Preliminary Geologic Evaluation
Radon Availability in
New Mexico
Open-file
of
Report OF-345
Virginia T. McLemore and John W. Hawley
New Mexico Bureau of Mines and Mineral Resources
Socorro, NM 87801
Summary
The primary
identify
and
objective
of
,characterize
this
areas
preliminaiy
in
New
report
Mexico
is
where
to
geologic
factors may significantly influence indoor radon'values. Areas
which
may
have
radon
need%o be
detectors
survey
can
potential
in
be
allocated
by
the
to
New
these
Mexico
levels
percentage
of
of
irdoor
redon
locaiitiesa statewide
during
Environmental
with U.S.
the Environmental
cooperation
. .
elevated
identifiedso that a .larger
conducted
Division
for-generating
Improvement
Protection
Agency. The first step in this evaluation is to identify large
areas
where
previous
geologic
studies
indicate
a probability
of
,.havingelevated levels of indoor radon. Assessment of any health
risks
due
to
exposure
of
radon
are
beyond
the
scope
of
this
study. Also, any potential exposure hazard may vary significantly from house to house. The only way to find out the
of. extent
exposure
house
due
for
to
indoor
this
study
grouped
into
three
to
house
is
to
test
that
radon.
In
tive
radon
a specific
in
each
rocks
New Mexico
soils
in
and
radon-availability
other
and
specific
to
were
initially
categories,
New
which
Mexico
are
based
rela-
on
geologic
interpretations. Sbsequently, each county and the major cities
in
the
state
predominant
'
were
given
a radon-availability
availability
category
rating
established
based
for
on
geologic
the
units
in that area. The health risks, if any, associated with thes?
geologically
indoor
Ten
radon
ranked
levels
counties
areas
is
are
are
hot
known
until
the
survey
rating
for
completed.
assigned
a high
availability
of
radon
basedon interpretation of .available
data;
they
are
Doka
Ana,
geologic
and
soil
.LosAi.amos, Luna, McKinley,
Hidalgo,
of the
Rio Arriba, Sandoval, Socorro, Santa Fe, and Taos. Seven
most populated cities
(1984 estimates) are rated high: Santa Fe,
La.s Cruces, Roswell, Carlsbad, Gallup, Deming,Losand
AlamosWhite Rock. Thirteen counties: Bernalillo, Catron,. Cibola,
Chavez, Colfax, Eddy, Grant, Lea, Lincoln; Quay., San Juan, Sier-.
ra, and Union: are assigned
a moderate availability rating. Six
of the
most
populated
cities
are
rated
moderate:
Albuquerque,
Rio
Rancho, Clovis, Kobbs,'Grants-Milan, and Lovington. The
remining
ten
counties-in
New
Curry, De Baca, Guadalupe, HsrdMexico:
.
.
ing, Mora, Otero, Roosevelt, San Miguel, Torrance, and Valen-ia,
are
assigneda low availability: although, some homes in these
areas may still have elevated levels of indoor radon.
Six
of the
most populated cities are rated low: Farmington, Alamogordo, Las
Vegas, Silver City, Portales, and Artesia. In addition it should
be
emphasized
ability
many
that
even
houses
may
in
counties
have
2
low
with
of
indoor
levels
moderate
radon.
and
high
avail-
Purpose
The U S . Environmental Protection Agency (EPA) is conduzting
'
surveyof indoor
a nationwide
the scope
and
magnitude
levels
in houses
radon'
health
risks associated
of
to
define
with
expo;iure
to radon and its decay products (Magno and'Guimond,
1987). The
actual
the
indoor
radon
Environmental
surveys
in
Improvement
NeQ
Mexico
Division-
will
(EID)
of
.be
the
conducted
New
by
Mexico
an inworHealth and Environment
Department. Since geology plays
. .
tant
role
Mineral
in
the
study,
the
New
Mexico
Bureau
of
Mines
and
Resources(NMBMMRJwas asked to provide the geologic
expertise
The
required.
EPA
will
in 1988-1989 to
of
EPA's
geologic
be
and
supply
the
aliocated
soil
EID2,000-3,000
with
radon
throughout
conditions,
New
which
detectors
Mexico
appear
on
to
the
basis
correlate
with
elevated radon levels, and population distribution. Radon dctectors are used to measure concentrations of indoor radon. The
first.step
mary
in
objective
areas
in
contribute
New
tion
can
of
this
be
areas
to
of
allocation
is
to
geologic
levels
percentage
is
report
where
elevated
objective
tions
of
Mexico
to
cate a larger
ary
formulating
a sample
of
with
a high
and
the
identify
and
characterize
factors
indoor
may
radon
in
pri-
significantly
order
to
allo-
detectors
to these areas. A seco7d-
determine.how
better
plan
used
a predictive
as
probability
of indoor radon.
