Water-Resources Investigations Report 99–4246

EFFECTS OF LAND USE AND HYDROGEOLOGY ON THE

WATER QUALITY OF ALLUVIAL AQUIFERS IN

EASTERN IOWA AND SOUTHERN MINNESOTA, 1997 
U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 99–4246

Effects of Land Use and Hydrogeology on the

Water Quality of Alluvial Aquifers in Eastern

Iowa and Southern Minnesota, 1997

By Mark E. Savoca, Eric M. Sadorf, S. Mike Linhart, and Kymm K.B. Akers

Iowa City, Iowa

2000
U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

The use of firm, trade, and brand names in this report is for identification purposes only and does

not constitute endorsement by the U.S. Geological Survey.

For additional information write to: Copies of this report can be purchased

U.S. Geological Survey

Information Services

Box 25286

Federal Center

Denver, CO 80225

from:

District Chief

U.S. Geological Survey

P.O. Box 1230

Iowa City, Iowa 52244
CONTENTS III

CONTENTS

Abstract.................................................................................................................................................................................. 1

Introduction............................................................................................................................................................................ 2

Purpose and Scope....................................................................................................................................................... 2

Description of Study Area ........................................................................................................................................... 5

Acknowledgments ....................................................................................................................................................... 5

Study Design and Methods.................................................................................................................................................... 5

Site Selection ............................................................................................................................................................... 5

Well Installation........................................................................................................................................................... 5

Land-Use Classification............................................................................................................................................... 7

Sample Collection........................................................................................................................................................ 7

Water-Quality Analysis................................................................................................................................................ 8

Statistical Analysis....................................................................................................................................................... 11

Effects of Land Use and Hydrogeology on Water Quality .................................................................................................... 12

Common Ions............................................................................................................................................................... 13

Nutrients ...................................................................................................................................................................... 13

Radiochemicals............................................................................................................................................................ 16

Pesticides and Metabolites........................................................................................................................................... 19

Volatile Organic Compounds....................................................................................................................................... 23

Summary and Conclusions .................................................................................................................................................... 25

References.............................................................................................................................................................................. 26

Appendix................................................................................................................................................................................ 31

FIGURES

1–3. Maps showing:

1. Location and extent of Eastern Iowa Basins study unit................................................................................... 3

2. Distribution of alluvial deposits and location of sampling sites...................................................................... 4

3. Land use and land cover in the study unit ....................................................................................................... 6

4–6. Boxplots showing:

4. Relation between land use and well depth, depth to water, and depth to top of sample interval.................... 12

5. Relation between land use and tritium concentration ..................................................................................... 13

6. Relation between land use and cumulative clay thickness.............................................................................. 13

7. Piper diagram showing major-ion composition of ground water from alluvial aquifers in the study unit.............. 14

8–13. Boxplots showing:

8. Relation between land use and dissolved-solids, sodium, and chloride concentrations ................................. 15

9. Relation between land use and ammonia, nitrate, and dissolved-oxygen concentrations............................... 16

10. Relation between dissolved-oxygen concentration and ammonia and nitrate concentrations in

samples from (A) agricultural areas, and (B) urban areas............................................................................... 17

11. Relation between nitrate concentration and well depth, depth below water table to top of sample

interval, and cumulative clay thickness above the sample interval in samples from (A) agricultural

areas, and (B) urban areas ............................................................................................................................... 17

12. Relation between land use and organic carbon and dissolved organic carbon concentrations ....................... 18

13. Relation between nitrate concentration and organic carbon and dissolved organic carbon

concentrations in samples from (A) agricultural, and (B) urban areas ........................................................... 18

14–16. Graphs showing:

14. Relation between radon-222 concentration and cumulative clay thickness above the sample interval .......... 19

15. Frequency of detection of pesticides in samples from agricultural and urban areas....................................... 20

16. Frequency of detection of pesticide metabolites in samples from agricultural and urban areas..................... 21

17. Boxplot showing relation between land use and total pesticide (parent compounds) and total metabolite

concentrations.......................................................................................................................................................... 22
IV CONTENTS

18–21. Graphs showing:

18. Relation between atrazine, deethylatrazine, and deisopropylatrazine concentrations and well depth

in samples from agricultural areas .................................................................................................................. 22

19. Relation between atrazine, deethylatrazine, and deisopropylatrazine concentrations and depth

below water table to top of sample interval in samples from agricultural areas ............................................. 23

20. Relation between atrazine concentration and cumulative clay thickness above the sample interval

in samples from urban areas............................................................................................................................ 23

21. Frequency of detection of volatile organic compounds in samples from urban areas .................................... 24

TABLES

1. Statistical summary of percent land use within 1,640 feet of agricultural and urban land-use

monitoring wells...................................................................................................................................................... 8

2. Laboratory analytical methods................................................................................................................................ 9

3. Constituents detected in equipment and field blanks .............................................................................................. 10

4. Constituents with relative percent differences greater than 10 percent in replicate samples.................................. 11

CONVERSION FACTORS, VERTICAL DATUM, AND ABBREVIATED WATER-QUALITY UNITS

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F = (1.8 × °C) + 32

Sea level: In this report, “sea level” refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929)—a geodetic datum derived

from a general adjustment of the first-order level nets of both the United States and Canada, formerly called Sea Level Datum of 1929.

Abbreviated water-quality units: Chemical concentrations are given in metric units of milligrams per liter (mg/L) and micrograms per

liter (μg/L). Milligrams per liter and micrograms per liter are units expressing the concentration of chemical constituents in solution as

mass (milligrams or micrograms) of solute per unit volume (liter) of water. For concentrations less than 7,000 mg/L, the numerical value of

milligrams per liter is the same as for concentrations in parts per million. The numerical value of micrograms per liter is the same as for

concentrations in parts per billion.

Multiply By To obtain

feet (ft) 0.3048 meter (m)

square mile (mi2) 2.59 square kilometer (km2)

pound (lb) 0.4536 kilogram (kg)

kilogram (kg) 0.001 milligram (mg)

milligram (mg) 0.001 microgram (μg)

gallon (gal) 3.785 liter (L)
Abstract 1

Effects of Land Use and Hydrogeology on the Water

Quality of Alluvial Aquifers in Eastern Iowa and

Southern Minnesota, 1997

By Mark E. Savoca, Eric M. Sadorf, S. Mike Linhart, and Kymm K.B. Akers

Abstract

Ground-water samples were collected from

monitoring wells at 31 agricultural and 30 urban

sites in the Eastern Iowa Basins study unit during

June–August 1997 to evaluate the effects of

land use and hydrogeology on the water quality

of alluvial aquifers. Ground-water samples were

analyzed for common ions, nutrients, dissolved

organic carbon, tritium, radon-222, pesticides

and pesticide metabolites, volatile organic

compounds, and environmental isotopes.

Calcium, magnesium, and bicarbonate were

the dominant ions in most samples and were

likely derived from solution of carbonate minerals

(calcite and dolomite) present in alluvial detrital

deposits. Chloride and nitrate were dominant

anions in samples from several wells. Sodium and

chloride concentrations were significantly higher

in samples from urban areas, where roads are

more numerous and road salts may be more

frequently applied, than in agricultural areas.

Nitrate was detected in 94 percent of samples

from agricultural areas and 77 percent of samples

from urban areas. Nitrate concentrations were

significantly higher in agricultural areas than in

urban areas and exceeded the U.S. Environmental

Protection Agency maximum contaminant level

for drinking water (10 milligrams per liter as N)

in 39 percent of samples from agricultural areas.

Nitrate concentrations in samples from urban

areas did not exceed the maximum contaminant

level. Greater use of fertilizers in agricultural

areas most likely contributes to higher nitrate

concentrations in samples from those areas.

Tritium-based ages indicate ground water

was most likely recharged after the 1950’s at all

but one sampling site. Agricultural and urban

land-use areas have remained relatively stable

in the study area since the 1950’s; therefore, the

effects of current land use should be reflected

in ground water sampled during this study.

Radon-222 was detected in all samples and

exceeded the U.S. Environmental Protection

Agency’s previously proposed maximum contaminant level for drinking water (300 picocuries per

liter) in 71 percent of samples.

Pesticides were detected in 84 percent of

samples from agricultural areas and 70 percent

from urban areas. Atrazine and metolachlor were

the most frequently detected pesticides in samples

from agricultural areas; atrazine and prometon

were the most frequently detected pesticides in

samples from urban areas. None of the pesticide

concentrations exceeded U.S. Environmental

Protection Agency maximum contaminant levels

or lifetime health advisories for drinking water.

Pesticide metabolites were detected in 94 percent

of samples from agricultural areas and 53 percent

from urban areas. Metolachlor ethane sulfonic

acid and deethylatrazine were the most frequently

detected metabolites in samples from agricultural

areas; metolachlor ethane sulfonic acid and

alachlor ethane sulfonic acid were the most

frequently detected metabolites in samples from

urban areas.

Total metabolite concentrations were significantly higher in samples from agricultural areas

than in samples from urban areas. Total pesticide

concentrations (parent compounds) tended to be
2 Effects of Land Use and Hydrogeology on the Water Quality of Alluvial Aquifers in Eastern Iowa and Southern Minnesota, 1997

higher in samples from agricultural areas; however,

this difference was not statistically significant.

Metabolites constituted the major portion of the

total residue concentration in the alluvial aquifer.

Volatile organic compounds were detected

in 40 percent of samples from urban areas and

10 percent from agricultural areas. Methyl tertbutyl ether was the most commonly detected

volatile organic compound and was present in

23 percent of samples from urban areas. Elevated

concentrations (greater than 30 micrograms

per liter) of methyl tert-butyl ether and BTEX

compounds (benzene, toluene, ethylbenzene, and

xylene) in two samples from urban areas suggest

the possible presence of point-source gasoline

leaks or spills.

Factors other than land use may contribute

to observed differences in water quality between

and within agricultural and urban areas. Nitrate,

atrazine, deethylatrazine, and deisopropylatrazine

concentrations were significantly higher in

shallow wells with sample intervals nearer the

water table and in wells with thinner cumulative

clay thickness above the sample intervals. These

relations suggest that longer flow paths allow

for greater residence time and increase opportunities for sorption, degradation, and dispersion,

which may contribute to decreases in nutrient

and pesticide concentrations with depth. Nitrogen

speciation was influenced by redox conditions.

Nitrate concentrations were significantly

higher in ground water with dissolved-oxygen

concentrations in excess of 0.5 milligram per

liter. Ammonia concentrations were higher in

ground water with dissolved-oxygen concentrations of 0.5 milligram per liter or less; however,

this relation was not statistically significant.

The amount of available organic matter may

limit denitrification rates. Elevated nitrate concentrations (greater than 2.0 mg/L) were significantly

related to lower dissolved organic carbon concentrations in water samples from both agricultural

and urban areas. A similar relation between

nitrate concentrations (in water) and organic

carbon concentrations (in aquifer material)

also was observed but was not statistically

significant.

INTRODUCTION

The goal of the U.S. Geological Survey (USGS)

National Water-Quality Assessment (NAWQA)

Program is to assess the status and trends in the quality

of the Nation’s surface and ground water and to better

understand the natural and human factors affecting

water quality (Hirsch and others, 1988). The Eastern

Iowa Basins study unit encompasses an area of about

19,500 mi2 in eastern Iowa and southern Minnesota

(fig. 1) and is one of 59 study units in the NAWQA

Program.

Land-use studies are an important component of

the NAWQA Program and are designed to assess the

concentration and distribution of water-quality constituents in recently recharged ground water associated

with the most significant land use and hydrogeologic

settings within a study unit. Land-use studies provide

information to better understand the natural and

human factors in each setting that affect ground-water

quality (Gilliom and others, 1995). The focus of the

land-use study in the Eastern Iowa Basins study unit is

agricultural and urban land uses and alluvial aquifers.

Agriculture is the dominant land use in the study unit.

Urban areas, although not extensive, represent important potential source areas of contaminants associated

with residential, commercial, and industrial activities.

Alluvial aquifers are present throughout much of the

study unit and constitute a major ground-water supply

that is susceptible to contamination from land-use

activities.

Purpose and Scope

This report presents the results of a study

to evaluate the effects of land use and hydrogeology

on the water quality of alluvial aquifers in the Eastern

Iowa Basins study unit. Shallow ground-water monitoring wells were completed in alluvial aquifers at

31 agricultural and 30 urban sites (fig. 2). Groundwater samples were collected from these wells

during June–August 1997 and analyzed to

determine the concentrations of common ions,

nutrients, dissolved organic carbon (DOC), tritium,

radon-222, pesticides and pesticide metabolites,

volatile organic compounds (VOCs), and environmental isotopes. Field measurements of temperature,

specific conductance, pH, dissolved oxygen, alkalinity, and turbidity also were obtained. Samples of
INTRODUCTION 3

Study area

Index

Map

Mississippi River

0 20 40 60 MILES

0 20 40 60 KILOMETERS

Base from U.S. Geological Survey, 1:250,000, 1967

Albers Equal-Area Conic Projection

Standard parallels 41°30' and 44°30', Central meridian-92°

Figure 1. Location and extent of Eastern Iowa Basins study unit.
4 Effects of Land Use and Hydrogeology on the Water Quality of Alluvial Aquifers in Eastern Iowa and Southern Minnesota, 1997

0 20 40 60 MILES

0 20 40 60 KILOMETERS

Base from U.S. Geological Survey, 1:250,000, 1967

Albers Equal-Area Conic Projection

Standard parallels 41°30' and 44°30', Central meridian-92°

Figure 2. Distribution of alluvial deposits and location of sampling sites.
STUDY DESIGN AND METHODS 5

alluvial material obtained during well drilling were

analyzed for particle size and organic carbon content.

Land use in the vicinity of each well was characterized

and quantified. The relations between shallow groundwater quality and land use and hydrogeology are

discussed.

Description of Study Area

The study unit includes the Wapsipinicon,

Cedar, Iowa, and Skunk River Basins (fig. 1), all of

which are tributary to the Mississippi River. Surficial

alluvial deposits are restricted to Holocene-age river

valleys (fig. 2) and commonly consist of 30 to 100 ft

of unconsolidated sands and gravels interbedded with

less permeable silts and clays (Steinhilber and Horick,

1970; Wahl and others, 1978; Hoyer and Hallberg,

1991; Olcott, 1992). Depth to the water table in these

alluvial aquifers typically is 5 to 20 ft. Recharge to

alluvial aquifers is primarily from precipitation that

infiltrates through overlying unsaturated surficial

materials. Water also enters the aquifers along losing

stream reaches. Ground water in alluvial aquifers

discharges to gaining stream reaches, providing base

flow (Anderson, 1983; Olcott, 1992). Underlying or

laterally adjacent bedrock aquifers may either receive

or contribute ground water to alluvial aquifers (Olcott,

1992).

Surficial alluvial aquifers and Quaternaryage buried-channel and glacial-outwash deposits

supply about 44 percent of the ground water used

in the study unit (E.E. Fisher and A.D. Arntson,

U.S. Geological Survey, written commun., 1998).

The presence of permeable sands and gravels,

shallow depths to the water table, and the absence

of overlying confining units make alluvial aquifers

in the study unit susceptible to contamination

from land-use activities (Hoyer and Hallberg,

1991).

Agriculture is the dominant land use and

is present across 92.8 percent of the study unit

(fig. 3). Forest land occurs across 4.5 percent of

the study area, urban 2.0 percent, water 0.3 percent,

wetland 0.2 percent, and barren 0.2 percent. Agriculture and urban land use are present across 84 and

2.6 percent (respectively) of alluvial deposits in the

study unit.

Acknowledgments

The authors thank the private landowners

and city and county governments in the Eastern Iowa

Basins study unit that allowed the USGS to install and

sample monitoring wells on private and public property. Ron Kuzniar’s (USGS) guidance and participation during well installation is greatly appreciated.

Former USGS employee Jennifer Tobias and current

USGS employees Ron Kuzniar and Joel Galloway

collected much of the data presented in this report.

STUDY DESIGN AND METHODS

This study was designed to evaluate the effects

of agricultural and urban land use and hydrogeology

on the water quality of alluvial aquifers in the Eastern

Iowa Basins study unit. Ground-water samples were

collected from shallow monitoring wells installed by

the USGS at randomly selected sites within the landuse and hydrogeologic settings of interest.

