U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2010–5130

Prepared in cooperation with the

District Department of the Environment

Pesticides in Groundwater in the Anacostia River 

and Rock Creek Watersheds in Washington, D.C., 

2005 and 2008
Cover.  Examples of extensively developed land within 500 meters of two wells, WE Ca 32 and WE Ba 11, which in 2008 yielded groundwater samples that contained mixtures of six or more different pesticide compounds, lower Anacostia River watershed,

Washington, D.C. [Aerial photographs from U.S. Department of Agriculture (USDA) National Agriculture Imagery Program (NAIP).]
Pesticides in Groundwater in the Anacostia 

River and Rock Creek Watersheds in 

Washington, D.C., 2005 and 2008

By Michael T. Koterba, Cheryl A. Dieter, and Cherie V. Miller

Scientific Investigations Report 2010–5130

U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with the 

District Department of the Environment
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2010

For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, 

natural hazards, and the environment, visit http://www.usgs.gov or call 1-888-ASK-USGS

For an overview of USGS information products, including maps, imagery, and publications, 

visit http://www.usgs.gov/pubprod

To order this and other USGS information products, visit http://store.usgs.gov

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Koterba, M.T., Dieter, C.A., and Miller, C.V., 2010, Pesticides in groundwater in the Anacostia River and Rock Creek 

watersheds in Washington, D.C., 2005 and 2008: U.S. Geological Survey Scientific Investigations Report 2010–5130, 

90 p.

ISBN 978-1-4113-2942-3
iii

Contents

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

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

National and Regional Studies ...........................................................................................................4

Coastal Plain and Piedmont Settings near Washington, D.C. .......................................................6

Purpose and Scope ..............................................................................................................................6

Description of Study Area ............................................................................................................................7

Geology...................................................................................................................................................7

Groundwater Chemistry.....................................................................................................................12

Data-Collection Methods and Data Quality.............................................................................................12

Data-Collection Methods ..................................................................................................................14

Data Quality..........................................................................................................................................15

Pesticides in Groundwater.........................................................................................................................18

Pesticide Types and Frequencies of Detection .............................................................................18

Pesticide Concentrations and Human- and Aquatic-Health Criteria and 

Guidelines...............................................................................................................................21

Comparison of Pesticides in Groundwater: Washington, D.C. and Nearby 

Coastal Plain and Piedmont Areas.....................................................................................22

Land Use and Hydrogeologic Factors Related to Pesticide Occurrence...........................................24

Land Use...............................................................................................................................................24

Hydrogeologic Factors.......................................................................................................................29

Pesticide Detections and Types of Surficial Sediment........................................................29

Pesticide Detections and Well Depths...................................................................................33

Pesticide Detections and Groundwater Ionic Chemistry....................................................33

Variability of Precipitation ..........................................................................................................................40

Summary and Conclusions.........................................................................................................................42

Pesticide Types and Frequencies of Detection .............................................................................42

Pesticide Concentrations and Human and Aquatic Health .........................................................43

Comparison of Pesticide Occurrence with Studies in the Nearby Coastal 

Plain and Piedmont ...............................................................................................................43

Land Use and Hydrogeologic Factors Related to Pesticide Occurrence..................................44

Comparison with Regional Groundwater Studies: Pesticide Occurrence 

and Land Use and Hydrogeologic Settings.......................................................................45

Acknowledgments.......................................................................................................................................45

References Cited..........................................................................................................................................45

Appendix A: Water-Quality and Quality-Control Data Tables, 2008....................................................49

Appendix B: Assessment of Quality of Data Collected in 2005 and 2008...........................................81
iv

Figures

1–2. Maps showing—

1. Location of study area, including lower parts of the Anacostia River 

and Rock Creek watersheds, and Federal and other parklands in 

Washington, D.C...................................................................................................................3

2. Geology of Washington, D.C. .............................................................................................8

3–4. Diagrams showing—

3. Generalized hydrogeologic cross sections A-A’ and B-B’ of the lower 

Anacostia River watershed, Washington, D.C..............................................................10

4. Generalized geologic cross section C-C’ of surficial geology of the 

lower Rock Creek watershed, which includes the Rock Creek shear 

zone, Washington, D.C......................................................................................................11

5. Map showing estimated altitude of the regional water table and generalized 

direction of groundwater flow in the surficial aquifer, lower Anacostia River 

watershed, Washington, D.C., April 2006................................................................................13

6. Trilinear diagrams showing major-ion chemistry of groundwater, by 

geologic unit, for the lower Anacostia River watershed, September to 

December 2005............................................................................................................................14

7. Graphs showing pesticide detections in groundwater samples collected 

in (A) 2005 and (B) 2008 in relation to the percentage of developed space

(low, medium, and high-density residential, commercial, governmental, 

thoroughfare, and other structural) and open space (woodland, maintained 

grassland, and water) within 500 meters of each well used for sampling, 

lower Anacostia River and Rock Creek watersheds, Washington, D.C. ...........................28

8–10. Aerial photographs showing—

8. Examples of extensively developed land within 500 meters of two wells, 

(A) WE Ca 32 and (B) WE Ba 11, which in 2008 yielded groundwater 

samples that contained mixtures of six or more different pesticide 

compounds, lower Anacostia River watershed, Washington, D.C. ..........................30

9. Examples of low-to-moderately developed land within 500 meters of 

two wells, (A) WE Ca 34 and (B) WW Bc 11, which in 2008 yielded 

groundwater samples that contained no detectable pesticide 

compounds, lower Rock Creek and Anacostia River watersheds, 

Washington, D.C.................................................................................................................31

10. Examples of extensively developed land within 500 meters of two 

wells, (A) WE Ca 33 and (B) WW Bc 8, which in 2005 yielded 

groundwater samples that contained one or no detectable pesticide 

compounds, lower Anacostia River watershed, Washington, D.C. ..........................32

11–12. Trilinear diagrams showing—

11. Pesticides in groundwater samples in relation to variations in the 

major-ion chemistry of groundwater associated with geologic units 

and sediments, lower Anacostia River and Rock Creek watersheds, 

Washington, D.C., 2005 and 2008.....................................................................................38

12. Changes in major-ion chemistry in groundwater samples collected 

from seven wells in the lower Anacostia River and Rock Creek 

watersheds, Washington, D.C., 2005 and 2008 .............................................................39
v

B1. Graphs showing relative percent difference as a function of mean 

concentration for: (A) inorganic constituents (in milligrams per liter, mg/L) 

including calcium, magnesium, sodium, potassium, nitrate plus nitritenitrogen and ammonium-nitrogen, chloride, sulfate, manganese, and iron 

[with iron having the extreme value (40 percent) for one of two sets of 

duplicate measurements]; and (B) pesticides (in micrograms per liter, μg/L) 

including atrazine, prometon, simazine, desethylatrazine, dieldrin, fipronil, 

fipronil sulfone, fipronil sulfide, aminomethylphosphonic acid (AMPA), 

heptachlor expoxide, metolachlor, dichlorodiphenyldichloroethane (p,p’-DDD), 

and tebuthiuron...........................................................................................................................87

Tables

1. Identification, location, and construction information for groundwater 

monitoring wells in Washington, D.C. used to obtain pesticide samples 

from September through December 2005, and (or) August through 

September 2008...........................................................................................................................16

2. Detected pesticide compounds by type and use, detection frequency 

using either only or shallowest well at each site, maximum concentration, 

and related human- and aquatic-health concentration criteria and 

guidelines, for groundwater in Washington, D.C., 2005 and 2008.......................................19

3. Water-quality human- and aquatic-health assessment for groundwater 

samples collected from the surficial aquifer in Washington, D.C., 

2005 and 2008...............................................................................................................................22

4. Land use, geologic setting, and pesticide detections for groundwatermonitoring wells in Washington, D.C. sampled from September through 

December 2005 and (or) August through September 2008 ..................................................25

5. Geologic formations, overburden sediment, and pesticide occurrence in 

groundwater samples collected from monitoring wells in Washington, D.C., 

2005 and 2008...............................................................................................................................34

6. Geologic setting, apparent redox state, and major-ion chemistry of 

groundwater samples collected in Washington, D.C., 2005 and 2008 ...............................36

7. Precipitation and streamflow in the Washington, D.C. greater metropolitan 

area, 2004 through 2008 .............................................................................................................40

8. Major-ion composition of groundwater samples, 2005 and 2008 .......................................41

A1. Concentrations of major ions, nutrients, and pesticides in groundwater 

samples collected in the Anacostia River and Rock Creek watersheds in 

Washington, D.C., August to September 2008, and selected water-quality 

standards .....................................................................................................................................50

A2. Description of quality-control samples obtained in conjunction with the 

collection of groundwater samples in the Anacostia River and Rock Creek 

watersheds in Washington, D.C., August to September 2008.............................................79

B1. Concentrations in field blanks and groundwater samples with constituents 

detected in at least one field blank collected during groundwater sampling 

in Washington, D.C. in 2008.......................................................................................................83

B2. Means and relative percent differences in the concentrations of inorganic 

and organic constituents obtained from two sequential duplicate 

groundwater samples collected from wells in Washington, D.C. in 2008 .........................84
vi

Conversion Factors and Datums

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

yard (yd) 0.9144 meter (m)

centimeter (cm) 0.3937 inch (in.)

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft)

kilometer (km) 0.6214 mile (mi)

Area

acre 0.004047 square kilometer (km2)

section (640 acres or 1 square mile) 259.0 square hectometer (hm2

)

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2)

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

 °F = (1.8 × °C) + 32

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 

25 °C).

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) 

or micrograms per liter (μg/L).

B3. Mean and relative standard deviation of pesticide surrogate compound 

recoveries for each laboratory method and from laboratory-spiked 

groundwater samples in 2005 and 2008, and results of the WilcoxonMann-Whitney rank sum test to determine if ranked recoveries in 2005 

differed from ranked recoveries in 2008 .................................................................................85

B4. U.S. Geological Survey laboratory reporting and detection levels for 

pesticide schedules used in 2005 and 2008, and for which at least one 

pesticide was detected in a groundwater sample in 2005 or 2008.....................................87

B5. Pesticide detections and concentrations in groundwater samples 

collected from wells sampled in 2005 and 2008 and analyzed for similar 

compounds using the same laboratory schedules in 2005 and 2008 .................................88

B6. Pesticide detections in groundwater attributed to the addition of a 

laboratory schedule (LS 2033) in 2008 that was not used in 2005, or the 

addition of new pesticide compounds into laboratory schedules .....................................89


Pesticides in Groundwater in the Anacostia River 

and Rock Creek Watersheds in Washington, D.C., 

2005 and 2008

By Michael T. Koterba, Cheryl A. Dieter, and Cherie V. Miller

Abstract

The U.S. Geological Survey (USGS), in cooperation 

with the District Department of the Environment, conducted 

a groundwater-quality investigation to (a) determine the presence, concentrations, and distribution of selected pesticides 

in groundwater, and (b) assess the presence of pesticides in 

groundwater in relation to selected landscape, hydrogeologic, and groundwater-quality characteristics in the shallow 

groundwater underlying the Anacostia River and Rock Creek 

watersheds in Washington, D.C. With one exception, well 

depths were 100 feet or less below land surface. The USGS 

obtained or compiled ancillary data and information on land 

use (2001), subsurface sediments, and groundwater samples 

from 17 wells in the lower Anacostia River watershed from 

September through December 2005, and from 14 wells in the 

lower Anacostia River and lower Rock Creek watersheds from 

August through September 2008.

Twenty-seven pesticide compounds, reflecting at least 

19 different types of pesticides, were detected in the groundwater samples obtained in 2005 and 2008. No fungicides 

were detected. In relation to the pesticides detected, degradate 

compounds were as or more likely to be detected than applied 

(parent) compounds. 

The detected pesticides chiefly reflected herbicides commonly used in urban settings for non-specific weed control or 

insecticides used for nonspecific haustellate insects (insects 

with specialized mouthparts for sucking liquid) or termitespecific control. Detected pesticides included a combination 

of pesticides currently (2008) in use, banned or under 

highly restricted use, and some that had replaced the banned 

or restricted-use pesticides. The presence of banned and 

restricted-use pesticides illustrates their continued persistence 

and resistance to complete degradation in the environment. 

The presence of the replacement pesticides indicates the susceptibility of the surficial aquifer to contamination irrespective 

of the changes in the pesticides used. 

A preliminary review of the data collected in 2005 and 

2008 indicated that differences in the surficial geology, land 

use (as a surrogate for pesticide use), and above-average 

precipitation for most of 2004 through 2008, as well as differences in the number and performance of USGS laboratory 

methods used, could have led to more pesticides detected in 

groundwater samples collected in 2008 than in groundwater 

samples collected in 2005. Thus, although data from both 

years of collection were used for interpretive analysis, emphasis was placed on the analysis of the data obtained in 2008. 

The presence of pesticides in shallow groundwater (less 

than approximately 100 ft (feet), or 30 m (meters), below 

land surface) indicated at least the upper surficial aquifer in 

Washington, D.C. was susceptible to contamination. One or 

more herbicides or insecticides were detected in groundwater 

samples collected from 50 percent of the shallow wells 

sampled in 2005, and from 62 percent of the shallow wells 

sampled in 2008. 

Differences among types of pesticides in shallow groundwater were apparent. The most frequently detected class of 

herbicides was the s-triazine compounds—atrazine, simazine, 

or prometon, or the atrazine-degradate compounds—2-chloro4-ethylamino-6-amino-s-triazine (desethylatrazine or CIAT) 

and 2-chloro-4-isopropylamino-6-amino-s-triazine (hydroxyatrazine or OIET). The next most frequently detected classes of 

herbicides were the chloroacetanilides, including metolachlor 

and acetochlor, and the ureic herbicides, including diuron (and 

degradate, 3,4-dichloroaniline), fluometuron, metsulfuron 

methyl, sulfameturon, bromacil, and tebuthiuron. 

Insecticides also were detected, but less frequently than 

herbicides, with one or more insecticides present in groundwater samples from 38 percent of shallow wells sampled in 2008. 

Detected insecticides included parent or degradate compounds 

commonly used for either nonspecific or haustellate (sucking) 

insects, including chlorpyrifos and dichlorodiphenyldichloroethane (p,p’-DDD; a degradate of dichlorodiphenyltrichloroethane, DDT), and for termite control, including dieldrin, 

chlordane, heptachlor epoxide, (a degradate of heptachlor), 

fipronil, and the sulfone and sulfide degradates of fipronil.

The concentrations of individual pesticides in shallow 

groundwater in both years were low. Maximum concentrations 

were no greater than a few tenths of a microgram per liter 

(μg/L); typical concentrations often were less than 
2 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

0.1 μg/L. Multiple pesticides, however, commonly were present in groundwater. For example, in 2008, approximately 88 

percent (7 of 8) of the wells that yielded a sample with at least 

one detectable pesticide contained five or more pesticides. 

The highest number of detections occurred in a groundwater 

sample from well WE Ca 32, which is located in a highly 

developed urban area; this sample contained 15 different 

pesticide residues.

In relation to human and aquatic health, no pesticide concentration in either 2005 or 2008 exceeded Federal drinkingwater standards. Groundwater samples from a few sites, 

however, contained levels of chiefly banned or restricted-use 

pesticides that exceeded other human-health and (or) aquatichealth guidelines. For example, concentrations of dieldrin 

in 2008 groundwater samples from three wells—WE Ca 32 

(0.028 μg/L), WE Ba 11 (0.016 μg/L), and WW Ac 8 (0.014 

μg/L)—fell within the range of concern for 2004 Federally 

approved non-regulatory USGS Health-Based Assessment 

benchmarks (0.002 to 0.2 μg/L), and exceeded earlier (1999) 

Federal criteria for drinking water (0.000052 μg/L). Other 

individual compounds whose concentrations exceeded 1999 

Federal guidelines for samples from one or more of these 

three sites, or another site, included p,p’-DDD, dichlorodiphenyldichloroethylene (p,p’-DDE; another degradate of DDT), 

chlordane, and heptachlor epoxide. Pesticide concentrations 

in groundwater also were compared to three aquatic-health 

guidelines for freshwater (United States, Great Lakes, or 

Canada). One or more of these guidelines were exceeded in 

groundwater samples obtained in 2005 or 2008 for one or 

more of the compounds chlordane, dieldrin, heptachlor epoxide, p,p’-DDE, p,p’-DDD, and chlorpyrifos.

The spatial distribution of pesticides in the shallow 

groundwater appeared to be related, in part, to land use, a surrogate for pesticide use. Although most of the wells sampled 

in this study are in parklands or other relatively open and 

accessible space, multiple pesticides most often were detected 

in 2008 groundwater samples collected from wells where a 

considerable percentage (in excess of 60 percent) of the land 

within a 500-m radius is developed space (residential, commercial, or other urban infrastructure). Insecticides were 

detected in wells surrounded by at least 50 percent, and most 

commonly by more than 80 percent, development. Well WE 

Ca 32, the site associated with the highest number of pesticide 

residues in groundwater (8 herbicides and 7 insecticides), 

is in a small residential park, where 99 percent of the surrounding land is well-maintained residential and commercial 

development.

The vertical distribution of detected pesticides in shallow 

groundwater appeared to be related, in part, to depth below 

land surface, surficial-bedrock type, and differences in the 

chemistry of shallow groundwater. Pesticides were detected 

at relatively shallow depths in wells that may not have fully 

penetrated the shallow aquifer. For wells in which at least one 

pesticide was detected, the median depth below land surface to 

the top of the well screen was 5.8 m, and the maximum depth 

was 8.5 m. 

Among the types of surficial materials in which wells 

were completed—alluvium, terrace deposits, or Potomac 

Formation sub- or outcrops in the Coastal Plain Province, 

and saprolite or fractured bedrock (Laurel and Sykesville 

Formations) underlying saprolite in the Piedmont Province—

no pesticides were detected in groundwater associated 

with wells completed in the alluvium or fractured bedrock. 

Detections occurred in some but not all wells completed in 

the other surficial materials. Overall, the pattern in occurrence 

appeared related to the local permeability of these sediments 

and groundwater chemistry. Groundwater with multiple 

pesticide detections tended to occur in permeable sediments 

(absent any appreciable overlying clay, silt, or clay-silt layers), 

in conjunction with other common urban contaminants 

(elevated chloride in excess of tens to hundreds of milligrams 

per liter (mg/L), and oxic, rather than reduced, groundwater as 

evidenced by elevated (in excess of 5 mg/L) concentrations of 

nitrate).

The results of this investigation were compared to results 

from two other similar and recent studies on pesticide occurrence in the shallow aquifer. These included a study in the 

nearby Maryland and Delaware Coastal Plain Physiographic 

Province and one in the Maryland and Virginia Piedmont 

Physiographic Province. Results from these studies were 

similar to the current study in relation to (a) the types, frequencies, concentrations, and mixtures of pesticides detected; (b) 

compounds that exceeded human-and aquatic-health criteria; 

and (c) the occurrence and distribution of pesticides within 

the surficial aquifer in relation to depths, sediment types, and 

groundwater chemistries.

Introduction

Potential contamination of shallow groundwater (defined 

in this report as 100 feet or less below land surface) by pesticides within the Piedmont and Coastal Plain Physiographic 

Provinces that underlie the Anacostia River and Rock Creek 

watersheds in Washington, D.C. (fig. 1) is of interest for two 

reasons. First, in the part of Washington, D.C. underlain by 

Piedmont rocks, the aquifer chiefly consists of in-situ weathered rocks (saprolite) and the underlying shallow fractured 

bedrock, which are the only major water-bearing units for 

groundwater supplies. In the part of Washington, D.C. underlain by Coastal Plain sediments, the surficial aquifer is the 

main source of recharge to deeper confined aquifers, which are 

major sources of groundwater for drinking or other supplies 

in the region. Second, the surficial aquifer is a major source of 

base flow to local streams within Washington, D.C., including 

the Anacostia River and Rock Creek (fig. 1). This base 

flow helps to maintain streamflows during dry weather into 

important estuaries—the Anacostia and Potomac Rivers, and 

ultimately the Chesapeake Bay. Thus, the quality of groundwater discharged from the surficial aquifer into streams in 

Washington, D.C. plays a role in the ecological health of local 

as well as larger downstream surface-water bodies.
Introduction 3

Figure 1. Location of study area, including lower parts of the Anacostia River and Rock Creek watersheds, and Federal and other 

parklands in Washington, D.C.
4 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Both Anacostia Park and Rock Creek Park, including 

their streams (fig. 1), are considered local resources by 

Washington, D.C. residents. Anacostia Park is managed by 

the National Park Service (NPS), and since the late 1980s, 

organizations such as the Anacostia Watershed Restoration 

Committee (AWRC) and the Anacostia Watershed Toxics 

Alliance (AWTA) have facilitated efforts to rehabilitate the 

watershed. Recent improvements in the Anacostia River 

include wetland and riparian-zone restoration, trash and 

debris reduction, replacement of leaking sewer infrastructure, 

and low-impact development (LID) that uses passive 

engineering improvements to redirect and process storm 

runoff (Metropolitan Washington Council of Governments 

(MWCOG), 1998, 2003; Anacostia Watershed Toxics Alliance, 

2001). 

The activities of the NPS, AWRC, AWTA, MWCOG, 

and citizens groups in Washington, D.C. reflect their concerns 

regarding the quality of park waters. Miller and others 

(2007) recently described some of the adverse water-quality 

conditions in Anacostia watershed streams, noting that this 

watershed is listed as one of three Regions of Concern by 

the Chesapeake Bay Program (CBP). The latter program has 

stressed that segments of the river are on Maryland’s 303(d) 

list for a number of contaminant issues, including bacteria, 

biological integrity, polychlorinated biphenyls (PCBs), and 

the pesticide heptachlor epoxide (Chesapeake Bay Program, 

2000). Recent studies by Pinkney and others (2001, 2004) 

reported severe chemical effects on brown bullhead in the 

Anacostia River in Washington, D.C., and stated that the likely 

causative chemicals for the observed diseases in brown bullhead in the Anacostia River are polyaromatic hydrocarbons 

(PAHs), DDT, PCBs, and (or) chlordane. 

Sedimentation remains a continuous and serious problem 

in the Anacostia River because of development. There has 

been a substantial narrowing of the Anacostia River channel 

(Williams, 1977). Yorke and Herb (1978) documented large 

increases in land clearing for urban and suburban development 

in the upper Northwest Branch of the Anacostia during the 

1960s and 1970s, and noted that this resulted in increased 

sediment loads in the urbanized areas of the watershed. They 

found that 73 percent of the annual load occurred during flows 

whose duration amounted to just 2.2 percent of the year, and 

94 percent of the annual load occurred during flows whose 

duration amounted to just 5.7 percent of the year. Yorke and 

Herb (1978) also concluded that major sources of sediment 

in the watershed were cropland, urban land, and construction 

sites.

Rock Creek and Rock Creek Park are managed by the 

NPS and the Maryland-National Capital Park and Planning 

Commission. Concerns have arisen regarding the quality 

of creek water. Although the effects of human activities on 

stream biota in Rock Creek Park possibly are not as severe as 

those found in the Anacostia River, several studies have demonstrated that many anthropogenic chemicals are present at 

relatively low to moderate concentrations in the bed sediments 

and the creek water (CH2M Hill, 1977; Anderson and others, 

2002; Miller and others, 2007; Phelan and Miller, in press). 

This has raised concerns among Washington, D.C. residents 

about the quality and chemistry of surface water and groundwater in Rock Creek Park and the watershed.

National and Regional Studies

As of 2005, little data and information were available 

to assess pesticide contamination of the surficial aquifer 

underlying Washington, D.C. Since the mid-1980s, however, investigations by the USGS National Water-Quality 

Assessment (NAWQA) Program and others have documented 

the presence and distribution of pesticides, and identified 

landscape and subsurface characteristics related to their presence, in surficial aquifers throughout the Nation, including the 

Coastal Plain near Washington, D.C. The evidence of possible 

adverse effects on groundwater quality in surficial aquifer 

settings described in NAWQA studies, combined with greater 

Federal regulation of pesticides in groundwater, and the lack 

of information and data on pesticides in groundwater within 

Washington, D.C., have been catalysts for this study, which 

was conducted by the USGS, in cooperation with the District 

Department of the Environment (DDOE) in 2005 and 2008.

From a national perspective, and given the abundance 

of row crops, pastureland, livestock, and other agricultural 

activities in the Nation, the occurrence and distribution of 

selected pesticides (parent and degradate compounds) in 

shallow groundwater beneath agricultural areas, including 

the Coastal Plain Physiographic Province in Maryland, have 

been examined through several NAWQA studies (Ator, 2008; 

Denver and Ator, 2006; Gilliom and others, 2006; Kiely and 

others, 2004; Kolpin and others, 1997; Shedlock and others, 

1999; Barbash and Resek, 1996; Gilliom and others, 1995). 

Additional NAWQA or other national and regional studies 

have addressed the occurrence and distribution of pesticides 

in shallow groundwater beneath urban areas—residential, 

commercial, and industrial—including the Coastal Plain (Ator, 

2008; Flanagan and others, 2001; Andrews and others, 1998; 

Berndt and others, 1998; Ator and Denis, 1997, Kolpin and 

others, 1997; and Bruce, 1995).

General results from these studies in agricultural and 

urban settings that are relevant to Washington, D.C. are as 

follows: 

a. Pesticides have been used in large metropolitan areas 

similar to Washington, D.C., as well as in agricultural 

areas, and their use likely will continue in order to 

control pests in these settings;

b. Shallow groundwater beneath large metropolitan 

areas similar to Washington, D.C., as well as beneath 

agricultural areas, has been contaminated by modern 

(post-1940s) pesticides;

c. The types, occurrence, and distribution of pesticides in 

shallow groundwaters reflect patterns in land use and 

pesticide application, the chemical and physical prop-
Introduction 5

erties of different pesticides, and natural factors—for 

example, rainfall amounts and soil or sediment permeability—all of which collectively determine the fate 

and movement of pesticides in these environments; 

d.The pesticides that have been most frequently detected 

generally are among the most frequently used, are 

relatively water soluble, and are highly mobile or at 

least highly persistent (resistant to degradation) in the 

environment;

e. The detected pesticides often include degradate forms, 

whose individual concentrations can exceed the concentrations of the applied parent forms of the compounds; and

f. Pesticides often are found at low concentrations, in 

mixtures, and with few exceedances of regulatory 

standards or guidelines for human and aquatic health, 

but for many of the detected parent or degradate 

compounds or mixtures of compounds, there are no 

standards or guidelines.

For example, nationally, in 2000 and 2001, approximately 75 

percent of all pesticide use for weed and insect control was 

agricultural. The other 25 percent of pesticide use occurred in 

nonagricultural settings—residential, commercial, industrial, 

transportation, public-health, and other nonagricultural applications (Kiely and others, 2004). In addition, Kiely and others 

(2004) noted that approximately 40 percent of all fungicide 

use in the Nation occurred in nonagricultural settings. 

The apparent relation between pesticide detections and 

pesticide mobility has been described by Barbash and Resek 

(1996). Mobility of a pesticide appears to be related to its 

solubility in water and its ability to move (partition) among 

different environmental media—air, water, soil, and biota. For 

example, a pesticide that is highly soluble in water, but does 

not readily volatilize or strongly sorb to organic matter, is apt 

to be detected in groundwater. A highly volatile pesticide that 

readily passes into the air, or a pesticide that strongly binds 

to organic matter in the soil, is unlikely to be detected in 

groundwater. 

Persistence also appears to play a role in pesticide detectability (Barbash and Resek, 1996). A pesticide that is highly 

resistant to degradation is considered persistent, and can 

remain detectable in the environment (air, soil, or water) for 

years to decades after application.

A pesticide often is transformed into one or more compounds commonly referred to as degradates. Furthermore, 

most pesticide degradation appears to occur in the soil zone 

where abiotic chemical and biotic (animal, plant, or microbial) 

processes are most active (Barbash and Resek, 1996). 

Upon transformation of the parent compound, a variety of 

degradates can form before the soil water that contains these 

degradates percolates through the vadose zone and reaches 

the water table. Thus, degradation could make detection of the 

applied form of the pesticide difficult; there could be multiple 

degradate forms of the pesticide present whose detectability 

depends on the state of current analytical methods.

Whether or not a water-soluble pesticide (parent or 

degradate compound) is mobilized depends in part on the ease 

with which water can infiltrate and percolate through the soil 

and surficial sediments. As noted earlier, national and regional 

studies have found pesticides generally are present most 

frequently in shallow groundwater beneath well-drained areas 

with highly permeable sandy soils and with sand and gravel 

aquifers; permeable shallow sediments occur commonly in 

Washington, D.C.

Whether the pesticides present in groundwater are 

cause for concern is the subject of considerable debate. In 

the previously cited national and regional studies, this concern chiefly was addressed on the basis of whether or not the 

detected pesticide compound(s) occurred at concentrations 

that are known or deemed likely to result in human-health or 

ecological effects. For human-health regulated compounds, 

the basis for comparison generally has been Federal drinkingwater standards (for example, U.S. Environmental Protection 

Agency, 2004). For selected compounds not covered by 

drinking-water standards, the U.S. Environmental Protection 

Agency (USEPA) initially provided recommendations 

(U.S. Environmental Protection Agency, 1999) and recently 

approved Health Assessment benchmarks developed by the 

USGS (Toccalino and others, 2004) to assess groundwater 

quality. In the national and regional studies noted earlier, pesticide compounds that are toxic or known or suspected carcinogens were present in shallow groundwater. In addition, other 

pesticide (parent and degradate) compounds, whose potential 

human-health effects, individually or as collective mixtures, 

are largely unknown, also were present in groundwater.

For ecological health, the basis for comparisons has 

varied and included USEPA national recommended long-term 

aquatic chronic-exposure criteria for continuous concentrations in freshwater (U.S. Environmental Protection Agency, 

1999), the U.S. and Canada International Joint Commission 

(International Joint Commission, 1989) Great Lakes aquatichealth objectives, and Canadian guidelines for the protection of aquatic health (Canadian Council of Ministers of the 

Environment, 2007). In addition, a number of other pesticides 

(parent and degradate) compounds, whose potential aquatichealth effects, individually or as collective mixtures, are 

largely unknown, were present in groundwater.

Exceedances of either human- or aquatic-health guidelines are a concern in the Anacostia River and Rock Creek in 

Washington, D.C., and therefore were considered in this study. 

Groundwater that contains concentrations of pesticides that 

exceed Federal drinking-water standards could prevent the use 

of this water as an alternative source of public drinking water 

in the future. In addition, there could be human-health implications where local supplies (such as private domestic-use 

wells) are not regulated or routinely monitored. Exceedances 

of aquatic-health guidelines also are of concern in Washington, 

D.C. because of the potential implications for the health of 

local streams, estuaries, and the Chesapeake Bay.
6 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Coastal Plain and Piedmont Settings near 

Washington, D.C.

National and regional studies can provide a broad indication of the types, occurrence, and distribution of pesticides 

detected in shallow groundwaters in different climatic, 

land-use, and hydrogeologic settings, and help to identify 

factors that could influence the occurrence, fate, and transport of pesticides to shallow groundwater. Therefore, the 

regional and local studies that have been conducted near and 

in Washington, D.C. and in Maryland, Virginia, and Delaware, 

and in relation to shallow groundwater in the Coastal Plain and 

Piedmont Provinces, are the most relevant to this study.

From a hydrologic perspective, annual rainfall in the 

Maryland-Virginia-Washington, D.C. area is relatively 

abundant, averaging approximately 41 inches per year from 

1901–2001, and is fairly well distributed throughout the year 

(Wheeler, 2003). About one-quarter to one-third of this annual 

rainfall infiltrates through the soil zone and percolates down 

through unconsolidated materials to recharge the unconfined 

surficial aquifer that underlies most of the Coastal Plain and 

Piedmont aquifers in this area (Denver and Ator, 2006). 

Although an adequate amount of low-ionic-strength rainfall and recharge occurs in the region, a number of local and 

regional studies have shown that the chemistry of groundwater 

in the surficial aquifer beneath recharge areas, such as in the 

Coastal Plain in Maryland, often reflects recent human activities (Desimone and others, 2009; Ator, 2008; Debrewer and 

others, 2007; Klohe and Debrewer, 2007; Focazio and others, 

1998, 2002). The main observed effects of human activities 

are elevated concentrations of chemicals (for example, nutrients and pesticides) from development and agriculture. This 

illustrates the susceptibility of these Coastal Plain landscapes 

to leaching of applied or disposed-of chemicals, including 

selected pesticides, during recharge to the underlying surficial 

aquifer.

Regional and local studies indicate that contaminated 

groundwater potentially can travel through the surficial aquifer 

and either discharge into streams or continue into outcrop or 

subcrop areas of the underlying confined aquifers (Potomac 

Formation). In either case, the time of travel could be relatively rapid. For example, Denver and Ator (2006) noted that 

groundwater in the surficial aquifer in the Coastal Plain of 

Maryland and Delaware that is contaminated with pesticides 

appears to be relatively young with an apparent age of 50 

years or less since the time of recharge. In addition, many of 

the same pesticides present in shallow groundwater also are 

present in nearby streams during base flow in the Coastal Plain 

of Maryland, Delaware, and Washington, D.C. (Shedlock and 

others, 1999; Denver and Ator, 2006; Miller and others, 2007), 

which indicates relatively short times of travel.

 Pesticides seldom have been detected downdip in the 

confined aquifers of the Coastal Plain. Ator (2008) attributed 

the lack of occurrence of pesticides in the confined aquifers 

to (a) the long times of travel for groundwater, given that 

the apparent age of water in the confined aquifers generally 

predates the use of modern pesticides, and (b) the relative 

impermeability of confining-bed silt and clay sediments that 

separate the shallow surficial aquifer from the underlying confined aquifers and the confined aquifers from one another.

Although groundwater quality in the surficial aquifer 

in the Coastal Plain near Washington, D.C. has been the 

subject of considerable investigation, less is known about the 

potential contamination of groundwater by pesticides in the 

surficial aquifer in the Piedmont Province near Washington, 

D.C. The most recent, relevant, and nearby study by Banks 

and Reyes (2009) indicates that the Piedmont surficial aquifer 

in Maryland and Virginia adjacent to parts of Washington, 

D.C. is likely as susceptible as the nearby surficial aquifer in 

the Coastal Plain of Maryland and Delaware to nutrient and 

pesticide contamination by human activities related to modern 

land use.

Recent and nearby studies clearly indicate the potential 

for human activities to adversely affect the quality of streamwater and groundwater in the surficial aquifer in the Piedmont 

and Coastal Plain settings in Washington, D.C. A key limitation to conducting such groundwater studies in Washington, 

D.C., however, has been the paucity of wells and, hence, the 

means to obtain data. Johnston (1964) noted this problem. 

He relied on historical articles and other anecdotal records to 

document that problems with stream and well contamination 

from development began affecting large communities throughout Washington, D.C. early in the 20th century. By the 1920s, 

many shallow wells and streams were abandoned as sources 

of public water supply as withdrawals of surface water for 

public water supplies increased from the Potomac River. By 

the 1960s, only a few deeply drilled and chiefly artesian wells 

in the Coastal Plain within Washington, D.C. continued to be 

used by commercial establishments. In conjunction with the 

increased reliance on the Potomac River rather than groundwater for public water supplies, increased development coincided with the loss of areas sufficiently accessible to install 

wells, which further limited the ability to conduct such studies.

Purpose and Scope

This report presents the types, frequencies of occurrence, 

and concentrations of selected pesticide (parent and degradate) 

compounds in shallow groundwater in the lower Anacostia 

River and lower Rock Creek watersheds within Washington, 

D.C. The concentrations of detected pesticides are described in 

relation to human- and aquatic-health criteria and guidelines. 

The types and frequencies of occurrence of detected pesticides 

are further discussed in relation to local, regional, and national 

studies of pesticide occurrence in groundwater that include 

nearby parts of the Coastal Plain and Piedmont Physiographic 

Provinces. In addition, the occurrence and distribution of the 

detected pesticides are examined in relation to local differences in land use, surficial materials, and the inorganic chemistry of groundwater associated with sampling sites distributed 

among both watersheds and physiographic settings within 
Description of Study Area 7

Washington, D.C. All data obtained in the field or from the 

analysis of groundwater and quality-control samples collected 

and analyzed in 2008 are summarized in this report.