3
geology
tool
of
and
in
having
related
the
soil
identifica-
elevated
levels
coydi-
What is
radon?
Radon isa radioactive, colorless, odorless,' and tasteless
gas
that
is
short-lived
naturally
radioactive
occurring
decay
in
. It is a
environment.
our
product
of
radium
which
is
in
turn
a radioactive decay product of'uranium. The radon gas decays
into a series
of
radioactive
daughter
products
to
which
most
of
the health risks are attributed. Exposure to elevated concentra-
-. tions of radon over long periods of time may increase chances of
developing lung cancer. The radioactive decay'products are
particularly
health
lung
risks
are
cancer
Radon
.
harmful
large
difficult
cases
is
at
are
concentrations,
to
establish
thought
a problem
not
to
outdoors
be
but
the
exact
because
the
majority
caused
because
by
the
cigarette
of
smoking.
atmosphere
dilutes the radon and associated health risks. However, radon
becomes
an
indoor
beneath a house
hazard
into
the
when
the
house
gas
through
leaks
from
cracks
in
the
the
,ground
foundations
and floors and around pipes and joints. Water may also
a
be
source
of
indoor
capillary-fringe
as
ground
centrated
radon
water
water
in
the
and
in
below
may
the
shallow
house,
occur
either
unsaturated
water
especially
soil
moisture
(vadose)'zone
tables.
in
as
Radon
colder
as
well
becomes
con-
months
when
or
the
house is closed. The gas decays.to the solid. daughter products
that adhere to dust particles, furniture, walls,
and-floorsand
tends
The
to
health
basements,
remain
risks
where
in
the
house
in areas
increase
the
gas
tends
4
until
of
to
it
poor
is
breathed
ventilation,
accumulate.
into
such
as
the
luqgs
Indoor
including
radon
levels
geology,
are
dependent
soil-water
content;
upon
many
building
variables,
construction.
weather changes, and life styles of the occupants. The source of
radon is.in the
rocks,
soils,
and
shallow
ground
water
but
an
adequate pathway for the gas to travel.is also required. The
flow
of
radon
pressure
Thus,
but
Soil
between
the
the
house,
is
soil,
generally
a
and
levels
are
found
onsoils with
high
concentrations
of radium
and
uranium;
are
extremely
and
It is
more
radium
permeable,
quickly
extremely
and
allowing
than
difficult
in
to
uranium
the
predict
for
to
not
only
in
concentrations
radon
impermeable
due
atmosphere.
indoor
low
radon
house
high
with
houses soils
on
farther
into
with
in
that
the
differential
houses
houses
from
gas
to
travel
soils:
an
individual
louse
if indoor radon may abe
hazard. Regional areas of increased
probability
of
having
identified
using
elevated
geologic
levels
data
as
of
in
this
indoor
radon
may
be
but
the
hazard
report:
still. variesfrom-house to house. Even in'areas low
of risk of
indoor
radon
hazards,
a few
houses
in
these
areas
may
have
e1.e-
vated levels of indoor radon. The only way
find.out
to
the
extent
of
the
risk
due
to
a specific
radon
in
indoor
housei F to
test that house for radon. If your home is above the EPA recommended
action
mitigate
the
level
4ofpCi/l,
problem:
there
prevent
are
its
basically
infiltration
two
by
ways
sealing
to
cracks
or dilute the gas inside the house by ventilation. For more
information on radon,
mitigate
the
the
problem,
the
associated
reader
is
health
risks,
referred
and
tc
to
(1988),
Green
Cohen and Nelson(1987), Hopke (1987), and U.S. Environmental
5
how
Protection Agency (1986a, b, c).
