U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 96-4062

Prepared in cooperation with the

PENNSYLVANIA DEPARTMENT OF ENVIRONMENTAL PROTECTION, 

BUREAU OF WATER QUALITY MANAGEMENT

Lemoyne, Pennsylvania 

1996
U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Gordon P. Eaton, Director

For additional information 

write to:

District Chief

U.S. Geological Survey

840 Market Street

Lemoyne, Pennsylvania 17043-1586

Copies of this report may be 

purchased from:

U.S. Geological Survey

Earth Science Information Center

Open-File Reports Section

Box 25286, MS 517

Denver Federal Center

Denver, Colorado 80225
CONTENTS

Page

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

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

Purpose and scope .....................................................................4

Previous investigations .................................................................4

Land use and agricultural practices....................................................... 5

Methods of data collection and analysis................................................... 6

Rainfall .........................................................................6

Physical properties of the soil...................................................... 6

Chemical properties of the soil..................................................... 6

Ground-water levels............................................................. 12

Aquifer properties............................................................... 12

Subsurface-water quality......................................................... 12

Quality assurance of chemical measurements ....................................... 14

Acknowledgments .................................................................... 14

Hydrogeologic setting of the field site ......................................................... 14

Soil..................................................................................16

Carbonate bedrock.................................................................... 19

Recharge mechanisms ................................................................. 20

Chemical measurements of soils and subsurface water..................................... 23

Pesticide concentrations in soils......................................................... 23

Subsurface-water quality............................................................... 27

Simulation of pesticide fate and transport...................................................... 33

Configuration of the screening model.................................................... 33

Assumptions and simplifications .................................................. 33

Soil hydrology.................................................................. 35

Pesticide transport .............................................................. 36

Sensitivity analysis of the model ........................................................ 37

Simulated pesticide fate and transport................................................... 39

Herbicides .....................................................................41

Fungicides .....................................................................41

Insecticides.....................................................................42

Relation of pesticide use and model-derived leaching potentials to pesticides

detected in ground water......................................................43

Implications for the development of agricultural best management practices.................. 46

Summary and conclusions ................................................................... 47

References cited ............................................................................48

Appendix 1. Pesticide human toxicity categories...............................................54

Appendix 2. Risk assessment ............................................................... 56
ILLUSTRATIONS

Page

Figures 1-3. Maps showing:

1. Carbonate rock terrains of southeastern and south-central Pennsylvania............ 2

2. Area of investigation and selected physical and hydrologic features in Cumberland

County, Pa. .......................................................... 3

3. Location of field site and rainfall, soil, and water-quality sampling sites

near Newville, Pa. .................................................... 7

4. Cross-sections illustrating completion methods for nested tube lysimeters and

piezometers and disk and trough lysimeters installed in culverts .............. 13

5-6. Graphs showing:

5. Relation between precipitation, potential evapotranspiration, and pesticide

application periods in southeast and south-central Pennsylvania........... 15

6. Water-level response of slug introduction for monitor wells MW1, MW2, and

MW3 near Newville, Pa............................................... 20

7. Ground-water levels at monitor wells near Newville, Pa., and precipitation at

Shippensburg, Pa., May 1991 through April 1993......................... 21

8. Idealized block diagram of unsaturated zone hydrogeologic features and

recharge mechanisms in a regolith mantled carbonate-rock terrain ............. 24

9. Flowchart for LEACHP digital computer model logic and options used to

simulate water and pesticide transport and chemical reactions in soils. ......... 34

10. Model sensitivity to variation in soil properties................................. 38

11. Model sensitivity to variation in pesticide properties............................ 39
TABLES

Page

Table 1. Selected herbicides, fungicides, and insecticides applied to agricultural land in

