Puerco
(1934-1976) Rio Puercoabove Chico Arroyo (near Guadalupe 1951-1980), Rio
San Jose at Correo(1943-1980), and Chico Arroyo (1943-1980) (seeFigure 1).
The seasonaldistribution of flows a t the stations(seeFigure
8) r e f l e c t s
the contrasting contributions of springrunoff and summer thundershower
runoffindifferentparts
of the drainagebasin.
A t Bernardo,nearthe
mouth of the Rio Puerco, the stream flows an average of only 20 percent
of the year. A t 4ioPuerco, the streamflows 55 percent of the year.
Near Guadalupe, the Rio Puerco flows 53 percent of the year,while Arroyo
Chico flows 45 percent of the year. Although RioSan Joseisperennial
nearGrants, a t Correo, the streamflowsonly
40 percent of theyear.
All
stations are marked by great fluctuations i n the amount of flow each
year(seeFigure9).
6.
C
U
B
I
C
n
E
T
E
R
s
OCT
w
ApIca
JUM
AU6
i,
JULY
SEPf
HARat
XAY
A.
A v e r a g em o n t h l yf l o wf o rw a t e ry e a r
f o r f i v eg a g i n g
t h e R i oP u e r c od r a i n a g be a s i n .
A . Rio
s t a t i o n si n
a t RioPuerco,
Puerco a t B e r n a r d o , 6. RioPuerco
C.
RioPuercoaboveArroyoChico,
D . ArroyoChico,
E . Rio
San
J o s e a tC o r r e o .
Nov
F i g u r e 8.
m
JAN
23
m-
n
I
L
L
I
0
N
C
U
B
I
16
-
12
-
C
n
E
8 -
T
E
R
s
B.
24
3
n
I
1
1
I
0
N
C
-.
2.4
U
3
I
I .8
n
1.2
E
T
E
R
s
r
L 51 1
C
B.6
a
r
L
25
AU'6
n
'* 1
I
L
L
I
0
N
C
U
B
I
C
n
E
T
E
R
S
D.
26
5 i
n
I
L
L
I
a
n
C
U
B
I
C
n
E
T
E
R
S
27
F i g u r e 9.
Annual (water year) flow for the period of record
for five gaging stations i n the Rio Puerco drainage
B. R i o P u e r c o
basin. A . R i o P u e r c o a t B e r n a r d o ,
at Rio Puerco, C. Rio Puerco above Arroyo Chico
n e a r G u a d a l u p e , 0. A r r o y o C h i c o , E. R i o S a n J o s e
at Correo.
28
B.
29
0
H38
rn
3
O25
-
L
15
-
4
-1
H 10
-
0
20
v)
z
r
-
t
195-8
1955
1960
t 965
YEAR
L.
30
1978
1975
1 Q80
YEAR
D.
31
YEAR
E.
32
In general, the amountof flow reflects the amount of precipitation
upstream, b u t precipitation gages w i t h i n the Rio Puekodrainagebasin
are so few t h a t individualfloods can not be traced from individualprecipitationevents.Individualflood
peaks and largedaily flows canbe
traced downstream from upper gaging stations t o lowergaging stations
(seeFigure 10). Commonly t h e r e i s a l o s s of water ina downstream
direction, as floods lose water t o the channel f l o o r and banks. As i n
otherstreams, the duration and s i z e of floods becomes longer and l e s s
peaked downstream.
The Rio Puerco i s infamous for large discharge and highsediment
loads. A t the gaging s t a t i o n near Rio Puerco, maximum discharge (Septempber 23, 1929; stage 5.5 m ) was estimated t o be 1,070 m 3/sec, which
destroyedtherailroad
bridge along w i t h the streamgage.
Suspended
sediment loads of u p t o 680,000 ppm have been recorded a t Bernardo, and
loads u p t o 400,000 ppm a r e n o t uncommon (Nordin 1963).
Two major problems were encountered w i t h the data sets compiled f o r
each of the gaging stations. One problem i s that daily averageflows are
recorded ratherthanindividual
f l o o d peaks. Second, floodslargerthan
baseflow (defined by the United States Geological Survey t o be a flood
with a recurrenceinterval of 1.15 years) were alsorecorded, b u t base
flow f o r most stations was redefinedevery few years, sometimes being
floods
increased or decreased by as much as 127 m3/sec.Thereforesimilar
were n o t treatedequally i n differentyears.
A l t h o u g h there i s some
correlation between peak flows and dailyaverageflows,thecorrelation
i s n o t strong enough t o predict peak flows from dailyaverageflows.
3
For example, a t Rio Puerco above Arroyo Chico, peak flows of 197 m /sec
(July 29, 1967) and 96 m 3/sec (August 1, 1966) yielded d a i l y average flows
3
of only 14 m 3/sec, and larger daily flows of 30-34 m /sec resulted
from
3
3
smaller peak flows of97 rn /sec (September 1 2 , 1972) and 128 m /sec
(August 18, 1961)(3.Boyle,1983,
personal communication). The result
of these two problems i s t h a t i t i s d i f f i c u l t t o compilecomplete records
of floods a t each gaging station withequal precision and therefore imposs i b l e t o determine the numberof floods which may have contributed t o
sedimentationin the oxbows. Nonetheless, an estimate of the magnitude
and frequency of largefloodspassing
each gage are shown inFigure 10.
These plots show the relative decrease in numbers of largefloods.
33
Rio Puerco
at Rio Puerco
September 1972
F i g u r e1 0 .
Rise a n df a l l
o f d a i l ya v e r a g ef l o w sf o rf l o o d
o f S e p t e m b e r 1 1 - 1 4 , 1 9 7 2 ,f r o mg a g i n gs t a t i o n s
a l o n g t h e Rio P u e r c o a n dA r r o y oC h i c o .
34
16
14
12
18
8
6
4
2
8
CUBIC METERS PER SECOND
A,
F i g u r e 11.
Number o ff l o o d sl a r g e rt h a nb a s e
flow a t five g
g a g i n gs t a t i o n s i n t h e R i oP u e r c od r a i n a g eb a s i n .
A.
Rio Puerco a t B e r n a r d 0 from 1950 t h r o u g h 1979.
Base f l o w i s 91 m 3 / s e c . B . R i o P u e r c o a t R i o
Puerco from 1 9 5 0t h r o u g h1 9 7 6B
. ase
f l o w i s 170
m3/sec. C . R i o P u e r caob o vA
e r r o yC
o hico
from
1 9 5 0t h r o u g h1 9 7 9B. a s e
f l o w i s 51 m 3 / s e c . D .
ArroyoChico
from 1 9 5 0t h r o u g h1 9 7 9B. a s ef l o w
i s 82 m 3 / s e c .
E.
Rio S a nJ o s ea C
t orreo
from
1 9 5 0t h r o u g h1 9 7 9 .
Base f l o w i s 23 m3/sec.
35
t
0
160 200
250
300
350
400
450
500
550
600
CUBIC METERS PER SECOND
B.
36
650
24
22
20
v)
18
Q
0 16
0
14
&
12
tx
10
W
E 8
3
2
6
4
2
0
60 40
n
100
120
140
160
80
180
200
220
CUBIC METERS PER SECOND
L.
37
I
14 12 10 16
8 -
-
6 4 -
2 0-
sa
I a0
1sa 408
350
300
258
208
CUBICMETERSPERSECOND
D.
38
40
35
v)
30
Q
0
5
0
20
48
60
88
100120
140
C U B I C METERS
PER
c.
39
160 180 200 228
SECOND
11.
METHODS AND PROCEDURES
A.
Selectionof
Sample S i t e s
In order t o s e l e c t sample s i t e s , t h e generalsources and transport
directions of sediments were determined by examination of mapsand aerial
photographs and by f i e l d reconnaissance of the drainages. Themaps used
included 1:250,000 and 1:100,000 scale maps of the region,
and 1:24,000 and
1:62,500 scale maps of segments of the drainage basin and 1:500,000 and
1:24,000 geologic maps. S i t e s were selected on thebasis of (1) t h e i r
location within the drainage basin,
( 2 ) the degree of development of
abandoned channels whichhavebeen
active loci of deposition d u r i n g the
past 40-50 years and contiguous active stream channels for
comparison, and
( 3 ) a c c e s s i b i l i t y . T h e generalareasconsideredforsitelocation
were (A)
upper part of Rio Puercoupstream from a l l uranium mines, ( B ) central part
of Rio Puerco in reaches of possible influence of mines and natural
radionuclides, ( C ) downstream portionsof Rio Puerco where radionuclides
wouldhave had t o havebeen transported, and (4) along major t r i b u t a r i e s
d i r e c t l y downstream from mine a c t i v i t y and natural exposures of mineralized
rocks (seeFigure 1).
Locations of sample s i t e s were chosen on the basis o f comparing the
position of the inner channels of streams on early mapsand aerial photographs
w i t h l a t e r photographs (seesitedescriptionsforcomparisons).
In each
case,thetime
of oxbow formation(neck and chute cutoffs) could be bracketed
by comparing dated sequences of photographs(e.g.
between 1935 and 1954,
between 1947 and 1954, or between1954and
1972). Locations and depths of
samples a r e given i n Table 2.
B.
Age of Samples
The age of the cutoffs was p a r t i a l l y determined by examination of aerial
photography. Historic photographs (Happ, 1948, p l a t e 4) were used a t one
s i t e t o helpdeterminetheage
of t h e s i t e .
In thefield,archeological
and historical items were sought i n relation t o the sample s i t e s . Unfortunately, the only site which yielded an h i s t o r i c a r t i f a c t ( p o r t i o n of o l d ,
l i g h t gauge r a i l f o r r a i l r o a d ) was unsuitable for sampling due t o lack o f
floodsaftercutoff.Recently,
i t wasshown thattamarisks can record
annual rings and that deposits may be dated by analyzing whereand when
40
tamariskgerminationtookplace
(R. Hereford, 1982; 1983, written communication). This technique was used successfully on the sample s i t e which had
the l e a s t time control (D. Heath, 1983, personal communication; seeSite 2 ,
below).Surveyors
notes,historicalaccounts
and archeologicalstudies
(Betancourt, 1980; Loveand others, 1983) were useful i n determining longterm behavior of the Rio Puerco, b u t were not used for selecting sample
s i t e s . The 1938 date for construction of PaguateReservoir was provided
by the Laguna Tribal Agency.
C.
Surveying
Procedures
Topographic profiles.across arroyos, detailed stream gradient
determinations and detailed profiles across inner channels
were done by
surveying w i t h a theodolite (commonly a 20" instrument w i t h 7.62 m rod).
In two locations, profiles across the inner
channel were measured w i t h
metrictapes.Elevations
were calculatedtothenearestcentimeter.
Distances were measured t o the nearest f o o t and converted t o meters.
D.
Estimation of Bank-Full Discharge a t Ungaged Locations
Williams(1978) investigated numerousmethods of estimatingbank-full
discharge. He found t h a t d e f i n i t i o n of "bank-full''varied from method t o
method and t h a t few of the previously proposed techniques came close to
predicting measured bank-fulldischarge i n his more extensive data set.
Williams found t h a t thebestestimators
of bank-fulldischarge(Qb)
was
thebank-fullcross-sectional.area
of thestream (Ab, i n m2) and theslope
(S, dimensionless, m/m):
1.21 s0.28
Qb=4.OAb
The equation has a standard error of 0.174 log units or an averagestandard
e r r o r of 41 percent. I t accountsfor 96 percent of the sums of squaresof
l o g Qb (Williams,1978).
Williams indicatedthatthereappearsto
bemore
error for streams w i t h small bank-fulldischa,rges (which would includethe
Rio Puerco). In s p i t e of the large possible error
of the estimate, the
equation i s better than other presently available techniques (including the
popular Gaukler-Manning equation, Williams,1978).
The cross-sectionalareas of bank-fulldischarge and slopes of reaches
nearthe sample sites (estimated using a theodolite) are presented i n Table 2
41
Location
Site
'area
Slope (m/m)
(m
1
5
Rank-full
Discharge (I&/=)
16.8
17.2
51.1 38.2
.0013
6
97.9
.0011
152.3
8
50.8
.0033
.0057
93.6
27.6
SJ 1
.00095
16.3
TABLE 2.
Estimates of "bank-full" discharge for Rio Puerco
at three locations and Rio San Jose at one location.
42
along w i t h a possiblerange i n bank-fulldischarge for each locality. Caution
should be used i n interpretingthese numbers, however, because the hydraulic
geometry (width, depth, gradient, etc) of the Rio Puercochangesalong
each
reach and changes w i t h eachflow.Studies
of the Rio Puercochannel
(Young, 1982) determined t h a t more than 90 percent of the channel along the
lower Rio Puerco has shifted laterally since 1954. The shapeof the' channel
has changed as well, being relatively wide w i t h low banks and unvegetated
pointbars i n the 1930's to being relatively narrow w i t h h i g h banks i n the
1980's. The change i n channelshape a f f e c t s the magnitude and frequency
of overbank floods and the efficiency of transport of sediments.
E.
ExaminationofSediments
and Sampling Procedures i n the Field
Sampling a t sites consisted of taking 2-kg samplesof typical surface
deposits near a designated sample s i t e and by digging and.augering below
thesurface.
Comonly the pits dug t o expose stratigraphy and sedimentary
structures were 1.5 m deep, 2 m long and 0.75 m wide, w i t h steps cut i n the
south wall t o l e t i n sunlight and t o f a c i l i t a t e e n t r y for description and
sampling.Approximately
2-kg sediment samples were taken i n vertical
succession from each u n i t of i n t e r e s t exposed i n the walls of the pits. Once
the f l o o r of the p i t had been cleaned, two augerholes were sunk approximately
40 cm apart, using a 7.62 cm-diameter auger which took 15 cm incremental
samples. Possiblycontaminatedmaterial
a t the verytop of eachsample was
discarded, as was any contamination visible on the sides of the sample.
Samples from the same depth i n bothholes were combined i n order t o insure a t
l e a s t 2 kg of sample for lab work. Depths ofeachhole
were checked d u r i n g
sampling t o insure t h a t the same intervals were being sampled i n b o t h holes.
Augers disrupt the sample i n p a r t , b u t chunks ofsediment remain i n t a c t t o
aiddescription ofeachsample
interval. The Munsell color (chromaand hue),
grain size and texture of eachsample were described i n the field along w i t h
sedimentarystructures and other notable features
(such as organic remains
The sample number and description
and evaporitecrystals w i t h i n thematrix).
were recorded i n one or more notebooks, and the sample was placed i n a p l a s t i c
sample bagand sealed.
F.
Sample Handling i n theLaboratory
In the laboratory, 450 mL of material were removedfrom eachsample,
using a r i f f l e s p l i t t e r w i t h 1L, cm openings. Any pebblescoarserthan 1% cm
were also removed a t this point, as wereany clay balls (armored mud b a l l s ) ,
twigs, and similar objects.
A s e r i e s of additional, smaller samples were further characterized by a
varietyoftechniques.
These includedwet-sieving t h r o u g h 80- and230-mesh
U.S. Standard s t a i n l e s s s t e e l s i e v e s (mesh openings 175 and63 microns,
respectively); examinationof the size fractions under a 400X optical
microscope,determination of the percentage of clay-size material i n the
finest s i z e f r a c t i o n , X-ray diffraction analysis of clay-size fractions
and
selectedsand-sizematerial,
and chemical a n a l y s i s . I t was found t h a t copper
contamination was signficant i f brass sieves were used so i t was necessary t o
use stainless steel sieves.
G.
Determination of Pb-210,Cs-137,and
otherRadionuclideActivities
The previously obtained 450 mL s p l i t s were mixed t o ensure homogeneity
and transferred t o p1asti.cMarinellibeakers.
These were sealed w i t h tape
and, if Pb-210 analysis were desired, allowed to stand for a minimum of two
hence Pb-214, ingrowth.Procedures
for
weeks t o allowfor Rn-222,and
Pb-210 followed those of Schery(1980).
Activities of the radioisotopes Pb-210,P-214,andCs-137
used for dating
were obtained by
gamma
spectrometry, using an N-type, h i g h purity germanium
detector. These gamma spectra were obtained using one of threelead-shielded
Ortec Gamma-X spectrometerslinkedto a 4096-channel pulse-heightanalyzer.
Minimum counting times for Cs-137 and Pb-210 were 4,000 and 16,000 seconds,
respectively, and the energyrangeof
the spectra i n both cases was approxiof about 40,000 seconds
mately 0-1500 KeV. For low levels,countingtimes
were found t o be sufficient.Activitiesoftheradionuclides
Th-234,Ra-226,
Th-230,Pb-214,andBi-214
from the U-238 decay s e r i e s andAc-228andPb-212
from the Th-232 decay s e r i e s were also determined.
The efficiency of each d e t e c t o r a t a number of different energies was
determined by countingseveralsediment
samplesimpregnated w i t h known
quantities of nineradionuclides(ReferenceStandard
QCY, 44, Amersham Corp.,
Amersham, England). As theefficiencies were found t o be largelyunaffected
by the mean grain size of the sedimentmatrix of the standards, values obtained
44
from amixtureofequal
quantities of medium sand and s i l t y c l a y were used.
Efficiencies at other energies were found by interpolation, using programs
provided f o r this purpose by Nuclear Data Corporation (ND 6600, 1980).
The areas of the Pb-210peak a t 46.5 Kev were calculated using a peak
areaextraction program also provided by Nuclear Data (1980). The areas of
selected peaks were 'checked visually to verify the accuracy of the
program,
and t o v e r i f y t h a t t h e s e peaks had been adequately resolved from neighboring
peaks i n the spectrum.
Activities of each isotope ( i n pCi/g) were calculated from the peak
areas, sample weights, and branching r a t i o s , u s i n g previouslydetermined
efficiencies at these energies. 'The
branching r a t i o s f o r measured Pb-210,
Pb-214,andCs-137
decays were taken t o be 4.05%,37.2%, and 84.6% respect i v e l y (Erdmannand Soyka,' 1979)'. Where necessary,corrections were made for
thepresence of peaks a t t h e same locations i n background spectra.
H.
Trace Metal Analysis
Selected 230- fractions and clay fractions were digested bv the following
hydrofluoric acid-aqua regia-perchloric acid digestion prior to determination
of metals (Johnson andMaxwell,
1981). The hydrofluoric,nitric, and hydrochloric acids used were r e d i s t i l l e d i n Teflon(Mattinson,1972)
fromBaker
Reagent Grade acids.
few m i l l i l i t e r s
For every1.00 gram of sample added t o a Teflon beaker, a
of d i s t i l l e d w a t e r were added. S i x mL of hydrofluoricacid and 6 mL of aqua
regia wereadded t o t h e r e s u l t i n g s l u r r y and the solution evaporated to near
dryness i n a hood. A mixture of 6 mL of hydrofluoricacid and 2 mL of
perchloricacid was added and subsequentlyevaporated t o densewhite fumes
neardryness.