6
Variation
radon
generation as a function of New Mexico geology
in
The
first
of.indoor
step
radon
in
formulating
a sample
levels
is
to
plan
evaluate
the rocks
for
and
the
survey
soils
fo-
radon-availability. Prediction of radon-availability requirzsa
knowledge
of
lithology
and
uranium
or
radium
content
of
various
rocks and soils, rock structure (shears and fractures), soil and
rock permeability, and nature of the ground water. The primary
sources
of
data
used
to
evaluate
the
rocks
and
soils
in
New
Mexico were'l) aerial radiometric data,2) geologic, especially
lithologic, data,3 ) uranium occurrence data,and
4)
soil perme-
ability data. Other sources of information include geochemical
data,
ground.water
data,
a
and
limited amountof indoor
radon
concentrations. These data were integrated to provide
a prel.iminary estimate of radon-availability in New Mexico. Since the
time
spent
four
, due
weeks)
preliminary
on
this
to
assessment
EPA
assessment
was
relatively
,and
EID constraints,
and
will
require
this
more
short
is
(less
thar
only
a
detailed
study.
Aerial radiometric data
Aerial
uranium
radiometric
concentrations
correlates
well
data
in
with
the
provides
a regional
the
surficial
of radon
amount
in
estimate
rocks
the
and
ground
of
soils
and
(Peake
and
Schumann, in press). However, it must be emphasized that the
amount
of
radon
that
is
available
to
a house
enter from
the
ground is dependent upon many other variables. The primary
so~rce€or
reports
aerial
prepared
radiometric
as
part
data
of
the
in
New
National
Mexico
a series
is
Uranium
Resource
1974
tion (NURE) program. .The NURE program was established in
7
of
Evalua-
and
an
terminated
assessment
2) to identify
in
1984 and
of
the
areas
The NURE aerial
ports
the
main
were
in the United
resources
uranium
of
objectives
uranium
1).to
States
provide
and
mineralization.
radiometric
data
basedon lo x 2O topographic
has
been
quadrangles
released
and
on
in
re-
magnetic
tape. The quadrangle reports inc1ude.a brief narrative and
graphs
of
the
flightline
data,
uranium
anomaly
maps,
and
hist.0-
A colored contour
grams of the radioactivity data by lithology.
map
of
New
Mexico
concentrations,was
showing
radiometric
prepared
equivalent
uranium
by U.S.
the Geological Survey at
a
scale
of1:1,000,000 from
data.
NMBP’MR.
A copy of this map is available for inspection
at
The
individual
were
used
in
Several
the
quadrangle
this
(eU)
computerized
reports
and
aerial
the
radiometric
state
compilation
map
assessment.
problems
exist
Most lo x 2O quadrangles
in
with
New
the
Mexico
aerial
were
radiometric
flown
with
data.
east-west
flight line spacings of three miles. However, parts of the
Tularosa and all of the Carisbad, Raton, and Ft. Sumner quadrangles
‘were.
exist
flown
between
with
these
six.
mile
flightlines
spacings.
and
Large
localized
unmeasured
anomalies
ke
are.as
may
overlooked. In addition, ,not all areas of New Mexico were flown.
The
largest
Missile
Range
In the
Sions
area
are
of
no
data
is
as Cruces
north Lof
southwestern
known
part
to.occur
in
and
of
the
west
New
frequently
vicinity
of
the
White
San
Alamogordo.
Mexico,
and
of
may
atmospheric
result
in
inv&runcompen-
sated U-air anomalies. Atmospheric plumes generated by copper
smelters
in
southwestern’
New
8
Mexico
and
southeastern
\
Arizona
also
may result.in uranium anomalies in the surveys. The effect of
these
atmospheric
indoor
radon
The
anomalies
is
in
predicting
elevated oflevels
unknown.
extremely
high
uranium
anomalies
in
the
aerial
radiomet-
1) near Grants, Cibola County, aare
ric data.(>5 ppm eU; Fig.
result of high values measured over uranium mill tailings. Four
in the
occur
Grants
area,
but
only
one
is
currently
uranium
mills
active.
Two of the mills are scheduled for cleanup. The com-
puter
generated
Geological
aerial
Survey
radiometric
exaggerates
map
the
produced
significance
by
the
of
U.S.
these
anomz-
lies: the actual area affected by the mill tailings is small and
probably
has
not
contributed
excessive
indoor
radon
to
nearby
houses.
Aerial
radiometric
data
are
dependent a upon
constant
alti-
tude above the ground. However, in some areas of New Mexico
where
there
altitude
are
could
steep
not
mountains
be
and
maintained,
deep
canyons,
constant
resulting
iri erroneous
measure-
ments. Both airplanes and helicopters were used to collect data
in
New
stant
Mexico
altitude
and
helicopters
than
were
able
to
better
maintain
ccn-
airplanes.
