88

385

Pump

Study

In

Single Monitoring Wells Multiple Monitoring Wells

Natural District

Base from U.S. Geological Survery digital data,

1:100,000 digital data, 1972,

Albers Equal Area Conic projection,

Standard parallels 29o30' and 45o30'

Central meridian -96o

42o

41o30'

104o

103o

102o

EXPLANATION

0 1 2 3 4 5 MILES

0 1 2 3 4 5 KILOMETERS

Surface water

Sioux County

Banner County

Morrill County

Ga

Lawre

Pumpkin Creek Valley

North Platte River Valley

Major roads

No detection

Pesticide detected

Pesticide and pesticide

degradate detected

No detection

Pesticide detected

Pesticide and pesticide degradate detected

88

385

Pump

Study

In

Single Monitoring Wells Multiple Monitoring Wells

Natural District

Base from U.S. Geological Survery digital data,

1:100,000 digital data, 1972,

Albers Equal Area Conic projection,

Standard parallels 29o30' and 45o30'

Central meridian -96o

42o

o30'

104o

103o

102o

EXPLANATION

0 1 2 3 4 5 MILES

0 1 2 3 4 5 KILOMETERS

Surface water

Sioux County

Banner County

Morrill County

Ga

Lawre

Pumpkin Creek Valley

North Platte River Valley

Major roads

No detection

Pesticide detected

Pesticide and pesticide

degradate detected

No detection

Pesticide detected

Pesticide and pesticide degradate detected

U.S. Department of the Interior

U.S. Geological Survey

 Fact Sheet 114-03

 December 2003 

 Prepared in cooperation with the

NORTH PLATTE NATURAL RESOURCES DISTRICT

 Occurrence of Pesticides in Ground Water of the North Platte 

Natural Resources District, Nebraska, 2002

 —G.V. Steele1 and J.C. Cannia2

 Ground water is the source of drinking 

water for all residents of the North Platte 

Natural Resources District (NPNRD). 

Most of the drinking water in the 

NPNRD comes from unconfined aquifers 

that are part of the regional High Plains 

aquifer. The water tables of these local 

aquifers lie close to the land surface. As 

a result, the aquifers can be affected by 

infiltration of irrigation waters that are 

prone to contain contaminants. Once in 

the aquifer, contaminants can adversely 

affect drinking-water supplies. 

 1

U.S. Geological Survey, Lincoln, Nebraska.

 2

North Platte Natural Resources District, Gering, 

Nebraska.

 In 2002, the U.S. Geological Survey 

(USGS) and the NPNRD began a cooperative study to determine whether or not 

112 pesticides and selected degradation 

products occur in ground water of the 

NPNRD. Forty-one monitoring wells at 

23 sites (fig. 1) throughout the NPNRD 

were selected for sampling to determine 

the areal occurrence of pesticides. This 

fact sheet summarizes the results of the 

2002 sampling.

 Introduction

 The study area encompasses all of the 

NPNRD (fig. 1). The dominant land use 

in the North Platte River and Pumpkin 

Creek Valleys of the NPNRD is agricultural row crop production, predominantly 

corn. Other crops include sugar beets, 

alfalfa, soybeans, and dry beans. Upland 

areas primarily are used as pastureland, but have some row crops. The 

primary aquifer in the NPNRD contains 

 Quaternary-age sand and gravel deposits 

interspersed with layers of clay. Most 

of the aquifer lies in the alluvial valleys 

of the North Platte River and Pumpkin 

Creek (fig. 1). 

 Previous studies, including Exner 

(1990), Verstraeten and others (1995), 

and Steele and others (1998), have 

 Figure 1. Location of the study area and wells with detections of pesticides and pesticide degradate compounds. 
reported that pesticide concentrations in 

the ground water of the NPNRD typically are low and occurrence is sporadic. 

However, the shallowest ground water 

would be the affected by a downward 

flux of agricultural chemicals from the 

land surface. For the study described 

in this report most of the emphasis 

was placed on determining pesticide 

concentrations in shallow ground water 

by sampling 41 wells during June 2002. 