Site Selection

Potential well locations in the study unit were

identified using a stratified random selection process

(Scott, 1990) and geographic information system

land-use coverages. Field reconnaissance within a

1-mi radius of each potential location was conducted

to determine if a suitable well site could be found.

Site-selection criteria were: the presence of selected

land use and hydrogeologic setting; no known

point source of contamination in vicinity of site; the

site was accessible to a drill rig; and permission to

drill and sample the well could be obtained from the

landowner or city/county government. If a suitable site

could not be found at a primary location, a search was

initiated at the closest alternative location.

Well Installation

Ground-water monitoring wells were completed

in alluvial aquifers at 31 agricultural and 30 urban

land-use sites using procedures described by Lapham

and others (1995). Boreholes were drilled using

4.25-inch inside-diameter continuous-flight hollowstem augers. The augers were left in place during well

construction to prevent borehole collapse. Wells were

constructed of 2-inch outside-diameter flush-threaded
6 Effects of Land Use and Hydrogeology on the Water Quality of Alluvial Aquifers in Eastern Iowa and Southern Minnesota, 1997

0 20 40 60 MILES

0 20 40 60 KILOMETERS

Land use and land cover

Agriculture

Developed

Forest

Water

Wetlands

Base from U.S. Geological Survey, 1:250,000, 1967

Albers Equal-Area Conic Projection

Standard parallels 41°30' and 44°30', Central meridian-92°

Data from EROS Data Center, 1994

Figure 3. Land use and land cover in the study unit.
STUDY DESIGN AND METHODS 7

polyvinyl-chloride (PVC) pipe and 5 ft of 0.02-inch

slotted PVC screen at the base of each well. Well

depths ranged from 10 to 37.5 ft below land surface.

The depth below the water table to the top of the well

screens ranged from 0 to 16 ft. Alluvial material was

allowed to fill the annular space around the screen

during removal of the augers to form a natural filter

pack extending about 2 ft above the top of the screen.

An artificial sand-filter pack was emplaced around the

screen in wells having fine-grained material adjacent

to the screened interval. A bentonite annular seal was

placed above the filter pack, and the remainder of the

borehole was backfilled with native material to within

a few feet of land surface. A lockable, protective steel

casing set in a cement pad was installed at land surface

to protect the well casing and prevent infiltration of

surface water down the borehole. Wells were developed after completion (mechanical surge and pump),

and the augers and associated drilling equipment were

cleaned between well sites.

Samples of alluvial material obtained during

well drilling were analyzed for particle size and

organic carbon content. A thickness-weighted average

organic carbon content was computed for each well,

and cumulative clay thickness above the water-sample

interval was estimated from drillers’ logs. Lithologies

classified as clay, for this analysis, include clay, silty

clay, and clayey silt.

Land-Use Classification

A comparison between land use and groundwater quality requires knowledge of land use within

the recharge area of the monitoring well. Information

on the rate and direction of ground-water flow can be

used to determine the size and shape of the recharge

area. However, this information was not readily available for the well sites used in this study. Several

studies have observed significant correlations between

ground-water quality in surficial aquifers and land use

within circular areas of probable recharge around

wells (Eckhardt and others, 1989; Barringer and

others, 1990; Ferrari and Ator, 1995; Ator and Ferrari,

1997; Kolpin, 1997).

Land use was classified within a 1,640-ft-radius

buffer around each well in the study unit using procedures described by Koterba (1998), which included

field observations and the use of high-resolution

aerial photography. The delineation of specific land

uses (for example, row crop, residential, commercial)

within agricultural and urban well buffers permits a

comparison between the occurrence of specific land

uses and ground-water quality. The land-use classification system used in this study is based on the work of

Anderson and others (1976).

Row crops (corn and soybeans) were the dominant land use around wells in agricultural areas and

had a median value of 90 percent of the buffer area.

Residential areas were the dominant land use around

wells in urban settings and had a median value of

44 percent of the buffer area. Urban areas in the study

unit typically are small and usually are surrounded by

agricultural cropland. Urban well buffers commonly

contained a greater variety of land uses than wells in

agricultural settings. A statistical summary of land use

is given in table 1.

Sample Collection

Ground-water samples were collected from

61 wells in agricultural or urban settings during

June–August of 1997. Sample collection followed

NAWQA protocols (Koterba and others, 1995). Prior

to sample collection, wells were purged of at least

three well-casing volumes using a submersible pump.

Pumping continued until field measurements of water

temperature, pH, specific conductance, and dissolved

oxygen stabilized, at which time, water samples were

collected for the analysis of common ions, nutrients,

DOC, tritium, radon-222, pesticides and pesticide

metabolites, VOCs, and environmental isotopes. Static

and pumping water levels also were recorded for each

well.

Nutrient, alkalinity, and selected common ion

samples were filtered using 0.45-micron pore-size

cellulose-fiber cartridge filters. Pesticide samples were

filtered using 0.7-micron pore-size baked glass-fiber

filters. DOC samples were filtered using 0.45-micron

pore-size silver membrane filters. VOC, tritium,

radon-222, and environmental-isotope samples were

not filtered. VOC and selected common ion samples

were acidified prior to shipping. Samples were chilled

and shipped by overnight delivery to USGS analytical

laboratories. All sampling and filtering equipment was

cleaned after each use (Koterba and others, 1995).

The analytical results for ground-water

samples collected during this study are presented

in Akers and others (2000). A statistical summary

of selected ground-water-quality data is given in

the appendix of this report.
8 Effects of Land Use and Hydrogeology on the Water Quality of Alluvial Aquifers in Eastern Iowa and Southern Minnesota, 1997

Water-Quality Analysis

Most samples collected for this study were

analyzed at the USGS National Water Quality

Laboratory (NWQL) in Arvada, Colorado. Selected

pesticides and pesticide metabolites were analyzed

at the USGS Organic Geochemistry Research

Laboratory (OGRL) in Lawrence, Kansas. NWQL

pesticide data and OGRL pesticide metabolite data

are used in this report. Tritium samples were analyzed

at the USGS Isotope Tracers Project Laboratory in

Menlo Park, California. Environmental-isotope

samples were analyzed at the National Research

Program Laboratory in Reston, Virginia. The analytical methods used in this study are summarized in

table 2.

Analyte detections were evaluated in the context

of minimum reporting levels (MRLs) and method

detection limits (MDLs) established by NWQL. The

MRL is the minimum concentration of an analyte that

can be reliably measured and reported by the laboratory using a given analytical method. MRLs are

commonly reported with analytical results for major

ions, nutrients, radiochemicals, and VOCs. The MDL

is the minimum concentration of a substance that can

be identified, measured, and reported with 99 percent

confidence that the analyte concentration is greater

than zero. MDLs are generally lower and more well

defined statistically than MRLs and are commonly

reported with analytical results for pesticides and

pesticide metabolites (Zaugg and others, 1995). MRLs

and MDLs provide information about relative analytical precision and detection sensitivity but do not

constitute low concentration reporting limits for

conclusively identified analytes (Zaugg and others,

1995). Concentration values below the lowest calibration standard are reported as estimated by NWQL.

Estimated values indicate analyte detection; however,

the reported concentration value is questionable.

Lowest calibration standards generally are higher than

MRLs and MDLs. Water-quality constituents and

associated MRLs and MDLs are listed in the appendix

of this report.

The U.S. Environmental Protection Agency

(USEPA) has established drinking-water regulations

for some of the constituents analyzed for this study

(U.S. Environmental Protection Agency, 1996). The

USEPA regulations include Maximum Contaminant

Levels (MCL), which are health-based, maximum

Table 1. Statistical summary of percent land use within 1,640 feet of agricultural and urban land-use monitoring wells

[All values in percent. Row crop, corn and soybeans; Ag infrastructure, farm residence, buildings, and related development; Livestock, cattle, pigs, and

horses; Residential, single- and multi-family housing, and mobile homes; Commercial, stores, shopping centers, and malls; Municipal facility, schools,

hospitals, and cemeteries; Right-of-way, highways, airports, railroads, and utilities, with associated grounds and structures; Industrial, manufacturing and

development; Vacant, abandoned and barren commercial and residential property; Waste management, landfills, recycling centers, and sewage-treatment

facilities]

Land use Agricultural areas Urban areas

Minimum Median Maximum Minimum Median Maximum

Row crop 20 90 100 0.0 2 49

Ag infrastructure 0.0 2 25 0.0 0.0 12

Fallow and grass 0.0 0.0 55 0.0 0.0 9

Livestock 0.0 0.0 16 0.0 0.0 15

Residential 0.0 0.0 4 1.0 44 93

Commercial 0.0 0.0 0.0 0.0 14 62

Municipal facility 0.0 0.0 1 0.0 0.1 20

Right-of-way 0.0 0.0 0.0 0.0 0.0 55

Park 0.0 0.0 0.0 0.0 0.0 45

Industrial 0.0 0.0 0.0 0.0 0.0 43

Vacant 0.0 0.0 0.0 0.0 0.0 4

Waste management 0.0 0.0 0.0 0.0 0.0 10

Water and wetland 0.0 0.0 14 0.0 0.0 22

Forest 0.0 0.0 23 0.0 0.0 32
STUDY DESIGN AND METHODS 9

permissible levels of contaminants that are enforceable

for public water-supply systems; Secondary Maximum

Contaminant Levels (SMCL), which are nonenforceable and relate to constituents that can affect the

esthetic quality of drinking water; and lifetime health

advisories (HAL), which define the maximum concentration of a chemical in drinking water that is not

expected to cause any adverse noncarcinogenic effects

over a lifetime of exposure and include a margin of

safety. USEPA regulations are used in this report as

guidelines to evaluate water quality.

Quality-control samples were collected during

the study to evaluate the potential effects of field and

laboratory methods on analytical results. Qualitycontrol samples consisted of equipment blanks, field

blanks, replicates (sequential samples), and laboratory

surrogate and field spike recoveries. One equipment

blank was analyzed for pesticides and two equipment

blanks were analyzed for VOCs. Three field blanks

were analyzed for common ions, nutrients, and pesticides and pesticide metabolites; four field blanks for

VOCs; and two field blanks for DOC. Three replicate

samples were analyzed for common ions, nutrients,

DOC, pesticides and pesticide metabolites, VOCs,

tritium, radon-222, and environmental isotopes. Laboratory surrogate recoveries were performed on

selected VOCs and pesticides for all ground-water

samples. One field-spiked sample was analyzed for

pesticides and VOCs. The results of quality-control

sampling are presented in Akers and others (2000).

Equipment blanks showed that for most pesticides and VOCs, sampling equipment did not introduce contaminants into the ground-water samples.

However, toluene and carbon disulfide were present

in equipment blanks at concentrations greater than

the MRL (table 3).

Field blanks showed that for most constituents,

sampling and laboratory procedures did not introduce

contaminants into the ground-water samples.

However, several constituents were detected in blank

samples at concentrations greater than the corresponding MRL (table 3). Calcium, magnesium, silica,

sulfate, and manganese were detected in field blanks

at substantially lower concentrations than those

measured in ground-water samples. Fluoride, bromide,

ammonia, and DOC were detected in field blanks at

concentrations similar to those measured in some

ground-water samples. As a result, concentrations of

fluoride, bromide, ammonia, and DOC that approach

field-blank concentration values should be used with

caution due to uncertainties concerning the extent to

which contamination may affect ground-water sample

results. Field-blank concentrations of VOCs listed in

table 3 were higher than some of the concentrations

Table 2. Laboratory analytical methods

[UV, ultraviolet; NWQL, National Water Quality Laboratory; OGRL, Organic Geochemistry Research Laboratory; GC/MS, gas chromatography/mass

spectrometry; HPLC, high-performance liquid chromatography]

Analytes Analysis method Reference

Major ions and nutrients Various methods Fishman and Friedman (1989)

Dissolved organic carbon UV-promoted persulfate oxidation and infrared spectrometry Brenton and Arnett (1993)

Organic carbon Induction furnace and modified Van Slyke Wershaw and others (1987)

Pesticides (NWQL

schedule 2010)

Extraction on C-18 cartridge and analyzed by GC/MS Zaugg and others (1995)

Pesticides (NWQL

schedule 2050)

Extraction on Carbopak-B cartridge and analyzed by HPLC Werner and others (1996)

Pesticides and metabolites

(OGRL)

Extraction on C-18 cartridge and analyzed by GC/MS and

Extraction on Carbopak-B cartridge and analyzed by HPLC

Zimmerman and Thurman (1999)

Ferrer and others (1997)

Volatile organic compounds Purge and trap GC/MS Rose and Schroeder (1995)

Tritium Electrolitic enrichment and liquid scintillation Ostlund and Dorsey (1977)

Radon-222 Liquid scintillation American Society for Testing

and Materials (1996)

Deuterium/hydrogen ratio Hydrogen equilibrium Coplen and others (1991)

Oxygen-18/oxygen-16 ratio Carbon dioxide equilibrium Epstein and Mayeda (1953)
10 Effects of Land Use and Hydrogeology on the Water Quality of Alluvial Aquifers in Eastern Iowa and Southern Minnesota, 1997

measured in ground-water samples. The analysis of

VOC results in this report is limited to ground-water

sample concentrations that are greater than field-blank

VOC concentrations. The presence of several major

ions, nutrients, and VOCs in field blanks may be the

result of their presence in the blank water used during

this study.

Replicate samples showed an acceptable

level of precision in field and laboratory procedures

for most constituents. However, several constituents

had relative percent differences (RPDs) of more than

10 percent between concentrations in environmental

and replicate samples (table 4). For many constituents

(bromide, ammonia, nitrite, phosphorus, orthophosphorus, butylate, bentazon, and toluene), small

concentration differences resulted in large RPDs

because environmental and replicate sample concentrations also were small. The cause of large RPDs for

iron, nitrite plus nitrate, DOC, and carbon disulfide is

not known. Changes in ground-water quality during

environmental and replicate sample collection can

affect replicate precision.

Laboratory surrogate and field-spike recoveries

were used to determine the precision and accuracy of

analyte recovery in the sample matrix and to evaluate

the effectiveness of the analytical methods for selected

analytes. Acceptable recoveries typically range from

80 to 120 percent for pesticides and 70 to 130 percent

for VOCs. Laboratory surrogate recoveries for

selected pesticides (HCH alpha and BDMC) ranged

from 67 to 129 percent; recoveries for selected VOCs

(ethane, toluene, and benzene) ranged from 88 to

133 percent. These results indicate that matrix effects

were minor and the analytical methods were effective.

Laboratory surrogate recoveries for diazinon ranged

from 56 to 152 and indicate possible matrix effects

or analytical method inefficiency. Field-spike

recoveries, given in the appendix of this report, for

NWQL schedule 2010 pesticides ranged from 36 to

Table 3. Constituents detected in equipment and field blanks

[MRL, minimum reporting level; mg/L, milligrams per liter; μg/L, micrograms per liter]

Constituent Blanks/detections

MRL

(mg/L, except

as indicated)

Range of concentrations

equal to or exceeding MRL

(mg/L, except as indicated)

Equipment blanks

Toluene (μg/L) 2/2 0.038 0.070–0.080

Carbon disulfide (μg/L) 2/2 0.080 0.50–1.45

Field blanks

Calcium 3/3 0.02 0.093–0.152

Magnesium 3/2 0.01 0.012–0.014

Silica 3/3 0.01 0.032–0.058

Sulfate 3/1 0.10 0.113

Fluoride 3/1 0.10 0.111

Manganese 3/1 1.0 1.166

Bromide 3/1 0.01 0.017

Ammonia, as N 3/1 0.015 0.02

DOC 2/2 0.10 0.70–3.80

Toluene (μg/L) 4/3 0.038 0.04–0.809

Benzene (μg/L) 4/2 0.032 0.05–0.09

Ethylbenzene (μg/L) 4/1 0.030 0.05

Tetrachloroethene (μg/L) 4/1 0.038 0.07

Carbon disulfide (μg/L) 4/1 0.080 0.07

1,2,4-Trimethylbenzene (μg/L) 4/1 0.056 0.07

Acetone (μg/L) 4/3 4.90 5.0–10.0

m- and p-Xylene (μg/L) 4/1 0.064 0.10

Bromodichloromethane (μg/L) 4/1 0.048 0.07

Chloroform (μg/L) 4/1 0.052 0.344
STUDY DESIGN AND METHODS 11

128 percent, and recoveries for schedule 2050 pesticides ranged from 0 to 133 percent. Field-spike recoveries for pesticides (schedules 2010 and 2050) that

were detected in ground-water samples ranged from

66 to 128 percent. Field-spike recoveries for selected

VOCs ranged from 48 to 99 percent and included 9

of 38 VOCs detected in ground-water samples.