Geologic data
Information
units
in
New
on
the
Mexico
is
type
and
important
distribution
of the
in
lithologic
identifying
areas
of
high
radon-availability f o r generating indoor radon. Geologic maps,
especially
were
the
New
Mexico
Geological
used.
9
Society.(1982)
State
map,
Very
the
'
little
rocks
exists
on radon
data
and
soils
of
centrations
in
rocks
and
Rocks
uranium
with
sufficient
to
New
or
Mexico,
soils
of
concentrations
produce
radium
elevated
concentrations
however
data
on
uranium
con-
Newis Mexico
more plentiful.
exceeding
5 ppm U are
levels
of
indoor
radon
(Peake
Hess, 1987).
In New Mexico, most rocks types could provide
a
source
indoor
for
in
and
radon.
In addition to lithology, structural features also play an
. -.
important role in some areas. Faults, shear zones, and areaF of
highly
and
jo'inted
they
also
rocks
and
migration
of
likely
provide
a pathway
sites
for
of
radon
uranium
to
mineralization;
migrate
into
horses
Karst (rock dissolution) features in
(Ogden et al.,1987).
carbonate
are
gypsiferous
terranes
may
also
provide
pathways
for
radon.
Uranium occurrence data
Areas
of
uranium
occurrences
and
mines
are
Mexico (McLemore, 1983; McLemore and Chenoweth,1989).
.majority
of
these
of New
Mexico,
tions.
Uraniferous
areas
however,
coals
are
found
in
there aare
number
in
the
well
Gallup
in
New
The
relatively
of
known
important
unpopulated
areas
excep-
area,.McKinley
County
.(Fig. l), were once mined for uranium and the host rocks are
probably a good source for radon. Other areas, such as northsrn
1) ,(Fig.
occ~r
Santa Fe County, and White Signal, Grant County
in
areas
of
numerous
uranium
occurrences
near
or
at
the
surfa5e
which could provide radon in nearby houses. Some indurated
caliche (calcrete) horizons in soils and surficial geologic
formations
may
also
be
sources
of
elevated
uranium-radium-radm
levels. A more detailed study
of the correlationof known uyani-
um occurrences,
is
population
distribution,
and indoor radon le7rels
required.
Soil permeability
Soil
aata
-
permeability
data
from
soil
surveys
prepared
by
the
Soil Conse.rvation Service
(SCS) of theU.S. Department of Agriculture are an important data base for this assessment. Well
drained,
permeable
Soils,
typically
exceeding6 in/hr,
measurements
with
hydraulic
provide'axcellent
conductivity
pathways
for
radon. Many areas of elevated radiometric equivalent uraniun.
concentrations
shown
on
the
aerial
radiometric
map
occur
in
e.reas
of permeable soils. However, the soil permeability is
data
generalized
and
based
on
very
few
Actual
measurements
of
hydrau-
lic conductivity. Also soil-moisture regimes vary significantly
on a seasonal
affect
as
well
permeability
as
an
annual
basis,
and
they
can
materially
values.
Other sources of data.
Other
sourcesof data,wereexamined to support
interpreta-
tions of aforementioned data. The
NURE geochemical data consists
of
uranium
analyses
of stream
sediment
(McLemore and Chamberlin,1986).
showing
the
in
Mexico
New
distribution
were
used
of
to
and
ground
water
samples
Geochemical reconnaissance maps
for each lo x
uranium
identify
2O
areas
quadrangle
of
high
uranium
areas.iden3trations. Most of these areas correlate well with
fied
using
aerial
radiometric
data.A few
problems
exist
with
the NURE geochemical data. Uranium concentrations in stream
conoen-
sediments are actually displaced
and diluted values. Very little
suchas host rock and depth of the grourid water
information,
samples, is available.
..
Mexico
were
not
In addition, inany populatedareas of New
sampled
and
no
data
exists.
Ground water datti, such as depth, flow direction, and chemical
composition,
provide
additional
information
on
hydrogeologic
conditions which may affect the levels of indoor radon. Other
-
-.
data such as distribution and character of geothermal areas,vere
also used in this assessment. In Idaho, houses built in geothermal
areas
1987).
have
higher
levels
of
indoor
radon
(Ogden
et
al.,
This relationship has not been tested in New Mexico.
amountof actual
Only a limited
indoor
radon
measurements
are available. Most of the past studies of EID are conf.identia1.
