New
MexicoBureau of Mines
Open-File
PHASE-I11
and
Mineral
Report 282
RECHARGE
STUDY
AT THE NAVAJO MINE-IMPACT OF MINING
ON
RECHARGE
bY
William J. Stone
Senior Hydrogeologist
November 1987
Resources
CONTENTS
Paqe
Introduction
Overview of Recharge
Background of Study
Problems and Purpose
Regional setting
1
1
7
7
8
Isotope Study
Methods
Hole 1: Custer Depression
Hole 2: Pinto Depression
Hole 3: North Barber Depression
Recovery of Reclaimed Areas
9
10
11
Impact of Mining on Recharge
Local Recharge
Areal Extent of Settings
Areal and Regional Recharge
26
26
27
30
Discussion
31
and
Conclusions
15
15
19
Acknowledgments
32
References
33
Cited
Figures
1
Location of Navajo Mine and sampling holes.
2
Premining landscape settings, mine area1
3
Premining landscape settings] mine area2
4
Example of post-mining landscape settings.
5
Chloride profile, Custer depression
6
Stable-isotope/tritium profiles, Custer depression
7
Oxygen-l8/deuterium plot, Custer depression
8
Chloride profile, Pinto depression
9
Stable-isotope/tritium profiles] Pinto depression
10 Oxygen-l8/deuterium plot, Pinto depression
11
Chloride profile, North Barber depression
12 Isotope profiles] North Barber depression
13
Oxygen-l8/deuterium plot, North Barber depression
14 Stable-isotope/tritium profiles, Yazzie depression
15
Oxygen-l8/deuterium plot, Yazzie depression
16
Frequency of occurrence of local recharge values
2
4
5
6
12
13
14
16
17
18
20
21
22
24
25
28
Tables
1
2
3
Summary of local recharge values, Phase I11
23
Local recharge values, all settings at Navajo Mine26
Volumetric recharge at Navajo Mine
29
Appendices
A
Isotopedata
B
Brief field descriptions of samples
C
Summary of premining landscapes
36
40
44
INTRODUCTION
Surface
mining
regulations
call
for
protection
of
the
hydrologic balance ofa mine area. More specifically, they
require
This
restoration
of
ground-water
recharge
through
reclamation.
isa tall order as it assumes several things:
1) that
recharge
pre-
can
and
recharge
indeed
be
post-mining
rate
can
measured,
2) that
will
have
both
that a desired
data, 3 )and
recharge
be
mines
achieved
by
customizing
reclamation
practices. Nonetheless, efforts have been made over the paqt
three
years
undisturbed
to
learn
and
as
reclaimed
much
as
areas
possible
at
of
BHP-Utah’s
recharge
Navajo
in
Mine,
San
Juan County, New Mexico (Figure
1).
This is the third and final
report on those
conducted
recharge
studies
by
the
Bureau.
OVERVIEW OF RECHARGE
Recharge
is
an
important
but
elusive
part
of
the
hydrologic
cycle. Water that infiltrates into arid-land soils is subjsct to
rapid evaporation and transpiration back to the atmosphere. Most
water
escaping
the
root
zone
eventually
reaches
the
water
table,
where it is added to (recharges) the saturated zone. This
assumes vertical movement under piston-flow conditions. Thst is,
for
every
slug
of
water
that
enters
the
top
of
the
soil-watl-r
column, an equal slug moves downward. However, low permeability
horizons
or
cause
(siltyor clayey
overlying
beds)
material
may
to
become
become
temporarily
saturated,
saturated
resulting
in
lateral flow. Such flow may also occur without impeding layers
in response to topography (McCord and Stephens,
1987).
Recharge
has
been
shown
to
vary
with
landscape
setting
4
i
8
I'
.. .
(Allison and others, 1985; Stone,
1986~). Each setting isa
unique combination of geology, landuse, soils, topography, and
vegetation. Premining (undisturbed) settings differ from postmining (reclaimed) settings (Figures2, 3, 4).
evaluate
impact
of
mining,
recharge
In order to
under
both
conditions
must
compared.
Recharge may be addressed in different ways. For example,
it
may
be
associated
expressed
in
witha point
flux,
associated
Also,
recharge
with
may
terms
a velocity-style
of
ina given
the
be
setting,or as a volumetric
area
viewed
valueor rate,
at
or
by more
one settings.
covered
three
different
scales:
local,
areal, and regional. Local recharge is the rate of deep
percolation
fora given
setting
as
or estimated
measured
ata
point. It may bea single observationor the average of se-reral
such measurements. Areal recharge is the volumetric flux for the
entire
extent
in
the
study
region
a given
of
setting
(local
recharge times area). Regional recharge is merely sum
the of all
of the areal recharge fluxes in the study region. Average
recharge
isa velocity-style
recharge
by
In these
the
total
studies,
value
area
local
of
obtained
the
recharge
by
study
has
dividing
regional
region.
been
determined
b:r the
chloride mass-balance method. Chloride is useful because ita is
conservative natural tracer. Details of the method are giv'sn in
the Phase-I and-11 reports (Stone, 1984 and 1986).
however,
it
is
based
on
the
premise
Briefly,
advanced
by
Allison
and
Hughes (1978) and others, that average annual precipitation
(P)
times
the
total
annual
chloride
content
of
precipitation
(Clp)
should equal the annual recharge rate (R) times the average
J
be
-
0
1nri
Figure 2- Premining landscape settings, mine erea 1.
i
I :
' I
..
.
.,
'I
I
.
I
.
!.\ ,
:I
3
. 1 ''
11.
-
0
1 mi
_.
Figure 3
-
.-
Premining landscape settings,mine area 2.