The solution was brought up to desired volume w i t h 10%n i t r i c
acid.
In general 2.00 g of 230- fraction samples and0.25 g of clay samples
were digested and brought up w i t h 10%n i t r i c a c i d t o a t o t a l f i n a l volume of
100 mL for analysis. To testtheanalyticalprocedures,
SY-2,SY-3,
(Canadian Certified Ref. Mat'l.), SL-1 (Canadian AtomicEnergy Commission),
and NBS 1645 r i v e r sediment were used as standard materials and digested
according to the procedure described
above.
Mercury (Hg) was determined by cold vapor atomicabsorption on a
Coleman MAS-50 spectrophotometeraccording t o EPA procedures (1979). The
45
trace metals As, Cd, Cr, Cu, Mo, Ni, Pb, Se, and V were determined on a
Perkin Elmer 403 atomic absorption spectrophotometer(A.A.) As and Se were
determined by hydride generation with a Perkin-Elmer Mercury Hydride System
(MHS-10) using electrodeless discharge lamps. Cr and Cu were determined by
direct aspiration techniques
as described by EPA standard methods218.1 and
220.1, respectively (1979). Mo, Ni, Pb, and V were determined by furnace
techniques on either a Perkin-Elmer 2000
HGA or HGA 400 graphite furnace
as described by EPA standard methods246.2, 249.2, 239.2, and 286.2
respectively (1979). Generally, charring temperatures50 to 100 degrees
lower than those recommended as general operating parameters
by the manufacturer were employedfor Pb. Uranium was analyzed spectrophotometrically with
dibenzoylmethane after separation
by solvent extraction' with tri-n-octylphosphine
oxide adapted fromthe procedure describedby Houston and White(1958).
Generally a5 mL aliquot of the acid digested material
was sufficient due to
the high U levels in the sediments,
in Table 2
Sensitivities for the various metals are shown
Metal
-
Sensitivity - ppg (ygb-1
As
Cd
Cr
2.0
0.3
1.0
0.5
1.0
1.0
1.0
2.0
5000
2.0
cu
H9
Mo
Ni
Se
U
V
Table 3. Analytical Sensitivities for Metals
I. Neutron Activation Analysis Procedurefor Ba, Cr, Cs,and'fe
by grinding and approximately0.500 grams
Samples were disaggregated
were placed in plastic vials. The weight, to the nearest milligram,of
each of these samples was recorded. After the vials were sealed, they
were irradiated at the Sandia National Laboratory reactory facility.
46
Data was collected on a s e r i e s of samples from the Rio Puerco i n the
form of seven day and t h i r t y day counts. Thesesamples variedinorderto
w i t h i n asample, the sample s i t e s
represent the various size fractions
of beds sampled a t each s i t e . Clays were
themselves, and thevarioustypes
chosen as the most representative portion for irradiation since
by surface
area phenomena they should concentrate the
most trace metals.
The samples were thencountedapproximately
sevendays a f t e r i r r a d i a t i o n
f o r 4000 seconds and again thirty days a f t e r i r r a d i a t i o n f o r 5000 seconds on
aNuclear Data ND6600 system u s i n g MIDAS 7 or MIDAS 8 operating systems. The
detector was aCanberra model 7229 ( w i t h a cryostat model 7500) operated a t
2000 volts. The dataare summarized in Appendix G.
The countsobtained werecompared t o standard materials SL-1,and
NBS 1645whichwere
irradiated w i t h each s e t of samples by standard routines
available from Nuclear Data Corporation. Bariumwas determined from the decay
of Ba-131which has a h a l f - l i f e of 12 days. The peaks used f o r this determination are a t h i r t y day peak a t 124 KeV, aseven daypeak a t 216KeV,and
aseven daypeak 496.2 KeV. These three peaks are averaged t o obtainthe
finalvalue and associatedanalyticalerror.
Chromiumwas determined from decaysof Cr-51 which has a h a l f - l i f e of
27.8 days. The concentration was determined from the peak a t 320.1 KeV i n the
t h i r t y day count.
Cesiumwas determined from the decay of Cs-134which has a half-life of
2.05 years. The concentration i s determined from the peak a t 797.0 KeV i n
t h e t h i r t y day counts.
Iron was determined from the decay of Fe-59which has a h a l f - l i f e of 45.6
days. The concentration is determined from the peaks a t 192.2,1099.3,
and
1291 KeV i n t h e t h i r t y day counts.
J.
DeterminationofRelativeProportions
of S i l t and Clay
A .representative portion of the
crushed <63 micron fractions of the
sample was obtained using a r i f f l e s p l i t t l e r w i t h 1.25 cm openings. This
material was weighed to the nearest 0.01 g and dispersed i n approximately
100 mL of water. A 1.0 mL volume of 50 g/L sodium hexametaphosphate solution
was added t o promote disaggregation of the sediment and prevent flocculation.
The sample was placed on a magnetic s t i r r e r and allowed t o s t i r for approximately18 hours. An alternativeprocedureinvolvedstirringforabout
47
3 hours in distilled water followed
by sonification with a Bronson Sonifier for
8 minutes a t a s e t t i n g of 6.5.
Additional water was then added t o the sample, such t h a t the final depth
of liquid was equal to the distance which a p a r t i c l e of 2 micron effective
sphericaldiameter would s e t t l e i n six hours accordingtoStokes' Law
(assuming a particle density of 2.6 g/cm 3 and a viscosity equal t o t h a t of
purewater a t theambient air temperature). The sample was stirred rapidly
f o r one minute to ensure complete homogeneity, and allowed t o s e t t l e f o r
the six hour period.
The majority of the liquid (the clay suspension)
was then removed by
siphoning and pipetting, in such a manner that the material whichhad s e t t l e d
t o the bottom of the beaker was n o t disturbed. The latter material was then
transferred to a weighed, stopperedglasstube,
and water added until the
level of liquid equalled the distance a 2 micron p a r t i c l e would s e t t l e i n
161 hours. The sample was mixedby
repeatedlyinvertingthetube,
and allowed
t o s e t t l e for the required time.This
was repeated two more times. The
majority of the liquid was again pipetted off,
and the settling tube dried at
8OoC and reweighed. The weight of the s i l t i n thetube was calculated by
difference, a n d converted t 0 . a weight percentage.
K.
X-Ray DiffractionAnalysis of the Clay SizeFraction
A small quantity of clay-size material was obtained for X-ray analysis
Four oriented
by the ultrasonicproceduretreatmentpreviouslydescribed.
mounts of t h i s fraction were thenprepared by placing 15-20 drops of clay
suspension on g l a s s s l i d e s and allowing the mounts t o air-dry. One mount
was subsequentlyheatedto 350°C for 1 hour and placedin a dessicator containing phosphorus pentachloride. A second mount was heated t o 550'C for
I+ hours and allowed t o cool i n a i r , and a t h i r d mount was placed i n an
ethylene glycol-saturated dessicator and heated t o 6OoC f o r 1.5-2hours.
A partially unoriented ("smear") mount was alsoprepared by placing a thick
past of < 2 micron material on a g l a s s s l i d e and spreading i t uniformlyover
the exposed surface.
Oiffractograms were made of each mount, extending from 3' t o 33' 20 f o r
theoriented mounts, and from 3" t o 65' 20 for the smear mounts. A Norelco
Philips Model 5001 X-Ray d i f f r a c t o r was used,with CuKa radiation (40KV/20mA),
1" - 4' - 1' s l i t s , 3% standarddeviation, and a recording speed of 2' 20/minute.
48
Peak intensities above background were measured, and normalized using the
intensity of the quartz peak26.65'
at 29.
The ratio of discrete montmorillonite to discrete illite was estimated
from the (normalized) heights of the montmorillonite and illite
(001) peaks
at approximately5.8 and 8.8' 29 in the glycolated slides, assuming a
characteristic intensity ratio
of 4:1(Dr. George Austin,NM Bureau of Mines,
Personal Communication). The ratio of montmorillonite to illitein mixed
layers was arbitrarily assumed to be the
same as thatof the discrete
minerals, and the proportionof mixed layering estimatedfrom the increase
in height ofthe peak at 8.8' 29 in the 350' slide over that resulting from
the shiftingof the montmorillonite (001) peak to thisposition.
The ratio of chlorite to kaolinite was estimated from the (normalized)
heights of the kaolinite (002) and chlorite (004) peaks at approximately
25' 29, assuming an intensity ratio
of 2:l (Dr. G. Austin).
The height of
the chlorite(004) peak-in this calculationwas that measured in the 550'
slide, and the height
of the kaolinite (002) peak was obtained by subtracting
this height from the height
of the combined peaks in the air-dried slide.
The ratio of illite to kaolinite was estimated from the (normalized)
heights of the illite (001) peak in the glycolated slide and the kaolinite
(001) peak, assuming an intensity ratio
of 1:l (Dr. G. Austin). Again,
the heightof the kaolinite peak was calculated from the height
of the
chlorite (002') peak at 12.5 - .13O 29 in the 550' slide and the height
of the
combined peak at this position in the air-dried slide. This ratiowas then
the fraction of each
used in conjunction with the previous ratios to calculate
clay mineral (expressed intenths).s
The calculations canbe summarized in the following equations:
, and
where
49
I and S1 are the normalized intensities of the montmorillonite and
illite (001) peaks in the glycolated slide, and
the combined peaks in the
550' slide.
It should be noted that the values obtainedby this methodare subject
to considerable inaccuracies, and are therefore only semiquantitative (as
are virtually all estimateso f this type).
in the clay-size
Relative amountsof the non-clay minerals present
fraction were estimated from smear slides.
The peaks used were those of
quartz at 26.65',
calcite at 29.4', and clay at 19.8' 20. The intensity
ratios of these peaks were assumed to be 20 : 10 : 2.5 : 1 (Schultz, 1964).
M,
50
111. RESULTS AND DISCUSSION
A.
Geologic Descriptionof
1.
Rio Puerco
a.Sites
Sample Locations
1, l A , 2 , 2A
The study s i t e s nearPopalitito Windmill (Table 4, s i t e s 1, l A , 2A;
Fig. 1) were chosen for their position i n the lower part o f the drainage
basin and because the oxbow is particularly welldeveloped (Fig. 12).
Figure13 shows positions of theinner channel in 1954and i n 1979. The
channel cutoffoccurred sometime a f t e r 1954. There a r e no
known
photographs
of t h e s i t e between1954and1972.
During reconnaissance and p i t excavation,
no h i s t o r i c a r t i f a c t s were found t o i n d i c a t e a possible time for channel
abandonment.However,
i n a relatedstudyofthecutoff,
Heath (1983,
written commun.) determined that tamarisks growing i n the sand plug about 2 m
above the present channel a t the downstreamend of the oxbow germinated i n
1960. Thereforethe sand p l u g was inplace i n 1960. Heath estimatesthat the
oxbow formed i n 1957. Theoxbow a t P o p a l i t i t o c o n t i n u e s t o be inundated.
Two floods i n 1982 (August 28; September 19) floodedthesite.
Water from the
second flood was s t i l l 24 cm deep i n February, 1983.
Figure 14 is a cross-arroyo profile of the
sample s i t e s , showing the
relative elevation of the present inner channel, the inner floodplain, the
o f the present inner channel
oxbow and the 10 m walls of the arroyo. Profiles
( F i g . 15) suggest that flooding o f the oxbow presently occurs at discharges
of greater thanabout 17 $75 (depending on channel geometry and formula used).
Even though channel geometry has changed i n the past 25 years, the size
distribution of floods at
Bernard0 ( F i g . 10A) andRio Puerco (Fig. 1 O B ) suggest
t h a t more than 22 floods have reached the oxbow since 1957.
Sediment within the oxbow i s dominated by overbank clay from the Rio
Puerco ( F i g . 16 and 17). Although naturalpipes and shortdendritic tribut a r i e s debouch from the. arroyo walls into the area
of the oxbow, a l l u v i a l
fans from t h e s e t r i b u t a r i e s a r e minor and do not a f f e c t sample s i t e 2-2A.
Detailed descriptions of the trench walls
and auger samples a r e given
i n Appendix A. Briefly, i n oxbow s i t e 2-2A, laminated s i l t s and claysoccur
from the surface t o a depthof 2.41 m (Figs. 17 and 18), resting on sand and
coarse sandy gravelofthe
1954 channel. Sand interpretedto be part of the
51
SITE
QUADRANGLE
1A
2A
3A
5
6
7
7A
Belen NW
Belen NW
Rio Puerco
Rio Pllerco
La Mesita Negra
La Mesita Negra
La Mesita Negra
Guadal upe
Guadal upe
Guadalupe
Guadalupe
South Garcia
Mesi ta
Mesi ta
"
8
9
10
11
SJ-1
SJ-5
PAG-1
(m)
DEPTH
COORDINATES
UTMG
3837000 N,
3837000 N,
3852950 N,
3833060 N,
3884940 N,
3884880 N,
3884880 N,
3940820 N,
3940700 N,
3940900 N,
3940900 N,
3868700 N,
3882760 N,
3883430 N,
326220 E
325825 E
317940 E
317760 E
322680 E
322800 E
322800 E
302700 E
302600 E
301520 E
301420 E
304950 E
286940 E
288145 E
4.27
5.05
6.71
3.94
5.18
8.62
1.72
0
2.54
0
0
1.50
2.0
2.20
TABLE 4. Site Numbers, Topographic Quadrangle Location, UTMG
Coordinates and Depth o f Sampling.
52
Figure 12.
Oxbow
and
arroyo walls a t s i t e 2.
C . J . P o p p1, 9 7 9 .
53
P h o t o g r a p hb y
B.
A.
Figure 13.
A e r i a pl h o t o g r a p h s
o f t h ea r e ai n c l u d i n gs i t e s
and 2 t a k e n i n 1954 ( A ) and1979
54
1
W
a
-I
0
f
w
LL
ELEVATION
(FEET ABOVE
SEA LEVEL)
3
4900
:
0
I
a:
1
a
W
0
LLO
I
02
[r
a
m
a
0
0
J
z
-
‘EARLIER
Figure 14.
C r o s ss e c t i o n
1 A a n d 2A.
DEPOSITS
OF
THE VALLEY FLOOR’
IO X VERTICALEXAGGERATION
o f Rio PuercoArroyo
55
a t s a m p l es i t e s
w
E
0
r
-
5m
c3
I
no vert;coI exaggeration
Figure 15.
P r o f i l ea c r o s s
i n n e r c h a n n eol R
f i oP u e r c on e a r
o f D. Heath, 1 9 8 3 ) .
s i t e 1 A [ f r o md a t a
56
F i g u r e1 7 .
P i t e x p o s i n gl a m i n a t e d
s i l t a n dc l a y
i n oxbow
a t s i t e 2 A . P h o t o g r a p hb y
D . W . L o v eF, e b r u a r y ,
1981.
58
Figure 18L
. a m i n a t e da n ds t r u c t u r e l e s ss i l ta n dc l a y
1 . 1 m o f oxbow d e p o s i t sa t s i t e 2 A .
i s 1 . 2 5 cm w i d e . Photograph by D.W.
1981.
59
i n upper
Tapemeasure
Love, February,
1954 channel continuesto a depth of 5.05 m (base of hole). Large c l a s t s a t
the base of the hole which prevented further augering suggest that the
base
of the 1954 channel was nearlyreached.
t o a depth
In s i t e s 1 and l A , along thepresentinnerchannel,deposits
of 2.07 m consist of f i n e sand, s i l t and clay in small cross-laminated beds
which appear t o be modern channel-marginal bars deposited underlow-discharge
m, thereare two coarse-grained channel sequences,
conditions. Below2.07
one t o a depthof 2.92 m andonebelow
3.09 m t o a t l e a s t 4.27 m a t the bottom
of theaugerhole.
The upper coarse-grainedsequence i s part of the modern
(post-1950)channel.
The lower coarse-grainedsequence may
be
e i t h e r modern
o r a buried channel i n t h e v a l l e y f i l l .
b.
Sites3,
3A, and
4
5
Study s i t e s 3-3A, 4and 5 were chosen because of their accessible
location downstreamfrom the confluence of the RioSan Jose and Rio Puerco
and because the oxbow appeared t o be receivingsediments b o t h before and
a f t e r 1950. Figure19 shows theposition of the channel i n 1936and 1954.
The present inner channelhas shifted about 60 m e a s t of i t s position i n
1954 (Fig. 20; Wells and others, 19821. Figure ( 19 ) suggeststhatthe
oxbow continued t o receive sediments after 1954.
The cross profile o f Rio Puerco Arroyo i n this reach (Fig. 20) shows
extensive development of the floodplain between the inner channel and the
oxbow.The
inner channel ( F i g . 21) is r e l a t i v e l y narrow compared t o t h e
channel a t l o c a l i t i e s upstream and downstream. Alluvialfans from natural
pipes debouching along thearroyowalls
(Figs. 20 , 22A) have buried. the
oxbow a t s i t e 3-3A.
The r e l a t i v e l y small w i d t h and depth of the inner channel a t this
l o c a l i t y (Fig. 21) andlow slope of the reach imply that the threshold bankf u l l discharge under presentconditions is about 51 m3/sec. Records a t t h e
Rio Puercogaging s t a t i o n 2 km downstream s u g g e s t t h a t a t l e a s t 22 overbank
floodevents have occurred a t this localitysince 1950.However,
because
the oxbow i s presently buried by sedimentsderived from t h e v a l l e y f i l l
section t o t h e e a s t ( F i g . 22 A and . B j , and the present gradient is toward
the present inner channel,
floods may not have reached sample site 3-3A
often in recent years.
'
19
w
3
62
VI
W
CI
VI
.r
0
h
0
L
L
0
u
L
W
3
a0
CT
.r
0
rc
W
'c
.r
7
0
L
a
VI
VI
0
L
V
0
W
cu
L
J
m
W
Figure 21.
E
P r o f i l ea c r o s si n n e rc h a n n e l
I
63
o f R i o P u e r c on e a r
s i t e 5.
F i g u r e 22A.
Sample s i t e 3A i n oxbow a n de d g eo ft r i b u t a ' r y
f a nP.h o t o g r a p h
by D . W . Love, F e b r u a r y , 1 9 8 1 .
64
Figure 22B.
D e t a i . l so fs e c t i o n
o f v a l l e yf i l le x p o s e d
in
a r r o y ow a l al d j a c e n t
t o s i t e 3A. Auger i s
5 . 2 m l o n g . P h o t o g r a p h by D . W . L o v eF, e b r u a r y ,
1981.
65
The sources of the deposits are indicated by the sedimentary structures
and grain sizes seen i n the pits and augerholes.
In p i t 3A ( F i g . 23 and
Appendix A), sedimentary structures i n the upper part of the p i t ( t o 1.04 m )
d i p westward and include cross-laminated sand and clay w i t h clay platelets.