These
published
and
unpublished
data
were
examined 2sfor
this
sessment.
Classification of Radon-Avai,lability
The
rocks
and
radon-availability
soils.in
categories
New
Mexico
according
to
were
grouped
into
three
interpretations
of
available geologic data. Radon-avaiiability categories are
relative to each other and specific to New Mexico. Because the
risk o f inhaling
or
ingesting
a dangerous
amount
of
radon
is
due
to complex architecture, atmospheric, and geologic factors, we
refrain.
from
using
the
term
"risk"
in
evaluating
areas
for
avai
ability of radon. The actual health risks associated with ea7h
availability
category
are
not
known
until
the
actual
indoor
radon
surveys are completed.The geologic character of each category
is described
below.
High radon-availability category
The
the
high
rocks
radon-availability
and
soils
are
category
believed
to
includes
have
the
areas
where
greatest
potential
for .generation of indoor radon. These areas consist of rocks
which
typically
2.7 ppm
exceed
eU
on
the
aerial
radiometric
rap
and, generally, but not always include well drained, permeable
- -_
2.7 ppm eU was chosen on the basis of prior
soils. The limit of
(T. Peake, USWE,
experiences of EPA elsewhere in the.country
personal commun., Sept., 1988).
This
category
granitic
rocks
includes
with
many
average
outcrop
uranium
areas
of
Proterozoic
concentrations
of
3-17 ppm
1970; Brookins and Della Valle,
1977; Broo(Sterling and Malan,
kins, 1978; Condie and Brookins,1980; McLemore, 1986; McLemore
and McKee,1988).
rocks
in
Tertiary rhyolitic and andesitic volcanic
southwestern
New
Mexico
contain
anomalously
high
uranium
1980; Bornhorst and Elston,
1931)
concentrations (Walton et al.,
and are included in this high category. For example,
a sample of
the
Alum
Mountain
andesite
near
Silver
City,
GrantCOYCounty,
tained 35.1 ppm U (Bornhorst and Elston,
1981). .The outcrop area
of
the
Bandelier
rated
Tuff
in
high;
a sample
the
Jemez
Mountains
in
north-central
contained14.8 ppm U (Zielinski,
Mexico
is
1981).
Tertiary alkalic rocks in central and eastern New Mexico
1982) are also rated high: ma2y
(New Mexico Geological Society,
uranium
and
thorium
occurrences
are
associated
sive rocks (McLemore and Chenoweth,
1989).
13
with
these
Some Paleozoic and
int-ru-
New
Mesozoic sandstones, shales, and limestones, locally contain tigh
concentrations of uranium (Brookins and Della Valle,
1977; Dick1977) and
son et al.,
are
rated
high
availability
for
generating
indoor radon. Some Cretaceous coals in the San Juan Basin ccntain 3-9 ppm U (Frank Campbell,NMBMMR, pers. Commun., Oct.3 ,
1988) and are rated high. Areas of permeable valley-fill sedi-
ments
of
Tertiary
to
Quaternary
age
are
high,
although
only
very
few analyses of these rocks are reported.
Areas'of intense
shearing
are
and
ranked
A few
:
faulting,
especially
in
areas
of
uraniferous
rocks,
high.
areas
in
New
Mexico
contain
rocks
with
greater
5
than
ppm eU from the aerial radiometric map (Fig.
1). These areas
typically
constitutea high
availabilityraking, with
one
exzep-
tion, the Grants area. The Grants anomaly
a result
is
of uranium
mill
tailings
Most
of
explained
and
the
has
aerial
geologically.'
been
assigned
a moderate
radiometric
The
availability.
( > 5 ppm eU) can be
anomalies
Gallup,anomaly
is
the
only
one
n'zar
a major city. It isa result of uraniferous coals, some of which
were mined for uranium. The other anomalies occur in sparsely
populated areas. The Vermejo Park anomaly is associated a with
uraniferous
um
veins
Proterozoic
may
occur
et al., 1980)
.. The
County
at
and
Tertiary
in
the
and
area
anomaliesin the
Laughlin
alkalic
granite
Peak,
intrusives;
pegmatites;
(Goodknight
Cornudas
Colfax
uranium
epithermal
Reid
and1984;
Dexter,
Mountains,
County
urani-
are
and'thorium
Otero
associated
veins
occur
the area (McLemore and Chenoweth,
1989; Zapp, 1941; Staatz, 1982,
1985, 1986, 1987).