I
\
0
/
\
(ave. 2%)
0 Otherreclaimed
-N
settings
(ave. 98%)
I .
1979 year revegetated
"____..
.-.-. . .
.
_"
Figure 4
-_
-.
- Example
".
.
-
. ..
of post-mining landscape settings.
chloride content of soil water (Clsw). Shown mathematically,
this is PClp
= RClsw. Rewritten for recharge it becomes
R =
-
(ClP/ClSW) P.
BACKGROUND OF STUDY
The
evaluationof recharge
at
the
Navajo
Mine
was
I was conducted to test the
accomplished in three phases. Phase
applicability
recharge
to
preliminary
settings
of
the
chloride
conditions
estimates
(three
in
of
mass-balance
northwest
local
undisturbed
New
recharge
and
two
method
Mexico
for
of
and
major
reclaimed)
determining
to
obtain
landscape
recognized
at
the
mine. Phase I1 was an expanded study of local recharge in
reclaimed settings. Phase 111, that reported on here, focu-jed on
areal
on
and
regional
recharge
volumes
and
the
net
impact
of
mining
recharge.
PROBLEMS AND PURPOSE
The
chloride
mass-balance
method
gives
reasonable
rech3rge
estimates in undisturbed settings (Allison and Hughes,
1978), but
to
my
knowledge,
it
had
not
been
applied
to
reclaimed
settings
prior to the Phase-I study. Even more chloride vs depth pr,2files
for
reclaimed
ground
were
obtained
in
the
Phase-I1(S'ostudy
ne,
1986a). Examination of these profiles reveals that all are one of
three basic types. Some show large variation in chloride
content,
Others
suggesting
have
equilibrium
uniformly
low
had
chloride
not
yet
values,
been
in
regained.
some
cases
a
above
deep peak (flushing bulge?). Still others are characterizeda by
shallow
peak
undisturbed
above
lower
settings.
7
values
at
depth,
as
in
profiles
from
These observations raise two important questions. Which
profile
type
represents
equilibrium
conditions
and
is
a good
thus
source of local recharge values? How can this equilibrium be
tested? The Phase-I1 study suggested natural isotopes may
a be
useful
means
of
testing
these
In order
to
get
impact
at
profiles.
of
mining
on
recharge,
pre-
and
post-mining regional recharge fluxes must be compared. This
requires local recharge rates, as discussed above, and arealextent values. Several questions arise as to areal extent. What
was the distribution
of premining landscape settings? What will
be the distribution of post-mining settings? How can their areas
be
approximated
without
exhaustive
surveys?
1) to further
The purposes of this study were, therefore,
evaluate
chloride
mass-balance
results
for
reclaimed
ground
by
2) to determine areal extents
fo- the
means of natural isotopes,
3 ) to calculate volumetric recharl-Je
major landscape settings,
to assess impact of
fluxes for each of these settings,4 ) and
mining
on
recharge
at
the
Navajo
REGIONAL
The
Navajo
Mine
lies
Mine.
SETTING
in
the
northwestern
part
of the
structural featureknown as the San Juan Basin,
a Laramide (Late
Cretaceous-Early
Tertiary)
depression
at
the
easternofedge
the
Colorado Plateau. More specifically, it is situated just east of
the
Hogback
Platform
from
Mountain
the
Monocline
central
San
which
Juan
separates
Basin
in
the
northwestern
Mexico.
Coal
is
strip-mined
from
a
the
Fruitland
Four
Formation
Corxers
New
(Cretaceous) which lies at the surface in this area. The
Fruitland
is
2 0 0 - 3 0 0 ft
generally
thick
and
consists
of
interbedded sandy shale, carbonaceous shale, clayey sandstoye,
coal, and sandstone (Stone and others, 1983).
Data collected at the mine (Utah International 1981)
Inc.,
indicate
the
climate
is
arid
with
an
average
annual
rainfall
of
5.7 inches, based on the period
1962-1980. Greatest
precipitation
Average
occurs
annual
class-A
nearly 10 times
The
in
the
reclaimed
the
period
August
through
October.
rate55.9
is inches
pan-evaporation
or
rainfall.
areas
studied
in
Phase
I11
were
regraded
or
revegetated during the period 1975 to 1979. Water added during
irrigation generally did not exceed
6 inches/year. The see3 mix
most
commonly
applied
for
revegetation
includes
alkali
sacaton,
galleta, globe mallow, Indian rice grass, saltbush, and san'l
dropseed. The average rooting depth is probably
<2 ft.
The
mine
area
is
tributaries (Figure 1).
tributaries
are
drained
site
and
San
Juan
River
and
its
ephemeral.
recharge
one
the
The San Juan is perennial, but the
ISOTOPE
Chloride
by
values
reclaimed
STUDY
from
depression
one
undisturbed
upland
flat
checked
the
stable
were
by
isotopes oxygen-18 (0-18) and deuterium (D), as well as tritium
(T), in the Phase-I1 study. Stable isotopes confirmed the
chloride
reclaimed
recharge
site
rate
was
not
in
the
yet
in
undisturbed
site,
but
suggestt..-d
equilibrium,
6 yrs after
revegetation. A major task of the Phase-I11 study was to
9
the
resample
of
three
the
of
three
the
basic
Phase-I1
ch1,oride
sites,
each
profile
characterized
by
one
for
were
types.
METHODS
Sample
preparation
and
analysis
methods
isotopes
the same as in the Phase-I1 study (Stone,
1986).
Samples were
taken
as
by
coring
chloride.
were
caps
large
auger
rig,
in
the
cas?
of
No water, mud, or air were introduced during drilling.