Description of Study Area

Washington, D.C. occupies a total area of about 68.3 mi2

(square miles) and is bordered by the States of Maryland to the 

southeast, northeast, and northwest, and Virginia to the southwest (fig. 1). As the Nation’s capital, Washington, D.C. generally is perceived as a major metropolitan area, but a considerable part of the capital is water and parkland. Approximately 

10 percent (6.9 mi2) of Washington, D.C. is open water (U.S. 

Census Bureau, 2008), with three major natural flowing 

streams—the Potomac River, which forms the southern border 

of Washington, D.C.; the Anacostia River, which drains most 

of the eastern part of Washington, D.C.; and Rock Creek, 

which drains most of the western part of Washington, D.C. 

(fig. 1). About 19.4 percent (13.3 mi2) of Washington, D.C. is 

parkland, and most (89 percent, 11.8 mi2) of this parkland is 

managed by the NPS, including the largest parks, Rock Creek 

and Anacostia, as well as a number of small parks, such as 

the Chesapeake and Ohio Canal National Historical Park, the 

National Mall, and Theodore Roosevelt Island (The Trust for 

Public Land, 2009).

Although surface-water watersheds are used in this 

report to define different parts of the study area that vary in 

hydrogeologic characteristics, the surface-water watershed 

boundaries are not necessarily coincident with the shallow 

groundwater-flow boundaries.

Geology

Washington, D.C. is located on the transition zone 

between the Piedmont and Coastal Plain Physiographic 

Provinces (fig. 1). Deeply weathered and exposed igneous 

and metamorphic rocks of the Piedmont are at land surface 

in the western part of Washington, D.C. and dip to the southeast at about 125 feet per mile (Johnston, 1964). These rocks 

are overlain by an eastward-thickening wedge of unconsolidated Coastal Plain sediments composed of silts, clays, 

sands, and gravels that increase in thickness to more than 

1,500 ft (feet) in the southeastern Coastal Plain of Washington, 

D.C. This unconformity between the Piedmont and Coastal 

Plain Physiographic Provinces is referred to as the Fall Line 

(Johnston, 1964).

The physiography of Washington D.C. can be described 

in relation to its two major watersheds—the Anacostia River 

watershed to the east, and the Rock Creek watershed to the 

west (fig. 1). The Anacostia River watershed covers approximately 26 mi2

 within Washington, D.C. and lies entirely 

within the Coastal Plain. The Rock Creek watershed covers 

approximately 15.9 mi2 within Washington, D.C. and includes 

Piedmont rock to the west and Coastal Plain sediments to the 

east.

Coastal Plain sediments beneath the Anacostia River 

watershed form a system of confined and unconfined aquifers 

(S.W. Ator, U.S. Geological Survey, written commun., 2010). 

To the north, coarse sediments (sand-dominated lithofacies) 

of the Cretaceous-age Potomac Formation (Kps) form an 

aquifer that crops out and subcrops in the northwestern 

part of the watershed (fig. 2, Kps, and fig. 3, section A-A’). 

Downdip from the outcrop and to the southeast, the aquifer 

is confined by an overlying clay-dominated lithofacies (Kpc) 

of the Potomac Formation (fig. 2, Kpc, fig. 3, section A-A’). 

Downriver to the south and as the river valley widens, cross 

sections of the watershed show an increasing series and thickness of interbedded Tertiary and Quaternary terrace deposits 

(sands, silts, and clays), with local heterogeneities, including 

fill (fig. 2 and fig. 3, section B-B’), that form an unconfined 

surficial aquifer, with local perched and semi-confined 

conditions above the Potomac Formation (clay-dominated 

lithofacies).

Rock Creek watershed lies on the transition zone between 

the Piedmont and the Coastal Plain (figs. 1, 2). Because of 

historical orogenic activity, this transition zone has a complex 

surficial geology (Southworth and Denenny, 2006). For brevity, only formations relevant to the locations of wells used for 

pesticide and other water-quality sampling in the Rock Creek 

watershed are discussed in the current report.

Surficial geologic formations associated with well 

sites used in this study and in Rock Creek watershed in 

Washington, D.C. include the Piedmont Sykesville (€s) and 

Laurel (€l) Formations, and the Coastal Plain Potomac (Kp) 

Formation and terrace and alluvial deposits (figs. 2, 4, €s, €l, 

and Kp). The Sykesville and Laurel Formations are the major 

exposed and fractured sedimentary rocks in Rock Creek watershed and where not truly exposed can be overlain by saprolite 

(bedrock weathered in place). 

Southworth and Denenny (2006) described the Sykesville 

Formation in Washington, D.C. as a sedimentary mélange of 

a gray matrix of quartz and feldspar that supports rounded 

and elliptical white and clear quartz cobbles, blocks of dark 

gray phyllonite, light gray migmatite and metagraywacke; 

dark greenish black mafic, ultramafic, and metagabbro rocks; 

and light gray metafelsite and plagiogranite. The Sykesville 

Formation (€s) is exposed at the mouth of Rock Creek and 

trends northerly and northwesterly through the Rock Creek 

watershed and Washington, D.C. (figs. 2, 4, €s). 

The Laurel Formation is described by Southworth and 

Denenny (2006) as a sedimentary mélange that is similar to 

some rocks in the Sykesville Formation. Rocks of the Laurel 

Formation have a matrix of quartz and feldspar that supports 

fragments, elongated cobbles, and bodies of meta-arenite 

and muscovite-biotite schist. The Laurel Formation (€l), 

however, locally consists of more than 50 percent meta-arenite 

clasts. This unit crops out in the Rock Creek drainage area in 

Klingle Valley and trends northerly through the watershed in 

Washington, D.C. (figs. 2, 4, €l).
8    Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Figure 2.  Geology of Washington, D.C. (modified from Southworth and Denenny, 2006).
Description of Study Area 9

West of Rock Creek is a set of long, near-vertical faults 

that trends north to south (figs. 2, 4) through Washington, D.C. 

The fault zone is named the Rock Creek shear zone (Fleming 

and others, 1998), and can be considered part of the Fall Line 

within Washington, D.C. Streambed meanders in Rock Creek 

are incised along bedrock fractures that strike northwest and 

northeast in this zone (figs. 2, 4). 

Collectively, the Piedmont rocks in Rock Creek Park 

(fig. 2) are foliated and dip steeply to the west with metasedimentary and metaigneous rocks strongly aligned north to 

south along the Rock Creek fault-shear zone. Southworth and 

Denenny (2006) noted that tectonic activity along this shear 

zone has been very complex since the first plutonic rocks 

appeared, and they described a system of post-Cretaceous-age, 

north-northwest-directed thrust faults in crystalline rocks that 

cut the Coastal Plain as late as 1.8 Ma (million years ago) at 

the beginning of the Quaternary Period. The current distribution of Cretaceous and Tertiary deposits and Quaternary 

terraces indicates that the west side of the Rock Creek shear 

zone was uplifted, incised, and eroded more than the east side 

through incision by the ancestral Rock Creek and Potomac 

River. This erosional incision left only isolated patches of the 

Coastal Plain sediments, which principally appear west of 

the park at isolated locations—Ward and Tenley Circles, and 

along Wisconsin Avenue. 

Coastal Plain sediments chiefly are found in the eastern 

part of Rock Creek watershed within Washington, D.C. The 

oldest Coastal Plain deposits are the Potomac Formation (fig. 

2, Kp). Both sand-dominated lithofacies (Kps) and claydominated lithofacies (Kpc) of this formation are found on the 

east side of Rock Creek Park. The Calvert Formation (Tc) is 

present only on the west side of Rock Creek Park in Cleveland 

Park.

Tertiary or Quaternary sediments compose at least four 

terrace levels along Rock Creek that Southworth and Denenny 

(2006) indicated could be related to the ancestral Potomac 

River. An older Tertiary upper-level terrace (Ttu) is present 

on a highly elevated flat bench east of Rock Creek Park near 

Walter Reed Army Medical Center (fig 2 and fig 4, Ttu). 

There also are at least three lower-level terraces (Tt) in the 

area (fig. 2, Tt): a high terrace that underlies the area of the 

Carter Barron Amphitheater; an intermediate-level terrace 

that underlies the broad area opposite the National Zoo, and a 

low-level terrace that is incised into the intermediate terrace 

south of the zoo. These terraces probably range from middle 

Miocene (~13.5 Ma) to late Pliocene (2.5 to 1.8 Ma) in age on 

the basis of pollen and stratigraphic correlation (McCartan, 

1989). Colluvium (Qc), derived from Tertiary deposits on the 

uplands, forms drapes of cobbles on the slopes near Woodley 

Park just west of the National Zoo (fig. 2, Qc). Fleming and 

others (1994) interpreted the deposits to be Tertiary in age. 

Southworth and Denenny (2006) indicated that the colluvium 

has probably been accumulating since then.

 To further add to the complexity of surficial sediments 

in Washington, D.C., both the lower Anacostia River and 

Rock Creek watersheds have undergone more than 200 years 

Figure 2. Geology of Washington, D.C. (modified from 

Southworth and Denenny, 2006).—Continued
10 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Figure 3. Generalized hydrogeologic cross sections A-A’ and B-B’ of the lower Anacostia River watershed, Washington, D.C. 

(S.W. Ator, U.S. Geological Survey, written commun., 2010). [Refer to figure 2 for location of cross sections and geologic units.]
Description of Study Area 11

of development. In the case of the Anacostia watershed, the 

stream was subjected to major sedimentation as the watershed 

cover changed from forest to agriculture, then from agriculture 

to urban and suburban land uses. Williams (1977) noted that 

the Anacostia River was navigable north of Washington, D.C. 

up until the early 1880s. Heavy sedimentation occurred in the 

river bottom and along streambanks throughout most of the 

watershed as a result of agricultural, then urban, development 

in the 19th and 20th centuries. Tenbus (2003) described various topographic maps and sediment cores collected along the 

river, which illustrate that considerable fill was deposited in 

wetlands and low-lying areas along streambanks as a result 

of development or dredging. Cut-and-fill operations likely 

have occurred in many other parts of the Anacostia River 

watershed. Johnston (1964) indicated that as late as the mid20th century, considerable suburban development occurred in 

Washington, D.C. and surrounding areas. Thus, there likely 

are widespread occurrences of fill and disturbed landscapes 

throughout the Anacostia River watershed outside the naturalarea parks, with only the largest areas of fill (dgf) appearing on 

Washington, D.C.-scale geologic maps (fig. 2).

In the case of the Rock Creek watershed, only about 30 

percent of the watershed lies within Washington, D.C. (fig. 

1). With the exception of Rock Creek Park, which is up to a 

mi (mile) wide and runs about 9.3 mi from the northern to 

southern boundaries of Washington, D.C., much of the Rock 

Creek watershed within Washington, D.C. is urban with 

commercial and residential developments (Anderson and 

others, 2002). Established in 1890, the park itself has not been 

highly disturbed. Historical development within Washington, 

D.C. outside the park, however, likely has led to considerable 

cutting and filling in of the original landscape, including 

many small first-order upland and headland streams beyond 

the boundaries of Rock Creek Park. As in the case of the 

Anacostia River watershed, only the largest areas of such fill 

appear on Washington, D.C.-scale geologic maps (fig. 2, dgf).

Figure 4. Generalized geologic cross section C-C’ of surficial geology of the lower Rock Creek watershed, which includes the 

Rock Creek shear zone, Washington, D.C. (modified from Southworth and Denenny, 2006). [Line of section is shown in figure 2.]
12 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Groundwater Chemistry

Some recent data exist to describe groundwater in the 

Anacostia River watershed, but there is little current (2008) or 

recent information on the quality of groundwater in the Rock 

Creek watershed.

Recharge differs among the major geologic formations 

in the Anacostia River watershed (S.W. Ator, U.S. Geological 

Survey, written commun., 2010). On the basis of groundwaterlevel contouring, Ator showed that groundwater flow in the 

unconfined aquifer generally is from upland recharge areas 

toward discharge areas along the Anacostia River and its tributaries (fig. 5). His analyses of hydraulic gradients illustrate 

that recharge to the confined Potomac aquifer occurs chiefly 

in the outcrop areas (for example, see fig. 3, sections A-A’ and 

B-B’). Recharge to the unconfined aquifer chiefly is the result 

of infiltration in areas with permeable surficial sediments. In 

both cases, the quality of infiltrated water in this urban setting 

can reflect not only natural precipitation but anthropogenic 

activities and structures, such as irrigation of landscapes and 

leakage from water-supply, storm, and sewer lines. 

An upward hydraulic gradient appears to occur beneath 

the Anacostia River (for example, see fig. 3 section B-B’; 

S.W. Ator, U.S. Geological Survey, written commun., 2010). 

Depending upon the depth of incision of the river channel, this 

could enhance groundwater flow into the river from the surficial aquifer or, if the confining clay lithofacies are removed 

by river down-cutting, lead to groundwater flow into the river 

from what otherwise would be a confined Potomac Formation.

Groundwater in terrace and Potomac Formation materials 

in the Anacostia River watershed commonly is oxic, with low 

concentrations of iron, and elevated concentrations of selected 

compounds that generally are considered indicators of anthropogenic contamination (fig. 6; S.W. Ator, U.S. Geological 

Survey, written commun., 2010). The latter include: 

a. Nitrate concentrations in excess of 10 mg/L in most 

groundwater samples taken from wells completed in 

this urban setting and these sediments; in contrast, 

nitrate concentrations in other Coastal Plain sites associated with forest or little human activity (for example, 

pastureland) are approximately 4 mg/L or less 

(Hamilton and others, 1993); 

b.Chloride concentrations in excess of 75 mg/L in most 

groundwater samples taken from wells completed in 

this urban setting and these sediments; in contrast, 

chloride concentrations in other Coastal Plain sites 

associated with undeveloped (for example, forest) or 

minimally developed (for example, pasture) lands are 

approximately 6 mg/L or less (Hamilton and others, 

1993); and 

c. Detectable and often quantifiably measureable concentrations of synthetic organic contaminants, such 

as volatile and semi-volatile organic compounds and 

pesticides in most groundwater samples taken from 

this urban setting and these sediments; in contrast, 

these compounds generally are undetected, or detected 

only at low concentrations (estimated with higher than 

normal uncertainty), in shallow groundwater in similar 

sediments underlying undeveloped or minimally developed landscapes (Hamilton and others, 1993). 

Other indicators of anthropogenic activities appear to have 

affected groundwater, including oil and grease, petroleum 

hydrocarbons, and gasoline- and diesel-related organics 

(S.W. Ator, U.S. Geological Survey, written commun., 2010). 

The frequency and variety in the types of organic compounds 

detected in groundwater generally were greater in wells 

located in high-density developments (residential, commercial, 

or municipal), than in low-density residential neighborhoods 

or parks.

In the Rock Creek watershed, stream rather than groundwater quality has been the focus of recent studies (Anderson 

and others, 2002; Miller and others, 2007; Phelan and Miller, 

in press). These studies have shown that streamflow, including 

base flow in Rock Creek, contains elevated concentrations of 

nutrients and selected trace elements, and a variety of synthetic organic compounds including pesticides. 

In relation to groundwater, Schneider and others (1993, 

Schneider, Montaser, and Watt, 1993) conducted two relatively 

targeted, local studies on the quality and chemistry of groundwater in the Rock Creek watershed in the 1990s. Johnston 

(1964) conducted the last large-scale assessment of shallow 

groundwater quality and chemistry in and near Washington 

D.C. that included the Piedmont setting. On the basis of 

limited historical data, he characterized natural groundwater 

as a calcium-bicarbonate water with soft-to-moderate hardness. Johnston (1964) noted that natural water-quality impairments for human use throughout Washington, D.C. and nearby 

areas were high iron concentrations (in excess of 0.3 mg/L), 

and high corrositivity, defined as dissolved carbon dioxide in 

excess of 10 μg/L. For example, he found that 40 percent of 

the wells that were analyzed for iron had iron concentrations 

in excess of 0.3 mg/L.

Data-Collection Methods and Data 

Quality

Samples and measurements for water quality were collected at 24 wells in the Anacostia River and Rock Creek 

watersheds in Washington, D.C. in 2005 and 2008 for this 

study. One of these wells was located west of the Rock Creek 

watershed. In addition, quality-control samples and data were 

collected to help determine the accuracy and comparability of 

the groundwater data.
Data-Collection Methods and Data Quality 13

Figure 5. Estimated altitude of the regional water table and generalized direction of groundwater flow 

in the surficial aquifer, lower Anacostia River watershed, Washington, D.C., April 2006 (S.W. Ator, U.S. 

Geological Survey, written commun., 2010).
14 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Data-Collection Methods

Previously installed monitoring wells (for example, 

from studies by Schneider and others, 1993 and 1993b) that 

could be located, that had reliable construction information, 

and that could be redeveloped and sampled, were included 

in this study. Additional wells were installed in locations that 

increased the spatial distribution of monitoring wells and in 

different geologic settings. Large open areas were required to 

provide access and lateral and vertical clearance for the drilling equipment and to avoid underground and overhead utilities. For these reasons, most monitoring wells were installed 

on either NPS property (in 2005 and 2008) or D.C. Parks and 

Recreation property (in 2005).

Inspection of previously installed wells and the installation of new wells by the USGS to meet DDOE recommendations are described by Miller and Klohe (2003), Tenbus 

(2003), Klohe and Debrewer (2007), and S.W. Ator 

(U.S. Geological Survey, written commun., 2010). In brief, 

most (20 of 24) wells were individually located at different 

sites (fig. 1 and table 1). At four sites, pairs of wells were 

installed at two different depths (table 1, shaded couplets). 

Most wells were installed in the surficial aquifer at shallow 

depths—less than 40 ft below land surface. Five wells were 

completed at depths in excess of 40 ft (table 1); these wells 

provided data from the deeper Piedmont bedrock or Potomac 

Group sediments. Information on the identification, construction, and location of wells was collected and compiled from 

well records or field inspections of the selected monitoring 

wells and from field observations and records obtained during 

the drilling and installation of new monitoring wells (table 1). 

Field measurements of selected water-quality properties were taken during sampling each year, and included pH, 

temperature, turbidity, specific conductance, and the concentration of dissolved oxygen. In addition, quality-control 

(QC) samples, including field blanks and duplicate sequential 

groundwater samples, were collected at each of two different 

wells during each year of data collection. 

 Sample collection and processing were similar in both 

years of data collection and have been described in Klohe 

and Debrewer (2007). In brief, groundwater samples were 

collected from each well with a peristaltic or stainless steel 

Figure 6. Trilinear diagrams showing major-ion chemistry of groundwater, by geologic unit, for the lower Anacostia River 

watershed, September to December 2005 (S.W. Ator, U.S. Geological Survey, written commun., 2010).
Data-Collection Methods and Data Quality 15

pump after the well was purged of generally a minimum of 

three well volumes to remove water that had been standing 

in the casing. Samples for the analysis of dissolved inorganic 

constituents were filtered during collection through an encapsulated, 0.45-μm (micrometer)-effective-pore-size, pleated, 

cellulose nitrate filter, and samples for dissolved organic 

constituents, including pesticides, were filtered through a 

0.70-μm-effective-pore-size, 142-millimeter-diameter baked, 

glass-fiber, plate filter.

All 2005 groundwater and QC samples were analyzed 

by the USGS National Water Quality Laboratory (NWQL) 

in Denver, Colorado, or by the USGS-certified Severn Trent 

Laboratory in Arvada, Colorado. Samples were analyzed for 

selected pesticides (78 chiefly nonpolar parent or degradate 

compounds), major ions, nutrients, and other selected chemical constituents whose occurrence or concentrations could be 

related to natural processes and human activities in the study 

area. All 2005 groundwater and QC data have been published 

(Klohe and Debrewer, 2007, appendixes).

Samples collected in 2008 (table 1) from seven of the 

same wells used in 2005, and seven additional wells not used 

for data-collection in 2005, were analyzed by the NWQL 

or the USGS Organic Chemistry Research Laboratory in 

Lawrence, Kansas. Samples were analyzed for selected pesticides (over 150 parent or degradate compounds), major ions, 

and nutrients. All 2008 groundwater and QC data are provided 

in this report (appendix A).

Data Quality

An evaluation of the quality of the data collected in 2005 

and 2008 was made on the basis of QC data obtained from 

field blanks and duplicate sequential groundwater samples, 

from USGS laboratory surrogate recoveries collected during 

the analysis of groundwater samples, and from groundwater 

samples taken from the same seven wells for both years of 

data collection (appendix B). The purpose of this evaluation 

was twofold: to assess the quality of the groundwater data 

collected in 2005 and in 2008, and to assess whether data from 

both years could be combined for selected interpretive analysis. The results of this evaluation are summarized below: 

a. For both years, and except for trace amounts of 

selected major ions, the concentrations of all groundwater constituents, including all pesticides, in fieldblank samples were below the Laboratory Reporting 

Levels (LRLs). In addition, no pesticide was detected 

in any field blank. Also, the magnitude of the concentrations of constituents found in groundwater samples 

exceeded the magnitude of any trace amounts of those 

constituents found in the field blanks. Thus, no appreciable bias due to contamination appears to have been 

introduced during the collection, processing, preservation, shipping, or analysis of groundwater samples in 

either year of data collection that could limit the interpretation of the pesticide and other water-quality data.

b. For both years, data obtained from sequential duplicate groundwater samples collected at selected wells 

revealed similar precision results—low variability 

between measurements of duplicate samples for most 

constituents, including pesticides. For inorganic constituents with measureable concentrations, the relative 

difference between concentrations in duplicate samples 

for most inorganic constituents typically was no more 

than approximately10 to12 percent, and usually less 

than 1 percent. For organic constituents and, in particular, for pesticides, the relative difference between 

concentrations in duplicate samples was generally 20 

percent or less, and for most of the constituents, less 

than 1 percent.

c. The differences in the type and number of pesticide 

detections in 2005 and 2008 groundwater samples, in 

part, could be due to differences in the number and 

performance of laboratory analytical methods used. 

In 2008, an additional pesticide method was used that 

resulted in detections of pesticides (15) in 2008 samples that were not detected in 2005 samples collected 

from the same wells. In addition, the performance of 

one USGS NWQL laboratory method varied between 

years in a manner that appears to have led to more 

pesticides detected in 2008 samples than were detected 

in 2005 samples collected from the same wells.

Given (a) and (b) above, the data collected within a given 

year were considered suitable for interpretation. Similarities in 

the quality of data collected for both years indicated that data 

possibly could be combined from both years for the purposes 

of interpretation. 

Given (c) above, pesticide detections in 2005 and 2008 

appeared to differ at least in part because of differences in the 

number and performance of the laboratory analytical methods 

used in 2005 and 2008. In addition, only 7 of the 17 wells 

sampled in 2005 were resampled in 2008. For these reasons, 

the interpretations of the pesticide data are constrained in this 

study. As an example, although temporal variation in hydrologic conditions could play a role in the differences in pesticide detections in 2005 and 2008, one cannot discount that the 

differences in pesticide detections between these years could 

simply reflect differences in the number and performance of 

laboratory methods. The constraints on interpretations of the 

pesticide data in this study affect the approaches used to (a) 

describe the occurrence and distribution of pesticides, and 

(b) assess pesticide occurrence in groundwater in relation to 

selected land-use and hydrogeologic characteristics, in the 

surficial aquifer.

Interpretations in this report chiefly were conducted 

using either the 2008 or the 2005 data, with an emphasis on 

the pesticide data collected in 2008. The 2008 data provide 

the most widespread and complete indication of pesticides 

in the shallow groundwater in both the Anacostia River and 

Rock Creek watersheds and the most diversity in geologic 

settings. Combined data from both years are used in some 
16 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008 Table 1. Identification, location, and construction information for groundwater monitoring wells in Washington, D.C. used to obtain pesticide samples from September through December 2005, and (or) August through September 2008 (modified from Klohe and Debrewer, 2007).—Continued [USGS, U.S. Geological Survey; DDOE, District Department of the Environment; NAD 83, North American Datum of 1983; NAVD 88, North American Vertical Datum of 1988; ft, feet; a.l.s, altitude of land surface; b.l.s., below land surface; unk, unknown; (° ‘ “), degrees, minutes, seconds; Pot Fm, S, Potomac Formation, sand lithofacies; Pot Fm, C, Potomac Formation, clay lithofacies; Ter, Terrace; dep, deposits; Sap, Saprolite; Fm, Formation; Shaded couplet indicates paired shallow and deep wells located at the same site] USGS well identifier USGS site identifier DDOE well number Latitude (° ‘ “, NAD 83) Longitude (° ‘ “, NAD 83) Altitude (ft a.l.s., NAVD 88) Date1 well constructed Well depth (ft b.l.s.) Cased interval (ft b.l.s.) Casing diameter (outer, inches)2 Screened interval (ft b.l.s.) Lithology of the screened interval3 Pesticide sampling 2005 2008 Anacostia River watershed AC Aa 1 385225076590101 DCMW001-03 38°52’25” 76°59’01” 5.7 2/5/1998 30 0-25 2 25-30 Alluvium

X

AC Aa 6 385138076585901 DCMW001-08 38°51’38.4” 76°58’59.3” 140.0 5/8/2008 18.5 0.24-12.5 2 12.5-18.5 Alluvium

X

AC Aa 7 385138076585902 DCMW002-08 38°51’38.4” 76°58’59.3” 140.0 5/8/2008 60 0.62-49.5 2 49.5-59.5 Pot Fm, S

X

WE Ba 9 385606076584101 DCMW012-05 38°56’06.5” 76°58’41.4” 81.3 8/15/2005 18 0.35-8 1 8-18 Pot Fm, S

X

X

WE Ba 10 385534076582101 DCMW007-05 38°55’34.4” 76°58’21.4” 74.4 8/18/2005 17 0.35-7 1 7-17 Alluvium

X

WE Ba 11 385649076584201 DCMW003-08 38°56’48.8” 76°58’21.4” 88.0 7/30/2008 28.5 0.47-18.5 2 18.5-28.5 Pot Fm, C

X

WE Bb 3 385504076563801 DCMW001-02 38°55’03.6” 76°56’37.7” 12.3 7/24/2002 25 -3.6-15 2 15-25 Alluvium

X4

WE Bb 4 385504076563802 DCMW004-02 38°55’03.6” 76°56’37.7” 12.4 7/26/2002 32 -3-22 2 22-32 Alluvium

X4

WE Ca 29 385238076581501 DCMW005-02 38°52’38.4” 76°58’15.3” 13.4 7/29/2002 48.5 0.15-38.5 2 38.5-48.5 Alluvium

X4

WE Ca 32 385332076594701 DCMW001-04 38°53’31.8” 76°59’47.1” 80.0 10/1/1992 29 0-19 4 19-29 Ter dep

X5 X

WE Ca 33 385349076592801 DCMW006-05 38°53’49.8” 76°59’28.3” 67.8 8/5/2005 38 0.47-28 2 28-38 Ter dep

X

WE Ca 34 385245076583501 DCMW005-05 38°52’45.6” 76°58’35.1” 19.6 8/10/2005 43 0.55-13, 

33-43

2 13-33 Alluvium 

-Ter dep

X

X

WE Cb 5 385443076562801 DCMW002-02 38°54’43.5” 76°56’28.4” 18.5 7/24/2002 22.6 0.2-12.6 2 12.6-22.6 Ter dep

X4 X

WE Cb 6 385443076562802 DCMW003-02 38°54’43.5” 76°56’28.4” 18.8 7/25/2002 46.3 0.2-36.3 2 36.3-46.3 Ter dep

X4

WE Cb 8 385252076572801 DCMW002-04 38°52’52.3” 76°57’28.0” 61.0 4/1/1992 265 0-255 4 255-265 Pot Fm, S

X

X

WE Cb 11 385332076564101 DCMW003-05 38°53’32.1” 76°56’41.2” 60.0 7/28/2005 21 0.32-16 1 16-21 Alluvium

X

WE Cb 12 385332076564102 DCMW004-05 38°53’32.1” 76°56’41.2” 60.6 8/3/2005 39 0.32-29 2 29-39 Pot Fm, C

X

WE Cc 3 385327076544801 DCMW008-05 38°53’27” 76°54’48.5” 88.7 8/16/2005 23 0.31-13 1 13-23 Pot Fm, C

X

X

WW Bc 8 385519077012601 DCMW009-05 38°55’19.3” 77°01’26.9” 123.4 8/18/2005 32 0.33-22 1 22-32 Pot Fm, S

X

WW Bc 9 385527077000701 DCMW011-05 38°55’27.8” 77°00’07.7” 133.6 8/17/2005 36 0.27-26 1 26-36 Pot Fm, S

X

X
Data-Collection Methods and Data Quality 17

Table 1. Identification, location, and construction information for groundwater monitoring wells in Washington, D.C. used to obtain pesticide samples from September through December 2005, and (or) August through September 2008 (modified from Klohe and Debrewer, 2007).—Continued[USGS, U.S. Geological Survey; DDOE, District Department of the Environment; NAD 83, North American Datum of 1983; NAVD 88, North American Vertical Datum of 1988; ft, feet; a.l.s, altitude of land surface; b.l.s., below land surface; unk, unknown; (° ‘ “), degrees, minutes, seconds; Pot Fm, S, Potomac Formation, sand lithofacies; Pot Fm, C, Potomac Formation, clay lithofacies; Ter, Terrace; dep, deposits; Sap, Saprolite; Fm, Formation; Shaded couplet indicates paired shallow and deep wells located at the same site]

USGS well 

identifier

USGS site 

identifier

DDOE well 

number

Latitude 

(° ‘ “, 

NAD 83)

Longitude 

(° ‘ “, 

NAD 83)

Altitude 

(ft a.l.s., 

NAVD 

88)

Date1 well 

constructed 

Well 

depth 

(ft b.l.s.)

Cased 

interval 

(ft b.l.s.)

Casing 

diameter 

(outer, 

inches)2

Screened 

interval 

(ft b.l.s.)

Lithology

of the

screened 

interval3

Pesticide 

sampling

2005 2008

Rock Creek watershed

WW Bc 10 385619077020701 DCMW005-08 38°56’19.3” 77°02’07.3” 120 7/29/2008 32 0.86-22 2 22-32 Laurel Fm XWW Bc 11 385707077021801 DCMW006-08 38°57’06.6” 77°02’17.9” 250 7/28/2008 38.4 0.45-28.4 2 28.4-38.4 Sap above 

Laurel Fm

X

WW Ac 8 385929077020901 DCMW007-08 38°59’29.3” 77°02’08.6” 265 7/31/2008 34 0.58-23.6 2 23.6-33.6 Sap above 

Laurel Fm

X

WW Ba 28 385644077061101 DCMW004-09 38°56’44” 77°06’11” 220 7/1/1992 100 0-50 4 50-100 Sykesville 

Fm

X

1 Except for well AC Aa 1, all wells are constructed of polyvinyl chloride casings and screens. Well AC Aa 1 is constructed of stainless steel materials.2 Except for well AC Aa 1 and well WE Cb 6, the diameter of the well screen is similar to the diameter of its casing. Diameters of the screens in well AC Aa 1 and well WE CB 6 are 1.25 inches and 0.75 

inches, respectively.

3 On basis of well drilling logs and geologic units described and mapped by Southworth and Denenny, 2006.4 Previously sampled in July–August 2002 (Miller and Klohe, 2003).5 Previously sampled quarterly in 1992–93 (Schneider and others, 1993).
18 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

circumstances, for example, to describe the general types and 

concentrations of pesticides found and to identify potential 

relations (future testable hypotheses) between pesticide occurrence in groundwater and selected surficial and subsurface 

characteristics in the study area. The interpretive results in 

each case of combined data use, however, are qualified to the 

extent possible in terms of limitations in the data.

Pesticides in Groundwater

Pesticides present in shallow groundwater can be 

described in relation to their types and frequencies of detection on the basis of the data obtained from the wells used for 

data collection in 2005 and 2008 (fig. 1). The concentrations 

of detected pesticides in shallow groundwater also can be 

assessed in relation to human- and aquatic-health criteria and 

guidelines.

Pesticide Types and Frequencies of Detection

Summary data from all sampling sites and, in the case 

of the paired-well sites, from just the shallowest well at 

each location, indicate that 27 different pesticides (parent or 

degradate compounds) were detected in groundwater samples 

collected in 2005 and 2008 (table 2). The detected compounds 

reflect at least 19 unique herbicides or insecticides—distinct 

parent compounds, or degradate compounds that can be 

associated with distinct parent compounds. Although analyses 

for fungicides were included, no fungicides were detected. 

Fungicides in laboratory analysis of groundwater samples 

included benomyl, metalaxy, and propiconazole.

The detected herbicides chiefly reflect compounds used 

for non-specific weed (broadleaf or grass) control, and the 

detected insecticides chiefly reflect compounds used for noncrop haustellate (sucking) insects or termite control (table 2). 

In addition, the detected compounds reflect parent or degradate pesticides (a) generally still in use, but perhaps currently 

at more restricted levels, for example, s-triazines; (b) wholly 

or highly restricted in use, for example, DDT, chlordane, heptachlor, and dieldrin; or (c) whose use was designed to replace 

banned pesticides, for example, fipronil, in place of dieldrin, 

chlordane, and heptachlor. The presence of pesticide parent 

or degradate compounds banned from further use (DDT and 

chlordane) illustrates their continued persistence and resistance to decomposition in the environment, possibly decades 

after their use was discontinued. Also the presence of replacement pesticides such as fipronil, which was developed in part 

to replace the discontinued termitic pesticides, indicates the 

permeable nature of the surficial aquifer in Washington, D.C. 

and its vulnerability to continued contamination by recently 

introduced pesticides.

For those pesticides for which analyses for degradates 

were conducted, it is apparent that degradate compounds were 

as likely, or more likely, to be detected than parent compounds 

(table 2, s-triazines, glyphosate, DDT, heptachlor, and fipronil). This finding highlights the importance of analyzing for 

degradate as well as parent pesticide compounds to accurately 

determine overall occurrence in groundwater. Recent studies of the surficial aquifer in the Coastal Plain and Piedmont 

Provinces near Washington, D.C. indicate that multiple 

degradates of these and other compounds are more likely to be 

detected in groundwater than the parent compounds (Denver 

and Ator, 2006; Banks and Reyes, 2009).

Different types of pesticides were detected at different 

frequencies in shallow groundwater in the study area (table 2). 

Herbicides were detected more frequently than insecticides. 

In 2005 and 2008, one or more herbicides were detected in 

shallow groundwater at 43 and 62 percent of the study sites, 

respectively. At each well-pair location, the deepest well 

contained no detectable pesticides. Therefore, frequencies 

of detection by well location were computed on the basis of 

the shallow well at each of these locations. In contrast, one 

or more insecticides were detected in shallow groundwater at 

only 29 and 38 percent of the study sites in 2005 and 2008, 

respectively.

Although fewer types and numbers of herbicides were 

detected in shallow groundwater in 2005 than in 2008 

(table 2), the most frequently detected herbicides in 2005 

were the s-triazines and s-triazine degradates, and the ureic 

herbicides. In each case, one or more parent and (or) degradate 

compounds for each type of herbicide were found in shallow 

groundwater at 21 percent of the study sites. No laboratory 

analysis was conducted for alachlor and metolachlor in 2005.

The most frequently detected type of herbicides in 

shallow groundwater in 2008 were the s-triazine compounds 

—atrazine, simazine, prometon, and the atrazine-degradate 

compounds, CIAT and OIET; one or more of these compounds 

were detected in shallow groundwater at 62 percent of the 

study sites. The next most frequently detected herbicides in 

2008 were chlorinated acetanilides, acetachlor and metolachlor, with one or both detected at 29 percent of the study 

sites, and the ureic herbicides (diuron, fluometuron, metsulfuron methyl, sulfameturon methyl, bromacil, and tebuthiuron), 

with one or more of these compounds also detected at 29 

percent of the study sites. The least frequently detected type 

of herbicide was an organophosphate compound—glyphosate 

and its degradate, amino-methyl-phosphonic acid (AMPA); 

each of these compounds was detected once at different sites. 

Although detections of herbicides differed by type, there 

was no marked difference in the frequency with which different types of insecticides were detected in shallow groundwater 

(table 2). Detections, however, could reflect resistance to degradation across general insecticide types. 