Several anomalies occur in southern Socor1-o
14
with
in
County,
east
of
Las Cruces in Dona Ana County, west-central
the Black Range (Fig.1) that
Hidalgo County, and in
are
asroci-
ated with Tertiary rhyolitic and andesitic volcanics. Only two
of
these
the
anomalies
Nogal
Bishop
cauldron
Cap
in
associatedknown
withuranium
are
in
Dona
County
(Berrjr et al.,1982) ard
Socorro
Ana
occurrences:
County
(McLemore
and
i989;
Chenoweth,
McAnulty, 1978).
One of the
McKinley
aerial
County,
radiometric
cannot
be
anomalies,
readily
north
of
Gallup
in
explained
kygeological inter-
It correlates with the Tertiary Chuska Sandstone,
pretations.
Cretaceous Menefee Formation;and associated surficial cover: no
mining activity is in the area. Field examination of this area
is required.
Moderate
availability
This
category
category
includes
areas
where.the
rocks
and
soils
only
have a moderate availability for radon. These areas include
rocks
with2.3-2.7 ppm eU on
generally
consist
of
the
aerial
moderately
includes
many
outcrop
Paleozoic
and
Mesozoic
radiometric
permeable
of Proterozoic
areas
sedimentary
soils..
metamorphic
map
and
This
categ2ry
rocks,
and Tertiary-Quaternary
rocks,
sedimentary rocks. Some rocks and soils in the Pecos Valley area
in
eastern
less
Mexico
than2.3 ppm
anomalies
mobile
New
occur
and
are
rated
eU
because
in
the
area,
result
in
could
moderate
numerous
suggesting
elevated
15
high
even
though
they
uranium
ground
water
that
1evels.of
uranium
indoor
is
have
highly
radon.
.Low availability
This
where
category
category
the
rocks
includes
and
soils
the
remaining
areas
of
New
Mexicc
are
believed a to
low have
availability
2.3 than
ppm eU
for radon. These areas include rocks with less
on
the
aerial
radiometric
map
and
include
areas
of
impermeable
soils. Some houses in these areas may still have elevated levels
of
indoor.radon,
obvious
therenoare
but
geologic
reasons
for
predicting their existence in the low availability areas. In
addition,
it
mbderate
levels
should
and
of
high
indoor
be
emphasized
availability
that
even
potential
in-.counties
with
many
houses
may
have
radon
leveis
in
ho-lses
low
radon.
classification of Counties
The EPA's nationwide
requires
that
Rankings
by
statistics
available
each
for
standardize
each
the
of
indoor
countyranked-for
be
radon-availability.
counties
required
survey
are'required
to
for
establish
a sample
county
reporting
allocation
throughout
of
indoor
1) population
reasons:
two
the
United
radon
plan
are
States
2) to and
surveys
throughout
the
country.
New
Mexico
is
the
fifth
largest
state
in
the
United
States,
3 3 counties. Some of these counties are as
yet it contains only
large
or
,(Table 1).
larger
than
some
states
in
the
eastern
United
States
The geology and terrain of New Mexico are quite di-
1982), and major geolog5.c
verse (New Mexico Geological Society,
and
landform
obvious
units
problems
in
cut
across
ranking
most
counties
16
county
for
boundaries,
creating
radon-availability.
For
Mexico
gory
the
is
purpose
ranked
of
according
established'for
category,
if
that
the
to
the
each
county
predominant
units
in
the
in
New
availability
state
(high,
cate-
moderate,
is represented by more than one availabili-
county
category
asses&ent,
geologic
or low). If. a county
ty
this
is
assigned
the
highest
of the
more 25%
than
represents
classification,
total
county
area. Some exceptions are explained below. Final county rank2. Similar procedures were used in
ings are listed in Table
countiesin Terihessee (Tennessee Department Health and
evaluating
'17, 1986).
Environment, written commun., Nov.
Since
New
geologically
Mexico
is
diverse,
the
sparsely
major
populated
cities
in
in
most
terns
of
places
an4
population
(Vigil-Giron, 1987-1988) were also assessed for radon-availabiliSome cities were rated higher than the rest of the
ty (Table3).
county. . In
counties
order
were
to
emphasize
assigned
the
population
higher
distributions,
the
classification 2).
