Effects of Agriculture and Urbanization on Quality of Shallow Ground Water in the Arid to Semiarid Western United States, 1993

Scientific Investigations Report 2007–5179

Table 8. Pesticide occurrence in shallow ground water beneath agricultural and urban areas within regional National Water-Quality Assessment Program study units in the arid to semiarid Western United States, 1993–2004.

[Concentration range: With the exception of EPTC, pesticides listed in this table where concentrations were reported as estimated were included in the data analyses within this report. There were no estimated concentrations of EPTC. Factors relating to pesticide detection: All parameters for 500-meter buffer zone around wells. The “+” and “–” signs indicate a positive or negative correlation, respectively, of pesticide occurrence to designated explanatory variable. Abbreviations: LT-MDL, long-term method detection level; MCL, maximum contaminant level; SACR, Sacramento River Basin; SANJ, San Joaquin-Tulare Basins; USEPA, U.S. Environmental Protection Agency; nd, not determined; µg/L, microgram per liter. Symbol: <, less than]

Pesticide	USEPA MCL (µg/L)	Maximum LT-MDL(µg/L)	Land use	Number of wells	Concentration range (µg/L)	Detection frequency (percent)	Important factors relating to pesticide detection
Simazine	4	0.006	Agricultural	272	<0.006–0.230	28	Dissolved oxygen	+
							Temperature	+
							Depth to screened interval	–
							Percent row crop	–
			Urban¹	176	<0.006–0.051	17	General soil permeability characteristics	–
Atrazine	3	0.004	Agricultural¹	272	<0.004–1.2	16	Temperature	+
							General soil permeability characteristics	–
			Urban	176	<0.004–1.58	24	Dissolved oxygen	+
							Percent households on sewer system	+
							Temperature	–
							General soil permeability characteristics	–
Prometon	nd	0.007	Agricultural^1,2	272	<0.007–0.230	7	Percent urbanization	+
							Depth to screened interval	–
							Percent clay and sand	–
			Urban^1,2	176	<0.007–0.518	25
Diuron	nd	0.007	Agricultural	234	<0.007–0.920	13	Dissolved oxygen	+
							Temperature	+
							General soil permeability characteristics	–
			Urban	127	<0.007–0.325	3	Population density	+
Tebuthiuron	nd	0.008	Agricultural	272	<0.008–0.012	<1	nd
			Urban¹	176	<0.008–2.12	5	Percent recreational grasses	+
Carbofuran	40	0.010	Agricultural	272	<0.010–0.686	1	nd
			Urban	176	<0.010–0.010	<1	nd
Thiobencarb	nd	0.0024	Agricultural¹	272	<0.002–0.025	<1	SACR (rice)
			Urban	176	<0.002–0.004	<1	nd
Molinate	nd	0.0008	Agricultural¹	272	<0.0008–0.056	2	SACR (rice)
			Urban	176	<0.0008	0	nd
EPTC	nd	0.001	Agricultural¹	272	<0.001–0.012	1	SANJ
			Urban	176	<0.001	0	nd
Bentazon	nd	0.006	Agricultural¹	233	<0.006–7.87	6	SACR (rice)
			Urban	128	<0.006–0.060	2	nd
Metolachlor	nd	0.006	Agricultural¹	272	<0.006–5.40	6	Percent row crop	+
							Sprinkler irrigation	–
			Urban	176	<0.006	0	nd
Dinoseb	7	0.019	Agricultural	233	<0.019–0.054	3	nd
			Urban	127	<0.019	0	nd
Norflurazon	nd	0.010	Agricultural	234	<0.010–0.032	2	nd
			Urban	128	<0.010–0.016	1	nd

Pesticide

USEPA
MCL (µg/L)

Maximum
LT-MDL(µg/L)

Land
use

Number
of wells

Concentration
range
(µg/L)

Detection
frequency
(percent)

Important factors relating
to pesticide detection

Simazine

0.006

Agricultural

272

<0.006–0.230

Dissolved oxygen

Temperature

Depth to screened interval

–

Percent row crop

–

Urban¹

176

<0.006–0.051

General soil permeability characteristics

–

Atrazine

0.004

Agricultural¹

272

<0.004–1.2

Temperature

General soil permeability characteristics

–

Urban

176

<0.004–1.58

Dissolved oxygen

Percent households on sewer system

Temperature

–

General soil permeability characteristics

–

Prometon

0.007

Agricultural^1,2

272

<0.007–0.230

Percent urbanization

Depth to screened interval

–

Percent clay and sand

–

Urban^1,2

176

<0.007–0.518

Diuron

0.007

Agricultural

234

<0.007–0.920

Dissolved oxygen

Temperature

General soil permeability characteristics

–

Urban

127

<0.007–0.325

Population density

Tebuthiuron

0.008

Agricultural

272

<0.008–0.012

Urban¹

176

<0.008–2.12

Percent recreational grasses

Carbofuran

0.010

Agricultural

272

<0.010–0.686

Urban

176

<0.010–0.010

Thiobencarb

0.0024

Agricultural¹

272

<0.002–0.025

SACR (rice)

Urban

176

<0.002–0.004

Molinate

0.0008

Agricultural¹

272

<0.0008–0.056

SACR (rice)

Urban

176

<0.0008

EPTC

0.001

Agricultural¹

272

<0.001–0.012

SANJ

Urban

176

<0.001

Bentazon

0.006

Agricultural¹

233

<0.006–7.87

SACR (rice)

Urban

128

<0.006–0.060

Metolachlor

0.006

Agricultural¹

272

<0.006–5.40

Percent row crop

Sprinkler irrigation

–

Urban

176

<0.006

Dinoseb

0.019

Agricultural

233

<0.019–0.054

Urban

127

<0.019

Norflurazon

0.010

Agricultural

234

<0.010–0.032

Urban

128

<0.010–0.016

¹A sufficiently strong logistic-regression model was not developed for this pesticide within areas of this land use. However, the parameters listed were determined to be important in the occurrence of the pesticide (p < 0.05).

²The logistic-regression model was analyzed for a combined dataset using both agricultural and urban land-use data.

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