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Urban Land-Use Study Plan for the
National Water-quality Assessment Program
U.S. Geological Survey Open-File Report 96-217
By Paul J. Squillace and Curtis V. Price
This is:
http://pubs.water.usgs.gov/ofr96217
Table of Contents
This study plan is for Urban Land-Use
Studies initiated as part of the U.S. Geological
Survey's National Water-Quality Assessment
(NAWQA) Program. There are two Urban Land-
Use Study objectives: (1) Define the water qual
ity in recharge areas of shallow aquifers underly
ing areas of new residential and commercial land
use in large metropolitan areas, and (2) determine
which natural and human factors most strongly
affect the occurrence of contaminants in these
shallow aquifers.
To meet objective 1, each NAWQA Study
Unit will install and collect water samples from at
least 30 randomly located monitoring wells in a
metropolitan area. To meet objective 2, aquifer
characteristics and land-use information will be
documented. This includes particle-size analysis
of each major lithologic unit both in the unsatur
ated zone and in the aquifer near the water table.
The percentage of organic carbon also will be
determined for each lithologic unit. Geographic
information system coverages will be created that
document existing land use around the wells.
These data will aid NAWQA personnel in relating
natural and human factors to the occurrence of
contaminants. Water samples for age dating also
will be collected from all monitoring wells, but
the samples will be stored until the occurrence of
contaminants has been determined. Age-date
analysis will be done only on those samples that
have no detectable concentrations of anthropo
genic contaminants.
The National Water-Quality Assessment
(NAWQA) Program was implemented by the U.S.
Geological Survey in 1991 as a systematic assessment
of the quality of the Nation's water resources. The
program will describe the status and trends in the qual
ity of a large, representative part of the Nation's
surface-water and ground-water resources and will
define the primary natural and human factors affecting
the quality of these resources. In meeting these goals,
the NAWQA Program will produce information useful
for policymakers, managers, and the general public at
the National, State, and local levels. The building
blocks of the NAWQA Program are 60 Study-Unit
Investigations that include parts of most of the
Nation's major river basins and aquifers (fig. 1). The
proposed starting dates of the Study-Unit Investiga
tions are staggered between 1991 and 1997. Gilliom
and others (1995) discuss the overall design of the
NAWQA Program in more detail.
The NAWQA study design for ground water
focuses on assessing the water-quality conditions of
major aquifers in each Study Unit (Study-Unit
Surveys) with emphasis on the quality of recently
recharged ground water associated with natural factors
and human activities (Land-Use Studies). The general
objective of the Land-Use Studies is to examine natu
ral factors and human activities that affect the quality
of recently recharged (generally less than 10 years old)
shallow ground water that underlies key types of land
use within each Study Unit. Land-Use Studies under
lying urban and agricultural settings have been the
primary focus in the NAWQA Program to date.
This document provides work-element guidance
for Urban Land-Use Studies to ensure consistency
among the studies and applies to Study-Unit Investiga
tions begun in 1994 or to begin in 1997. Consistency
of data collection and study design is a goal of
NAWQA and allows for comparison among Study
Units in different climatic and hydrogeologic settings;
this is necessary to address questions of national
importance.
To provide a more comprehensive understand
ing of the water-quality issues within urban areas, it is
necessary for each Study Unit with large metropolitan
areas to include as many of the NAWQA's study
components as possible in those areas. For example,
Integrator and Indicator Surface-Water Sites, Flow
path Studies, Land-Use Studies, Sub-Unit Surveys,
and Synoptic Studies as defined in Gilliom and others
(1995), could all be located within urban areas. This
nested study design would greatly increase the under
standing of water quality in urban areas.
 Figure 1. (32K)
Study Units are encouraged to locate Urban
Land-Use Studies in areas where shallow ground
water is most vulnerable to contamination due to
anthropogenic and hydrogeologic factors. Anthropo
genic factors such as pesticide and nutrient use, toxic
chemical use and release, and population density may
contribute to the presence of contamination in shallow
ground water. Large metropolitan areas with underly
ing shallow unconfined bedrock or sand and gravel
aquifers are ideal for Urban Land-Use Studies.
Hydrogeologic factors such as the amount of precipi
tation and thickness and permeability of the
unsaturated zone also may affect the movement of
contaminants to the shallow ground water.