The lower part of the p i t and augerhole below include horizontal clay layers
up t o 8 cm thickinterlaminated w i t h very fine sand and s i l t . Between 1.67
and 2.54 m, f i n d sand and clay of the formerchannelmarginspredomina.te,
i t is difficult
overlyingcoarser channelsand and pebblysand.Although
t o choose a lower boundary f o r the 20thcenturydepositsbecause
the modern
sands overlie a channel sand w i t h i n the older valley
f i l l , there i s a break
i n grain size andamount of moisture a t 4.17 m, which may indicate the base of
modern' deposits. This elevation i s nearly the same as the base of the present
inner channel t o the west ( F i g . 20). The lowerchannel depositscontinue
t o a d e p t h of a t l e a s t 6.71 m.
S i t e 4 was an i n i t i a l augerhole i n the 1980 channel and was not
studied further.
The location for p i t 5 was chosen along the marginsof the present
channelbecause the sediments beneath the inner channel were water-saturated
sand was reached a t a depth of 3.94 m
and inipossibie t o excavate.Saturated
i n the augerholebeneath
the p i t a t e s s e n t i a l l y the same level as the channel
floor. Sediments sampled i n the p i t and augerhole (Appendix A ) a r e predominantlycross-laminated fine sand (including climbing ripples) separated
by westward-dipping claydrapes.
Near the baseof the augerhole, 0.45 m of
coarse sand w i t h mud balls occur, suggesting t h a t the level of the former
(20thcentury) channel had been,reached. The grainsize,sedimentary
the sediments above the coarsestructures and clay drapes all indicate that
grained layers were deposited by floodsalong the margin of the inner channel.
c.
Sites6,
7 and 7A
The oxbow a t sample sites 6 , 7 and 7A was selected for i t s position i n
the drainagebasinupstream from the RioSan Jose and downstream from Arroyo Chico
and other t r i b u t a r i e s of the Grants Uranium region and i t s age. The oxbow
was abandoned between 1935 and 1954 ( F i g . 24 ) and was capableofreceiving
overbank sediments d u r i n g the period of uranium mining. As b o t h aerial
photographs show, the inner channel is relatively wide (seealso Figs. 5, 25
and 26). The tamarisk-dominated leveesalong the e a s t bankof
the channel
66
F i g u r e 23.
C r o s s - l a m i n a t e d f i n e s a n d i n u p p e rp a r t
P h o t o g r a p hb y
D.W. L o v e F, e b r u a r y 1, 9 8 1 .
67
of p i t 3A.
F i g u r e 24.
O x b o w a t s i t e s 6 a n d 7 i n 1 9 3 5 ( A ) a n d 1 9 5 4 (6)
68
W
E
double
fence
-0
post
0
25 m
5% vertical exaggerolion
F i g u r e 25.
P r o f i l ea c r o s s
982 tributary arroyo!
"
"
"
"
R i o PuercoArroyo
a t s i t e s 6 and 7.
U
3
W
70
La
a,
c,
v)
.r
L
0
.r
a,
ce
.!2
c
0
h
7
W
E
E
m
u
c
L
a,
E
E
.r
a,
c,
c
v)
v)
0
W
F.C
L
LC.
0
Q
a,
L
a r e r e l a t i v e l y h i g h , while the floodplain east
of thelevees is low.
Alluvialfans from active soil pipes and from a recently breached watercontrol structure on the valley floor to the east presently
dominate
deposition on thefloodplain.
West of theinner channel i s an older,higher
floodplain which i s abandoned as an insetterrace.Locally-derivedsediments
from t r i b u t a r i e s and natural pipes west of the arroyo continue to
aggrade
this terrace.
Because theinner channel a t t h i s l o c a t i o n is wide (Fig. 261, discharge
must exceed about 150 m3/s i n order to reach the floodplain. The distribution
of f l o o d s a t Rio Puerco (Fig.10 B ) downstreamand Arroyo Chico (Fig.10 E ) and
Rio Puerco above Arroyo Chico (Fig.10 C ) suggest a t l e a s t 18 floods may have
exceeded the minimum for flooding.
a t an intermediate
Sample s i t e 6 was placed on a channel-marginalbar
level 9 m west of t h e e a s t bankof the channel ( F i g . 5 above)because the
f l o o r of the inner channel was water-saturated and wascomposed of coarse
sand.Sedimentary
structureswithinthebarincludeddiscontinuously
laminated and cross-laminatedsand, f i n i n g upward couplets of f i n e sand, s i l t
and clay, and coarser, low-angle cross-laminated channelsand
(Fig. 27). Below
different stratigraphy although
about 3 m, the two augerholesencountered
they were only 40 cm apart. One holepenetrated predominantly coarse sand
w i t h some pebbles and mud balls. The water table was encountered a t 4.2 m.
The otheraugerholepenetratedpredominantly
sandy clay deposits (mudballs
i n part?) below 4 m and continued t o be r e l a t i v e l y , d r y t o a depth o f 5.18 m.
The differences i n the two holes may r e f l e c t extremely localized deposition
ofmudballs o r perhaps a clay deposit crosscut by a l a t e r channel sand.
The upper 50.8 cm of s i t e 7 i n the oxbow t o the east (Fig. 28; Appendix A )
consists of cross-laminated fine sand,
s i l t and gray.clay platelets deposited
i n t h i n (5-10 cmj layers as part of an alluvial fan complex derived from the
valley,floortotheeast.
Below theseclay-richlayers,thedepositsconsist
of layers of cross-laminated fine sand, coarsening
downward t o pebbly sand
a t a depth of 3.31 m. The gravelly sand a t this depth may indicate the base
of20thcenturydeposits.
Clay and rusty sand layers below the gravelly
sand t o a depth 8.6 m probably are older valley fill.
Because the upper50.8 cm of clayey deposits a t s i t e 7 had unexpected
geochemistry(seebelow),
the e n t i r e oxbow area was searched for thicker
sections of clay-rich f i l l . S i t e 7A was selected 36 m northwest of s i t e 7
F i g u r e 28.
S t r a t i g r a p h y o f p i t a t s i t e 7 . Note c h a n g e o f
d e p o s i t s a t 50 cm. P h o t o g r a p h by D . W . L o v e ,
Ma,y, 1 9 8 1
.
73
i n order to sample more than 70 cm of similar clay (Appendix A). Fine sand was
encountered from 1.28 t o 1.72 m, suggesting t h a t channel-marginalbars had
been reached below the clays. Geochemical properties of the claylayers i n
s i t e 7A, however, were somewhat different from clay layers i n si.te 7 (see
discussion of geochemistry), b u t no .other thick clay deposits were found i n
the oxbow, so further checks on natural variations i n chemistryofa
single
oxbow f i l l sequencecouldnot
be made.
During the 1982 summer rainyseason, an a r t i f i c i a l l e v e e and the valley
The arroyowall
f l o o r e a s t of s i t e 7 were erodedbadly by aflashflood.
north of s i t e 7 underwent rapid gullying and the alluvial fan at the surface
of s i t e s 7 and 7A received 15-25 cm of new locally derived sediment. The
floodcuta
new tributary arroyo channel i n the vicinity of s i t e 6 (F,ig. 251,
exposing the stratigraphy of the natural .levees and floodplain.
From these new exposuresaswellas
from severalshallowaugerholes
and
the augerholes a t 7 and 7A, ' i t i s apparent that sedimentation i n this
abandoned meander was predominantlysandy, w i t h l i t t l e c l a y derived from
overbank floodingnear the sample s i t e s . Even the channelmargins
(both.past
and present) a r e dominated by sand.
d.
Sites 8 and 9
sites .8 and 9 was selected because i t i s upstream from
a l l major uranium mining, and because meander cutoff occurred between1936and
1954 ( F i g . 29; c.f. Happ, 1948, Plate 4). The cross-profile of the l o c a l i t y
(Fig. 30) shows the relative elevations of the oxbow and present inner channel.
Extrapolatedonto the l i n e of the profile are the p i t a t s i t e 9 and a remnant
of older v a l l e y f i l l . Flood access t o s i t e 9 may be provided by lower banks
along the inner channel downstream from thecross-profile.
Upstream from the
cross-profile, the banks a t the head of the oxbow a r e a t l e a s t as h i g h as
those of the cross-profile, and no overbank floodingappears t o have occurred
The location of
recently.
The two crosssectionsof
the channel near s i t e 8 ( F i g . 31) were used
toestimatebank-fulldtscharge
a t about 93 m3/sec. This amount offlow has
been exceeded a t the gaging station 2.4 km upstream between 8 and 10 times
(Fig.10 C ) . However, configuration of the inner channelhas changed considerably d u r i n g the past 30 years. I t is n o t clear whether la,rgedischarges
ofequalmagnitude
have flooded similar areas i n the past.
74
Figure 29.
C o n f l u e n c e o f RioPuerco
( A ) a n d 1 9 5 4 (.E),
75
and A r r o y oC h i c oi n
1935
3
76
E
.r
0
m
a
L
S
m
.r
LL
77
The s u r f i c i a l d e p o s i t s w i t h i n the oxbow a r e predominantlysandy.
It
remains t o be determinedwhether floods d i d n o t deposit s i l t and clay or
whetherfloods d i d notreach mostof the oxbow. I t maybe
that the inner
channel has incised to the p o i n t where floods do n o t reachthe oxbow.
Alternatively, the gradient of the
oxbowmaybe
large enough that floodwaters drain rapidly back to the inner channel without depositing much s i l t
and clay.
A major natural pipe debouches into the oxbow 45 m upstream from s i t e 9.
The gradient of the fan and the fine grain size of the sediments suggest
that the clay-rich surficial
sediments a t s i t e 9 a r e reworked from the valley
f i l l west of the river.
The uppermost 36 cm of deposits of s i t e 9 ( F i g . 32;Appendix A) includes
beds of dry sandy clay which may havebeen reworked from upstream i n the oxbow.
Below these beds t o a depth of 81 cm i s asequence of couplets 2-to-3 cm thick
composed of sandy claygrading upward t o clay. These coupletsreflectrepeated
from upstream i n the oxbow. Below 91 cm
depositionaleventsprobablyderived
a r e sandy to gravelly sand layers of the abandoned channei. The base of the
clay and cohesive sandy loam which may Se
hole a t 2.54 m reachedpebblysandy
the base of the 2 0 t h century sandy channel.
Only surface samples were takenalongthe channel a t s i t e 8 because the
channel consisted of water-saturatedcoarse sand.
e.
S i t e s 10 and 11
Arroyo Chico was examined a fewhundred meters upstream from the confluence w i t h Rio Puerco (Figs. 1, 33) where there was anabandoned channel.
Although an inner channel and floodplain had developed, and formerchannels
had been c u t o f f , t h e e n t i r e
system was dominated by sand, so t h a t no thick
clay layers were encountered in augered t e s t holes i n the abandoned channel.
Therefore, only surficial samples were taken near the line
of the profile
i n Figure 33 along w i t h samples of muddy water (discharge from mine-dewatering)
2.
Site
a.
Rio
San
Jose
SJ-1
S i t e SJ-1 was chosenbecause of i t s location between Correo and the
confluence w i t h Rio Puerco (Figs. 1 and 34). Small subsidiarychannels
78
A.
Figure 32.
Sample p i t i n oxbow a ts i t e9 .S c a l e
is i n
increments o f 0.1 m . A.
Oxbow a n d p i t .
P h o t o g r a p h by J.W. Hawley,November,1981.
B. D e t a i l e d s t r a t i g r a p h y i n w a l l o f p i t .
P h o t o g r a p h by D. H e a t h , November,1981.
79
80
A.
8.
F i g u r e 3 4A
. e r i a pl h o t o g r a p h s
s h o w i n g t h e a r e aa r o u n d
SJ-1 i n 1935(A)and1954
(8).
82
site
appeared t o parallel the main inner channel as seen i n the 1954 aerial
photographs ( F i g . 34 8). The channels were located on the ground and tested
One w i t h severalclaylayers was sampled althoughthe
forclaylayers.
ageof t h e f i l l could not be determined i n t h e f i e l d .
The present inner channel,
10 to 15'm t o t h e n o r t h of the sample s i t e ,
has
small
a
crosssection (Fig. 35).Bank-full
dischargeappears t o be
about 27 m3/sec.
Stratigraphy i n p i t SJ-1 includes two .major fining-upwardsequences
from gravel to clay, b u t individual units w i t h i n eachsequence suggest that
depositionoccurredas
f i l l of an auxiliary channel. The gravel may havebeen
deposited when large floods s p i l l e d from the main channel andwere routed down
With smallerfloods,thesubsidiarychannelsreceived
thesubsidiarychannels.
finer-grained deposits such as cross-laminated sand,
s i l t and clay layers.
Thick clay layers may represent settiing of clay i n backwater areas. Thus
w i t h i n the major cycles are lesser fining-upward deposits 10 t o 12 cm thick.
Another f a c e t of t h e l a y e r s a t this s i t e a r e the variety of colors of sands
and clays (Appendix A ). Red sands and claysgenerallyarederived
from the
Triassic-Paleozoic terrane which predominates i n southern tributaries of the
RioSan Jose. Grayandbrown
sands and claysarederived from Cretaceous
strata to the north.
b.
S i t e SJ-5
S i t e SJ-5 is located near the upstream inlet
of a large oxbow of the Rio
San Joseimmediately upstream from the mouth of Rio Paguate (Fig. 1). The
oxbowwas formed when Rio San Jose was rerouted along an a r t i f i c i a l c h u t e
cutoff (related t o railroadbridges?) sometimebetween1954
(Fig. 36) and 1971
(Mesita 7% minutequadrangle).
The dateofcutoff
remains t o be established.
Between 1971 and 1980, 14 floods have been greater than base flow
a t Correo.
.Many of thesefloods s'hould have reached the oxbow. Fieldreconnaissance of
the oxbow revealed that parts of the oxbow are isolated from flooding by eolian
sand dunes and receive only eolian sand and reworked clay eroded from valley
f i l l exposed i n low arroyowalls. Although the Rio San Josepresentlyappears
t o have perenni.al..flow of muddy water in the nearby new channel and the sand
plugblocking the oxbow is r e l a t i v e l y low, t h e r e i s more sand than clay i n the
t h i n oxbow deposits.
83
S
N
I
r
5 m
no vertical exaggeration
Figure 35.
P r o f i l ea c r o s si n n e rc h a n n e l
s i t eS J - 1 .
a4
o f R i o San J o s en e a r
B.
A.
Figure 36.
Aerialphotographs o f theareaincluding
and PAG-1 in 1935 (A) and 1954 (B).
85
sample sites SJ-5
The stratigraphy of site
SJ-5 (Fig. 37) includes t h i n (1-2 cm) clay
layers interbedded w i t h unlaminated-tocross-laminated. sand (Appendix A ) .
The lowest (70-85 cm below thesurface)cross-laminated sand includes pebbles
and clay balls up t o cobble size indicative of the base of the channel. The
coarse-grained deposits rest
on a reddish brown (7% Yr 3/2) mottled clay w i t h
crystals of an unidentified evaporite mineral(probably sodium s u l f a t e ) .
This clay layer and the sequence of thin sand and clay below i s a widespread
i n the oxbowand i n exposures
deposit which was noted i n otheraugerholes
This depositappears t o be part of the
alongthepresentstreamchannel.
older valley fill.
PAG-1
S i t e PAG-1 is located on the delta of Rio Paguate where i t encroaches
i n t o PaguateReservoir (Fig. 36). Paguate Reservoir,builtin
1938, i s f i l l i n g
w i t h sedimentsderived from the Rio Paguate drainagebasin.
The drainagebasin
includes over 10 km2 of uranium mine workings whichbegan t o accumulate i n
1950. The sample s i t e was located above a topographically low part of the
Rio Paguatechannelupstream
from the dam, based on the 1935 aertiil photographs
( F i g . 36).
Because the surface sediments were nearly water-saturated, no p i t was dug.
Stratigraphy i n the auger hole included
an upper s e r i e s of layers of dark
grayish brown (10 YR, 4/21 clay and s i l t y c l a y 90 cm thick (Appendix A 1.
From 90 t o 220 cm areinterbeddedclays, sandy clays and t h i n sand beds. The
water table was reached midway through a clayey sand l a y e r a t a depth of 110 cm.
I t was impossible t o sample below 220 cm because the walls of theaugerhole
keptcollapsing.
The upper claylayersareinterpreted
t o be overbank flood
deposits between distributarychannels on the delta. The interbedded sand
and clay below are interpreted t o be adjacent to -a distributary. Perhaps
w i t h i n the reservoir.
some of the clay layers are lake deposits
Site
c.
B.
Sample Characterization
-
Physical and MineralogicalAspects
Optical and XRD analyses were performed on eighteenselected samples from
f o u r s i t e s and r e s u l t s a r e shown in Appendix B. As expected, samples of similar
mean grainsize were also shown t o be relativelysimilarin
mineralogy. S i t e s
1 and 4 were channel s i t e s and s i t e s 2 and 3 were oxbow s i t e s .
F i g u r e 37.
S t r a t i g r a p h y exposed i n pit SJ-5.
D.W. L o v e , A u g u s t , 1982.
87
Photograph by
The most abundantnon-claymineralin
a l l s i z e f r a c t i o n s was found t o
be quartz. Feldspar(apparentlylargelyalbite,
with minor microcline) and
c a l c i t e were alsopresentinsmallerquantitiesinallsizefractions.
Evapo r i t e s and magnetite were n o t detectable by XRD, b u t were notedin f i e l d samples
from l a t e r s i t e s .
The presence of tracequantities of otherminerals,including
mica and dolomite, was also suggested, a1 though optical and XRD evidence was
not conclusive.
The most abundant clay mineral i n all eighteen samples was found t o be
kaolinite.Significantquantities
of montmorillonite, i l l i t e , and c h l o r i t e
were sometimes found b u t variedconsiderably between samples. Mixed layering
of themontmorillonite and i l l i t e was also noted.
No systematicvariations i n mineralogy of individual size fractions with
e i t h e r s i t e o r depth were noted, except f o r a possibleincreaseintheproportion of chloritein the clay-sizefraction w i t h d e p t h . Furthermore, no
systematic variations were apparentin the proportion of fine-grained material
i n samples of a given mean grain size, or
i n the relative proportions of s i l t
and clay i n this material.
C.
Dating the Sediments Using
Pb-210,
Pb-214, and
Cs-137
BothPb-210and
Pb-214 peaks were clearly resolved by gamma spectrometry,
w i t h f u l l peak widths a t half the maximum peak height above background (FWHM)
of approximately 1.1 and 1.3 KeV, respectively, Peak shapes were consistently
Gaussian, and centroid energies were in good agreementwith one another and
withpublishedvalues
(NCRP 1978),againindicatingthat
no significant interferences were present.