Few insecticides were detected in shallow groundwater in 

2005, and as in 2008, detections chiefly reflected insecticides 

resistant to degradation. Detections consisted of one or two 

detections of five different types of insecticides or insecticide 

degradates—p,p’-DDE , dieldrin, heptachlor epoxide, chlordane, and imidacloprid.
Pesticides in Groundwater 19

Table 2. Detected pesticide compounds by type and use, detection frequency using either only or shallowest well at each 

site, maximum concentration, and related human- and aquatic-health concentration criteria and guidelines, for groundwater in 

Washington, D.C., 2005 and 2008.—Continued

[n/a, not analyzed; E, quantified above the long-term method detection limit but below the laboratory reporting level with higher uncertainty; M, present, but 

not quantified; μg/L, micrograms per liter; ---, no recommended or established standard; P, pending; <, less than]

Detected pesticide General use

Number of shallowest 

wells at different 

locations with at least 

one detection

Maximum 

concentration 

(μg/L)

Humanhealth 

criteria 

(μg/L)

Aquatichealth 

criteria 

(μg/L) 2005 

(14 wells)

2008 

(13 wells) 2005 2008

Any herbicide or insecticide: 6 8 0.301 0.11 --- ---

Any herbicide Used for nonspecific 

broadleaf or grass 

control

4 8 0.193 0.11 --- ---

Any s-Triazine: 3 8 0.02 0.106 --- ---

Atrazine Crop and noncrop 1 5 0.02 0.106 32 1.87

Simazine Crop or noncrop n/a 5 n/a 0.022 42 107

Prometon Crop or noncrop n/a 3 n/a E 0.01 1003 ---

2-chloro-4-isopropylamino-6-

amino-s-triazine (CIAT)2

Degradate of atrazine 2 7 E 0.02 E 0.025 P ---

2-hydroxy-4-isopropylamino6-ethylamino-s-triazine 

(OIET)2

Degradate of atrazine 1 2 E 0.007 E 0.034 P ---

2-chloro-6-ethylamino-4-

amino-s-triazine (CEAT)2

Degradate of atrazine 1 0 E 0.01 < 0.08 P ---

Any chloroacetanilide: n/a 4 n/a 0.053 --- ---

Acetochlor Crop n/a 1 n/a 0.019 1/1003 ---

Metolachlor Crop n/a 4 n/a 0.053 P, 7003 7.87

Any ureic: 3 4 0.193 0.11 --- ---

Diuron Crop 0 1 < 0.01 M P, 2/2003 ---

3,4-dichloroaniline Degradate of diuron1 n/a 1 n/a E 0.006 --- ---

Fluometuron Crop, chiefly cotton 0 1 < 0.02 E 0.01 43 ---

Metsulfuron methyl Crop and noncrop 1 0 E 0.04 < 0.14 2,0003 ---

Sulfometuron methyl Noncrop 0 1 < 0.038 E 0.007 2,0003 ---

Bromacil Noncrop 1 2 E 0.01 0.04 703 57

Tebuthiuron Noncrop 1 1 0.193 0.11 1,0003 1.67

Any organochlorine: 0 2 < 0.31 0.02 --- ---

Glyphosate Crop and noncrop 0 1 < 0.150 0.02 7002 657

aminomethylphosphonic acid 

(AMPA)2

Degradate of 

glyphosate

0 1 < 0.31 0.02 --- ---

Any insecticide: Nonspecific use unless 

other specified 

4 5 0.301 0.028 --- ---

Chlorpyrifos Crop n/a 1 n/a E 0.005 23 0.00357

Any acyclic chlorophenyl: Crop-noncrop 1 3 0.004 0.002 --- ---

Dichlorodiphenyldichloroethane (p,p’-DDD)2Degradate of dichlorodiphenyltrichloroethane (DDT)

(Discontinued 1972)

0 3 < 0.002 0.002 0.000314 0.0016, for 

either degradate
20 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Table 2. Detected pesticide compounds by type and use, detection frequency using either only or shallowest well at each 

site, maximum concentration, and related human- and aquatic-health concentration criteria and guidelines, for groundwater in 

Washington, D.C., 2005 and 2008.—Continued

[n/a, not analyzed; E, quantified above the long-term method detection limit but below the laboratory reporting level with higher uncertainty; M, present, but 

not quantified; μg/L, micrograms per liter; ---, no recommended or established standard; P, pending; <, less than]

Detected pesticide General use

Number of shallowest 

wells at different 

locations with at least 

one detection

Maximum 

concentration 

(μg/L)

Humanhealth 

criteria 

(μg/L)

Aquatichealth 

criteria 

(μg/L) 2005 

(14 wells)

2008 

(13 wells) 2005 2008

Dichlorodiphenyldichloroethylene (p,p’-DDE)2Degradate of DDT 

(Discontinued 1972)

1 0 0.004 < 0.002 P; 0.000214 0.0036, for DDT 

plus degradates

Dieldrin Crop-noncrop 2 3 0.065 0.028 0.002/0.23; 

0.0000524

0.056/0.00195; 

0.0016

Imidacloprid Crop, sucking insects 1 0 0.301 < 0.060 4003 ---

Any chlorinated cyclodiene: Crop-noncrop 

(termites)

2 3 E 0.1 0.021 --- ---

Chlordane Discontinued all uses 

1988

1 0 E 0.1 < 0.1 22; 0.000814 0.0043/0.0045; 

0.066

Heptachlor expoxide Degradate of 

Heptachlor (Highly 

restricted, 1988)

2 3 0.007 0.021 0.22;

0.0000394

0.0038/0.00365; 

0.0016

Any phenopyrazole: Noncrop, termites and 

pet pests

n/a 2 n/a E 0.009 --- ---

Fipronil n/a 2 n/a E 0.009 --- ---

Fipronil sulfide Degradate of fipronil n/a 2 n/a E 0.007 --- ---

Fipronil sulfone Degradate of fipronil n/a 1 n/a E 0.005 --- ---

1

 Dichloroaniline is a possible degradate of diuron, linuron, neburon, swep (methyl-N(3,4-diphenyl) carbamate), chlorpyrifos, and propanil 

(J.E. Barbash, U.S. Geological Survey, written commun., 2009); only diuron was detected in the sample with 3,4 dichloroaniline.

2

 U.S. Environmental Protection Agency (USEPA) Maximum Contaminant and Health Advisory Levels for drinking water (U.S. Environmental Protection 

Agency, 2004). 

3

 U.S. Geological Survey, Health Based Assessment Benchmark (Toccalino, 2007), low/high values or single value for both. 

4

 USEPA recommended human-health criteria for consumption of water and organisms (U.S. Environmental Protection Agency, 1999); and P, USEPA pending candidate on drinking-water contaminant list (U.S. Environmental Protection Agency, 2005). 

5

 USEPA national recommended long-term aquatic chronic-exposure criteria for continuous concentration for freshwater/saltwater (U.S. Environmental 

Protection Agency,1999). 

6

 Great Lakes aquatic-health objectives (International Joint Commission, 1989). 

7

 Canadian Council of Ministers of the Environment guidelines for the protection of aquatic health (Canadian Council of Ministers of the Environment, 

2007).
Pesticides in Groundwater 21

The most frequently detected insecticides in 2008 were 

p,p’-DDD, dieldrin, and heptachlor epoxide (a degradate of 

heptachlor); each pesticide was detected at 23 percent of the 

study sites, but not necessarily the same sites. Use of all three 

of these insecticides has been completely or highly restricted 

for decades (table 2). In addition to the resistant insecticides, 

fipronil and one or both fipronil degradates were detected 

in shallow groundwater at 15 percent of the study sites, and 

chlorpyrifos was detected at one study site. 

Comparison of the pesticide data collected in 2008 with 

the data collected in 2005 indicates that groundwater samples 

in 2008 contained considerably more types of pesticides and 

had higher frequencies of detections by pesticide type than 

groundwater samples collected in 2005 (table 2). In addition, 

except for four pesticide compounds, most pesticides detected 

in shallow groundwater samples collected in 2005 were again 

detected in groundwater samples collected from those same 

wells in 2008. The four exceptions are the single-occurrence 

detections in 2005 of the herbicides 2-chloro-6-ethylamino-4-

amino-s-atrazine (desisopropylatrazine or CEAT), metsulfuron 

methyl, glyphosate, and a degradate of the insecticide DDT, 

p,p’-DDE.

Pesticide Concentrations and Human- and 

Aquatic-Health Criteria and Guidelines

Concentrations of pesticides in shallow groundwater samples obtained in either 2005 or 2008 were quite low. Maximum 

concentrations for all parent or degradate compounds were no 

greater than a few tenths of a microgram per liter and often 

were less than 0.1 μg/L (table 2). In particular, many residue concentrations were less than the LRL of the analytical 

method (appendix A, table A1), which implies a higher than 

normal uncertainty in the measured concentrations.

In relation to human-health criteria, summary data 

indicate that no pesticide covered by Federal drinking-water 

standards for public supplies was found at concentrations in 

shallow groundwater that exceeded the USEPA Maximum 

Contaminant Level (MCL) for drinking water (table 2). Absent 

USEPA MCL criteria, human-health standards other than the 

USEPA MCL have been considered for groundwater, including 

the USEPA recommended human-health criteria for consumption of water (U.S. Environmental Protection Agency, 1999) 

and the USEPA-approved non-regulatory USGS health-based 

assessment benchmarks (Banks and Reyes, 2009; Toccalino, 

2007; Denver and Ator, 2006; Toccalino and others, 2004). 

Groundwater data obtained from monitoring wells in the 

surficial aquifer in Washington, D.C. do not directly reflect 

water that is consumed, and therefore, are not directly relevant 

to human health. Nevertheless, DDOE protects the shallow 

groundwater as if it were a drinking-water source. Embassies 

and other government buildings often have wells as back-up 

water supplies, which could potentially be used as drinking 

water. Furthermore, the contamination of groundwater in the 

surficial aquifer in this study, as in other studies where these 

criteria have been applied, may indicate potential for future 

contamination in deeper aquifers and in base flows to surface 

water, both of which are used for drinking-water supplies in 

Washington D.C. or nearby areas.

Application of human-health criteria and guidelines to 

the pesticides present in shallow groundwater in this study 

indicates that concentrations of p,p’-DDD, p,p’-DDE, dieldrin, 

chlordane, and heptachlor epoxide did exceed the USEPA 

national recommendations for the consumption of water for 

these compounds (table 3, human-health assessment). Dieldrin 

concentrations in groundwater samples from three wells—

WE Ca 32 (0.028 μg/L), WE Ba 11 (0.016 μg/L), and WW 

Ac 8 (0.014 μg/L)—in 2008, and two paired wells—WE Ca 

32 (0.065 μg/L) and WE Ca 33 (0.002 μg/L)—in 2005, fell 

within the range of concern denoted by the non-regulatory 

USGS health-based assessment criterion for this compound 

(table 3, human-health assessment, dieldrin, 0.002 μg/L to 

0.2 μg/L). In particular, dieldrin also has been identified as a 

pesticide of concern on the basis of the USGS health-based 

assessment benchmark for shallow groundwater in other areas 

of the Coastal Plain and Piedmont Provinces near Washington, 

D.C. (Denver and Ator, 2006; Banks and Reyes, 2009).

Pesticide concentrations in shallow groundwater in 2005 

and 2008 were compared to several available aquatic-health 

criteria and guidelines for freshwater (tables 2 and 3) including (a) the USEPA criteria for long-term chronic-exposure 

to continuous concentration (U.S. Environmental Protection 

Agency, 1999), (b) the 1989 U.S. and Canada International 

Joint Commission Great Lakes aquatic-health objectives, and 

(c) the 2007 Canadian Council Ministers of the Environment 

(CCME) guidelines for the protection of aquatic health. 

Although these aquatic-health criteria and guidelines chiefly 

were designed for constituents in surface water, their use 

in relation to groundwater in this study may be warranted 

because the shallow surficial aquifer likely is the chief source 

of water to local streams and wetlands in Washington, D.C.

The assessment of aquatic health demonstrated that 

refractory legacy compounds chiefly were responsible for 

most exceedances of aquatic-health criteria and guidelines 

(table 3). The 2005 concentrations of p,p’-DDE (one site), 

dieldrin (one site), and chlordane (one site) and the 2008 concentrations of heptachlor epoxide (three sites) and p,p’-DDD 

(three sites) exceeded the USEPA long-term chronic exposure 

concentrations for each of these compounds. In addition, the 

concentrations of dieldrin at three sites in 2008 and two sites 

in 2005, and of p,p’-DDE at one site in 2005, exceeded the 

U.S. Great Lakes aquatic-health criteria for each of these compounds. The concentration of chlorpyrifos at one site in 2008 

also exceeded the Canadian aquatic-health guideline for this 

compound. Currently (2010), there are no drinking-water standards, other human-health criteria, or aquatic-health guidelines 

for the degradate compounds detected in shallow groundwater 

in this study (table 2). 
22 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

There also are no human- and aquatic-health criteria 

or guidelines for the effects of mixtures of pesticides in 

groundwater. The data obtained in 2008 (appendix A, table 

A1) provide the most comprehensive assessment of pesticide 

mixtures in Washington, D.C. groundwater. As already noted 

(table 2), samples from 8 of the 13 wells completed in shallow 

groundwater had at least one detectable pesticide. Seven of 

these eight wells, or 88 percent, had five or more different 

pesticide compounds (appendix A, table A1). The highest 

number of detections occurred in the groundwater sample 

from well WE Ca 32, which contained 15 different pesticide 

compounds. The effects of such mixtures on human and 

aquatic health are relatively unknown.

Comparison of Pesticides in Groundwater: 

Washington, D.C. and Nearby Coastal Plain and 

Piedmont Areas

The occurrence of pesticides detected in shallow groundwater in Washington, D.C. is similar to patterns found for 

pesticides in shallow groundwater in nearby and similar 

Coastal Plain and Piedmont surficial aquifers. Denver and 

Ator (2006) described the occurrence of pesticides in the 

surficial aquifer in the Maryland Coastal Plain north and 

east of Washington, D.C. They identified parent or degradate 

compounds that represented at least 19 unique herbicides or 

insecticides in shallow groundwater. The concentrations of 

individual pesticide compounds generally were less than 

Table 3. Water-quality human- and aquatic-health assessment for groundwater samples collected from the surficial aquifer in 

Washington, D.C., 2005 and 2008.—Continued

[μg/L, micrograms per liter; E, quantified above the long-term method detection limit but below the laboratory reporting level with higher uncertainty; 

USEPA, U.S. Environmental Protection Agency; USGS, U.S. Geological Survey]

Constituent USGS 

well identifier

Pesticide guidelines 

or criteria

(μg/L)

Pesticide sample 

concentration 

(μg/L)

Year of 

collection

Human-health assessment

USEPA recommended human-health criteria for 

consumption of water1

Dichlorodiphenyldichloroethane (p,p’-DDD) WE Ca 32 0.00031 0.002 2008

WE Ba 11 0.00031 E 0.001 2008

WE Cb 8 0.00031 E 0.001 2008

Dichlorodiphenyldichloroethylene (p,p’-DDE) WE Ba 9 0.00021 0.004 2005

Dieldrin WE Ca 32 0.000052 0.028 2008

WE Ba 11 0.000052 0.016 2008

WW Ac 8 0.000052 0.014 2008

Chlordane WE CA 32 0.00081 E 0.1 2005

Heptachlor epoxide WE Ca 32 0.000039 0.003 2008

WE Ba 11 0.000039 0.021 2008

WE Cb 8 0.000039 0.014 2008

USGS health-based assessment benchmark2

Dieldrin WE Ca 32 0.002-0.2 0.028 2008

WE Ca 32 0.002-0.2 0.065 2005

WE Ba 11 0.002-0.2 0.016 2008

WE Cb 8 0.002-0.2 0.014 2008

WE Ca 33 0.002-0.2 0.002 2005
Pesticides in Groundwater 23

0.1 μg/L. More herbicides were detected than insecticides. 

The most commonly detected herbicides were atrazine, 

prometon, simazine, alachlor, metolachlor. and their multiple 

degradates. They found that herbicides, such as simazine, 

prometon, bromacil, and tebuthiuron, and the termitic insecticides, such as dieldrin, and selected degradates of these 

compounds, appeared most often in groundwater associated 

with urban settings. Denver and Ator (2006) described pesticide mixtures similar to those described for Washington, D.C. 

that occurred with a relatively high frequency. Groundwater 

samples from 68 percent of the wells used in their study contained at least one detectable pesticide. Groundwater samples 

from 94 percent of the wells that had detectable pesticides, 

however, contained more than one pesticide, and 53 percent 

of these wells yielded samples with at least five detectable 

compounds—chiefly s-triazines, acetanilides, and their degradates. Groundwater from one well contained eleven different 

pesticide compounds.

Banks and Reyes (2009) completed a groundwater study 

that involved 15 randomly selected community water-supply 

wells completed in the Piedmont bedrock in Maryland and 

Virginia and located in the lower Potomac River Basin near 

Washington, D.C. They identified 24 unique herbicides or 

insecticides. Concentrations of pesticides typically were less 

than 0.1 μg/L. All 15 wells yielded the atrazine degradate 

CIAT. Seventy-three percent of the wells contained mixtures 

of five or more detectable pesticide residues—typically 

s-triazines, acetanilides, and their degradates. Groundwater 

obtained from one well contained 27 different pesticide and 

degradate compounds.

Table 3. Water-quality human- and aquatic-health assessment for groundwater samples collected from the surficial aquifer in 

Washington, D.C., 2005 and 2008.—Continued

[μg/L, micrograms per liter; E, quantified above the long-term method detection limit but below the laboratory reporting level with higher uncertainty; 

USEPA, U.S. Environmental Protection Agency; USGS, U.S. Geological Survey]

Constituent USGS 

well identifier

Pesticide guidelines 

or criteria

(μg/L)

Pesticide sample 

concentration 

(μg/L)

Year of 

collection

Aquatic-health assessment

Long-term chronic-exposure to continuous 

concentration1

Chlordane WE Ca 32 0.0043 E 0.1 2005

Dieldrin WE Ca 32 0.056 0.065 2005

Heptachlor epoxide WE Ca 32 0.0038 0.005 2005

WE Ba 11 0.0038 0.021 2008

WW Ac 8 0.0038 0.014 2008

Dichlorodiphenyldichloroethane (p,p’-DDD) WE Ca 32 0.001 E 0.001 2008

WE Ba 11 0.001 0.002 2008

WW Ac 8 0.001 E 0.001 2008

Dichlorodiphenyldichloroethylene (p,p’-DDE) WE Ba 9 0.001 0.004 2005

Great Lakes aquatic-health objectives3

Dieldrin plus aldrin WE Ca 32 0.001 0.065 2005

WE Ca 32 0.001 0.028 2008

WE Ca 33 0.001 0.002 2005

WE Ba 11 0.001 0.016 2008

WW Ac 8 0.001 0.014 2008

Dichlorodiphenyltrichloroethane (DDT) plus 

metabolites 

WE Ba 9 0.003 0.004 2005

Canadian guidelines for the protection of aquatic 

health4

Chlorpyrifos WE Cb 8 0.0035 E 0.005 2008

1

 U.S. Environmental Protection Agency, 1999.

2

 Toccalino, 2007.

3

 International Joint Commission, 1989.

4

 Canadian Council of Ministers of the Environment, 2007.
24 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

The Anacostia River and Rock Creek derive their lowflow source waters at least in part from the surficial aquifer 

in the Coastal Plain and Piedmont within and outside of 

Washington, D.C. (fig.1). The combined results of this study 

with those from the studies by Denver and Ator (2006) and 

Banks and Reyes (2009) indicate that similar types, concentrations, and mixtures of pesticides are present in the surficial 

aquifer in Coastal Plain and Piedmont settings beneath these 

watersheds in and around Washington, D.C. Many of these 

detected pesticides reflect parent and degradate compounds 

that currently have no drinking-water or aquatic-health regulatory or non-regulatory standards, criteria, or guidelines, leaving the effects of these mixtures on human and aquatic health 

uncertain.

Land Use and Hydrogeologic Factors 

Related to Pesticide Occurrence

Land use (as a surrogate for pesticide use) and hydrogeologic characteristics, such as sediment permeability, have been 

shown to be related to the presence of pesticides in shallow 

groundwater. To assess whether or not such relations hold for 

the surficial aquifer in Washington, D.C., selected landscape 

and hydrogeologic characteristics associated with the wells 

used in this study were examined in relation to the pesticides 

present in shallow groundwater. The ability to conduct this 

evaluation, however, is at least partially limited because of the 

following two factors:

a. A possible bias exists in well locations toward open, 

accessible space and parks. Most wells that were 

sampled are located in open accessible space and few 

are in close proximity to locations in urban areas that 

generally would reflect high pesticide use on the basis 

of land use, such as highly developed residential, 

commercial, or other infrastructure. This bias could 

differ in relation to wells used for data collection in 

2005 compared to those used in 2008. In 2005, wells 

were located chiefly in larger Federal or other parks in 

the lower Anacostia River watershed (fig.1). In 2008, 

seven of the wells used in 2005 were re-sampled, and 

seven additional wells were sampled that were located 

in smaller recreational parks or on relatively undeveloped open space in the lower Anacostia River watershed, Rock Creek watershed, or west of Rock Creek 

watershed (fig. 1).

b. Differences in the number of methods used to analyze 

for pesticides in groundwater and the performance of 

these methods could have resulted in more pesticides 

being detected in groundwater in 2008 than were 

detected in 2005.

Hence, this assessment chiefly was conducted to identify 

testable hypotheses between land use and hydrogeologic 

characteristics and the occurrence and distribution of pesticides in shallow groundwater in Washington, D.C.

Land Use

A lack of information on pesticide use in urban areas 

within Washington, D.C. precludes a direct comparison of 

actual use in areas in proximity to each of the wells used for 

groundwater sample collection. To address this issue, patterns 

in land use in the Mid-Atlantic Coastal Plain have been used 

as surrogates for pesticide use and have been related to the 

occurrence and distribution of pesticides in Coastal Plain 

groundwater (Ator, 2008; Denver and Ator, 2006). A similar approach was adopted for this study. Land use within a 

circular buffer (500-m radius) of each well (Tyler and Belitz, 

2009; Koterba and others, 1995) was characterized (table 4) 

on the basis of 2001 land-use data (Homer and others, 2004). 

For each circular buffer, the relative amounts of developed 

space (such as residential and commercial, major thoroughfares, and other structural development), and open space (such 

as water, woodland, and low-maintenance grassed areas) were 

determined.

Pesticide detections in groundwater in 2005 and 2008 

were examined in relation to the amount of developed and 

open space within the circular buffer of each well in 2001 

(fig. 7). Although fewer pesticides were detected in groundwater in 2005 than in 2008, the relation between the number 

of pesticides detected in groundwater and amount of developed land use is apparent in 2005 (fig. 7A). In 2008, with the 

exception of well WE Cb 8, the number of pesticides detected 

in groundwater also appeared to increase with increases in the 

amount of developed space in the vicinity of the well (fig. 7B). 

Well WE Cb 8 was excluded from this analysis because the 

data were considered suspect.

Differences in the type of parkland, as well as proximity 

of parkland to development, could account for differences 

in the number and types of pesticides detected in shallow 

groundwater. In both years of data collection, most study sites 

associated with a high number of pesticide detections (at least 

five or more) in shallow groundwater tended to be in small 

municipal parks within developed areas, or near boundaries 

of large parks or other open space in close proximity to 

developed space (table 4, wells WE Ba 11, WE Ca 32, WE 

Cc 3, WW Bc 9, and WW Ac 8). Study sites associated with 

no or few pesticide detections tended to be located within the 

interior of large parklands or other open space (table 4, wells 

AC Aa 1, WE Bb 3, WE Ba 11, and WW Ba 28). Illustrative 

examples of the different land-use settings are provided as 

follows:

a. Examples of wells that yielded groundwater with high 

numbers of pesticide detections, located in open space 

(municipal parkland or wood and grasslands), but surrounded predominantly by extensively developed lands 

(fig. 8), and
Land Use and Hydrogeologic Factors Related to Pesticide Occurrence 25

Table 4. Land use, geologic setting, and pesticide detections for groundwater-monitoring wells in Washington, D.C. sampled from 

September through December 2005 and (or) August through September 2008.—Continued

[USGS, U.S. Geological Survey; b.l.s., below land surface; L-M-H, sum of low-, medium-, and (or) high-density land-use areas, and as with other land uses, 

expressed as a fraction of circular area (in percent) within 500 meters of the well; parentheses around one of the categories, (-L), (-M), or (-H), indicate that 

category of residential land use is less than a few percent; Pot Fm, S; Potomac Formation, sand lithofacies; Pot Fm, C; Potomac Formation, clay lithofacies; 

Ter dep, Terrace deposits; Sap, Saprolite; Fm, Formation; H, herbicide(s); I, Insecticide(s); %, percent; shaded areas denote paired-well sites]

USGS 

well 

identifier

Dominant land uses1

Detailed geologic setting2 Number of pesticide 

compounds detected

Depth of 

screened 

interval of 

the well 

(feet b.l.s.)

Overburden 

from land 

surface to 

screened 

interval 

Geologic unit 

of screened 

interval 

(feet b.l.s.)

2005 2008

Anacostia River watershed

AC Aa 1

Federal park on riverbank; 50% open 

water and low-maintenance chiefly 

grassed open space, 39% L-M-H density residential with sports complex

25-30

Unknown, 

assumed fill 

and clay

Alluvium None Not sampled

AC Aa 6

and

AC Aa 7

Federal park boundary area; 28% open 

and low-maintenance grassed and 

wooded open space; 71% L-M(-H) density residential and built-up parkland

12.5-18.5 Alluvium, 

no clay Alluvium Not sampled None

49.5-59.5 Clay layer,

~17 feet thick Pot Fm, S Not sampled None

WE Ba 9

Residential recreational sports park; 13% 

maintained grassed open space, 87% 

L-M(-H) density residential and commercial

8-18 Clay layer, 

~4 feet thick Pot Fm, S 1 I 1H

WE Ba10

Residential park boundary area; 10% lowmaintenance grassed and wooded open 

space, 90% L-M-H density residential 

and commercial

7-17

Silty, clayey 

sand,~7 feet 

thick

Alluvium None Not sampled

WE Ba11

Maintained grass median between roadways along development and recreational park; 22% grassed and wooded 

open space, 77% L-M(-H) residential 

and commercial

18.5-28.5 Clay layer, 

~15 feet thick Pot Fm, C Not sampled 2 H, 4 I

WE Bb 3

and

WE Bb 4

Grassed Federal park area boundary 

adjacent major thoroughfare and river; 

66% open water and low-maintenance 

grassed and wooded open space; 19% 

commercial and built-up parkland

15-25 Clay, silty clay, 

~15 feet thick Alluvium None Not sampled

22-32 Clay, silty clay, 

~22 feet thick Alluvium None Not sampled

WE Ca 29

Grassed Federal park area along riverbank 

adjacent major built-up complex; 43% 

open water and maintained grassed 

open space; 53% L-M-H residential, 

sport, commercial, and built-up parkland

38.5-48.5

Fill, ~14 feet 

thick, clay, 

~26 feet thick

Alluvium None Not sampled

WE Ca 32

Grassed residential minipark; 1% open 

and wooded open space; 99% (L-)M-H 

density well-maintained residential and 

commercial development 

19-29 Sand Ter dep 3 H, 4 I 8 H, 7 I

WE Ca 33

Grassed residential minipark; 1% grassed 

and wooded open space; 99% (L-) M-H 

density well-maintained residential and 

commercial development

28-38 Silty sand Ter dep 1 I Not sampled
26 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Table 4. Land use, geologic setting, and pesticide detections for groundwater-monitoring wells in Washington, D.C. sampled from 

September through December 2005 and (or) August through September 2008.—Continued

[USGS, U.S. Geological Survey; b.l.s., below land surface; L-M-H, sum of low-, medium-, and (or) high-density land-use areas, and as with other land uses, 

expressed as a fraction of circular area (in percent) within 500 meters of the well; parentheses around one of the categories, (-L), (-M), or (-H), indicate that 

category of residential land use is less than a few percent; Pot Fm, S; Potomac Formation, sand lithofacies; Pot Fm, C; Potomac Formation, clay lithofacies; 

Ter dep, Terrace deposits; Sap, Saprolite; Fm, Formation; H, herbicide(s); I, Insecticide(s); %, percent; shaded areas denote paired-well sites]

USGS 

well 

identifier

Dominant land uses1

Detailed geologic setting2 Number of pesticide 

compounds detected

Depth of 

screened 

interval of 

the well 

(feet b.l.s.)

Overburden 

from land 

surface to 

screened 

interval 

Geologic unit 

of screened 

interval 

(feet b.l.s.)

2005 2008

Anacostia River watershed—Continued

WE Ca 34

Grassed roadside area of wooded strip 

between thoroughfare and river; 58% 

open water and space (cemetery), 39% 

L-M-H density residential and commercial

13-33 Sand, silty sand Alluvium /

Ter dep None None

WE Cb 5

and

WE Cb 6

Grassed wooded area near aquatic gardens 

and nursery; 48% open (aquatic ponds) 

water and maintained grassed and 

wooded space; 36% L-M(-H) residential and commercial

12.6-22.6 Gravel and sand Ter dep None 5 H

36.3-46.3 Clay-silt layer, 

~10 feet thick Ter dep None Not sampled

WE Cb 8

Grassed edge of Federal park complex in 

woodlands; 48% open maintained-grass 

and woodland space, 46% L-M(-H) 

density residential, sport recreational, 

and built-up Federal parklands

255-265 Clay layer, 

~215 feet thick Pot Fm, S 1 H 6 H, 2 I3

WE Cb 11 

and 

WE Cb 12

Grass (maintained) and wooded (stream) 

buffer strip; 30% open wooded park 

and maintained-grass space; 69% wellmaintained L-M-H density residential 

and commercial development 

16-21 Fill and silt Alluvium None Not sampled

29-39 Sandy clay layer, 

~20 feet thick Pot Fm, C None Not sampled

WE Cc 3

Wooded strip bordering built-up park 

complex and recreational sports area in 

residential park; 15% maintained grass 

and woodland space; 82% L-M-(-H) 

density residential and commercial 

space (including ongoing development 

construction) 

13-23 Silt and sand Pot Fm, C 1 H, 2 I 4 H, 3 I

WW Bc 8

Grass (maintained) edge of residential 

sports park surrounded by commercial 

development; 6% maintained grass 

open space; 93% (L-)M-H density 

residential and commercial, including 

multiple-sport complex, developments 

22-32 Clay layer, 

~10 feet thick Pot Fm, S None Not sampled
Land Use and Hydrogeologic Factors Related to Pesticide Occurrence 27

Table 4. Land use, geologic setting, and pesticide detections for groundwater-monitoring wells in Washington, D.C. sampled from 

September through December 2005 and (or) August through September 2008.—Continued

[USGS, U.S. Geological Survey; b.l.s., below land surface; L-M-H, sum of low-, medium-, and (or) high-density land-use areas, and as with other land uses, 

expressed as a fraction of circular area (in percent) within 500 meters of the well; parentheses around one of the categories, (-L), (-M), or (-H), indicate that 

category of residential land use is less than a few percent; Pot Fm, S; Potomac Formation, sand lithofacies; Pot Fm, C; Potomac Formation, clay lithofacies; 

Ter dep, Terrace deposits; Sap, Saprolite; Fm, Formation; H, herbicide(s); I, Insecticide(s); %, percent; shaded areas denote paired-well sites]

USGS 

well 

identifier

Dominant land uses1

Detailed geologic setting2 Number of pesticide 

compounds detected

Depth of 

screened 

interval of 

the well 

(feet b.l.s.)

Overburden 

from land 

surface to 

screened 

interval 

Geologic unit 

of screened 

interval 

(feet b.l.s.)

2005 2008

Rock Creek watershed

WW Bc 10

Grass (maintained) and wooded park area 

along roadway between developments; 

19% open grass and woodland space; 

79% L-M-H density residential and 

commercial

22-32

Silt ~10 feet 

thick, clay 

~5 feet thick

Laurel Fm Not sampled None

WW Bc 11

Grass (maintained) area near parking lot 

of sports complex between reservoir 

woodlands and development; 46% open 

grass (maintained) and woodland space; 

49% L-M(-H) density residential and 

commercial

28.4-38.4 Silty clay 

(saprolite)

Sap above 

Laurel Fm Not sampled None

WW Ac 8

Grass (maintained) and wooded (stream) 

residential park buffer strip; 18% open 

maintained grass and woodland space, 

wooded park and maintained-grass 

space; 81% well-maintained L-M-H 

density residential and commercial 

23.6-33.6 Sand Sap above 

Laurel Fm Not sampled 2 H, 3 I

WW Ba 283

Grass and wooded area between major thoroughfare dividing reservoir 

woodland and development; 56% open 

(water) woodlands and maintained thoroughfare right-of-way; 33% L-M(-H) 

density residential and commercial

50-100

Silty clay 

(saprolite), 

~15 feet thick

Sykesville Fm Not sampled None

1

 2001 land use(s) by type and area are from Homer and others (2004) and are expressed as a percentage of a circular area within 500 meters of the well 

(Tyler and Belitz, 2009; Koterba and others, 1995).

2

 Determined on the basis of available drilling logs from well installation and geologic units described and mapped by Southworth and Denenny (2006).

3

 WW Ba 28 is not located in Rock Creek watershed, but the geologic setting is similar and, therefore, is included in the table with Rock Creek watershed 

wells.
28 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Figure 7. Pesticide detections in groundwater samples collected in (A) 2005 and (B) 2008 in relation to the 

percentage of developed space (low, medium, and high-density residential, commercial, governmental, thoroughfare, 

and other structural) and open space (woodland, maintained grassland, and water) within 500 meters of each well 

used for sampling, lower Anacostia River and Rock Creek watersheds, Washington, D.C.
Land Use and Hydrogeologic Factors Related to Pesticide Occurrence 29

b.Examples of wells that yielded groundwater with no 

detectable pesticides, located in open space (large 

parklands), and surrounded predominantly by open 

space or as much open as developed space (fig. 9).

Although no data generally are readily and routinely 

available on actual pesticide use in proximity to well locations, 

the policy on pesticide use at least within the large NPS parklands, such as Rock Creek Park and Anacostia Park, appears 

to be conservative and restricted to the local control of pests 

and invasives in selected recreational areas (for example, golf 

courses) and along roadways and bridges (Anderson and others, 2002). For example, Anderson and others (2002) found 

that in 1999, only two pesticides (glyphosate and triclopyr) 

were used along selected roadways throughout Rock Creek 

Park. They also noted that during 1999–2000, nine other 

pesticides were used on selected greens, approaches, or tees 

in the park golf course—carbaryl, chlorothalonil, lambda-cyhalothrin, dithiopyr, iprodione, mancozeb (dithio-carbamate), 

proprioconazole, proprionic acid, and thiophenate methyl. Of 

these 11 pesticides, laboratory analyses were conducted in the 

current study for glyphosate (including degradates), triclopyr, 

carbaryl, and proprioconazole in 2005 (Klohe and Debrewer, 

2007, appendix 1) and in 2008 (appendix A, table A1). With 

the exception of glyphosate and its degradates, however, none 

of the above pesticides was detected in any 2005 or 2008 

groundwater samples. Glyphosate was detected in the groundwater sample collected in 2008 from well WE Ba 11 in Fort 

Stanton Park, which is managed by the NPS. 

Anderson and others (2002) found that almost four dozen 

different pesticides were applied to agricultural areas in nearby 

Montgomery County, Maryland in 1994 and 1997, including 

all the pesticides detected in groundwater in the current study. 

Montgomery County immediately borders the northern part 

of Washington, D.C. and includes the upper part of the Rock 

Creek watershed (fig.1). If similar pesticide uses occurred in 

developed lands within Washington, D.C. that border Rock 

Creek and other large parks, then multiple types of pesticides 

detected in groundwater at selected sites used in the current 

study could originate in the developed lands that border park 

sites.

Using land use as a surrogate for pesticide use has two 

notable limitations. First, at most only a few wells in this study 

are located in areas that could be considered almost entirely 

developed residential or commercial lands (wells WE Ca 32, 

WE Ba 9, WE Cc 3, WW Ac 8, and WW Bc 9). Second, pesticides were not always detected in shallow groundwater from 

wells surrounded by extensive urban development (fig. 10). 