Statistical Analysis

Water-quality data were graphically represented

using boxplots to show the 10th, 25th, 50th (median),

75th, and 90th percentiles, and concentration values

outside the 10th and 90th percentiles. Boxplots also

were used to illustrate differences between groups of

data—for example, nitrate concentrations in samples

from agricultural and urban areas.

Frequency-of-detection plots were used to show

the percentage of samples with detectable concentrations of analytes. An inverse relation between MDLs

and the frequency of pesticide and metabolite detections has been documented (Kolpin and others, 1998a;

Barbash and Resek, 1996), and it has been suggested

that analyte data might be adjusted to a common

detection limit to compensate for this effect. The

selection of common detection limits for pesticides

and metabolites detected in this study, 0.01 and

0.2 μg/L, respectively, resulted in the loss of several

previously detected analytes but did not alter the

ranking of most frequently detected analytes. Therefore, unadjusted data were used in frequency-ofdetection plots in this report.

Wilcoxon rank sum and Kruskal-Wallis

nonparametric statistical tests (Ott, 1993, p. 279, 792)

were used to evaluate the statistical significance of

differences between groups of data. Values were

generated by the tests to describe the probability that

observed differences between groups occurred by

chance. A probability (p) value of 0.05 indicates a

95-percent confidence that observed differences are

not the result of chance occurrence. Differences

between groups with probability values of 0.05 or less

were considered significant. Spearman’s rank order

correlation nonparametric statistical test (Ott, 1993,

p. 465) was used to measure the monotonic relation

(rho) between two continuous variables—for example,

atrazine concentration and well depth. The magnitude

of rho (−1 ≤ rho ≤ 1) determines the strength of the

relation.

Due to the small number of detections, statistical comparisons of most pesticides, pesticide metabolites, and VOC’s with land use and other potential

factors affecting water quality were not performed.

However, statistical comparisons were performed

using summed (total) concentrations per sample—for

example, the relation between total pesticide concentration per sample and land use.

Table 4. Constituents with relative percent differences greater than 10 percent in replicate samples

[RPD, relative percent difference; mg/L, milligrams per liter; μg/L, micrograms per liter; >, greater than]

Constituent Replicates/

RPDs>10 percent

Average concentration

(environmental plus

duplicate sample)

(mg/L, except as indicated)

Concentration difference

(mg/L, except as indicated)

RPD

(percent)

Iron (μg/L) 3/2 28.5 and

62.0

10.0 and

49.1

16 and

172

Bromide 3/1 0.038 0.004 11

Ammonia, as N 3/1 0.016 0.002 13

Nitrite, as N 3/1 0.012 0.002 17

Nitrite plus nitrate, as N 3/1 0.808 1.50 186

Phosphorus, as P 3/1 0.019 0.017 90

Orthophosphorus, as P 3/1 0.0255 0.005 20

DOC 3/1 2.20 0.40 18

Bentazon (μg/L) 3/1 0.055 0.01 18

Butylate (μg/L) 3/1 0.00225 0.0003 13

Carbon disulfide (μg/L) 3/1 0.1325 0.145 109

Toluene (μg/L) 3/1 0.099 0.042 42
12 Effects of Land Use and Hydrogeology on the Water Quality of Alluvial Aquifers in Eastern Iowa and Southern Minnesota, 1997

EFFECTS OF LAND USE AND

HYDROGEOLOGY ON WATER

QUALITY

Ground-water quality can be affected by human

activities and natural (physical, chemical, and microbial) processes. Anthropogenic activities may affect

ground-water quality if associated chemicals and

nutrients infiltrate the subsurface, and the occurrence

of specific suites of contaminants may relate to

specific land-use types (Eckhardt and others, 1989;

Burkart and Kolpin, 1993; Squillace and others, 1995;

Kolpin, 1997). Predominant ions commonly reflect the

mineral composition of geologic materials contacted

by the ground water. The presence of clay and other

materials of low hydraulic conductivity may provide

aquifers with some protection from the infiltration of

some contaminants, and the presence of fine-grained

materials with large specific grain-surface areas facilitate sorption. Geochemical environments can influence constituent speciation, and microbially mediated

processes have the potential to alter or degrade a

variety of constituents.

Differences in selected hydrogeologic factors,

common to agricultural and urban land-use sampling

sites, were evaluated to better understand the significance of land use on water quality. Well depth and

depth to water were significantly greater (p<0.001) at

urban sampling sites than at agricultural sites (fig. 4)

and may contribute to observed differences in water

quality between the land-use settings. Depth below the

water table to the top of the sampling interval, tritium

concentration (and tritium-based ground-water age),

and cumulative clay thickness above the sampling

interval were not significantly different (p=0.829,

0.530, and 0.981, respectively) between agricultural

0

40

5

10

15

20

25

30

35

DEPTH, IN FEET BELOW LAND SURFACE

EXPLANATION

10th percentile

25th percentile

50th percentile (median)

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

 (31) Number of observations

WELL DEPTH

10th percentile

25th percentile

50th percentile (median)

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

DEPTH TO WATER

10th percentile

25th percentile

50th percentile (median)

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

DEPTH BELOW WATER LEVEL TO

TOP OF SAMPLE INTERVAL

AGRICULTURE URBAN

LAND USE

(31) (30)

Figure 4. Relation between land use and well depth, depth to water, and depth to top of sample

interval.
EFFECTS OF LAND USE AND HYDROGEOLOGY ON WATER QUALITY 13

and urban sites (figs. 4, 5, and 6) and most likely do

not contribute to observed differences in water quality

between the land-use settings. It was assumed that

cumulative clay thickness at the well location was

representative of cumulative clay thickness upgradient

from the well in the recharge area.

Limestone and dolomite are common bedrock

lithologies throughout the study unit (Hershey, 1969)

and are likely sources of erosional material incorporated in alluvial deposits. Large concentrations of

calcium, magnesium, and bicarbonate ions in groundwater samples from the alluvial aquifer probably are

the result of solution of carbonate minerals (calcite

and dolomite) present in the alluvial deposits. Clay

weathering and cation exchange also could contribute

significant concentrations of calcium, magnesium, and

bicarbonate to ground water as precipitation percolates

through the unsaturated zone. The USEPA SMCLs

were exceeded in 46 percent of samples for manganese (50 μg/L), 23 percent for dissolved solids

(500 mg/L), 16 percent for iron (300 μg/L), and

2 percent for chloride (250 mg/L) and sulfate

(250 mg/L).

Nutrients

Sources of nutrients to ground water include

precipitation, the decay of organic matter, and microbial fixation. Anthropogenic sources of nutrients such

as chemical fertilizers, septic tank effluent, and

manure from feedlots may increase nutrient concentrations in ground water. Nitrate concentrations greater

than 2 to 3 mg/L are generally attributed to anthropogenic sources (Madison and Brunett, 1985; Hallberg,

1989; Mueller and others, 1995). The physical properties of soil and aquifer materials can affect the rate of

(31) (30)

0

150

50

100

TRITIUM CONCENTRATION, IN PICOCURIES PER LITER

EXPLANATION

10th percentile

25th percentile

50th percentile (median)

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

(31) Number of observations

TRITIUM

AGRICULTURE URBAN

LAND USE

Figure 5. Relation between land use and tritium

concentration.

Common Ions

Ground water from alluvial aquifers in the

study area was commonly of a calcium bicarbonate

type (fig. 7). Chloride and nitrate were the predominant anions in samples from several wells. Magnesium

commonly accounted for 20 to 40 percent of the total

cations; sodium accounted for less than 30 percent.

Road salts are used throughout the study unit during

winter, especially in urban areas where roads are more

numerous and road salts may be more frequently

applied than in agricultural areas. Dissolved-solids,

sodium, and chloride concentrations were significantly

higher (p<0.001) in samples from urban areas than

from agricultural areas (fig. 8). Sodium concentrations

in samples from urban sites were positively correlated

(p=0.046, rho=0.37) with percentage of land use classified as commercial (retail stores and services), where

road density and maintenance are high; chloride

concentrations were negatively correlated (p=0.01,

rho=−0.46) with percentage of land use classified as

row crops (corn and soybeans).

(31) (30)

0

20

5

10

15

CUMULATIVE CLAY THICKNESS, IN FEET

EXPLANATION

10th percentile

25th percentile

50th percentile (median)

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

(31) Number of observations

CUMULATIVE CLAY THICKNESS

AGRICULTURE URBAN

LAND USE

Figure 6. Relation between land use and cumulative clay

thickness.
14 Effects of Land Use and Hydrogeology on the Water Quality of Alluvial Aquifers in Eastern Iowa and Southern Minnesota, 1997

downward movement of water and nitrate. The presence of fine-grained materials of low hydraulic

conductivity, such as clays, can reduce ground-water

infiltration rates and limit the amount of nitrate at

depth (Mueller and others, 1995; Hinkle, 1997;

Tesoriero and Voss, 1997).

Nitrite plus nitrate was detected in 94 percent

of samples from agricultural areas and 77 percent of

samples from urban areas. Nitrite concentrations were

at or below the MRL (0.01 mg/L as N) in 92 percent of

samples and were detected at a maximum concentration

of 0.99 mg/L; therefore, nitrite plus nitrate will be

referred to as nitrate in this report. Nitrate exceeded the

USEPA MCL for drinking water (10 mg/L as N)

in 39 percent of samples from agricultural areas. Other

studies of shallow aquifers in the Midwest (Buchmiller

and Squillace, 1988; Hallberg, 1989; Kross and others,

1990; Blevins and others, 1996; Schapp and Linhart,

1998) indicate nitrate exceeds its MCL in 10 to

40 percent of samples. Nitrate did not exceed the

MCL in samples from urban areas. Ammonia was

detected in 36 percent of samples from agricultural

areas and 70 percent of samples from urban areas.

Orthophosphate was the most commonly

detected nutrient and was present in 94 percent of

samples from agricultural areas and 87 percent of

samples from urban areas. Phosphorus was present

in 71 percent of samples from agricultural areas and

60 percent of samples from urban areas. Orthophosphate and phosphorus are readily sorbed to sediments

and are not very mobile (Hem, 1985; Kolpin and

others, 1994), resulting in detection concentrations

at or near the MRL (0.01 mg/L).

Nitrate concentrations were affected by a

combination of factors, including land use, dissolvedoxygen concentrations, and hydrogeology. Nitrate

concentrations were significantly higher (p=0.008) in

agricultural areas than in urban areas, and ammonia

concentrations were significantly higher (p=0.008) in

urban areas than in agricultural areas (fig. 9). Greater

Figure 7. Major-ion composition of ground water from alluvial aquifers in the study unit.
EFFECTS OF LAND USE AND HYDROGEOLOGY ON WATER QUALITY 15

use of fertilizers in agricultural areas most likely

contributes to higher nitrate concentrations in those

areas. Dissolved-oxygen concentrations tended to be

higher in agricultural areas (fig. 9), and although this

difference was not statistically significant (p=0.058), it

may explain the higher ammonia concentrations associated with more reducing conditions in the urban

areas. Nitrogen speciation within agricultural and

urban areas was influenced by redox conditions

(fig. 10). Nitrate concentrations were significantly

higher in ground water with dissolved-oxygen concentrations greater than 0.5 mg/L in both agricultural

and urban areas (p=0.039 and 0.042, respectively).

Ammonia concentrations were higher in ground water

with dissolved-oxygen concentrations of 0.5 mg/L or

less; however, this relation was not statistically significant in either agricultural or urban areas (p=0.094 and

0.089, respectively).

Elevated nitrate concentrations (greater than

2.0 mg/L) in samples from agricultural areas (fig. 11)

were significantly related to wells with sample intervals nearer the water table (p=0.001) and wells with

thinner cumulative clay thickness above sampling

intervals (p=0.010). The relation between elevated

nitrate concentrations, well depth, and depth to water

was not significant (p=0.149 and 0.205, respectively).

Elevated nitrate concentrations (greater than

2.0 mg/L) in samples from urban areas (fig. 11) were

significantly related to shallower wells (p=0.022) and

wells with sample intervals nearer the water table

(p=0.023). The relation between elevated nitrate

concentrations, cumulative clay thickness above

sample intervals, and depth to water was not significant (p=0.281 and 0.494, respectively). Significantly

greater (p<0.001) well depths at urban sampling sites

may contribute to observed differences in nitrate

concentrations with land use.

The observed differences in nitrate concentrations in urban and agricultural areas also were likely

affected by differing organic carbon content in soils

and ground water. Organic carbon (aquifer material)

and dissolved organic carbon concentrations (groundwater sample) were significantly higher (p=0.021 and

0.008, respectively) in urban areas than in agricultural

0.7

1,000

1

2

3

4

5

7

10

20

30

40

50

70

100

200

300

400

500

700

CONCENTRATION, IN MILLIGRAMS PER LITER

EXPLANATION

10th percentile

25th percentile

50th percentile (median)

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

 (31) Number of observations

DISSOLVED SOLIDS

10th percentile

25th percentile

50th percentile (median)

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

CHLORIDE

10th percentile

25th percentile

50th percentile (median)

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

SODIUM

AGRICULTURE URBAN

LAND USE

(31) (30)

Figure 8. Relation between land use and dissolved-solids, sodium, and chloride concentrations.
16 Effects of Land Use and Hydrogeology on the Water Quality of Alluvial Aquifers in Eastern Iowa and Southern Minnesota, 1997

areas (fig. 12). Microbial denitrification requires

the presence of reduced electron-donating substrates

(organic matter) and terminal electron acceptors

(nitrogen oxides) (Chapelle, 1993; Hallberg and

Keeney, 1993). The amount of available organic

matter may limit denitrification rates (Starr and

Gillham, 1993). Elevated nitrate concentrations

(greater than 2.0 mg/L) were significantly related

to lower dissolved organic carbon concentrations

in water samples from both agricultural and urban

areas (p=0.031 and 0.014, respectively; fig. 13).

A similar relation between nitrate concentrations

(in water) and organic carbon concentrations (in

aquifer material) also was observed but was not statistically significant in either agricultural or urban areas

(p=0.063 and 0.756, respectively). These results

suggest that, in addition to lower nitrogen inputs,

lower nitrate concentrations from urban areas may

be due in part to the greater availability of organic

material at urban sampling sites, resulting in higher

denitrification rates and the conversion of greater

amounts of nitrate to more reduced nitrogen species

than at agricultural sites. The potential for higher

denitrification rates at urban sampling sites is

supported by the presence of lower dissolvedoxygen concentrations and higher ammonia concentrations (fig. 10), indicating reducing conditions at

these sites. Higher ammonia concentrations also

may reflect the partial microbial reduction of nitrate

to ammonia, which is common for many bacteria

(Chapelle, 1993).

Radiochemicals

Tritium concentrations found in the alluvial

aquifers indicate that shallow ground water in the

aquifers has been recharged in the last 30 years.

Tritium was present at concentrations above the

1.0-pCi/L MRL in 98 percent of samples. Tritium

is a radioactive isotope of hydrogen with a half-life

of about 12.3 years (Hem, 1985). Small amounts

(31) (30)

0.01

40

0.02

0.05

0.1

0.2

0.5

1

2

5

10

20

CONCENTRATION, IN MILLIGRAMS PER LITER

EXPLANATION

Detection limit

10th percentile

25th percentile

50th percentile (median)

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

 (31) Number of observations

AMMONIA

10th percentile

25th percentile

50th percentile (median)

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

DISSOLVED OXYGEN

10th percentile

25th percentile

50th percentile (median)

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

NITRATE

AGRICULTURE URBAN

LAND USE

Figure 9. Relation between land use and ammonia, nitrate, and dissolved-oxygen concentrations.
EFFECTS OF LAND USE AND HYDROGEOLOGY ON WATER QUALITY 17

0

40

5

10

15

20

25

30

35

DEPTH OR THICKNESS, IN FEET

EXPLANATION

10th percentile

25th percentile

50th percentile (median)

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

(10) Number of observations

WELL DEPTH

10th percentile

25th percentile

50th percentile (median)

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

DEPTH BELOW WATER TABLE T0

TOP OF SAMPLE INTERVAL

10th percentile

25th percentile

50th percentile (median)

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

CUMULATIVE CLAY THICKNESS

ABOVE THE SAMPLE INTERVAL

(10) (21)

<=2.0 >2.0

NITRATE CONCENTRATION,

IN MILLIGRAMS PER LITER

<=2.0 >2.0

NITRATE CONCENTRATION,

IN MILLIGRAMS PER LITER

AGRICULTURE LAND USE URBAN LAND USE

(15) (15)

A B

Figure 11. Relation between nitrate concentration and well depth, depth below water table to top of sample interval,

and cumulative clay thickness above the sample interval in samples from (A) agricultural areas, and (B) urban areas.