Cs-137 peaks were occasionally less clearly resolved,
on account of the
greater full width a t half maximum (approximately 1.7 KeV) and thepresence of
a neighboring peak a t 665 KeV. The iterative nature of the peak areacalcul a t i o n , however, does appear t o accuratelyseparate the peaks in most cases.
In the remaining cases (marked by small Cs-137 a c t i v i t i e s and atypical centroid energies of FWHM values),visualestimation
of the peak areas was occasionally necessary.
No other interferences were indicated for any o f theisotopes i n tables
of known peaks from major fissionproducts and isotopesin the U-238,U-235,
andTh-232 decay series.
Because of the random nature of the individualradioactivedecays,the
measured a c t i v i t i e s were subject t o statistical uncertainties whichwere inverselyproportional t o the square r o o t of the number ofdecays measured. I t
was therefore possible, for example, t o halve the uncertaintyin a particular
measurement by increasingthecountingtime
by a factor of four. The typical
countingtimes of 16 - 24 hours f o r Cs-137,and 4 - 48 hours f o r Pb-210, Pb-214,
and Cs-137, thus r e f l e c t an attempt t o balance the r e l a t i v e e r r o r s of the activi t y measurements against the countingrequired.
(For example, the longercounting timeswithin each range oftencorrespond t o those samples which, on account
of their grain size or depth,could be expected t o have relatively lowPb-210
or Cs-137 a c t i v i t i e s ) . Counting times of about 12 hours were f i n a l l y adopted.
Thistimeallowed
counting statistics t o generate relative errors of usually
l e s s than l o % , even f o r the low levelisotopes.
In addition t o s t a t i s t i c a l errors, the measured a c t i v i t i e s may also be
subject to systematic errors in
the peak areas and efficiencies used, due t o
such factors as differences i n self-absorption between sand and clay samples.
The resulting relative errors are expected t o be on the order of 10 percent,
and will varydepending on both the nuclide and the detector. Although such
systematic errors should n o t s i g n i f i c a n t l y a f f e c t any CS-137 d a t i n g , they
would seriously affect the accuracy of Pb-210 dating of any sample in which
supported Pb-210 levels are h i g h , or i n which unsupported Pb-210 levels are
low due t o age.Thisdifficulty
may be p a r t i a l l y overcome by dealingwiththe
r a t i o of Pb-210 t o Pb-214, rather than the difference between the two values.
In accordancewith the radiometric decay equation, this r a t i o will decay exponentially with time t o a value of unity in any closedsystem.
Finally, the measured Pb-214 a c t i v i t i e s w i l l be subject t o a further
systematicerror due t o differencesin the r a t e of radon emanation w i t h
depth.Continualescape
of gaseous Rn-222 from a sample can, over time,
substantially lower the amount of supported Pb-210 present.Aftersealing
of a sample, however, Rn-222 (and hence Pb-214) would re-equilibrate at a
higher level. The calculated Pb-210/Pb-214 r a t i o , which likethecalculated
unsupported Pb-210 a c t i v i t y i s based on assumed secular equilibrium between
the measured Pb-214 and supported Pb-210, would therefore be too low in those
samples nearest the surface. To estimate the magnitudeof t h i s e r r o r , a
previously counted sand sample was unsealed and allowed t o stand for two weeks,
The decrease i n the measured Pb-214 a c t i v i t y was found t o be
thenrecounted.
0.21i0.04 pCi/g, or 27%. The resultingincrease in the measured Pb-210/Pb-214
Pb-210 a c t i v i t i e s were neglected, would
ratio,ifstatisticalvariationsinthe
be 0.40. The typicalincrease for finer-grained sample would presumably be l e s s .
D.
Pb-210, Pb-214, and
Cs-137
Activities
The a c t i v i t y ofPb-210 in the 213 samples was found t o range from 0.55 t o
15.6 pCi/g, w i t h a mean of 1.35. Pb-214 a c t i v i t i e s ranged from 0.51 t o 13.6
pCi/g, w i t h a mean of 1.18.Typical
uncertaintiesforthe
two nuclides were
on the order of 0.1 and 0.025 pCi/g,respectively; the larger uncertainty for
Pb-210 as a r e s u l t of the low probability of y emission.
The r a t i o of Pb-210 t o Pb-214 a c t i v i t i e s i n the samples generally fell in
0.2, w i t h a typicaluncertainty of 0.1 - 0.2. Again, the
the range of 0.7
uncertainties are due primarily t o the relatively h i g h uncertainty in the Pb-210
activities.
The highest Pb-214 r a t i o found in any of the samples,includingtheadditionalsurface samples c o l l e c t e da t other nearby s i t e s , was 2.3. Thus, in sharp
contrast t o previouslystudied areas, the level of supported Pb-210 on the
lower Rio Puerco i s g r e a t e r than the atmospheric(unsupported) Pb-210 flux.
This i s presumably the r e s u l t of natural and mining-relatederosion of uraniumrichmaterial(suchas
Morrison Formation outcrops and mine-mill t a i l i n g s ) i n
the upper portions of thedrainagebasin.
Such erosion would resultinthe
transport of elevated amounts of U-238 and i t s decay products i n b o t h soluble
and particulate form.
The measured Cs-137 a c t i v i t i e s of the samplesranged from <0.002 pCi/g
t o 0.73 pCi/g, w i t h most upper core samples f a l l i n g i n the 0.1-0.3 pCi/g range.
Uncertainties were typically on the order of 0.01 - 0.03 pCi/g with0.03 pCi/g
background 1 eve1 s.
The radionuclide activities of theindividual samples a r e summarized i n
Appendix C.
-
E.
Correlation of Pb-210, Pb-214, and Cs-137 Activities withGrain
Size
The Pb-210/Pb-214 a c t i v i t y r a t i o s o f the surface clay and clayey s i l t .
(For thepurposes of theplots,' the mean
samples areplotted inFigure38.
90
F i g u r e 38.
Pb-210/Pb-214 A c t i v i t y R a t i o s i n S u r f a c e C l a y
2.08
*
h
1.00
0.25
1.0
1.52.5
0.5
2.0
Mean Grain S i z e (mic ro n s)
91
Samples
grain sizes of the clay samples were a r b i t r a r i l y taken t o be approximately l p ,
those of silty clays approximately 2p and those of s i l t s approximately 3 0 ~ ) .
The a c t i v i t y r a t i o s of the s i l t and sand samples are plottedinFigure
39.
As expected, the r a t i o i s h i g h e s t i n theclay and s i l t samples (as are
the Pb-210 and Pb-214 a c t i v i t i e s themselves)..Despite
the large uncertainties
in the individual ratios, however, i t alsoappearsthat the ratio varies significantly even among samplesof similar mean grain size.
The Cs-137 a c t i v i t i e s of the same samples,plottedinFigures
40 and 41,
also show increases i n finer-grained samples a n d large variations among similar
samples (as i l l u s t r a t e d by the seven claysamples, which range in activity from
0.078 t o 0.248 pCi/g).
These variations maybe partially explained by fluctuations i n the rates
of Pb-210 andCs-137 depositionover the course of the yearduring which these
surface samples were collected, and by random variations in the
mineralogy of
theclay-sizefractions,asindicatedin
Appendix B. Nevertheless,thevariationsappear t o be only p a r t i a l l y random, asindicated by significantly higher
Cs-137 a c t i v i t i e s i n thoseclay samples from the upper (oxbow) portion of s i t e
2A, r e l a t i v e t o clay samples from similar depths a t o t h e r s i t e s .
As shown i n Appendix B, neitherthepercentage
of clay minerals, nor t h e i r
relative proportions, are
markedly different in the upper portion of s i t e 2.
The r e l a t i v e proportion of s i l t - and clay-size material also show no gross
differences.
Nevertheless, the higher s i t e 2 a c t i v i t i e s , a s well as the generally
higheractivities of surface samples from theother oxbow s i t e s 3A and 7,
San Jose 1, 4, and 5, and PaguateReservoir f i l l i n d i c a t e t h a t some factor
or factors i n the depositional environmentof t h e s e s i l t s and claysplays a
significant role in
Cs-137 deposition.
In determining an empiricalrelationship betweenCs-137 a c t i v i t y and mean
grain size, oxbow and active-channelsurface samples were thereforeconsidered
separately. The points were f i t t e d t o a curvein which the activitydecreased
exponentially w i t h increasinggrainsize,
and t h i s curve was then used t o
derive a set of approximatenormalizationfactors(Table
5) used incorrecting
the a c t i v i t i e s of samples from d e p t h for the effects of grain size variations.
92
F i g u r e 39.
'2.00
'1.75
1 .SO
Pb-2lO/Pb-214 A c t i v i t y R a t i o s i n S u r f a c e
Sand ana S i l t Samples
r
I
"
1.25
-
e 1.00
-
x
F
.r(>
.A
F
0
3
4
N
I
P
s
I
0.75
-
0.50
-
0.25
-
P
PI
,
200 100
I
I
1
300
400
Mean G r a i n ' S i z e (microns)
93
I
500
F i g u r e 40. Cs-137 A c t i v i t y i n S u r f a c e Clay S a m p l e s
0.7~
0.60
0.50
0 .bo
0.30
0.20
0.10
Mean Grain S i z e ( a i c r o n s )
94
F i g u r e 41.
0.7~
0.6C
0.59
0.40
0.30
0.20
0.10
I
I
+
.
100
+
200
300
I
I
400
500
Mean Grain S i z e (microns)
95
Mean Grain Size
Cs-137 Activity of Sample
Cs-137 Activity of Clay
1
1.oo
2
0.99
30
0.86
61
0.73
88
0.63
125
0.52
177
0.39
250
0.27
350
0.16
500
0.07
1500
0.01
Table 5.
Normalization f a c t o r s used i n Cs-137 dating.
96
-
F.
Correlation of Pb-210, Pb-214, and Cs-137 Activities w i t h Depth
Interpretation of the activity profiles of the small s i t e s i s complicated
with
by the existence of systematic as well a s random variations in grain size
depth; even in thesandiest channel deposits,for example, thesurfacelayer
may consist of s i l t or clay.Nevertheless,
i t does appear t h a t the Pb-210
a c t i v i t i e s - and hence the Pb-210/Pb-214 r a t i o s - a r e higher i n surfacesamples,
reflecting the e f f e c t s of atmospheric Pb-210 deposition. In contrast, the nonatmospherically-derived Pb-214 typically reaches i t s maximum a t some point below
thesurface.
The Pb-210/Pb-214 r a t i o does n o t , as expected,decrease to unity w i t h depth.
Rather, i t immediatelydrops fromavalue of 1 - 2 t o a value of approximately
0.8
0.9, and generally remains between 0.8 and 1.0 throughout the remainder
of thecore.Thisclearlyindicatesthat
the majority of the samples.had n o t
remained closedwith respect t o the immediate precursors of Pb-210 (presumably
Rn-222 in particular) d u r i n g the time between their deposition and the sampling.
The magnitudeof thediscrepancyappears
t o be approximately 0.1 t o 0.5 p C i / g ,
in good agreement w i t h the value of0.4 pCi/g obtained(aspreviouslydescribed)
by measuring the e f f e c t ofradonemanation
on a typical sandsample.
The
radon loss from individual samples will presumablyvary w i t h both grain size
and proximity t o the surface, being highestinshallow
sand samples.
Profiles of normalized Cs-137 a c t i v i t i e s of samples from s i t e s 1-7
(Appendix D ) also show a consistent pattern, with a broad subsurface maximum
followed by a t r a n s i t i o n , a t a depth of a few meters, to samples with l i t t l e
or no detectableactivity.
Although smallervariationsare
superimposed on
this generalpattern,these
show l i t t l e or no correlation between cores, and
may be due t o the samerandom variations in Cs-137 a c t i v i t y seen inthesurface
samples. Alternately,in the case of relativelycoarse-grained samples,they
may represent artifacts of the normalizationprocess.
In those samples below the transition in
which Cs-137 was reported,
measured a c t i v i t i e s a r e t y p i c a l l y l e s s
t h a n 2 standarddeviations above background a f t e r background correctionsare made. These occurrences may therefore
represent either contamination of the samples withsmall quantities of Cs-137
during sampling or handling, or statistical fluctuations in the
background.
In the latter case, the correspondence of thereportedcentroidenergies
with
t h a t of Cs-137can be largely accounted for by the inclusion of the background
-
97
Cs-137 counts in the energy calculation.
G.
Pb-210 Dating
Pb-210 dating of the samples was n o t possibleforseveralreasons,the
most important of which involves the errorintroduced by radon emanation.
Although i t i s possible t o correct for the effects of radon emanation
(Christensen 1982; Imboden and S t i l l e r 1982) theactual emanation r a t e sa t
the s i t e s studied are expected t o depend i n a complex fashion on theindividual
sedimentsequence.
the variaAdditional factors preventingdating of thesedimentsinclude
b i l i t y of t h e i n i t i a l unsupported Pb-210 a c t i v i t y among relatively similar
surfacesamples, and the high levels of supported Pb-210. The l a t t e r w i l l tend
t o magnify the e f f e c t of systematic errors i n the efficiency calculations, in
additiontoincreasing
the uncertainty due t o counting errors.
H.
Cs-137 Dating
Relatively narrow and well-defined maxima in the Cs-137 profiles, on which
most previousdating has been based, were n o t seen in any of the oxbow sample
sites(Figures 42-44). This may be due e i t h e r t o non-deposition or subsequent
erosion of the sedimentscorresponding t o times of peakCs-137 f a l l o u t , o r l a t e r
redistribution of the sediments. Such redistribution, if i t produces sufficient
upward t a i l i n g of the individual maxima, could result in the observed pattern
of a single very broad maximum. The most stable or regulardepositionalenvironment was a t thePaguate s i t e where sediments were deposited behind the Paguate
Reservoir dam (Figure44).
A t t h i s s i t e s e v e r a l maxima were indicated b u t
a more detailed core segment wouldbe necessary t o corroborate these data.
In the absence of datable maxima in the profiles, the scope of the Cs-137
dating i s limited t o determining whether or n o t significant levels of Cs-137
are present, and therefore whether or notthe samples i n questionpostdate 1950.
S i t e 1 A - Rio Puerco
The sedimentsequence a t s i t e l A , a n active channel s i t e , consistsprimarily
of alternating fine sands and clays (0-208 cm), underlain by coarsersands
(208-249 cm), gravel (249-259 cm), and further sands. The gravellayer i s
1.
0
I-
a
io
5
15
SAMPLE
NUMBER
F i g u r e 42.
20
25
30
35
(REFLECTS
DEPTH)
Cs-137 a c t i v i t y as a f u n c t i o n o f depth. S i t e 7 oxbow.
A
ll samples greater than number 9 were z e r o o r l e s s t h a n t h e d e t e c t i o n
1 imit.
C
C
c
0
C
I-
a
4
Figure 43.
ai;!
16
2b
SAMPLE NUMBER (REFLECTS DEPTH)
'
~~~1
2b
-..
2a
Cs-137 activityas a function o f depth. S i t e 9 oxbow.
Samples greater than number 8'werezero or less than the detection limit.
CS-137 ACTIVITY IN PCI/GAT PAGUATE
* 200
presumed t o correspond t o the base of the channel sequence, and thus t o a
date of circa 1950.
With a few exceptions,the Cs-137 a c t i v i t i e s of the samples i.n the upper
208 cm were sufficient t o indicate post-1950 ages,inaccordancewiththe
stratigraphic d a t e (Appendix C ) . Below208cm,
the a c t i v i t i e s f e l l t o zero.
As the mean grain size of these samples was relatively large, however, t h i s
does not necessarily indicate pre-1950 ages for the sedimentsinquestion.
Cs-137 dating of this portion of the core was therefore n o t possible.
-
S i t e 2A Rio Puerco
The sedimentsequence a t s i t e ZA, an abandoned-channel (oxbow) s i t e ,
consists of clays (0-152 cm), underlain by furtherclaysinterbeddedwith
increasing amounts of f i n e sand and s i l t (152-267 cm), and sandscoarsening
t o gravel
(279-523 cm). The upper claysare presumed torepresentthelater
stages of oxbow deposition, and the underlyingclays and the f i n e sandsthe
earlier stages.
The position of thebase of the oxbow sequence can n o t be
preciselydetermined, b u t should f a l l between152and
267cm.
With only one exception, the Cs-137 a c t i v i t i e s of the samples inthe
upper 185 cm were high t o extremelyhigh,againclearlyindicatingpost-1950
ages. From 185 t o 262 cm, a c t i v i t i e s were lower b u t s t i l ls i g n i f i c a n t .
Thus,
assuming the Cs-137 evidence i s c o r r e c t , the base of the oxbow depositshould
f a l l much closer t o 267 than t o 152 cm. Activities were zeroornearzero
below 262 cm, although the evidence was againinconclusive on account of the
coarsegrainsize
of the sediments (Appendix C ) .
2.
S i t e 3A - Rio Puerco
The sedimentsequence a t s i t e 3A, an abandoned channel (oxbow) s i t e ,
consists of a mixture of f i n e sands and clayclasts(apparently
from the
nearby bluff face) and oxbow clays (0-163cm), underlain by f i n e sands
(163-213 cm). The base of the oxbow deposits is presumed t o l i e between
163 and 254 cm.
The Cs-137 a c t i v i t i e s of the samples i n the upper 68 cm are, w i t h two
exceptions,sufficiently h i g h t o clearlyindicatetheir
post-1950ages.
Very
low levels ofCs-137 were also detected i n most of the samples from 168 t o
254 cm. Because of thelongercountingtimes
and lowered levels of background Cs-137, however, t h e a c t i v i t i e s of many of these samples were s t i l l
3.
102
s t a t i s t i c a l l ys i g n i f i c a n t .
TheCs-137
dating,therefore,againindicatesthat
the 1950 horizon l i e s c l o s e t o the lower l i m i t s e t by the stratigraphic evidence.
Cs-137 dating of the samples below254 cm was a g a i n n o t possible because of the
coarse grain size of these sediments (Appendix C ) .
4.
-
S i t e 5 Rio Puerco
The sedimentsequence a t s i t e 5, an active channel site, consists of gene r a l l y f i n e sand with minor clay and s i l t (0-290cm), underlain by sandscoarsening t o gravel (290-353 cm), and further sands. Once again,thegravelpresumably represents the baseof the post-1950channel.
The Cs-137 a c t i v i t i e s of these samples are low, even i n comparison with
the channel sediments from s i t e 1A. The a c t i v i t i e s of several of the samples
in the upper 198-213 cm are sufficient, however, t o indicate post-1950ages f o r
t h i s portion of the core. Below213cm,
the Cs-137 evidence i s once again
inclusive on account of the coarsegrainsize
of the samples (Appendix C ) .
-
S i t e 6 Rio Puerco
The sedimentssequence a t s i t e 6, an active channel site, consists of
generally fine t o medium sand,with rare clays and pebbles(0-295 cm), underl a i n by gravel (295-345 cm) and further sands and clays. The principalgravel
layer, rather t h a n e i t h e r of the s l i g h t l y pebbly horizons, i s presumed t o represent the baseof the recentchannel.