Study Units should locate their Urban Land-Use
Study in a single metropolitan area. By limiting each
Urban Land-Use Study to a single metropolitan area,
there is a better chance that there will be similar
climate, hydrogeology, and chemical use within the
study area. The effects of selected natural and anthro
pogenic factors on the water quality of these shallow
aquifers can then be investigated. Although metropol
itan areas can be very large and in some cases are adja
cent to other metropolitan areas, limiting the size of
the actual study area is also necessary so that it will be
easier to collect ancillary information and to create
geographic information system (GIS) coverages of the
study area.
Large metropolitan areas are being emphasized
because population density has been related to
contamination of shallow ground-water quality
(Eckhardt and Stackelberg, 1995). Furthermore,
89 percent of the urban population of the United States
lives in metropolitan areas of greater than 250,000
persons (U.S. Bureau of the Census, 1992). Areas
with air pollution problems--that is, metropolitan
areas classified by the U.S. Environmental Protection
Agency as ozone or carbon-monoxide nonattainment
areas--are preferred for study. Metropolitan areas
with shallow ground water and permeable unsaturated
zones are preferred for study. If the depth to water is
great, then recharge probably would be smaller, and
one would expect to see less contamination from land-
use activities. There will also be some Urban Land-
Use Studies initiated where the unsaturated zone is not
as permeable and the depth to water is variable
(table 1).
The results of the Urban Land-Use Studies will
be more directly relevant if the water in the shallow
aquifer investigated in metropolitan areas is used for
drinking. Therefore, it is preferred that the shallow
aquifer in the selected metropolitan areas be (1) used
as a source of drinking water, (2) considered a poten
tial source of drinking water, or (3) hydraulically
connected to surface water or deeper ground water
used as a source of drinking water. If the shallow
ground water does not meet the preceding criteria,
then it is preferred that the aquifer be similar to aqui
fers that are used as a water supply in other parts of the
Study Unit or region. For example, an Urban Land-
Use Study designed to look at natural and human
effects on an alluvial aquifer in one part of the country
may have transfer value to other similar areas of the
country even if the ground water is not used in that
particular metropolitan area.
Urban Land-Use Studies are to be distributed
across the United States. NAWQA plans are to
conduct Urban Land-Use Studies in three general
climatic settings and three general hydrogeologic
settings of the unsaturated zone (table 1). The climatic
settings are based on annual precipitation; the amount
of ground-water recharge is assumed to increase as
annual precipitation increases. The hydrogeologic
settings are based on the permeability and thickness of
the unsaturated zone; the amount of ground-water
recharge is assumed to increase as permeability
increases. Two studies (n=2) are anticipated to be
conducted in each of the six categories where the
unsaturated zone is permeable, and one study (n=1)
will be conducted in each of the three categories where
the unsaturated zone is less permeable (table 1).
Table 1. National design matrix to distribute Urban Land-Use Studies across
various climatic and hydrogeologic settings in the United States
[The aquifers can be bedrock or unconsolidated, although drilling cost
probably will necessitate that most Urban Land-Use Studies investigate
unconsolidated aquifers. n=minimum number of Urban Land-Use Studies;
<, less than; >, greater than; >=, greater than or equal to]
------------------------------------------------------------------------
Unsaturated-zone hydrogeologic
characteristics
Annual -------------------------------------------------------
precipitation Permeable1 Permeable1 Less permeable2
and and and variable
<8 meters >=8 meters thickness
thick thick
------------------------------------------------------------------------
>122 cm n=2 n=2 n=1
61-122 cm n=2 n=2 n=1
<61 cm n=2 n=2 n=1
------------------------------------------------------------------------
1Permeable is defined as sand and gravel with a continuous clay layer no greater than 1.5 meters thick; because these clay layers are near land surface, they are assumed to contain macropores due to fractures, roots, and so forth.
2Less permeable is defined as a continuous silt or clay layer >=1.5 meters thick.
Residential and commercial areas compose the
largest land use within metropolitan areas, and little is
known nationally about the associated effects of this
land use on water quality. Because of the predomi
nance of the residential and commercial land use, an
understanding of the shallow ground-water quality
beneath these areas is important for well-head protec
tion of municipal and private supply wells. Also, resi
dential areas are important because population density
has been directly correlated to contamination in shal
low ground water (Eckhardt and Stackelberg, 1995).
The targeted residential and commercial areas
should be "new" development constructed between
about 1970 and 1990. Large industrial areas and the
central downtown will be excluded from the NAWQA
Urban Land-Use Study. Industrial areas will not be
investigated by NAWQA because some data already
are being collected in these land-use areas by other
Federal and State agencies. The central downtown is
excluded for three reasons: (1) the ground water is
generally not used in that area, (2) urban land use in
that area is generally much older than 1970, and
(3) land use in that area is likely to have changed with
time. If the land use has changed, the cause of
contamination may be difficult to determine on the
basis of current land use. Furthermore, the only
national data base of land use is the land-use and land-
cover digital data from 1:250,000- and 1:100,000-
scale maps that were developed from aerial photo
graphs taken during the 1970's and mid-1980's (U.S.