Samples
The
with
a hollow-stem
placed
were
zip-top
covered
500 ml
sealed
with
plastic
bags,
sunlight to minimize
Soil
in
water
widemouth
plastic
and
tape,
bags
plastic
bottles.
bottles
were
stored
were
out
placed
of
in
dir?ct
evaporation.
was
extracted
by
solvent
distillation
using
toluene, as described by Snell and Biffen
(1964). Samples were
analyzed commercially (Environmental Isotope Laboratory,
University of Waterloo, Waterloo, Ontario, Canada). Data are
A.
given in Appendix
Concentration vs depth profiles 0-18
and vs
deuterium plots were made by hand. Regressions and correlation
coefficients
0-18/D
slope of 8 .
1961).
were
determined aon
hand-held
values
for
precipitation
calculator.
plot
along
a line
havinga
This is called the meteoric water line (Craig,
In arid settings, 018/D data plot aon
line below and
diagonal to the meteoric line (slopes5 of
or less). The
decrease
in
slope
shallow
part
of
results
the
from
profile
less
because
negative
of
values
enrichment
in
the
(evaporat,ion).
Displacement of deuterium from the meteoric line (D) provides
recharge (R) using a proportionality
(Allison and others,1983).
10
constant (k): R=(k/D)
'I2
HOLE 1: CUSTER DEPRESSION
This
site
Hole 1 was
was
drilled
chosen
to
test
approximately
10
an
ft
erratic
due
chloride
east
profile.
of
16 Hole
in the
Phase-I1 study. More specifically, it lies in
a depression just
south of Ramp6 in the Custer area. It was located southwest of
a large
rock
pile
and
southwesta Forest
of
Service
experimental
plot sign.
Although
profile
is
the
area
quite
variable,
of
is given
hole
the
Oxygen-18
and
suggesting
in
chloride
equilibrium
Total depth was56 ft.
been regained (Figure5).
log
reclaimed 1975,
in the
was
has
not
y?-t
A brief field
Appendix
B.
deuterium
profiles
parallel
each
other
qlite
well, except for the deepest point (Figure
6). The hard drilling
that
caused
heating
the
sampling
water
Stable-isotope
diagonal
to
(Figure 7 ) .
the
in
to
56 ft
halted
at may
be
the
sample
and
have
resu1te"l
altering
points
plot
on
an
meteoric
line
having
a slope
its
evaporation
of
in
isotopic
line
below
approximately
6
Regression analysis givesa good correlation
coefficient (r = 0.88).
Deuterium displacement givesa recharge
rate of0.04 in/yr; chloride gave0.03 in/yr for the same site
(Hole 16, Phase 11). Although results of the two methods agree
quite
well,
appropriate
the
for
deuterium
this
displacement
method
may
not
be
profile.
Tritium results look quite erratic (Figure
6). This may be
due
well
to
as
or movement
inequilibrium
liquid
phase
in
11
of
these
water
arid
(and
T) in
the
conditions.
vapor
as
mskeup.
and
'I
'I
""1
Chloride (mg/t)
0
500
1000
I
1500
-2000
I
c
'",
5
a
4c
V
D
60
II"
.
80
. . -..
-,
Figure 5
..
U
-
NV It 1b
Chloride profile, Custer depression (hole NV I1 16).
O l
I
I
I
1
1
.
v)
m
.
NV
.Y
HOLE 2: PINTO DEPRESSION
This
site
was
chosen
as
an
example
of
the
undisturbed-type
chloride profile. Hole 2 was drilled approximately
20 ft
northeast of Hole19 of the Phase-I1 study. More specifically,
it
lies
and
in
a depression
east
of
a radio
north
of
the
a deep
above
road
the
chloride
areas (Figure8).
cut
tower.
Like Hole 1, it was reclaimed in
1975/1976.
however,
open
profile
looks
like
By contra-;t,
those
of
undisturbsd
Total depth was25 ft; a log appears in
Appendix B.
At
first
glance
0-18,andD profiles
don’t
seem
to
parallel
9).
each other very well (Figure
However, closer examination
reveals
are
that
only
two
points
not
in
agreement
10
(those
at
and 5 4 ft, respectively).
Points
plot
on
an
evaporation
approximately 4 (Figure 10).
linea slope
with
of
Regression analysis showsa high
degree of correlation(r = 0.94).
Deuterium displacement gives
a
recharge rate of0.06 in/yr. Chloride gives a value of 0.0%
.
in/yr
Interestingly,
the
tritium
vs
depth
plot
resembles
the
chloride profile (Figures8 and 9) and may be reasonable. The
implication
is
that
this
profile
is
in
10 yrs after
equilibrium,
reclamation.
HOLE 3 : NORTH BARBER DEPRESSION
This site was chosen to evaluate the flushed profile. Hole
3
was
drilled
approximately
25 ft
southwest
of
Hole
24 of
the
Phase-I1 study. More specifically, it lies ainlarge depr?ssion
15
Chloride (mg/L)
Moirlure (rn'/ml)
0.4
.
0.6
1000
1so0
E
20
2
40J
Figure 8
1
- Chloride.profile, Pinto
._
NVll'o
depression (hole NV I1 19).
*
11'
7
4
Y
Y
.
-
"
0
I . . . . .,
0
(7
..
..
60”,
.
.
.
.
.
NV I 1 19
80-
.
h
8
\
100-
0
w
.... .
0’
m
-
.
.
.
120-
140
.
1
-20
1
1
1
~
1
-1 5
1
1
1 1 1
1
-1 0
1
1
-5
1
1
1
0
..”. -~o‘8(o/oo)
- ..
.. .
”
-
Figure 10
Oxygen-l8/deuterium plot, Pinto depression (h71e N V
I1 19).