TheCs-137
a c t i v i t i e s of only 2 of the samples ( a t 0-3 and46-64 cm) were
found t o be s t a t i s t i c a l l y s i g n i f i c a n t , and therefore indicative of post-1950
ages. The level ofCs-137
presentinthe
post-1950samplesthusappears
t o be
extremely low a t t h i s s i t e , presumably due primarily to the coarser
grain sizes
of most of the channel sands. In s p i t e of t h i s f a c t , however, one additional
Cs-137 date was obtained. The sample i n question, a clay sample from a depth
a t 457-475 cm,was found t o have less than 0.004 pCi/g of 13-137, clearly
indicating i t s pre-1950 age (Appendix C ) .
5.
-
S i t e s 7 and 7A Rio Puerco
The sedimentsequence a t s i t e 7, an abandoned channel (oxbow) s i t e , cons i s t s of s i l t and clay(0-51 cm), underlain by f i n e sand (51-213cm), and
sand gradingintogravel
(213-437 cm). The base of the oxbow depositsis
6.
103
presumed t o l i e a t a depth of s l i g h t l y g r e a t e r t h a n 51 cm.
The high Cs-137 a c t i v i t i e s of the samples inthe upper 41 cm once again
clearlyindicate their post-1950 ages. TheCs-137 a c t i v i t y of theclay sample
a t 41-51 cm, however, i s l e s s t h a n 0.010 pCi/g,suggesting that the 1950 horizon
has been reached.This
i s once againin good agreement w i t h the depth indicated
by the stratigraphic evidence (Figure
42).
7.
-
S i t e 9 Rio Puerco
The sedimentsequence a t s i t e 9 , an abandoned channel (oxbow) s i t e upstream
from a l l a c t i v e uranium m i n i n g and milling activity consists of s i l t and clay
(0-99 cm) underlain by coarse sand and gravel (99-183 cm) grading t o sandy clayloam (183-254 cm). The base of the oxbow deposit is presumed t o be a t a depth
o f about 100 m.
The high Cs-137 values i n the upper 110 cm again clearly indicate a post1950 age. All samples lower i n the core have Cs-137 a c t i v i t i e s <0.01 pCi/g
includingseveralclay
samples which i s in good agreement w i t h depth indicated
by the stratigraphicevidence(Figure43).
S i t e 1 - San Jose
The sedimentsequence a t s i t e on the Rio San Jose consists of interbedded
sands and s i l t clays t o a depth of 120 cm
followed by a bluish-grayclay
presumed t o be quite old and a t the base of the oxbow deposit.
TheCs-137 valuesdecreaseto
background i n the bottom two samples, again
in agreement w i t h the stratigraphicevidence (Appendix C ) . This oxbow s i t e was
probably p a r t of the active channel a number of times due t o t h e narrow,confined nature of thestream bed.
8.
Paquate
Reservoir
This s i t e i s l o c a t e d i n t h e f i l l d e p o s i t s
of the PaguateReservoir which
i s only 6 km downstreamfrom theJackpile open p i t uranium mine (see sample
The entirecore was quite uniform
being
primarily
sites,Section I11 A.c.
coredid n o t penetrate
siltyclayinterbedded-withfine
sand t o 220cm.The
t o below thereservoirdeposits.
Cs-137was <.02 pCi/g below 120 cm which
clearlyindicates pre-1950 age f o r the bottom 5 samples (Figure 44). Because
the grain size was uniform in this case, there is
no ambiguity t o thisconclusion.
9.
104
I.
Radionuclide
Distribution
1.
General
Naturallyoccurringradionuclides
which are commonly presentin uranium
deposits as daughters of U-238 decay (seeFigure 2 ) and which may be transported
away from mining and milling activities are Pb-210, Pb-214, Ra-226, and Th-234.
These radionuclides are n o t soluble under oxidizing conditions, as opposed t o
uranium i t s e l f , and therefore maybe transported within the sedimentload of
streams. Iffiner-grainedmaterial
i s responsiblefor the transport of the
oxbow deposits (or
radionuclides,they may be expected t o accumulateinthe
further downstream inreservoirs).Individual
sample radionuclidevaluesare
summarized in Appendix C.
2.
Pb-210
Data f o r Pb-210 a r e shown p l o t t e d as a function of depth a t oxbow and
PaguateReservoir sample s i t e s on Figures 45-51
A generaldecrease i n Pb-210
a c t i v i t y from recent t o older samples from S i t e s 2 (Figure 4 5 ) , 7 (Figure 47),
.
San Jose 1 (Figure 50), and Paguate(Figure51)
i s evident. The most striking
d i f f e r e n c e s a r e a t Paguate and Rio San Jose-1 which a r e the closest sites t o
the Grants Mineral Belt. The highest values found were a t Paguate a t 16 pCi/g
which i s about lox the average level ofPb-210 intheoldestsedimentstested.
No trendsareapparent
a t S i t e 9-Rio Puerco (Figure49).This
s i t e i s above
the confluence of the Chico Arroyo which i s t h e f u r t h e s t upstream from contribution of active uranium mining. Samples from S i t e 9 should then be indicative
of regionaleffects andnone areapparent.
The valuesforrecentsediments
(from Cs-137 concentrations and aerial photography) a r e about the same as for
the valley-fill and deep-core sedimentsamples which may be thousands of years
o l d . Pb-214, which i s insecularequilibrium
w i t h Pb-210, shows similar trends
and data are summarized in Appendix E .
A somewhat puzzling set of dataforSite
7A i s shown inFigure
48. In
order t o test the results from Site 7, which showed a decreasing trend i n radioa c t i v i t y withage, a second f i e l d t r i p t o the s i t e wasmade t o sample another
portion o f the oxbow, As previouslydescribed,located
upstream from the Rio
San Jose and a minimal amount of mining activity (with the exception of exploration and some dewatering) was present. I t was unexpected thatradionuclides
105
rn
a
0.400
0.800
PB-210 ACTIVITY IN PCI/G AT RIO PUERCO 2
0 000
0
107
108
I
OOP'Z
I
OOO'Z
I
009'F
I
OOZ'F
I
008'0
I
OOP'O
VL 0 3 E l k I OItf 1 V 9/13d NI AlIAI13V O'GZ-&j
109
I
000'0
N
z
H
>g
t"?.
HO
>
H
I
m
Q
0
0
0
"
0
0
4
ii
i6
20
SAMPLE NUMBER (REFLECTSDEPTH)
Figure 49.
Pb-210 a c t i v i t y a s a function of depth.
2h
2;3
S i t e 9 Rio Puerco.
0
0
P
Nl
a
0
00
-14
N O
I
m
a
0
0
0
0
0
12
4
24 16
20
28
S d P L E NUMBER (REFLECTS DEPTH)
Figure 50.
Pb-210 a c t i v i t y as a function o f d e p t h .
S i t e 1. Rio San Jose.
112
such as Pb-210 wouldshow increasedlevelsand,in
f a c t , as opposed t o S i t e 7,
the 7A levels were relatively constant. S i t e 7A may show d i l u t i o n of t h e s i l t clay samples by older valley fill clays
from the side walls and t r i b u t a r i e s and
w h a t was f o u n d f o r the auger core a t 7 may simply be a function of grain size
(more s i l t - c l a y , more adsorption of radionuclides).
3.
Ra-226,
Th-234
These radionuclides,as expected, show exactly the same trends as those
observed f o r Pb-210. This i s expectedbecausethey
a r e a l l members of the U-238
decay series, are insoluble and are stronglysorbed by sediments. The datafor
these two isotopes are summarized ashistograms i n Appendix E. The highestvalue
found for any radionuclide of 26.85 pCi/g was found f o r Ra-226 in Paguate Reservoir
sanple #2 which was found a t a d e p t h of 15-30 cm.
4.
Ac-228
Actinium-228 i s a relativelylong-livedisotope
i n the Th-232 natural decay
series. The natural thorium concentations f o u n d in uranium deposits may not
be elevatedlike the Th-234 levels because Th-234 i s a daughter of U-238. I f
this is the case,the
Ac-228 levels would not show the drastic increases shown
byU-238
daughtersin the mining region. The Ac-228 values a t Paguate (Figure
52) does not show any trends w i t h depth which i s i n starkcontrast t o the
U-238 daughters. However, the Ac-228 trends a t S i t e s 2 and 7 (Rio Puerco
Figures53,54)
and S i t e 1-Rio San Jose (Figure 55) mimic those shown
by
the
U-238 daughters and suggest t h a t the trends indicated a t these s i t e s a r e simply
a function of grain size as was previouslydiscussed f o r Cs-137 dating(Section I11
E).
This relationshipwarrantsfurtherinvestigation.
-
J.
Trace Metal Distribution
The 230-(<6311) fraction of sediments from thecore samples were analyzed
f o r a numberof
tracemetalsincluding
As, Cd, Cr, C u , Hg, Mo, Pb, Se, V, and
U. A number of thesetracemetals
have been found t o have concentrations i n
streamsediments i n the region which a r e much higher than crustal abundance
(Brandvold e t a1 . 1981,1981 ) and the Grants Mineral Belt i s suspected a s a
source. Also, the composition of uranium milltailings often shows high levels
of these same tracemetals (Dreesen e t a l . 1982) and if the tailings material
113
h
0
J
0.400
AC-228
0.800
1.600
1.200
2 * 000
ACTIVITY IN PCI/G AT PAGUATE
..
111111111111111111111111111111111111111111111111111111111111111u
000
2.400
,400
I
OOP'Z
I
I
I
I
I
l
t
I
OOO'Z
009'F
ooz 7
008 ' 0
OOP'O
ooo'loo
L 03tlXId OItf 1 V 9/13d NI AlIAI13V 8ZZ-3V
116
0
m
W
n
m
0.000
m
N
P
N
b
0
0.400
AC-228 ACTIVITY I N PCI/G AT SAN
JOSE 1
.400
i s transported by surfacewaters, the metals may be enriched downstream. In
order t o compare similar sediments, the 230- sieved fractions were digested
and analyzed.
1.
Trace metals i n post- and pre-1950 oxbow sediments
Data f o r trace metalsin core samples from oxbow s i t e s i n thestreams and
in the PaguateReservior f i l l a r e shown i n Table 6. The elements As, Se, Cd,
Hg, and U areconsiderablyelevated
above crustal abundances(Krauskopf 1979).
Mercury values are an order ofmagnitude higher and uranium two orders of
magnitude higher and mercury i s considerablyhigher i n the Rio San Josesediments.
As, Se, and U areassociated i n manyof
the ore deposits i n theregion.
These
same five elements have previously been reported t o be elevatedinregional
sediments (Popp and Laquer 1980;Brandvold e t a l . 1980). Theredoes not appear
t o be any significanttrend w i t h depth a t any of thesites.
This i s q u i t e
different than the radionuclide results. Apparentlythesolubilities
of As, Se,
Cd, Hg, and U under oxidizing conditions are sufficiently
h i g h t h a t they are
eventually transported downstream whiletheradioactive
species measured
(Th-234, Ra-226,Pb-210,
and Pb-214) a r el e s sl i k e l yt o
be transported. Because
most of the Pb i s n o t radioactive,theoverall
Pb values need not be present
i n elevatedconcentrations even though the radioactive Pb i s h i g h .
2.
Tracemetals
i n surfacesediments
-
230- fractions
Surfacesedimentscollectedinthe
oxbow s i t e s and in Paguate Reservoir
would r e f l e c t very recentdepositionalevents
and thetrace metal analyses
a r e shown i n Table 7
These sediments show the same trendsinconcentration
J . 1.) inthat As, Se, Hg, Cd, and U are
a s do the coresediments(Section
elevated above crustal abundance w i t h Hg again highestinthe
Rio San Jose
sediments. The PaguateReservoir s i t e has higher U and V valuesin i t s surface
sediments a s well aselevated Pb-210, Ra-226,andTh-234which
a r e U-238
daughters. These radioactivespecies plus U and V a r e probablyelevated due
t o the proximity of the Jackpile mine. The Rio San Jose does n o t seem t o have
a s i g n i f i c a n t e f f e c t on the Rio Puerco sedimentsexceptperhaps
f o r mercury
as judged by values i n the Rio Puerco surfacesediments above and below i t s
confluencewith the San Jose.
.
118
Rio
Rio Puerco
As
Se
U
L
U
L
Cd
U
L
Cr
U
L
b-
San Jose
2
-
3
-
7
-
7A
-
9
-
12.4
8.8
10.4
15.0
12.0
11.1
6.3
16.8
12.9
-
SJ1
11.8
8.3
Paguate
PAG
-
Crustal
Abundance
6.7
7.2
1.8
-
0.40
0.29
0.40
0.58
0.41
0.33
0.13
0.19
0.26
0.19
0.20
0.13
1.3
0.5
0.05
0.22
0.46
0.30
0.39
0.28
0.24
0.37
0.48
0.32
0.37
0.33
0.37
0.62
0.83
0.15
-
-
57
57
55
49
53
48
53
29
44
37
51
45
38
32
100
31
61
79
68
36
49
29
20
63
27
19
17
18
18
50
-
Y
\o
cu
u
L
0.16
0.15
Pb
U
L
Mo U
L
v
u
L
u
u
L
22
30
0.24
0.22
32
41
1.4
5.3
3.4
2.8
0.22
0.18
19
31
1.5
3.1
0.51
-
47
2.7
1.6
0.22
-
0.98
2.30
-
42
27
1.8
1.8
2.4
2.3
0.13
0.56
25
30
1.4
2.2
115
106
124
97
115
104
108
93
99
134
94
82
110
91
352
373
243
343
560
398
284
370
375
425
300
368
380
Table
6.
-
-
0.02
-
13
-
1.5
-
123
-
2.7
-
Tracemetalconcentrations
i n augercore
2 3 0 - ( < 6 3 ~ ) sediments.Values
i n ppm dryweight.
U stands f o r uppersectionsdeterminedto
be deposited
post-1950 and L stands f o r l o w e r s e c t i o n s d e t e r m i n e d t o
be pre-1950.
Rio Puerco
AboveSan Jose
Rio Puerco
BelowSan Jose
14
0.29
0.32
48
73
0.17
40
1.3
110
420
0.138
1.27
1.93
0.906
1.19
8.5
0.20
0.35
37
39
0.67
13
2.2
61
340
0.167
1.16
2.57
1.23
1.55
As
Se
Cd
Cr
cu
Hg
Pb
Mo
v U
CS-137
Pb-210
Ra-226
Th-234
Ac-228
Table 7
.
Rio San Jose
22
0.15
0.92
34
19
0.93
9.7
1.4
95
310
0.184
1.92
2.41
1.06
1.48
Paguate
4.6
2.0
0.31
43
20
0.06
16
2.4
180
550
0.195
5.39
11.5
4.45
2.02
Trace metal concentrations i n 230-(<63p) fraction i n
surfacesediments a t oxbow s i t e s . Values i n ppm dry
weight.
120
3.
Tracemetalsinactive
channelsedimentcore
samples
-
230- fraction
The trace metal data shown inTable 8 f o r the 230- i n active channel
sediment core samples show about the same trendsasalltheothersediments.
Again, Hg, Cd, and As show slight elevations in
the Rio San Josesediments.
However, because the 230- fraction is so much larger in the oxbow sediments
than i n active channel sediments, the totalmetalsstored
i n the oxbow sediments will also be much greater.
121
Rio Puerco
BelowSan Jose
As
Se
Rio Puerco
AboveSan Jose
10.2
.30
.49
52
53
.42
22
2.6
91
353
Cd
Cr
cu
Hg
Pb
Mo
V
U
Table 8
.
10.6
.45
.37
44
55
.49
21
2.4
92
361
Rio San Jose
35.1
.14
1.32
33
23
1.23
35
.95
88
380
Trace metal concentrations i n 230-(c63p) fraction i n
sediments from a c t i v e channel sites. Values i n ppm
dry weight.
122
IV.
SUMMARY, CONCLUSIONS,
AN0
SUGGESTIONS
FOR FURTHER WORK
A methodology for establishing the age of recentsediments i n streams
draining a major uranium mining and millingregionhas
been established
based on combined geomorphic, stratigraphic, and radiometricdatingtechniques.
the region,environIn theabsence of historic geochemical baselinedatafor
mental changes resulting from uranium mine-mill a c t i v i t i e s can only be determined by indirect methods.
The primarygoal of geologicalstudies was t o determine the age of recent
sediments i n order t o evaluatepossiblecontributions
of radionuclides and
heavy metals t o alluvial deposits of the lower Rio Puerco-San Jose drainage
system. These studies focused on (1) processes of sediment transport and
depositionalongthe
Rio Puerco and Rio San Jose downstream from the lower
Arroyo Chico andRio Paguate areas, and ( 2 ) identification of stream deposits
t h a t immediately predate and postdate the onset of uranium mine-mill a c t i v i t y
i n the early1950's.
Because clay-sized sediment i s primarilyresponsiblefor
sorption of radionuclides andheavy metals,datable sites of clay-richsediments were sought along the drainage system downstream from the majormine-mill
areas of theeastern Grants Uranium Belt. Abandoned channel loops (oxbows)
were chosen f o r studybecausethey
are easy t o locate on aerial photographs
takensince 1935, canbe assigned an age for development, and commonly have
thick clay-rich fill.
Adjacentreaches of .thepresentstream
channel were
studied f o r comparison.
Pits were dug a t oxbow s i t e s t o determine stratigraphy and composition
of deposits. Samples collected from pit walls and augerholes below the p i t s
gamma
rayspectrometry for the
were subjected t o radiometric analysis by
artificial radionuclide Cs-137and thenaturalradionuclide
Pb-210 a s well
a s other U-238 and Th-232 daughters. Because of the dynamic nature of the
system,absolutedating
w i t h Cs-137was notpossible b u t samplescould be
datedaseither
pre- or post-early1950's.
The Pb-210 dating was n o t possible
because background Pb-210was very h i g h r e l a t i v e t o f a l l o u t Pb-210.
Sediments dated by the correlative Cs-137, stratigraphic, and h i s t o r i c
techniques were thenanalyzed for radionuclides and trace metals which would
be associated with uranium ores. The U-238 daughtersaregenerally h i g h in
the region and l i t t l e d i f f e r e n c e was observed for their values between the
control s i t e and the sites in the
uranium mining and millingregionexceptfor
thePaguateReservoir
s i t e . Recent sediments a t Paguate clearly show elevated
123
levels of U-238 daughtersinsediments
unambiguously dated a f t e r the mid 1950's.
Sediments from the Jackpile uranium mine have been trappedin the r e s e r v o i r f i l l .