Geological Survey, 1990). The data are stored in digi
tal format called the "Geographic Information
Retrieval and Analysis System" (GIRAS), which can
be converted to ARC/INFO format (polygon cover
age). Study Units may use a modified version of the
GIRAS coverage that delineates new growth areas
(Hitt, 1994); however, more detailed local information
may be available. The targeted residential and
commercial land-use areas should be at least 5 years
old because it takes some time for new development to
affect shallow ground-water quality.
A study designed to investigate new residential
and commercial areas is a forward-looking plan.
Older residential and commercial areas may have
ground-water contamination that resulted from prac
tices that have already been banned, and studies done
in these areas may be unable to distinguish between
old and new contamination problems. NAWQA study
results should be helpful to resource managers and
policymakers at Federal, State, and local levels in
making sound decisions. There are probably three
situations that most urban ground-water managers and
suppliers face: (1) the existing well field lies within an
established urban area, and they are considering
expanding the well field within the established urban
area; (2) the existing municipal well field lies at the
edge of the urban area, and new development is begin
ning to encroach on the recharge area; and (3) new
residential developments at the edge of the urban area
have their own wells and do not use the municipal
water supply. Studying the new residential and
commercial areas will provide the most valuable infor
mation to city planners and municipal water suppliers
in the last two situations, although some information
will be helpful to municipalities in the first situation
also. The information derived from Urban Land-Use
Studies of new areas will provide an understanding of
water-quality issues and insights on how to better plan
for new developments so as to minimize water-quality
degradation.
Recharge areas in the Urban Land-Use Study
areas are selected for study so that a relation between
land use and shallow ground-water quality can be
established. Furthermore, knowledge of the shallow
ground-water quality may provide an early warning of
contaminants that are reaching the water table before
the contaminant reaches the deeper ground water used
for water supplies.
What effect does new residential and commer
cial land use have on the shallow ground-water qual
ity? Does this effect vary throughout the United
States? What contaminants are commonly found in
ground-water beneath new residential and commercial
land-use areas?
The study area will be defined as the intersec
tion of two coverages: (1) the areal extent of the surfi
cial aquifer and (2) the areal extent of the new
residential and commercial land-use areas in the single
metropolitan area targeted for study. The first cover
age can be easily derived from the known geohydrol
ogy of the study area. The second coverage can be
created using land-use, land-cover, and transportation
data.
Residential and commercial land, golf courses,
parks, roadways, and business highways are consid
ered part of residential and commercial land use.
Agricultural land use should be avoided or minimized
in the Urban Land-Use Study area.
Industrial areas, the central downtown, and wide
transportation corridors such as railway yards and
limited-access highways, should be carefully excluded
from the study area. Sampled monitoring wells need
to be located at least 1 km (kilometer) from heavy
industry. Light industry that is mixed with commer
cial areas may be very difficult to avoid and is
allowed. Railways and limited-access highways
consisting of two or more lanes should be excluded
from the study area if they are not already excluded by
the land-use coding system. This can be determined
using U. S. Geological Survey digital line graph
(DLG) 1:100,000-scale transportation data, or more
detailed local information if available. In DLG data,
railways, primary roads, and secondary roads are
included in the coding system for transportation data
(U.S. Geological Survey, 1989). The DLG coding
system does not differentiate highways with adjoining
businesses from limited-access highways, so this
distinction should be done on the basis of local infor
mation.
After the study area is defined as the intersection
of the geohydrology and land-use coverages, a subarea
will be created for use in selecting drilling sites for
monitoring wells. The selection of a subarea is neces
sary to avoid well sites near the edge of the study area
that may be affected by features outside the study area.
The residential and commercial land use, as defined
previously, should make up more than 75 percent of
the land use within a 500m (meter) radius of the final
drilling sites. An ARC/INFO Arc Macro Language
(AML) program has been written for this purpose, and
is given in the "Appendix."
Land-use, land-cover, and aerial photography
data are available from many sources. Some useful
Federal, State, and local government data sets and
services include:
- U.S. Geological Survey 1:250,000-scale GIRAS data, updated using census population (U.S. Geological Survey, 1990; Hitt, 1994).
- Land cover based on satellite remote-sensing data.