Given such limitations, at least several questions arise 

that, if answered, may explain variations in pesticide occurrence in shallow groundwater:

a. Do pesticide mixtures in shallow groundwater in parks 

and other open spaces reflect actual pesticide use 

within the parks or open spaces, or do they represent 

pesticide uses and groundwater transported from 

nearby developed space? 

b. Does markedly different pesticide usage exist in developed space in Washington, D.C. (for example among 

residential or commercial areas) that could account for 

groundwater samples with minimal pesticide concentrations from wells in nearby parkland? 

c. Do differences in land use or subsurface infrastructure 

(for example, irrigation, density, direction, or age of 

storm or sewer drains) account for differences in pesticide detection in parklands bordering developments? 

d. How do natural subsurface hydrogeologic conditions 

affect the transport and thus presence of pesticides in 

shallow groundwater in parklands or other open space? 

Given the scope of the current study, only question (d) can be 

addressed (see following section).

Hydrogeologic Factors

Hydrogeologic setting affects the occurrence of pesticides 

in groundwater both nationally and regionally in the Coastal 

Plain and Piedmont Physiographic Provinces. In the surficial 

aquifer in the Coastal Plain adjacent to Washington, D.C., pesticides in groundwater occur mostly in well-drained areas with 

highly permeable soils and aquifer sediments (Ator, 2008; 

Denver and Ator, 2006). Regional studies in the Coastal Plain 

adjacent to Washington, D.C. have shown that in recharge 

settings that favor the transport of water-soluble pesticides, 

the vertical distribution of pesticides in the shallow surficial 

aquifer is a function of well depth. Pesticides in these settings 

often are accompanied by other anthropogenic contaminants, 

such as elevated concentrations of nutrients—presumably 

from fertilizers, septic systems, and leaky sewer lines; and 

(or) chloride—presumably from septic systems, leaky sewer 

lines, or road-salt applications (Ator, 2008; Denver and Ator, 

2006; Shedlock and others, 1999; Focazio and others, 1998; 

Hamilton and others, 1993).

Pesticide Detections and Types of Surficial 

Sediment

Recharge to the unconfined surficial aquifer in the 

Anacostia River watershed in Washington, D.C. chiefly is the 

result of infiltration in areas with permeable surficial sediments (S.W. Ator, U.S. Geological Survey, written commun., 

2010). A similar argument can be made in relation to groundwater in the Rock Creek watershed. One can hypothesize that 

the presence of pesticides in groundwater could be related to 

differences in the permeability of surficial sediments in the 

vicinity of the wells used for this study. Specific wells were 

selected or installed to reflect different surficial geologic 

materials (table 1). To test this hypothesis, detailed drilling 

logs were examined for most of the wells. Wells initially were 

grouped by geologic unit, and within each unit, lithologic logs 

were examined for the presence of low-permeability sediment 
30 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Figure 8. Examples of extensively developed land within 500 meters of two wells, (A) WE Ca 32 and (B) WE Ba 11, which in 

2008 yielded groundwater samples that contained mixtures of six or more different pesticide compounds, lower Anacostia 

River watershed, Washington, D.C. [Aerial photographs from U.S. Department of Agriculture (USDA) National Agriculture 

Imagery Program (NAIP).]
Land Use and Hydrogeologic Factors Related to Pesticide Occurrence 31

Figure 9. Examples of low-to-moderately developed land within 500 meters of two wells, (A) WE Ca 34 and (B) WW Bc 

11, which in 2008 yielded groundwater samples that contained no detectable pesticide compounds, lower Rock Creek and 

Anacostia River watersheds, Washington, D.C. [Aerial photographs from U.S. Department of Agriculture (USDA) National 

Agriculture Imagery Program (NAIP).]
32 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Figure 10. Examples of extensively developed land within 500 meters of two wells, (A) WE Ca 33 and (B) WW Bc 8, which 

in 2005 yielded groundwater samples that contained one or no detectable pesticide compounds, lower Anacostia River 

watershed, Washington, D.C. [Aerial photographs from U.S. Department of Agriculture (USDA) National Agriculture Imagery 

Program (NAIP).]
Land Use and Hydrogeologic Factors Related to Pesticide Occurrence 33

layers, defined as having appreciable silt, silty-clay or clay 

layers at least 10 feet thick (table 4). Pesticide detections were 

examined in relation to this characterization of overburden 

sediments, and the results are summarized by geologic unit 

(table 5). 

Except for wells completed chiefly in outcrop or subcrop 

areas of the Potomac Formation, pesticide mixtures were 

present in groundwater samples in most wells completed in 

geologic units that were not overlain by low-permeability 

layers (table 5). In most settings, groundwater that contained 

pesticide mixtures occurred where clay, silty-clay, or silt layers 

10 or more feet in thickness were absent.

For wells completed in the outcrop or subcrop areas of 

the Potomac Formation, with either clay or sand lithofacies, 

the presence or absence of pesticides in groundwater samples 

did not appear to relate to the proximity of low-permeability 

sediments (table 5). Why this discrepancy chiefly occurs for 

wells located in the Potomac Formation is unknown. It could 

be the result of the heterogeneous interbedding of sand, silt, 

and clay lenses of limited spatial extent. If low-permeability 

sediments are limited in spatial extent, groundwater contaminated with pesticides could move through the surficial aquifer 

into the Potomac Formation (for example, table 4, wells WE 

Ba 11 or WW Bc 9).

Pesticide Detections and Well Depths

Concentrations of pesticides in groundwater in the 

Maryland Coastal Plain have been shown to generally decline 

with depth in the surficial aquifer; the decline has been related 

to differences in the apparent age of the water since recharge, 

with most pesticides occurring in recently recharged and relatively young or modern age (post-1950) water (Debrewer and 

others, 2007; Shedlock and others, 1999; Focazio and others, 

1998; Koterba and others, 1993; Shedlock and others, 1993). 

Apparent age is used because the age of modern (post-1940) 

groundwater generally is determined relative to the measured 

concentrations of modern contaminants—such as tritium from 

atomic weapons testing, and chlorofluorocarbon (CFC) compounds associated with commercial aerosol products—and 

necessarily presumes that the occurrence and concentrations of 

these contaminants in groundwater relate to natural groundwater recharge from atmospheric precipitation. Thus, the apparent age is relative and approximate, and, in urban areas, often 

cannot be accurately estimated because CFC concentrations 

in groundwater often reflect sources other than recharge from 

atmospheric precipitation. In urban areas such as Washington, 

D.C., local sources of modern contaminants commonly used 

to determine groundwater age, chiefly CFC concentrations, 

reflect recharge from multiple sources, such as atmospheric 

precipitation, landscape irrigation, and leaky infrastructure 

(water, sewer, and septic systems), which preclude the use of 

current dating methods. 

Despite the limitations for dating groundwater within 

the surficial aquifer of the Coastal Plain in Washington, 

D.C., the presence of pesticides does appear to be associated 

with groundwater that is relatively shallow in depth and, 

therefore, relatively young in age. Pesticide detections chiefly 

occurred in samples collected from wells completed at shallow 

depths—median depth 19 ft and maximum depth 28 ft below 

land surface to the top of the well screen. The notable exception to the above was well WE Cb 8, which yielded groundwater samples in 2005 and in 2008 with detectable pesticides, 

but has a screened interval of 255 ft to 265 ft below land 

surface, and an overburden that contains a clay layer approximately 215 ft thick, which indicates this well is completed 

in the Potomac Group confined aquifer. The quality of the 

data obtained from this well, however, is considered suspect 

(appendix B).

Pesticide Detections and Groundwater Ionic 

Chemistry

Regional studies of the surficial aquifer in the Maryland 

Coastal Plain have shown that under natural conditions, the 

major-ion chemistry of groundwater typically reflects: (a) 

the low-level contributions of dissolved solids (cations and 

anions) found in precipitation, and (b) elevated concentrations of selected cations and anions from the dissolution of 

natural bedrock or unconsolidated sediments under either 

unconfined (oxic) or semi-to-confined (hypoxic-to-anoxic) 

conditions (Ator, 2008; Denver and Ator, 2006; Hamilton and 

others, 1993). Under oxic conditions, natural groundwater has 

been described as having low ionic strength, chiefly calcium/

magnesium carbonate waters with nitrate-nitrogen concentrations less than 0.4 mg/L, chloride concentrations less than 6 

mg/L, and sulfate concentrations of approximately 6 to 7 mg/L 

(Hamilton and others, 1993). 

When pesticides are detected in groundwater in the 

Coastal Plain in Maryland, other evidence of human activities 

is usually present, and can include many of the same chemical indicators noted above, but at concentrations greater than 

those noted above (Klohe and Debrewer, 2007; Shedlock and 

others, 1999; Denver and Ator, 2006; Ator, 2008; Focazio and 

others, 1998; Hamilton and others, 1993). Examples include: 

a. Elevated concentrations of nutrients, such as nitrate or 

ammonium, that presumably relate to human activities, 

such as the disposal and transport of human sewage 

(septic systems and leaky sewer lines), the disposal or 

use of domestic animal wastes, and the use of fertilizers, whether for agriculture or residential lawns and 

gardens; and

b.Elevated concentrations of sodium and chloride that 

relate to the disposal and transport of human sewage 

(septic systems and leaky sewer lines), the disposal or 

use of domestic animal wastes, or the use of deicing 

agents along transportation corridors.

Contaminated groundwater also may contain synthetic organic 

compounds, such as pesticides that are used in agricultural 

or urban settings, and in urban areas, and semi-volatile and 
34 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

volatile organic compounds in urban settings from fuels, paint 

thinners, degreasing solvents, and dry-cleaning operations.

The major-ion chemistry for groundwater data obtained 

by Klohe and Debrewer (2007) in 2005 was analyzed for 

the surficial aquifer in the Anacostia River watershed in the 

eastern part of Washington, D.C. (S.W. Ator, U.S. Geological 

Survey, written commun., 2010). These data were related to 

three different geologic settings—Holocene alluvium (including overlying fill deposits), upper Tertiary and younger terrace deposits, and outcrop and subcrop parts of the Potomac 

Formation. Although the limited number of sites (17), different 

geologic settings (3), complexity of sediment types and redox 

conditions, and variability in land use made it difficult to 

broadly and quantitatively define the chemistry of natural and 

contaminated groundwater in the Coastal Plain in Washington, 

D.C., it was concluded that groundwater chemistry in this 

Coastal Plain setting reflects redox conditions. 

Little information is available on the chemistry of natural 

and contaminated groundwater in the Piedmont or PiedmontCoastal Plain transition zone in the Rock Creek watershed in 

and near Washington, D.C. There are few monitoring wells, 

particularly wells completed in the weathered bedrock (saprolite); existing wells generally are completed in the fractured 

bedrock below the saprolite. The geologic composition of that 

bedrock has been described as highly variable and this variability would be reflected in the chemistry of groundwater. 

To assess whether the presence of pesticides in groundwater in this study could be related to differences in surficial 

geologic settings or their groundwater chemistry, the approach 

used by S.W. Ator (U.S. Geological Survey, written commun., 

2010) was adopted and modified for this study. An emphasis 

was placed on (a) identifying and describing the major-ion 

chemistry of groundwater at each well site within a geologic 

setting and in relation to pesticide detections, and (b) identifying the apparent redox state of groundwater at each well 

site and relating this state to pesticide detections in groundwater. Major-ion chemistry is described with trilinear diagrams. Groundwater is defined as oxic if (a) nitrate-nitrogen 

occurred in excess of 5 mg/L, and was generally greater than 

10 mg/L, (b) there was little to no measureable ammonium 

(approximately 0.2 mg/L or less), and (c) the iron concentration was less than 0.25 mg/L; otherwise, groundwater is 

considered to reflect reduced conditions or a mixture of oxic 

and reduced waters. In addition, the scope of characterization 

was expanded on the Anacostia River watershed to include all 

geologic settings represented by wells located in Washington, 

D.C. used in this study. Thus, groundwater data collected from 

all wells sampled in the current study were considered.

The major-ion chemistry of shallow groundwater differed 

among and within the selected surficial geologic settings 

(table 6 and fig. 11). The presence of pesticides in groundwater, however, appeared to depend more on the permeability of 

the sediments within the geologic setting and the chemistry of 

groundwater associated with those sediments. The results by 

setting follow.

Alluvium—(Wells: AC Aa 1, AC Aa 6, WE Ba 10, 

WE Ca 29, WE Cb 11, WE Bb 3, and WE Bb 4)—Under oxic 

conditions (table 6), groundwater generally appeared as a 

moderately acidic (pH less than 5.5 standard units) calciumbicarbonate water (for example, well WE Ba 10). At very 

Table 5. Geologic formations, overburden sediment, and pesticide occurrence in groundwater samples collected from monitoring 

wells in Washington, D.C., 2005 and 2008.

[NS, no samples collected]

Surficial geologic formation of 

screened interval of well

Number of wells with one or 

more pesticide detections 

(Total number of wells sampled)

Overburden sediment characteristics 

and relation to pesticide occurrence

2005 2008

Alluvium deposits 0(6) 0(1) All wells had apparent silt, clay, or silty clay layers at least 10 

feet thick.

Terrace deposits 2(5) 2(3) Wells with detections had no apparent silt or clay layers; wells 

without detections had apparent silt or clay layer at least 10 

feet thick.

Potomac Formation, sand lithofacies 3(4) 3(4) Detection occurrence did not relate to wells with overlying clay, 

silt, or silty clay layers.

Potomac Formation, clay lithofacies 1(2) 2(2) Detection occurrence did not relate to wells with overlying clay 

or sandy clay layers.

Saprolite overlying Laurel Formation NS 1(2) Well with detection had no apparent silt or clay layer; well without detection had apparent clay layer at least 10 feet thick.

Laurel and Sykesville Formations NS 0(2) Both wells had either silt plus clay layer or silty clay layer at 

least 10 feet thick.
Land Use and Hydrogeologic Factors Related to Pesticide Occurrence 35

shallow depths (for example, well WE Ba 10, 7 ft to top of 

screen) or sandier sediments (for example, well AC Aa 6), 

groundwater appeared to be affected by human activities and 

was a calcium-sulfate/chloride water with elevated nitrate 

(>5 mg/L). Groundwater samples from most (5 of 7) wells 

completed in alluvium, however, reflected reduced, or mixed 

redox conditions, and a weakly acidic (pH 6 to 7), calcium/

iron-bicarbonate water. These waters also contained measurable ammonium (in excess of 0.2 mg/L), but no measurable 

nitrate (<0.01 mg/L), variable chloride, and low-to-no measureable sulfate (<2.7 mg/L).

Regardless of redox condition, and despite evidence 

that groundwater appeared to be affected by anthropogenic 

activities as indicated by elevated concentrations of inorganic 

nitrogen (ammonium or nitrate) and, in some locations, 

elevated concentrations of chloride and sulfate (>60 mg/L), no 

pesticide residues were detected in any of the wells completed in alluvium (table 6, and fig. 12). Ator (2008) noted 

that pesticides were less likely to occur in alluvial (silty-clay) 

sediments than in other Coastal Plain sediments and attributed 

this to their relatively low permeability, and the absorption and 

possible degradation of pesticides.

Except for well AC Aa 6, no sampling was conducted in 

2008 in wells completed in alluvium sediments. Well AC Aa 

6 is surrounded by 70 percent development, and was completed at relatively shallow depth in sandy sediments with no 

indication of an impermeable layer (table 6), but there were no 

measureable pesticide residues in this well. Other indications 

of anthropogenic effects at this location suggest that this may 

have been an anomaly and these results remain unexplained.

Terrace deposits—(Wells WE Cb 5, WE Cb 6, 

WE Ca 32, WE Ca 33, and WE Ca 34)—Results of analysis of 

groundwater samples from wells screened in terrace deposits 

indicate groundwater chemistry differed among sites (fig. 11) 

at least in part because of redox conditions (table 6). Shallow 

groundwater at two sites (table 6, well WE Ca 32 and well WE 

Cb 5), was present under oxic conditions, acidic (pH 5.5), and 

a calcium- (or sodium-) sulfate (or chloride) type water, with 

elevated concentrations of sodium (>9 mg/L), nitrate 

(>25 mg/L), and chloride (>27 mg/L). Samples of groundwater from these oxic terrace wells contained five or more 

pesticide compounds. Groundwater at the three other terrace 

sites was under reducing or mixed redox conditions, weakly 

acidic-to-neutral (pH 6.2 to 7.4), and defined as a calcium/

sodium/iron-bicarbonate water type, possibly with low-to-elevated ammonium, and no measureable nitrate. At well WE Cb 

6, groundwater appeared to be in a reduced state, and did not 

appear to be affected by human activities. Groundwater samples from wells WE Ca 33 and WE Ca 34 indicated anthropogenic contamination, in the form of elevated concentrations of 

sodium, ammonium, chloride, and (or) sulfate. Among these 

three wells, only well WE Ca 33 had a detectable pesticide.

Collectively, the groundwater chemistry of terrace 

deposits indicated that, except for well WE Cb 6, groundwater 

in permeable sediments under oxic conditions was affected 

by human activities and contains pesticide mixtures, whereas 

groundwater in permeable sediments under mixed redox 

conditions also was affected by human activities, but contained few if any pesticides. Groundwater in terrace deposits 

with impermeable sediments (for example, WE Cb 6) was in 

a reduced state, and did not appear to be affected by human 

activities.

Potomac Formation, sand or clay lithofacies—(Wells 

WE Cc 3, WE Ba 11, WW Bc 8, WW Bc 9, WE Cb 12, WE 

Ba 9, WE Cb 8, and AC Aa 7)—Except for WE Cb 8, wells 

in the Potomac Formation had 68 to 93 percent developed 

land use within the buffer area and were completed in shallow 

outcrop and subcrop areas with screened intervals beginning 

approximately 13 to 50 ft below land surface (table 4). Well 

WE Cb 8 was considered an outlier of the study. Although 

completed in the Potomac Formation, it is surrounded by 

46 percent development, and completed in the confined part 

of this formation below 215 ft of clay at a depth of approximately 255 ft below land surface. Except for the detection 

of pesticides (one in 2005 and eight in 2008), analysis of the 

chemistry of groundwater at this well indicated groundwater 

was present under reducing conditions with no other evidence 

of anthropogenic contamination, which indicated a well whose 

water quality possibly had been compromised (appendix B). 

Except for well WE Cc3, the shallow overburden for each of 

the Potomac Formation wells contained relatively thick 

(generally 10 ft or more) impermeable (clay, silty clay, or 

sandy clay) sediments above the well screen, regardless of 

whether the sediments had been classified as sand or clay 

lithofacies (table 4). Well WE Cc 3 had a silty sand overburden with no evidence of an impermeable layer.

Groundwater chemistry in the shallow part of this formation differed among sites (fig. 11). Under oxic conditions 

(table 6), samples from four wells indicated groundwater was 

moderately to slightly acidic (pH 4.7 to 6.6), of a sodium/

calcium-chloride/sulfate water type, and contained elevated 

concentrations of nitrate (>12 mg/L). Shallow wells with 

oxic groundwater (WE Cc 3, WE Ba 11, and WW Bc 9) and 

elevated concentrations of anthropogenic-related contaminants 

also contained five or more pesticides. Groundwater with 

reduced, or mixed redox conditions did not appear to be as 

affected by human activity as oxic groundwater, as evidenced 

by only slightly acidic (pH 5.7 to 6.8), and, except for well 

WE Ba 9, a calcium-bicarbonate signature with little nitrate 

or ammonium (table 6). Only one pesticide was detected in 

groundwater with mixed redox state. That detection was in the 

groundwater sample from well WE Ba 9 along with other indicators of contamination (table 6), namely, elevated concentrations of ammonium (>0.8 mg/L), chloride (>25 mg/L), and 

sulfate (>85 mg/L).

Collectively, the presence of pesticide mixtures and contamination in shallow groundwater in this formation appeared 

related to redox conditions, and independent of the sand or 

clay lithofacies, or even the presence of an observed impermeable layer in the overburden sediments of the wells used in this 

study. One possible explanation for the occurrence of anthropogenically contaminated groundwater beneath impermeable 
36 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008 Table 6. Geologic setting, apparent redox state, and major-ion chemistry of groundwater samples collected in Washington, D.C., 2005 and 2008.—Continued [USGS, U.S. Geological Survey; Redox, reduction-oxidation; std, standard; mg/L, milligrams per liter; <, less than; Pot, Potomac; Fm, Formation; Ca2+, calcium; Mg2+, magnesium; Na+, sodium; 

K+, potassium; Fe3+, ferrous iron; Mn2+, manganese; NO3

-, nitrate; NH4

+, ammonium; HCO3

-, bicarbonate; Cl-, chloride; SO42-, sulfate; E, quantified above the long-term method detection limit but below the 

laboratory reporting level with higher uncertainty]

Geologic 

setting

USGS well 

identifier

Redox 

state Water types 

pH

(std 

units) 

Concentrations of dissolved major ions1

Year Ca2+ Mg2+ Na+ K+ Fe3+ Mn2+ NO3

- NH4

+ HCO3

- Cl- SO42-

(mg/L)

Alluvium WE Ba 10

Oxic Ca-Mg, SO4-HCO3 5.4 26.3 10.9 9.45 1.22 < 0.01 0.18 5.08 < 0.05 45 11.4 61.1 2005

Alluvium AC Aa 6 Ca-Na-Mg, SO4-Cl 4.0 68.6 31.6 77.9 8.25 0.21 1.58 25.05 0.029 < 0.01 151 349 2008Alluvium AC Aa 1

Reduced 

or mixed 

Ca-Fe-Mg, HCO3 6.7 19.5 8.67 7.23 2.66 22.5 0.06 < 0.01 4.37 159 9.39 < 0.2 2005

Alluvium WE Ca 29 Fe, HCO3-Cl 6 6.05 3.43 4.97 1.89 23.9 0.14 < 0.01 0.62 78 17.8 < 0.2 2005Alluvium WE Cb 11 Ca-Mg, HCO3-Cl 6.2 23.7 11.6 7.33 3.82 17.2 5.89 < 0.01 0.15 133 37 2.7 2005Alluvium WE Bb 3 Fe, HCO3 5.9 12 4.3 9.02 2.49 54.4 2.33 < 0.01 5.03 171 23 < 0.2 2005Alluvium WE Bb 4 Ca-Fe, HCO3 6.0 10.5 4.63 9.13 3.33 36.9 1.6 < 0.01 2.02 123 24.2 < 0.2 2005Terrace WE Ca 32

Oxic Na-Ca, Cl 5.5 60.5 15.9 164 8.42 < 0.01 < 0.01 34.39 < 0.02 22.9 322 70.0 2008

Terrace WE Cb 5 Ca-SO4, NO3-Cl 5.5 41.8 6.09 8.95 4.09 < 0.01 0.01 28.37 < 0.02 19.9 26.5 67.7 2008Terrace WE Ca 33

Reduced 

or mixed 

Na-Mg-Ca, FeHCO3-Cl 6.7 28.7 18.7 39.2 3.72 37.8 6.83 < 0.01 0.24 220 108 14.1 2005

Terrace WE Cb 6 Fe, HCO3-Cl 6.2 2.47 1.03 1.65 1.25 5.21 0.09 < 0.01 0.11 32 5.58 6.4 2005Terrace WE Ca 34 Ca, HCO3 7.4 109 14.2 16.6 6.64 3.14 0.58 < 0.01 2.13 435 27.1 1.36 2008Pot Fm 

Clay

WE Cc 3

Oxic

Na-Ca, Cl 5.8 40.0 9.04 95.8 3.70 < 0.01 0.15 12.84 < 0.02 52.1 185 55.2 2008

Pot Fm 

Clay

WE Ba 11 Na-Mg-Ca, Cl-SO4 4.8 11.6 7.54 20.1 6.12 0.18 0.56 20.01 0.11 4.6 39.0 32.9 2008

Pot Fm 

Sand

WW Bc 9 Na-Mg-Ca, Cl 4.7 14.8 10.3 34.7 4.52 < 0.01 0.28 12.22 < 0.02 5.8 79.8 31.2 2008

Pot Fm 

Sand

WW Bc 8 Ca-Mg-Na, ClNO3 5.0 27.2 14.6 25.7 10.1 < 0.01 0.48 49.51 < 0.05 15 97.4 11.4 2005

Pot Fm 

Clay

WE Cb 12

Reduced 

or mixed 

Ca-Mg, HCO3 5.8 14.4 5.66 4.21 3.28 3.06 1.40 < 0.01 0.13 60 9.14 12.5 2005

Pot Fm 

Sand

WE Ba 9 Ca-Mg, HCO3-SO4 6.1 71.3 22.2 15.3 5.31 < 0.01 0.97 0.58 0.806 230 25.8 85.1 2008

Pot Fm 

Sand

WE Cb 8 Ca-Mg, HCO3 6.8 8.5 3.71 2.2 4.35 3.49 0.16 < 0.01 0.48 49.7 1.98 6.24 2008

Pot Fm 

Sand

AC Aa 7 Na-Fe, HCO3-SO4 5.7 2.43 1.31 3.49 3.27 4.23 0.57 < 0.01 0.03 18.7 2.73 11.5 2008
Land Use and Hydrogeologic Factors Related to Pesticide Occurrence 37

Table 6. Geologic setting, apparent redox state, and major-ion chemistry of groundwater samples collected in Washington, D.C., 2005 and 2008.—Continued[USGS, U.S. Geological Survey; Redox, reduction-oxidation; std, standard; mg/L, milligrams per liter; <, less than; Pot, Potomac; Fm, Formation; Ca2+, calcium; Mg2+, magnesium; Na+, sodium; K+, potassium; Fe3+, ferrous iron; Mn2+, manganese; NO3

-, nitrate; NH4

+, ammonium; HCO3

-, bicarbonate; Cl-, chloride; SO42-, sulfate; E, quantified above the long-term method detection limit but below the 

laboratory reporting level with higher uncertainty]

Geologic 

setting

USGS well 

identifier

Redox 

state Water types 

pH

(std 

units) 

Concentrations of dissolved major ions1

Year Ca2+ Mg2+ Na+ K+ Fe3+ Mn2+ NO3

- NH4

+ HCO3

- Cl- SO42-

(mg/L)

Saprolite WW Ac 8

Oxic

Na-Ca-Mg, Cl 5.1 93.0 47.3 129 9.04 < 0.01 0.54 29.22 E 0.16 10.1 448 57.4 2008

Saprolite WW Bc 11 Mg-Ca-Na, ClHCO3 5.2 5.87 4.10 6.73 1.65 < 0.01 0.23 14.56 E 0.16 19.9 14.6 E 0.16 2008Laurel 

Fm

WW Bc 10

Reduced 

or mixed

Ca-Mg, HCO3-Cl 6.4 98.9 29.1 39.0 15.1 38.6 3.82 < 0.01 5.95 440 84.8 12.0 2008

Sykesville 

Fm

WW Ba 28 Ca, HCO3-Cl-SO4 7.1 48.2 8.54 15.6 3.40 0.05 0.47 < 0.01 0.02 108 35.2 47.1 2008

1 For the purposes of this analysis, all nitrate and nitrite are assumed to be in the form of nitrate. Nitrate, ammonium, sulfate, and bicarbonate are reported as mass of the ion per liter.
38 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

sediments is that these wells are located in shallow outcrop 

and subcrop parts of this formation, where permeable and 

impermeable sediments are often highly interbedded and discontinuous in nature.

Piedmont Saprolite and Fractured Rock (Laurel and 

Sykesville Formations)—Four Piedmont wells (fig. 1) were 

completed in saprolite (wells WW Ac 8 and WW Bc 11) or in 

fractured rock in the Laurel (well WW Bc 10) and Sykesville 

(WW Ba 28) Formations (table 4). The land area in the vicinity of these wells was 33 to 81 percent developed. Except 

for well WW Ba 28, the wells were completed in unconsolidated materials, with the tops of the screened intervals within 

approximately 22 to 28 ft of land surface. Well WW Ba 28 

was screened in bedrock from 50 to 100 ft below land surface. 

The saprolite wells had either a sandy (WW Ac 8) or silty clay 

(well WW Bc 11) overburden throughout. The overburden for 

well WW Bc 11 consisted of silty sand with thick silt and clay 

layers; and for well WW Bc 10, the unconsolidated overburden was saprolite with silty sand and a thick silty clay layer.

Groundwater chemistry differed among the four well sites 

(fig. 11) and appeared to depend on a combination of sediment 

permeability, and anthropogenic effects. Groundwater samples 

from the two Piedmont saprolite wells were very different 

from each other. The groundwater sample from well WW Ac 

8, which has a sandy overburden, contained high concentrations of calcium and magnesium, elevated concentrations 

of sodium (>128 mg/L), nitrate (>29 mg/L), chloride (>480 

mg/L), and sulfate (>57 mg/L), and five detections of pesticide 

compounds. The groundwater sample from well WW Bc 11 

(which has a silty clay overburden, table 4) had an elevated 

concentration of nitrate (>14 mg/L), low concentrations of calcium, magnesium, and sodium, and no detectable pesticides. 

Groundwater from the wells completed in the Laurel and 

Sykesville Formations, which both have thick silt, clay, or 

silty clay layers in the overburden, appeared to reflect reduced 

or mixed redox conditions, being slightly acidic to neutral in 

pH (6.7 to 7.1), with no measureable nitrate, but otherwise 

possibly affected by anthropogenic inputs. The chemistry of 

groundwater at well WW Bc 10 (table 6) indicated a calciumbicarbonate type water that contained elevated concentrations 

of ammonium (>5 mg/L), chloride (>84 mg/L) and possibly 

sulfate (12 mg/L). Groundwater from well WW Ba 28 also 

Figure 11. Trilinear diagrams showing pesticides in groundwater samples in relation to variations in the major-ion chemistry of 

groundwater associated with geologic units and sediments, lower Anacostia River and Rock Creek watersheds, Washington, D.C., 

2005 and 2008.
Land Use and Hydrogeologic Factors Related to Pesticide Occurrence 39

was calcium-bicarbonate type water, but with low concentrations for most dissolved cations, no measurable nitrate, and 

little ammonium, but elevated concentrations of chloride 

(>35 mg/L) and sulfate (>47 mg/L). Groundwater samples 

from both wells, however, contained no detectable pesticides.

The groundwater chemistry for all four wells in the 

Piedmont regardless of redox condition indicated some vulnerability to groundwater contamination. Only the groundwater 

sample from well WW Ac 8 with a sandy overburden had 

detectable pesticides. The fact that no pesticides were detected 

in groundwater samples from the other three Piedmont wells 

could be due in part to the low permeability and predominantly silty or silty clay overburden materials that occur at 

each well site. These layers could have physically limited the 

rate of vertical groundwater flow and thus pesticide transport 

at depth, or enhanced pesticide adsorption and degradation.

The lack of pesticide detections in groundwater samples 

from two Piedmont wells also could have been due in part to 

land use. Only 33 percent and 49 percent of the land in the 

vicinity of wells WW Ba 28 and WW Bc 11, respectively, was 

developed (table 4). Approximately 80 percent of the land 

within the vicinity of wells WW Bc 10 and WW Ac 8 was 

developed.

Differences in data-collection methods between 2005 

and 2008 were not likely influential in relating groundwater 

chemistry to pesticide detections for wells completed in the 

Piedmont areas.

Although differences in data collection in relation to 

wells and analytical methods used in 2005 compared to 2008 

possibly could have affected the determination of a relation 

between the presence of pesticides in groundwater and the 

chemistry of groundwater, mixtures of five or more pesticides 

generally occurred in shallow groundwater in or beneath 

generally permeable sediments and under oxic conditions as 

evidenced by the co-occurrence of elevated concentrations of 

other mostly anthropogenic contaminants—sodium, nitrate, 

chloride, and sulfate. With a few exceptions, mixtures of pesticides were not detected in reduced groundwater, or mixtures 

of oxic and reducing groundwater, in or beneath generally 

impermeable sediments or sediments that clearly contained 

relatively thick silt or silty clay, or clay layers. Groundwater 

at selected locations in most of the geologic units studied that 

Figure 12. Trilinear diagrams showing changes in major-ion chemistry in groundwater 

samples collected from seven wells in the lower Anacostia River and Rock Creek watersheds, 

Washington, D.C., 2005 and 2008.
40 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

exhibited other than oxic conditions also exhibited elevated 

concentrations of ammonium, chloride, sodium, nitrate, chloride, and (or) sulfate, but few if any pesticides. The absence 

of pesticides, however, could reflect a physical impediment to 

the rate of vertical groundwater flow and thus transport of contaminated groundwater that contained pesticides through these 

sediments or the adsorption and degradation of pesticides as 

contaminated groundwater moved through these sediments. 

For selected surficial geologic units, the presence or 

absence of relatively impermeable sediments was consistent 

enough among sites within the formation to possibly indicate 

the vulnerability of shallow groundwater in the formation to 

pesticide contamination. For example, groundwater obtained 

from wells completed in the Holocene alluvium and Piedmont 

saprolite (silt and silty clay materials), was least likely to 

contain multiple pesticides. Groundwater from terrace deposits 

which often contain abundant sand and (or) silty sand, was 

most likely to have pesticides present. Wells completed in 

the Potomac Formation outcrop or subcrop areas were the 

most difficult to characterize due to the apparent interbedded and discontinuous nature of permeable and impermeable 

sediments. 

Variability of Precipitation

The transport of soluble pesticides to and within the shallow surficial aquifer is dependent upon groundwater recharge 

and flow, respectively. Therefore, differences in pesticide 

detections in groundwater samples collected in 2005 compared 

to 2008 were examined in relation to possible variations in 

precipitation and thus potential recharge during the period of 

data collection. 

For the purposes of this report, precipitation and streamflow are summarized from 2004 through 2008. Climatic data 

indicate the annual precipitation and streamflow for most of 

the period from 2004 through 2008 were higher than average, 

with only 2007 being a below-average year (table 7). 

Table 7. Precipitation and streamflow in the Washington, D.C. greater metropolitan area, 2004 through 2008.

[NOAA, National Oceanic and Atmospheric Administration; USGS, U.S. Geological Survey; MD, Maryland; ft3/s; cubic feet per second; water years are 

defined as the period from October through September]

NOAA or 

USGS station 

identifier

Station location 

Total annual precipitation1

(inches)

Long-term 

total annual 

precipitation 

(inches)

Period of record for 

long-term annual 

precipitation

(water years) 2004 2005 2006 2007 2008

DCA Ronald Reagan Washington 

National Airport, Virginia 42.49 44.38 47.77 32.93 46.49 40.8 1871–2008

NOAA or 

USGS station 

identifier

Station location

Annual mean discharge

(ft3/s)

Long-term 

annual mean 

discharge

(ft3/s)

Period of record for 

long-term annual 

mean discharge

(water years) 20042 20053 20064 20075 20086

01648000 Rock Creek at Sherrill Drive, 

Washington, D.C. 93.1 79.7 77.4 54.4 57.6 64.3 1930–2008

01651000 Northwest Branch Anacostia 

River near Hyattsville, MD 80.2 57.8 78.2 49.1 55.7 50.1 1938–2008

01649500 Northeast Branch Anacostia 

River at Riverdale, MD 132 89.5 98.7 75.8 94.0 87.6 1938–2008

01651800 Watts Branch at Washington, 

D.C. 5.99 4.46 4.65 4.57 6.21 4.70 1992–2008

1

 National Oceanic and Atmospheric Administration (NOAA), 2010.

Streamflow data from U.S. Geological Survey Annual Data Reports:

2

 Saffer and others, 2005.

3

 Saffer and others, 2006.

4

 U.S. Geological Survey, 2007.

5

 U.S. Geological Survey, 2008.

6

 U.S. Geological Survey, 2009.
Variability of Precipitation 41

The relatively wet period from 2004 through 2008 

enhanced recharge in the study area. The effects of enhanced 

recharge on the mobility and transport of pesticides in 2005 or 

2008 were not determined in this study.

Changes in inorganic chemical composition of groundwater from 2005 to 2008 at most well locations were relatively 

small (fig. 12), and reflected only minor increases or decreases 

in the concentrations of individual ions (table 8). Although 

these changes could be related to changes in groundwater 

recharge, they are not entirely consistent with the previous 

discussion relating pesticide detections and the inorganic 

chemistry of groundwater at these sites. Specifically, increases 

in pesticide detections in groundwater at a site were not necessarily accompanied by the expected increases in the concentrations of other indicators of anthropogenic contamination, for 

example, nitrogen, chloride, and (or) sulfate, that one could 

anticipate given the redox condition at that site. Furthermore, 

the differences in pesticide detections between years due to 

differences in the number and type of laboratory methods used 

confounds the interpretation of the possible effect of climate 

on pesticide detections between years.