Tracemetals were also analyzed i n old and more recentsediments and As,
Se, Cd, Hg, and U show elevatedvalues on a regionalbasis b u t no correlation
w i t h age (i.e.preo r post-1950). These elevatedtrace metal values may
simply be due t o their association with the regionally mineralized material.
From study of aerial photographs, thereappears t o be much larger changes
inconfiguration of the inner channel and innerfloodplain between 1954 and
thepresent(29years)
t h a n between 1935 and 1954 (19 years). These changes
may be related t o hydrologic changes in the drainagebasin and t o changes in
vegetation on theinnerfloodplain.
Many oxbows, particularlythose abandoned
prior t o 1954, have n o t developed extensiveclay-richdeposits.Instead,
the
f i l l i s predominantly sand alongwithpoorly-sortedsediments
from small
tributaries eroding adjacent valley fill.
Along the Rio San Jose and the
lower Rio Puerco,sediments from different source areas may be distinguished
in a general wayby color.
Although deposits have been placedin a generaltime framework, correlations
between individualfining-upward deposits and individualrecordedfloods
remain
t o be completed. Changes i n the geometry of theinner channel and complexities
in the records for g a g i n g stations along the Rio Puerco make i t d i f f i c u l t t o
determine the number of floods which inundate each sample area. By tracing
floods downstream from d i s t i n c t i v e headwater areas, i t may y e t be possible
t o correlate some sand-plug or inner-floodplaindeposits based on further
work w i t h tamariskgerminationages
and depth of burial of former surfaces.
The following recommendations a r e made:
1) The approachdeveloped inthisstudy
canbe used t o evaluate mine-mill
e f f e c t s i n fluvial environments downstream from theactivity.
The
procedures should be generally applicable t o western mining regions.
2)
Sediments deposited i n environments closer t o mine-mill operations
should be studied,especially i n areas which appear t o be 'sinks' such
as PaguateReservoir and the McCarty's marshes along the RioSan Jose.
3) A studyof this nature i n the Rio Puerco of the West nearGallup may help
answer questionsregarding the e f f e c t s from the United Nuclear t a i l i n g s
pond s p i l l in 1979.
4)
I t may be possible t o separateeffects of uranium mining and milling
a c t i v i t y from natural background by comparing U-238 daughteraccumulation
t o daughters i n the Th-232 series.
124
REFERENCES CITED
Alberts, J.J., L. J. Tilly, and T. J. Vigerstad (1979). Seasonal cycling
of Cs-137 in a reservoir. Science 203, pp. 649-651.
Anderson, 0. J. (1981). Abandoned or inactive uranium minesin New Mexico.
778 p.
New Mexico Bureauof Mines and Mineral Resources Open-file Report 148,
Bachman, G. O., J. D. Vine, C. B. Read, and G. W. Moore (1959). Uraniumin the La Ventana Mesaarea,
bearing coal and carbonaceous shale
Sandoval County, New Mexico. U.S. Geological Survey Bulletin 1055-5,
pp. 295-307.
Benninger, L. K. (1978). Pb-210 balance in Long Island Sound. Geochimica &
Cosmochimica Acta 42, pp. 1165-1174.
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'
"_
"
127
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%
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w i t h '
"
129
VI.
ACKNOWLEDGEMENTS
We are grateful to the Huning Land Trust, Westland Corporation, Benjamin
Benavidez, and the Laguna Indian Tribe f o r permission t o sample on their land.
Virginia McLemore was very helpfulinproviding
background data and production
figures for theGrants Uranium Belt.Several
of theideas and procedures
discussed i n this report, especially relating t o radioisotopedating, were
i n i t i a l l y pursued by Michael Dehn, who incorporated some of the s i t e data
i n hisMaster'sthesis
( i n preparation). Kevin Novo-Gradac carried o u t much
of the analysis of radionuclides and heavy metals as part of his Master's
thesis (inpreparation). John Young (1982) investigated long-termbehavior
and aidedindigging
of the lower Rio Puerco as part of his Master's thesis,
pits and describing samples alongthe Rio Puerco. Jim Boyle, Dough Heath,
Steve Rosen, Jack Purson, and Phil Coleman helpedinsurveying
sample s i t e s ,
i n digging p i t s , and compilinghydrologic and sedimentological d a t a on the
Rio Puerco drainagesystem.
W
e areparticularlygrateful
t o Lois Devlin and
Margo Moore who typed themanuscript and aidedwith the compilation of the
report and t o TeresaMueller who drafted several of the figures.
130
0-5
1.4-7
5-25
1A-3
81-94
LA-6
94-122 13-7
122-135 1A-n
152-163 1A-19 a l i i t o s tw a t e r - s a t u r a t e dc l a y e y
s a n d ; " 5 % broXn
and r e a cl.ayf (177-25Q u ) sand
163-173 1 A - 1 1 v e r y Wet l o o s e f i n o sand (5R&: 62-350 u) with
orokln c l a y a t b a s e . Colors p r e d o m i n a n t l y 10
YR 5 / 3 d r y , 10 YR 4 / 3 wet; s o m e c l a y has
r e d d i s ht i n g e
173-183 1A-12 c l a y a t t o p ,f i n e
c o a r s e rb e l o # .
wet
5and (83%: 577-250 u l g e t t i n g
C o l o r 1 0 YH 7- 1 3 dry, 10 Y R 5 / 3
183-1Sb 1 A - 1 3 v e r y f i n e send ( 6 5 % ; 6 2 - 7 1 0 u l a r t o p ,
( I 0 Y R 4 / 5 1 c l a y e y * e t sana at base.
196-200 1 A - 1 4 c l a y e y s a n d (62-1.410 u). p a r t i c u l a r l yc l a y e y
at hdse. Sand ( 4 7 % ) , sllt and c l a y (53%).
C o l o r s 10 kp, 7 / 3 dry. 1 3 YR 5 1 3 klet
site
Deptn
( c in )
0-2.5
6ar~olr
28)
uescrlptian
KO*
zA-surface
c l a y vita c o i o r I O YK
0/.3
a r y l 10 YR 4 / 3
*-et
2A-1
c l a y and silt :+$.rich c o l o r
413 wet
15-30
2A-2
c l a ya n d
5 1 2 wet
30-41
2.4-3
Laminated s i l t J.nd c l a y w i t h c o l o r 10 YR 6/3
d r y , l o 1 P 4/3 w e t ,g r a i n
s i z e from < 2 u t o
61 u
41-bl
2A-4
c l a y ancl s i l t w i t h c o l o r 10
1/3 a e t
61-81
2L-5
c 1 . a ~an'd s i l t w i t h color 10 YR 6 / 3 d r y , 1 0 YH
4 / 3 wet
81-91
2P-6
c l a ya n d
4 1 3 wet
2.5-15
91-112 2A-7
1 0 kP. 6 / 3 d r y ,
s i l t w i t n c o l o r 10
YP 7 / 2 d r y ,
YR
I!!
Yli
15 YK
h/3 d r y , 10 Y h
s i l t w i t h col.or 10 Y l i 6 / 3 d r y , 10 YR
c l a y and s i l t w i t h c o l o r 10
YR 6/3 d r y ,
10 Yli
4 / 3 wet
112-132
2A-8
132-1552 2A-9
c l a y and s i l t w i t h c o l o r 11 YR 6/3 dry, 10 YH
4 / 3 wet
base of p i t a t 152; c l a y and s i l t w i t h c o l o r
10 YR 6/3 dry, 10 YF 4/3 w e t
152-160 2A-10 c h o c o l a t e brOWn (7.5 YFC 4 / 2 1 c l a y w i t h s t r e a K s
and CraciCs c o n t a i n i n g r e d d i s h f i n e
( 5 Y4 7/61
sand
160-168 2A-ll brown ( 1 0 XI? 4/31 c l a y
witn
. .
whitish evaporite
crystals a n dc o a t i n q s on f r a c t u r e s ;o n l y
s J f s h t l y n l o i s t , some h o r i z o n t a lp a r t i n g s
168-178 2P-12 r e d d i s hb r o w n
(5 YR 5/31 c l a yb r o k e ni nb l o c K s ,
mixea W i t h brown c h y w i t h e v a p o r i t e c o a t i n g s
1 7 8 - 1 8 5 2A-13 m i x t u r e of brown ( 1 0 YR 5/61 c l a y a n d f i n e
'
(61-88 u l sand w i t h small g l o b u l e s o f
evaporites
185-193
2.4-14 f i n e ( 8 8 ~ u ) 1@ YR 6/4 v e r yL o o s es a n d
193-203 2A-15
iniXtUre o f f i n e .s a n da n db r o w n
( 1 0 YK 6/41
c l a yC o n t a i n i n go r g a n i c s
( d a r k brown-black1
a n d r u s t yr o o th o l e s
.
203-213 2A-16 35% s i l t y strong brown (7.5 YR 6/8) s a n d
(61-88 ul w i t h c l a y t o make f n i x t u r e p l a s t i c
213-224 2A-17 v e r y f i n e (61-88
11)
sand i n t e r o e u d e d w i t h 40%
.....
.
..,.
224-23524-12
235-241
2a-1.3
. _. . ~ .,
..
.
__
.
,
~
,......
.
......
L .
Drovn cJ.6~. (:t YK 6/4.S, 6 / 4 a t R a s e ) €311 o f
r o o t s d n d r c s t - s t s i n e f l q a r y i n s a r o u n df o r n e r
r o o t noles
top:
" 7 C % c l a y s i m i l a rt oa u o v c
(10 YR 5 / 4 1 ;
f i n e ( 6 1 - 8 0 11) s i l t y s a n d ( 1 0 Yic 7 / 4 1
241 C I I I , i r o no x i d e
stain ranges t o 5YH S I 8
base:
at
2 4 1 - 2 5 12 h - 2 07 . 5
251-262
2A-21
YR
6/6 sanu a n d s i l t (30-61 u)
v e r y f i n e 130-61 u) (7.5 Y K
a n d c l a y , v e r yu n i f o r mt e x t u r e
sand, s i l t
w i t n some m o t t l e s
0/4)
262-2722A-22
v e r y f i n e ( R t l u ) 1 a o s p sand (Xu 'IP 6 / 4 )
272-2792A-23
f i n e ( 8 8 u ) s a n d w i t h brown (10 P R 5 / 4 1 c l a y
lairtinae (sctual1.y 3 c l a y l a m i n h e 0.5 ctn thicicl
279-2902A-24
f i n e (ti8
290-305
2A-25 v e r yf i n e
UJ
1 0 YR 7 / 4 c l e a n f r i a b l e s a n d
(<88
no c l a y
305-3L5
u ) 10 Y R
7/4
c l e a n sand w i t n
nu sample v e r y fine unifornl send, almost d r y , rio
c l a y ; may be e o l i a n
3 1 5 - 3 2 52 1 - 2 6
same very t i n e ( 8 8 u ) s a n d witn a i e * h a r dn o d u l e s
of s t r a t i f i e d s a n d
325-338
n o sample fine sand w i t h C l a p n o d u l e s
338-348
2A-27
348-361
no sample f i n es a n do v e rC l a yl a m i n a eo fd i f f e r e n tC o l o r s
(5 YR 6 / 6 a n d 10 YR 5 / 4 3
361-36it2A-28
368-381
Same f i n e (177-250 u ) s a n d ( 1 0 YR 7 / 4 1
f i n e ( 1 2 5 - 1 7 7 u) s a n d w i t h c l a y e ys a n d b l e b s
(10 YR 6 / 4 ) ; ' s a n d a t b a s e (7.5 YH 7 / 4 1
no sample f i n e ( 1 0 YK 7 / 4 1 s a n d
3 8 1 - 3 9 12 h - 2 9
.
f i n e ( 1 2 5 - 1 7 7 ul ( 1 0 Y R 7 / 4 1 s a n d
391-404
n os a m p l en e a r l yd r y
f i n e ( 1 0 YR 7 / 4 ) sand, s l i g n t l y
caarserthanoverlyingsand
404-417
2A-30
417-4272A-31
f i n e sand (7.5
and sorue c l a y
YR
7/41
f i n e with some c o a r s e rg r a i n s
f l n e s a n do v e rh r e c c i a t e dr e d
( 5 YR 416.) c h u n k s
o fc l a y i n b r m n (In YR 5 / 4 1 c l a y
427-432
nosamyle
f i n e sand w i t h chunks
432-4812
n os a m p l ev e r yf i n e
sand w i t h brown s i l t y c l a y
lalflinations ( 6 i l t y clifnbing ripples1
Of
r e d clay ( 5 Y H 4 / 4 1
7
. ~.
.
...
.
I.
. .
~
. ." . .
.
...
..
..
~ ...
.
442-452 (io sahple
Sahple f i r b e (177-250 111 (ll! Y H b / 4 1 s a n d
452-462
110
sa!r8le c o a r s e r CSC.0-71" V I
coarsest arakc
1 !+m
-
-
462-472 n o sample f i n e ( 2 5 r i - S 5 0
( 1 0 ' i R 6 / 4 1 saner
u) sand, Largest g r a i n
2 103
472-482 no sa!tple f i n e sana w i t h l a r g e r rocK fragments UP
to 2 inlll
482-493 n o sample f i n e (350 u ) s a n d w i t h l a r s e r c l a s t s
quartz grfrin, fragment o f a snail)
493-503 2A-32
(5
mn
f i n e (35u-500 u) (ICYP 6/41 sand and l a r g e r
cl.asts u p f o 3 rnm
u ) w i t h pebhles a t base o f hole:
l a r g e c l a s t r i l l n o t f i t i t i t 0 auger
503-505 no s a m p l es a n d( 3 5 0
. .~
..
. -.
~
I
..
..
.
..
.
..
..
"
.
. .. .
,.
.
. .
.
., .
... ..
.
5-28
38-2
f i n e l y i n t e r i m i n a t e n 1 0 Yi( 5 / 4 s a i d a n d 7 . 5 YK
4 1 2 c l a p , 1 c o~ f 1.0 Y R 4 1 3 c l a y at b a s e
28-51
3R-3
10 YR 414
Scnd 1177-25ii
U)
w i t h (10 YR 3 / 3 1
1 0 YR 3 / 3 c l a y
Clay C l a s t s , and c r o s s - b e d d e a
oleb l a y e rb e l o w
51-69
3A-4
c r o s s - l a m i n a t e d v e r y f i n e (88-125 u ) s a n d t o
c l a y : clay-streaked r i p c l e o s a n d
63-94
3A-5
f i n e (125-177 u) f r i a b l e 1.0 Y R 5 / 3 t o 614 s a n d
t o c l a y ;c l a y - s t r e a k e du n d u l a t o r yr i p p l e lairkinaredsand
94-135
3h-6
10 YR 4 / 2
( 3 3 - b l u)
'
t o 3 / 3 c l a y g r a d e s downward i n t o f i n e
s a n d y c l a y and 1 0 ZR 4 / 4 S a n d ; "60%
clay
105-122
3A-7
122-137
3A-8
l a m i n a t e d medium ("177 u ) sand (-10 YR 6 / 4 1
f i n i n g upwara; many 10 YH 4 / 2 c l a y c l a s t s ana
carbonates
10 YR 3 / 3 a n a 5 Y R 4 / 3 c l a y with f i n e s a n d
l a m i n a e , g r a d i n g upivard to u n i f o r m 1 0 Y R 6 / 4
sand
, ,
137-152
3A-9
l a y e r e d (10 Y R 412 i o 3 / 3 1 c l a y and t h i n very
f i n e ( 1 0 YR 413) s a n d and silt l a m i n a e
,
,~
. .
'
152-167 n a . s a m p l e. l a y e r e d
1 0 YR 4 1 2 c l a ya n dv e r y
fine
10 YR 6 / 4 sand and silt;. b a s e of p i t a t 1 5 7
cm
167-1783A-10"30%
>
178-1823
3A-11
188-1983A-12
.
.
f i n e ( a 2 ul 10 YR 6/4 sarld a n d 4 cm
t h i c k , 1 0 YR 5 / 3 , c lbaeyd ;
sand l a y e r s 4 cm.
t h i c k c r a c m c i i n t o polygons.
f i n e ( 1 2 5 - 1 7 7 u) c o n t i n u o u s 10 YK 5'.5/4
very f i n e (86-125
u)
I O YR 5 . 5 1 3
sand
sand w i t h
somecement
196-208 3A-13 f i n e l y l a n i n a t e d f i n e (125-177
5.5/4 sancl
208-218 38.-14 f i n e c125-177 u) 1 0 Y R 5.5/4
21'3-2263x-15
218-226
3A-16
226-2343A-17
U ) : 1 0 YK
..
. .
sand
nard f i n e ( 1 2 5 - 1 7 7 [I] 10 Yi< 7 / 4 sand With
T30% 10 YR 5 1 3 s i l t y b r o w n c l a y ,
10 YR 4 / 2 c l a yc r a c k e d
dry c l a y e y s i l t
with fiile
sand
'
.
:
.
'
.
~
.
..,:
X
..
.
.~..
.. ..
.
. .. ..
....
.,..
..
."
.
,
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.
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.
.
.
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. .
Site 5
Dectn
Sanple
(cm)
i:o.
uescription
5-su c l a y
u-5
5-13
5 - 3 V e r y flRe (88-125 u) brown ( L O Y K 3 / 3 1s a n d
Srownisn (1u kP 5 / 3 ) f i n e ("125 u ) s a n d
13-25
5-4
25-33
5-5
r e d d i s h (10 Y f i b / 4 ) v e r y f i n e (ijR-L25 u) s a n d
33-61
5-6
loose d i s c o n t i n u o u s l a r i n a e of .tine (177-250 u )
1.iJ Y R 5 / 3 Sanci
61-86
5-7
f i n e C-177 ul 10 Y R 6 / 3 sand
86-1j.2
5-3
h a r d COlnDacteci f i n e t o rrrediuin (177-350 u )
laminated 10 YP 513sand:upper
part i s coarser
112-119 5-9
, ? i S t i n C t l y t i n e r ("8P 111 10 Y H 5 / 3 t i n e sand
1 ~ 1 t h s i l t 1.0 Y R h/3; r u s t y root molds
10 YR 6 / 3 f i n e ("177
1 1 9 - 3 3 2 5-10 c l a y - c o a t e d
u ] sand
132-140 5-11 s i l t y (125-177 u ) saw3 v i i t h minorcnunks
P l a s t i c black c l a y
140-150 5 - 1 2
u)
h a r d f i n ?( 1 2 5 - 1 7 7
of
10 YR 5 1 3 sand
150-168 5 - 1 3f i n e( 1 7 7
u l 10 YK 6 / 3 sa'nd a n d some s i l t y 10
YH 6 / 3 sa1;d ( 8 8 - 1 2 5 . ~ 1 ) i n r i p p l e s ; coarsest sand
(250-350 u)
, .
i
..
.