0.01

40

0.02

0.05

0.1

0.2

0.5

1

2

5

10

20

CONCENTRATION, IN MILLIGRAMS PER LITER

EXPLANATION

Detection limit

10th percentile

25th percentile

50th percentile (median)

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

 (8) Number of observations

AMMONIA

10th percentile

25th percentile

50th percentile (median)

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

NITRATE

<=0.5 >0.5

DISSOLVED OXYGEN CONCENTRATION,

IN MILLIGRAMS PER LITER

AGRICULTURE LAND USE

DISSOLVED OXYGEN CONCENTRATION,

IN MILLIGRAMS PER LITER

URBAN LAND USE

(8) (22)

A

<=0.5 >0.5

(13) (16)

B

Figure 10. Relation between dissolved-oxygen concentration and ammonia and nitrate concentrations in samples

from (A) agricultural areas, and (B) urban areas.
18 Effects of Land Use and Hydrogeology on the Water Quality of Alluvial Aquifers in Eastern Iowa and Southern Minnesota, 1997

of tritium are produced naturally in the upper

atmosphere and introduced into ground water through

precipitation recharge. Elevated amounts of tritium

began entering the atmosphere in the 1950’s as a result

of above-ground nuclear testing. Plummer and others

(1993) estimate that ground water derived from

precipitation prior to above-ground testing would

have a maximum decayed tritium concentration in

the 1990’s of 0.6 to 2.6 pCi/L. Based on this criterion,

98 percent of samples represent ground water that

most likely was recharged after the 1950’s; 2 percent

of samples represent ground water that most likely

was recharged prior to the 1950’s. The comparison

between land use and ground-water quality requires

that land use at the time of precipitation recharge

was similar to the current land use characterized at the

well site. Agricultural and urban areas have remained

relatively stable in the study unit for many decades

(U.S. Geological Survey, 1990; Hitt, 1994). The presence of ground water that most likely recharged after

the 1950’s at all but one sampling site increases the

0.1

100

0.2

0.5

1

2

5

10

20

50

ORGANIC CARBON CONCENTRATION, IN GRAMS PER KILOGRAM

DISSOLVED ORGANIC CARBON CONCENTRATION, IN MILLIGRAMS PER LITER

EXPLANATION

10th percentile

25th percentile

50th percentile (median)

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

 (31) Number of observations

ORGANIC CARBON

10th percentile

25th percentile

50th percentile (median)

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

DISSOLVED ORGANIC

 CARBON

AGRICULTURE URBAN

LAND USE

(31) (30)

Figure 12. Relation between land use and organic carbon

and dissolved organic carbon concentrations.

0.3

100

0.4

0.5

0.7

1

2

3

4

5

7

10

20

30

40

50

70

ORGANIC CARBON CONCENTRATION, IN GRAMS PER KILOGRAM

DISSOLVED ORGANIC CARBON CONCENTRATION, IN MILLIGRAMS PER LITER

EXPLANATION

10th percentile

25th percentile

50th percentile (median)

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

 (10) Number of observations 

ORGANIC CARBON

10th percentile

25th percentile

50th percentile (median)

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

DISSOLVED ORGANIC CARBON

<=2.0 >2.0

NITRATE CONCENTRATION,

IN MILLIGRAMS PER LITER

AGRICULTURE LAND USE

(10) (21)

NITRATE CONCENTRATION,

IN MILLIGRAMS PER LITER

URBAN LAND USE

(15) (15)

<=2.0 >2.0

A B

Figure 13. Relation between nitrate concentration and organic carbon and dissolved organic carbon concentrations in

samples from (A) agricultural, and (B) urban areas.
EFFECTS OF LAND USE AND HYDROGEOLOGY ON WATER QUALITY 19

likelihood that the effects of current land use are

reflected in ground water sampled during this study.

As noted earlier, tritium concentrations (and tritiumbased ground-water ages) were not significantly

different (p=0.530) between agricultural and urban

samples (fig. 5).

Radon-222 is a naturally occurring gas

produced by the decay of uranium and is radioactive

(half-life of 3.8 days) and water soluble (Hem, 1985).

Radon-222 was present at concentrations above the

MRL (24 pCi/L) in all samples. Concentrations

exceeded the USEPA previously proposed drinkingwater MCL (300 pCi/L) in 71 percent of samples.

Currently, there is no USEPA regulation for radon-222

in drinking water. Radon-222 concentrations were not

significantly different (p=0.589) between agricultural

and urban samples. Schumann (1993) suggests that

clays derived from uranium-bearing glacial deposits

might be a source of radon-222 in the Upper Midwest.

However, the relation between radon-222 concentrations and cumulative clay thickness above the sample

interval from agricultural and urban areas (fig. 14)

was not statistically significant.

Environmental-isotope analyses were not

interpreted in this report. A statistical summary

of environmental-isotope analyses is given in the

appendix of this report.

Pesticides and Metabolites

Synthetic organic pesticides are widely used in

agricultural and nonagricultural areas (Rao and Alley,

1993; Barbash and Resek, 1996) to control unwanted

vegetation and insects. Widespread use has led to the

detection of pesticides and their metabolites in shallow

ground-water aquifers throughout the United States

(Barbash and Resek, 1996; Kolpin and others, 1998a).

Following application, pesticides may be leached

directly to ground water or enter the atmosphere

through volatilization or attached to dust particles. The

subsequent transport and redeposition of airborne pesticides can significantly affect water quality far from

application sites (Majewski and Capel, 1995; Goolsby

and others, 1997; Majewski and others, 1998).

Pesticides were detected in 84 percent of

samples from agricultural areas and 70 percent from

urban areas. A total of 10 pesticides were detected in

samples from agricultural areas (fig. 15); 13 pesticides

were detected in urban areas. Atrazine and metolachlor were the most commonly detected pesticides

in samples from agricultural areas; atrazine and

prometon were the most commonly detected pesticides in samples from urban areas. None of the pesticide concentrations exceeded USEPA drinking-water

MCLs or HALs. Pesticides have generally not

exceeded MCLs or HALs in other studies of shallow

aquifers in the midwest (Kolpin and others, 1998b;

Schapp and Linhart, 1998).

Some pesticides may be degraded in the subsurface by biotic and abiotic processes that result

in the removal of functional groups and occasional

cleavage of the pesticide’s recalcitrant central ring

structure (Dhileepan and Schnoor, 1992; McMahon

and others, 1992; Chapelle, 1993; Aga and others,

1996; Alvey and Crowley, 1996; Field and Thurman,

1996; Kalkhoff and others, 1998). Microbial degradation may result in the complete mineralization of pesticides to carbon dioxide, water, and other simple

products (Rao and Alley, 1993; Alvey and Crowley,

1995). Research suggests that microbial activity and

pesticide degradation rates decrease with increasing

depth in response to decreasing organic carbon and

dissolved-oxygen concentrations, lower temperatures,

and smaller microbial populations that may lack the

metabolic diversity necessary for pesticide degradation (Lavy and others, 1973; Pothuluri and others,

1990; Dhileepan and Schnoor, 1992; McMahon and

others, 1992; Johnson and Lavy, 1994).

0 20 5 10 15

CUMULATIVE CLAY THICKNESS, IN FEET

0

1,600

200

400

600

800

1,000

1,200

1,400

RADON-222 CONCENTRATION, IN PICOCURIES PER LITER

Figure 14. Relation between radon-222 concentration

and cumulative clay thickness above the sample interval.
20 Effects of Land Use and Hydrogeology on the Water Quality of Alluvial Aquifers in Eastern Iowa and Southern Minnesota, 1997

Pesticide metabolites were detected in

94 percent of samples from agricultural areas and

53 percent of samples from urban areas. All 10 of

the pesticide metabolites analyzed for were detected

in samples from agricultural areas (fig. 16); 8 of the

metabolites were detected in samples from urban

areas. Metolachlor ESA and deethylatrazine were

the most commonly detected metabolites in samples

from agricultural areas; metolachlor ESA and alachlor

ESA were the most commonly detected metabolites

in samples from urban areas. There are currently

no USEPA drinking-water regulations for pesticide

metabolites.

The presence of corn herbicides (such as

atrazine, metolachlor, and alachlor) and their metabolites in samples from urban areas was unexpected.

However, many urban areas in the study unit consist

of smaller towns surrounded by row crops (corn and

soybean), which, in some cases, occupied a portion

of the 1,640-ft land-use buffer around urban land-use

wells (table 1). It is likely that local ground-water flow

from cropland areas could account for the presence of

corn herbicides and metabolites in the ground water of

adjacent urban areas. The presence of corn herbicides

in precipitation (Nations and Hallberg, 1992) also

could provide a source to urban ground water.

Total metabolite concentrations were significantly higher (p<0.001) for samples from agricultural

areas than for urban areas (fig. 17). Total pesticide

concentrations (parent compounds) tended to be

higher in samples from agricultural areas; however,

this difference was not statistically significant

(p=0.279). Metabolites constituted the major portion

of the total residue concentration in the alluvial

aquifer. Total metabolite concentrations were significantly higher (p<0.001) than total pesticide concentrations (parent compounds) in samples from agricultural

areas (fig. 17). Total metabolite concentrations tended

to be higher than total pesticide concentrations

(parent compounds) in samples from urban areas;

however, this difference was not statistically significant (p=0.273). Previous investigations in the

Midwestern United States have indicated that pesticide

metabolites frequently are present in concentrations

exceeding those of the parent compounds (Kolpin and

others, 1997; Kalkhoff and others, 1998; Kolpin and

others, 1998b).

Longer ground-water flow paths allow for

greater residence time and increase opportunities

for sorption, degradation, and dispersion, which

may contribute to decreases in pesticide concentration with depth. Atrazine, deethylatrazine, and

Atrazine

Prometon

Metolachlor

Chlorpyrifos

Bentazon

Tebuthiuron

Acetochlor

2,6-Diethylaniline

Simazine

Alachlor

Butylate

Cyanazine

Bromocil

Malathion

Trifluralin

Picloram

CONSTITUENT

0

80

20

40

60

PERCENT DETECTION

Agricultural

Urban

Figure 15. Frequency of detection of pesticides in samples from agricultural and urban areas.
EFFECTS OF LAND USE AND HYDROGEOLOGY ON WATER QUALITY 21

deisopropylatrazine concentrations in samples from

agricultural areas were negatively correlated with well

depth (p=0.022, rho=−0.41; p=0.018, rho=−0.42; and

p=0.016, rho=−0.43, respectively) (fig. 18) and

depth below the water table to the top of the sample

interval (p=0.018, rho=−0.42; p<0.001, rho=−0.65;

and p=0.004, rho=−0.50, respectively) (fig. 19).

Deethylatrazine concentrations in samples from urban

areas also were negatively correlated with well depth

(p=0.049, rho=−0.36). Metolachlor concentrations

in samples from agricultural areas were negatively

correlated with well depth (p=0.035, rho=−0.38) and

showed a weak negative correlation with depth below

the water table to the top of the sampling interval

(p=0.06, rho=−0.34). Previous studies have related

higher pesticide concentrations to shallow well depths

and wells with sample intervals nearer the water table

(Kross and others, 1990; Kalkhoff and others, 1992;

Koterba and others, 1993). Statistically significant

relations between pesticide and metabolite concentrations and depth to water were not observed; however,

weak negative correlations were present between

deethylatrazine and deisopropylatrazine concentrations and depth to water (p=0.063, rho=−0.34; and

p=0.10, rho=−0.31, respectively) in samples from agricultural areas.

Pesticide mobility and fate in the subsurface are

influenced by sorption and degradation processes. The

effectiveness of these processes is determined, in part,

by the physical and chemical properties of the pesticide, such as organic-carbon and mineral-surface

sorption coefficients, aqueous solubility, and soil

dissipation half-life (Rao and Alley, 1993). Sorption of

pesticides onto clays and solid-phase organic material

can slow their movement in the subsurface (Hance,

1988; Barbash and Resek, 1996; Kolpin and others,

1998a). However, pesticide mobility may be increased

as a result of sorption onto dissolved organic material

(Madhun and others, 1986; Pennington and others,

1991; Barbash and Resek, 1996). Dissolved organic

material also may compete with pesticides for available sorption sites on clay and solid-phase organic

material (Lee and others, 1990; Celis and others,

1998), resulting in increased pesticide mobility.

Atrazine concentrations in samples from

urban areas were negatively correlated with

cumulative clay thickness above the sample interval

(p=0.023, rho=−0.41; fig. 20). Prometon concentrations showed a weak negative correlation with

cumulative clay thickness above the sample interval

(p=0.077, rho=−0.33). Weak negative correlations

also were observed between deethylatrazine and

Metolachlor ESA

Deethylatrazine

Alachlor ESA

Deisopropylatrazine

Metolachlor OA

Alachlor OA

Cyanazine-amide

Acetochlor ESA

Hydroxy-Atrazine

Acetochlor OA

CONSTITUENT

0

80

20

40

60

PERCENT DETECTION

Agricultural

Urban

Figure 16. Frequency of detection of pesticide metabolites in samples from agricultural and urban areas.
22 Effects of Land Use and Hydrogeology on the Water Quality of Alluvial Aquifers in Eastern Iowa and Southern Minnesota, 1997

deisopropylatrazine concentrations and cumulative

clay thickness above the sample interval (p=0.052,

rho=−0.35 and p=0.098, rho=−0.30, respectively) in

samples from urban areas.

Statistically significant relations between pesticide and metabolite concentrations and organic

carbon, and dissolved organic carbon concentrations

were not observed. However, a weak negative correlation between atrazine concentrations and organic

carbon content (p=0.067, rho=−0.34) and a weak positive correlation between alachlor ESA and dissolved

organic carbon concentrations (p=0.078, rho=0.33)

were present in samples from urban areas.

Microbial deethylation of atrazine results in

the formation of the metabolite deethylatrazine. The

deethylatrazine to atrazine ratio (DAR) has been used

as an indicator of atrazine residence time in the unsaturated zone and of the probable source (point or

nonpoint) of atrazine in ground water (Adams and

Thurman, 1991; Thurman and others, 1992). DAR

values greater than 0.3 have been attributed to longer

residence times in the unsaturated zone and nonpoint

sources of atrazine in ground water (Kolpin and

others, 1994). DAR values were calculated for

58 percent of samples (those with detections of both

analytes) from agricultural areas and ranged from

0.37 to 14.8, with a median value of 1.85. These

0.005

200

0.01

0.02

0.05

0.1

0.2

0.5

1

2

5

10

20

50

100

CONCENTRATION, IN MICROGRAMS PER LITER

EXPLANATION

Detection limit

10th percentile

25th percentile

50th percentile (median)

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

 (31) Number of observations

TOTAL PESTICIDE CONCENTRATION

(PARENT COMPOUNDS)

Detection limit

10th percentile

25th percentile

50th percentile (median)

75th percentile

90th percentile

10th and 90th percentiles

Data values outside the

TOTAL METABOLITE CONCENTRATION

(31) (30)

AGRICULTURE URBAN

LAND USE

Figure 17. Relation between land use and total pesticide (parent compounds) and total

metabolite concentrations.