.
.
.
(the
second
one
north
of
2 Ramp
in
the
The area was reclaimed 1 in
979.
a possible
flushing
North
Barber
area).
The chloride profile shows
bulge aatdepth
3 5 ft
approximately
of
(Figure 11). Total depth was6 0 ft; a log is given in Appendix
B.
The 0-18/D
profiles
track
a bulge at depth (Figure
12).
each
other
very
well
and
als-,
show
The stable-isotope bulge is
It may be that
curiously 1 0 ft deeper than the chloride bulge.
sampling
for
chloride
profile.
In
isotopes
the0-18/D
missed
plot
the
small
(Figure1 3 ) points
upper
peak
seen
describea line
in
the
below
but nearly parallel to the meteoric line. The slope is
approximately 6 .
Regression analysis gives
a high correlation
coefficient (r = 0 . 9 3 ) .
Recharge based on deuterium displazement
is 0.05 in/yr. Chloride gave a recharge rate of0 . 1 6 in/yr.
The tritium profile is erratic. Vapor-phase movement may be
responsible.
RECOVERY
The
OFRECLAIMED AREAS
chloride
and
stable-isotope
profiles
suggest
that
all
I11 are in equilibrium. The times
three sites restudied in Phase
of reclamation
indicate
that
moisture
and
solute
profiles
are
re-
established between6 and 1 0 yrs after revegetation. This is
based
on
the
equilibrium
sites reclaimed1 0 yrs
behavior
previously
of
stable
isotopes
for
(Holes
1 and 2 ) and 1 of 2
sites reclaimed 6 years previously (Hole3 ) .
Another hole ( 2 8 of
6 yrs previously, was
the Phase-I1 study), also reclaimed
characterized
by
erratic
stable-isotope/depth
19
profiles
(Figlre
all
0
-
20
Moisiure
0.2
0
(rn3/rn3)
0.4
I
’
. 0.6
0
Chloride (rng/L)
500
1000
1500
2000
I
-
.
-.
s_
5u
40-
a
60-
80
-
Figure 11
-
Chlorideprofile,NorthBarberdepression
(tole NV 11
24).
i
a
I
a
a
a
a
a
c
S
t
Ol
...
.
n
-.
I
~
..
20, NV It
.
40
.
..
24
'
/
60
.
h
z
8
.
.
80
..
100
120
T
140
-
.
Figure 13 -'Oxygen-l8/deuterium plot, North Barber
(hole NV I1 24).
depression
!
Y
14). Slope of the evaporation line for these data
3 . 3 and
is the
correlation coefficient is only 0.54 (Figure
15).
The
flushing
bulge
seen
in 3Hole
and
others
is
appareltly
more a matter of active recharge than nonequilibrium. Periodic
flooding
of
such
depressions
by
and others, 1985; Stone, 1984a,
b).
North
Barber
Great
care
drilling
had
rig
Local
depressions
depression
to
be
was
taken
during
sampling.
recharge
values
obtained
in
the
clayey
get
the
for
just
field
the
see
2.
Table
Chloride
Type
D e p r e sRsei oc n
l aP
im
r oefdi l e
1 (11
1975
variable
2 (11
3 ( I 1 24)
II 28
i n Phase 111.
Summary of l o c a lr e c h a r g ev a l u e sf o rr e c l a i m e dd e p r e s s i o n ss t u d i e d
Year
Hole No.
NorthBarber
Yazzie
vehicle
Phase
I11 are summarized in Table 1.
F o r other
rates
1979
flushing
1979
variable/flushing(?)
Rcl
(in/yr) 2
RDd ( i n / y r ) 3
0.03
0.04
0.04
0.06
0.16
0.05
0.36
#A4
numbersprecededby
"II"a r eP h a s e - I 1h o l e
numbers
Rcl = rechargebasedonchloridemass-balancemethod
R D d = rechargebasedondeuteriumdisplacement;
may n o t b e a p p l i c a b l e t o t h e s e p r o f i l e s
NA = n o t a p p l i c a b l e ; s t a b l e i s o t o p e s
do n o t t r a c k one another
23
was
reclaimed
median is 0.095 in/yr; the mean is
0 . 0 8 in/yr.
area
(Allison
bottom
in/yr. The
Table 1.
19)
not
stuck
evaluated
recharge
On the several occasio7s the
visited,
to
enhances
0.03-0.16
Values (based on chloride) range from
reclaimed
16)'
runon
soft.
and
2
0
s ' q
-0
0
h
0
i
0
8
I
1
v).I
I
F
0
N
0
9
t o
+
m
0.
I
rg-
5
i
Y
I
I
1
I '
I
I
l
(
l
1
tu
N
4
N
cd
M
L
v1
tu
rl
0
!-I
a
.I .
..
I
i
-1'00 1
I
I
I
I
I
I
-
-5
-10
."
I
6 018
1
I
1
I
1
0
(O/OO)
-
Figure 15
Oxygen-l8/deuterium plot, Yazzie depression (hole NV
I1 2 8 ) .
u4
J '.
'
'.i
i
Table 2 .
Local recharge rates for Navajo Mine landscape settings.
specific values.