Pennsylvania.............................................................. 8

2. Rainfall, ground-water level, water-quality, and soil sampling sites near

Newville, Pa.............................................................. 10

3. Chemical data collected at water-quality and soil sampling sites near

Newville, Pa.............................................................. 11

4. Textural data for soil samples from monitor well MW1 and culvert Cl

near Newville, Pa.......................................................... 17

5. Selected physical and chemical data for soil samples at the monitor well MW1

and culvert Cl near Newville, Pa. ........................................... 18

6. Gravity yield of the regional aquifer for selected periods of recharge from

precipitation near Newville, Pa.............................................. 19

7. Pesticides detected in soil samples from monitor well MW1 and culvert Cl

near Newville, Pa., April 1991 .............................................. 25

8. Concentrations of pesticides detected in top 0.30 m of soil near Newville, Pa. ........ 26

9. Field measurements of water quality for samples from lysimeters near

Newville, Pa.............................................................. 28

10. Concentrations of major ions and dissolved organic carbon in ground water

from monitor wells near Newville, Pa. ....................................... 30

11. Concentrations of pesticides detected in water from lysimeters near Newville, Pa..... 30

12. Pesticide concentrations in water from monitor wells near Newville, Pa. ............ 32

13. Physical and chemical properties of herbicides................................... 37

14. Physical and chemical properties of fungicides................................... 38

15. Physical and chemical properties of insecticides.................................. 40

16. Properties of soils and pesticides used in model sensitivity analysis and relative

effect on simulated pesticide leaching........................................ 40

17. Fate of herbicides after simulated 2-year period, evaluation of leaching potentials,

and human toxicity class ................................................... 42

18. Fate of fungicides after simulated 2-year period, evaluation of leaching potentials,

and human toxicity class ................................................... 43

19. Fate of insecticides after simulated 2-year period, evaluation of leaching potentials,

and human toxicity class ................................................... 44

20. Pesticides detected in ground water from selected wells, lysimeters, and springs

in southeastern and south-central Pennsylvania, 1983 through 1993.............. 45
CONVERSION FACTORS, VERTICAL DATUM, AND ABBREVIATED WATER-QUALITY UNIT*

Multiply By To obtain

millimeter (mL) 0.03937 inch

centimeter (mL) 0.3937 inch

meter (m) 3.281 foot

kilometer (km) 0.6214 mile

meter per kilometer (m/km) 5.28 foot per mile

Area

hectare 2.4710 acre 

square meters (m2) 10.76 square foot

Volume

cubic meters (m3) 0.0004087 cubic foot per second-day

Flow

cubic meter per second (m3 /s) 35.31 cubic foot per second 

liter per second (L/s) 15.85 gallon per minute

Mass

kilogram (kg) 2.205 pound 

kilogram per hectare (kg/ha) 0.8924 pound per acre

Temperature 

degree Celsius (°C) °F=1.8°C+32 degree Fahrenheit

Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 a geodetic 

datum derived from a general adjustment of the first-order level nets of the United States and Canada, 

called Sea Level of 1929.

Abbreviated water-quality units used in report: 

milliliters (mL) 

milligrams (mg) 

milligrams per liter (mg/L) 

micrograms per liter (ug/L) 

milliequivalents per liter (meq/L)
HYDROGEOLOGIC SETTING AND SIMULATION OF PESTICIDE FATE AND

TRANSPORT IN THE UNSATURATED ZONE OF A REGOLITH-MANTLED,

CARBONATE-ROCK TERRAIN NEAR NEWVILLE, PENNSYLVANIA

By Daniel J. Hippe and David W. Hall

ABSTRACT

Physical and chemical data were collected from May 1991 through April 1993 at a 4.5 hectare field 

site in Cumberland County, Pa., about 5 kilometers southeast of Newville. These data were used to define 

the hydrogeologic setting of a field site representative of the intensively farmed carbonate valleys oc 

southeastern and south-central Pennsylvania. The environmental processing of commonly used pesticides 

(herbicides, fungicides, and insecticides) in the unsaturated zone was simulated with a process-oriented 

digital model to evaluate the environmental fate and transport of pesticides to ground water. Site data and 

modelling results provide a basis for a discussion of water-quality implications of agricultural bestmanagement practices.