For example, in the case of well WE Cb 5, one pesticide 

was present in the groundwater sample collected in 2005, 

and five pesticides were present in the groundwater sample 

collected in 2008. Given that this well was completed in a 

terrace deposit and groundwater appears oxic, one might have 

expected the change in the number of pesticides to coincide 

with an increase in the concentrations of chloride and sulfate. 

However, of the five pesticides detected in groundwater in 

2008, two (prometon and simazine) were not in the analytical 

schedules used in the analysis of groundwater samples in 

2005. In addition, CIAT was detected in the groundwater 

sample in 2008, but at a concentration below the 2005 reporting level of 0.03 μg/L.

Artifacts occur for other wells also. Well WE Cb 8 had a 

marked increase from one to eight pesticide detections from 

2005 to 2008. The presence of oxic groundwater and declines 

in the concentrations of most inorganic constituents from 2005 

to 2008 likely reflect artificial recharge from a nearby leaking fire hydrant, rather than an increase in natural recharge 

(appendix B).

Table 8. Major-ion composition of groundwater samples, 2005 and 2008.

[USGS, U.S. Geological Survey; mg/L, milligrams per liter; <, less than; std, standard; E, estimated; Na+, sodium; K+, potassium; Mg2+, magnesium; Ca2+, 

calcium; Mn, manganese; Fe, iron; NH4

+

, ammonium; Cl-, chloride; SO4

2-, sulfate; NO3-

, nitrate; HCO3

-

, bicarbonate]

USGS 

well 

identifier 

Year of 

sample 

collection

pH

(std 

units)

Concentrations of dissolved major ions1

Na+ K+ Mg2+ Ca2+ Mn Fe NH4

+ Cl- SO42- NO3- HCO3-

(mg/L)

WE Ba 9

2005 6.2 11.7 5.12 25.9 91.7 0.55 < 0.01 0.31 24.2 81.1 6.02 260

2008 6.1 15.3 5.31 22.2 71.3 0.97 < 0.01 0.70 25.8 85.1 0.58 230

WE Ca 32

2005 5.6 122 7.73 14.3 57.4 < 0.01 0.01 < 0.05 257 79.7 34.26 21.0

2008 5.5 164 8.42 15.9 60.5 < 0.01 < 0.01 < 0.02 322 70.0 34.39 22.9

WE Ca 34

2005 7.3 13.9 6.72 13.8 103 0.64 7.93 3.75 27.6 0.10 < 0.03 386

2008 7.4 16.6 6.64 14.2 109 0.58 3.14 2.13 27.1 1.36 < 0.01 435

WE Cb 8

2005 6.8 4.72 5.53 6.63 11.2 0.19 3.07 0.07 2.91 11.8 < 0.03 70.6

2008 6.8 2.20 4.35 3.71 8.50 0.16 3.49 0.41 1.98 6.24 < 0.01 49.7

WE Cb 5

2005 5.2 9.40 4.39 5.21 34.7 0.02 < 0.01 < 0.05 11.9 76.7 23.95 12.0

2008 5.5 8.95 4.09 6.09 41.8 0.01 < 0.01 < 0.02 26.5 67.7 28.37 19.9

WE Cc 3 

2005 5.9 85.3 4.29 10.4 55.7 0.26 0.82 E 0.03 170 46.7 13.41 104

2008 5.8 95.8 3.70 9.04 40.0 0.15 < 0.01 < 0.02 185 55.2 12.84 52.1

WW Bc 9

2005 4.8 30.1 4.52 10.9 15.6 0.30 0.01 < 0.05 77.3 30.6 12.93 7.40

2008 4.7 34.7 4.52 10.3 14.8 0.28 < 0.01 < 0.02 79.8 31.2 12.22 5.80

1

 For the purposes of this analysis, all nitrate and nitrite are assumed to be in the form of nitrate. Nitrate, ammonium, sulfate, and bicarbonate are reported 

as mass of the ion per liter.
42 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Summary and Conclusions

The U.S. Geological Survey (USGS), in cooperation with 

the District Department of the Environment (DDOE), conducted a groundwater-quality investigation in 2005 and 2008 

to assess groundwater in the surficial aquifers of the Anacostia 

River and Rock Creek watersheds in Washington, D.C. The 

area was investigated to (a) determine the types, presence, 

concentrations, and distribution of selected pesticides; and (b) 

assess pesticide presence in relation to selected land-use and 

hydrogeologic characteristics. Data and information for this 

investigation were obtained from 2001 land-use data layers, 

well drilling logs, and groundwater samples collected in 2005 

and 2008. In 2005, 17 monitoring wells were completed 

in the surficial aquifers with locations selected to target 

representative geologic units and land use, and were located 

chiefly in parks or other accessible settings. Similar data and 

information were obtained in 2008 from seven of the wells 

sampled in 2005, as well as seven additional monitoring wells 

located in similar land-use settings.

The groundwater samples collected in 2005 and 2008 

were analyzed for pesticides, major ions, nutrients, and 

selected trace elements that may reflect the effects of human 

(urban) activities or natural processes on the chemistry of 

shallow groundwater. Quality-control (QC) samples, including 

field blanks and duplicate groundwater samples were 

concurrently collected with groundwater samples at two or 

more different well sites and analyzed with the groundwater 

samples during each year of data collection. Additional QC 

data associated with the analysis of pesticide samples were 

obtained from the USGS National Water Quality Laboratory in 

Denver, Colorado, and the USGS Organic Chemistry Research 

Laboratory in Lawrence, Kansas.

For the purposes of data interpretation, results from 

an analysis of the QC data from field blanks and duplicate 

groundwater samples indicated that the quality of groundwater 

data in 2005 and 2008 was similar, and that data from both 

years were suitable for combining and interpreting. Results 

from comparisons of the pesticide groundwater and laboratory 

QC data obtained from the seven wells used in both 2005 and 

2008 indicated that (a) enhanced method performance and the 

addition of compounds to the USGS laboratory methods used 

in 2005, and (b) inclusion of an additional USGS laboratory 

method for polar pesticides in 2008, led to an increase in 

the types and numbers of pesticides detected in groundwater 

samples obtained in 2008 compared to groundwater samples 

obtained from the same wells in 2005. Therefore, the interpretation of the pesticide data chiefly was made by year of 

collection. Interpretation of combined data from both years 

was limited to basic descriptions of the types of pesticides 

detected and discussions of the presence or absence of 

pesticides in groundwater in relation to different land-use and 

hydrogeologic features. 

Pesticide Types and Frequencies of Detection 

Groundwater samples were analyzed for more than 75 

different individual parent or degradate pesticide compounds, 

including those compounds of concern to DDOE and either 

suspected or known to occur in urban groundwater. Twentyseven different parent or degradate compounds, representing 

at least 19 unique herbicides and insecticides, were detected 

in groundwater samples collected from the surficial aquifer 

in Washington, D.C. in 2005 and 2008. No fungicides were 

detected in any groundwater samples collected in either 2005 

or 2008. General findings related to the types of compounds 

detected are:

a. The pesticide compounds detected were herbicides 

commonly used in urban settings for non-specific 

weed (broadleaf or grass) control—for example, the 

s-triazines (atrazine, prometon, simazine) and chloroacetanilides (metolachlor and alachlor)—and several 

different types of insecticides for nonspecific haustellate (sucking) insects or termite control—for example, 

diuron; chlorpyrifos; imidacloprid; fipronil; p,p’-DDT; 

chlordane; and heptachlor.

b. Detected parent or degradate compounds were pesticides (1) generally still in use, for example, the 

s-triazines; (2) no longer in use, or whose use has been 

highly restricted, for example, dieldrin, chlordane, heptachlor, and p,p’-DDT; or (3) whose use has replaced 

banned or restricted pesticides, for example, fipronil, in 

place of dieldrin, chlordane, and heptachlor. 

c. For those pesticides for which degradate analyses were 

conducted—s-triazines; diuron; glyphosate; p,p’-DDT; 

heptachlor; and fipronil—the degradate compounds 

were at least as likely to be detected in groundwater 

than the parent compounds. 

On the basis of frequency of detections and types of pesticides found, groundwater in the surficial aquifer (within 100 

feet of land surface) in the Anacostia River and Rock Creek 

watersheds in Washington, D.C. appeared susceptible to pesticide contamination. In 2008, at least one herbicide or insecticide was detected in the groundwater samples collected from 

61 percent of the study sites. Multiple pesticides were quite 

likely to be detected in groundwater that contained at least one 

pesticide. Five or more different pesticides were detected in 

groundwater samples collected from 88 percent of the study 

sites, and 15 different pesticide compounds were detected in 

groundwater at one site (well WE Ca 32). 

The most frequently detected pesticides in 2008 were the 

herbicides atrazine, simazine, and prometon, and the atrazine 

degradates CIAT, CEAT, and OIET. At least one or more 

of these compounds was detected in groundwater at eight 

different study sites. Acetachlor and metolachlor were the 

next most frequently detected herbicides, and one or both of 

these compounds were found in groundwater at four different 
Summary and Conclusions 43

sites. Ureic herbicides were found in various combinations in 

groundwater from three different sites. Bromacil was detected 

in groundwater from two sites; diuron, a degradate compound 

(3,4-Dichloroaniline), and tebuthiuron, were detected along 

with bromacil at one of the above sites; and fluometuron and 

sulfometuron methyl were detected in groundwater from the 

third site. The organophosphate herbicide glyphosate was 

detected in groundwater from one site, and its degradate 

AMPA in groundwater from another site.

Insecticide and insecticide-degradate residues also were 

detected in groundwater samples collected in 2008 but less 

frequently than herbicides. Two to six different parent and (or) 

degradate compounds of insecticides were present in groundwater from five different sites. The frequencies of detections 

were fairly evenly distributed among several different types of 

insecticides, which included chlorpyrifos; p,p’-DDD; dieldrin; 

chlordane; heptachlor epoxide; fipronil; and the sulfide and 

sulfone degradates of fipronil. 

Because of the previously noted differences in the analytical capabilities between years, fewer pesticides were detected 

in groundwater in the surficial aquifer in 2005 than in 2008. 

Nevertheless, in 2005 at least one herbicide or insecticide was 

detected in groundwater from 50 percent of the study sites. 

Although a variety of pesticides were detected in the shallow 

groundwater in 2005 and 2008, maximum concentrations for 

any parent or degradate compound were no greater than a few 

tenths of a microgram per liter (μg/L), and, for most detected 

compounds, concentrations were less than 0.1 μg/L. For many 

of the compounds, the detected concentration was below the 

laboratory reporting level but above the laboratory detection 

level; therefore, the concentration is reported as estimated 

(coded with an “E”) with a greater than normal uncertainty.

Pesticide Concentrations and Human and 

Aquatic Health

Human and aquatic health assessments were conducted 

on the types and concentrations of pesticides detected in 

groundwater. Assessment criteria were selected to provide 

guidance on most of the frequently detected compounds. For 

human health, three assessment criteria or guidelines were 

used—the U.S. Environmental Protection Agency (USEPA) 

Maximum Contaminant Level (MCL) for drinking water, the 

USEPA recommended criteria for the consumption of freshwater, and the non-regulatory and USEPA-approved USGS 

health-based assessment benchmarks. For aquatic health, three 

assessment guidelines also were used—the USEPA long-term 

chronic-exposure continuous concentration, the U.S. Great 

Lakes aquatic-health objectives, and the Canadian Council 

of Ministers of the Environment (CCME) guidelines for the 

protection of aquatic health.

Except for several banned insecticides that are resistant 

to degradation, no other pesticides were found in 2005 or 2008 

at any study site at a concentration that exceeded any of the 

three human-health standards. At a few sites and during both 

years of sampling, groundwater concentrations exceeded the 

USEPA recommended criteria for the consumption of freshwater for p,p’-DDD; p,p’-DDE; dieldrin; heptachlor epoxide; 

and chlordane. Concentrations of dieldrin also exceeded the 

USGS health-based assessment benchmark for this compound 

at several sites.

The same legacy compounds were responsible for most 

exceedances of aquatic-health guidelines. At several wells and 

in both years, groundwater concentrations of heptachlor epoxide; p,p’-DDE; p,p’-DDD; dieldrin; and chlordane exceeded 

the USEPA long-term chronic-exposure concentrations for 

each of these compounds. U.S. Great Lakes objectives were 

exceeded for dieldrin and p,p’-DDE at several sites in both 

years, and the CCME guidelines for the protection of aquatic 

health were exceeded for chlorpyrifos at one site in 2008.

The concentrations of the pesticide compounds that 

exceeded either a human or aquatic action level were low, and 

in some cases the concentrations were estimated (with a higher 

than normal uncertainty). However, no human- or aquatichealth standards existed for some of the parent compounds 

or for most of the degradates, including some of the most 

frequently detected chemicals. Neither human- or aquatichealth standards had been established for mixtures of different 

pesticides that were observed in groundwater in 2005 and 

2008 from the majority of study sites.

Comparison of Pesticide Occurrence with 

Studies in the Nearby Coastal Plain and 

Piedmont

In many respects, the occurrence of pesticides in shallow 

groundwater in the Coastal Plain and Piedmont Physiographic 

Provinces within Washington, D.C. mirrored regional patterns 

found in shallow groundwater in similar physiography adjacent to Washington, D.C. Findings from two other studies, one 

in the Coastal Plain and another in the Piedmont, in particular, 

were similar to the findings in the current study:

a. Both of the other studies found many of the same types 

of herbicides and insecticides as were found in this 

study, and at similarly low concentrations (often less 

than 0.1 μg/L). 

b.Both studies found, as in this study, that the most 

frequently detected herbicides in shallow groundwater 

chiefly were the s-triazines, alachlor, and metolachlor, 

and their degradate compounds.

c. Both studies found, as in the current study, a relatively 

high frequency of sites that yielded groundwater 

with pesticide-residue mixtures. In the Coastal Plain 

study, groundwater from many of the wells had 5 or 

more detectable pesticide residues, and groundwater 

from one well contained 11 different pesticides. In the 

Maryland-Virginia Piedmont study, 73 percent of the 

wells yielded groundwater samples that contained mix-
44 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

tures of 5 or more pesticide compounds, and groundwater from one well contained 27 different pesticide 

residues.

d.Both studies, as in the current study, identified degradation-resistant legacy insecticides as pesticides of 

concern in relation to the USGS health-based assessment benchmarks for shallow groundwater.

Land Use and Hydrogeologic Factors Related to 

Pesticide Occurrence

The presence of pesticides in shallow groundwater in 

Washington, D.C. appears to be related to land use and hydrogeologic factors that in turn reflect the use and subsequent 

mobility of pesticides. The relative amounts of developed 

(residential or commercial) space and open (water, forest, grassland, or other low-maintenance) space within 500 

meters of a well were used as surrogates for pesticide use. 

In 2008, multiple pesticide detections in groundwater were 

chiefly associated with wells with at least 50 percent, and 

most commonly 60 percent or more, of the surrounding area 

under development. Insecticides in particular were detected 

in groundwater associated with wells whose surrounding area 

was at least 50 percent, and commonly at least 80 percent, 

developed. The site associated with the highest number of 

pesticide detections (well WE Ca 32, eight herbicide and 

seven insecticide compounds) was in an area with 99 percent 

development. 

However, hydrogeologic setting also plays a role in 

whether pesticides are detected in groundwater. Although data 

were insufficient to conduct a rigorous statistical analysis, 

three hydrogeologic factors appeared to have some bearing on 

the presence of pesticides in shallow groundwater—the depth 

of the well within the aquifer, the type of surficial sediment 

in which the well was completed or that overlies the screened 

interval of the well, and the chemistry of groundwater.

Pesticide occurrence appeared to be inversely related to 

the depth of the well in the surficial aquifer, which presumably 

relates to the age of groundwater from its time of recharge. 

Pesticides chiefly occurred in groundwater samples collected 

from wells in 2005 and 2008 that were completed at shallow 

depths—28 feet or less below land surface to the top of the 

well screen. This could indicate that groundwater that contains 

pesticide residues had not fully penetrated the surficial aquifer 

in all geologic settings, which on the basis of wells used, 

extends to a depth of at least 50 feet below land surface.

The presence of pesticides in groundwater was examined 

in relation to major types of surficial material, including: (a) 

alluvium and terrace deposits, (b) sediments classified as sand 

or clay lithofacies in shallow outcrop and subcrop areas of 

the Potomac Formation in the Coastal Plain, (c) Piedmont 

saprolite, and (d) Piedmont fractured bedrock beneath the saprolite (Sykesville and Laurel Formations). Examination of the 

presence of mixtures of five or more pesticides in groundwater 

within each of these surficial aquifers indicated groundwater 

pesticide contamination is less a function of the general classification of bedrock, and more a function of the overlying 

materials that can affect the rate of groundwater flow, the 

groundwater chemistry, and ultimately pesticide mobility. 

Mixtures of five or more pesticides in groundwater generally were linked to two conditions: (a) wells that were completed in generally permeable sediments, as evidenced by the 

absence in drilling logs of any description of silt, silty clay, or 

clay layers 10 or more feet thick; and (b) groundwater associated with oxic conditions, elevated concentrations of some 

possibly anthropogenic indicators—sodium, nitrate, chloride, 

and (or) sulfate, and low to no measureable concentrations of 

iron. With a few exceptions, mixtures of pesticides were not 

detected in or beneath materials with low permeability, such 

as thick silt, silty clay, or clay layers, or at sites with reducing 

groundwater. 

The absence of measureable pesticides in groundwater 

in or beneath low-permeability sediments and under reducing 

or mixed redox conditions could reflect settings with reduced 

rates of vertical groundwater flow that slow the transport of 

pesticide-contaminated groundwater deeper into the surficial 

aquifer. It could also be that in such settings, pesticides are 

adsorbed and degraded as contaminated groundwater moves 

through the surficial aquifer. Some combination of both of 

these processes might explain why pesticides generally did not 

appear throughout the surficial aquifer. 

The role of sediment permeability as a factor in pesticide 

transport in the surficial aquifer can be extrapolated to 

provide some indication of the vulnerability of groundwater 

to pesticide contamination in each type of surficial material 

described earlier. No pesticides were detected in wells completed in the Coastal Plain alluvium, nor in wells completed 

in the Piedmont fractured bedrock. Wells in these locations 

were completed below thick layers of low-permeability silt, 

silty-clay, or clay materials in beds ten or more feet thick, and 

groundwater reflected either a reduced state or mixed redox 

conditions. Groundwater from terrace deposits, which often 

contain abundant sand and (or) silty sand, was most likely to 

contain pesticide mixtures. Groundwater chemistry in wells 

completed in the Potomac Formation outcrop or subcrop areas 

was the most difficult to characterize due to the apparent interbedded and discontinuous nature of permeable and impermeable sediments. 

The preceding analysis of the relation between the presence of pesticides in shallow groundwater and sediment permeability and groundwater chemistry was conducted with data 

from 2005 and 2008, and under the assumption that groundwater chemistry did not markedly change from 2005 to 2008. To 

address this assumption, annual precipitation and streamflow 

were evaluated from 2004 to 2008 and both climate indicators 

were found to be above average in 4 of the 5 years. Due to 

differences in analytical methods, however, it was not possible 

to determine if there were differences in the occurrence of 

pesticides between 2005 and 2008.
References Cited 45

Comparison with Regional Groundwater 

Studies: Pesticide Occurrence and Land Use 

and Hydrogeologic Settings

The presence of pesticides in shallow groundwater in 

the surficial aquifer as a function of developed lands, depths, 

permeable and oxic environments, and the co-occurrence of 

other chemical indicators in groundwater contamination from 

human activities mirrored regional patterns found by other 

studies on shallow groundwater in the Coastal Plain and the 

Piedmont surficial aquifers near Washington, D.C. Patterns 

in land use in the Coastal Plain have frequently been used 

as surrogates for pesticide use and have related pesticide 

occurrence and distribution in groundwater to agricultural 

and urban development. From a regional perspective, pesticide concentrations in groundwater generally decline with 

depth in the surficial aquifer, and groundwater that contains 

pesticides likely reflects recently recharged water that is 

relatively young (post-1940s or 1950s). As is the case in the 

current study, previously conducted Coastal Plain studies have 

indicated the highest frequency of occurrence of pesticides in 

groundwater were linked to areas with permeable sediments 

and oxic conditions, and when pesticides were detected in 

groundwater, other anthropogenic contaminants were found 

as well. Co-contaminants included elevated concentrations 

of nutrients, and in particular, nitrogen, which possibly was 

associated with the disposal and transport of human sewage, 

the disposal or use of domestic animal wastes (as manure), 

and the use of fertilizers for crops or residential lawns and 

gardens. In Washington, D.C., nitrogen in the form of nitrate 

or ammonium was a major co-contaminant with pesticides in 

groundwater.

Acknowledgments

The authors would like to thank the District Department 

of the Environment for support of this study. The U.S. 

National Park Service and the Washington, D.C. Department 

of Parks and Recreation are thanked for their cooperation 

and permission to install monitoring wells on their respective properties. Review comments from the following U.S. 

Geological Survey (USGS) colleagues also were greatly 

appreciated: Linda Debrewer, Hydrologist, Reston, Virginia; 

and Connie Loper, Hydrologist, Pennsylvania Water Science 

Center, Harrisburg, Pennsylvania. The authors would also like 

to thank the USGS personnel from the MD-DC-DE Water 

Science Center who contributed to the preparation, collection, 

and processing of the analytical samples, especially Jessica 

Teunis, David Brower, and Wendy McPherson.

References Cited

Anacostia Watershed Toxics Alliance, 2001, Charting a 

course toward restoration: A toxic chemical strategy for 

the Anacostia River, Washington, D.C.: Washington, D.C., 

Metropolitan Council of Governments, 103 p.

Anderson, A.L., Miller, C.V., Olsen, L.D., Doheny, E.J., and 

Phelan, D.J., 2002, Water quality, sediment quality, and 

stream-classification of Rock Creek, Washington, D.C., 

1999–2000: U.S. Geological Survey Water-Resources 

Investigations Report 02–4067, 91 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 WaterResources Investigations Report 97–4248, 54 p.

Ator, S.W., 2008, Natural and human influences on water 

quality in a shallow regional unconsolidated aquifer, 

Northern Atlantic Coastal Plain: U.S. Geological Survey 

Scientific Investigations Report 2008–5190, 19 p. 

Ator, S.W., and Denis, J.M., 1997, Relation of nitrogen and 

phosphorus in ground water to land use in four subunits of 

the Potomac River Basin: U.S. Geological Survey WaterResources Investigations Report 96–4268, 26 p.

Banks, W.S.L., and Reyes, B., 2009, Anthropogenic organic 

compounds in source and finished groundwater of community water systems in the Piedmont Physiographic Province, 

Potomac River Basin, Maryland and Virginia, 2003–04: 

U.S. Geological Survey Scientific Investigations Report 

2009–5064, 33 p.

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

groundwater: Distribution, trends, and governing factors: 

Chelsea, Michigan, Ann Arbor Press, 588 p.

Berndt, M.P., Galeone, D.R., Spruill, T.B., and Crandall, C.A., 

1998, Ground-water quality in three urban areas in the 

coastal plain of the southeastern United States, 1995: U.S. 

Geological Survey Water-Resources Investigations Report 

97–4234, 25 p.

Bruce, B.W., 1995, Denver’s urban ground-water quality: 

Nutrients, pesticides, and volatile organic compounds: U.S. 

Geological Survey Fact Sheet FS–106–95, 2 p.

Canadian Council of Ministers of the Environment, 2007, 

Water-quality guidelines for the protection of aquatic life, 

Chap. 4: Summary table 7.1, 9 p., accessed March 8, 2010 

at http://www.ccme.ca/assets/pdf/aql_summary_7.1_en.pdf.
46 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Chesapeake Bay Program, 2000, Appendix A: Fact Sheet on 

Chesapeake Bay Watershed Chemicals of Concern—as of 

September 26, 2000, 2 p., accessed March 8, 2010 at http://

www.chesapeakebay.net/content/publications/cbp_12210.

pdf.

CH2M Hill, 1977, Rock Creek storm water and water-quality 

management study, prepared for the Montgomery County 

Planning Board: CH2M Hill, 409 p.

Debrewer, L.M., Ator, S.W., and Denver, J.M, 2007, Factors 

affecting spatial and temporal variability in nutrient pesticide concentrations in the surficial aquifer of the Delmarva 

Peninsula: U.S. Geological Survey Scientific Investigations 

Report 2005–5257, 44 p. 

Denver, J.M., and Ator, S.W., 2006, Pesticides in ground water 

of the Maryland Coastal Plain: U.S. Geological Survey 

Fact Sheet 2006–3119, 8 p. 

Desimone, L.A., Hamilton, P.A., and Gilliom, R.J., 2009, 

Quality of water from domestic wells in principal aquifers 

of the United States, 1991–2004—Overview of major findings: U.S. Geological Survey Circular 1332, 48 p.

District of Columbia, 1993, Water quality standards for 

groundwater, District of Columbia Municipal Regulations, 

Final rulemaking: (renumbered) 41 DCR 1075 (March 4, 

1994) Title 21 DCMR, Chap. 11, sections 1150–1158 

[variously paged].

District of Columbia, 2006, Water quality standards for surface 

waters, District of Columbia Municipal Regulations, Final 

rulemaking (February 15, 2006): Title 21 DCMR, chap. 11, 

sections 1100 to 1106, 1158, and 1199 [variously paged], 

accessed March 8, 2010 at http://ddoe.dc.gov/ddoe/frames.

asp?doc=/ddoe/lib/ddoe/wqd/WaterFinalRules06.pdf.

Flanagan, S.M., Montgomery, D.L., and Ayotte, J.D., 2001, 

Shallow ground-water quality in the Boston, Massachusetts 

metropolitan area: U.S. Geological Survey WaterResources Investigations Report 01–4042, 12 p.

Fleming, A.H., and Drake, A.A., Jr., and McCartan, L., 1998, 

Structure, age, and tectonic setting of a multiply reactivated 

shear zone in the Piedmont in Washington, D.C. and vicinity: Southeastern Geology, v. 37, no. 3, p. 115–140.

Focazio, M.J., Plummer, L.N., Böhlke, J.K., Busenberg, 

Eurybiades, Bachman, L.J., and Powars, D.S., 1998, 

Preliminary estimates of residence time and apparent 

ages of ground water in the Chesapeake Bay Watershed, 

and the water-quality data from a survey of springs: U.S. 

Geological Survey Water- Resources Investigations Report 

97–4225, 75 p.

Focazio, M.J., Reilly, T.E., Rupert, M.G., and Helsel, D.R., 

2002, Assessing ground-water vulnerability to contamination: Providing scientifically defensible information for 

decision makers: U.S. Geological Survey Circular 1224, 33 

p.

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

of the National Water Quality Assessment Program—

Occurrence and distribution of water-quality conditions: 

U.S. Geological Survey Circular 1112, 33 p.

Gilliom, R.J., Barbash, J.E., Crawford, C.G., Hamilton, P.A., 

Martin, J.D., Nakagaki, N., Nowell, L.H., Scott, J.C., 

Stackelberg, P.E., Thelin, G.P., and Wolock, D.M., 2006, 

Pesticides in the Nation’s streams and ground water: U.S. 

Geological Survey Circular 1291, 172 p.

Hamilton, P.A., Denver, J.M., Phillips, P.J., and Shedlock, 

R.J., 1993, Water-quality assessment of the Delmarva 

Peninsula, Delaware, Maryland, Virginia—effects of agricultural activities on, and distribution of, nitrate and inorganic constituents, in the surficial aquifer: U.S Geological 

Survey Open-File Report 93–40, 87 p.

Helsel, D.R, and Hirsch, R.M., 2002, Statistical methods 

in water resources: U.S. Geological Survey Techniques 

of Water-Resources Investigations, book 4, chap. A3, 

Hydrologic Analysis and Interpretation, 524 p. (available at 

http://pubs.usgs.gov/twri/twri4a3/html/pdf_new.html).

Homer, C., Huang, C., Yang, L., Wylie, B., and Coan, M., 

2004, Development of a 2001 national land cover database 

for the United States: Photogrammetric Engineering and 

Remote Sensing, v. 70, no. 7, p. 829–840.

International Joint Commission (Consolidator), U.S. and 

Canada, 1989, Revised Great Lakes Water Quality 

Agreement of 1978 as Amended by Protocol Signed 

November 18, 1987, Windsor, Ontario, Canada, accessed 

March 8, 2010 at http://www.ijc.org/en/activities/

consultations/glwqa/agreement.php.

Johnston, P.M., 1964, Geology and ground-water resources 

of Washington, D.C. and vicinity: U.S Geological Survey 

Water Supply Paper 1776, 97 p. 

Kiely, T., Donaldson, D., and Grube, A., 2004, Pesticide 

industry usage and sales: 2000 and 2001 market estimates, 

Washington, D.C.: U.S. Environmental Protection Agency, 

Biological and Economic Analysis Division, Office of 

Pesticide Programs (7503C), 48 p.

Klohe, C.A., and Debrewer, L.M., 2007, Summary of groundwater-quality data in the Anacostia River Watershed, 

Washington, D.C., September–December, 2005: U.S. 

Geological Survey Open-File Report 2006–1392, 64 p.
References Cited 47

Kolpin, D.W., Squillace, P.J., Barbash, J.E., and Zogorski, J.S., 

1997, Pesticides and volatile organic compounds in shallow 

urban groundwater of the United States, in Chilton, John 

and others, eds., Groundwater in the urban environment, 

v. 1, problems, processes, and management: Rotterdam, 

Netherlands, A.A. Balkema Publishers, p. 469–474.

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. 550–518.

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 water-quality samples and 

related data: U.S. Geological Survey Open-File Report 

95–399, 113 p.

McCartan, L., 1989, Geologic map of Charles County, 

Maryland: Maryland Geological Survey County Geologic 

Map Series, scale 1:62,500. 

Metropolitan Washington Council of Governments, 1998, 

Washington, D.C., Anacostia watershed restoration progress 

and conditions report, 1990–1997: Anacostia Watershed 

Restoration Committee Report, 44 p.

Metropolitan Washington Council of Governments, 2003, 

Working together to restore the Anacostia Watershed: 

Washington, D.C., Anacostia Watershed Restoration 

Committee, Annual Report, 20 p.

Miller, C.V., Gutiérrez-Magness, A.L., Feit-Majedi, B., and 

Foster, G.D., 2007, Water quality in the Upper Anacostia 

River, Maryland: Continuous and discrete monitoring with 

simulations to estimate concentrations and yields, 2003–05: 

U.S. Geological Survey Scientific Investigations Report 

2007–5142, 51p. 

Miller, C.V., and Klohe, C.A., 2003, Summary of waterand sediment-quality data for Anacostia River well sites 

sampled in July–August 2002: U.S. Geological Survey 

Open-File Report 03–73, 48 p.

National Oceanographic and Atmospheric Administration 

(NOAA), 2010, Precipitation data, accessed May 19, 2010 

at http://www.erh.noaa.gov/lwx/climate/dca/dcaprecip.txt.

Phelan, D.J., and Miller, C.V., in press, Occurrence of organic 

wastewater compounds in Rock Creek Park, Washington, 

D.C., 2007–08: U.S. Geological Survey Scientific 

Investigations Report 2010–5162.

Pinkney, A.E., Harshberger, J.C., May, E.B., and Melancon, 

M.J., 2001, Tumor prevalence and biomarkers of exposure 

in brown bullhead (Ameiurus nebulosus) from the 

tidal Potomac River Watershed, USA: Environmental 

Toxicology and Chemistry, v. 20, no. 6, p. 1,196–1,205.

Pinkney, A.E., Harshberger, J.C., May, E.B., and Reichert, 

W.L., 2004, Tumor prevalence and biomarkers of exposure 

and response in brown bullhead (Ameiurus nebulosus) 

from the Anacostia River, Washington, D.C., and Tuckahoe 

River, Maryland, USA: Environmental Toxicology and 

Chemistry, v. 23, no. 3, p. 638–647. 

Saffer, R.W., Pentz, R.H., and Tallman, A.J., 2005, Waterresources data for Maryland, Delaware, and Washington, 

D.C., Water Year 2004, v. 1, surface-water data, 540 p.

Saffer, R.W., Pentz, R.H., and Tallman, A.J., 2006, Waterresources data for Maryland, Delaware, and Washington, 

D.C., Water Year 2005, v. 1, surface-water data, 530 p.

Schneider, J., Montaser, A., and Watt, H.M., 1993, Ground 

water resource assessment study for the District of 

Columbia, Sampling and analysis report for the Group 

B wells—Phase III: Washington, D.C. Water Resources 

Center Research Report No. 138, 24 p. plus appendix. 

Schneider, J., O’Connor, J.V., Chang, F.M., Wade, C., Pao, 

H.P., Montaser, A., Johnson, J., and Atobrah, K., 1993, 

Ground water resource assessment study for the District 

of Columbia, Sampling and analysis report for the Group 

A wells—Phase III: Washington, D.C., Water Resources 

Center Research Report No. 137, 31 p. plus appendix.

Shedlock, R.J., Denver, J.M., Hayes, M.A., Hamilton, P.A., 

Koterba, M.T., Bachman, L.J., Phillips, P.J., and Banks, 

W.S.L., 1999, Water-quality assessment of the Delmarva 

Peninsula, Delaware, Maryland, and Virginia: Results of 

investigations, 1987–91: U.S. Geological Survey WaterSupply Paper 2355–A, 41 p. 

Shedlock, R.J., Hamilton, P.A., Denver, J.M., and Phillips, 

P.J., 1993, Multiscale approach to regional ground-waterquality assessment of the Delmarva Peninsula, in Alley, 

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

Nostrand Reinhold, p. 563–587.

Southworth, C. and Denenny, D., 2006, Geologic map of the 

National Parks in the National Capital region, Washington, 

D.C., Virginia, Maryland, and West Virginia: U.S. 

Geological Survey Open-File Report 2005–1331, 32 p.

Tenbus, F.J., 2003, Lithologic coring in the lower Anacostia 

tidal watershed, Washington, D.C., July 2002: U.S. 

Geological Survey Open-File Report 03–318, 62 p.
48 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

The Trust for Public Land, 2009, City park facts 2009: San 

Francisco, California, Center for City Park Excellence, 

32 p., accessed March 8, 2010 at http://www.tpl.org/

content_documents/CityParkFacts_2009.pdf.

Toccalino, P.L., 2007, Development and application of healthbased screening levels for use in water-quality assessments: 

U.S. Geological Survey Scientific Investigations Report 

2007–5106, 12 p., accessed March 8, 2010 at http://pubs.

usgs.gov/sir/2007/5106/pdf/sir20075106.pdf. 

Toccalino, P.L., Norman, J.E., Phillips, R.H., Kaufmann, L.J., 

Stackelberg, P.E., Nowell, L.H., Krietman, S.J., and Post, 

G.B., 2004, Application of health-based screening levels 

to ground-water quality data in state-scale effort: U.S. 

Geological Survey Scientific Investigations Report 2005–

5174, 64 p.

Tyler, T.D., and Belitz, K., 2009, Assigning land use to supply 

wells for the statistical characterization of regional groundwater quality: Correlating urban land use and VOC occurrence: Journal of Hydrology, v. 37, nos. 1–4, p. 100–108.

U.S. Census Bureau, 2008, Quickfacts: Washington, D.C., 

U.S. Census Bureau, accessed March 8, 2010 at http://

quickfacts.census.gov/qfd/states/11000.html.

U.S. Environmental Protection Agency, 1999, National recommended water-quality criteria: Washington, D.C., Office 

of Water, Office of Science and Technology Report 4304T, 

22 p., accessed March 8, 2010 at http://www.epa.gov/

waterscience/criteria/wqctable/nrwqc-2009.pdf.

U.S. Environmental Protection Agency, 2004, 2004 Edition 

of the drinking water standards and health advisories: 

Washington, D.C. Office of Water, U.S. Environmental 

Protection Agency Report 822–R–04–005, 12 p., accessed 

March 8, 2010 at http://web.epa.ohio.gov/dsiwm/document/

newsPDFs/2004dwstandards.pdf.

U.S. Environmental Protection Agency, 2005, Fact Sheet: 

The drinking water contaminant candidate list—The source 

of priority contaminants for the Drinking Water Program: 

Washington, D.C., Office of Water, U.S. Environmental 

Protection Agency Report. No. EPA 815–F–05–001, 6 p., 

accessed March 8, 2010 at http://www.epa.gov/ogwdw/ccl/

pdfs/fs_ccl2_final-02-23-05.pdf.