0 2.0 0.5 1.0 1.5

CONCENTRATION, IN MICROGRAMS PER LITER

0

30

10

20

WELL DEPTH, IN FEET

ATRAZINE

0 2.0 0.5 1.0 1.5

CONCENTRATION, IN MICROGRAMS PER LITER

0

30

10

20

WELL DEPTH, IN FEET

DEETHYLATRAZINE

DEISOPROPYLATRAZINE

Figure 18. Relation between atrazine, deethylatrazine,

and deisopropylatrazine concentrations and well depth in

samples from agricultural areas.
EFFECTS OF LAND USE AND HYDROGEOLOGY ON WATER QUALITY 23

results suggest that the atrazine detected in samples

from these wells moved slowly through the unsaturated zone and was derived from nonpoint sources.

DAR values could not be interpreted in samples from

urban areas due to the small number of detections

(10 percent) of both analytes.

Volatile Organic Compounds

Volatile organic compounds are associated with

a variety of manufacturing processes and are present

in many commodities, including gasoline, paints,

solvents, dry-cleaning agents, pharmaceuticals, and

liquid formulations of some pesticides (Verschueren,

1983; Wang and others, 1995). Widespread use has led

to the detection of VOCs in ground water throughout

the United States (Westrick, 1990; Mackay and Smith,

1993). VOCs can enter ground water directly from

near-surface leaks and spills or through atmospheric

deposition following volatilization (Mackay and

Smith, 1993; Squillace and others, 1995; Pankow

and others, 1997). VOCs comprise a diverse group

of compounds that exhibit a wide range of physical

and chemical properties (molecular weight, vapor

pressure, aqueous solubility, and organic carbon and

sediment sorption coefficients). These properties influence partitioning, sorption, advection-dispersion, and

degradation processes and affect VOC mobility and

fate in the subsurface (Verschueren, 1983; Gillham

and Rao, 1990; Chapelle, 1993).

VOCs were detected in 40 percent of samples

from urban areas and 10 percent from agricultural areas.

Thirty-seven VOCs were detected in samples from

urban areas (fig. 21); 3 VOCs (1,2,4-trimethylbenzene,

methylene chloride, and carbon disulfide) were detected

in agricultural areas. The VOCs detected during this

study are used as fuel oxygenates, gasoline hydrocarbons, solvents, organic synthesizers, fumigants, and

refrigerants. Methyl tert-butyl ether (MTBE), a fuel

oxygenate, was the most frequently detected VOC

and was present in 23 percent of samples from urban

areas but was not detected in samples from agricultural

areas. Trichloroethene and cis-1,2-dichloroethene

were the most frequently detected solvents and were

present in 13 percent of samples from urban areas.

1,2,4-trimethylbenzene, chloroform, o-ethyltoluene, and

methyl iodide were the most frequently detected VOCs

used in organic synthesis and were present in 7 percent

0 2.0 0.5 1.0 1.5

CONCENTRATION, IN MICROGRAMS PER LITER

15

0

5

10

DEPTH BELOW WATER TABLE TO TOP

OF SAMPLE INTERVAL, IN FEET

ATRAZINE

0 2.0 0.5 1.0 1.5

CONCENTRATION, IN MICROGRAMS PER LITER

0

15

5

10

DEPTH BELOW WATER TABLE TO TOP

OF SAMPLE INTERVAL, IN FEET

DEETHYLATRAZINE

DEISOPROPYLATRAZINE

0.001 0.01 0.1 1

CONCENTRATION, IN MICROGRAMS PER LITER

0

20

5

10

15

CUMULATIVE CLAY THICKNESS ABOVE 

THE SAMPLE INTERVAL, IN FEET

ATRAZINE

Figure 19. Relation between atrazine, deethylatrazine, and

deisopropylatrazine concentrations and depth below water

table to top of sample interval in samples from agricultural

areas.

Figure 20. Relation between atrazine concentration and

cumulative clay thickness above the sample interval in

samples from urban areas.
24 Effects of Land Use and Hydrogeology on the Water Quality of Alluvial Aquifers in Eastern Iowa and Southern Minnesota, 1997

of samples from urban areas. 1,2,4-trimethylbenzene

was detected in 3 percent of samples from agricultural

areas. The USEPA has tentatively classified MTBE as

a possible human carcinogen and has issued a draft

HAL of 20 to 200 μg/L (U.S. Environmental Protection

Agency, 1996). MTBE concentrations exceeded 20 μg/L

in 7 percent of samples from urban areas. USEPA

drinking-water MCLs were exceeded in 7 percent of

urban samples for benzene (5.0 μg/L) and 3 percent of

samples for 1,2-dichloroethane (5.0 μg/L) and chloroethene (2.0 μg/L).

MTBE has been widely used to increase gasoline octane levels since 1979 (Garrett and others,

1986) and as a fuel oxygenate since 1988 (Begley and

Rotman, 1993). Widespread use has led to frequent

detection of MTBE in ground water from urban areas

throughout the United States (Squillace and others,

1995); however, it was not detected during a recent

study of urban ground-water quality in an area of the

Upper Midwest where oxygenated gasoline use is

required during winter months (Andrews and others,

1998).

MTBE concentrations in samples from urban

sites were positively correlated (p=0.017, rho=0.43)

with percentage of land use classified as commercial

(retail stores and services) where gas stations and

automotive-repair shops are likely to be present.

Statistically significant relations between MTBE

concentrations and factors other than land use, such

as well depth, cumulative clay thickness, and organic

matter concentration, were not observed. Elevated

concentrations (greater than 30 μg/L) of MTBE and

BTEX compounds (benzene, toluene, ethylbenzene,

and xylene) in two samples from urban areas suggest

the possible presence of point-source gasoline leaks or

spills (Squillace and others, 1996). Insufficient

numbers of detections prevented a statistical analysis

of the remainder of detected VOCs.

Methyl tert-butyl ether

Toluene

1,3,5-Trimethylbenzene

Benzene

o-Xylene

1,2,3-Trimethylbenzene

m- and p-Xylene

Ethylbenzene

n-Butylbenzene

Ethyl tert-butyl ether

tert-Amyl methyl ether

Trichloroethene

cis-1,2-Dichloroethene

1,1-Dichloroethane1,2-Dichloroethane

Tetrachloroethene

1,1,1-Trichloroethane

Chloroethene

Diisopropylether

2-Butanone

1,2-Dichlorobenzene

sec-Butylbenzene

1,2-Dichloropropane

trans-1,2-Dichloroethene

Chloroethane

1,2,3-Trichloropropane

1,2,4-Trimethylbenzene

Chloroform

o-Ethyltoluene

Methyl Iodide

Isopropylbenzene

1,2,3,5-Tetramethylbenzene

1,4-Dichlorobenzene

Bromodichloromethane

1,1-Dichloroethene

Chloromethane

Acetone

0

25

5

10

15

20

PERCENT DETECTION

Oxygenates and

gasoline hydrocarbons

Solvents Organic synthesis, fumigants,

and refrigerants

Figure 21. Frequency of detection of volatile organic compounds in samples from urban areas.
SUMMARY AND CONCLUSIONS 25

SUMMARY AND CONCLUSIONS

The Eastern Iowa Basins study unit encompasses

an area of about 19,500 mi2

 in eastern Iowa and

southern Minnesota and is one of 59 study units in the

USGS NAWQA Program. Ground-water samples were

collected from monitoring wells at 31 agricultural and

30 urban sites in the Eastern Iowa Basins study unit

during June–August 1997 to evaluate the effects of

hydrogeology and agricultural and urban land use on

the water quality of alluvial aquifers. Ground-water

samples were analyzed for common ions, nutrients,

DOC, tritium, radon-222, pesticides and pesticide

metabolites, VOCs, and environmental isotopes.

Land use and hydrogeology affect the water

quality of alluvial aquifers in the study area. Calcium,

magnesium, and bicarbonate were the dominant ions in

most samples and were likely derived from solution of

carbonate minerals (calcite and dolomite) present in

alluvial detrital deposits. Chloride and nitrate were

dominant anions in samples from several wells. Road

salts are used throughout the study unit during winter,

especially in urban areas where roads are more

numerous and road salts may be more frequently

applied than in agricultural areas. Sodium and chloride

concentrations were significantly higher in samples

from urban areas than from agricultural areas. Sodium

concentrations in samples from urban sites were positively correlated with percentage of land use classified

as commercial (retail stores and services); chloride

concentrations were negatively correlated with

percentage of land use classified as row crops (corn

and soybeans). Nitrate was detected in 94 percent

of samples from agricultural areas and 77 percent of

samples from urban areas. Nitrate concentrations were

significantly higher in agricultural areas than in urban

areas and exceeded the USEPA MCL for drinking water

(10 mg/L as N) in 39 percent of samples from agricultural areas. Nitrate concentrations in samples from

urban areas did not exceed the MCL. Chemical fertilizer and livestock manure applications to cropland in

agricultural areas most likely contribute to higher

nitrate concentrations in samples from those areas.

Tritium-based ages indicate ground water was

most likely recharged after the 1950’s at all but one

sampling site. Agricultural and urban areas have

remained relatively stable in the study unit for many

decades, and the presence of ground water that was

most likely recharged after the 1950’s increases the

likelihood that the effects of current land use are

reflected in ground water sampled during this study.

Tritium-based ground-water ages were not significantly different between agricultural and urban

samples. Radon-222 was detected in all samples and

exceeded the USEPA previously proposed MCL for

drinking water (300 pCi/L) in 71 percent of samples.

Pesticides were detected in 84 percent of

samples from agricultural areas and 70 percent from

urban areas. Atrazine and metolachlor were the most

frequently detected pesticides in samples from agricultural areas; atrazine and prometon were the most

frequently detected pesticides in samples from urban

areas. None of the pesticide concentrations exceeded

USEPA MCLs or HALs for drinking water. Pesticide

metabolites were detected in 94 percent of samples

from agricultural areas and 53 percent from urban

areas. Metolachlor ESA and deethylatrazine were the

most frequently detected metabolites in samples from

agricultural areas; metolachlor ESA and alachlor ESA

were the most frequently detected metabolites in

samples from urban areas. There are currently no

USEPA drinking-water regulations for pesticide

metabolites.

Total metabolite concentrations were significantly higher in samples from agricultural areas than

in samples from urban areas. Total pesticide concentrations (parent compounds) tended to be higher in

samples from agricultural areas; however, this difference was not statistically significant. Metabolites

constituted the major portion of the total residue

concentration in the alluvial aquifer. Total metabolite

concentrations were significantly higher than total

pesticide concentrations (parent compounds) in

samples from agricultural areas. Total metabolite

concentrations tended to be higher than total pesticide

concentrations (parent compounds) in samples from

urban areas; however, this difference was not statistically significant.

Volatile organic compounds were detected in

40 percent of samples from urban areas and 10 percent

from agricultural areas. MTBE was the most frequently

detected VOC and was present in 23 percent of samples

from urban areas. Elevated concentrations (greater

than 30 μg/L) of MTBE and BTEX compounds in two

samples from urban areas suggest the possible presence

of point-source gasoline leaks or spills. MTBE concentrations in samples from urban sites were positively

correlated with percent of land use classified as

commercial, where gas stations and automotive-repair

shops are likely to be present. MTBE was not detected

in samples from agricultural areas.
26 Effects of Land Use and Hydrogeology on the Water Quality of Alluvial Aquifers in Eastern Iowa and Southern Minnesota, 1997

Factors other than land use may contribute to

observed differences in water quality between and

within agricultural and urban areas. Nitrate, atrazine,

deethylatrazine, and deisopropylatrazine concentrations were significantly higher in shallow wells

with sample intervals nearer the water table and in

wells with thinner cumulative clay thickness above

the sample intervals. These relations suggest that

longer flow paths allow for greater residence time

and increase opportunities for sorption, degradation,

and dispersion, which may contribute to decreases

in nutrient and pesticide concentrations with depth.

Nitrogen speciation was influenced by redox conditions. Nitrate concentrations were significantly higher

in ground water with dissolved-oxygen concentrations

in excess of 0.5 mg/L. Ammonia concentrations were

higher in ground water with dissolved-oxygen concentrations of 0.5 mg/L or less, however, this relation was

not statistically significant. Microbial denitrification

requires the presence of reduced electron-donating

substrates (organic matter) and terminal electron

acceptors (nitrogen oxides). The amount of available

organic matter may limit denitrification rates. Elevated

nitrate concentrations (greater than 2.0 mg/L) were

significantly related to lower dissolved organic carbon

concentrations in water samples from both agricultural

and urban areas. A similar relation between nitrate

concentrations (in water) and organic carbon concentrations (in aquifer material) also was observed but

was not statistically significant.

REFERENCES

Adams, C.D., and Thurman, E.M., 1991, Formation and

transport of deethylatrazine in the soil and vadose

zone: Journal of Environmental Quality, v. 20, no. 3,

p. 540–547.

Aga, D.S., Thurman, E.M., Yockel, M.E., Zimmerman,

L.R., and Williams, T.D., 1996, Identification of a new

sulfonic acid metabolite of metolachlor in soil: Environmental Science and Technology, v. 30, no. 2,

p. 592–597.

Akers, K.K.B., Montgomery, D.L., Christiansen, D.,

Savoca, M.E., Schnoebelen, D.J., Becher, K.D., and

Sadorf, E.M., 2000, Water-quality assessment of the

Eastern Iowa Basins—Hydrologic data, October 1996

through September 1998: U.S. Geological Survey

Open-File Report 00–67, 300 p.

Alvey, S., and Crowley, D.E., 1995, Influence of organic

amendments on biodegradation of atrazine as a

nitrogen source: Journal of Environmental Quality,

v. 24, no. 6, p. 1156–1162.

Alvey, S., and Crowley, D.E., 1996, Survival and activity of

an atrazine-mineralizing bacterial consortium in rhizosphere soil: Environmental Science and Technology,

v. 30, no. 5, 1596–1603.

American Society for Testing Materials, 1996, Annual book

of ASTM standards, section 11, Water and environmental technology: v. 11.02.

Anderson, J.R., Hardy, E.E., Roach, J.T., and Witmer, R.E.,

1976, A land use and land cover classification for use

with remote sensor data: U.S. Geological Survey

Professional Paper 964, 8 p.

Anderson, W.I., 1983, Geology of Iowa—Over two billion

years of change: Ames, Iowa State University Press,

268 p.

Andrews, W.J., Fong, A.L., Harrod, L., and Dittes, M.E.,

1998, Water-quality assessment of part of the Upper

Mississippi River Basin, Minnesota and Wisconsin—

Ground-water quality in an urban part of the Twin

Cities metropolitan area, Minnesota, 1996: U.S.

Geological Survey Water-Resources Investigations

Report 97–4248, 54 p.

Ator, S.W., and Ferrari, M.J., 1997, Nitrate and selected

pesticides in ground water of the Mid-Atlantic region:

U.S. Geological Survey Water-Resources Investigations Report 97–4139, 8 p.

Barbash, J.E., and Resek, E.A., 1996, Pesticides in ground

water—Distribution, trends, and governing factors:

Chelsea, Michigan, Ann Arbor Press, 588 p.

Barringer, T., Dunn, D., Battaglin, W., and Vowinkel, E.,

1990, Problems and methods involved in relating

land use to ground-water quality: American Water

Resources Association, Water Resources Bulletin,

v. 26, no. 1, p. 1–9.

Begley, R., and Rotman, D., 1993, Health complaints fuel

federal concern over MTBE: Chemical Week, v. 152,

no. 10, p. 7.

Blevins, D.W., Wilkison, D.H., Kelly, B.P., and Silva, S.R.,

1996, Movement of nitrate fertilizer to glacial till and

runoff from a claypan soil: Journal of Environmental

Quality, v. 25, no. 3, p. 584–593.

Brenton, R.W., and Arnett, T.L., 1993, Methods of analysis

by the U.S. Geological Survey National Water-Quality

Laboratory—Determination of dissolved organic

carbon by UV-promoted persulfate oxidation and

infrared spectrometry: U.S. Geological Survey OpenFile Report 92–480, 12 p.
REFERENCES 27

Buchmiller, R.C., and Squillace, P.J., 1988, Ground-water

quality—Iowa, in U.S. Geological Survey National

Water Summary 1986: U.S. Geological Survey WaterSupply Paper 2325, p. 251–258.

Burkart, M.R., and Kolpin, D.W., 1993, Hydrologic and

land-use factors associated with herbicides and nitrate

in near-surface aquifers: Journal of Environmental

Quality, v. 22, no. 4, p. 646–656.

Celis, R., Barriuso, E., and Houot, S., 1998, Sorption

and desorption of atrazine by sludge-amended

soil—Dissolved organic matter effects: Journal of

Environmental Quality, v. 27, no. 6, p. 1348–1356.