- U.S. Geological Survey 1:100,000-scale DLG transportation data.
- Census Topographically Integrated Geographic Encoding and Referencing (TIGER) system data (similar to 1:100,000-scale DLG data).
- U.S. Geological Survey digital orthophoto quadrangles (DOQ's). DOQ's are aerial photographs registered to a map base. They are available in limited areas from the U.S. Geological Survey, State, or local agencies.
- U.S. Geological Survey provides an aerial photography search service at Earth Science Information Centers (Denver, Colorado; Menlo Park, California; Reston, Virginia). The archive includes references to aerial photography from many agencies outside the U.S. Geological Survey. Aerial photography is available also from the U.S. Department of Agriculture, National Resource Conservation Service, and from State and local agencies.
- Land-use, land-cover, and local-zoning maps from other sources.
The following six GIS processing steps are
suggested to delineate the targeted study area using
nationally available GIS data sets. If available, more
detailed local GIS information should be used in place
of the nationally available data sets.
- Obtain updated 1990 GIRAS land-use, land-use change coverage (see Hitt, 1994).
- Select new urban land-use areas (this is coded in the 1990 coverage as NEWLU=10). Local information should be checked at this point for accuracy, and changes or edits made, if needed.
- Select industrial land-use areas from the GIRAS coverage (LUCODE = 13 or 15) and buffer these areas by 1,000 m.
- Create a coverage of transportation areas (railways and nonbusiness, limited-access highways) from 1:100,000-scale DLG data.
- From coverage (step 2), remove industrial and transportation areas (steps 3 and 4).
- Intersect coverage (step 5) with a coverage representing the areal extent of the aquifer being studied.
- Run SHRINK.AML (Appendix) to first select a subarea in which 75 percent of a 500-m radius circular buffer is inside the study area and then remove areas that are within 250 m of the outside edge of the 75-percent area. The "75-percent" selection assures that monitoring wells are mostly affected by the target area, and the removal of edge areas allows any randomly selected site to be moved 250 m in any direction and preserve the 75-percent criterion.
Monitoring wells for the Urban Land-Use Study
need to be distributed randomly throughout the land-
use setting after the land-use areas have been delin
eated. It is important not to skew the locations of the
wells either toward or away from possible point
sources of contamination. Primary and alternate loca
tions should be randomly selected using a computer
program written by Scott (1990). This program will
be used with the well-selection subarea created from
the study area using the SHRINK.AML (see Appen
dix).
If a drill site cannot be located within 250 m of
the primary location, then it will be necessary to move
to an alternate random location. Once the primary or
alternate random locations have been identified on-site,
the actual drill site should be located as close to the
primary or alternate random locations as possible to
avoid biasing the site either toward or away from
known contamination; the drill site needs to be within
250 m of the random location.
Drilling sites for monitoring wells must not be
closer than 1 km from each other to avoid the overlap
of buffer areas around the wells. Overlapping buffer
areas may introduce spatial autocorrelation effects,
which can invalidate statistical analysis of the water-
quality data (Barringer and others, 1990). This mini
mum separation distance can be specified as input to
the random site-selection program (Scott, 1990). If
the delineated study area is too small to allow selec
tion of 30 wells using this separation distance, the
following approaches should be followed in this order:
(1) reevaluate the land-use and other data sets to see
if more accurate data sets may generate more area;
(2) alter SHRINK.AML to reduce the final 250-m
shrink or use the output area with no final shrink
applied (if this is done, the actual drill site can only be
moved toward the center of the study area from the
random location); (3) run the site-selection program
(Scott, 1990) with a smaller separation distance and
then, after a drill site has been selected during onsite
verification, iteratively disqualify random location
sites that fall within 1 km of the drill site; and (4) add
areas of slightly older development (but after 1960) to
the study area (this requires local information which
may be difficult to obtain).
Drill sites should be located in areas where shal
low ground water originates within the designated
land-use area. Therefore, drill sites can be located
immediately downgradient from the selected urban
land-use area.
Thirty wells is considered the minimum number
of monitoring wells; some Study Units may want to
install additional wells if their study area is very large.
However, large study areas may encompass several
cities with a variety of socioeconomic factors that may
affect ground-water quality. Therefore, adjacent cities
may look similar on a map, but there may be important
differences that affect the occurrence and distribution
of contaminants in the adjacent areas. Combining
these adjacent areas into a single Urban Land-Use
Study would make interpretation of the data very diffi
cult.