Twenty-eight shallow monitoring wells 

(less than 100 feet deep) and 13 deep 

monitoring wells (greater than 100 feet 

deep) were sampled at sites with single 

and multiple monitoring wells (fig. 1). 

 Ground-water samples were analyzed 

for 112 pesticide compounds, including 90 parent compounds (original 

compounds intended for pest control use) 

and 22 degradation products (compounds 

derived from biochemical breakdown of 

parent compounds). Pesticides include 

compounds most commonly used to 

control weeds (herbicides) and insects 

(insecticides). For this report, measurable 

amounts of pesticides, herein referred 

to as detected, describe samples where 

the concentration was greater than or 

equal to a laboratory reporting limit of 

0.005 micrograms per liter (or parts per 

billion). Below this threshold, the quantification of the concentration and confidence in the presence of the pesticide or 

degradation products are less reliable. 

In June 2002, ground-water samples 

were collected for determination of field 

measurements (specific conductance, pH, 

water temperature, and dissolved-oxygen 

concentration), and analysis for concentrations of major ions (including calcium, 

magnesium, potassium, chloride, and 

sulfate), nutrients (nitrate as nitrogen (N), 

and phosphate), and pesticides. Collection, preparation, and shipment of all 

ground-water samples were completed 

using standard USGS protocols (U.S. 

Geological Survey, 1997-present). All 

samples were analyzed at the USGS 

National Water Quality Laboratory in 

Denver, Colorado. Methods for analytical procedures used by the NWQL can 

be found on the World Wide Web at URL 

http://nwql.usgs.gov/Public/ref_list.html 

(accessed Dec. 4, 2003). These analytical data are stored in the USGS National 

Water Inventory System and are accessible at http://waterdata.usgs.gov/nwis. 

Seven quality-control samples (three 

blanks and two replicates) were sequentially collected with the environmental 

samples. Results from analysis of the 

quality-control samples indicate good 

reproducibility of the laboratory techniques, and that no contamination was 

introduced during field activities.

 Table 1. Pesticide detections in ground-water samples, North Platte Natural Resources District, Nebraska, 2002

 [All concentrations in micrograms per liter; MRL, minimum reporting limit; italicized text indicates pesticide degradation products; ESA, ethane sulfonic acid; 

OXA, oxanilic acid; --, none or not applicable]

Pesticide

Number

of

detections

Percentage

of sites with 

detections

Median 

concentration 

above MRL

Maximum

concentration 

Maximum

contaminant

level 

CASRN#1

Herbicide

Deethylatrazine 28 68 0.02 0.91 -- --

Atrazine 21 51 .009 .20 3.0 --

Deethyldeisopropylatrazine 21 51 .02 .89 -- --

Alachlor ESA 20 49 .10 3.0 -- --

Metolachlor ESA 11 27 .10 1.2 -- --

Prometon 10 24 .01 .07 -- 1610-18-0

Deisopropylatrazine 9 22 .01 .10 -- --

2-Hydroxyatrazine 8 20 .012 .06 -- --

Simazine 7 17 .01 .07 4.0 --

Metolachlor OXA 5 12 .10 .20 -- --

Metolachlor 3 7 .009 .011 -- 51218-45-2

Acetochlor ESA 2 5 -- .20 -- --

Bromacil 1 2 -- .01 -- --

Diuron 1 2 -- .02 -- 330-54-1

Imazethapyr 1 2 -- .05 -- --

Nicosulfuron 1 2 -- .01 -- --

Tebuthiuron 1 2 -- .03 -- --

Insecticide

Picloram 1 2 -- .67 500 --

 1

Chemical Abstract Service Registration Number (CASRN#) for unregulated drinking water contaminants regulatory compliance documents 

(U.S. Environmental Protection Agency, 2001, http://www.epa.gov/OGWDW/dw_unregcontaminants.html#1, accessed June 10, 2003). 
 Pesticides

 Nine herbicides, eight herbicide 

degradation products, and one insecticide were detected in water samples 

from the NPNRD sites (fig. 2, table 1). 