Range 2
(inlyr)
No. of
sites
Setting
( 0 . 0 3(7)
)
UNDISTURBED
badlands
31
upland flat
3
valley terrace
1
-0.05
flat0.23
0.01-
Ranking 5
by recharge
0.002-0.01
0.006
0.006
5
0.02
0.035
0.03
4
0.09
0.09
2
(0.25)
(0.09)
0.09
(0.01
9
depression
Mean4
(inlyr)
( 0 . 0 4 6 )( 0 . 0 0 2 - 0 . 0 9 )
(22)
RECLAIMED
Median3
(inlyr)
See Stone (1984 and 1986) for
-0.49)
0 . 0 3 - 0.16
0.49
0.26
13
1
0.12
0.04
3
1 .
includes valley bottom site of Phase-I study as in badlands
recharge values based on mean (not median) C l s u
median = (range12) + low value
mean = totallnumber o f values
I = highest; 5 = louest
IMPACT OF MINING ON RECHARGE
The
the
ultimate
Navajo
capacity
Mine
due
to
objective
was
to
mining,
of
the
Bureau’s
recharge
determine
the
net
change
especially
the
impact
of
in
studies
at
recharge
depression2
in
reclaimed areas. This change may be assessed by comparing
premining and postmining recharge values. For example, local
recharge rates may give an indication of change. Better ye?, the
total
volume
of
water
recharged
before
and
after
mining
(reclamation) can be compared.
LOCAL
RECHARGE
The
first
step
in
calculating
26
volumetric
recharge
is
t-,
determine local recharge rates. Values were obtained in Phxses
I
and I1 of this study (Stone,
1984b and 1986a) and the isoto?e
work in PhaseI11 shows that such values are usable. Local
recharge
rates
summarized
in
for
settings
recognized
at
Navajo
Mine
are
Table
2.
Local recharge ranges from
0.002 in/yr (Bitsui badland:
valley) to 0.49 in/yr (Doby depression). The frequency of
occurrence of local recharge values
is shown in Figure16.
The
0.10 in/yr. The most comonly
vast majority of values fall below
obtained value is0.02 in/yr (five sites). Three valuess h x e
0.01, 0.03, and 0.05 in/yr (four sites
the next most common slot:
each). Values of 0.04 and 0.10 in/yr occurred at three sites
each. The values of <0.01, 0.07, 0.08, 0.09, 0.34, and 0.49
in/yr were obtained at one site each. Some values were not
obtained at any site:
0.06, 0.12-0.34, and 0.35-0.49 in/yr.
Local
whereas,
recharge
that
in
0.09 in/yr. Based
settings
would
in
undisturbed
reclaimed
areas
areas
averages
0.03 in/yr,
averages
three
times
that
or
on decreasing orderof local recharge rate,
be
ranked
as
reclaimed
depression,
valley
terrace,
reclaimed flat, undisturbed upland flat, and badlands (Table
2).
AREAL
EXTENTOF SETTINGS
The
next
determination
step
of
the
in
calculating
areal
extent
volumetric
of
various
recharge
landscape
is
thz
settings
in the study region. This may be accomplished through the use of
field studies, aerial photographs, topographic maps, soils maps,
geologic maps, or some combination of these tools. Differe?t
methods should give similar results. Stone (1985a) found t’lat
27
Y
0
...
0
R&&&
Figure 16
-
(in/yr)
Frequency of occurrence of l o c a l recharge values.
Table 3.
Summary of pre- and postmining recharge rates and fluxes at Naval0 ~ i n e
(Stone, 1987).
Recharge
range
(inlyr)
setting (sites)
Median
recharge
(inlyr)
Mean
recharge'
(inlyr)
Volumetric
recharge
(sc-ftlyr)
Area
(ac)
~-~"~~""""""_____________________~~~~~".
UNDISTURBED
(7)
(0.002-0.09)
(0.046)
0.002-0.01
0.02 -0.05
badlands (3)
upland flat (3)
valley terrace (1)HA
(0.03)
0.006
0.03
0.006
0.035
0.09
HA
(16.05)
(8,821)
4,240
4,090
491
2.12
10.23
3.7
Mean regional recharge = 0.02 in/yr 2
UNDISTURBEDAREA
REDUCEDTOMATCH
RECLAIMEDAREANA
NA
(22)
depression (9)
flat (13)
(0.01 -0.49)
(0.25)
0.03
-0.49
0.26
0.01
0.12-0.23
RECLAIMED
0.02
2,881
4.9
(0.09)
0.16
(2,881)
68
2,813
(10.05)
0.04
0.68
9.37
Mean regional recharge = 0.04 inlyr2
(30.88)
RECLAIMEDAREA
EXPANDEDTOMATCH
UNDISTURBEDAREA
depression
flat
NA
NA
0.16
0.04
NA
NA
176
8.645
2.35
28.53
Mean regional recharge = 0.04 inlyr
U I T H O U TD E P R E S S I O N S
NA
I N RECLAIMEDAREA
8,821
HA
0.04
2
29.40
___________"""-______________________""""""~~~~"""""""
1 slrnple
.
arithmetic average
weighted by acreage (volumetric recharge dividedby area)
areal extents, and thus volumetric recharge results, based
a
on
geologic
map
map
of
the
In
this
were
same
very
and
Premining
acreages
to
those
obtained
a soils
from
area.
study,
premining
comparable
it
was
post-mining
were
necessary
to determine
settings
based
on
by
soils
areal
different
maps
1977 (Keetch and others,1980; see Appendix C).
extent
of
methods.
made 1953
between
and
Boundaries
2 and
between settings were determined and digitized (Figures
3).
Areas were determined by
a digital planimeter (Table
3).
Areal
extentof post-mining
settings
was
based
on
the
latest
aerial photographs (1:6,000) and field checking. This covered
29
only areas in which mining had occurred:
1 and 2.
floors
were
delineated
on
photos
by
Depression
means
a lox of
mirror
stereoscope. Depressions larger than0.15 acres (6500 ft2) were
located in this way. Smaller ones escaped detection. Outlines
of
depression
maps
and
floors
areal
were
extents
transferred1 to
inch-to-500
determined
by
ft
mine
means
a digital
of
planimeter (Figure 4). The size and location of each depression
was then verified in the field. Areal extents of postminin7
settings
are
AREAL AND
given
REGIONAL
For a given
local
in
recharge
Table
3.