Permission to drill in residential areas may be
obtained by advertising in the local paper, contacting
individual landowners in person or by mail, or work
ing closely with city and county officials or home
owner associations. Local officials that are
represented on the NAWQA Study-Unit liaison
committee also may be helpful in obtaining permis
sion and may act as intermediaries between landown
ers and the U.S. Geological Survey. Although getting
permission may be easier, the study results will not be
as useful if all monitoring wells are located in a single
land-use setting. For example, do not locate all wells
along roads. Instead, mix well locations among
church lots, school yards, edge of roads, parks, golf
courses, boulevards, parking lots, private land, and so
forth. An advertisement could emphasize the objec
tives of the NAWQA study and the need for landown
ers who would be willing to have 5cm (centimeter)
wells installed on their property for a long-term study
of the ground-water quality. Flush-mounted monitor
ing wells, in some cases, can be used to minimize the
inconvenience to the landowner. Names and
addresses of landowners within 250 m of the random
location point, in some situations, can be obtained
from the city or county. Permission to install a moni
toring well could then be requested by direct mailing
to these landowners. The monitoring wells cannot be
used as drinking-water or irrigation supply wells by
the landowners. Permission to drill monitoring wells
also may be obtained from city and State governments
and the U.S. Department of Transportation.
Local or State governments may have regula
tions concerning the installation and sampling of
monitoring wells, and the NAWQA Study Units
should comply with these regulations. Furthermore,
the U.S. Geological Survey form SF 9-1483 should be
completed and signed by the landowner. This form
specifies the rights and responsibilities of the land
owner and the U.S. Geological Survey. Landowners
should be informed that the water-quality results will
be made available to the public, that their names will
not be published in U. S. Geological publications, and
that the water-quality results will be mailed to them.
Landowners also should be told that some States
require that the U.S. Geological Survey report any
analysis with a constituent concentration that exceeds
water-quality regulations.
Urban Land-Use Studies should be conducted
by drilling monitoring wells rather than using existing
wells. Drilling the monitoring wells provides the best
control for well construction, ensures that the wells
under U.S. Geological Survey ownership can be
sampled in the future for trends analysis, ensures a
random distribution of wells, and probably saves time
and money when compared to finding existing wells in
urban areas. Some NAWQA Study Units that started
in 1991 spent much time trying to locate existing wells
and to obtain permission to sample the well. In the
end, very few could be found and the selected wells
were not randomly located. Therefore, new Study
Units will almost always be required to drill their own
wells. By drilling wells for future Urban Land-Use
Studies, NAWQA can minimize the possibility that
monitoring well locations are biased toward known
point-source contamination, or that the construction
technique is inadequate.
In addition, in almost all cases, existing urban
wells are not constructed according to NAWQA protocols
and, therefore should not be sampled. Wells need
to be randomly located, screened near the top of the
water table, have flush-threaded polyvinyl-chloride
casings, and be sealed. Existing monitoring wells
drilled to define the upgradient conditions at a point-
source contamination site are not acceptable. Most
domestic drinking-water wells normally are screened
deeper in the aquifer and not at the top of the aquifer.
If existing wells are used, they must meet the criteria
outlined in table 2. Use of existing wells may be
allowed in the following situations: (1) If depth to
water is great and the aquifer is bedrock, domestic
wells may be sampled because drilling new wells
would be cost-prohibitive; and (2) if a network of
monitoring wells satisfies the requirements in table 2.
Each monitoring well installed for Urban Land-Use
Studies should have a short screened interval
(ideally less than 3 m in length). Generally, the top of
the screen should be 0.6 to 1.5 m below the lowest
anticipated position of the water table to reduce the
chances of the well being dry during parts of the year
and to avoid problems with interpreting data from
wells with partially saturated, open intervals.
The 5cm monitoring wells installed for Urban
Land-Use Studies should be drilled following the
guidelines outlined by Lapham and others (1995).
Wells should be installed using a hollow-stem auger in
unconsolidated material. Auger drilling is the most
suitable drilling technique because no drilling fluids
are introduced into the aquifer. Air-rotary drilling is
not advisable because air compressors use oils that
may be introduced into the aquifer. Mud-rotary drill
ing introduces mud into the aquifer.
Table 2. Well location and construction criteria for monitoring wells used in
UrbanLand-Use Studies
-------------------------------------------------------------------------------
Well location
(1) Wells are located in residential and commercial areas developed between
about 1970 and 1990.
(2) Monitoring-well locations are randomly distributed throughout the
occurrence of the land-use setting (combination of land-use and
hydrogeologic setting) of interest. Selected wells need to be located
within 250 m of the random location identified using a computer program
developed by Scott (1990). An existing network of randomly distributed
monitoring wells can be sampled.