The carbonate valleys of Pennsylvania comprise regolith-mantled carbonate-rock terrains that 

consist of broad undulating upland areas dissected by mostly dry valleys and widely spaced spring-fed 

creeks. The upland areas are farmed and exhibit possess a doline karst topography with many closed 

depressions, sinkholes, and bedrock outcrops.

Unsaturated materials at the field site consist of an almost continuous soil cover composed of finegrained residuum underlain by an intermediate vadose zone composed of karstified limestone. Soils are 

absent on scattered bedrock outcrops and are more than 12 meters thick in other areas of the site. The soil 

profile stores appreciable quantities of water with a volumetric average of about 36 percent water at field 

capacity. Organic carbon content of soil materials is about 1.7 percent in the Ap-horizon and from 0.1 to 

0.3 percent throughout the full thickness of the B- and C-horizons.

Atrazine, metolachlor, simazine, and the atrazine soil metabolites deethylatrazine and 

deisopropylatrazine were detected at concentrations above 0.05 ug/L in just the upper 0.6 meters of soil 

materials. However, detectable concentrations of atrazine, simazine, and atrazine soil metabolites were 

measured in water samples from lysimeters installed in soil materials at depths of 1.2, 2.1, and 3.7 meters 

and from monitor wells completed in the saturated zone to depths of 122 meters.

Data collected from the field site were used to configure a pesticide screening model based on the 

pesticide version of the leaching estimation and chemistry model (LEACHP) developed by Wagenet and 

Hutson (1987). Model simulations show that most field-applied pesticides volatilize to the atmosphere, 

accumulate in soils, degrade in the subsurface environment, or leach to ground water. Model results were 

used to rank the leaching potentials of 66 pesticides. Eighteen of 32 herbicides, 4 of 9 fungicides, and 10 o* 

25 insecticides have moderate to large potential for leaching to ground water.

A review of available pesticide monitoring data suggests that many compounds given moderate or 

high leaching potentials have not been tested for in ground water and the presence of pesticides ir 

Pennsylvania's ground water may be underreported. Monitoring data do not exist for more than twothirds of the pesticide compounds currently used in agricultural, carbonate areas of Pennsylvania.

Knowledge of processes that govern fate and transport of pesticides is needed to facilitate 

development of effective pesticide best-management practices. In addition to comprehensive monitoring 

for pesticides and pesticide degradation products in ground water downgradient of areas of pesticide use, 

improved (1) characterization of unsaturated flow and transport through regolith mantled carbonate 

rocks, (2) estimates of pesticide degradation rates, (3) understanding of soil-property controls on pesticide 

movement, and (4) management models developed from process-oriented research would aid in 

understanding the processes.

Water-Resources Investigations Report 96-4062
INTRODUCTION

Although synthetic organic pesticides have been used on cropland in the United States since the 

1940's, few studies of pesticide contamination of ground water from nonpoint sources were conducted 

before the 1970's. Numerous monitoring studies have shown that some pesticides applied to agricultural 

areas have leached to ground water in many hydrogeologic settings, especially karst aquifers and surficial 

aquifers in coastal plain, fluvial, and glacial deposits (Garner and others, 1986). Karst areas in 

Pennsylvania underlie much of the row-crop production in the state and are susceptible to contamination 

from both point and nonpoint sources.

Triazine and chloroacetamide herbicides commonly used in corn and soybean production have been 

detected in ground water in the regolith-mantled carbonate-rock terrains of southeastern and southcentral 

Pennsylvania (Fishel and Lietman, 1986; Lietman and Hall, 1991; DJ. Wangsness, U.S. Geological Survey, 

written commun., 1990; Hippe and others, 1992,1994) (fig. 1). The widespread detection and persistence of

-o

77

/ \ L, '

S DELAWARE

PHILADELPHIA

EXPLANATION

mm AREA UNDERLAIN BY 

^S CARBONATE BEDROCK

- COUNTY BOUNDARY

PENNSYLVANIA 

Figure 1. Carbonate rock terrains of southeastern and south-central Pennsylvania.