RECHARGE
setting,
rate
areal
and
its
recharge
areal
is
extent,
the
in
product
of
similar
its
units.
Local recharge is converted to ft/yr (divided by 12) and acreage
.
is converted to ft2 (multiplied by 43,560)
Multiplying thzse
gives a value
This
of
calculation
ft3/yr;
is
division
made
for
by
both
43,560
gives
premining
and
acre-ft/yr.
post-mining
settings.
As
shown
in
Table
3, premining areal recharge in areas
1 and
2 ranges from 2 ac-ft/yr to 10 ac-ft/yr. Upland flats accomt
for
the
greatest
premining
recharge
( 6 4 % ) and badlan-ls
volume
contribute the least (13%). The valley/terrace setting is
intermediate
Recharge
Table 3.
with
23%
volumes
of
for
the
recharge.
reclaimed
settings
are
also
given
in
However, the acreage is less than that of the
undisturbed area. More specifically, 67% of the area is still
taken up by open pits, ramps, roads, etc., features
wo~ld
that
not be present at end of mining. Recharge volumes cannot b'z
30
compared
and
postmining
areas
Areas
acreage
impact
may
to
of
are
be
that
cannot
be assessed
unless
pre-
and
identical.
made
of
mining
equal
the
in
two
reclaimed
ways:
reducing
undisturbed
analyzed
o r increasing
ground
reclaimed acreage to that of the undisturbed ground. In ths
first
case,
recharge
volume
is
calculated
using
recharge rate and an area 2,881
of ac (Table 3).
premining
volume 4.9
of ac-ft/yr
recharge
as
the
mean
regional
This givesa
compared
to
a post-
mining recharge volume of
10.05 ac/ft/yr. The difference is an
increase of5 ac-ft or 105%.
is
calculated
for
the
using
settings,
In the second case, recharge volume
the
respective
based
on
the
recharge
observation
rates
that
and
acreaJes
depressions
account for only
2% of the reclaimed ground. This gives
a postmining
30.88 ac-ft/yr (2.35 ac-ft/yr for depressioys and
of
value
28.53 ac-ft/yr f o r other reclaimed settings). This represe’lts an
increase
recharge
with
mining
and
15 ac-ft
reclamation
of o r
As recharge is higher in depressions and they are no
108%.
longer
be
in
being
determined
constructed,
a more
by
calculating
realistic
recharge
impact
volumes
of
mining
can
without
depressions. This gives 29 ac-ft/yr, o r an increase of only
83%
(Table 3).
DISCUSSION AND CONCLUSIONS
In all
cases,
mining
and
reclamation
appear
to
increas?
recharge. Those scenarios involving depressions suggest re7harge
is approximately doubled. With no depressions the indicate83
9-22% less. The increase in recharl~e
increase in recharge is
with
mining
and
reclamation
31
is
attributed
to
better
infiltration
capacity
of
the
spoil
improved
vegetative
recharge
in
as
well
cover,
depressions
as
enhanced
due
to
the
blow
sand
availability
ponding
of
used
of
for
water
runoff,
top
soi
for
and ofaddition
supplementary water during irrigation. Although the latter is
short-lived,
An
the
other
increase
in
conditions
recharge
at
prevail.
Navajo
Mine
should
not
be
detrimental to the water resources of the region. As one
parameter of the
hydrologic
budget
changes,
others
also
change
to
maintain the balance. In the case of an increase in recharge,
the expected response would abedecrease in runoff. This is not
unfavorable
at
Navajo
Mine
as
the
mine
plan
calls
for
zero
runoff. A further consequence would be enhanced ground-water
flow toward discharge areas. The amount of increase would be
minimal,
equaling
Results
the
rate
of
presented
here
are
increased
believed
recharge.
to
be
realistic
an3
representative. Additionally, this is the first time, to my
knowledge,
that
impact
of
mining
on recharge
has
been
addressed
or documented to this extent. This study should servea model
as
for
such
studies
at
other
surface
coal
mines.
ACKNOWLEDGMENTS
Funding for sampling, isotope analyses, and recharge
calculations
was
provided
a
bycontract
with
BHP-Utah
International Inc. Mapping and determination of areal exte-ks of
landscape settings was done by Dr. Bruce A. Buchanan (Department
of
Crop
and
Soil
Science,
New
Mexico
State
University)
and
B. Korsmo (graduate research assistant, New Mexico State
University). Sterling Grogan (manager of environmental quality),
32
Thomas
and Orlando Estrada (senior environmental specialist), BHPUtah/Navajo
Mine,
provided
valuable
assistance
during
the
work.
Darla Curtis (undergraduate student, New Mexico Tech) assisted in
the
laboratory.
REFERENCES CITED
Allison, C. B., Barnes, C. J., Hughes, M. W., and Leaney, F. W.
J., 1983, Effect of climate and vegetation on oxygen-18 and
deuterium
profiles
in
soils:
International
Atomic
Energy
Agency, Report SM-270120, p.
105-121.
Allison, G. B., and Hughes,M. W., 1978, The use of environTenta1
chloride
and
tritium
to
estimate
total
recharge
to
an
unconfined aquifer: Australian Journal of Soil Researcl,
v.
16, p. 181-195.
Allison, G. B., Stone, W. J., and Hughes, M.W., 1985, Rechwge
through
karst
indicated
by
and
dune
natural
elementsa semiarid
of
isotopes
and
landscap?
chloride:
as
Journal
of
Hydrology, v. 76, p . 1-25.