Pesticide compounds (includes parent 

and degradation products) were detected 

in 78 percent of water samples (32 of 

the 41). Pesticide degradation products 

were prevalent, accounting for 7 of the 

10 most frequently detected compounds 

(table 1). None of the pesticides detected 

in ground-water samples exceeded the 

U.S. Environmental Protection Agency’s 

(EPA) Maximum Contaminant Level 

(MCL) (U.S. Environmental Protection 

Agency, 2001) for pesticides in drinking 

water (table 1). The herbicide atrazine 

and its degradation products were the 

most frequently detected compounds 

consistent with the extensive use of 

atrazine in the NPNRD for decades. 

Atrazine and/or four atrazine degradation 

 products were detected in 68 percent of 

the samples collected.

 Of the 32 monitoring wells whose 

water samples contained pesticide 

compounds, 29 contained more than 

one p esticide. Two to eleven different 

pesticides were detected in each of these 

29 wells. Pesticide compounds were 

detected in 86 percent (24 of 28) of the 

samples from wells less than 100 feet 

 Table 2. Minimum and maximum concentrations of pesticides by depth of well and number of 

detections in ground-water samples, North Platte Natural Resources District, Nebraska, 2002

 [All results in micrograms per liter; italicized text indicates pesticide degradation product; number, number of 

monitoring wells with detections; ESA, ethane sulfonic acid; OXA, oxanilic acid; --, not detected or maximum 

concentration equals minimum concentration]

Pesticide

Monitoring wells shallower

than 100 feet

Monitoring wells deeper

than 100 feet

Number Minimum Maximum Number Minimum Maximum

Deethylatrazine 20 0.005 0.417 8 0.01 0.91

Atrazine 15 .005 .177 6 .01 .20

Deethyldeisopropylatrazine 15 .01 .14 6 .01 .89

Alachlor ESA 15 .1 1.3 5 .1 .6

Metolachlor ESA 9 .1 1.2 2 .1 .3

Prometon 9 .01 .07 1 .01 --

Deisopropylatrazine 6 .01 .02 3 .01 .1

2-Hydroxyatrazine 6 .005 .055 2 .008 .031

Simazine 4 .007 .069 3 .006 .01

Metolachlor OXA 5 .1 .2 -- -- --

Metolachlor 3 .008 .011 -- -- --

Acetochlor ESA 1 .1 -- 1 .2 --

Bromacil 1 .01 -- -- -- --

Diuron 1 .02 -- -- -- --

Imazethapyr 1 .05 -- -- -- --

Nicosulfuron 1 .01 -- -- -- --

Tebuthiuron 1 .03 -- -- -- --

Picloram 1 .67 -- -- -- --

0

5

10

15

20

25

30

Deethylatrazine

Atrazine

Deethyldeisopropylatrazine

Alachlor ESA

Metolachlor ESA

Prometon

Deisopropylatrazine

2-Hydroxyatrazine

Simazine

Metolachlor OXA

Metolachlor

Acetochlor ESA

Bromacil

Diuron

Imazethapyr

Nicosulfuron

Tebuthiuron

Picloram

N

U

MBER OF DETECTIO

NS

 Figure 2. Frequency of pesticide detections in ground-water samples, North Platte Natural Resources District, 2002. 
deep, with 18 compounds detected. 

In comparison, pesticide compounds 

were detected in 62 percent (8 of 13) 

of the samples from wells deeper than 

100 feet, with 10 compounds detected 

(table 2). Although pesticide compounds 

were detected less frequently at greater 

depths, the results indicate that pesticide 

compounds are being transported to deep 

ground water of the NPNRD in places.

 Concentrations of nitrate as N in 

ground-water samples ranged from 

0.31 milligrams per liter (mg/L, or parts 

per million) to 35 mg/L, with a median 

concentration of 6.1 mg/L. Eleven water 

samples contained concentrations higher 

than the EPA MCL of 10 mg/L of nitrate 

as nitrogen in drinking water (U.S. 