(3) Only wells located in recharge areas, underlying or immediately
downgradient from the land use of interest are selected.
(4) Monitoring wells that were installed to detect a known or suspected
contaminant are not selected. Even wells directly upgradient of these
contaminant areas are not suitable for sampling.
Type of well
(1) Wells are observation, monitoring, or small-capacity water-supply wells
to avoid the complexities of determining contributing areas to large-
capacity wells (Lapham and others, 1995).
(2) Wells can be pumped at a rate that is adequate for sampling---typically,
on the order of at least 0.06 liters per second.
Well construction
(1) Wells have short open intervals, generally 3 meters or less in length.
The hydrogeologic unit represented by the water level being measured is
known; the hydrogeologic unit contributing water to the well is known.
The screened interval of the well is located beneath the top of the
water table.
(2) Well-casing material is polyvinyl chloride (PVC) or stainless steel,
and wells that are constructed of PVC have threaded, not glued, joints.
(3) Well screens are continuous-slot, wire-wound screens or machine-slotted
casing made of PVC or stainless steel.
(4) Well construction and annular seals are sufficient to prevent
infiltration of surface runoff from land surface.
(5) The integrity of well construction is assured using verification
checks where practical, such as depth-to-bottom measurements.
(6) The well construction and pumping equipment in the well are known to
be of a type that is not likely to affect the water-quality
constituents of concern. For existing wells with pumps, only those
with submersible pumps are selected. Wells with water-lubricated
pumps are selected; no wells are selected with oil-lubricated,
suction-lift, or gas-contact pumps.
(7) The sampling point is located before any water treatment, pressure
tanks, or holding tanks.
Well-log information
(1) A well log of the lithologic units is required.
(2) Particle-size analysis and organic carbon content of major
lithologic units is very desirable.
-------------------------------------------------------------------------------
Study Unit personnel will collect standard qual
ity-control and quality-assurance samples and stan
dard ground-water quality samples, however, it is
recommended that a total of six field-blank samples be
collected (20 percent of the 30 ground-water samples
collected in an Urban Land-Use Study). Previous
protocol required two to three samples (Koterba and
others, 1995), but recent Urban Land-Use Studies
have shown that this number of field blanks were inad
equate to verify the ground-water data. To better
quantify the type and potential magnitude of contami
nation bias, collect the six field-blank samples begin
ning with the 1st, then 6th, 12th, 18th, 24th, and 30th
ground-water sample. To better relate contamination
bias to possible site conditions, arrange the order of
sampling sites so that the field blanks are collected at
diverse site conditions.
Chemical analysis may include, but are not
limited to, major ions, nutrients, pesticides, volatile
organic chemicals (VOCs), and tritium which is
discussed under objective 2. Sampling procedures
have been described by Koterba and others (1995).
Once contaminants have been identified, defin
ing the source of contamination is of critical interest.
In past Urban Land-Use Studies, little has been done
to define the source of contamination. Therefore, more
detailed ancillary data will be collected for future
Urban Land-Use Studies to help define the source of
contamination.
Natural and human factors affect the occurrence
of contaminants in shallow aquifers. Natural factors,
such as the organic carbon content of the aquifer mate
rial, may limit the amount of contamination detected
in shallow ground water. Human factors, such as prox
imity to commercial areas and highways, may explain
the presence or absence of contaminants at a particular
location. Within the residential and commercial land-
use area, there are many potential sources of contami
nation, but there may be certain land-use activities that
are major contributors of contaminants to shallow
ground water. For example, ground-water contamina
tion in residential areas may be related to the use of
pesticides by homeowners or the release of VOC's by
certain industries; industrial areas may contribute
VOC's to other land-use areas via air emissions,
stormwater runoff, and ground-water flow.
It is also important to determine how climate
affects the shallow ground-water quality given the
same land use and similar aquifers. This knowledge
could help indicate if uniform Federal regulations for
ground-water quality monitoring are appropriate for
all parts of the United States or if such monitoring
might be better tailored to climatic regions. Further
more, the knowledge gained could help guide future
land development in certain areas of the United States
to protect the water quality of shallow aquifers that
contribute to drinking-water supplies.
What natural and human factors most effec
tively explain the presence or absence of contaminants
in shallow ground water? In which setting(s) (hydro
logic, geologic, climatic, land use, and so forth) are
contaminants most commonly detected? What is the
relation between natural factors and the quality of
shallow ground water underlying key types of urban
land use? Are contaminants less likely to be detected
in older waters? What are the possible human sources
of contamination in shallow urban ground water?