Water-Resources Investigations Report 96-4062
trace concentrations of these herbicides and their degradation products in ground water in these areas 

indicate a nonpoint source of contamination, probably from leaching of materials applied to crop land. A 

better understanding of processes that control ground-water recharge and the fate and transport c( 

pesticides (herbicides, fungicides, insecticides, and their toxic degradation products) in the unsaturated 

zone is needed to reduce possible ground-water contamination from use of these chemicals in agriculturr 1 

areas underlain by carbonate rocks. In 1991, a 4.5 hectare field site in the Cumberland Valley about 5 kn 

southeast of Newville, Pa. (fig. 2), was selected for investigation of these processes as part of a cooperativ0 

study between the U.S. Geological Survey (USGS) and the Pennsylvania Department of Environment? 1 

Protection, Bureau of Water Quality Management. Subsequently, a digital computer model, LEACH0 

(Hutsen and Wagenet, 1992), was configured by use of data from the field site and nearby areas in 

cultivated carbonate terrains to evaluate pesticide leaching potentials. Monitoring data and model resultr 

provide a number of potential implications for development of agricultural best-management practices.

Mount Rock Spring Creek 

Big Spring^Creek 77'

\ **

»^ _ 

X

PLAIN FIEL.D

n MOUNT

ROCK

yellow ._ ;*' 

' '' / 

CARLISLE

Breeches

Creek

PENNSYLVANIA

V SHJPPENSBURG

CUMBERLAND COUNTY

 /

Base from U. S. Geological Survey 

Cumberland County, Pa, 1-50,000. 1974

10 MILES

_J

10 KILOMETERS

EXPLANATION

O FIELD SITE

~"~ COUNTY BOUNDARY

STREAMS 

 TOWNS

Figure 2. Area of investigation and selected physical and hydrologic features in Cumberland County, Pa.

Water-Resources Investigations Report 96-4062
Purpose cind Scop®

This report presents (1) a detailed description of the hydrogeologic setting of the field site relevant to 

the fate and transport of agricultural pesticides and some of their soil metabolites; and (2) an evaluation of 

the fate and transport of pesticides applicable to the unsaturated zone of regolith-mantled carbonate rock 

terrains of southeastern and south-central Pennsylvania by use of chemical and physical data from the 

field site and digital computer simulations; the evaluation includes a discussion of the results of model 

simulations that provide significant inforamtion for the development of agricultural best-management 

practices in carbonate-rock areas of southeastern and south-central Pennsylvania. The hydrogeologr 

setting of the field site is described on the basis of chemical, physical, and hydrologic data collected from 

May 1991 through April 1993. Physical and chemical properties of soils representative of regolith-mantle'1 

carbonate-rock aquifer systems in southeastern and southcentral Pennsylvania were used in a digital 

computer model, LEACHP, to simulate the fate and transport of 66 agricultural pesticides. The discussion 

of agricultural-management practices for pest control is based on model results and ground-water quality 

data collected in Pennsylvania, primarily from wells in the carbonate-rock terrains.

Previous Investigations

A number of water-resource investigations have been conducted to assess the effects of land use and 

agricultural practices on the ground- and surface-water quality of these environmentally sensitive area?. 

These investigations have documented (1) the presence of agricultural pesticides in stream base flow of 

carbonate-rock terrains, (2) the vulnerability to ground-water contamination in carbonate-rock terrairs 

from agricultural chemicals compared with nearby noncarbonate areas, (3) the brief lag time between 

applications of agricultural chemicals and their transport to ground water, and (4) the widespread 

occurrence and persistence of trace levels of agricultural chemicals in ground water.