Chapelle, F.H., 1993, Ground-water microbiology and

geochemistry: New York, John Wiley & Sons, Inc.,

424 p.

Coplen, T.B., Wildman, J.D., and Chen, J., 1991, Improvements in the gaseous hydrogen-water equilibrium technique for hydrogen isotope ratio analysis: Analytical

Chemistry, v. 63, p. 910–912.

Dhileepan, R.N., and Schnoor, J.L., 1992, Effect of two

electron acceptors on atrazine mineralization rates in

soil: Environmental Science and Technology, v. 26,

no. 11, p. 2298–2230.

Eckhardt, D.A., Flipse, Jr., W.J., and Oaksford, E.T.,

1989, Relation between land use and groundwater quality in the upper glacial aquifer in Nassau

and Suffolk Counties, Long Island, New York:

U.S. Geological Survey Water-Resources Investigations Report 86–4142, 35 p.

Epstein, S., and Mayeda, T., 1953, Variation of O-18

content of water from natural sources: Geochimica et

Cosmochimica Acta, v. 4, p. 213–224.

Ferrari, M.J., and Ator, S.W., 1995, Nitrate in ground water

in the Great Valley Carbonate Subunit of the Potomac

River Basin: U.S. Geological Survey Water-Resources

Investigations Report 95–4099, 6 p.

Ferrer, I., Thurman, E.M., and Barcelo, D., 1997, Identification of new ionic chloroacetanilide-herbicide metabolites in surface and ground water by HPLC/MS using

negative ion detection: Analytical Chemistry v. 69,

p. 4547–4553.

Field, J.A., and Thurman, E.M., 1996, Glutathione conjugation and contaminant transformation: Environmental

Science and Technology, v. 30, no. 5, p. 1413–1418.

Fishman, M.J., and Friedman, L.C., eds., 1989, Methods for

determination of inorganic substances in water and

fluvial sediments: U.S. Geological Survey Techniques

for Water-Resources Investigations, book 5, chap. A1,

545 p.

Garrett, P., Moreau, M., and Lowry, J.D., 1986, MTBE

as a ground water contaminant, in Proceedings of

petroleum hydrocarbons and organic chemicals in

ground water—Prevention, detection and restoration,

November 12–14, 1986: Houston, Texas, National

Water Well Association and American Petroleum

Institute, p. 227–238.

Gillham, R.W., and Rao, P.S., 1990, Transport, distribution,

and fate of volatile organic compounds in groundwater,

in Ram, N.M., Christman, R.F., and Cantor, K.P., eds.,

Significance and treatment of volatile organic

compounds in water supplies: Chelsea, Michigan,

Lewis Publishers, p. 141–181.

Gilliom, R.J., Alley, W.A., and Gurtz, M.E., 1995,

Design of the National Water-Quality Assessment

Program—Occurrence and distribution of waterquality conditions: U.S. Geological Survey

Circular 1112, 33 p.

Goolsby, D.A., Thurman, E.M., Pomes, M.L., Meyer, M.T.,

and Battaglin, W.A., 1997, Herbicides and their metabolites in rainfall—Origin, transport, and depositional

patterns across the Midwestern and Northeastern

United States, 1990–91: Environmental Science and

Technology, v. 31, no. 5, p. 1325–1333.

Hallberg, G.R., 1989, Nitrate in ground water in the United

States, in Follett, R.F., ed., Nitrogen management and

ground-water protection: New York, Elsevier Science

Publishing Co., p. 35–74.

Hallberg, G.R., and Keeney, D.R., 1993, Nitrate, in Alley,

W.M., ed., Regional ground-water quality: New York,

Van Nostrand Reinhold, p. 297–322.

Hance, R.J., 1998, Adsorption and bioavailability, in

Grover, R., ed., Environmental chemistry of herbicides, v. I: Boca Raton, Florida, CRC Press, Inc.,

p. 1–19.

Hem, J.D., 1985, Study and interpretation of the chemical

characteristics of natural water: U.S. Geological

Survey Water-Supply Paper 2254, 264 p.

Hershey, H.G., 1969, Geologic map of Iowa: Iowa Geological Survey, 1 sheet.

Hinkle, S.R., 1997, Quality of shallow ground water in

alluvial aquifers of the Willamette Basin, Oregon,

1993–95: U.S. Geological Survey Water-Resources

Investigations Report 97–4082–B, 48 p.

Hirsch, R.M., Alley, W.M., and Wilber, W.G., 1988,

Concepts for a national water-quality assessment

program: U.S. Geological Survey Circular 1021, 42 p.

Hitt, K.J., 1994, Refining 1970’s land-use data with 1990

population data to indicate new residential development: U.S. Geological Survey Water-Resources Investigations Report 94–4250, 15 p.

Hoyer, B.E., and Hallberg, G.R., 1991, Groundwater

vulnerability regions of Iowa: Energy and Geological

Resources Division, Geological Survey Bureau, Iowa

Department of Natural Resources, Special Map

Series ll.
28 Effects of Land Use and Hydrogeology on the Water Quality of Alluvial Aquifers in Eastern Iowa and Southern Minnesota, 1997

Johnson, W.G., and Lavy, T.L., 1994, In-situ dissipation

of benomyl, carbofuran, thiobencarb, and triclopyr at

three soil depths: Journal of Environmental Quality,

v. 23, no. 3, p. 556–562.

Kalkhoff, S.J., Detroy, M.G., Cherryholmes, K.L., and

Kuzniar, R.L., 1992, Herbicide and nitrate variation

in alluvium underlying a corn field at a site in Iowa

County, Iowa: Water Resources Bulletin, v. 28, no. 6,

p. 1001–1011.

Kalkhoff, S.J., Kolpin, D.W., Thurman, E.M., Ferrer, I., and

Barcelo, D., 1998, Degradation of chloroacetanilide

herbicides—The prevalence of sulfonic and oxanilic

acid metabolites in Iowa groundwaters and surface

waters: Environmental Science and Technology, v. 32,

no. 11, p. 1738–1740.

Kolpin, D.W., 1997, Agricultural chemicals in groundwater

of the midwestern United States—Relations to land

use: Journal of Environmental Quality, v. 26, no. 4,

p. 1025–1037.

Kolpin, D.W., Burkart, M.R., and Thurman, E.M., 1994,

Herbicides and nitrate in near-surface aquifers in the

Midcontinental United States, 1991: U.S. Geological

Survey Water-Supply Paper 2413, 34 p.

Kolpin, D.W., Barbash, J.E., and Gilliom, R.J., 1998a,

Occurrence of pesticides in shallow groundwater of the

United States—Initial results from the National WaterQuality Assessment Program: Environmental Science

and Technology, v. 32, no. 5, p. 558–566.

Kolpin, D.W., Stamer, J.K., Goolsby, D.A., and Thurman,

E.M., 1998b, Herbicides in groundwater of the

Midwest—A regional study of shallow aquifers,

1991–94: U.S Geological Survey Fact Sheet

FS–076–98.

Kolpin, D.W., Kalkhoff, S.J., Goolsby, D.A., Sneck-Fahrer,

D.A., and Thurman, E.M., 1997, Occurrence of

selected herbicides and herbicide degradation products

in Iowa’s groundwater, 1995: Ground Water, v. 35,

no. 4, p. 679–688.

Koterba, M.T., 1998, Ground-water data-collection protocols and procedures for the National Water-Quality

Assessment program—Collection, documentation,

and compilation of required site, well, subsurface,

and landscape data for wells: U.S. Geological Survey

Water-Resources Investigations Report 98–4107, 91 p.

Koterba, M.T., Banks, W.S.L., and Shedlock, R.J., 1993,

Pesticides in shallow groundwater in the Delmarva

Peninsula: Journal of Environmental Quality, v. 22,

no. 3, p. 500–518.

Koterba, M.T., Wilde, F.D., and Lapham, W.W., 1995,

Ground-water data-collection protocols and procedures for the National Water-Quality Assessment

program—Collection and documentation of waterquality samples and related data: U.S. Geological

Survey Open-File Report 95–399, 113 p.

Kross, B.C., Hallberg, G.R., Bruner, D.R., Libra, R.D.,

Rex, K.D., Weih, L.M.B., Vermace, M.E., Burmeister,

L.F., Hall, N.H., Cherryholmes, K.L., Johnson, J.K.,

Selim, M.I., Nations, B.K., Seigley, L.S., Quade, D.J.,

Dudler, A.G., Sesker, K.D., Culp, M.A., Lynch, C.F.,

Nicholson, H.F., and Hughes, J.P., 1990, The Iowa

state-wide rural well-water survey water-quality

data—Initial analysis: Iowa Department of Natural

Resources Technical Information Series 19, 142 p.

Lapham, W.W., Wilde, F.D., and Koterba, M.T., 1995,

Ground-water data-collection protocols and procedures 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 95–398, 69 p.

Lavy, T.L., Roeth, F.W., and Fenster, C.R., 1973, Degradation of 2,4-D and atrazine at three soil depths in the

field: Journal of Environmental Quality, v. 2, no. 1,

p. 132–137.

Lee, D.Y., Farmer, W.J., and Aochi, Y., 1990, Sorption

of nopropamide on clay and soil in the presence of

dissolved organic matter: Journal of Environmental

Quality, v. 19, no. 3, p. 567–573.

Mackay, D.M., and Smith, L.A., 1993, Organic contaminants, in Alley, W.M., ed., Regional groundwater quality: New York, Van Nostrand Reinhold,

p. 323–343.

Madhun, Y.A., Young, J.L., and Freed, V.H., 1986, Binding

of herbicides by water-soluble organic materials from

soil: Journal of Environmental Quality, v. 15, no. 1,

p. 64–68.

Madison, R.J., and Brunett, J.O., 1985, Overview of the

occurrence of nitrate in ground water of the United

States, in U.S. Geological Survey National Water

Summary 1984: U.S. Geological Survey Water-Supply

Paper 2275, p. 93–105.

Majewski, M.J., and Capel, P.D., 1995, Pesticides in the

atmosphere—Distribution, trends, and governing

factors: Chelsea, Michigan, Ann Arbor Press, 214 p.

Majewski, M.J., Foreman, W.T., Goolsby, D.A., and

Nakagaki, N., 1998, Airborne pesticides along the

Mississippi River: Environmental Science and Technology, v. 32, no. 23, p. 3689–3698.

McMahon, P.B., Chapelle, F.H., and Jaguckl, M.L., 1992,

Atrazine mineralization potential of alluvial-aquifer

sediments under aerobic conditions: Environmental

Science and Technology, v. 26, no. 8, p. 1556–1559.

Mueller, D.K., Hamilton, P.A., Helsel, D.R., Hitt, K.J.,

and Ruddy, B.C., 1995, Nutrients in ground water and

surface water of the United States—An analysis of

data through 1992: U.S. Geological Survey WaterResources Investigations Report 95–4031, 74 p.
REFERENCES 29

Nations, B.K., and Hallberg, G.R., 1992, Pesticides in Iowa

precipitation: Journal of Environmental Quality, v. 21,

no. 3, p. 486–492.

Olcott, P.G., 1992, Ground water atlas of the United

States—Segment 9, Iowa, Michigan, Minnesota,

Wisconsin: U.S. Geological Survey Hydrologic

Investigations Atlas 730–J, 31 p.

Ostlund, H.G., and Dorsey, H.G., 1977, Rapid electrolytic

enrichment of hydrogen gas proportional counting

of tritium: Proceedings of International Conference

on Low Radioactivity Measurement and Applications,

High Tatras, Czechoslovakia, October, 1975, 6 p.

Ott, R.L., 1993, An introduction to statistical methods and

data analysis: Belmont, California, Duxbury Press,

Wadsworth Publishing Company, 1051 p.

Pankow, J.F., Thomson, N.R., Johnson, R.L., Baehr, A.L.,

and Zogorski, J.S., 1997, The urban atmosphere as

a non-point source for the transport of MTBE and

other volatile organic compounds (VOCs) to shallow

groundwater: Environmental Science and Technology,

v. 31, no. 10, p. 2821–2828.

Pennington, K.L., Harper, S., and Koskinen, W.C., 1991,

Interactions of herbicides with water-soluble soil

organic matter: Weed Science, v. 39, p. 667–672.

Plummer, L.N., Michel, R.L., Thurman, E.M., and Glynn,

P.D., 1993, Environmental tracers for age dating young

ground water, in Alley, W.M., ed., Regional groundwater quality: New York, Van Nostrand Reinhold,

p. 255–294.

Pothuluri, J.V., Moorman, T.B., Obenhuber, D.C., and

Wauchope, R.D., 1990, Aerobic and anaerobic

degradation of alachlor in samples from a surfaceto-groundwater profile: Journal of Environmental

Quality, v. 19, no. 3, p. 525–530.

Rao, P.S., and Alley, W.M., 1993, Pesticides, in Alley,

W.M., ed., Regional ground-water quality: New York,

Van Nostrand Reinhold, p. 345–382.

Rose, D.L., and Schroeder, M.P., 1995, Methods of

analysis by the U.S. Geological Survey National

Water-Quality Laboratory—Determination of

volatile organic compounds in water by purge and

trap capillary gas chromatography/mass spectrometry:

U.S. Geological Survey Open-File Report 94–708,

26 p.

Schapp, B.D., and Linhart, S.M., 1998, Quality of ground

water used for selected municipal water supplies in

Iowa, 1982–96 water years: U.S. Geological Survey

Open-File Report 98–3, 67 p.

Schumann, R.R., 1993, Geologic radon potential of the

glaciated Upper Midwest—Proceedings of the 1992

International Symposium on Radon and Radon

Reduction Technology, v. 2, Symposium Oral Papers,

Technical Sessions VII–XII: Research Triangle Park,

N.C., U.S. Environmental Protection Agency Report

EPA–600/R–93/083b, p. 8–33—8–49.

Scott, J.C., 1990, Computerized stratified random siteselection approaches for design of a ground-waterquality sampling network: U.S. Geological Survey

Water-Resources Investigations Report 90–4101,

109 p.

Squillace, P.J., Zogorski, J.S., Wilber, W.G., and Price, C.V.,

1995, A preliminary assessment of the occurrence

and possible sources of MTBE in ground water of the

United States, 1993–94: U.S. Geological Survey OpenFile Report 95–456, 16 p.

Squillace, P.J., Pankow, J.F., Korte, N.E., and Zogorski, J.S.,

1996, Environmental behavior and fate of methyl tertbutyl ether (MTBE): U.S. Geological Survey Fact

Sheet FS–203–96, 6 p. (revised February 1998).

Starr, R.C., and Gillham, R.W., 1993, Denitrification and

organic carbon availability in two aquifers: Ground

Water, v. 31, no. 6, p. 934–946.

Steinhilber, W.L., and Horick, P.J., 1970, Ground-water

resources of Iowa, in Horick, P.J., ed., Water resources of

Iowa: Iowa City, University Printing Service, p. 29–49.

Tesoriero, A.J., and Voss, F.D., 1997, Predicting the

probability of elevated nitrate concentrations in the

Puget Sound Basin—Implications for aquifer susceptibility and vulnerability: Ground Water, v. 35, no. 6,

p. 1029–1039.

Thurman, E.M., Goolsby, D.A., Meyer, M.T., Mills, M.S.,

Pomes, M.L., and Kolpin, D.W., 1992, A reconnaissance study of herbicides and their metabolites in

surface water of the midwestern United States using

immunoassay gas chromatography/mass spectrometry: Environmental Science and Technology, v. 26,

no. 12, p. 2240–2247.

U.S. Environmental Protection Agency, 1996, Drinking

water regulations and health advisories: Office of

Water 4304 [unpaginated].

U.S. Geological Survey, 1990, Land use and land cover

digital data from 1:250,000- and 1:100,000-scale

maps: U.S. Geological Survey Data User Guide 4,

25 p.

Verschueren, K., 1983, Handbook of environmental data

on organic chemicals: New York, Van Nostrand

Reinhold, 1310 p.

Wahl, K.D., Ludvigson, G.A., Ryan, G.L., and Steinkampf,

W.C., 1978, Water resources of east-central Iowa:

Iowa Geological Survey Water Atlas 6, 91 p.