What are the relations between nutrient and pesticide
use, toxic chemical release, and the detection of
contaminants in shallow urban ground water? Are
point or nonpoint sources of contamination the great
est threat to water quality in urban areas?
Aquifer characteristics, such as percentage of
organic carbon, type of aquifer, particle size, and soil
pH, should be documented for each monitoring well.
When drilling the wells, all drill cuttings will be
logged, and split-spoon samples will be collected from
all major lithologic units and the screened interval for
analysis of grain size, organic carbon content, and soil
pH. It is expected that about three split-spoon samples
per well location will be collected.
The guidance was modified on 3/19/03 to require a sample from the
top six inches of soil. Please refer to
this addendum
Dry-sieve analyses is recommended and can be
obtained from the U.S. Geological Survey in Iowa
City, Iowa, for $45.00 (1996 cost); although any labo
ratory that uses standard U.S. Geological Survey
procedures (Guy, 1969) can be used. About 200 to
300 g (grams) of sediment should be collected. Litho
logic-unit samples can be stored in a freezer while a
subsample is sent in for analysis of percentage of
organic carbon (Powell and others, 1989).
Analysis of organic carbon, to a reporting level
of 0.01 percent, can be obtained by requesting sched
ule 2503 from the U.S. Geological Survey National
Water Quality Laboratory in Arvada, Colorado.
However, the results will be meaningful only if the
sample has not been contaminated by drilling fluids.
The laboratory needs 10 g of sample for analysis
collected in a wide-mouth, 500mL (milliliter), amber,
baked-glass jar. The sample should be chilled or
frozen until analysis. These data are important
because the fraction of organic carbon controls the
sorption of organic chemicals and because the data for
the deep part of the unsaturated zone and for the aqui
fer are not available from other data bases. It is not
necessary to sample the uppermost soil horizon at the
well site because information on organic carbon
content can be obtained from the U.S. Department of
Agriculture's Natural Resource Conservation Service
county survey reports. To obtain the organic carbon
content of the soil, first locate the monitoring-well site
on the appropriate Natural Resource Conservation
Service map and determine the soil type. The percent
age of organic carbon of the soil (given as a range) can
be found with the soil description in the same report.
Soil pH is obtained by mixing 5 g of soil with
5 mL of distilled water for 10 minutes and measuring
the pH with a pH meter. This measurement is impor
tant because the degradation of methyltert-butyl ether
(commonly detected in shallow ground-water in urban
areas) and ethyl tert-butyl ether occurs only in soil
with small organic matter content and with a pH of
about 5.5 (Yeh and Novak, 1994). It is strongly
suggested that borehole-geophysical logging (such as
gamma and electromagnetic logging) be performed on
all monitoring wells. This information will improve
understanding of the geology at the well site.
Other information, such as depth to the water
table, depth of screen below land surface, estimated
annual recharge, and presence of confining units also
need to be documented for each well. If available, a
water-table map showing equal water-level contours
should be provided in an ARC/INFO coverage for a
500m radius around the well, similar to land-use
information discussed in a later section of this report.
A polygon coverage showing surficial geology, soil
map, and bedrock geology should also be obtained.
Water samples for age dating, based on concen
trations of tritium, should be collected from all moni
toring wells, but the samples should be stored until the
concentrations of contaminants have been determined.
Age-date analysis should be done using U.S. Geologi
cal Survey lab code 624 (at a 1996 cost of about $210
per sample) for samples which have no contamination.
This analysis will define the age of the water relative
to 1953--that is, pre or post 1953. Tritium analyses
will verify that the water is recently recharged water
and not old water where one would not expect to find
contamination. There are other methods of age dating,
such as using concentrations of tritium/helium and
Freon®, that have been recommended by Lapham and
others (1995). These other methods have the potential
to actually date the age of the water to a specific year.
The best method of age dating for each Land-Use
Study should be discussed between Study Unit person
nel, National Synthesis Teams, and the National Lead
ership Team.
According to the U.S. Geological Survey's
National Water Quality Laboratory (NWQL) Techni
cal Memorandum 95.11, all tritium samples (lab code
624) are to be sent directly to the U.S. Geological
Survey, Water Resources Division, Attn: Bob Michel,
MS 434, 345 Middlefield Road, Menlo Park, Califor
nia 94025. Analytical Services Request (ASR) forms
are to be sent with the samples. After logging in the
samples in Menlo Park, copies of the ASR forms will
be sent to the NWQL. Bottles should be completely
filled so that no air is in the bottle and the screw caps
secured with tape. Requests for bottles for tritium
analysis or more information can be made by email
(tritium@usgs.gov).