Water-resource investigations conducted in the Pequea Creek Basin, Lancaster County, PC., 

identified both nitrate and herbicide contamination of surface water from nonpoint sources (Lietman and 

others, 1983; Ward, 1987). Estimates of the annual load and yield under stormflow and base-flow 

conditions were made for selected herbicides and nutrients. Investigators determined that a substantial 

part of the loads of nitrate and herbicide in streams draining this carbonate-rock terrain was during baseflow conditions. However, these studies did not determine whether herbicides present in base flow were 

from discharges of ground water from the regional aquifer or from instream or nearstream sources.

Water-resource investigations conducted in the Conestoga River headwaters, Lancaster and Berl's 

Counties, Pa., showed that high concentrations of nitrate and detectable concentrations of triazine and 

chloroacetanilide herbicides were present in ground-water samples collected from a number of domestic 

wells (Fishel and Lietman, 1986). Herbicides were detected exclusively in water samples from wells in 

agricultural areas underlain by carbonate bedrock. Investigators indicated the source of herbicide 

contamination in the carbonate-rock terrain was from leaching of herbicides applied to agricultural land, 

which is a nonpoint source of contamination.

At an agricultural field site in the carbonate-rock terrain of Lancaster Valley, Lancaster County, Ps., 

the timing of herbicide applications was linked to herbicide detections in ground water beneath the site 

(Lietman and Hall, 1991). Herbicide concentrations were below detectable levels before herbicide 

applications at planting time but were detected for several months beginning with the first appreciate 

rainfall after the herbicide applications. Herbicide contamination of ground water was believed to 

originate in part from rapid downward movement of herbicides applied on the land surface to the aquifer, 

facilitated by transport through structured soils and karst features (sinkholes and shafts).

In the spring and summer of 1989, a reconnaissance study of water from wells, springs, and stream 

base flow in Cumberland County, Pa., indicated that triazine herbicides were present at low 

concentrations (generally less than 1 |^g/L) in ground water throughout much of the carbonate-rock 

terrain of the valley (DJ. Wangsness, U.S. Geological Survey, written commun., 1990). A resampling of 

sites in August and September indicated that triazine herbicides had persisted in ground water at mof?t 

sites in the regolith-mantled carbonate-rock aquifer.

Water-Resources Investigations Report 96-4062
In the spring and fall of 1991 and 1992, reconnaissance studies of water from wells and springs in the 

Pequea, Mill, and Muddy Creek Basins of Lancaster County, Pa., indicated that high concentrations o( 

nitrate and detectable triazine herbicides were present in ground water throughout much of the carbonate - 

rock aquifer (Durlin and Schaffstall, 1993, p. 279-337). A resampling of sites later in 1991 indicated that 

nitrate and herbicides persisted in ground water at most sampling locations.

A water-resource investigation of two karst springs in the carbonate-rock terrain of the Cumberland 

Valley, Cumberland County, Pa., during 1990 and 1991 indicated that the herbicide atrazine and 

deethylatrazine (a soil metabolite) were the only pesticides present in spring discharges throughout the 

study period, although a number of triazine and amid herbicides were applied to agricultural land in the 

recharge areas to the springs (Hippe and others, 1994). Daily mean concentrations of atrazine and 

deethylatrazine in the spring discharges were 0.2 and 0.4 (ig/L, respectively. A spring flush associated 

with rainfall after the application period during planting was not apparent. The high ratio o( 

deethylatrazine to atrazine and the rarity of detectable deisopropylatrazine (an additional soil metabolite) 

in spring discharges suggest that much of the atrazine in the carbonate-rock aquifer was introduced b^ 

leaching through soils rather than by direct entry of surface runoff through sinkholes. About 0.6 percent o* 

the annual atrazine applied to agricultural land in contributing areas to the springs was discharged from 

the springs.

The development of agricultural best-management practices related to chemical use and wate~ 

quality has been an active area of research during the past 20 years. Some recent contributions include 

Brown (1987), Pimentel (1987), Wolf (1987), Gates (1988), Logan (1990), Belluck and others (1991), 

Chambers (1993, p. 3-8), Hammond (1992), and Furtick (1993). However, few contributions address the 

range of water-quality concerns in environmentally sensitive carbonate-rock terrains.