Wang, W., Liszewski, M., Buchmiller, R., and

Cherryholmes, K., 1995, Occurrence of active

and inactive herbicide ingredients at selected sites

in Iowa: Water, Air and Soil Pollution, v. 83,

p. 21–35.
30 Effects of Land Use and Hydrogeology on the Water Quality of Alluvial Aquifers in Eastern Iowa and Southern Minnesota, 1997

Werner, S.L., Burkhardt, M.R., and DeRusseau, S.N., 1996,

Methods of analysis by the National Water Quality

Laboratory—Determination of pesticides in water

by carbopak-B solid-phase extraction and highperformance liquid chromatography: U.S. Geological

Survey Open-File Report 96–261, 42 p.

Wershaw, R.L., Fishman, M.J., Grabbe, R.R., and Lowe,

L.E., eds., 1987, Methods for the determination of

organic substances in water and fluvial sediments:

U.S. Geological Survey Techniques of WaterResources Investigations, book 5, chap. A3, 80 p.

Westrick, J.J., 1990, National surveys of volatile organic

compounds in ground and surface waters, in Ram,

N.M., Christman, R.F., and Cantor, K.P., eds., Significance and treatment of volatile organic compounds in

water supplies: Chelsea, Michigan, Lewis Publishers,

p. 103–138.

Zaugg, S.D., Sandstrom, M.W., Smith, S.G., and Fehlberg,

K.M., 1995, Methods of analysis by the National

Water Quality Laboratory—Determination of pesticides in water by C-18 solid-phase extraction

and capillary column gas chromatography/mass

spectrometry with selected-ion monitoring:

U.S. Geological Survey Open-File Report 95–181,

60 p.

Zimmerman, L.R., and Thurman, E.M., 1999, Method

of analysis by the U.S. Geological Survey Organic

Geochemistry Research Group—Determination of

triazine and chloroacetanilide herbicides in water

by solid-phase extraction and capillary-column gas

chromatography/mass spectrometry with selectedion monitoring: U.S. Geological Survey Open-File

Report 98–634, 21 p.
APPENDIX
APPENDIX 33

Table A1. Statistical summary of selected ground-water quality data from land-use wells in the Eastern Iowa Basins

study unit

[Ag, agricultural land use area; Ur, urban land use area; MRL, minimum reporting level; MDL, method detection limit for pesticides and pesticide metabolites; na; not applicable; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter; °C, degrees Celsius; <, less than; pCi/L, picocuries per liter;

μg/L, micrograms per liter; NWQL, U.S. Geological Survey National Water Quality Laboratory]

Constituent

or property

Samples/

detections

Ag wells

Samples/

detections

Ur wells

MRL or

MDL

Maximum/median

Ag wells

Maximum/median

Ur wells

Spike

recovery

(percent)

Field measurements and physical characteristics

Well depth (feet below land surface) 31 / na 30 / na na 28.0 / 17.5 37.5 / 22.5 na

Water level (feet below land surface) 31 / na 30 / na na 13.6 / 6.2 20.5 / 10.9 na

Dissolved oxygen (mg/L) 30 / na 29 / na na 10.2 / 3.5 7.34 / 1.1 na

pH (standard units) 31 / 31 30 / 30 na 7.50 / 6.94 7.15 / 6.79 na

Specific conductance (μS/cm at 25°C) 31 / 31 30 / 30 na 810 / 512 1,490 / 791 na

Water temperature (°C) 31 / na 30 / na na 21.5 / 11.2 26.0 / 13.7 na

Common ions, dissolved (mg/L, except as indicated)

Alkalinity (mg/L as CaCO3) 31 / na 30 / na 1.0 460 / 168 431 / 267 na

Bicarbonate (mg/L as HCO3) 31 / na 30 / na na 556 / 206 526 / 326 na

Bromide 30 / 27 30 / 30 0.01 0.094 / 0.039 0.407 / 0.076 na

Calcium 31 / 31 30 / 30 0.02 110 / 68 187 / 96 na

Chloride 31 / 31 30 / 30 0.10 139 / 12 312 / 42 na

Fluoride 31 / 21 30 / 25 0.10 0.35 / 0.16 0.57 / 0.19 na

Iron (μg/L) 31 / 11 30 / 22 3.0 3,520 / <3.0 5,760 / 24 na

Magnesium 31 / 31 30 / 30 0.01 37 / 19 67 / 27 na

Manganese (μg/L) 31 / 22 30 / 23 1.0 1,600 / 8.8 2,210 / 174 na

Potassium 31 / 31 30 / 30 0.10 5.4 / 0.7 21 / 2.7 na

Silica 31 / 31 30 / 30 0.01 30 / 19 39 / 18 na

Sodium 31 / 31 30 / 30 0.20 42 / 5.6 68 / 23 na

Sulfate 31 / 31 30 / 30 0.10 70 / 22 255 / 45 na

Dissolved solids 31 / 31 30 / 30 1.0 506 / 304 849 / 439 na

Nutrients and organics, dissolved (mg/L)

Ammonia, as N 31 / 11 30 / 21 0.015 0.97 / <0.015 1.01 / 0.024 na

Ammonia plus organic, as N 31 / 5 30 / 8 0.2 1.25 / <0.2 1.59 / <0.2 na

Nitrite, as N 31 / 5 30 / 8 0.01 0.99 / <0.01 0.149 / <0.01 na

Nitrite plus nitrate, as N 31 / 29 30 / 23 0.05 32.1 / 5.13 9.54 / 1.83 na

Orthophosphate, as P 31 / 29 30 / 26 0.01 0.148 / 0.033 0.117 / 0.023 na

Phosphorus, as P 31 / 22 30 / 18 0.01 0.163 / 0.033 0.108 / 0.015 na

Organic carbon 31 / 31 30 / 30 0.10 10.0 / 1.10 9.70 / 1.65 na

Radiochemicals and environmental isotopes

Radon-222 (pCi/L) 31 / 31 30 / 30 24 1,500 / 396 1221 / 378 na

Trtitium (pCi/L) 31 / 30 30 / 30 1.0 58.2 / 33.0 124 / 33.9 na

Oxygen-18/Oxygen-16 (per mil) 31 / na 30 / na na −6.72 / −8.15 −7.07 / −8.39 na

Deuterium/Protium (per mil) 31 / na 30 / na na −41.8 / −52.2 −45.7 / −55.1 na

Pesticides (NWQL schedule 2010) and pesticide metabolites, dissolved (μg/L)

Acetochlor 31 / 2 30 / 0 0.002 0.031 / <0.002 <0.002 / <0.002 104

Acetochlor ESA 31 / 3 30 / 0 0.20 1.42 / <0.20 <0.20 /<0.20 na

Acetochlor oxanilic acid 31 / 1 30 / 0 0.20 0.63 / <0.20 <0.20 /<0.20 na

Alachlor 31 / 1 30 / 1 0.002 0.003 / <0.002 0.082 / <0.002 104

Alachlor ESA 31 / 17 30 / 11 0.20 35.06 / 0.31 1.89 / <0.20 na

Alachlor oxanilic acid 31 / 3 30 / 4 0.20 0.63 / <0.20 5.40 / <0.20 na
34 Effects of Land Use and Hydrogeology on the Water Quality of Alluvial Aquifers in Eastern Iowa and Southern Minnesota, 1997

Pesticides (NWQL schedule 2010) and pesticide metabolites, dissolved (μg/L)—Continued

Atrazine 31 / 24 30 / 15 0.001 0.824 / 0.033 0.792 / 0.004 107

Atrazine, deethyl- 31 / 19 30 / 3 0.05 1.98 / 0.22 0.23 / <0.05 na

Atrazine, deisopropyl- 31 / 9 30 / 2 0.05 1.11 / <0.05 0.29 / <0.05 na

Atrazine, hydroxy- 31 / 1 30 / 2 0.20 0.38 / <0.20 2.12 / <0.20 na

Azinphos, methyl- 31 / 0 30 / 0 0.001 <0.001 / <0.001 <0.001 / <0.001 96

Benfluralin 31 / 0 30 / 0 0.002 <0.002 / <0.002 <0.002 / <0.002 85

Butylate 31 / 0 30 / 1 0.002 <0.002 / <0.002 0.0024 / <0.002 97

Chlorpyrifos 31 / 4 30 / 2 0.004 0.021 / <0.004 0.005 / <0.004 96

Cyanazine 31 / 0 29 / 1 0.004 <0.004 / <0.004 0.007 / <0.004 128

Cyanazine-amide 31 / 4 30 / 1 0.05 0.21 / <0.05 0.08 / <0.05 na

DCPA 31 / 0 30 / 0 0.002 <0.002 / <0.002 <0.002 / <0.002 108

DDE, p,p’- 31 / 0 30 / 0 0.006 <0.006 / <0.006 <0.006 / <0.006 67

Diazinon 31 / 0 30 / 0 0.002 <0.002 / <0.002 <0.002 / <0.002 106

Dieldrin 31 / 0 30 / 0 0.001 <0.001 / <0.001 <0.001 / <0.001 87

Diethylaniline, 2,6- 31 / 1 30 / 1 0.003 0.044 / <0.003 0.031 / <0.003 105

Disulfoton 31 / 0 30 / 0 0.017 <0.017 / <0.017 <0.017 / <0.017 92

EPTC 31 / 0 30 / 0 0.002 <0.002 / <0.002 <0.002 / <0.002 105

Ethalfluralin 31 / 0 30 / 0 0.004 <0.004 / <0.004 <0.004 / <0.004 84

Ethoprop 31 / 0 30 / 0 0.003 <0.003 / <0.003 <0.003 / <0.003 111

Fonofos 31 / 0 30 / 0 0.003 <0.003 / <0.003 <0.003 / <0.003 90

HCH, alpha- 31 / 0 30 / 0 0.002 <0.002 / <0.002 <0.002 / <0.002 97

Lindane 31 / 0 30 / 0 0.004 <0.004 / <0.004 <0.004 / <0.004 86

Linuron 31 / 0 30 / 0 0.002 <0.002 / <0.002 <0.002 / <0.002 109

Malathion 31 / 0 30 / 1 0.005 <0.005 / <0.005 0.010 / <0.005 99

Metolachlor 31 / 9 30 / 7 0.002 32.8 / <0.002 0.556 / <0.002 105

Metolachlor ESA 31 / 24 30 / 15 0.20 63.67 / 0.56 12.36 / 0.22 na

Metolachlor oxanilic acid 31 / 6 30 / 8 0.20 13.39 / <0.02 3.60 / <0.20 na

Metribuzin 31 / 0 30 / 0 0.004 <0.004 / <0.004 <0.004 / <0.004 104

Molinate 31 / 0 30 / 0 0.004 <0.004 / <0.004 <0.004 / <0.004 113

Napropamide 31 / 0 30 / 0 0.003 <0.003 / <0.003 <0.003 / <0.003 89

Parathion 31 / 0 30 / 0 0.004 <0.004 / <0.004 <0.004 / <0.004 97

Parathion, methyl- 31 / 0 30 / 0 0.006 <0.006 / <0.006 <0.006 / <0.006 108

Pebulate 31 / 0 30 / 0 0.004 <0.004 / <0.004 <0.004 / <0.004 98

Pendimethalin 31 / 0 30 / 0 0.004 <0.004 / <0.004 <0.004 / <0.004 92

Permethrin, cis- 31 / 0 30 / 0 0.005 <0.005 / <0.005 <0.005 / <0.005 36

Phorate 31 / 0 30 / 0 0.002 <0.002 / <0.002 <0.002 / <0.002 92

Prometon 31 / 0 30 / 12 0.018 <0.018 / <0.018 0.356 / <0.018 107

Pronamide 31 / 0 30 / 0 0.003 <0.003 / <0.003 <0.003 / <0.003 100

Propachlor 31 / 0 30 / 0 0.007 <0.007 / <0.007 <0.007 / <0.007 105

Propanil 31 / 0 30 / 0 0.004 <0.004 / <0.004 <0.004 / <0.004 122

Table A1. Statistical summary of selected ground-water quality data from land-use wells in the Eastern Iowa Basins

study unit—Continued

[Ag, agricultural land use area; Ur, urban land use area; MRL, minimum reporting level; MDL, method detection limit for pesticides and pesticide metabolites; na; not applicable; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter; °C, degrees Celsius; <, less than; pCi/L, picocuries per liter;

μg/L, micrograms per liter; NWQL, U.S. Geological Survey National Water Quality Laboratory]

Constituent

or property

Samples/

detections

Ag wells

Samples/

detections

Ur wells

MRL or

MDL

Maximum/median

Ag wells

Maximum/median

Ur wells

Spike

recovery

(percent)
APPENDIX 35

Pesticides (NWQL schedule 2010) and pesticide metabolites, dissolved (μg/L)—Continued

Propargite 31 / 0 30 / 0 0.013 <0.013 / <0.013 <0.013 / <0.013 92

Simazine 31 / 1 30 / 1 0.005 0.011 / <0.005 0.011 / <0.005 107

Tebuthiuron 31 / 0 30 / 3 0.01 <0.01 / <0.01 0.10 / <0.01 114

Terbacil 31 / 0 30 / 0 0.007 <0.007 / <0.007 <0.007 / <0.007 58

Terbufos 31 / 0 30 / 0 0.013 <0.013 / <0.013 <0.013 / <0.013 87

Thiobencarb 31 / 0 30 / 0 0.002 <0.002 / <0.002 <0.002 / <0.002 103

Triallate 31 / 0 30 / 0 0.001 <0.001 / <0.001 <0.001 / <0.001 101

Trifluralin 31 / 1 30 / 0 0.002 0.004 / <0.002 <0.002 / <0.002 93

Pesticides (NWQL schedule 2050), dissolved (μg/L)

2,4,5-T 31 / 0 30 / 0 0.035 <0.035 / <0.035 <0.035 / <0.035 68

2,4-D 31 / 0 30 / 0 0.035 <0.035 / <0.035 <0.035 / <0.035 64

2,4-DB 31 / 0 30 / 0 0.035 <0.035 / <0.035 <0.035 / <0.035 55

Acifluorfen 31 / 0 30 / 0 0.035 <0.035 / <0.035 <0.035 / <0.035 76

Aldicarb 31 / 0 30 / 0 0.016 <0.016 / <0.016 <0.016 / <0.016 31

Aldicarb sulfone 31 / 0 30 / 0 0.016 <0.016 / <0.016 <0.016 / <0.016 19

Aldicarb sulfoxide 31 / 0 30 / 0 0.021 <0.021 / <0.021 <0.021 / <0.021 52

Bentazon 29 / 1 30 / 3 0.014 0.110 / <0.014 0.150 / <0.014 66

Bromacil 31 / 0 30 / 1 0.035 <0.035 / <0.035 0.120 / <0.035 69

Bromoxynil 31 / 0 30 / 0 0.035 <0.035 / <0.035 <0.035 / <0.035 67

Carbaryl 31 / 0 30 / 0 0.008 <0.008 / <0.008 <0.008 / <0.008 74

Carbofuran 31 / 0 30 / 0 0.028 <0.028 / <0.028 <0.028 / <0.028 71

Carbofuran, 3-hydroxy- 31 / 0 30 / 0 0.014 <0.014 / <0.014 <0.014 / <0.014 70

Chloramben 31 / 0 30 / 0 0.011 <0.011 / <0.011 <0.011 / <0.011 na

Chlorothalonil 31 / 0 30 / 0 0.035 <0.035 / <0.035 <0.035 / <0.035 45

Clopyralid 31 / 0 30 / 0 0.05 <0.05 / <0.05 <0.05 / <0.05 32

Dacthal, mono-acid- 30 / 0 30 / 0 0.017 <0.017 / <0.017 <0.017 / <0.017 133

Dicamba 30 / 0 30 / 0 0.035 <0.035 / <0.035 <0.035 / <0.035 71

Dichlobenil 31 / 0 30 / 0 0.020 <0.020 / <0.020 <0.020 / <0.020 42

Dichlorprop 31 / 0 30 / 0 0.032 <0.032 / <0.032 <0.032 / <0.032 66

Dinoseb 31 / 0 30 / 0 0.035 <0.035 / <0.035 <0.035 / <0.035 67

Diuron 31 / 0 30 / 0 0.020 <0.020 / <0.020 <0.020 / <0.020 72

DNOC 31 / 0 30 / 0 0.035 <0.035 / <0.035 <0.035 / <0.035 49

Esfenvalerate 31 / 0 30 / 0 0.019 <0.019 / <0.019 <0.019 / <0.019 22

Fenuron 31 / 0 30 / 0 0.013 <0.013 / <0.013 <0.013 / <0.013 71

Fluometuron 31 / 0 30 / 0 0.035 <0.035 / <0.035 <0.035 / <0.035 78

Linuron 31 / 0 30 / 0 0.018 <0.018 / <0.018 <0.018 / <0.018 71

MCPA 31 / 0 30 / 0 0.05 <0.05 / <0.05 <0.05 / <0.05 85

MCPB 31 / 0 30 / 0 0.035 <0.035 / <0.035 <0.035 / <0.035 54

Methiocarb 31 / 0 30 / 0 0.026 <0.026 / <0.026 <0.026 / <0.026 69

Methomyl 31 / 0 30 / 0 0.017 <0.017 / <0.017 <0.017 / <0.017 75

Table A1. Statistical summary of selected ground-water quality data from land-use wells in the Eastern Iowa Basins

study unit—Continued

[Ag, agricultural land use area; Ur, urban land use area; MRL, minimum reporting level; MDL, method detection limit for pesticides and pesticide metabolites; na; not applicable; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter; °C, degrees Celsius; <, less than; pCi/L, picocuries per liter;