166-10e
. .
u)
5-14 v e r y f i n e ( 8 8 - 1 2 5
Pit a t 198 cm
198-213.5-15fine(125-177
u) 10
213-229 5-16 f i n e ( 1 2 5 - 1 7 7
u ) 7.5 YP
f i n e( 1 7 7
244-2545-18
f i n e (177 u) 10 'CR
254-2675-19
f i n e( 1 7 7
> 2 mm
base o f
.
.. ..
.. ..
. .
Y i 6/3 s a n d
u ) 7.5 YR
229-2445-17
5 / 3s a n d :
10 YR
6/4
sand
ti/&
b/4
sand
sand
'
u] 1 0 YR 614 s a n d ? v e r y few g r a i n s
. .
. .
.
267-279 5 - 2 0 f i n e (177-250 u l 1 0 .YR 6 / 4 s a n d
279-290 5-21
( 1 7 f7i.n~e1
290-3005-22
300-3!U
-
i0
YR 614 s'and
c
.
medlum (250-350 u) 10 YR 6/4, a few g r a i n s
2
mu
5-23 f i n e( 1 7 7 - 2 5 0
clay b a l l s
u ) 10
YR 6 / 3 sand; I0
YH 5 / 3
310-320 5-24 v e r y Csarse (1,000 u ) p o o r l y sorteci 2.5 Y R . 5 / 8
s a n d and g r a v e l w i t h 1 0 YR 5c /l 4a y
balls
. .
",__
~
.
_,^,~,,__,_"..__.
,",
~___
. .
".._"._ "..
~
I
._.I.
. .,
.,~....-,-.-
.
_.--_.;..----.-.-.-
.
.
very f i n e (Ra-125
u ) sand
t h i nd i s f o n t i i l u o u sl e r n i n a e ,
r i p p l e d , 10 YIc 013
t o 513 f i n e( 1 2 5 - 1 7 7
u ) sana
-
10-36
0-2
t i l i n d i s c o n t i n u o u sl a m i n a e ,
rippled,
t o 5 1 3 f i n e (125-177 u ) sand
10 YR 0/3 t o
36-4G
0-3
g r a n u l e s a t base of c o a r s e (350-500 u ) crossl a m i n a t e r l sand
46-64
5-4
two f i n i n g
64-65
6-5
wavy c l i a b l n ~ - r i r p l e - l a r i n a t e d ( <
15 % s i 1 . t - c l a y
u p w a r d 7.5-10 C I P l a y e r s ; v e r y f i n e
(dB-125 ul s a n d a t b a s e t o c l a y a t t o p
88
u l sanu;
d i s c o n t i n u o u s l yc r o s s - l a m i n a t e d
lour a n g l e c o a r s e
(350-500 u ) 1 u f R 6/5 t o 5 1 4 sand; p e o h l e 2.5 cm
Long at base; sone f i n e r l a y e r s
109-122
'
6-7
1 0 YR 6/4 u n i t o r n ; f i n e (125-177
122-137 6-8
u n i f o r m f i n e ("177 u l . sand
137-147 fi-9
f i n e (177-2517 u) sand
141-163 6-10 medium (250-350
u) sand
1 6 3 - i 7 3 6-11 iediuio. (250-35n
u) sand
173-188
ul.sand
0-12
1813-198.6-13 w d i u m (250-350
u ) sand
.
198-213 6-14 medium (350-500 Ul'sand; some g r a i n s u p t o 4 m m
'
. .
213-229 6-15 medium-(350-500
u) sa'nd;
some g r a i n s up to 2 mm
225-244 6-16 mediuln (350-500 u ) Sane
244-264 6-17 c o a r s e( " 5 0 0
u ) s a n d w i t h p e b ~ l e sUP t o 1. e m
c o a r s e (y500 u) 'moister sand Nith c i a y b l e b s 2
m m and s h e.l l. . fragments u p 4 mln
. .
.
. .
274-284 6-10 medium (250-350 . u l s a n d U P to' 3 mm
.
254-295 6-20 medium (250-350 u l sand
295-305 6-21. c o a r s e (>1,U 0 0
u)
sand with gravel
305-3.18 6-22 coarse (500-710 u) sand: base 2.5-5
10 YR 4 / 3 c l a y ball
318-3306-23
U P t o 1.2
cm
cm i n c l u d e s
10 YR 4 / 3 c l a y f i l o t t l e d with r u s t , mud balls in
~
..
.
Site ?A
Description
Sample
Depth
.(crnl NO.
0-10
7A-su
10
2.5
10-18
YR 5/2.discontlnuous sandy clay crust. and
YR 4 / 2 loose sandy (62-500 u) cover
10 Y R 5/3 ripple cross-laminated sandr l0 YR
- 4 / 2 fine sand and sllt w1th.clay layer at base;
7A-1
discontinous clay layer at top as above
18-26
7A.-2
1 0 YR 5/2 Very slightly tipple-laminated
subangular to sUbroundedr fine (62-250 u.) sand
26-31
7A-3
10 YR 3 1 3 clay wlth fine.discontinuous sand
zones; rounded PelLet structure common in clay
Zones with possible worm castings
31-38
7A-4
10
38-54
7A-5
10 YR 4/3 very fine silty sand: tubular voids
wlth worm CaStings and rounded clay pellets
54-57
7A-6
10 YR 312 laminated clay with scattered tubular
Pores fllled with worm castings
YR-2.5
Y 414 very fine (e125 u) sandy clay
57-60 no sample very fine 10 YR 4/3 laminated sand
60-70
7A-7
10 YR 3/2 Laminated undulatory clay8 upper part
of thick clay layer
70-79
7A-8
lower part. o f thick c l a y layer; 10 YR 3/2
laminated undulatory clay wlth discontinuous
thin i o YR'4/3 sand laminae
79-85
7A-9
2;s YR. 4/2m Very fine laminated sandy clay
loam
85-88
7A-9
2.5 YR 4/2m very fine laminated sandy clay
loam with a 2.5 YR 4 / 2 clay streak at 85 cm
88-91
7A-10
10
10 YR 412 and 2.5 Y 4/2 very fine (e88 u)
sandy
clay loam with navy lamlnations
-.
91-97 7Aril
97-102
YR. 312 laminated undulatory clay
7A-12 3-4 cm of 10 YR 3 / 2 and 2.5
YR 3/2'laminated
clay with a layer of 10 YR 412 sandy clay loam
beLou
102-107 7A-13 I O YR 3/2 c l a y with very thin sandy partings
and UnduPetory laminations
107-113 7A-14 10 YR.4/2 laminated very fine sandy.1oarn to
very fine. sandy clay loam
113-115 7A-15 10 Y R 3 / 2 laminated clay: thins to south
115-125 7A-16 10 YR 5/3-4/3 laminated very fine sand with
"
-
..
.
,.
., .
.
-
-.
.
,
~
.
- . . ...,. ,.
.
.....
,-
._.-..-.
. .
.-
-.. .
.. . .
"
..
...
sandy loam to sandy clay loam interbeds
m m o f 10 YR 3/2 clay
sand; base o f pit
125-128
7A-17 5
128-133
7A-18
133-150
7A-19 very
150-1?2 7R-20
€lne (g125 u) sand
fine (c88 u)' sand
very f i n e (e125 u) s a n d
o v e r 10
YR 5/3
very
fine
..,. .
.
.
. .
.
. .. .. .
.
.
.. .
site 7
Deptn
Sai-ple
uescription
do.
0-1.37-Su-0
e ; r ? n u l a r pLaci. c l a y
(CR)
b-2.5
7-1
g r a n u l a r P l a t y 10 YH 5 / 3 c l a y
hreaKS i n blocks
'9-2
cm t h i c K t h a t
2.5-18
7-2
s a n d yc l a y
wubch h o r i z o n t a p
l l a t yb r e a k a g ea l o n g
and mudcrhcXeu, 1 0 Y R 6 / 3 s a n d
b e d d i n g( l a m i n a e )
Is l e s st h a n 1 2 5 u
18-30.5
7-3
brown ( 1 0 Y R 3 / 2 1 damn f l s k e s o fc l a yw h i c h
breaK
i n t ol i g b t e r - c o l o r e a
( 1 0 W 6 / 4 1 h1oc)cs a t 3 0 cm
30.5-41
7-4
s i l t y ( 6 2 - P l I u J 1 0 YF 6/4 c l a y i
r
,
discrete
h l o c i c s nt o n - s t r a t i f i e d
41-51
7-5
10 YR 4/2 c l a y w i t h 30YR 6 / 4 l a m i r i a t a ds a n d
u ) e a r C i n g s ,D o t t o m
is undulatory
51-58
7-h
5
5 8 - 774- 7
74-69
7-8
89-104 7-9
(88
cm o f s a n ao v e r
2 . 5 cm o f hdra f t n e (61 u),
Laminated 10 Y R G/3 sand w i t h wavy c r o s s b e d s
l o w - a n g l de i s c o n t i n u o u s l cy r o s s - l a m i n a t e d
( i 7 7 u) 10 ZR 6 1 3 sand
fine
l o w - a n g l de i s c o n t i n u o u s l cy r o s s - l a n i n a t e d
1 1 7 7 u ) 10 Y R 6 / 4 S a n d
fine
l a x - a n g l ed i s c o n t i n u o u s l yc r o s s - l a m i n a t e df i n e
( 1 2 5 u ) 10 Y R 6 / 4 .sand
..
. .
,
i
1 0 4 - 1 1 47 - 1 0
f i n e ( 1 2 5 u) 20 YR 6 / 3s a n d ;f l o o r
of p i t s t
107 C ~ I I
1 1 4 - 1 2 77 - 1 1
f i n e ( 8 8 u ) 10 YR 6 1 3 sand
1 2 7 - 1 3 77 - t 2
f i n e ( 8 8 - 1 2 5 u) 10 XR 6 / 3 s a n d
1 3 7 - 1 5 27 - 1 3
f i n e ('125 u j 10 YR 6 / 3 s a n d
152-166
f i n e (125-177
7-14
168-1337-15
183-198
U)
10 YR 6 / 3 dah@ sand
f i n e ( 1 7 7 - 2 5 0 u) 10 YR 6 / 3 $and with l a m i n a t e d
claylayer
7-16 f i n e ( 1 2 5 - 1 7 7 u) X0 YR 6 / 3 ' s a n d w i t h nard
sand chunKs and 1 0 Y'R 5 / 3 c l a y l a y e r
1 9 8 - 2 1 37 - 1 7
fine ( 1 2 5 - 1 7 7 u) 10 YR 6 / 3 Sand w i t h chunks
213-229 7 - 1 3 t r a n s i t i o n t o c o a r s e r ( 2 5 0 - 3 5 0
g r a i n s t o 1 mm
229-244
u)
10
YR
613
Sand,
7-19 c o a r s e (500 u ) 10 !iR 6 / 3 S a n d ,r n i n o r ' e e b b l e s
t o 9 mm
2 4 3 - 2 6 97 - 2 0
c o a r s e C350-50(!
111
(10 YR 6 / 3 ) Sand, g r a v e l t o
S i t e gr
Deptn Sample
cescriptioa
0-2.5
l<o.
9-sii
2.5-15
9-1
rhen a r y :s t r u c t u r e l e s s
loam w i t 1 1 l o t s o f r o g t s :
when moist: 1(! YH 5 / 6 l o a 3 w l t n f i n e sana
15-25
9-2
:,;hen d r y r: i p p l e - l a m i n a t e d
sand ( l u X R 4 / 3 m l ;
'dnsn l e o i s t :
c e x t u r e i s a c l a y loam .
25-36
9-3
:.+i?en d r y : 10 Yi3 4 / 3 m a s s i v e ana s a n d y c l a y ;
''Then I i l O i S t : sai?dY loam a n d 49% c l a y loam
30-43
9-4
s e q u e n c e o f d o t l o l e t s of 10 YR 5 1 4 c l a yo v e r
s a n d yc l a y
43-43
9-4
(cml
".tien d r y :
s t r u c % u r e l c s sl o a n wlitn l c t s o i r o o t s ;
when z o i s t : lr: YR 5/0 loam witn f i n e S a n d
1 0 YE 3 / 3 c l a y o v e r s a n d y c l a y ; c l a yi a y e r sf r o m
2.5-5
cin t h i c i c ,s a n ol a y e r s
grace from loanySand
t o clay
48-55
9-5
10 TR 3 / 3
cm
to clay
2.5-5
c l a yo v e r s a n d y c l a y ; c l a y l s y e r s
sand l a y e r s g r a a e fromloamy
from
thiCKr
sand
55-60
9-5
10 YR 3 / 3 . c L a yo v e r
sandy c l a y : c l a y l a y e r s from
2.5-5 cin t h i c l t , s a n dl a y e r sg r a Q e
from loamy sana
t o clay
60-69
'2-5
1 0 Y R 3 / 3 c l a yo v e rs a n d y ' c l a y ;c l a y
2.5-5 cin thiCK, sand l a y e r sg r a d e
layers from
broin 1.oamY s a n d
to clay
69-61
9-6
moist rassive F.l.a5tiC S O YR 4 / 4 s t r o n g c l a y
81-69
9-7
10 YR 5/4 J a n i n a t e d .loamy f i n e sar~rl
89-92
9-7
l a Y R 4 / 3 c l a y e y sand with e v a p o r i t e s
91-99
9-7
Sand ( 1 7 7 u; s u b r o u n d e d )
99-112
9-8
C o a r s e 10 YK W 3 s a n d yc l a y t
cn i n c l u d i n g c o a l
r a r e p e b o l e st o
112-122 9-9
p e h b l e g r a v e l w i t h sandy c l a y m a t r i x :
122-137
9-3
b o t t o m of p i t , moist c l e a ns a n d
With p e b b l e s
137-152
9-10
c o a r s e (lr000-L,400 u l s a n d with 5-mn p e b b l e s
152-168
9-11 c o a r s e (710-1,000
1.2
gravel
i n c l u d e s . f l a t p i e c e s o f s a n d s t o n e and mudstone
C l O YK 4 / 4 1
u ) 10 YR 6/4 sand w i t h c l a y
balls and p e t m l e s t o 5 cm
.
.
Cescription
1.3 Y:Z
513 to 5 lR $ / a
~ n o t c l e dc l a y
r e J d l s h : ~ r o i . ( n(S Y O C / 3 ) c l a y o u c o p o f ? a l e
t . r @ c n (I!? Y h 7 / 4 1f i n e
( 1 7 7 - 2 5 0 ill s a n d
14-26
S.11-3
r e d d i s h ( 7 . 5 Yff 5/1) c l a y i n t h e form of
p l a t e s ana granules w i t h (10 YR 7/41 l a m i r l a t e d
s a n u ( 1 7 7 - 2 5 0 u)
26-3%
SJ1-3
r i p P L e - l a a i n a t e d 10 Y K 7 / 4 s a n d (710-1000 u
aaximum, 35u-509 u p r e e o n i n a t e l y ) .
32-39
5.71-4
f i n i n y - u p s a r ds e q u e n c e f r o m b a s a l sand t o
c l a y l o a n t o s i l t y c l a y ;i n c l u d e s
redbrown o l s t e s o f c l a y
sandy
10 Y R 7 / 4 SdDd ( 3 5 0 - 5 6 0 U
; suR-aogularr
S u b - r o u n d e d )b a g g e ds e p a r a t e l y ;
2.5 c n b a s a l t
pebale
44-45'
5.71-5
red b r o w n (2.5 Y R 4./4) c l a y betweensand:
well s o r t e d medium (250-350 u j 10 Y R 7 1 4
sand b e l o w ; ( s a n d t a k e ns e o e r d t e l y as SJ1-5
sane)
c l a y l e s st n a n 1 cnl t h i c k : 2 d i f f e r e n t - c o l o r e d
l a m i n a ep i n c h w t t o s o u t n
l a m i n a t e a f i n e r o sediurn (250-500 u) I O YR 7 / 4
subroundedSand
t w o d i s t i r i c t c l a y l a y e r s (10 YR 4/2and
4/31
s e p a r a t e d b y 3-4 mn o f medium (500 u) sand
which i s c o n t i n u o u s around t r e n c h b u t w n i c h
t h i n s t o dest t o Decorne sandy c l a y ; 5 YR
4/5 f o r r e d a l s h s t r e a k s i n
clay
laminated f i n e to mediulri (259-500 u) 10 YR
614 sand
68-17
SJI-9
77-80
S J I - 1 0 I O YR 1 / 3 t o 5 / 4 s a n d yc l a y ,e v a p o r i t e s
in
c l a y :m o i s tl a m i n a t . e d
sand 0 5 0 u) w i t h c l a y
a t base
86-89
SJ1-11 fine-medium. (80-125 u; up t o . 3 5 0 u l l a m i n a t e d
sand; laminae are c o a r s e , ue t o 1 m m t h i C K
88-91
SJ1-12 1ti YR 4 / 4 and 7 . 5 YR 4 / 6c l a y - r i c h
layer
tvnich t h i c k e n s c o 4 cm i n some places
91-98
633-13 7.5
YR 5/4 a n d I O YR 7 / 4 latairlacrd, m o d e r a t e l y
d r y sand vrith 10 YP 4 / 3 c l a y Detween 93-94 cm
9 8 - 1 0 0 Sdi-14 g r a v e l l ys a n d y 7.5 YR 4 1 4 c l a y l a y e r l o c a l l y
on g r a v e l ,p o o r l ys o r t e d ,s u b r o u n d e d
clasts,
.__ . _ _ _ _ _ _ ~ _ c ___.__"__r
_I
.__,____._"___,,_","._"._I.__
_I...
..
"~
.-
~
.
..
~..
..
.. .... . . ,.
SaAplc
120.
none
SJ5-l
u p p e r c l a y (10 YE 4/2 in); p l c l t y c l a y less
t h a n 1 CIO t h i c k (10 YR 3 / 3 m )
none
b e l ls o r t e d
(177-250
u) s t r u c t u r e l e s s s a n d
(10 Y R 6/4 n)
$55-2
clay
none
P o o r l y s o r t e d (avn. 250 ‘1: w i t 1 1 yrains t o 1
m n l 13mlnated sanrl (I9 Yt3 4 / J a )
SJ5-3
t h i n clay l a y e r s w i t n i n t e r m e d i a t e sand
l a y e rf r o m
I t o 3 C F t h i c k ; l l ~ ec l a y and
s a n d above
555-4
s a n d w i t h c r o s s - l a m i n a t e a Zones, and s c a t t e r e d
c l a y b a l l s up t o sinall C o b b l e s i z e ; o n e p e o b l e
o f b a s a l tn o t e d ;
sand ( a v g 1 7 7 - 2 5 0 u ; Y r a i n s
up t o i mal 10 YR 5/3 m o i s t d; i s c o n C i n u o Y s
l e n s e s o f s a n d and coarse sand w i t n granules
from 40-50 c r b e l o ws u r f a c e
SJ5-5
sand w i t n t i h e pekb1.e g r a v e l , g r a n u l eg r a v e l
a n a c l a y b a l l s up t o large c o b b l e size; b a s e
of P i t
( 1 0 Yt? 3 1 2
1n1 l e s s t h a n
1. crfl ChicK
CVJO
brown c l a y (7.5 YP 3/21 w i t h 7.5 YH 416 m o t t l e s
and gray-white e v a p o r i t e[ s u l f a t e ? )c r y s t a i s ;
s o i l - l i k e I t b l a c k alkali”: mottles of e v a p o r i t e
i n c r e a s e downward: some C h a r c o a l ;o t h e rc o l o r s
i n c l u d e 7.5 YR 4 / 4 , 4 1 6
110-130
none
simiisr t o c l a y above
130-145
none
v e r y f i n e sand igi v e r t i c a l c r a c k s i n
y l e y e dc l a y (5 Y 5/11
145-160
none
c l a y of 2.5
moist
360-185
none
t h i n l a y e r s o f water-saturated g r a ys a n d i n
c l a y layers; d o m i n a n tc o l o r sa r e
7.5 YR
browns w i t h gray m o t t l e s . no more e v a p o r i t e
crystals
185-200
none
X and N 5/ c o l o r s ;o e c o r n i n g
. .