U.S. Environmental Protection Agency, 2009, Drinking 

Water Standards and Health Advisories, 2009 Edition: 

Washington, D.C., Office of Water, U.S. Environmental 

Protection Agency Report No. 822–R–011, 12 p. 

U.S. Geological Survey, 2007, Water-resources data for the 

United States, Water Year 2006, accessed May 19, 2010 at 

http://wdr.water.usgs.gov/wy2006/search.jsp.

U.S. Geological Survey, 2008, Water-resources data for the 

United States, Water Year 2006, accessed May 19, 2010 at 

http://wdr.water.usgs.gov/wy2007/search.jsp.

U.S. Geological Survey, 2009, Water-resources data for the 

United States, Water Year 2006, accessed May 19, 2010 at 

http://wdr.water.usgs.gov/wy2008/search.jsp.

Wheeler, J.C., 2003, Water withdrawal and use in Maryland, 

1990-91: U.S. Geological Survey Water-Resources 

Investigations Report 93–4225, 42 p.

Williams, G.P., 1977, Washington, D.C.’s vanishing springs 

and waterways: U.S. Geological Survey Circular 752, 19 p.

Yorke, T.H., and Herb, W.J., 1978, Effects of urbanization on 

streamflow and sediment transport in the Rock Creek and 

Anacostia River Basins, Montgomery County, Maryland, 

1962–74: U.S. Geological Survey Professional Paper 1003, 

71 p. 
Appendix A: Water-quality and quality-control data tables, 2008 49

Appendix A: Water-quality and quality-control 

data tables, 2008

Tables

A1. Concentrations of major ions, nutrients, and pesticides in 

groundwater samples collected in Washington, D.C., August to 

September 2008, and selected water-quality standards.....................................................50

A2. Description of quality-control samples obtained in conjunction 

with the collection of groundwater samples in Washington, D.C., 

August to September 2008........................................................................................................79
50 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Date Time 

Flow 

rate, 

instantaneous 

(gal/min)

Pumped 

period 

prior to 

sampling

(minutes)

Turbidity 

(NTU) 

Dissolved 

oxygen 

(mg/L)

pH

(standard 

units)

Specific 

conductance

(μS/cm)

Water

temperature

(

OC)

CASRN® na na na na na na na

385138076585902 AC Aa 7 8/26/2008 1315 0.13 111 22 < 1.0 5.7 74 18.0

385138076585901 AC Aa 6 8/26/2008 1000 0.09 58 1.1 < 1.0 4.0 1,110 20.9

385606076584101 WE Ba 9 8/25/2008 0900 0.05 44 4.4 1.2 6.1 621 19.7

385649076584201 WE Ba 11 8/28/2008 1115 0.2 39 <1.0 6.4 4.8 276 18.6

385332076594701 WE Ca 32 8/27/2008 0900 0.34 42 0.3 5.5 5.5 1,350 19.0

385245076583501 WE Ca 34 8/27/2008 1115 0.73 39 3.1 < 1.0 7.4 763 16.4

385252076572801 WE Cb 8 9/4/2008 1515 1.8 228 16 0.5 6.8 112 17.1

385443076562801 WE Cb 5 8/28/2008 0915 0.1 40 13 6.3 5.5 347 17.8

385327076544801 WE Cc 3 9/7/2008 0930 0.08 45 8.8 3.6 5.8 813 18.1

385929077020901 WW Ac 8 9/2/2008 1100 0.19 44 1.4 4.5 5.1 1,550 16.8

385644077061101 WW Ba 28 9/3/2008 1200 0.04 52 2.9 <1.0 7.1 407 18.4

385527077000701 WW Bc 9 8/25/2008 1130 0.1 39 1.7 5.3 4.7 386 17.9

385619077020701 WW Bc 10 9/3/2008 0915 0.09 80 160 1.3 6.4 1,180 19.3

385707077021801 WW Bc 11 9/2/2008 1000 0.14 73 3.9 3.5 5.2 117 17.0

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- 5 -- 6.5-8.5 -- --

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- *** -- 6.0-8.5 -- --

B -- -- *** -- 6.0-8.5 -- --

C -- -- *** 4.3-5 6.0-8.5 -- 32.2

D -- -- -- -- -- -- --

USEPA National Primary 

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

-- -- -- -- -- -- --
Appendix A: Water-quality and quality-control data tables, 2008 51

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Calcium

(mg/L)

Magnesium

(mg/L)

Potassium

(mg/L)

Sodium

(mg/L)

Alkalinity, 

field 

(mg/L as 

CaCO3)

Bicarbonate

(mg/L as 

HCO3)

Chloride

(mg/L)

CASRN® 7440-70-2 7439-95-4 7440-09-7 7440-23-5 na na 16887-00-6

385138076585902 AC Aa 7 2.43 1.31 3.27 3.49 15.3 18.7 2.73

385138076585901 AC Aa 6 68.6 31.6 8.25 77.9 -- -- 151

385606076584101 WE Ba 9 71.3 22.2 5.31 15.3 189 230 25.8

385649076584201 WE Ba 11 11.6 7.54 6.12 20.1 3.8 4.6 39.0

385332076594701 WE Ca 32 60.5 15.9 8.42 164 18.8 22.9 322

385245076583501 WE Ca 34 109 14.2 6.64 16.6 357 435 27.1

385252076572801 WE Cb 8 8.50 3.71 4.35 2.20 40.7 49.7 1.98

385443076562801 WE Cb 5 41.8 6.09 4.09 8.95 16.3 19.9 26.5

385327076544801 WE Cc 3 40.0 9.04 3.70 95.8 42.8 52.1 185

385929077020901 WW Ac 8 93.0 47.3 9.04 129 8.3 10.1 448

385644077061101 WW Ba 28 48.2 8.54 3.40 15.6 88.5 108 35.2

385527077000701 WW Bc 9 14.8 10.3 4.52 34.7 4.8 5.8 79.8

385619077020701 WW Bc 10 98.9 29.1 15.1 39.0 361 440 84.8

385707077021801 WW Bc 11 5.87 4.10 1.65 6.73 16.3 19.9 14.6

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- -- -- -- -- 250

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- -- -- -- --

B -- -- -- -- -- -- --

C -- -- -- -- -- -- --

D -- -- -- -- -- -- --

USEPA National Primary 

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

-- -- -- -- -- -- --
52 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Fluoride

(mg/L)

Silica

(mg/L as SiO2)

Sulfate

(mg/L as SO4)

Ammonia

(mg/L as N)

Nitrate + nitrite

(mg/L as N)

Nitrite

(mg/L as N)

CASRN® 16984-48-8 7631-86-9 14808-79-8 7664-41-7 na 14797-65-0

385138076585902 AC Aa 7 E.07 16.3 11.5 0.026 <.016 E.002

385138076585901 AC Aa 6 1.64 16.7 349d 0.025 5.66d 0.006

385606076584101 WE Ba 9 E.09 7.4 85.1 0.702 0.130 E.002

385649076584201 WE Ba 11 E.10 12.1 32.9 0.110 4.52 0.002

385332076594701 WE Ca 32 <.12 7.7 70.0 <.020 7.77d <.002

385245076583501 WE Ca 34 0.34 23.0 1.36 2.13 <.016 E.002

385252076572801 WE Cb 8 E.10 8.6 6.24 0.414 <.016 E.001

385443076562801 WE Cb 5 < .12 5.1 67.7 <.020 6.41d < .002

385327076544801 WE Cc 3 0.13 6.4 55.2 <.020 2.90 <.002

385929077020901 WW Ac 8 < .12 20.7 57.4d E.014 6.60 E .001

385644077061101 WW Ba 28 E.09 26.4 47.1 <.020 <.016 < .002

385527077000701 WW Bc 9 E.06 12.6 31.2 <.020 2.76 <.002

385619077020701 WW Bc 10 0.19 29.8 12.0 5.18 <.016 0.003

385707077021801 WW Bc 11 <.12 26.3 E.16 E.014 3.29 0.003

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

4.0 -- 250 -- 10 1

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- -- -- --

B -- -- -- -- -- --

C -- -- -- *** -- --

D -- -- -- -- -- --

USEPA National Primary 

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

4 -- -- -- 10 1
Appendix A: Water-quality and quality-control data tables, 2008 53

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Orthophosphate

(mg/L as P)

Total Phosphorus

(mg/L as P)

Iron

(μg/L)

Manganese

(μg/L)

CASRN® na 7723-14-0 7439-89-6 7439-96-5

385138076585902 AC Aa 7 E.006 0.016 4,230 566

385138076585901 AC Aa 6 0.013 0.009 210 1,580

385606076584101 WE Ba 9 0.01 0.008 < 8 974

385649076584201 WE Ba 11 E.006 <.006 184 559

385332076594701 WE Ca 32 0.006 <.006 E 4 3.9

385245076583501 WE Ca 34 0.218d 0.219 3,140 576

385252076572801 WE Cb 8 0.384d 0.38 3,490 159

385443076562801 WE Cb 5 E.004 <.006 E6 7.8

385327076544801 WE Cc 3 <.006 <.006 < 8 149

385929077020901 WW Ac 8 0.012 0.012 E5 539

385644077061101 WW Ba 28 0.006 E.004 51 465

385527077000701 WW Bc 9 0.009 E.004 < 8 281

385619077020701 WW Bc 10 E.003 0.105 38,600d 3,820

385707077021801 WW Bc 11 0.017 0.018 E5 231

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- 300 50

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- --

B -- -- -- --

C -- -- 1,000 --

D -- -- -- 100

USEPA National Primary 

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

-- -- -- --
54 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Pesticides and pesticide degradates

1-

Naphthol

(μg/L)

2,4-Dichlorophenoxy acetic 

acid methyl 

ester 

(2,4-D ME)

(μg/L)

2,4-D plus 

2,4-D ME

(μg/L as 

2,4-D)

(μg/L)

2,4-Dichlorophenoxy 

acetic acid 

(2,4-D)

(μg/L)

2,4-Dichlorophenoxy 

butyric acid 

(2,4-DB)

(μg/L)

2,6-Diethylaniline

(μg/L)

Alachlor 

2nd amide

(μg/L)

CASRN® 90-15-3 1928-38-7 na 94-75-7 94-82-6 579-66-8 na

385138076585902 AC Aa 7 <.04 <.040 <.02 <.02 <.02 <.006 <.010

385138076585901 AC Aa 6 <.04 <.040 <.02 <.02 <.02 <.006 <.010

385606076584101 WE Ba 9 <.04 <.040 <.02 <.02 <.02 <.006 <.010

385649076584201 WE Ba 11 <.04 <.040 <.02 <.02 <.02 <.006 <.010

385332076594701 WE Ca 32 <.04 <.040 <.02 <.02 <.02 <.006 <.010

385245076583501 WE Ca 34 <.04 <.040 <.02 <.02 <.02 <.006 <.010

385252076572801 WE Cb 8 <.04 <.040 <.02 <.02 <.02 <.006 <.010

385443076562801 WE Cb 5 <.04 <.040 <.02 <.02 <.02 <.006 <.010

385327076544801 WE Cc 3 <.04 <.040 <.02 <.02 <.02 <.006 <.010

385929077020901 WW Ac 8 <.04 <.040 <.02 <.02 <.02 <.006 <.010

385644077061101 WW Ba 28 <.04 <.040 <.02 <.02 <.02 <.006 <.010

385527077000701 WW Bc 9 <.04 <.040 <.02 <.02 <.02 <.006 <.010

385619077020701 WW Bc 10 <.04 <.040 <.02 <.02 <.02 <.006 <.026

385707077021801 WW Bc 11 <.04 <.040 <.02 <.02 <.02 <.006 <.010

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- -- 100 -- --

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- -- --

B -- -- -- -- --

C -- -- -- -- --

D -- -- -- -- --

USEPA National Primary 

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

-- -- 70 -- --
Appendix A: Water-quality and quality-control data tables, 2008 55

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Pesticides and pesticide degradates

2-hydroxy-4-

isopropyl-amino6-ethylamino-striazine (CIAT)

(μg/L)

2-chloro-4-

ethylamino-6-

amino-s-triazine 

(CEAT)

(μg/L)

2-Ethyl-6-

methylaniline

(μg/L)

2-chloro-4-isopropylamino-6-

amino-s-triazine 

(OIET)

(μg/L)

3,4-Dichloroaniline

(μg/L)

3,5-Dichloroaniline

(μg/L)

CASRN® 1007-28-9 2163-68-0 24549-06-2 2163-68-0 95-76-1 626-43-7

385138076585902 AC Aa 7 <.014 <.08 <.010 <.040 <.006 <.008

385138076585901 AC Aa 6 <.014 <.08 <.010 <.040 <.006 <.008

385606076584101 WE Ba 9 E.006 <.08 <.010 <.040 <.006 <.008

385649076584201 WE Ba 11 <.014 <.08 <.010 <.040 <.006 <.008

385332076594701 WE Ca 32 E.022 <.08 <.010 <.040 E.006 <.008

385245076583501 WE Ca 34 <.014 <.08 <.010 <.040 <.006 <.008

385252076572801 WE Cb 8 E.025 <.08 <.010 <.040 <.006 <.008

385443076562801 WE Cb 5 E.013 <.08 <.010 E.034 <.006 <.008

385327076544801 WE Cc 3 E.014 <.08 <.010 E.013 <.006 <.008

385929077020901 WW Ac 8 E.020 <.08 <.010 <.040 <.006 <.008

385644077061101 WW Ba 28 <.014 <.08 <.010 <.040 <.006 <.008

385527077000701 WW Bc 9 E.013 <.08 <.010 <.040 <.006 <.008

385619077020701 WW Bc 10 <.014 <.08 <.010 <.040 <.070 <.008

385707077021801 WW Bc 11 <.014 <.08 <.010 <.040 <.006 <.008

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- -- -- -- --

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- -- -- --

B -- -- -- -- -- --

C -- -- -- -- -- --

D -- -- -- -- -- --

USEPA National Primary 

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

-- -- -- -- -- --
56 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Pesticides and pesticide degradates

3-Hydroxy 

carbofuran

(μg/L)

4-Chloro-2-

methylphenol

(μg/L)

Acetochlor

(μg/L)

Acifluorfen

(μg/L)

Alachlor

(μg/L)

Aldicarb 

sulfone

(μg/L)

Aldicarb 

sulfoxide

(μg/L)

CASRN® 16655-82-6 1570-64-5 34256-82-1 50594-66-6 15972-60-8 1646-88-4 1646-87-3

385138076585902 AC Aa 7 <.040 <.005 <.006 <.040 <.006 <.08 <.060

385138076585901 AC Aa 6 <.040 <.005 <.006 <.040 <.006 <.08 <.060

385606076584101 WE Ba 9 <.040 <.005 <.006 <.040 <.006 <.08 <.060

385649076584201 WE Ba 11 <.040 <.005 <.006 <.040 <.006 <.08 <.060

385332076594701 WE Ca 32 <.040 <.005 <.006 <.040 <.006 <.08 <.060

385245076583501 WE Ca 34 <.040 <.005 <.006 <.040 <.006 <.08 <.060

385252076572801 WE Cb 8 <.040 <.005 0.019 <.040 <.006 <.08 <.060

385443076562801 WE Cb 5 <.040 <.005 <.006 <.040 <.006 <.08 <.060

385327076544801 WE Cc 3 <.040 <.005 <.006 <.040 <.006 <.08 <.060

385929077020901 WW Ac 8 <.040 <.005 <.006 <.040 <.006 <.08 <.060

385644077061101 WW Ba 28 <.040 <.005 <.006 <.040 <.006 <.08 <.060

385527077000701 WW Bc 9 <.040 <.005 <.006 <.040 <.006 <.08 <.060

385619077020701 WW Bc 10 <.040 <.005 <.006 <.040 <.006 <.08 <.060

385707077021801 WW Bc 11 <.040 <.005 <.006 <.040 <.006 <.08 <.060

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- -- -- -- -- --

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- -- -- -- --

B -- -- -- -- -- -- --

C -- -- -- -- -- -- --

D -- -- -- -- -- -- --

USEPA National Primary 

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

-- -- -- -- 2 2 4
Appendix A: Water-quality and quality-control data tables, 2008 57

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Pesticides and pesticide degradates

Aldicarb

(μg/L)

Aldrin

(μg/L)

alpha-Endosulfan

(μg/L)

alphaEndosulfan, 

Method 2

(μg/L)

Aminomethylphosphonic 

acid (AMPA)

(μg/L)

Atrazine

(μg/L)

Azinphosmethyl oxon

(μg/L)

CASRN® 116-06-3 309-00-2 959-98-8 959-98-9 1066-51-9 1912-24-9 961-22-8

385138076585902 AC Aa 7 <.12 <.002 <.006 <.002 <.02 <.007 <.04

385138076585901 AC Aa 6 <.12 <.002 <.006 <.002 <.02 <.007 <.04

385606076584101 WE Ba 9 <.12 <.002 <.006 <.002 <.02 <.007 <.04

385649076584201 WE Ba 11 <.12 <.002 <.006 <.002 <.02 <.007 <.04

385332076594701 WE Ca 32 <.12 <.002 <.006 <.002 0.02 0.032 <.04

385245076583501 WE Ca 34 <.12 <.002 <.006 <.002 <.02 <.007 <.04

385252076572801 WE Cb 8 <.12 <.002 <.006 <.002 <.02 0.106 <.04

385443076562801 WE Cb 5 <.12 <.002 <.006 <.002 <.02 0.009 <.04

385327076544801 WE Cc 3 <.12 <.002 <.006 <.002 <.02 0.009 <.04

385929077020901 WW Ac 8 <.12 <.002 <.006 <.002 <.02 <.007 <.04

385644077061101 WW Ba 28 <.12 <.002 <.006 <.002 <.02 <.007 <.04

385527077000701 WW Bc 9 <.12 <.002 <.006 <.002 <.02 0.008 <.04

385619077020701 WW Bc 10 <.12 <.002 <.006 <.002 <.02 <.007 <.04

385707077021801 WW Bc 11 <.12 <.002 <.006 <.002 <.02 <.007 <.04

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- -- -- -- -- --

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- -- -- -- --

B -- -- -- -- -- -- --

C -- 0.4-0.3 0.056-0.22 0.056-0.23 -- -- --

D -- 0.00005 89 89 -- -- --

USEPA National Primary 

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

3 -- -- -- -- 3 --
58 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Pesticides and pesticide degradates

Azinphosmethyl

(μg/L)

Bendiocarb

(μg/L)

Benfluralin

(μg/L)

Benomyl

(μg/L)

Bensulfuronmethyl

(μg/L)

Bentazon

(μg/L)

Bromacil

(μg/L)

CASRN® 86-50-0 22781-23-3 1861-40-1 17804-35-2 83055-99-6 25057-89-0 314-40-9

385138076585902 AC Aa 7 <.120 <.04 <.010 <.040 <.06 <.04 <.02

385138076585901 AC Aa 6 <.120 <.04 <.010 <.040 <.06 <.04 <.02

385606076584101 WE Ba 9 <.120 <.04 <.010 <.040 <.06 <.04 <.02

385649076584201 WE Ba 11 <.120 <.04 <.010 <.040 <.06 <.04 <.02

385332076594701 WE Ca 32 <.120 <.04 <.010 <.040 <.06 <.04 <.02

385245076583501 WE Ca 34 <.120 <.04 <.010 <.040 <.06 <.04 <.02

385252076572801 WE Cb 8 <.120 <.04 <.010 <.040 <.06 <.04 <.02

385443076562801 WE Cb 5 <.120 <.04 <.010 <.040 <.06 <.04 <.02

385327076544801 WE Cc 3 <.120 <.04 <.010 <.040 <.06 <.04 <.02

385929077020901 WW Ac 8 <.120 <.04 <.010 <.040 <.06 <.04 0.04

385644077061101 WW Ba 28 <.120 <.04 <.010 <.040 <.06 <.04 <.02

385527077000701 WW Bc 9 <.120 <.04 <.010 <.040 <.06 <.04 E.01

385619077020701 WW Bc 10 <.120 <.04 <.010 <.040 <.06 <.04 <.02

385707077021801 WW Bc 11 <.120 <.04 <.010 <.040 <.06 <.04 <.02

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- -- -- -- -- --

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- -- -- -- --

B -- -- -- -- -- -- --

C 0.01 -- -- -- -- -- --

D -- -- -- -- -- -- --

USEPA National Primary 

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

-- -- -- -- -- -- --
Appendix A: Water-quality and quality-control data tables, 2008 59

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Pesticides and pesticide degradates

Bromoxynil

(μg/L)

Caffeine

(μg/L)

Carbaryl

(μg/L)

Carbaryl

(μg/L)

Carbofuran

(μg/L)

Carbofuran

(μg/L)

Chloramben methyl 

ester

(μg/L)

Chlordane 

(technical)

(μg/L)

CASRN® 1689-84-5 58-08-02 63-25-2 63-25-3 1563-66-2 1563-66-3 7286-84-2 57-74-9

385138076585902 AC Aa 7 <.12 <.060 <.04 <.060 <.020 <.020 <.10 <.1

385138076585901 AC Aa 6 <.12 <.060 <.04 <.060 <.020 <.020 <.10 <.1

385606076584101 WE Ba 9 <.12 <.060 <.04 <.060 <.020 <.020 <.10 <.1

385649076584201 WE Ba 11 <.12 <.060 <.04 <.060 <.020 <.020 <.10 <.1

385332076594701 WE Ca 32 <.12 <.060 <.04 <.060 <.020 <.020 <.10 <.1

385245076583501 WE Ca 34 <.12 <.060 <.04 <.060 <.020 <.020 <.10 <.1

385252076572801 WE Cb 8 <.12 <.060 <.04 <.060 <.020 <.020 <.10 <.1

385443076562801 WE Cb 5 <.12 <.060 <.04 <.060 <.020 <.020 <.10 <.1

385327076544801 WE Cc 3 <.12 <.060 <.04 <.060 <.020 <.020 <.10 <.1

385929077020901 WW Ac 8 <.12 <.060 <.04 <.060 <.020 <.020 <.10 <.1

385644077061101 WW Ba 28 <.12 <.060 <.04 <.060 <.020 <.020 <.10 <.1

385527077000701 WW Bc 9 <.12 <.060 <.04 <.060 <.020 <.020 <.10 <.1

385619077020701 WW Bc 10 <.12 <.060 <.04 <.060 <.020 <.020 <.10 <.1

385707077021801 WW Bc 11 <.12 <.060 <.04 <.060 <.020 <.020 <.10 <.1

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- -- -- -- -- -- --

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- -- -- -- -- --

B -- -- -- -- -- -- -- --

C -- -- -- -- -- -- -- 0.0043-2.4

D -- -- -- -- -- -- -- 0.00081

USEPA National Primary 

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

-- -- -- -- 40 40 -- 2
60 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Pesticides and pesticide degradates

Chlorimuronethyl

(μg/L)

Chlorpyrifos 

oxon

(μg/L)

Chlorpyrifos

(μg/L)

cisPermethrin

(μg/L)

cisPropiconazole

(μg/L)

Clopyralid

(μg/L)

Cyanazine

(μg/L)

CASRN® 90982-32-4 5598-15-2 2921-88-2 54774-45-7 60207-90-1 1702-17-6 21725-46-2

385138076585902 AC Aa 7 <.080 <.06 <.005 <.010 <.006 <.06 <.020

385138076585901 AC Aa 6 <.080 <.06 <.005 <.010 <.006 <.06 <.020

385606076584101 WE Ba 9 <.080 <.06 <.005 <.010 <.006 <.06 <.020

385649076584201 WE Ba 11 <.080 <.06 <.005 <.010 <.006 <.06 <.020

385332076594701 WE Ca 32 <.080 <.06 <.005 <.010 <.006 <.06 <.020

385245076583501 WE Ca 34 <.080 <.06 <.005 <.010 <.006 <.06 <.020

385252076572801 WE Cb 8 <.080 <.06 E.005 <.010 <.006 <.06 <.020

385443076562801 WE Cb 5 <.080 <.06 <.005 <.010 <.006 <.06 <.020

385327076544801 WE Cc 3 <.080 <.06 <.005 <.010 <.006 <.06 <.020

385929077020901 WW Ac 8 <.080 <.06 <.005 <.010 <.006 <.06 <.020

385644077061101 WW Ba 28 <.080 <.06 <.005 <.010 <.006 <.06 <.020

385527077000701 WW Bc 9 <.080 <.06 <.005 <.010 <.006 <.06 <.020

385619077020701 WW Bc 10 <.080 <.06 <.005 <.010 <.006 <.06 <.020

385707077021801 WW Bc 11 <.080 <.06 <.005 <.010 <.006 <.06 <.020

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- -- -- -- -- --

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- -- -- -- --

B -- -- -- -- -- -- --

C -- -- -- -- -- -- --

D -- -- -- -- -- -- --

USEPA National Primary 

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

-- -- -- -- -- -- --
Appendix A: Water-quality and quality-control data tables, 2008 61

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Pesticides and pesticide degradates

Cycloate

(μg/L)

Cyfluthrin

(μg/L)

lambdaCyhalothrin

(μg/L)

Cypermethrin

(μg/L)

Dacthal 

monoacid

(μg/L)

Dimethyl 

tetracholoroterephthalate 

(DCPA)

(μg/L)

Desulfinylfipronil

(μg/L)

CASRN® 1134-23-2 68359-37-5 91465-08-6 52315-07-8 887-54-7 1861-32-1 --

385138076585902 AC Aa 7 <.02 <.016 <.004 <.014 <.02 <.003 <.012

385138076585901 AC Aa 6 <.02 <.016 <.004 <.014 <.02 <.003 <.012

385606076584101 WE Ba 9 <.02 <.016 <.004 <.014 <.02 <.003 <.012

385649076584201 WE Ba 11 <.02 <.016 <.004 <.014 <.02 <.003 <.012

385332076594701 WE Ca 32 <.02 <.016 <.004 <.014 <.02 <.003 <.012

385245076583501 WE Ca 34 <.02 <.016 <.004 <.014 <.02 <.003 <.012

385252076572801 WE Cb 8 <.02 <.016 <.004 <.014 <.02 <.003 <.012

385443076562801 WE Cb 5 <.02 <.016 <.004 <.014 <.02 <.003 <.012

385327076544801 WE Cc 3 <.02 <.016 <.004 <.014 <.02 <.003 <.012

385929077020901 WW Ac 8 <.02 <.016 <.004 <.014 <.02 <.003 <.012

385644077061101 WW Ba 28 <.02 <.016 <.004 <.014 <.02 <.003 <.012

385527077000701 WW Bc 9 <.02 <.016 <.004 <.014 <.02 <.003 <.012

385619077020701 WW Bc 10 <.02 <.016 <.004 <.014 <.02 <.003 <.012

385707077021801 WW Bc 11 <.02 <.016 <.004 <.014 <.02 <.003 <.012

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- -- -- -- -- --

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- -- -- -- --

B -- -- -- -- -- -- --

C -- -- -- -- -- -- --

D -- -- -- -- -- -- --

USEPA National Primary 

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

-- -- -- -- -- -- --
62 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Pesticides and pesticide degradates

Diazinon

(μg/L)

Diazoxon

(μg/L)

Dicamba

(μg/L)

Dichlorprop

(μg/L)

Dicrotophos

(μg/L)

Dieldrin

(μg/L)

Dieldrin, 

Method 2

(μg/L)

CASRN® 333-41-5 962-58-3 1918-00-9 120-36-5 141-66-2 60-57-1 60-57-1

385138076585902 AC Aa 7 <.005 <.01 <.04 <.02 <.08 <.009 <.002

385138076585901 AC Aa 6 <.005 <.01 <.04 <.02 <.08 <.009 <.002

385606076584101 WE Ba 9 <.005 <.01 <.04 <.02 <.08 <.009 <.002

385649076584201 WE Ba 11 <.005 <.01 <.04 <.02 <.08 0.014 0.016

385332076594701 WE Ca 32 <.005 <.01 <.04 <.02 <.08 0.026 0.028

385245076583501 WE Ca 34 <.005 <.01 <.04 <.02 <.08 <.009 <.002

385252076572801 WE Cb 8 <.005 <.01 <.04 <.02 <.08 <.009 <.002

385443076562801 WE Cb 5 <.005 <.01 <.04 <.02 <.08 <.009 <.002

385327076544801 WE Cc 3 <.005 <.01 <.04 <.02 <.08 <.009 <.002

385929077020901 WW Ac 8 <.005 <.01 <.04 <.02 <.08 0.017 0.014

385644077061101 WW Ba 28 <.005 <.01 <.04 <.02 <.08 <.009 <.002

385527077000701 WW Bc 9 <.005 <.01 <.04 <.02 <.08 <.009 <.002

385619077020701 WW Bc 10 <.005 <.01 <.04 <.02 <.08 <.009 <.002

385707077021801 WW Bc 11 <.005 <.01 <.04 <.02 <.08 <.009 <.002

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- -- -- -- -- --

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- -- -- -- --

B -- -- -- -- -- -- --

C -- -- -- -- -- .056-0.24 .056-0.24

D -- -- -- -- -- 0.000054 0.000054

USEPA National Primary 

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

-- -- -- -- -- -- --
Appendix A: Water-quality and quality-control data tables, 2008 63

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Pesticides and pesticide degradates

Dimethoate

(μg/L)

Dinoseb

(μg/L)

Diphenamid

(μg/L)

Disulfoton 

sulfone

(μg/L)

Disulfoton

(μg/L)

Diuron

(μg/L)

Endosulfan 

sulfate

(μg/L)

Endrin

(μg/L)

CASRN® 60-51-5 88–85–7 957-51-7 2497-06-5 298-04-4 330-54-1 1031-07-8 72-20-8

385138076585902 AC Aa 7 <.006 <.04 <.04 <.01 <.04 <.04 <.022 <.002

385138076585901 AC Aa 6 <.006 <.04 <.04 <.01 <.04 <.04 <.022 <.002

385606076584101 WE Ba 9 <.006 <.04 <.04 <.01 <.04 <.04 <.022 <.002

385649076584201 WE Ba 11 <.006 <.04 <.04 <.01 <.04 <.04 <.022 <.002

385332076594701 WE Ca 32 <.006 <.04 <.04 <.01 <.04 E.0016 <.022 <.002

385245076583501 WE Ca 34 <.006 <.04 <.04 <.01 <.04 <.04 <.022 <.002

385252076572801 WE Cb 8 <.006 <.04 <.04 <.01 <.04 <.04 <.022 <.002

385443076562801 WE Cb 5 <.006 <.04 <.04 <.01 <.04 <.04 <.022 <.002

385327076544801 WE Cc 3 <.006 <.04 <.04 <.01 <.04 <.04 <.022 <.002

385929077020901 WW Ac 8 <.006 <.04 <.04 <.01 <.04 <.04 <.022 <.002

385644077061101 WW Ba 28 <.006 <.04 <.04 <.01 <.04 <.04 <.022 <.002

385527077000701 WW Bc 9 <.006 <.04 <.04 <.01 <.04 <.04 <.022 <.002

385619077020701 WW Bc 10 <.006 <.04 <.04 <.01 <.04 <.04 <.022 <.002

385707077021801 WW Bc 11 <.006 <.04 <.04 <.01 <.04 <.04 <.022 <.002

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- -- -- -- -- -- 0.2

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- -- -- -- -- --

B -- -- -- -- -- -- -- --

C -- -- -- -- -- -- -- 0.036-0.086

D -- -- -- -- -- -- 89 0.06

USEPA National Primary 

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

-- 7 -- -- -- -- -- 2
64 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Pesticides and pesticide degradates

s-ethyldipropylthiocarbamate 

(EPTC) 

(μg/L)

Ethion 

monoxon

(μg/L)

Ethion

(μg/L)

Ethoprop

(μg/L)

Fenamiphos 

sulfone

(μg/L)

Fenamiphos 

sulfoxide

(μg/L)

Fenamiphos

(μg/L)

CASRN® 759-94-4 17356-42-2 563-12-2 13194-48-4 31972-44-8 31972-43-7 22224-92-6

385138076585902 AC Aa 7 <.002 <.02 <.006 <.012 <.053 <.20 <.03

385138076585901 AC Aa 6 <.002 <.02 <.006 <.012 <.053 <.20 <.03

385606076584101 WE Ba 9 <.002 <.02 <.006 <.012 <.053 <.20 <.03

385649076584201 WE Ba 11 <.002 <.02 <.006 <.012 <.053 <.20 <.03

385332076594701 WE Ca 32 <.002 <.02 <.006 <.012 <.053 <.20 <.03

385245076583501 WE Ca 34 <.002 <.02 <.006 <.012 <.053 <.20 <.03

385252076572801 WE Cb 8 <.002 <.02 <.006 <.012 <.053 <.20 <.03

385443076562801 WE Cb 5 <.002 <.02 <.006 <.012 <.053 <.20 <.03

385327076544801 WE Cc 3 <.002 <.02 <.006 <.012 <.053 <.20 <.03

385929077020901 WW Ac 8 <.002 <.02 <.006 <.012 <.053 <.20 <.03

385644077061101 WW Ba 28 <.002 <.02 <.006 <.012 <.053 <.20 <.03

385527077000701 WW Bc 9 <.002 <.02 <.006 <.012 <.053 <.20 <.03

385619077020701 WW Bc 10 <.002 <.02 <.006 <.012 <.053 <.20 <.03

385707077021801 WW Bc 11 <.002 <.02 <.006 <.012 <.053 <.20 <.03

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- -- -- -- -- --

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- -- -- -- --

B -- -- -- -- -- -- --

C -- -- -- -- -- -- --

D -- -- -- -- -- -- --

USEPA National Primary 

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

-- -- -- -- -- -- --
Appendix A: Water-quality and quality-control data tables, 2008 65

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Pesticides and pesticide degradates

Fenuron

(μg/L)

Desulfinylfipronil amide

(μg/L)

Fipronil 

sulfide

(μg/L)

Fipronil 

sulfone

(μg/L)

Fipronil

(μg/L)

Flumetsulam

(μg/L)

Fluometuron

(μg/L)

CASRN® 101-42-8 na 120067-83-6 120068-36-2 120068-37-3 98967-40-9 2164-17-2

385138076585902 AC Aa 7 <.04 <.029 <.013 <.024 <.020 <.06 <.04

385138076585901 AC Aa 6 <.04 <.029 <.013 <.024 <.020 <.06 <.04

385606076584101 WE Ba 9 <.04 <.029 <.013 <.024 <.020 <.06 <.04

385649076584201 WE Ba 11 <.04 <.029 <.013 <.024 <.020 <.06 <.04

385332076594701 WE Ca 32 <.04 <.029 E.007 E.005 E.009 <.06 <.04

385245076583501 WE Ca 34 <.04 <.029 <.013 <.024 <.020 <.06 <.04

385252076572801 WE Cb 8 <.04 <.029 <.013 <.024 <.020 <.06 E.01

385443076562801 WE Cb 5 <.04 <.029 <.013 <.024 <.020 <.06 <.04

385327076544801 WE Cc 3 <.04 <.029 E.007 <.024 E.005 <.06 <.04

385929077020901 WW Ac 8 <.04 <.029 <.013 <.024 <.020 <.06 <.04

385644077061101 WW Ba 28 <.04 <.029 <.013 <.024 <.020 <.06 <.04

385527077000701 WW Bc 9 <.04 <.029 <.013 <.024 <.020 <.06 <.04

385619077020701 WW Bc 10 <.04 <.029 <.013 <.024 <.020 <.06 <.04

385707077021801 WW Bc 11 <.04 <.029 <.013 <.024 <.020 <.06 <.04

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- -- -- -- -- --

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- -- -- -- --

B -- -- -- -- -- -- --

C -- -- -- -- -- -- --

D -- -- -- -- -- -- --

USEPA National Primary 

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

-- -- -- -- -- -- --
66 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Pesticides and pesticide degradates

Fonofos

(μg/L)

Glufosinate

(μg/L)

Glyphosate

(μg/L)

Heptachlor 

epoxide

(μg/L)

Heptachlor

(μg/L)

Hexazinone

(μg/L)

Imazaquin

(μg/L)