NOTE: Also see
NWQL technical memo 97.04
Land-use information covering the Urban Land-
Use Study area will be documented by creating ARC/
INFO coverages from a variety of sources. Because
the monitoring wells will not be spread across large
areas, a single coverage should be applicable for all
urban wells. At a broad scale, coverages such as land
use are available from U.S. Geological Survey's
National Mapping Division and can be developed
from satellite data. For a smaller area, coverages such
as locations of gas stations can be compiled at a scale
of 1:24,000. Locations can be determined onsite using
global positioning systems and aerial photography.
The following coverages should be created:
- Point coverage showing possible contaminant-release areas---for example, gas stations, dry cleaners, underground storage tanks, chemical plants, aboveground storage facilities.
- Point coverage showing locations of known contaminant-release areas---for example, leaking underground storage tanks, Toxic Release Inventory sites identified by the U.S. Environmental Protection Agency, waste-disposal ponds, landfills, oil wells, injection wells.
- Line coverages of pipelines, roadways, hypsography, sewers, septic fields, hydrography (perennial and ephemeral streams, rivers, creeks, lined and unlined drainage ditches, ground-water drains, lined and unlined irrigation canals, natural and manmade lakes, lined and unlined reservoirs, bays or estuaries, springs, dry or wet playas).
- Polygon coverages showing golf courses, lakes, airports, military bases, mines, and population density.
- Polygon coverage showing industrial, commercial, residential, and highway land-use areas around each monitoring well.
- Barringer, Thomas, Dunn, Dennis, Battaglin, W.A., and
Vowinkel, E.F., 1990, Problems and methods involved
in relating land use to ground-water quality: Water
Resources Bulletin, v. 26, no. 1, p. 1-9.
- Eckhardt, D.A.V., and Stackelberg, P.E., 1995, Relation of
ground-water quality to land use on Long Island, New
York: Ground Water, v. 33, no. 6, p. 1019-1033.
- Gilliom, R.J., Alley, W.M., and Gurtz, M.E., 1995, Design
of the National Water-Quality Assessment Program--
Occurrence and distribution of water-quality condi
tions: U. S. Geological Survey Circular 1112, 33 p.
- Guy, H.P., 1969, Laboratory theory and methods for sedi
ment analysis: U.S. Geological Survey Techniques of
Water-Resources Investigations, book 5, chap. C1,
58 p.
- Hitt, K.J., 1994, Refining 1970's land-use data with 1990
population data to indicate new residential develop
ment: U.S. Geological Survey Water-Resources
Investigations Report 94-4250, 15 p.
- Koterba, M.T., Wilde, F.D., and Lapham, W.W., 1995,
Ground-water data-collection protocols and proce
dures for the National Water-Quality Assessment
Program--Collection and documentation of water-
quality samples and data: U.S. Geological Survey
Open-File Report 95-399, 113 p.
- Lapham, W.W., Wilde, F.D., and Koterba, M.T., 1995,
Ground-water data-collection protocols and proce
dures for the National Water-Quality Assessment
Program--Selection, installation, and documentation of
wells, and collection of related data: U.S. Geological
Survey Open-File Report 95398, 69 p.
- Powell, R.M., Bledsoe, B.E., Curtis, G.P., and Johnson,
R.L., 1989, Interlaboratory methods comparison for
the total organic carbon analysis of aquifer materials:
Environmental Science and Technology, v. 23, no. 10,
p. 1246-1249.
- Scott, J.C., 1990, Computerized stratified random site-
selection approaches for design of ground-water-
quality sampling network: U.S. Geological Survey
Water-Resources Investigations Report 90-4101,
109 p.
- U.S. Bureau of the Census, 1992, Statistical abstract of the
United States (112th ed.): Washington, D.C., 979 p.
- U.S. Geological Survey, 1989, Digital line graphs from
1:100,000-scale maps, Data user guide 2: Reston, Va.,
U.S. Geological Survey, 88 p.
- -----1990, Land use and land cover digital data from
1:250,000-and 1:100,000-scale maps, Data user guide
4: Reston, Va., U.S. Geological Survey, 25 p.
- Yeh, C.K., and Novak, J.T., 1994, Anaerobic biodegradation
of gasoline oxygenates in soils: Water Environment
Research, v. 66, no. 5, p. 744-752.
Go to APPENDIX
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Figure 1.