(Table
Results
Ten
counties
(Table 2; Fig.
contain
rocks
2).
are
assigned
a high
availability
for
radon
Large areas of these counties typically
and
soils
2.7 than
ppm eU
greater
with
and
the
soils are permeable. Two counties, Dona Ana and Santa Fe Counties,
the
were
rocks
assigned
a high
in
the
ranking
county
even
contain
2.3-2.7 ppm
though
the
majority
eU,
because
of
major
cities in both counties (Las Cruces and Santa Fe,
Table
3) were
ranked as having
a high radon-availability. Gallup in McKinley
County
is
ter a large
probably
number.
the
of
most
in New
likely
area Mexico
houses
17.
with
elevated
to
levels
encounof
indoor
is
It must be emphasized that the health risks associated
radon.
with
these
determine
house
geologically
the
must
health
be
Thirteen
ranked
are
not
known.
areas
specific
associated a with
risks
tested
for
radon.
counties
are
assigned
a moderate
(Table 2, Fig. 2).
In order
to
house,
that
availability
Large areas of these counties contain rocks
and soils with
2.3-2.7
ppm eU. Soil permeabilities and litholo-
gies vary. Three counties, Chavez, Eddy, and Lea, are assigned
a
moderate
rating'even
though
most
geologic
evidence asuggests
low
ranking because cities in these counties are rated moderate. In
addition, NURE ground
water
data
suggest
that
uranium
in
ground
water is highly mobile and could contribute radon.
A study of
uranium
and
Mexico
high.
radium
indicates
chloride
occurred
in
mobility
uranium
in
and
radium
concentrations,
chemically
ground
but
reducing
water
1"ew
southeastern
in
concentrations
higher
ground
radium
water
correlate
concentratiors
(Hecrzeg
et
al.,
1988).
Four counties, Colfax, San Juan, Grant,
and Sierra, cont.ain
large
areas
of
rocks
that
exceed
2.7 ppm
eU
and
could
be
assigned
a high rating. A moderate ratingwas assigned to these count.ies
because 1) the
uranium
in
the
rocks
and of
soils
many areas are
2) the cities in
in moderately permeable to impermeable ground,
these
areas
taining
portions
are
rocks
of
rated
moderate,
2.7 ppm
exceeding
the
eU
not
are
high,
and areas
3) the
in
sparsely
ccn-
populated
county.
Ten counties were assigned
a low availability. These counppm eU. The
ties are underlain by rocks with less2.3than
18
with
lithology and permeability of the rocks vary. Undoubtedly, some
houses in these counties
level,
their
but.there
are
will
no
exceed
obvious
the
EPA's recommended
geologic
action
reasons
for
predicting
existence.
Recommendations
1)
Nonrandom surveys should be conducted in areas
of high
availability,
especially
in
areas
containing
5 than
greater
ppm eU (Fig.l), although many of these areas are'sparsely
populated.
2)
Detailed geologic maps and soil survey maps should be completed
3)
for
the
major
cities
in
New
Mexico.
Site specific studiesof individual houses with elevated
levels of indoor radon should be completed. These studies
should
include
detailed
examination
.of
lithology,
mineralo-
g y , and structural features and analyses of soil permeability,
soil
gas
composition,
concentrations
of
uranium
and
radium in the soil, and radioactivity.
4)
This preliminary' assessment must be revised as new data is
collected and analyzed. Continued detailed interpretation
of
the
data
used
in
this
preliminary
assessment
may
also
of known
require revision of this report. Correlation
uranium occurrences, population distribution, and indoor
radon levels should
be examined. Indoor radon measurements
are
required
from
relationship.. A more
houses
in
complete
19
geothermaltoareas
test
data
base
of
this
uranium
concen-
trations
in
rocks
and
soils,
especially
Tertiary
and
Queter-
nary sedimentary rocks, is needea. Eventually, when the
indoor
ated
radon
with
surveys
each
the health.risks
complete,
are
availability
category
may
be
assccidetermined.
Acknowledgments
Discussions
Jacques
son, and
Renault,
and
critical
Richard
reviews
of this
Chamberlin,
manuscript
George
Austin,
by
James
Frank Kottiowski,
NMBM?lR, were’appreciated. Richard
Chamberlin
’
also
provided
the
NURE geochemical
1:1,000,000.