μg/L, micrograms per liter; NWQL, U.S. Geological Survey National Water Quality Laboratory]

Constituent

or property

Samples/

detections

Ag wells

Samples/

detections

Ur wells

MRL or

MDL

Maximum/median

Ag wells

Maximum/median

Ur wells

Spike

recovery

(percent)
36 Effects of Land Use and Hydrogeology on the Water Quality of Alluvial Aquifers in Eastern Iowa and Southern Minnesota, 1997

Pesticides (NWQL schedule 2050), dissolved (μg/L)—Continued

1-Naphthol 31 / 0 30 / 0 0.007 <0.007 / <0.007 <0.007 / <0.007 0

Neburon 31 / 0 30 / 0 0.015 <0.015 / <0.015 <0.015 / <0.015 68

Norflurazon 31 / 0 30 / 0 0.024 <0.024 / <0.024 <0.024 / <0.024 72

Oryzalin 31 / 0 30 / 0 0.019 <0.019 / <0.019 <0.019/ <0.019 54

Oxamyl 31 / 0 30 / 0 0.018 <0.018 / <0.018 <0.018 / <0.018 63

Picloram 31 / 1 30 / 0 0.05 0.83 / <0.05 <0.05 / <0.05 124

Propham 31 / 0 30 / 0 0.035 <0.035 / <0.035 <0.035 / <0.035 84

Propoxur 31 / 0 30 / 0 0.035 <0.035 / <0.035 <0.035 / <0.035 94

Silvex 31 / 0 30 / 0 0.021 <0.021 / <0.021 <0.021 / <0.021 65

Triclopyr 31 / 0 30 / 0 0.05 <0.05 / <0.05 <0.05 / <0.05 69

Volatile organic compounds, total (μg/L)

1,1,1,2-Tetrachloroethane 31 / 0 30 / 0 0.044 <0.044 / <0.044 <0.044 / <0.044 na

1,1,1-Trichloroethane 31 / 0 30 / 2 0.032 <0.032 / <0.032 0.134 / <0.032 93

1,1,2,2-Tetrachloroethane 31 / 0 30 / 0 0.132 <0.132 / <0.132 <0.132 / <0.132 na

1,1,2-Trichloroethane 31 / 0 30 / 0 0.064 <0.064 / <0.064 <0.064 / <0.064 na

1,1,2-Trichloro-1,2,2-trifluoroethane 31 / 0 30 / 0 0.032 <0.032 / <0.032 <0.032 / <0.032 na

1,1-Dichloroethane 31 / 0 30 / 3 0.066 <0.066 / <0.066 0.364 / <0.066 na

1,1-Dichloroethene 31 / 0 30 / 1 0.044 <0.044 / <0.044 0.256 / <0.044 78

1,1-Dichloropropene 31 / 0 30 / 0 0.026 <0.026 / <0.026 <0.026 / <0.026 na

1,2,3,4-Tetramethylbenzene 31 / 0 30 / 0 0.23 <0.23 / <0.23 <0.23 / <0.23 na

1,2,3,5-Tetramethylbenzene 31 / 0 30 / 1 0.24 <0.24 / <0.24 15 / <0.24 na

1,2,3-Trichlorobenzene 31 / 0 30 / 0 0.266 <0.266 / <0.266 <0.266 / <0.266 na

1,2,3-Trichloropropane 31 / 0 30 / 1 0.070 <0.070 / <0.070 0.207 / <0.070 na

1,2,3-Trimethylbenzene 31 / 0 30 / 2 0.124 <0.124 / <0.124 0.242 / <0.124 na

1,2,4-Trichlorobenzene 31 / 0 30 / 0 0.188 <0.188 / <0.188 <0.188 / <0.188 na

1,2,4-Trimethylbenzene 31 / 1 30 / 2 0.056 0.193 / <0.056 4.49 / <0.056 na

1,2-Dibromo-3-chloropropane 31 / 0 30 / 0 0.214 <0.214 / <0.214 <0.214 / <0.214 na

1,2-Dibromoethane 31 / 0 30 / 0 0.036 <0.036 / <0.036 <0.036 / <0.036 na

1,2-Dichlorobenzene 31 / 0 30 / 1 0.048 <0.048 / <0.048 0.749 / <0.048 na

1,2-Dichloroethane 31 / 0 30 / 3 0.134 <0.134 / <0.134 33.4 / <0.134 95

cis-1,2-Dichloroethene 31 / 0 30 / 4 0.038 <0.038 / <0.038 58.8 / <0.038 na

trans-1,2-Dichloroethene 31 / 0 30 / 1 0.032 <0.032 / <0.032 3.87 / <0.032 na

1,2-Dichloropropane 31 / 0 30 / 1 0.068 <0.068 / <0.068 0.416 / <0.068 na

cis-1,3-Dichloropropene 31 / 0 30 / 0 0.092 <0.092 / <0.092 <0.092 / <0.092 na

1,3,5-Trimethylbenzene 31 / 0 30 / 2 0.044 <0.044 / <0.044 9.48 / <0.044 na

1,3-Dichlorobenzene 31 / 0 30 / 0 0.054 <0.054 / <0.054 <0.054 / <0.054 na

1,3-Dichloropropane 31 / 0 30 / 0 0.116 <0.116 / <0.116 <0.116 / <0.116 na

trans-1,3-Dichloropropene 31 / 0 30 / 0 0.134 <0.134 / <0.134 <0.134 / <0.134 na

1,4-Dichlorobenzene 31 / 0 30 / 1 0.050 <0.050 / <0.050 0.166 / <0.050 83

trans-1,4-Dichloro-2-butene 31/0 30 / 0 0.692 <0.629 / <0.629 <0.629 / <0.629 na

Table A1. Statistical summary of selected ground-water quality data from land-use wells in the Eastern Iowa Basins

study unit—Continued

[Ag, agricultural land use area; Ur, urban land use area; MRL, minimum reporting level; MDL, method detection limit for pesticides and pesticide metabolites; na; not applicable; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter; °C, degrees Celsius; <, less than; pCi/L, picocuries per liter;

μg/L, micrograms per liter; NWQL, U.S. Geological Survey National Water Quality Laboratory]

Constituent

or property

Samples/

detections

Ag wells

Samples/

detections

Ur wells

MRL or

MDL

Maximum/median

Ag wells

Maximum/median

Ur wells

Spike

recovery

(percent)
APPENDIX 37

Volatile organic compounds, total (μg/L)—Continued

2,2-Dichloropropane 31 / 0 30 / 0 0.078 <0.078 / <0.078 <0.078 / <0.078 na

2-Butanone 31 / 0 30 / 2 1.65 <1.65 / <1.65 47.4 / <1.65 na

2-Chlorotoluene 31 / 0 30 / 0 0.042 <0.042 / <0.042 <0.042 / <0.042 na

2-Hexanone 31 / 0 30 / 0 0.746 <0.746 / <0.746 <0.746 / <0.746 na

3-Chloropropene 31 / 0 30 / 0 0.196 <0.196 / <0.196 <0.196 / <0.196 na

4-Chlorotoluene 31 / 0 30 / 0 0.056 <0.056 / <0.056 <0.056 / <0.056 na

1-Isopropyl-4-methylbenzene 31 / 0 30 / 0 0.110 <0.110 / <0.110 <0.110 / <0.110 na

4-Methyl-2-pentanone 31 / 0 30 / 0 0.374 <0.374 / <0.374 <0.374 / <0.374 na

Acetone 31 / 0 30 / 1 4.9 <4.9 / <4.9 20.0 / <4.9 na

Acrolein 31 / 0 30 / 0 1.432 <1.432 / <1.432 <1.432 / <1.432 na

Acrylonitrile 31 / 0 30 / 0 1.226 <1.226 / <1.226 <1.226 / <1.226 na

tert-Amyl methyl ether 31 / 0 30 / 1 0.112 <0.112 / <0.112 0.158 / <0.112 na

Benzene 31 / 0 30 / 2 0.032 <0.032 / <0.032 230 / <0.032 na

Bromobenzene 31 / 0 30 / 0 0.036 <0.036 / <0.036 <0.036 / <0.036 na

n-Butylbenzene 31 / 0 30 / 1 0.186 <0.186 / <0.186 0.555 / <0.186 na

sec-Butylbenzene 31 / 0 30 / 1 0.048 <0.048 / <0.048 0.080 / <0.048 na

tert-Butylbenzene 31 / 0 30 / 0 0.096 <0.096 / <0.096 <0.096 / <0.096 na

Bromochloromethane 31 / 0 30 / 0 0.044 <0.044 / <0.044 <0.044 / <0.044 na

Bromodichloromethane 31 / 0 30 / 1 0.048 <0.048 / <0.048 0.611 / <0.048 99

Bromoform 31 / 0 30 / 0 0.104 <0.104 / <0.104 <0.104 / <0.104 81

Bromomethane 31 / 0 30 / 0 0.148 <0.148 / <0.148 <0.148 / <0.148 na

Bromoethene 31 / 0 30 / 0 0.100 <0.100 / <0.100 <0.100 / <0.100 na

Carbon disulfide 31 / 1 30 / 0 0.080 0.769 / <0.080 <0.080 / <0.080 na

Chlorobenzene 31 / 0 30 / 0 0.028 <0.028 / <0.028 <0.028 / <0.028 na

Chloroethane 31 / 0 31 / 1 0.120 <0.120 / <0.120 1.00 / <0.120 na

Chloroethene 31 / 0 30 / 2 0.112 <0.112 / <0.112 8.13 / <0.112 48

Chloroform 31 / 0 30 / 2 0.052 <0.052 / <0.052 15.8 / <0.052 na

Chloromethane 31 / 0 30 / 1 0.254 <0.254 / <0.254 0.400 / <0.254 na

Dibromochloromethane 31 / 0 30 / 0 0.182 <0.182 / <0.182 <0.182 / <0.182 92

Dibromomethane 31 / 0 30 / 0 0.05 <0.05 / <0.05 <0.05 / <0.05 na

Dichlorodifluoromethane 31 / 0 30 / 0 0.096 <0.096 / <0.096 <0.096 / <0.096 na

Dichloromethane 31 / 1 30 / 0 0.382 25.8 / <0.382 <0.382 / <0.382 na

Diethyl ether 31 / 0 30 / 0 0.170 <0.170 / <0.170 <0.170 / <0.170 na

Diisopropyl ether 31 / 0 30 / 2 0.098 <0.098 / <0.098 2.50 / <0.098 na

Ethyl methacrylate 31 / 0 30 / 0 0.278 <0.278 / <0.278 <0.278 / <0.278 na

Ethyl tert-butyl ether 31 / 0 30 / 1 0.054 <0.054 / <0.054 0.188 / <0.054 na

Ethylbenzene 31 / 0 30 / 1 0.030 <0.030 / <0.030 3.58 / <0.030 94

Hexachlorobutadiene 31 / 0 30 / 0 0.142 <0.142 / <0.142 <0.142 / <0.142 na

Table A1. Statistical summary of selected ground-water quality data from land-use wells in the Eastern Iowa Basins

study unit—Continued

[Ag, agricultural land use area; Ur, urban land use area; MRL, minimum reporting level; MDL, method detection limit for pesticides and pesticide metabolites; na; not applicable; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter; °C, degrees Celsius; <, less than; pCi/L, picocuries per liter;

μg/L, micrograms per liter; NWQL, U.S. Geological Survey National Water Quality Laboratory]

Constituent

or property

Samples/

detections

Ag wells

Samples/

detections

Ur wells

MRL or

MDL

Maximum/median

Ag wells

Maximum/median

Ur wells

Spike

recovery

(percent)
38 Effects of Land Use and Hydrogeology on the Water Quality of Alluvial Aquifers in Eastern Iowa and Southern Minnesota, 1997

Volatile organic compounds, total (μg/L)—Continued

Hexachloroethane 31 / 0 30 / 0 0.362 <0.362 / <0.362 <0.362 / <0.362 na

Isopropylbenzene 31 / 0 30 / 1 0.032 <0.032 / <0.032 0.371 / <0.032 na

Methyl acrylate 31 / 0 30 / 0 0.612 <0.612 / <0.612 <0.612 / <0.612 na

Methyl acrylonitrile 31 / 0 30 / 0 0.57 <0.57 / <0.57 <0.57 / <0.57 na

Methyl iodide 31 / 0 30 / 2 0.076 <0.076 / <0.076 0.60 / <0.076 na

Methyl methacrylate 31 / 0 30 / 0 0.350 <0.350 / <0.350 <0.350 / <0.350 na

Methyl tert-butyl ether 31 / 0 30 / 7 0.112 <0.112 / <0.112 100 / <0.112 86

Naphthalene 31 / 0 30 / 0 0.25 <0.25 / <0.25 <0.25 / <0.25 na

n-Propylbenzene 31 / 0 30 / 0 0.042 <0.042 / <0.042 <0.042 / <0.042 na

Styrene 31 / 0 30 / 0 0.042 <0.042 / <0.042 <0.042 / <0.042 na

Tetrachloroethene 31 / 0 30 / 2 0.038 <0.038 / <0.038 2.78 / <0.038 93

Tetrachloromethane 31 / 0 30 / 0 0.088 <0.088 / <0.088 <0.088 / <0.088 91

Tetrahydrofuran 31 / 0 30 / 0 1.148 <1.148 / <1.148 <1.148 / <1.148 na

Toluene 31 / 0 30 / 2 0.038 <0.038 / <0.038 12.1 / <0.038 na

o-Ethyl toluene 31 / 0 30 / 2 0.100 <0.100 / <0.100 <0.100 / <0.100 na

Trichloroethene 31 / 0 30 / 4 0.038 <0.038 / <0.038 0.946 / <0.038 95

Trichlorofluoromethane 31 / 0 30 / 0 0.092 <0.092 / <0.092 <0.092 / <0.092 na

m- and p-Xylene 31 / 0 30 / 2 0.064 <0.064 / <0.064 12.1 / <0.064 na

o-Xylene 31 / 0 30 / 2 0.064 <0.064 / <0.064 2.13 / <0.064 na

Table A1. Statistical summary of selected ground-water quality data from land-use wells in the Eastern Iowa Basins

study unit—Continued

[Ag, agricultural land use area; Ur, urban land use area; MRL, minimum reporting level; MDL, method detection limit for pesticides and pesticide metabolites; na; not applicable; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter; °C, degrees Celsius; <, less than; pCi/L, picocuries per liter;

μg/L, micrograms per liter; NWQL, U.S. Geological Survey National Water Quality Laboratory]

Constituent

or property

Samples/

detections

Ag wells

Samples/

detections

Ur wells

MRL or

MDL

Maximum/median

Ag wells

Maximum/median

Ur wells

Spike

recovery

(percent)
USGS/WRIR 99–4246 M.E. Savoca and others—EFFECTS OF LAND USE AND HYDROGEOLOGY ON THE WATER QUALITY OF ALLUVIAL

 AQUIFERS IN EASTERN IOWA AND SOUTHERN MINNESOTA, 1997