Environmental Protection Agency, 2002). 

Figure 3 shows that pesticide compounds 

were detected more frequently as nitrate 

as N concentrations increased.

 Implications

 The results of the study indicate that 

pesticides were frequently detected in 

ground-water samples of the NPNRD. 

Nine herbicides, eight herbicide degradation products, and one insecticide of the 

112 selected pesticides and degradation 

products analyzed for were detected in at 

least one water sample. Atrazine and two 

of its degradation products—deethylatrazine and deethyldeisopropylatrazine—were the three most commonly 

detected pesticide compounds in the 

NPNRD. These three constituents 

were detected in over 50 percent of the 

samples. However, no concentration of 

pesticide exceeded the EPA MCL for 

drinking water. Other frequently detected 

pesticides and degradation products 

(listed in frequency of occurrence) 

included alachlor ESA, metolachlor 

ESA, prometon, deisopropylatrazine, 

2-hydroxyatrazine, simazine, metolachlor 

OXA, metolachlor, and acetochlor ESA. 

The remaining pesticides either were 

detected in a single water sample (7 of 

41) or were not detected. Pesticide degradates were prevalent in ground water 

of the NPNRD, being 7 of the 10 most 

frequently detected compounds.

 This study shows that pesticides 

compounds are present in many parts of 

the NPNRD, but they do not occur everywhere. Pesticide compounds are typically 

present in shallow (less than 100 feet 

deep) ground water areally across the 

NPNRD and are being transported to the 

deep parts (greater than 100 feet deep) of 

the aquifer in places.

 References

 Exner, M.E., 1990, An investigation 

to determine the source of elevated 

nitrate concentrations in the ground 

water of the North Platte Valley west 

of Oshkosh, Nebraska: Report for 

the North Platte Natural Resources 

District, February 26, 1990, 23 p.

 Steele, G.V., Cannia, J.C., and Stanton, 

J.S., 1998, Geohydrology and water 

quality of the North Platte River alluvial aquifer, Garden County, western, 

Nebraska, 1993-94: U.S. Geological 

Survey Water-Resources Investigations 

Report 98-4033, 75 p.

 U.S. Environmental Protection Agency, 

2002, Current drinking water standards—National Primary and Secondary Drinking Water Regulations: U.S. 

Environmental Protection Agency, 

Office of Ground Water and Drinking 

Water, accessed on March 22, 2003 at 

URL http://www.epa.gov/safewater/

mcl.html.

 U.S. Geological Survey, 1997 to present, 

National field manual for the collection 

of water-quality data: U.S. Geological 

Survey Techniques of Water-Resources 

Investigations, book 9, chaps. A1-A9, 

2 v., variously paged. [Also available 

online at http://pubs.water.usgs.gov/

twri9A. Chapters originally were 

published from 1997-1999; updates 

and revisions are ongoing and are 

summarized at: http://water.usgs.gov/

owq/FieldManual/mastererrata.html]

 Verstraeten, I.M., Sibray, S.S., Cannia, 

J.C., and Tanner, D.Q., 1995, Reconnaissance of ground-water quality in 

the North Platte Natural Resources 

District, western Nebraska, JuneJuly 1991: U.S. Geological Survey 

Water-Resources Investigations Report 

94-4057, 114 p.

0

25

50

75

100

FREQ

UENCY

OF PESTICIDE OR DEGRADA

TIO

N PRODUCT

DETECTIO

NS, IN PERCEN

T

Less than

2.0

2.0 to 4.9 5.0 to 9.9 Greater than

10.0

NITRATE CONCENTRATION, IN MILLIGRAMS PER LITER

 Figure 3. Pesticide detections as a function of nitrate concentrations in water samples, North 

Platte Natural Resources District, 2002. 

 For more information, contact:

 District Chief

 U.S. Geological Survey

 Federal Building, Room 406

 100 Centennial Mall North

 Lincoln, NE 68508

 Phone: 402-437-5082

 e-mail: dc_ne@usgs.gov

 Web site: http://ne.water.usgs.gov 

Printed on recycled paper