20
data
at
a scale of
Rotert-
Table 1--Size and population
of counties inNew.Mexico
a1 states (Williams,1986; A-W Publishers, Inc., 1983).
county
Land Area
(square
miles)
Population
1987
and
population
Density per
square mile
Bernalillo
1,169
Catron
6,929
Chaves
6,066
Colfax
3 ,762
Curry
1,408
De Baca
2 ,323
Dona Ana
3,819
Eddy
4,184
Grant
3,969
Guadalupe
3,032
Harding
2,122
Hidalgo
3 ,445
4,390
Lea
Lincoln
4,832
109
LOS.Blamos
2,965
Luna
5,442
McKinley
1,930
Mora
6,626
Otero
2,874
Quay
5,856
Rio Arriba
Roosevelt
2,453
3 ,707
Sandoval
San Juan
5,522
4 ,709
San Miguel
Saqta Fe
1,905
sierra
4,178
socorro
6,625
Taos
2,204
3,335
Torrance
3,830
union .
Valencia
5,616
and Cibola
TOTAL NEW MEXICO
121,336
64 ,700
1,498,100
11.5
12.3
STATE
Rhode Island
Delaware
Connecticut
Massachusetts
Maryland
Vermont
New Hampshire
New Jersey
947,154
638,432
3 ,107,576
5,737,037
4’,216,975
511,456
920,610
7,364,823
897.8
479,000’
2,800
58 ,100
14 ,500
42,400
2,400
126,600
53 ,900
. “27,200
4,300
1,000
6,200
68 ,000
15 ,000
18 ,600
18 ,000
63 ,300
4,700
51,000
12,000
33,100
-16,700
.47,200
94 ,000
25,400
87,500
9,800
13,900
22 ,600
9,000
5,200
’
1,055
1,932
4 ,872
7,824
9,837
9,273
8 ,993
7.,468
21
sever-
409.8
0.4
9.6
3.9
30.1
1.0
33.2
12.9
6.9
1.4
0.4
1.8
15.5
3.1
170.6
6.1
11.6
2.4
7.7
4.2
5.7
6.8
12.7
17.0
5.4
45.9
2.3
2.1
10.3
2.7
1.4
637.8
733.3
428.7
55.2
102.4
986.2
Table 2--Preliminary radon-availability
New Mexico.
rating
for counties
High
Dona Ana
Hidalgo
Los Alamos
Luna
McKinley
riba
Rio
Sandoval
Santa Fe
incoln. Socorrd
Taos
in
Moderate LOW
Bernalillo
Catron
Cibola
.
Curry
De Baca
Guadalup
Chavez
Mora
Colfax
Otero
GrantRoosevelt
San Miqvel
Torrance
Valenci?
Lea
_.
Sierra
Quay
union
Table 3"PreliminaW radon-availability rating for some the
largest cities in New Mexico (population from Vigil-Giron,
19871988).
City
Albuquerque
Santa Fe
Las Cruces
Roswell
Farmington
Hobbs
Clovis
Carlsbad
Alamogordo.
Gallup
Los AlamosWhite Rock
Las Veqas
Grants-Milan
Rio Rancho
Artesia
Lovington
silver City
Portales
Deming
County
Population
estimates
Classification
1984
Bernalfllo
Santa Fe
Dona Ana
Chaves
San Juan
Lea
Curry
Eddy
Otero
McKinley
Los Alamos
San Miguel
Cibola
Sandoval
Eddy
Lea
Grant
Roosevelt
Luna
350,575
52,274
50,275
45,702
37,332
35,029
33,424
28,433
27 I 485
20,959
moderate
high
high
high
low
moderate
moderate
high
low
hiqh
,
,
,
,
,
high
low
moderate
moderate
.1
ow
moderate
low
low
high
19 040
1 5 364
1 2 823
1.2 310
11,938
11 IO4
11,014
10,456
10,609
22
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27
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GP-979,
1:750,000.
scale
. .
28
TY
a
AVAILABILITY
LOW RADON
F I G U R E 2 : RADON A V A I L A B I L I T Y I N NEW MEXICO
.
NOTE: THE ACTUAL HEALTH RISKS ASSOCIATED WITH
EACH.AVAlLCATEGORY ARENOTKNOWNUNTIL
THEACTUALINDOOR
RADON SURVEYSARECOMPLETED.
FIGURE I
:
AREASEXCEEDING
5 p p m eU FROM NURE AERIALRADIOMETRICDATA