CASRN® 944-22-9 51276-47-2 1071–53–6 1024–57–3 76–44–8 51235-04-2 81335-37-7

385138076585902 AC Aa 7 <.010 <.02 <.02 <.002 <.002 <.008 <.04

385138076585901 AC Aa 6 <.010 <.02 <.02 <.002 <.002 <.008 <.04

385606076584101 WE Ba 9 <.010 <.02 <.02 <.002 <.002 <.008 <.04

385649076584201 WE Ba 11 <.010 <.02 0.02 0.021 <.002 <.008 <.04

385332076594701 WE Ca 32 <.010 <.02 <.02 0.003 <.002 <.008 <.04

385245076583501 WE Ca 34 <.010 <.02 <.02 <.002 <.002 <.008 <.04

385252076572801 WE Cb 8 <.010 <.02 <.02 <.002 <.002 <.008 <.04

385443076562801 WE Cb 5 <.010 <.02 <.02 <.002 <.002 <.008 <.04

385327076544801 WE Cc 3 <.010 <.02 <.02 <.002 <.002 <.008 <.04

385929077020901 WW Ac 8 <.010 <.02 <.02 0.014 <.002 <.008 <.04

385644077061101 WW Ba 28 <.010 <.02 <.02 <.002 <.002 <.008 <.04

385527077000701 WW Bc 9 <.010 <.02 <.02 <.002 <.002 <.008 <.04

385619077020701 WW Bc 10 <.010 <.02 <.02 <.002 <.002 <.008 <.04

385707077021801 WW Bc 11 <.010 <.02 <.02 <.002 <.002 <.008 <.04

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- -- -- -- -- --

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- -- -- -- --

B -- -- -- -- -- -- --

C -- -- -- 0.0038-0.52 0.0038-0.52 -- --

D -- -- -- 0.000039 0.000079 -- --

USEPA National Primary 

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

-- -- 700 0.2 0.4 -- --
Appendix A: Water-quality and quality-control data tables, 2008 67

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Pesticides and pesticide degradates

Imazethapyr

(μg/L)

Imidacloprid

(μg/L)

Iprodione

(μg/L)

Isofenphos

(μg/L)

Lindane

(μg/L)

Linuron

(μg/L)

Malaoxon

(μg/L)

CASRN® 81335-77-5 138261-41-3 36734-19-7 25311-71-1 58–89–9 330-55-2 1634-78-2

385138076585902 AC Aa 7 <.04 <.060 <.01 <.006 <.0014 <.02 <.020

385138076585901 AC Aa 6 <.04 <.060 <.01 <.006 <.0014 <.02 <.020

385606076584101 WE Ba 9 <.04 <.060 <.01 <.006 <.0014 <.02 <.020

385649076584201 WE Ba 11 <.04 <.060 <.01 <.006 <.0014 <.02 <.020

385332076594701 WE Ca 32 <.04 <.060 <.01 <.006 <.0014 <.02 <.020

385245076583501 WE Ca 34 <.04 <.060 <.01 <.006 <.0014 <.02 <.020

385252076572801 WE Cb 8 <.04 <.060 <.01 <.006 <.0014 <.02 <.020

385443076562801 WE Cb 5 <.04 <.060 <.01 <.006 <.0014 <.02 <.020

385327076544801 WE Cc 3 <.04 <.060 <.01 <.006 <.0014 <.02 <.020

385929077020901 WW Ac 8 <.04 <.060 <.01 <.006 <.0014 <.02 <.020

385644077061101 WW Ba 28 <.04 <.060 <.01 <.006 <.0014 <.02 <.020

385527077000701 WW Bc 9 <.04 <.060 <.01 <.006 <.0014 <.02 <.020

385619077020701 WW Bc 10 <.04 <.060 <.01 <.006 <.0014 <.02 <.020

385707077021801 WW Bc 11 <.04 <.060 <.01 <.006 <.0014 <.02 <.020

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- -- -- 4 -- --

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- -- -- -- --

B -- -- -- -- -- -- --

C -- -- -- -- 0.08-0.95 -- --

D -- -- -- -- 1.8 -- --

USEPA National Primary 

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

-- -- -- -- 0.2 -- --
68 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Pesticides and pesticide degradates

Malathion

(μg/L)

2-methyl-4-

chlorophenoxyacetic acid 

(MCPA)

(μg/L)

4-(2-methyl-4-

chlorophenoxy) 

butyric acid 

(MCPB)

(μg/L)

Metalaxyl

(μg/L)

Metalaxyl

Method 2

(μg/L)

Methidathion

(μg/L)

Methiocarb

(μg/L)

CASRN® 121-75-5 94-74-6 94-81-5 57837-19-1 57837-19-1 950-37-8 2032-65-7

385138076585902 AC Aa 7 <.016 <.06 <.06 <.02 <.007 <.004 <.040

385138076585901 AC Aa 6 <.016 <.06 <.06 <.02 <.007 <.004 <.040

385606076584101 WE Ba 9 <.016 <.06 <.06 <.02 <.007 <.004 <.040

385649076584201 WE Ba 11 <.016 <.06 <.06 <.02 <.007 <.004 <.040

385332076594701 WE Ca 32 <.016 <.06 <.06 <.02 <.008 <.004 <.040

385245076583501 WE Ca 34 <.016 <.06 <.06 <.02 <.007 <.004 <.040

385252076572801 WE Cb 8 <.016 <.06 <.06 <.02 <.007 <.004 <.040

385443076562801 WE Cb 5 <.016 <.06 <.06 <.02 <.020 <.004 <.040

385327076544801 WE Cc 3 <.016 <.06 <.06 <.02 <.015 <.004 <.040

385929077020901 WW Ac 8 <.016 <.06 <.06 <.02 <.007 <.004 <.040

385644077061101 WW Ba 28 <.016 <.06 <.06 <.02 <.007 <.004 <.040

385527077000701 WW Bc 9 <.016 <.06 <.06 <.02 <.007 <.004 <.040

385619077020701 WW Bc 10 <.016 <.06 <.06 <.02 <.007 <.004 <.040

385707077021801 WW Bc 11 <.016 <.06 <.06 <.02 <.015 <.004 <.040

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- -- -- -- -- --

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- -- -- -- --

B -- -- -- -- -- -- --

C 0.1 -- -- -- -- -- --

D -- -- -- -- -- -- --

USEPA National Primary 

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

-- -- -- -- -- -- --
Appendix A: Water-quality and quality-control data tables, 2008 69

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Pesticides and pesticide degradates

Methomyl

(μg/L)

Methyl 

paraoxon

(μg/L)

Methyl 

parathion

(μg/L)

Metolachlor

(μg/L)

Metribuzin

(μg/L)

Metsulfuronmethyl

(μg/L)

Mirex

(μg/L)

CASRN® 16752-77-5 950-35-6 298-00-0 51218-45-2 21087-64-9 74223-64-6 2385-85-5

385138076585902 AC Aa 7 <.120 <.01 <.008 <.010 <.012 <.14 <.001

385138076585901 AC Aa 6 <.120 <.01 <.008 <.010 <.012 <.14 <.001

385606076584101 WE Ba 9 <.120 <.01 <.008 <.010 <.012 <.14 <.001

385649076584201 WE Ba 11 <.120 <.01 <.008 <.010 <.012 <.14 <.001

385332076594701 WE Ca 32 <.120 <.01 <.008 0.013 <.012 <.14 <.001

385245076583501 WE Ca 34 <.120 <.01 <.008 <.010 <.012 <.14 <.001

385252076572801 WE Cb 8 <.120 <.01 <.008 0.053 <.012 -- <.001

385443076562801 WE Cb 5 <.120 <.01 <.008 <.010 <.012 <.14 <.001

385327076544801 WE Cc 3 <.120 <.01 <.008 <.010 <.012 -- <.001

385929077020901 WW Ac 8 <.120 <.01 <.008 E.008 <.012 <.14 <.001

385644077061101 WW Ba 28 <.120 <.01 <.008 <.010 <.012 <.14 <.001

385527077000701 WW Bc 9 <.120 <.01 <.008 E.008 <.012 <.14 <.001

385619077020701 WW Bc 10 <.120 <.01 <.008 <.010 <.012 <.14 <.001

385707077021801 WW Bc 11 <.120 <.01 <.008 <.010 <.012 <.14 <.001

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- -- -- -- -- --

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- -- -- -- --

B -- -- -- -- -- -- --

C -- -- -- -- -- -- 0.001

D -- -- -- -- -- -- --

USEPA National Primary 

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

-- -- -- -- -- -- --
70 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Pesticides and pesticide degradates

Molinate

(μg/L)

Myclobutanil

(μg/L)

N-

(4-Chlorophenyl)-

N’-methylurea

(μg/L)

Neburon

(μg/L)

Nicosulfuron

(μg/L)

Norflurazon

(μg/L)

Oryzalin

(μg/L)

CASRN® 2212-67-1 88671-89-0 -- 555-37-3 111991-09-4 27314-13-2 19044-88-3

385138076585902 AC Aa 7 <.003 <.010 <.12 <.02 <.10 <.02 <.04

385138076585901 AC Aa 6 <.003 <.010 <.12 <.02 <.10 <.02 <.04

385606076584101 WE Ba 9 <.003 <.010 <.12 <.02 <.10 <.02 <.04

385649076584201 WE Ba 11 <.003 <.010 <.12 <.02 <.10 <.02 <.04

385332076594701 WE Ca 32 <.003 <.010 <.12 <.02 <.10 <.02 <.04

385245076583501 WE Ca 34 <.003 <.010 <.12 <.02 <.10 <.02 <.04

385252076572801 WE Cb 8 <.003 <.010 <.12 <.02 <.10 <.02 <.04

385443076562801 WE Cb 5 <.003 <.010 <.12 <.02 <.10 <.02 <.04

385327076544801 WE Cc 3 <.003 <.010 <.12 <.02 <.10 <.02 <.04

385929077020901 WW Ac 8 <.003 <.010 <.12 <.02 <.10 <.02 <.04

385644077061101 WW Ba 28 <.003 <.010 <.12 <.02 <.10 <.02 <.04

385527077000701 WW Bc 9 <.003 <.010 <.12 <.02 <.10 <.02 <.04

385619077020701 WW Bc 10 <.003 <.010 <.12 <.02 <.10 <.02 <.04

385707077021801 WW Bc 11 <.003 <.010 <.12 <.02 <.10 <.02 <.04

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- -- -- -- -- --

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- -- -- -- --

B -- -- -- -- -- -- --

C -- -- -- -- -- -- --

D -- -- -- -- -- -- --

USEPA National Primary 

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

-- -- -- -- -- -- --
Appendix A: Water-quality and quality-control data tables, 2008 71

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Pesticides and pesticide degradates

Oxamyl

(μg/L)

Oxyfluorfen

(μg/L)

dichlorodiphenyldichloroethane 

(p,p’-DDD)

(μg/L)

dichlorodiphenyldichloro

ethylene 

(p,p’-DDE)

(μg/L)

dichlorodiphenyl

trichloro

ethane 

(p,p’-DDT)

(μg/L)

p,p’-Methoxychlor

(μg/L)

Polychlorinated 

biphenyls

(μg/L)

CASRN® 23135-22-0 42874-03-3 72-54-8 72-55-9 50-29-3 72-73-5 1336-36-3

385138076585902 AC Aa 7 <.12 <.006 <.001 <.002 <.001 <.002 <.1

385138076585901 AC Aa 6 <.12 <.006 <.001 <.002 <.001 <.002 <.1

385606076584101 WE Ba 9 <.12 <.006 <.001 <.002 <.001 <.002 <.1

385649076584201 WE Ba 11 <.12 <.006 E.001 <.002 <.001 <.002 <.1

385332076594701 WE Ca 32 <.12 <.006 0.002 <.002 <.001 <.002 <.1

385245076583501 WE Ca 34 <.12 <.006 <.001 <.002 <.001 <.002 <.1

385252076572801 WE Cb 8 <.12 <.006 E.001 <.002 <.001 <.002 <.1

385443076562801 WE Cb 5 <.12 <.006 <.001 <.002 <.001 <.002 <.1

385327076544801 WE Cc 3 <.12 <.006 <.001 <.002 <.001 <.002 <.1

385929077020901 WW Ac 8 <.12 <.006 <.001 <.002 <.001 <.002 <.1

385644077061101 WW Ba 28 <.12 <.006 <.001 <.002 <.001 <.002 <.1

385527077000701 WW Bc 9 <.12 <.006 <.001 <.002 <.001 <.002 <.1

385619077020701 WW Bc 10 <.12 <.006 <.001 <.002 <.001 <.002 <.1

385707077021801 WW Bc 11 <.12 <.006 <.001 <.002 <.001 <.002 <.1

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- -- -- -- 100 --

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- -- -- -- --

B -- -- -- -- -- -- --

C -- -- 0.001-1.1 0.001-1.1 0.001-1.1 -- 0.014

D -- -- 0.00031 0.00022 0.00022 -- 0.000064

USEPA National Primary 

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

200 -- -- -- -- -- 0.0005
72 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Pesticides and pesticide degradates

Pendimethalin

(μg/L)

Phorate 

oxygen

(μg/L)

Phorate

(μg/L)

Phosmet 

oxon

(μg/L)

Phosmet

(μg/L)

Picloram

(μg/L)

Prometon

(μg/L)

CASRN® 40487-42-1 2600-69-3 298-02-2 3735-33-9 732-11-6 1918–02–1 1610-18-0

385138076585902 AC Aa 7 <.012 <.03 <.040 <.05 <.008 <.12 <.01

385138076585901 AC Aa 6 <.012 <.03 <.040 <.05 <.008 <.12 <.01

385606076584101 WE Ba 9 <.012 <.03 <.040 <.05 <.008 <.12 <.01

385649076584201 WE Ba 11 <.012 <.03 <.040 <.05 <.008 <.12 <.01

385332076594701 WE Ca 32 <.012 <.03 <.040 <.05 <.008 <.12 E.01

385245076583501 WE Ca 34 <.012 <.03 <.040 <.05 <.008 <.12 <.01

385252076572801 WE Cb 8 <.012 <.03 <.040 <.05 <.008 <.12 <.01

385443076562801 WE Cb 5 <.012 <.03 <.040 <.05 <.008 <.12 E.01

385327076544801 WE Cc 3 <.012 <.03 <.040 <.05 <.008 <.12 E.01

385929077020901 WW Ac 8 <.012 <.03 <.040 <.05 <.008 <.12 <.01

385644077061101 WW Ba 28 <.012 <.03 <.040 <.05 <.008 <.12 <.01

385527077000701 WW Bc 9 <.012 <.03 <.040 <.05 <.008 <.12 <.01

385619077020701 WW Bc 10 <.012 <.03 <.040 <.05 <.008 <.12 <.01

385707077021801 WW Bc 11 <.012 <.03 <.040 <.05 <.008 <.12 <.01

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- -- -- -- -- --

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- -- -- -- --

B -- -- -- -- -- -- --

C -- -- -- -- -- -- --

D -- -- -- -- -- -- --

USEPA National Primary 

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

-- -- -- -- -- 500 --
Appendix A: Water-quality and quality-control data tables, 2008 73

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Pesticides and pesticide degradates

Prometryn

(μg/L)

Propyzamide

(μg/L)

Propanil

(μg/L)

Propargite

(μg/L)

Propham

(μg/L)

Propiconazole

(μg/L)

Propoxur

(μg/L)

CASRN® 7287-19-6 23950-58-5 709-98-8 2312-35-8 122-42-9 60207-90-1 114-26-1

385138076585902 AC Aa 7 <.006 <.004 <.006 <.04 <.040 <.04 <.040

385138076585901 AC Aa 6 <.006 <.004 <.006 <.04 <.040 <.04 <.040

385606076584101 WE Ba 9 <.006 <.004 <.006 <.04 <.040 <.04 <.040

385649076584201 WE Ba 11 <.006 <.004 <.006 <.04 <.040 <.04 <.040

385332076594701 WE Ca 32 <.006 <.004 <.006 <.04 <.040 <.04 <.040

385245076583501 WE Ca 34 <.006 <.004 <.006 <.04 <.040 <.04 <.040

385252076572801 WE Cb 8 <.006 <.004 <.006 <.04 <.040 <.04 <.040

385443076562801 WE Cb 5 <.006 <.004 <.006 <.04 <.040 <.04 <.040

385327076544801 WE Cc 3 <.006 <.004 <.006 <.04 <.040 <.04 <.040

385929077020901 WW Ac 8 <.006 <.004 <.006 <.04 <.040 <.04 <.040

385644077061101 WW Ba 28 <.006 <.004 <.006 <.04 <.040 <.04 <.040

385527077000701 WW Bc 9 <.006 <.004 <.006 <.04 <.040 <.04 <.040

385619077020701 WW Bc 10 <.006 <.004 <.006 <.04 <.040 <.04 <.040

385707077021801 WW Bc 11 <.006 <.004 <.006 <.04 <.040 <.04 <.040

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- -- -- -- -- --

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- -- -- -- --

B -- -- -- -- -- -- --

C -- -- -- -- -- -- --

D -- -- -- -- -- -- --

USEPA National Primary

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

-- -- -- -- -- -- --
74 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Pesticides and pesticide degradates

Siduron

(μg/L)

Simazine

(μg/L)

Sulfometuronmethyl

(μg/L)

Tebuconazole

(μg/L)

Tebuthiuron

(μg/L)

Tefluthrin

(μg/L)

Terbacil

(μg/L)

CASRN® 1982-49-6 122–34–9 74222-97-2 107534-96-3 34014-18-1 79538-32-2 5902-51-2

385138076585902 AC Aa 7 <.02 <.006 <.060 <.02 <.02 <.003 <.040

385138076585901 AC Aa 6 <.02 <.006 <.060 <.02 <.02 <.003 <.040

385606076584101 WE Ba 9 <.02 <.006 <.060 <.02 <.02 <.003 <.040

385649076584201 WE Ba 11 <.02 0.022 <.060 <.02 <.02 <.003 <.040

385332076594701 WE Ca 32 <.02 0.016 <.060 <.02 0.11 <.003 <.040

385245076583501 WE Ca 34 <.02 <.006 <.060 <.02 <.02 <.003 <.040

385252076572801 WE Cb 8 <.02 <.007 E.007 <.02 <.02 <.003 <.040

385443076562801 WE Cb 5 <.02 0.01 <.060 <.02 <.02 <.003 <.040

385327076544801 WE Cc 3 <.02 0.008 <.060 <.02 <.02 <.003 <.040

385929077020901 WW Ac 8 <.02 <.006 <.060 <.02 <.02 <.003 <.040

385644077061101 WW Ba 28 <.02 <.006 <.060 <.02 <.02 <.003 <.040

385527077000701 WW Bc 9 <.02 E.006 <.060 <.02 <.02 <.003 <.040

385619077020701 WW Bc 10 <.02 <.006 <.060 <.02 <.11 <.003 <.040

385707077021801 WW Bc 11 <.02 <.006 <.060 <.02 <.02 <.003 <.040

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- -- -- -- -- --

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- -- -- -- --

B -- -- -- -- -- -- --

C -- -- -- -- -- -- --

D -- -- -- -- -- -- --

USEPA National Primary 

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

-- 4 -- -- -- -- --
Appendix A: Water-quality and quality-control data tables, 2008 75

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Pesticides and pesticide degradates

Terbufos oxon 

sulfone

(μg/L)

Terbufos

(μg/L)

Terbuthylazine

(μg/L)

Thiobencarb

(μg/L)

Toxaphene

(μg/L)

transPropiconazole

(μg/L)

CASRN® 56070-15-6 13071-79-9 5915-41-3 28249-77-6 8001-35-2 60207-90-1

385138076585902 AC Aa 7 <.04 <.02 <.01 <.010 <1 <.02

385138076585901 AC Aa 6 <.04 <.02 <.01 <.010 <1 <.02

385606076584101 WE Ba 9 <.04 <.02 <.01 <.010 <1 <.02

385649076584201 WE Ba 11 <.04 <.02 <.01 <.010 <1 <.02

385332076594701 WE Ca 32 <.04 <.02 <.01 <.010 <1 <.02

385245076583501 WE Ca 34 <.04 <.02 <.01 <.010 <1 <.02

385252076572801 WE Cb 8 <.04 <.02 <.01 <.010 <1 <.02

385443076562801 WE Cb 5 <.04 <.02 <.01 <.010 <1 <.02

385327076544801 WE Cc 3 <.04 <.02 <.01 <.010 <1 <.02

385929077020901 WW Ac 8 <.04 <.02 <.01 <.010 <1 <.02

385644077061101 WW Ba 28 <.04 <.02 <.01 <.010 <1 <.02

385527077000701 WW Bc 9 <.04 <.02 <.01 <.010 <1 <.02

385619077020701 WW Bc 10 <.04 <.02 <.01 <.010 <1 <.02

385707077021801 WW Bc 11 <.04 <.02 <.01 <.010 <1 <.02

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- -- -- 5 --

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- -- -- --

B -- -- -- -- -- --

C -- -- -- -- 0.0002-0.73 --

D -- -- -- -- 0.00028 --

USEPA National Primary 

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

-- -- -- -- 3 --
76 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Pesticides and pesticide degradates

Tribuphos

(μg/L)

Triclopyr

(μg/L)

Trifluralin

(μg/L)

Dichlorvos

(μg/L)

CASRN® 78-48-8 55335-06-3 1582-09-8 62-73-7

385138076585902 AC Aa 7 <.035 <.08 <.009 <.01

385138076585901 AC Aa 6 <.035 <.08 <.009 <.01

385606076584101 WE Ba 9 <.035 <.08 <.009 <.01

385649076584201 WE Ba 11 <.035 <.08 <.009 <.01

385332076594701 WE Ca 32 <.035 <.08 <.009 <.01

385245076583501 WE Ca 34 <.035 <.08 <.009 <.01

385252076572801 WE Cb 8 <.035 <.08 <.009 <.01

385443076562801 WE Cb 5 <.035 <.08 <.009 <.01

385327076544801 WE Cc 3 <.035 <.08 <.009 <.01

385929077020901 WW Ac 8 <.035 <.08 <.009 <.01

385644077061101 WW Ba 28 <.035 <.08 <.009 <.01

385527077000701 WW Bc 9 <.035 <.08 <.009 <.01

385619077020701 WW Bc 10 <.035 <.08 <.009 <.01

385707077021801 WW Bc 11 <.035 <.08 <.009 <.01

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- -- --

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- --

B -- -- -- --

C -- -- -- --

D -- -- -- --

USEPA National Primary 

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

-- -- -- --
Appendix A: Water-quality and quality-control data tables, 2008 77

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL) with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Surrogates

2,4,5-T, surrogate

(percent recovery)

a-HCH-d6, surrogate, 

Schedule 1398

(percent recovery)

alpha-HCH-d6, surrogate, 

Schedule 2033

(percent recovery)

Barban, surrogate, 

Schedule 2060

(percent recovery)

CASRN® na na na na

385138076585902 AC Aa 7 67.4 90.9 78.9 98.2

385138076585901 AC Aa 6 65.1 88.1 92.7 91.1

385606076584101 WE Ba 9 57.7 90.5 82.8 72

385649076584201 WE Ba 11 94 118 91 91

385332076594701 WE Ca 32 62.2 95.7 80 94.9

385245076583501 WE Ca 34 62.6 86.8 76.6 53.4

385252076572801 WE Cb 8 80.1 113 98.1 85

385443076562801 WE Cb 5 91.9 102 95.3 82.3

385327076544801 WE Cc 3 73 E115 80.6 93.7

385929077020901 WW Ac 8 84.9 E115 96.7 69.4

385644077061101 WW Ba 28 87.4 E114 85.4 78.2

385527077000701 WW Bc 9 66.8 87.9 91.7 102

385619077020701 WW Bc 10 75.1 98 76.8 38

385707077021801 WW Bc 11 87.4 95.8 96.4 81

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- -- --

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- --

B -- -- -- --

C -- -- -- --

D -- -- -- --

USEPA National Primary 

Drinking Water Standards

(U.S. Environmental Protection 

Agency, 2009)

-- -- -- --
78 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Table A1. Concentrations of major ions, nutrients, and pesticides in groundwater samples collected in the Anacostia River and Rock 

Creek watersheds in Washington, D.C., August to September 2008, and selected water-quality standards.—Continued

[CASRN®, Chemical Abstracts Service Registry Number; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; mg/L, 

milligrams per liter; μg/L, micrograms per liter; oC, degrees Celsius; NTU, nephelometric turbidity unit; gal/min, gallons per minute; CaCO3, calcium carbonate; HCO3

, bicarbonate; SiO2, silicate; SO4, sulfate; N, nitrogen; P, phosphate; <, less than; --, no value available; na, not applicable; E, quantified above the 

long-term method detection limit (LT-MDL) but below the laboratory reporting level (LRL with higher uncertainty; bold type, detected pesticide concentration; District of Columbia surface-water standards A, B, C, and D refer to different surface-water uses: A = primary contact recreation; B = secondary contact 

recreation and aesthetic enjoyment; C = protection and propagation of fish, shellfish, and wildlife; D = protection of human health related to consumption of 

fish and shellfish (District of Columbia, 2006); d, diluted sample, method high end of range exceeded; ***, refer to District of Columbia (2006) for this value]

USGS 

site identifer 

USGS 

well 

identifer

Surrogates

Caffeine-13C, surrogate, 

Schedule 2060

(percent recovery)

Diazinon-d10, surrogate, 

Schedule 2033

(percent recovery)

Isodrin, surrogate, 

Schedule 1398

(percent recovery)

Polychlorinated biphenyl 207, surrogate

(percent recovery)

CASRN® na na na na

385138076585902 AC Aa 7 102 82.9 81.8 92.1

385138076585901 AC Aa 6 84.4 129 81.2 104

385606076584101 WE Ba 9 84.9 90.9 81.2 108

385649076584201 WE Ba 11 88.8 106 77.1 111

385332076594701 WE Ca 32 84.9 100 96.5 108

385245076583501 WE Ca 34 81.3 104 71.6 105

385252076572801 WE Cb 8 88.3 117 86.7 117

385443076562801 WE Cb 5 80.7 94.5 55.5 84.1

385327076544801 WE Cc 3 86.5 96.1 67 116

385929077020901 WW Ac 8 80.6 128 91.1 115

385644077061101 WW Ba 28 87.8 128 88.7 111

385527077000701 WW Bc 9 95.1 107 79.7 104

385619077020701 WW Bc 10 67.9 199 86.5 108

385707077021801 WW Bc 11 80.6 126 96.8 106

Selected water-quality standards

District of Columbia groundwater 

standards (District of Columbia, 

1993)

-- -- -- --

District of Columbia surfacewater standards (District of 

Columbia, 2006)

A -- -- -- --

B -- -- -- --

C -- -- -- --

D -- -- -- --

USEPA National Primary 

Drinking Water Standards

U.S. Environmental Protection 

Agency, 2009)

-- -- -- --
Appendix A: Water-quality and quality-control data tables, 2008 79

Table A2. Description of quality-control samples obtained in conjunction with the collection of groundwater samples in the Anacostia River and Rock Creek watersheds in Washington, D.C., August to September 2008.—Continued[Bold type, detected pesticide concentration; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees Celsius; mg/L, milligrams per liter; μg/L, micrograms per liter; CACO3, calcium carbonate; SiO2, silicate; <, less than; ---, analysis not conducted; E, quantified above the long-term method detection limit but below the laboratory reporting level with higher uncertainty; std, standard]

Sample 

type

USGS 

well identifier

Nicosulfuron

(μg/L)

Norflurazon

(μg/L)

Oryzalin

(μg/L)

Oxamyl

(μg/L)

Oxyflourfen

(μg/L)

Dichlorodiphenyl-dichloroethane 

(p,p’-DDD)

(μg/L)

Dichlorodiphenyldichloroethylene 

(p,p’-DDE)

(μg/L)

Dichlorodiphenyltrichloroethane 

(p,p’-DDD)

(μg/L)

p,p’-Methoxychlor

(μg/L)

Field blank WE Cc 3 < 0.10 < 0.02 < 0.04 < 0.12 < 0.006 < 0.001 < 0.002 < 0.001 < 0.002Field blank WW Ba 28 < 0.10 < 0.02 < 0.04 < 0.12 < 0.006 < 0.001 < 0.002 < 0.001 < 0.002

Duplicate 

samples

WE Ca 32 < 0.10 < 0.02 < 0.04 < 0.12 < 0.006 0.002 < 0.002 < 0.001 < 0.002WE Ca 32 < 0.10 < 0.02 < 0.04 < 0.12 < 0.006 0.002 < 0.002 < 0.001 < 0.002

Duplicate 

samples 

WW Bc 11 < 0.10 < 0.02 < 0.04 < 0.12 < 0.006 < 0.001 < 0.002 < 0.001 < 0.002WW Bc 11 < 0.10 < 0.02 < 0.04 < 0.12 < 0.006 < 0.001 < 0.002 < 0.001 < 0.002

Sample 

type

USGS 

well identifier

Polychlorinated 

biphenyl (PCB 207), 

surrogate, recovery

(percent)

Polychlorobiphenyls

(μg/L)

Pendimethalin

(μg/L)

Phorate oxon

(μg/L)

Phorate

(μg/L)

Phosmet oxon

(μg/L)

Phosmet

(μg/L)

Picloram

(μg/L)

Prometon

(μg/L)

Field blank WE Cc 3 108 < 0.1 < 0.012 < 0.03 < 0.040 < 0.05 < 0.008 < 0.12 < 0.01Field blank WW Ba 28 108 < 0.1 < 0.012 < 0.03 < 0.040 < 0.05 < 0.008 < 0.12 < 0.01

Duplicate 

samples

WE Ca 32 108 < 0.1 < 0.012 < 0.03 < 0.040 < 0.05 < 0.008 < 0.12 E 0.01WE Ca 32 111 < 0.1 < 0.012 < 0.03 < 0.040 < 0.05 < 0.008 < 0.12 E 0.01

Duplicate 

samples 

WW Bc 11 105 < 0.1 < 0.012 < 0.03 < 0.040 < 0.05 < 0.008 < 0.12 < 0.01WW Bc 11 106 < 0.1 < 0.012 < 0.03 < 0.040 < 0.05 < 0.008 < 0.12 < 0.01

Sample 

type

USGS 

well identifier

Prometryn

(μg/L)

Propyzamide

(μg/L)

Propanil

(μg/L)

Propargite

(μg/L)

Propham

(μg/L)

Propiconazole

(μg/L)

Propoxur

(μg/L)

Siduron

(μg/L)

Simazine

(μg/L)

Field blank WE Cc 3 < 0.006 < 0.004 < 0.006 < 0.04 < 0.040 < 0.04 < 0.040 < 0.02 < 0.006Field blank WW Ba 28 < 0.006 < 0.004 < 0.006 < 0.04 < 0.040 < 0.04 < 0.040 < 0.02 < 0.006

Duplicate 

samples

WE Ca 32 < 0.006 < 0.004 < 0.006 < 0.04 < 0.040 < 0.04 < 0.040 < 0.02 0.016WE Ca 32 < 0.006 < 0.004 < 0.006 < 0.04 < 0.040 < 0.04 < 0.040 < 0.02 0.014

Duplicate 

samples 

WW Bc 11 < 0.006 < 0.004 < 0.006 < 0.04 < 0.040 < 0.04 < 0.040 < 0.02 < 0.006WW Bc 11 < 0.006 < 0.004 < 0.006 < 0.04 < 0.040 < 0.04 < 0.040 < 0.02 < 0.006
80 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008 Table A2. Description of quality-control samples obtained in conjunction with the collection of groundwater samples in the Anacostia River and Rock Creek watersheds in Washington, D.C., August to September 2008.—Continued

[Bold type, detected pesticide concentration; USGS, U.S. Geological Survey; μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees Celsius; mg/L, milligrams per liter; μg/L, micrograms per liter; CACO3, calcium carbonate; SiO2, silicate; <, less than; ---, analysis not conducted; E, quantified above the long-term method detection limit but below the laboratory reporting level with higher uncertainty; std, standard]

Sample 

type

USGS 

well identifier

Sulfometuron 

methyl

(μg/L)

Tebucanazole

(μg/L)

Tebuthiuron

(μg/L)

Tefluthrin

(μg/L)

Terbacil

(μg/L)

Terbufos oxon 

sulfone

(μg/L)

Terbufos

(μg/L)

Terbuthylazine

(μg/L)

Thiobencarb

(μg/L)

Field blank WE Cc 3 <.060 <.02 <.02 <.003 <.040 <.04 <.02 <.01 <.010Field blank WW Ba 28 <.060 <.02 <.02 <.003 <.040 <.04 <.02 <.01 <.010

Duplicate 

samples

WE Ca 32 <.060 <.02 0.11 <.003 <.040 <.04 <.02 <.01 <.010WE Ca 32 <.060 <.02 0.10 <.003 <.040 <.04 <.02 <.01 <.010

Duplicate 

samples 

WW Bc 11 <.060 <.02 <.02 <.003 <.040 <.04 <.02 <.01 <.010WW Bc 11 <.060 <.02 <.02 <.003 <.040 <.04 <.02 <.01 <.010

Sample 

type

USGS well 

identifier

Toxaphene

(μg/L)

trans-Propiconazole

(μg/L)

Tribuphos

(μg/L)

Triclopyr

(μg/L)

Trifluralin

(μg/L)

Dichlorvos

(μg/L)

Aminomethyl-phosphonic acid 

(AMPA)

(μg/L)

Field blank WE Cc 3 < 1 < 0.02 < 0.035 < 0.08 < 0.009 < 0.01 < 0.02Field blank WW Ba 28 < 1 < 0.02 < 0.035 < 0.08 < 0.009 < 0.01 < 0.02

Duplicate 

samples

WE Ca 32 < 1 < 0.02 < 0.035 < 0.08 < 0.009 < 0.01 0.02WE Ca 32 < 1 < 0.02 < 0.035 < 0.08 < 0.009 < 0.01 0.04

Duplicate 

samples 

WW Bc 11 < 1 < 0.02 < 0.035 < 0.08 < 0.009 < 0.01 < 0.02WW Bc 11 < 1 < 0.02 < 0.035 < 0.08 < 0.009 < 0.01 < 0.02
Appendix B: Assessment of quality of data collected in 2005 and 2008 81

Appendix B: Assessment of quality of data 

collected in 2005 and 2008

Data-Quality Analyses.................................................................................................................................82

Contamination Bias.............................................................................................................................82

Measurement Precision ....................................................................................................................82

Laboratory Methods...........................................................................................................................83

Site-Specific Observations ...............................................................................................................89

Summary and Implications for Analysis and Interpretation.................................................................90

Figures

B1. Graphs showing relative percent difference as a function of mean 

concentration for: (A) Inorganic constituents (in milligrams per liter, 

mg/L), including calcium, magnesium, sodium, potassium, nitrate plus 

nitrite-nitrogen, ammonium-nitrogen, chloride, sulfate, manganese, 

and iron (with iron having the extreme value (40 percent) for one of 

two sets of duplicate measurements); and (B) pesticides (in micrograms 

per liter, μg/L), including atrazine, prometon, simazine, desethylatrazine, 

dieldrin, fipronil, fipronil sulfone, fipronil sulfide, aminomethylphosphonic 

acid (AMPA), heptachlor expoxide, metolachlor, 

dichlorodiphenyldiphenylethane (p,p’-DDE), and tebuthiuron............................................85

Tables

B1. Concentrations in field blanks and groundwater samples with 

constituents detected in at least one field blank collected during 

groundwater sampling in Washington, D.C. in 2008 .............................................................83

B2. Means and relative percent differences in the concentrations of 

inorganic and organic constituents obtained from two sequential 

duplicate groundwater samples collected from wells in 

Washington, D.C. in 2008 .............................................................................................................84

B3. Mean and relative standard deviation of pesticide surrogate 

compound recoveries for each laboratory method and from 

laboratory-spiked groundwater samples in 2005 and 2008, and 

results of the Wilcoxon-Mann-Whitney rank sum test to 

determine if ranked recoveries in 2005 differed from ranked 

recoveries in 2008.......................................................................................................................85

B4. U.S. Geological Survey laboratory reporting and detection levels 

for pesticide schedules used in 2005 and 2008, and for which at 

least one pesticide was detected in a groundwater sample in 2005 or 2008 ...................87

B5. Pesticide detections and concentrations in groundwater samples 

collected from wells sampled in 2005 and 2008 and analyzed for 

similar compounds using the same laboratory schedules in 2005 and 2008 ....................88

B6. Pesticide detections in groundwater attributed to the addition of a 

laboratory schedule (LS 2033) in 2008 that was not used in 2005, or 

the addition of new pesticide compounds into laboratory schedules...............................89
82 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Data-Quality Analyses

Pesticide data for this study were collected from 17 

monitoring wells in the lower Anacostia River watershed in 

Washington, D.C. during fall 2005, and from 14 wells in the 

lower Anacostia River and Rock Creek watersheds in fall 

2008. Some wells were previously installed and some were 

established for this project. Quality-control (QC) samples were 

collected with groundwater samples, and included field blanks 

and duplicate groundwater samples. The QC data from the 

chemical analysis of field blanks and duplicate groundwater 

samples obtained in 2005 are provided in Klohe and Debrewer 

(2007). The QC data from the chemical analysis of field 

blanks and duplicate groundwater samples obtained in 2008 

are provided in this report (table A2).