Buchanan, B. A., and Korsmo, T. B.,1987, Distribution and extent
of
pre-mine
and
post-mine
landscapes
on
the
Navajo
Min?-,
Mexico: unpublished report to BHP-Utah International Inc.,
12 p.
Craig, H., 1961, Isotopic
V. 133,
p
variations
. 1702.
33
in
meteoric
water:
Science,
New
Keetch, C. W., Ruiz, J. E., Parham, T. L., Bulloch, H. E.,
Anderson, T. J., King, D., Seagraves, C., Boyer, J., Kossie,
A., Roybal, M.W., and Childs, S.,
Juan
County,
New
1980, Soil survey of San
Mexico--eastern
part:
Soil
Conservation
Service, 173 pp.
McCord, 3. T., and Stephens, D. B., 1987, Lateral moisture flow
beneath a sandy
hillslope
without
an
apparent
impeding
layer: Hydrological Processes, v.1, p.225-238.
Snell, F. D., and Biffen,F. M., 1964, Commercial methods of
analysis: Chemical Publishing Company, Incorporated, New
York, p. 41-43.
Stone, W. J., 1984a, Preliminary estimates of Ogallala-aquifer
recharge
using
chloride
in
the
unsaturated
zone,
Curry
County, New Mexico: Proceedings, Ogallala Aquifer
Sympxium
11, Lubbock, p. 376-391.
Stone, W. J., 198433, Preliminary estimates of recharge at the
Navajo
Mine
Mexico
Bureau
based
on
of
Mines
chloride
and
in
Mineral
the
unsaturated
Resources,
zone:
New
Open-file
Report 213, 60 p.
Stone, W. J., 1985a, Determining recharge in coal surface mining
areas:
Proceedings,
2nd
National
Meeting
of
the
American
Society for Surface Mining and Reclamation, Denver, p. 394403.
34
Stone, W. J., 1985b,A simple approach to determining recharge
in
surface
taught
coal
at
mining
areas;
a study
the
1985 National
guide
Symposium
for
a mini-course
on
Surface
Mining,
Hydrology, Sedimentology, and Reclamation, Lexington,
Kentucky, 63 p.
Stone, W. J., 1986a, Phase-I1 recharge study at the Navajo Mine
based on chloride, stable isotopes, and tritium in the
unsaturated
zone:
New
Mexico
Bureau
of
Mines
and
Mineral
Resources, Open-file Report 216,
244 p.
Stone, W. J., 1986b, Comparison of ground-water recharge rates
based on chloride, stable-isotope, and tritium content of
vadose
v.
8,
water
at
the
Navajo
Mine
(abs.):
New
Mexico
Geology,
no. 3, p. 70.
Stone, W. J., 1986c, Natural recharge in Southwestern
1ands:apes
--examples
Association
from
New
Focus
Mexico:
Proceedings,
Conference
on
National
Southwestern
Wate-
Well
Ground-Water
Issues, Tempe,p . 595-602.
Stone, W. J., Lyford, F. P., Frenzel, P. F., Mizell, N. H., and
Padgett, E. T., 1983, Hydrogeology and water resources
of
San
Juan
Basin,
New
Mexico:
New
Mexico
Bureau
of
Mines
Mineral Resources, Hydrologic Report
6, 70 p.
Utah International Inc., 1981, Permit application for Navajo
Mine, v. 1, chpt. 15.
35
and
APPENDIX A
ISOTOPE DATA
36
Hole 1 Custer Depression
(ft)
Sample
Depth
*
Vol.
(ml)
018 (o/oo)
D(O/OO)
T (TU)
1
0.5
35
-
3.03
-
51.6
51+/-8
2
1
35
-
6.48
-
74.7
50+/-7
3
1.5
25
NES *
NES
NES
4
2
23
-14.63
-108.5
22+/-8
5
2.5
45
-12.46
-
<6+/-8
6
3
2
NES
NES
NES
7
5
45
NES
NES
NES
8
6
43
-17.3 8
-123.7
<6+/-8
9
7
36
-13 .78
-112.5
<6+/-7
10
8
25
-17.44
-132.8
<6+/-7
11
10
34
-14.73
-125.5
34+/-8
12
15
35
-
-111.1
13
20
50
-11.67
-112.9
<6+/-7
14
25
45
-
9.94
-104.4
19+/-7
15
30
43
-
9.70
-100.6
9+/-8
16
35
30
-12.83
-108.8
18+/-8
17
40
32
NES
NES
<6+/-7
18
45
32
87.9
2 1+/-7
19
51
NES
NES
20
56
70.0
<6+/-7
-
NES = lab reported not enough
37
8.24
-
NES
1
38
9.70
sample
9.80
-
97.6
9+/-8
Hole 2
Sample
Depth (ft)
Vol.
P i n t o Depression
(ml)
018 (o/oo)
D(o/oo)
T (Tu)
-
66.2
38+/-8
81.8
7+/-7
87.5
13+/-8
21
1
43
22
2
35
23
3
32
-
24
5
42
-10.87
-100.1
ll+/-7
25
6
48
-12.58
-103.8
12+/-8
26
7
38
-13.54
-107.5
21+/-7
27
10
27
-14.17
-101.5
<6+/-7
28
15
22
-13.80
-106.7
<6+/-7
29
20
35
-14.21
-123.1
<6+/-7
30
25
33
-14.77
-123.5
<6+/-8
38
1.29
5.60
8.22
-
Hole 3
North Barber Depression
Sample
Depth (ft)
Vol. (ml)
31
0.5
37
32
1
26
-
33
1.5
46
-
34
2
46
-
35
2.5
37
-12.80
36
3
35
-
37
5
45
38
6
39
D(o/oo)
T (TU)
37.7
41+/-7
51.6
20+/-8
6.64
-
62.1
<6+/-7
8.72
-
67.1
36+/-8
-
80.2
<ti+/-?
