0 1 2 MILES

96

o

52'30"

32

o

22'30"

32

o

20'

Digital orthophoto quadrangle,

1-meter resolution, derived from

photos taken 1994–97 (Texas Natural

Resource Information System, 2002).

TE

LOCATIO

Lake

Waxahac

not on the finished drinking water. Therefore, the U.S. Environmental Protection Agency (USEPA), in conjunction with the

NAWQA Program, has initiated a nationwide pilot project to collect information on concentrations of pesticides and their breakdown products in finished drinking water, in source waters such as

reservoirs, and in the basins that contribute water to the reservoirs.

The pilot project was designed to collect water samples from

finished drinking-water supplies and the associated source water

from selected reservoirs that receive runoff from a variety of land

uses. Lake Waxahachie, in Ellis County in north-central Texas,

was chosen to represent a reservoir receiving water that includes

runoff from cotton cropland. This fact sheet presents the results of

pesticide sampling of source water from Lake Waxahachie and in finished drinking water from the lake.

Analyses are compared to indicate differences in pesticide detections and concentrations between lake water

and finished drinking water.

Sampling and Analysis

Sampling of the selected reservoirs involved collecting water of three types—finished drinking water at the

water treatment plant, water from the treatment plant

intake site (source water), and water from the reservoir

outflow. For Lake Waxahachie only water from the

intake site and finished water from the treatment plant

were sampled because no water flowed out of the

reservoir during the sampling period. Samples of both

waters were collected primarily during May to September 1999, a period selected to follow the annual period

of peak pesticide use. (One sample was collected in

December 1999.) The USGS collected the samples

using protocols developed by the NAWQA Program

(Shelton, 1994) and specifically adapted for this

project.

Samples of source water and finished drinking water

from Lake Waxahachie were analyzed for concentrations of 184 pesticides and their breakdown products by

the USGS National Water Quality Laboratory (NWQL).

The pesticide data from the source-water samples will

provide baseline data for human-health exposure

Pesticides in Lake Water (Source Wat

Eighteen pesticides were detected in source water 

sampling site. Sixteen of the 18 were herbicides and 

down products; one was an insecticide and one was a 

The most frequently detected pesticides in source wa

atrazine, metolachlor, simazine, prometryn, and four 

breakdown products; all were detected at frequencies 

60 percent (table 1). Average concentrations of pestic

source water ranged from 0.0018 microgram per liter 

p,p'-DDE to 0.53 mg/L for atrazine. Eleven of the 18 

detected have USEPA-established standards for drink

U.S. Department of the Interior

U.S. Geological Survey

USGS Fa

Runoff from cotton cropland in the watershed of Lake Waxahachie 

the lake.
and seven have aquatic-life guidelines established by USEPA,

Environment Canada, or a joint U.S.-Canada commission. Concentrations of one pesticide—p,p'-DDE, a breakdown product of

DDT—were greater than the aquatic-life guidelines in four of six

samples with detections, and no concentrations were greater than

drinking-water standards.

Pesticides in Finished Drinking Water

Ten pesticides, all of which were herbicides and their breakdown products, were detected in the finished drinking-water

samples. Pesticide concentrations in all drinking-water samples

were well below applicable drinking-water standards and aquaticlife guidelines. All the pesticides detected in finished drinking

water also were detected in source water. The most frequently

detected pesticides in finished drinking water were atrazine,

metolachlor, simazine, and four atrazine breakdown products—

the same pesticides most frequently detected in source water

(except for prometryn, which was not detected in finished water).

Atrazine, deethylatrazine, and metolachlor were detected in all of

the drinking-water samples (and all of the source-water samples).

These compounds are among the top pesticides detected nationally in agricultural settings across the United States (U.S. Geological Survey, 1999). Average concentrations of the pesticides

detected in drinking-water samples ranged from nondetectable to

0.52 μg/L for atrazine. Two atrazine breakdown products had

greater frequencies of detection and three had larger average concentrations in the drinking-water samples than in the source-water

samples, which suggests that breakdown of atrazine might have

occurred during the time of treatment. Average concentrations of

the other pesticides detected in finished drinking water were similar to their concentrations in lake water.

References

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.

Shelton, Larry, 1994, Field guide for collecting and processing

stream-water samples for the National Water-Quality

Assessment Program: U.S. Geological Survey Open-File

Report 94–455, 42 p.

Texas Natural Resource Information System, 2002, Data

distribution system—Forreston 7-1/2-minute quadrangle:

Accessed March 15, 2002, at URL

http://www.tnris.state.tx.us/DigitalData/doqs.htm

U.S. Geological Survey, 1999, The quality of our Nation’s waters—

Nutrients and pesticides: U.S. Geological Survey Circular

1225, 82 p.

— Patricia B. Ging

Any use of trade, product, or firm names is for descriptive purposes

only and does not imply endorsement by the U.S. Government.

Information on technical reports and hydrologic data related to

this study can be obtained from:

Trinity NAWQA Chief Phone: (512) 927–3500

U.S. Geological Survey FAX: (512) 927–3590

8027 Exchange Drive World Wide Web:

Austin, Texas 78754 http://tx.usgs.gov/

Table 1. Pesticides detected in Lake Waxahachie (source water) and finished drinking water

[μg/L, micrograms per liter; --, not detected]

Compound Use

Source water Finished drinking water

Number

of

samples

Frequency

of detection

(percent)

Average

concentration

(μg/L)

Average

concentration

(μg/L)

Frequency

of detection

(percent)

Number

of

samples

2,4-D herbicide 21 52.4 0.0510 0.0413 42.9 7

2,4-D methyl ester 2,4-D breakdown product 21 9.5 .0235 -- -- 7

Atrazine herbicide (corn) 22 100 .5297 .5194 100 9

Deethylatrazine atrazine breakdown product 22 100 .0928 .1155 100 9

Deethyldeisopropylatrazine atrazine breakdown product 21 61.9 .0115 .0100 57.1 7

Deisopropylatrazine atrazine breakdown product 21 90.5 .0132 .0151 100 7

Hydroxyatrazine atrazine breakdown product 21 85.7 .4180 .5107 100 7

Alachlor herbicide 21 4.8 .0040 -- -- 9

Bentazon herbicide 21 9.5 .0044 -- -- 7

Diuron herbicide (cotton) 21 9.5 .0076 -- -- 7

Metolachlor herbicide 21 100 .0456 .0372 100 9

Prometon herbicide 21 28.6 .0054 .0059 33.3 9

Prometryn herbicide 22 77.3 .0068 -- -- 8

Simazine herbicide 21 81 .0161 .0154 88.9 9

Tebuthiuron herbicide (highway) 22 40.9 .0050 .0070 44.4 9

p,p'-DDE DDT breakdown product 21 28.6 .0018 -- -- 9

Diazinon insecticide 21 28.6 .0035 -- -- 9

Metalaxyl fungicide 21 4.8 .0030 -- -- 7