7.5 .yR c o l o r s w i t h gray r n o t t h e q i n c l a y
. .-
1 2 0 - 1 3 0 PAGI-12 clay rith i n t e r b e d s o f s a t u r a t e d s a n d
130-150 P A G l - 1 3 . C l a y e y sand i n t e r b e d d e d w i t h s a n d y c l a y
15u-365 PAG1-14 s o u p ys a n d y
c l a y w i t h o r g a n i c s (muck)
165-375 P A G I - I 5 soupy s a ~ l dw i t h c o h e s i v e c l a y a t b a s e
175-200 PAG1-16 collesive. brown ( i n Y R 4 / 2 1 c l a y i a y e r
200-220 P W I - 1 7
brawn (10 YR 4 / 3 ) clay
b a s e o f h o l e due t o colia@siny s i d e s
2Q4-305 7 - 2 5 c o a r s e ( 1 , n o O
c ) 1 0 url 6 / 3 s a n d w i t n c l a y b a l l
base; o t h e r tiole h a s L O YH * / X c o 5 / 3 c l a y , # i t h
qypsurn, e v a p o r i t e s , 5 re p e o h l e s
3 0 5 - 3 2 07 - 2 3
c o a r s e (>1,000 u 7 10 YP 5/4 sand w i t h p e b b l e s
t o 2 cm a n d 1.0 YR 4 / 3 clay D a l l
320-335
medium (250-3SC
7-21.
11) 10 Y R 5 / 3 sand w f t n sonie
clay w i t ne v a p o r i t e sa n dc o a r s e
@ e h b l e s at o a s e ; c l a y l a y e r ac 3 3 3 cln is 5 cm
10 Y R 4 / 3 1
thick
3 3 5 - 3 5 17 - 2 5
h a r d b r o w n I n YR 4/2 clay Vrltir some 10 Y R 4 / 3
s a n d arid peoi-les, p o s s j b l y f r o mc r a c k s
clay w i t h r o o th a i r s
and evaporites
351-356
7-26
.. "99.5%
360-370
7-21- c l a y # 3s above w i t h f i n e ( 1 7 7 - 2 5 0 u ) 10 YH 6 1 3
sand a t bottom
3 7 h - 3 8 67 - 2 8
coarser ( 2 5 0 - 3 5 0 u) r u s t y sand w i t n o c c a s i o n a l
p e b b l e s , s o m e c l a y from a b o v e ;c o i o r s
, - - l o YR 6/13 and 10 YR 6/3
include
38a-396
7-2G r u s t y (10 XR 5/41 medium ( 2 5 0 - 3 5 0
396-427
7 - 3 0 r u s t y (10 YK 5 / 4 1 mediurti 1350-400 u) sand w i t n '
pebbles, ( 1 0 YR 4 / 3 ) RUdballSr and ( l , O X R 6 / 6 1
clay
.
.
u] sand
'
Appendix
B
Selected X-Ray Diffraction Data
( <2p fractions)
Composition
Sample
Clays
1-2
25
Qtz.
59
Relative Abundance ( % )
(%)
Calc.
Alb.
Ill.
Mont.
Kaol.
Chlor.
8
8
16
24
49
12
.
1-6
82
9
5
4
6
9
80
4
1-16
64
18
10
9
9
8
77
6
1-20
80
14
3
<8
14
18
52
16
2-1
67
19
11
5
19
28
47
6
2-20
60
18
8
14
10
12
67
11
2-27
59
18
13
11
7
3
82
7
2-30
69
14
9
8
14
9
46
31
3-1
18
15
54
12
3-2
23
9
60
8
8
8
6
11
64
19
5
5
13
-3
63
12
15
6
6
12
14
68
6
11
2-3
6
9
16
66
9
11
18
53
18
3-8
74
11
3-23
53
36
; a
3-27
75
-.
4-1
80
4-3
24 21
. 2037
4-12
74
16
5
9
16
18
47
19
4-14
72
10
12
4
14
16
49
20
Appendix C.
Radionuclide Activities f o r IndividualSamples
-
pCi/g Dry Weight.
u
5
CI
v1
.............
u
Ql
&4
zi
CL
............................
.+"*
Mrl-t.4
..r(.
..irtdrl.
.
d
....
.r(.
4.4
**
.e
.....&I........A. .
..+.....r( ......V. I ....
.
d
..
L.
.Ad*
......-I" ...........
,
,,
. . ., . . ..,... :. .
.
.
Nmtnmommm-m+m-rm
NOONNdOaWK-t-Om-
. .
..............
: , .
Lom
mrn
mN
mP-
t0-J
m
N
d.
r(
m
P-
OK-
wm
"
0
N
ON
mm
u
4-
.. .
OW
.*
rnN
ma
m
*
d
m
.............
..
...............
.. .
......-t...
rn
."4rl
L1
V
at
e
at
ZI
a
.
I
C
a
v)
2.883
2.963
.8752
1.348
1.398
,8310
1.360
1.444
1.370
1.451.
1.722
1.70b
.3439
.9889
1.705
1.603
1.996
.E352
.E691
,9132
1.281
1.178
4.835
1.602
1.313
2.543
2.034
.E493
.5680
,9886
2 517
.f54a
.0531
1.260
2.505
,6911
.6327
1.275
1.447
-5861
,6882
1.328
1.387
.5111
.6185
i .293
2.562
1.624
.9240
-9117
1.204
.7627
1.215
.SO80
1.531
,8861
1.4R6
.5488
4.450
7.864
9.350
4.205
2.522
2.064
3.696
1.45b
.EO60
5.376
12.72
13.61
3.539
1.910
1.803
1.789
1.556
.9940
1.115
1.,308
3,209
1.476
1.044
1.135
1.454
1.404
5 294
15.50
14.36
3.494
1.828
1.784'
1. .770
1.499
.go90
1,109
1.387
3.083
1.466
0.978
1.161
1.410
1.400
2.017
2.044
1.962
1.989
1.851
1.850
1.573
1.624
,8909
1.145
1.335
1.883
1.509
0,974
1.695
Rlo San J o s eS i t e
sui
.3427
4
2.058
Rio San J o s e Site 5
1
3.291
.5488
2
.2068
1.107
3
6
.1814
.n000
.9+67
1.183
R i o San J o s eS i t e
Old
SUl
.0000
-0329
,
O
1.339
1.077
Paguate R e s e v o i rS i t e
su
5.391
1
2
3
5
6
7
8
9
10
11
12
13
14
15
16
17
.3214
11.93
15.62
3.472
1.952
1.820
1.751
2.459
e9790
1.184
1.338
3.023
1.491
1.169
1.154
1.559
1.445
1
1.001
1.369
3.000
1.550
0.777
1.211
1.382
1.260
1e143
1. 8 5
1.806
Appendix D.
Normalized Cs-137 A c t i v i t i e s of Samplesfrom
S i t e s 1-7.
C s - 1 3 7 A c t i v i t y a t S i t e 1A
cs-137 A c t i v i t y ( p c i / g )
0.125,
0.250
0.375
0.500
t'
t
+
+
t
Red =. C l a y
Blue = S i l t
Black = Sand
0.625
0.750
I
0.250
0.125
r+
75
-l-
0
375
0.500
I
I
li t i -
Red = Clay
Blue = Silt
B l a c k = Sand
0.625
0.750
I
Cs-137 A c t i v i t y (pCi/g)
0.250
0.375
0.500
0.125
t
t
+4
75
+
+
I
+
+
A
.E
V
300
+
+
375
tRed = Clay
Blue = Silt
Black = Sand
0.625
.
0.750
1
CS-137 Activity (pCi/g)
0.125
I
+
0.250
0 * 375
0.500
" f .
I
+
t
+
I
+ +
+
-+
Red = Clay
Blue = S i l t
Black = Sand
0.625
0 * 750
"
I
Red = Clay
Blue = Silt
Black = Sand
Red = Clay
Blue =
silt
Black = Sand
horrnalized Cs-137 A c t i v i '.y a t Site 7
Cs-137 A c t i v i t y (pCi/g)
0.250 .
00.500
* 375
0.125
-4-
4
$-
75
++
I
_-
It+
3'
225
3
.
"
300 -- .
h
8
0
v
5
a
aill
375"
4.50 --
525
-
0.625
i
I
Red = Clay
Blue = Silt
Black = Sand
I
0.750
Appendix E.
Histograms of R a d i o n u c l i d e D i s t r i b u t i o n i n CoreSamples
(grouped according to Radionucl ide).
0.000
0
0.400
0. a00
1 20
PB-214 ACTIVITY IN PCI/G AT RIO PUEACO 1
400
UI
0.BOO
i .200
i .800
2 * 000
ACTIVITY IN PCI/G AT RIO PUERCO 2
0.400
PB-214
0.000
0
2.400
,400
0.000
0
0.800
1
1.600
2 * 000
ACTIVITY IN PCI/G AT R I O PUERCO 5
0.400
PB-214
2.400
I
Y
m
h
2
2
I
n
0
n
-I
=
r
uZ
rn
ffl
?-
m
Q
00
0.400
0,800
I
1.200
I
1.600
”
2.000
PB-214 ACTIVITY I N PCI/G AT R I O PUERCO 6
2.400
Y
P
0
000
0. BOO
i .200
i .800
2.000
ACTIVITY IN PCI/G AT RIO PUERCO 9
0.400
PB-214
2.400
I
LI)
h
0.000
0
0.400
0. BOO
I.200
2.000
2.400
”
-
1.600
PB-214 ACTIVITY IN PCI/G AT SAN JOSE 1
8
0
m
0
z
H
>-I
H
I-
o
a
m
a
0
0
0
I
0'
I
I
2
3
I
I
,
"
*
SAMPLE
NUMBER
I
4. '
I
5.
(REFLECTSDEPTH)
6'
7'
-0
4-
8'
i2
SAMPLE
NUMBER
ii3
I
I
1
20
24
28
(REFLECTS DEPTH)
“1
P
u
UI
w
0
w
rlz:
I
rn
0
rn
“I
CJ
IT0
I-N
7
rn
n
h
E
;
i
13
x
z
c
rn
I-
-00
r,
rn
UI
0.000
0
0.400
0. BOO
1.200
I.600
2.000
TH-234 ACTIVITY IN PCI/G AT RIO PUERCO 2
2.400
I
ooz ' F
I
000' F
I
008'0
008'0
I
I
OOP'O
I
ooz'o
9 03H3Ild OIH 1 V !3/13d NI AlIhI13V PEZ-HI
000
m
0
0
I
0.000
1
0.BOO
I,200
I.800
2.000
ACTIVITY IN PCI/G ATRIO PUERCO 7
0.400
TH-234
2.400
0
I
0.400
0 *BOO
I
1.200
1.600
2.400
2.000
TH-234 ACTIVITY IN PCI/G AT RIO PUERCO 7
0.000
1
0
0.000
1
I
0.200
0.400
0.600
0. BOO
i 000
.
TH-234 ACTIVITY IN PCI/G AT RIO PUERCOQ
i .200
OI
0.IO0
0,400
0. BOO
TH-234ACTIVITY
1.200
1,800
I N PCI/G ATSAN
2.400
1_L___I
JOSE2.000
1
------O
l
0.000
0.400
0.800
TH-234ACTIVITY
i .200
.800
2..000
I N PCI/G AT SAN JOSE 5
2.400
H
>
E!0
a
0
0
4
12
16
SAMPLE
NUMBER
(REFLECTS
DEPTH)
20
24
28
Y
B-
A-
N
A
R A - 2 2 6A C T I V I T Y
2.400
I N P C I / GA TR I O
4.000
PUERCO 1
3.200
4.800
0.000
0
0.800
1A00
2.400
3.200
4.000
RA-226 ACTIVITY IN PCI/G AT RIO PUERCO 2
4.800
D
%E
C
z
rn
I-
u c
=w
zr
Ln
u
C
i A00
2.400 .
3.200
4.000
ACTIVITY IN PCI/G AT RIO PUERCO 3
0. BOO
RA-226
,000
4.800
m
tn
rn
P
0
0.000
1
RA-226
ACTIVITY
IN3.200
PCI/G
AT RIO PUERCO 6
0.800
i4.800
.600
4.000
2.400
W
W
UI
0
I
0.000
0 ,
0.500
i 000
.
i .500
2.000
2.500
RA-226 ACTIVITY IN PCI/G AT RIO PUERCO 7
3.000
0.000
1.600
2.400
3.200
4.000
RA-226 ACTIVITY IN PCI/G AT RIO PUERCO 7
4.800
0.000
0.500
i 000
.
i ,500
2.000
2.500
RA-226 ACTIVITY IN PCI/G AT RIO PUERCO 9
3.000
P
0.000
0
0.800
i .600
RA-226 ACTIVITY
2,400
3.200
IN PCI/G ATSAN
JOSE 1
800
1
z
a
cn U
t
>N
H
c
b
a
CD
cu
iI
,
1
I
I
2
3'
4'
I
I
I
I
cuI
a
fI:
0
I'
SAMPLE
NUMBER
(REFLECTS
I
5
DEPTH)
8
7
m
N
b
0
RA-226 ACTIVITY IN PCI/G AT PAGUATE
KJ
3
L
i
1
3
3-
Y
0-
J
s-
J
3
I
m
0
-!
KJ
m2
n -.
n
3
I
m
13
h
2
.
-.
n
c
m
z
r
%O
>
.-.
I
0.400
I
0.800
I
w
1.200
I
1.600
2. 000
AC-228 ACTIVITY IN PCI/G AT RIO PUERCO 1
0. 000
CJ
2.400
"I
P' " "' " """""""' " ' ~
0.500
1 .ooo
A C - 2 2 8A C T I V I T Y
0.000
0 ,
1.500
I N P C I / GA T
2.000
2.500
RIO PUERCO 3
3.000
0
w
0.
0.400
a
0 800
1.200
1A00
2.400
2.000
AC-228 A C T I V I T Y IN PCI/G AT RIO PUERCO 5
Cj.0 '00
I
0.000
0 ,
0.400
0.8002.000
1.600
1.200
AC-228 ACTIVITY IN PCI/G AT RIO PUERCO 6
2.400
0.000
0
AC-228
ACTIVITY
IN PCI/G
AT RIO
PUERCO
7
0.400
0.800
1.200
1.600
2.000
2.400
P
0
000
0.400
I
0.
e00
I
I
~
~~
~
1.200
i
-
..6cl
"10
2 * 000
AC-228 ACTIVITY IN PCI/G AT RIO PUERCO 9
2.400
0
0.000
II
I.200
I II I I
0.400
1.600
2.000
AC-228 ACTIVITY IN PCI/G AT SAN JOSE 5
2.400
Appendix F.
Trace Metal Concentrations for Individual Samples. ppm
Dry Weight.
..
Y
"
WWWWWWWWWWWWWWWWWWWW
P.
Y
WW
SI-
wwwww
Wo'OU.0
.......
n
L:
m
r.
0
V I P
NNNNNNNNNNUWNNNNNNNNNNrCNtGWNN TT
I
!
.......................
w..
.
N
N
*.-I.+
00000000000
4
4
.-I
30m00WmmmON=Vmwm0mmm0
oodmmo+amm~r-aam~wmm
~ m r . mmomr.mda.+am
mmm
mdawmummrnwm
300
..... . . ..............
....................
.....
NOWNP.
NNNNM
........
...
.
.A. ....
.
. .
rO&O
m o
w w
NN.V
ma4
c
0
N
c
0-0
c
c
.IOP
...
N W”
u1 o w -
0
G
w
0
I - &
h: 0
VI0
G O O C n ~ N P W r r h l O N W 4
COOUlOGGGCGCOOGUl
PwPWNwNwmNwtGWUlUl
u1-z4UllnUltG‘uI4.OVlUl-zlJlUl
GUlUlCGGinOUlOCOUlOC
NULO
GCUl
............... . . . . .
............... . .
. . . . . . . . . .
CNG
OGV-4
*ONN
UlO5CU04-lU3ONCu1mWW
WWWNWWWWPWPWWW-
............... . . . . .
.....
....
...
m
Appendix G.
Neutron Activation Analysis o f Clays
Neutron Activation Analysisof C l a y s
Site Depth
1
1.
1
1
1
1.
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
36
4
4
77
71
4
5
5
5
5
5
5
5
5
5
PPm Cr
1.
2
6
10
13
16
20
20
1
2
8
15
19
25
26
30
31
32
1 (80+)
l(80-230)
1(230-)
32
l(c1ay)
2
5
8
8
14
23
23
24
26
26
28
33
3
12
14
~~
0
3
5
7
71
60
32
52
70
60
51
66
56
59
56
23
69
60
89
68
70
. -
29
16
20
36
38
67
34
50
45
49
36
34
66
87
34
50
70
49
40
72
p w Ba
330
390
400
280
370
440
440
500
295
400
290
450
420
372
430
420
360
718
410
460
600
532
582
330
341
503
340
436
430
440
440
716
617
300
440
390
370
648
493
546
390
388
520
390
395
47 0
PPm C s
% Fe
3.6
4.3
4.3
3.9
4.3
5.0
4.8
5.2
4.0
4.4
3.8
4.0
4.2
4.5
5.2
4.4
3.9
6.9
.28
.72
3.0
4.2
4.8
3.8
3.6
3.8
3.3
3.8
2.8
4.1
3.6
4.5
6.1
3.2
3.6
4.1
3.9
3 ,9
4.6
5.3
4.0
5.1
4.1
3.6
4.6
4.1
11
13
13
13
14
I. 2
14
13
12
11
10
13
10
11
12
12
13
13
1.8
2.5
6.9
10
11
12
9.6
7.2
10
9.4
8.7
11
11
7.2
11
7.5
9.2
11
10
8.0
9.5
10
10
10
11
11
10
11