Additional QC data were provided by the USGS analytical laboratories on the performance of their methods. 

Laboratory QC data included (a) the recoveries of pesticidesurrogate compounds added to each groundwater or QC 

sample at the time of analysis, and (b) the laboratory detection 

and reporting levels, determined from estimates of method 

precision for each pesticide. Pesticide surrogate recoveries, 

long-term method detection levels (LT-MDLs), and laboratory 

reporting levels (LRLs) data for 2005 and 2008 are provided 

in this report in conjunction with their use in the assessment of 

the quality of groundwater pesticide data.

Comparisons were made of (a) field and laboratory QC 

samples obtained for each year of data collection, (b) the laboratory methods used for each year of data collection, including 

the addition of new compounds to previously existing schedules, and (c) general observations of site characteristics associated with the wells. The degree to which data from both years 

could be combined and compared for analysis and interpretation is evaluated. 

Field blanks typically are collected to assess whether 

sampling apparatus were adequately cleaned before reuse, 

and whether chemical sample preservatives, or the collection, 

processing, shipping, and laboratory analysis of samples led 

to contamination of the samples (Koterba and others, 1995). 

Sequential (duplicate) groundwater samples assess the consistency of measurement precision of a given analytical constituent (Koterba and others, 1995). Pesticide surrogate recovery 

data from laboratory-spiked groundwater samples, and the 

analytical method detection and reporting were used to compare method performance between 2005 and 2008 (Koterba 

and others, 1995).

Contamination Bias

Klohe and Debrewer (2007) found that except for the 

presence of low levels of 10 of 32 major ions and selected 

trace elements, no other compounds, including any pesticides, 

were detected at concentrations that exceeded LRLs in three 

field blanks collected at different times and well locations 

in 2005. No pesticides were detected in these field blanks at 

concentrations equal to or greater than the LT-MDLs. Results 

from a source-water blank indicated that for the 10 detected 

inorganic constituents, the lot of blank water used had a higher 

than normal pH, specific conductance, and concentrations of 

aluminum, barium, and strontium. Overall, and except for 

aluminum, the authors concluded that the low concentrations 

of the 10 inorganic constituents present in one or both field 

blanks appeared negligible compared to the concentrations 

typically found in groundwater samples. Therefore, except for 

aluminum, no bias from contamination appears to have been 

introduced during sample processing or analysis in 2005 that 

would limit interpretation of the groundwater data, including 

the pesticide data. For aluminum, field blanks had concentrations about three to seven times greater than the median concentration (2.2 micrograms per liter, μg/L) found in groundwater samples (Klohe and Debrewer, 2007). Use of this blank 

water temporarily could have contaminated equipment when 

blanks were collected. The groundwater samples collected 

immediately after these field blanks at wells AC Aa 1, WE Ba 

10, WE Ca 33, however, had aluminum concentrations that 

ranged from the less than 2 μg/L (LRL) to 4 μg/L, which is 

near the median value for aluminum in groundwater samples 

collected in 2005 (2.22 μg/L). Thus, if the process of running blanks through the equipment temporarily did introduce 

aluminum into groundwater samples collected immediately 

after the blanks, the contamination was minor in magnitude 

and at most resulted in low, but measureable, concentrations of 

aluminum in those particular groundwater samples.

Conclusions similar to those drawn from the field-blank 

data obtained in 2005 can be drawn from the analysis of 

the field-blank data collected in 2008 (table A2). Except for 

trace amounts of selected major ions and trace elements, the 

concentrations of all constituents, including all pesticides, 

analyzed in two field-blank samples were less than the LRLs. 

No pesticides were detected in the field blanks. 

For each of the constituents detected in one or more field 

blanks in 2008 (table B1), the blank concentration was near, 

or considerably less than, the minimum concentration, and 

well below the median concentration, found in groundwater 

samples. As was the case in 2005, the 2008 field-blank data 

indicated no appreciable bias was introduced during the processing and analyses of samples that would limit interpretation 

of the pesticide and other groundwater data.

Measurement Precision

The degree of precision in the measurement of concentrations of pesticides and other constituents was evaluated 

with two sets of sequentially collected duplicate groundwater 

samples. 

Results of analyses of the duplicate samples obtained 

from each of two different wells in 2005 indicated that duplicate measureable values were reasonably precise for most 

inorganic and organic constituents (Klohe and Debrewer, 

2007). The uncertainty in duplicate measurements, estimated 
Data-Quality Analyses 83

as the relative percent difference (RPD), typically was 10 

percent or less. The RPD exceeded 10 percent for several trace 

elements (cadmium, copper, uranium, and zinc), nitrite and 

organic nitrogen, and caffeine. 

Evaluation of data obtained from sequential duplicate 

groundwater samples collected at each of two wells in 2008 

revealed precision results similar to the results described 

above for the groundwater data collected in 2005 (table B2). 

With the exception of iron in one set of duplicate samples, the 

RPD in duplicate-sample concentrations for most inorganic 

constituents was less than 1 percent, and no more than about 

10 to 12 percent (fig. B1A). For pesticides, the RPD between 

duplicate-sample concentrations was usually less than 10 percent, and not more than 20 percent (fig. B1B).

Laboratory Methods

All groundwater samples analyzed for pesticides by the 

USGS National Water Quality Laboratory (NWQL) were 

spiked with known amounts of pesticide surrogate compounds 

before analysis to assess the method recovery. Surrogate 

recovery results for each laboratory schedule for the groundwater samples analyzed in 2005 (Klohe and Debrewer, 2007, 

appendix 3) and in 2008 (table A1) were compared to determine if method performances were similar between years.

For a given NWQL pesticide laboratory schedule and surrogate, the recovery data for 2005 and 2008 were combined, 

transformed into ranked data, and tested for significant differences in recovery between years using a Wilcoxon-MannWhitney rank sum test (Helsel and Hirsch, 2002). Except for 

NWQL laboratory schedule 2060, test results indicate there are 

no significant differences in the recovery of a surrogate compound in 2005 samples compared to 2008 samples analyzed 

with the same laboratory (table B3, Wilcoxon-Mann-Whitney 

test on ranked surrogate recoveries: significance level set at 

α=.05 for a one- or two-tailed test). For NWQL schedule 2060, 

ranked recoveries for each surrogate compound in 2005 were 

significantly different from the ranked surrogate recoveries in 

2008. Mean surrogate recoveries in 2005 samples were 39, 24, 

and 15 percent higher than in 2008 samples for 2,4,5-trichlorophenol, barban, and caffeine-13C, respectively.

The difference in 2,4,5-trichlorophenol recoveries 

between 2005 and 2008 appears to mainly result from high 

individual spiked-sample recoveries in 2005. Thirteen of 17 

spiked-sample recoveries for this surrogate compound in 2005 

were between 101 percent and 154 percent. Each of these 

13 recovery values was estimated (E coded), which generally indicates sample-matrix interference and (or) spiking 

problems.

The difference in barban surrogate recoveries between 

2005 and 2008 also appeared to result in part from elevated 

and estimated recoveries of this surrogate compound in 

2005—where 11 of 17 recoveries of barban from spiked 

samples in 2005 ranged from 104 to 162 percent. In addition, 

there were two unusually low spiked-sample recoveries for 

barban in 2008—54 percent for WE Ca 34 and 34 percent for 

WW Bc 10.

The mean recovery of caffeine-13C in 2005 groundwater 

samples was about 15 percent greater than its mean recovery 

in 2008 groundwater samples. This difference (bias) in recoveries is not unusual given year-to-year variations in laboratory 

performance in estimating low-level pesticide concentrations.

Collectively, the main effect of the notably higher 

recoveries of at least two of the surrogate compounds in 2005 

groundwater samples compared to their recoveries in 2008 

groundwater samples is that the higher recoveries led to an 

increase in the LRLs (and LT-MDLs) for selected pesticide 

compounds in 2005 compared to the censoring levels for these 

same compounds in 2008 (table B4). For example, comparison 

Table B1. Concentrations in field blanks and groundwater samples with constituents detected in at least one field blank collected 

during groundwater sampling in Washington, D.C. in 2008.

[mg/L, milligrams per liter; μg/L, micrograms per liter; CaCO3, calcium carbonate; <, concentration is below the laboratory reporting level (LRL) for the 

constituent; E, quantified above the long-term method detection limit but below the laboratory reporting level with higher uncertainty; std, standard]

Type of 

sample

Number of 

samples Statistic

Water-quality constituent and actual or range in concentration

Calcium

(mg/L)

Sodium

(mg/L)

Carbonates1

(mg/L as 

CaCO3)

Fluoride 

(mg/L)

Iron

(μg/L)

Manganese

(μg/L)

Field blank 1 1 Concentration < 0.04 <0.12 E 3 < 0.12 < 8 < 0.4

Field blank 2 1 Concentration 0.06 E 0.09 E 3 E 0.11 E 4 E 0.03

Groundwater

14 Minimum

concentration 2.43 2.20 3.80 E 0.06 E 4 3.9

14 Median

concentration 41.8/48.2 16.6/20.1 18.8 < 0.12 < 0.8/51 465/539

1

 Calculated from the acid neutralization capacity determined from unfiltered field blanks and from the alkalinity determined for filtered groundwater 

samples; only 13 samples were analyzed for carbonates as alkalinity was not determined for one sample that had a pH of less than 4.3.
84 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Table B2. Means and relative percent differences in the concentrations of inorganic and organic constituents obtained from two 

sequential duplicate groundwater samples collected from wells in Washington, D.C. in 2008.

[RPD, relative percent difference, calculated as the difference between the two duplicate-sample concentrations, divided by their mean concentration, 

expressed in percent; ---, concentration in one or both of the duplicate samples was below laboratory reporting level; USGS, U.S. Geological Survey; mg/L, 

milligrams per liter; μg/L, micrograms per liter]

Constituents Mean

(mg/L or μg/L)

RPD

(percent)

Sample collection information

USGS 

well identifier Date

Inorganic compound or element

Calcium

60.7 0.66 WE Ca 32 08/27/2008

5.80 2.4 WW Bc 11 09/02/2008

Magnesium

15.8 1.9 WE Ca 32 08/27/2008

4.04 3.2 WW Bc 11 09/02/2008

Potassium

8.48 1.4 WE Ca 32 08/27/2008

1.61 5.0 WW Bc 11 09/02/2008

Sodium

166 1.8 WE Ca 32 08/27/2008

6.44 2.0 WW Bc 11 09/02/2008

Chloride

323 0.62 WE Ca 32 08/27/2008

14.7 1.4 WW Bc 11 09/02/2008

Sulfate

70.1 0.29 WE Ca 32 08/27/2008

0.17 12 WW Bc 11 09/02/2008

Nitrate-nitrite nitrogen

7.58 5.0 WE Ca 32 08/27/2008

3.28 0.92 WW Bc 11 09/02/2008

Ammonia-nitrogen1 --- --- WE Ca 32 08/27/2008

0.014 0 WW Bc 11 09/02/2008

Iron1 5 40 WE Ca 32 08/27/2008

--- --- WW Bc 11 09/02/2008

Manganese

3.9 0 WE Ca 32 08/27/2008

231 0.43 WW Bc 11 09/02/2008

Organic (pesticide) compound

Desethylatrazine (CIAT)1 0.020 20 WE Ca 32 08/27/2008

Aminomethylphosphonic acid (AMPA) 0.020 0 WE Ca 32 08/27/2008

Atrazine 0.031 9.8 WE Ca 32 08/27/2008

3,4-Dichloroaniline1 0.006 18 WE Ca 32 08/27/2008

Dieldrin 0.026 0 WE Ca 32 08/27/2008

Dieldrin 0.030 3.4 WE Ca 32 08/27/2008

Diuron1 0.0018 17 WE Ca 32 08/27/2008

Fipronil1 0.009 0 WE Ca 32 08/27/2008

Fipronil sulfone1 0.005 0 WE Ca 32 08/27/2008

Fipronil sulfoxide1 0.007 0 WE Ca 32 08/27/2008

Heptachlor epoxide1 0.003 0 WE Ca 32 08/27/2008

Metolachlor 0.013 8 WE Ca 32 08/27/2008

Dichlorodiphenyldichloroethylene (p,p’-DDD) 0.002 0 WE Ca 32 08/27/2008

Prometon1 0.010 0 WE Ca 32 08/27/2008

Simazine 0.150 13 WE Ca 32 08/27/2008

Tebuthiuron 0.105 9.5 WE Ca 32 08/27/2008

1

 Statistics were derived from duplicate sample concentrations that were both estimated (E-coded values), and therefore, concentrations were derived from 

values with inherently higher than normal uncertainty. 
Data-Quality Analyses 85

Figure B1. Relative percent difference as a function of mean concentration for: (A) inorganic constituents (in milligrams per liter, 

mg/L) including calcium, magnesium, sodium, potassium, nitrate plus nitrite-nitrogen and ammonium-nitrogen, chloride, sulfate, 

manganese, and iron [with iron having the extreme value (40 percent) for one of two sets of duplicate measurements]; and (B)

pesticides (in micrograms per liter, μg/L) including atrazine, prometon, simazine, desethylatrazine, dieldrin, fipronil, fipronil sulfone, 

fipronil sulfide, aminomethylphosphonic acid (AMPA), heptachlor expoxide, metolachlor, dichlorodiphenyldichloroethane (p,p’-DDD), 

and tebuthiuron.

Table B3. Mean and relative standard deviation of pesticide surrogate compound recoveries for each laboratory method and from 

laboratory-spiked groundwater samples in 2005 and 2008, and results of the Wilcoxon-Mann-Whitney rank sum test to determine if 

ranked recoveries in 2005 differed from ranked recoveries in 2008.

[%, percent; RSD, relative standard deviation; n, number of groundwater samples spiked in laboratory with the indicated surrogate compound; U, calculated 

sum of ranks statistic; p, power of test; α, alpha; HCH, Hexachlorocyclohexane; PCB, 2,2’,3,3’,4,4’,5.6.6’-nonachlorobiphenyl; ---, Laboratory schedule 2033 

was not used in 2005; LS, laboratory schedule]

Laboratory schedule 

(LS) and surrogate 

compound

2005 2008 Wilcoxon-Mann-Whitney rank sum test1

Mean

recovery

(%)

RSD

(%) n

Mean 

recovery

(%)

RSD

(%) n

U, Rank sum 

statistic, 

calculated

p, for 2-tailed 

test, α=0.05

p, for 1-tailed 

test, α=0.05

LS 2060

2,4,5-Trichlorophenol2 114 20 17 75 16 14 224 0.000004 0.000002

Barban2 104 21 17 81 22 14 194 0.002 0.001

Caffeine-13C 100 20 17 85 9.1 14 188 0.005 0.003

LS 1398

alpha-HCH-d6 98 8.3 17 101 12 14 134 0.57 0.28

Isodrin 90 10 17 82 14 14 167 0.06 0.03

PCB, 207 105 12 17 106 8.4 14 129 0.71 0.35

LS 2033

Diazinon-d103 --- --- --- 115 25 14 --- --- ---

alpha-HCH-d6 --- --- --- 87 9.15 14 --- --- ---

1

 Helsel and Hirsch (2002).

2

 In 2005, recoveries from most individual samples were estimated and are commonly near 100 percent. Also in 2008, and for samples 

collected from wells WE Ca 34 and WW Bc 10, barban recoveries are unusually low, 54 percent and 38 percent, respectively.

3

 In 2008, and for the sample collected from well WW Bc 10, barban recovery was unusually high (199 percent), indicating that sample possibly was 

spiked twice with this surrogate.
86 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

between 2005 and 2008 for the LT-MDLs and LRLs in NWQL 

schedule 2060 indicates that both censoring levels for metsulfuron methyl and tebuthiuron were notably higher in 2005 

than those in 2008. These compounds, however, were seldom 

detected in groundwater in either year of data collection.

There was no evidence that the differences between surrogate recoveries in 2005 and 2008 affected the quantification 

of individual pesticide concentrations in groundwater samples 

analyzed with NWQL schedule 2060. For example, few if 

any estimated concentrations (compounds that were detected 

and quantified below the LRL) appear for schedule 2060 in 

the 2005 groundwater samples (Klohe and Debrewer, 2007, 

appendix 3), or for that matter, for any laboratory schedule in 

2008 samples (appendix A, table A1, this report).

All of the evidence above indicates that the higher surrogate recoveries in NWQL schedules 2060 in 2005 likely reflect 

analytical differences related to the individual surrogates and 

not the detection and quantification of most compounds. Given 

there also appeared to be no significant differences in the 

surrogate recoveries between years associated with the other 

NWQL schedules used for pesticide analysis in both years 

(table B3), the basis by which to determine whether pesticide 

data could be combined for both years for interpretive purposes were (a) whether there were notable differences between 

years for LRLs and LT-MDLs in the same schedule and (b) 

whether the use of the additional laboratory schedule in 2008 

added to the number of pesticides detected in groundwater.

A comparison of the LRLs and LT-MDLs in 2005 with 

those in 2008 for pesticide compounds analyzed with the same 

laboratory method and detected at least once in either or both 

years (table B4) indicated that:

a. Compounds with higher LRLs and (or) LT-MDLs in 

2005 compared to those in 2008 were atrazine, CIAT, 

metsulfuron methyl, tebuthiuron, glyphosate, and 

AMPA;

b.Compounds with similar LRLs and (or) LT-MDLs in 

2005 and 2008 were atrazine, CIAT, bromacil, p,p’-

DDE, dieldrin (schedule 2033), chlordane, fipronil 

sulfide and sulfone; and

c. Compounds which had lower LRLs and (or) LT-MDLs 

in 2005 compared to those in 2008 were OIET, diuron, 

fluometuron, dieldrin (schedule 1398), imidacloprid, 

heptachlor epoxide, fipronil, and sulfometuron methyl. 

In relation to (a) above, more detections generally 

occurred for these pesticide compounds in groundwater 

samples collected in 2008 than were detected in groundwater 

samples collected in 2005. This result is consistent with the 

differences in the LRLs and (or) LT-MDLs in 2005 and 2008. 

In relation to (b) and (c), however, more or as many detections 

generally occurred for most of the pesticide compounds in 

groundwater samples collected in 2008 than were detected 

in groundwater samples collected in 2005. The results for 

(b) and (c) are inconsistent with the differences in LRLs 

and LT-MDLs between years, and imply factors other than 

laboratory method performance affected pesticide detections. 

To address this issue, pesticide detections were compared for 

the most frequently detected compounds in either year of data 

collection for those laboratory schedules used in both years to 

analyze groundwater samples collected from the same seven 

wells in both years (table B5).

The comparison of pesticide detections in samples from 

wells used in both years with similar laboratory schedules 

generally supports the hypothesis that differences in the detection of pesticides occurred between years (table B5). It also 

appears that these differences possibly occurred in part as a 

result of changes in the performance of analytical methods 

in 2005 and 2008. Only six pesticides were detected in 2005 

samples that were not redetected in the corresponding 2008 

samples (table B5). In two cases (imidacloprid and metsulfuron methyl) the LRLs in 2005 were notably less than the LRLs 

in 2008. For most of these compounds, however, degradation 

could have led to a decline in the concentration of these compounds in groundwater from 2005 through 2008, and, thus, an 

inability to detect these compounds in groundwater samples 

in 2008. Of greater importance is that considerably more 

pesticide detections (16) occurred in 2008 than 2005 (table 

B5). Most of these detections are for compounds present at 

low concentrations, and likely were detected in 2008 but not in 

2005 because of the lower LRLs (and hence LT-MDLs, Table 

B4) in 2008 than the corresponding LRLs (and LT-MDLs) in 

2005.

Other method-related factors possibly could be postulated 

to account for more frequent pesticide detections in 2008 compared to 2005. The differences could reflect the inability of 

the methods to accurately reproduce pesticide concentrations 

chiefly near or below the LRLs in both years of data collection. Given the uncertainty in the measurements of most of the 

detected pesticides at low concentrations (table B2), it would 

be a challenge to repeatedly detect and quantify pesticides 

present at what are relatively low concentrations. One would 

expect, however, that such variations in detections would be 

random for each compound, and not biased towards improved 

detections for each of a number of different pesticide compounds in one year compared to another year, which was the 

case given the results described above.

Differences in the frequency of pesticide detections 

between 2005 and 2008 could have occurred because of the 

introduction of an additional laboratory method (NWQL 

schedule 2033) and because of new pesticide compounds 

added to the laboratory methods previously used in 2005. 

These additions enabled the detection of 10 chiefly polar 

pesticide compounds using NWQL schedule 2033 and three 

additional nonpolar pesticide compounds using the revised 

schedules (table B6). Collectively, these method additions 

led to the frequency of detections in 2008 samples of (a) the 

s-triazines, simazine and prometon; (b) the chloracetanilides, 

alachlor and metolachlor; (c) the phenopyrazoles, fipronil and 

its sulfide and sulfone degradates; (d) a degradate of diuron, 

3,4-dichloroaniline; and (e) the organochlorine insecticide, 

chlorpyrifos. Each of these compounds was detected in one or 
Data-Quality Analyses 87

Table B4. U.S. Geological Survey laboratory reporting and detection levels for pesticide schedules used in 2005 and 2008, and for 

which at least one pesticide was detected in a groundwater sample in 2005 or 2008.

[USGS, U.S. Geological Survey; LRL, laboratory reporting level; LT-MDL, long-term method detection limit; μg/L, micrograms per liter; CEAT, 2-chloro-4-

ethylamino-6-amino-s-triazine; CIAT, desethylatrazine; OIET, 2-chloro-4-isopropylamino-6-amino-s-triazine; AMPA, aminomethylphosphonic acid; ---, not 

analyzed; NA, not available; LCGY, U.S. Geological Survey Kansas laboratory code for glyphosate and degradates]

USGS

laboratory reporting 

and detection levels

Date

(year)

Atrazine

(μg/L)

Simazine

(μg/L)

Prometon

(μg/L)

CIAT

(μg/L)

OIET

(μg/L)

CEAT

(μg/L)

Acetochlor

(μg/L)

Metolachlor

(μg/L)

LRL 2005 0.008 --- --- 0.028 0.032 0.08 --- ---

LT-MDL 2005 0.004 --- --- 0.014 0.016 0.04 --- ---

LRL 2008 0.007 0.006 0.01 0.014 0.040 0.08 0.006 0.010

LT-MDL 2008 0.004 0.003 0.002 0.007 0.020 0.04 0.003 0.005

USGS

laboratory reporting 

and detection levels

Date

(year)

Metsulfuron 

methyl

(μg/L)

Bromacil

(μg/L)

Tebuthiuron

(μg/L)

Chlorpyrifos

(μg/L)

p,p’-DDD

(μg/L)

p,p’-DDE

(μg/L)

Dieldrin

(2 methods)

(μg/L)

LRL 2005 0.025 0.018 0.026 --- 0.0024 0.0019 0.009 0.0010

LT-MDL 2005 NA 0.009 0.013 --- 0.0012 0.0009 0.004 0.0005

LRL 2008 0.14 0.02 0.016 0.005 0.0012 0.0019 0.009 0.0016

LT-MDL 2008 0.07 0.01 0.008 0.003 0.0006 0.0009 0.004 0.0008

USGS

laboratory reporting 

and detection levels

Date

(year)

Glyphosate

(μg/L)

AMPA

(μg/L)

Fipronil

(μg/L)

Fipronil 

sulfide

(μg/L)

Fipronil 

sulfone

(μg/L)

Sulfometuron 

methyl

(μg/L)

Diuron

(μg/L)

3,4-Dichloroaniline

(μg/L)

LRL 2005 0.15 0.31 0.016 0.013 0.024 0.038 0.015 ---

LT-MDL 2005 0.08 0.16 0.008 0.006 0.012 0.019 0.015 ---

LRL 2008 0.02 0.02 0.02 0.013 0.024 0.06 0.04 0.006

LT-MDL 2008 NA NA 0.01 0.006 0.012 0.03 0.02 0.003

USGS

laboratory reporting 

and detection levels

Date

(year)

Fluometuron

(μg/L)

Imidachloprid

(μg/L)

Chlordane

(μg/L)

Heptachlor 

epoxide

(μg/L)

LRL 2005 0.016 0.020 0.1 0.0012

LT-MDL 2005 0.008 0.010 NA 0.0006

LRL 2008 0.04 0.06 0.1 0.0016

LT-MDL 2008 0.02 0.03 NA 0.0008
88 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Table B5. Pesticide detections and concentrations in groundwater samples collected from wells sampled in 2005 and 2008 and 

analyzed for similar compounds using the same laboratory schedules in 2005 and 2008.

[USGS, U.S. Geological Survey; μg/L, micrograms per liter; <, less than; E, quantified above the long-term method detection limit but below the laboratory 

reporting level with higher uncertainty; ---, not analyzed; shaded data reflect analyses with lab schedule 2060, and unshaded are from schedule 2033, USGS 

National Water Quality Laboratory]

USGS 

well identifier Pesticide detected

Pesticide concentration

(μg/L)

Laboratory reporting level

(μg/L)

2005 2008 2005 2008

Detected in 2005, but not in 2008, samples

WW Bc 9 2-chloro-4-ethylamino-6-amino-s-triazine (CEAT) E 0.01 < 0.08 < 0.08 < 0.08

WE Ba 9 Dichlorodiphenyldichloroethylene (p,p’-DDE) 0.004 < 0.002 < 0.002 < 0.002

WE Ca 32 Chlordane E 0.1 < 0.1 < 0.1 < 0.1

WE Ca 32 Imidacloprid 0.301 < 0.060 < 0.020 < 0.060

WE Cc 3 Heptachlor epoxide 0.007 < 0.002 < 0.001 < 0.002

WE Cb 8 Metsulfuron methyl E 0.04 < 0.025 < 0.14 < 0.025 

Detected in 2008, but not in 2005, samples

WW Bc 9 Atrazine < 0.008 0.008 < 0.008 < 0.007

WE Cb 5 Atrazine < 0.008 0.009 < 0.008 < 0.007

WE Cb 8 Atrazine < 0.008 0.106 < 0.008 < 0.007

WE Cc 3 Atrazine < 0.008 0.009 < 0.008 < 0.007

WE Ba 9 Desethylatrazine (CIAT) < 0.03 E 0.006 < 0.03 < 0.014

WE Cb 5 CIAT < 0.03 E 0.013 < 0.03 < 0.014

WE Cb 8 CIAT < 0.03 E 0.025 < 0.03 < 0.014

WE Cc 3 CIAT < 0.03 E 0.014 < 0.03 < 0.014

WE Cb 5 2-chloro-4-isopropylamino-6-amino-s-triazine (OIET) < 0.032 E 0.034 < 0.032 < 0.040

WE Ca 32 Aminomethylphosphonic acid (AMPA) < 0.310 0.02 < 0.310 < 0.02

WE Ca 32 Dichlorodiphenyldichloroethane (p,p’-DDD) < 0.002 0.002 < 0.002 < 0.001

WE Cb 8 p,p’-DDD < 0.002 E 0.001 < 0.002 < 0.001

WE Cb 8 Fluometuron < 0.02 E 0.01 < 0.02 < 0.04

WE Cb 8 Sulfometuron, methyl < 0.038 E 0.007 < 0.038 < 0.006

WE Ca 32 Diuron < 0.01 E 0.0016 < 0.01 < 0.04

WE Ca 32 3,4-Dichloroaniline --- E 0.006 --- 0.006

Detected in both 2005 and 2008 samples

WE Ca 32 Atrazine 0.02 0.032 < 0.007 < 0.008

WE Ca 32 CIAT E 0.02 E 0.022 < 0.03 < 0.014

WW Bc 9 CIAT E 0.01 E 0.013 < 0.03 < 0.014

WE Cc 3 OIET E 0.007 E 0.013 < 0.032 < 0.040

WW Bc 9 Bromacil E 0.01 E 0.01 < 0.02 < 0.02

WE Ca 32 Dieldrin 0.065 0.026 < 0.001 < 0.002

WE Ca 32 Heptachlor epoxide 0.005 0.003 < 0.001 < 0.002
Data-Quality Analyses 89

more groundwater samples in 2008 and, except for simazine in 

well WE Ba 11 and metolachlor in well WW Ac 8, all of these 

pesticides were detected in samples taken from wells that were 

previously sampled in 2005.

Site-Specific Observations 

During field visits in 2008, it was observed that a leaking 

fire hydrant near well WE Cb 8 had been draining into and 

saturating the area around the wellhead for an indeterminate 

period of time. The groundwater sample collected from this 

well in 2008 contained eight pesticide and (or) degradate 

compounds (table B6). Only one pesticide was detected in 

the groundwater sample collected from this well in 2005 

(metsulfuron methyl, at E 0.04 μg/L). This pesticide was not 

detected in 2008, although most likely because there were 

notable increases in the LRL and LT-MDL for this compound 

after 2005 (table B4), implying its detection in 2005 is suspect 

and quantification was at a high level of uncertainty. Given all 

of the above and given that the screened interval of well WE 

Cb 8 is 255 to 265 feet below land surface with an intervening 215-feet-thick clay layer (table 4), the water-quality data, 

including pesticide data, for 2005 and 2008 for this well may 

not accurately reflect the groundwater at this site.

Table B6. Pesticide detections in groundwater attributed to the addition of a laboratory schedule (LS 2033) in 2008 that was not used 

in 2005, or the addition of new pesticide compounds into laboratory schedules.

[USGS, U.S. Geological Survey; μg/L, micrograms per Liter; ---, not analyzed; <, less than; E, quantified above the long-term method detection limit but 

below the laboratory reporting level with higher uncertainty; shaded data indicate wells that also were used for data collection in 2005 but without the additional laboratory schedule or additional compounds]

USGS 

well identifier Pesticide residue

Sample concentration

(μg/L)

2008 laboratory 

reporting level 

(μg/L) 2005 2008

2008 detections associated with the use of laboratory schedule 2033

WW Bc 9 Simazine --- E 0.006 < 0.006

WE Cb 5 Simazine --- 0.01 < 0.006

WE Cc 3 Simazine --- 0.008 < 0.006

WE Ba 11 Simazine --- 0.022 < 0.006

WE Ca 32 Simazine --- 0.016 < 0.006

WE Cb 5 Prometon --- E 0.01 < 0.01

WE Cc 3 Prometon --- E 0.01 < 0.01

WE Ca 32 Prometon --- E 0.01 < 0.01

WE Cc 3 Fipronil --- E 0.005 < 0.020

WE Ca 32 Fipronil --- E 0.009 < 0.020

WE Ca 32 Fipronil sulfide --- E 0.007 < 0.013

WE Cc 3 Fipronil sulfide --- E 0.007 < 0.013

WE Ca 32 Fipronil sulfone --- E 0.005 < 0.024

WE Cb 8 Acetochlor --- 0.019 < 0.006

WW Bc 9 Metolachlor --- E 0.008 < 0.010

WE Cb 8 Metolachlor --- 0.053 < 0.010

WW Ac 8 Metolachlor --- E 0.008 < 0.010

WE Ca 32 Metolachlor --- 0.013 < 0.010

2008 detections associated with compound additions to laboratory schedules

WE Cb 8 Chlorpyrifos --- E 0.005 < 0.005

We Ca 32 3,4-Dichloroaniline --- E 0.006 < 0.006

WE Cb 8 Sulfameturon methyl --- E 0.007 < 0.030
90 Pesticides in Groundwater in the Anacostia River and Rock Creek Watersheds in Washington, D.C., 2005 and 2008

Summary and Implications for Analysis 

and Interpretation 

Quality-control data from blanks and duplicate sequential 

groundwater samples obtained in the field, and from laboratory surrogate recovery data, were analyzed to assess the 

quality of the groundwater data collected from 17 monitoring 

wells in the lower Anacostia River watershed in 2005, and 

from 14 monitoring wells in the Anacostia River and Rock 

Creek watersheds in 2008. Results of this analysis indicate the 

following:

a. For both years, field-blank data indicate no appreciable 

bias due to contamination was introduced during the 

processing and analysis of groundwater samples that 

would limit interpretation of the data. Except for trace 

amounts of selected major ions, the concentrations of 

all groundwater constituents, including all pesticides, 

in field-blank samples were less than their respective 

method LRLs. No pesticides were detected in any field 

blanks. For each constituent that was detected in one or 

more field blanks, the blank concentration was found 

to be near, or considerably less than, the minimum 

concentration and generally well below the median 

concentration in groundwater samples collected in 

either year. 

b. For both years, sequential duplicate groundwater 

samples collected from selected wells revealed similar 

precision results—low variability in duplicate measurements for most constituents. For inorganic constituents at measureable concentrations in duplicate 

samples, the relative percent difference between the 

two concentrations for most constituents was near or 

less than 12 percent, and often less than 1 percent. For 

pesticides at measureable concentrations in duplicate 

samples, the relative percent difference between the 

two concentrations generally was 20 percent or less, 

and for most organic constituents less than 10 percent.

c. For the 2 years in which data were collected, differences in the type and number of pesticides detected in 

groundwater samples collected in 2005 and 2008 could 

be due in part to differences in analytical methods. 

Variations in method performance based on LRLs and 

LT-MDLs possibly led to six pesticide detections in 

2005 samples that were not repeated in 2008 samples 

collected from the same wells. Lower censoring levels 

for other pesticide compounds in 2008 compared to 

those in 2005 possibly led to 16 detections in groundwater samples collected in 2008, most of which (10 of 

16) were not initially detected in groundwater samples 

collected from the same wells earlier in 2005. Also 

in 2008, the addition of pesticide method NWQL 

schedule 2033 resulted in a large number of pesticide 

detections (18) for 6 polar compounds. No analyses 

for these polar compounds, however, were conducted 

in 2005, and most of the detected compounds (16 of 

18) in 2008 came from wells previously used for data 

collection in 2005. In addition, three new pesticide 

compounds were added to the laboratory methods used 

in 2008, and were each detected once in groundwater 

samples collected in 2008 from two different wells.

Data-quality review from (a) and (b) above indicate 

pesticide and other water-quality data collected in each year 

could be combined for interpretive purposes. Review results 

from (c) above, however, indicate there are limitations in the 

extent to which pesticide data from both years can be compared. Pesticide data obtained from the same seven wells in 

2005 and 2008 differed at least in part because of year-to-year 

differences in laboratory analytical methods. In addition, only 

7 of 14 wells used to obtain data in 2005 were reused in 2008. 

Therefore, constraints were placed on the extent to which the 

pesticide data were combined and interpreted. 

Only simple descriptions and analyses were conducted 

on the occurrence and distribution of pesticides in shallow 

groundwater, and for the assessment of pesticide occurrence 

in relation to land use, surficial-aquifer sediment types, and 

groundwater chemistry. No major statistical analyses or 

hypothesis testing were conducted. Selected pesticide data 

were combined in order to describe the general types of 

pesticides present in groundwater, and their concentrations 

in relation to human-health and aquatic-health criteria and 

guidelines. Pesticide detections and some selected landscape 

and hydrogeologic data were combined in order to identify potential relations (future testable hypotheses) between 

pesticide occurrence in groundwater and selected subsurface 

characteristics. If combined data were used, the results were 

qualified to the extent possible in relation to limitations in the 

combined data.
Prepared by USGS West Trenton Publishing Service Center.

Edited by Ruth M. Larkins and Valerie M. Gaine.

Graphics and layout by Timothy W. Auer.

For additional information, contact:

Director, MD-DE-DC Water Science Center

U.S. Geological Survey

5522 Research Park Drive

Baltimore, MD 21228

or visit our Web site at:

http://md.water.usgs.gov
Koterba, M.T., Dieter, C.A., and Miller, C.V.—Pesticides in Groundwater in Washington, D.C., 2005 and 2008—Scientific Investigations Report 2010–5130

Printed on recycled paper