83.3
61+/-7
-12.94
-116.1
<6+/-7
38
-12.54
-
97.6
70+/-8
7
42
-12.89
-101.0
6+/-7
40
10
35
NES
NES
8+/-7
41
15
42
-11.70
-104.2
<6+/-7
42
20
28
NES
NES
7+/-7
43
25
26
NES
NES
49+/-9
44
30
21
NES
NES
42+/-8
45
35
27
-13.17
-111.8
<6+/-7
46
40
29
-13.51
-109.5
<6+/-7
47
45
49
<6+/-8
50
35
-
80.9
48
-
60.0
19+/-8
49
55
70
NES
35+/-9
50
60
70
72.0
7+/-8
51
65
27
39
0 1 8 (o/oo)
3.23
3.90
9.39
9.06
7.38
NES
-
6.95
NES
-
NES
54+/-8
APPENDIX B
BRIEF
FIELD
40
DESCRIPTIONOF SAMPLES
Hole 1 Custer Depression
Drilled 10 ft due
Sample No.
east
of
hole
16 of Phase-I1
study.
General
Lithology
(ft)
Depth
Spoil
green
-
light gray
claystone
sandstone
and
some
1-6
0.5-3
7-10
3-8
Spoil - sandstone as above with
carbonaceous shale, coaly spoil at
base.
8-10
Spoil
gray
spoil.
11
-
carbonaceous
shale/coaly
10-75
Spoil - upper 6" carbonacems shale,
rest sandstone as above.
15
25-30
Spoil - as above except
carbonaceous shale.
16
30-35
spoil - mostly
shale.
17
35-40
12-14
Spoil
-
lower
18
19
20
green
lover
1 ft
carbo7aceous
coaly spoil in upp?r
half gray claystone.
40-45
spoil - green claystone as
some sandstone at base
45-50
Hard
zone- no sample.
50-51
Spoil
-
51-55
Hard
zone- no
sample.
55-56
Spoil
-
carbonaceou?
41
half;
above;
hard, white sandstone
mostly
sandstone.
Hole 2
Drilled 20 ft
Pinto Depression
northeastof hole 19 of Phase-I1
study.
Sample No.
General
Lithology
(ft)
Depth
21, 22, 23
0-4
Spoil - yellow
claystone
24,25,
4-14
Spoil
-
half
- tophalfyellowsand;lower
claystone as above.
28
29
26, 27
15-19Spoil
19-21Spoil
30
Fruitland
24-25
42
and
green
green
claystone
as
above
- upper 6" spoil;restFruitland
Fm(?)-moist, very carbonaceous dark
shale
Hard
zone
21-24
sand
-
nosample.
Fm(?)
above.
as
gra
Hole 3
NorthBarberDepression
Drilled 25 f t southwest of hole
Sample No.
24 ofPhase-I1study.
Depth ( f t )
Lithology
General
~~~~~
-
3 1-3 6
0-3
Spoil
c l a y e y ,c a r b o n a c e o x
37-39
3-8
Spoil
40, 41
8-13
Spoil
a s above,moist:gray
sandstone a t b a s e
mudstone
a s above, but dark green
-
-
13-23
Spoil
a s above, but w i t h b i t s of
hard carbonaceous mudstone
44
23-28
s p o i l a s above w i t h f i s s i l e
carbonaceous s i l t s t o n e
45
28-33
S p o i l - dark gray carbonac?-ous
claystone
46, 47
33-48
S p o i l - carbonaceousshaleand
claystone
48
48-53
S p o i l - l o o s e ,v e r yc o a l y ;
blocks
49
53-58
Spoil
base
50
58-63
S p o i l - carbonaceousclaystone/
mudstone
42-43
cable problem:
dropped rod
43
-
loose, clayey:
no f u r t h e r sampling
some hard
v e ~ 7w e t near
APPENDIX C
SUMMARY OF PREMINING LANDSCAPES
(modified from Buchanan and
Korsmo, 1987)
44
Setting
Badlands
U p l a n dF l a t s
Description
Associated
SoiS
l eries
b aur p
r el ad
n ni sdessp
e bh
c yteemdFear rabl
Pmesertsasrbaa
nehrsydae
i lom
al sks,s, ,
F m ) e xi sp o sMeodn i e r c o
u h eb reed r o( F
c kr u i t l a n d
o r c o v e r e d by v e r yt h i ns o i l s
p l a t e a u sm
, e s a s h, i g ht e r r a c e s a, n d
a l l u v i a lf a n su n d e r l a i nb yF r u i t l a n d
F m a n dc a p p e d
b y a l l u v i a la n d / o re o l i a n
d e p o s i t ss ;o i l s
ma
bt hyei cm
k ;ocsot m p l e
Dxo a k
s e t t i n gw i t hg r e a t e s tv a r i e t yo fs o i l
types
Valley/Terre
ap
ce
h e m es rt ar el a m - c h a nf nl oeaol nr d
s
a s s o c i a t e df l o o d p l a i n sa n dt e r r a c e s ;
c o n s i s to fa l l u v i u m ;s o i l sa r ey o u n g
b u tt y p i c a l l yt h i c k
45
Avalon
Blackston
Elan-ot
Farb
Huerfano
Mayq'leen
Monierco
Muff
Notal
Persayo
Shepqard
Ship-ock
Stumble
Uffeqs
BeebFruitland
Glenton
Stumble
Turley
Youn3ston