Field studies and digital computer models have been used to facilitate the development of 

agricultural-management practices having water-quality goals. Digital computer models to evaluate 

pesticide fate and transport in agricultural soils have been developed by numerous researchers, including 

Jury and others (1983; 1984a; 1984b; 1984c; 1987; 1989), Rutledge and Helgesen (1989), Mackay (1991), and 

Mackay and Stiver (1991). Rao and others (1985) compared ranks of pesticide leaching potentials produced 

by six simple models. Two models of moderate complexity currently used to simulate pesticide fate and 

transport mechanisms in agricultural soils are LEACHM (Hutson and Wagenet, 1992, 1993) and PRZM2 

(Mullins and others, 1993). Recent models designed to simulate water and solute flow in complex 

Pennsylvania terrains include work by Jabro and Fritton (1990), Grant and others (1991), and Jabro and 

others (1991).

A number of digital computer models to evaluate pesticide fate and transport have been designed 

for screening purposes by use of readily available soil, chemical, and climatic data. The U.S. Soil 

Conservation Service (SCS) Soil Pesticide Interaction Screening Procedure (SPISP) was designed to 

provide a preliminary assessment of pesticide leaching and runoff for all agricultural areas in the United 

States (Goss and Wauchope, 1991; Goss 1992; Kellogg and others, 1992). In the SPISP screening model, the 

SCS/Agricultural Research Service/Cooperative Extension Service Pesticide Properties Database 

(Wauchope and others, 1992) was combined with nationwide SCS soils data to provide input to the 

GLEAMS model of Leonard and others (1987). Although the current generation of screening models doe? 

not currently provide a reliable base of information from which to predict concentrations or to draf* 

regulations (Wauchope, 1992), it is possible that models may be developed better to evaluate 

environmental risks associated with agricultural chemical use.

Land Use And Agricultural Practices

Land use in the carbonate valleys of southeastern and southcentral Pennsylvania is predominantly 

agricultural, but areas are undergoing additional urbanization around the Reading-Allentown, Lancaster, 

Lebanon, and Harrisburg metropolitan areas. The central part of the Cumberland Valley west of Carlisle 

(fig. 2.) is agricultural land. Smaller areas are forested and developed. Agricultural land includes fields 

cultivated for either animal feed or seed production, pasture for dairy or livestock grazing, and fallow 

fields. The field site and surrounding fields are used for production feed for dairy cattle. No-till and

Water-Resources Investigations Report 96-4062
minimum tillage crop-production systems are used at the field site. A broader spectrum of cropproduction systems is used elsewhere in the valley, depending on factors such as soil erosion hazards ar d 

depth to bedrock.

Most of the agricultural-pesticide usage in southeastern and southcentral Pennsylvania is en 

cropland. Usually, the pesticides are used to control weeds, fungus, and insects so that they will not 

adversely affect the use and value of cropland, reduce the yield or the quality of crops, or increase the costs 

of production and harvest. The principal crops receiving pesticide applications in southeastern ard 

southcentral Pennsylvania are corn, alfalfa, tobacco, and soybeans (Gianessi and Puffer, 1991, 1992a, 

1992b). Herbicides, fungicides, and insecticides commonly applied to these and other crops are listed in 

table 1 along with the quantity used in Pennsylvania, typical application rates, and water-quality 

standards for longterm exposure (U.S. Environmental Protection Agency, 1986,1991).

Methods Of Data Collection and Analysis

Rainfall, physical and chemical properties of soil, ground-water levels, aquifer properties, ard 

subsurface water-quality data were collected at the field site (table 2). Locations of data-collection sites are 

shown in figure 3. The following sections describe the instrumentation and methods used to collect these 

data.

Rainfall

Rainfall data were collected by use of a tipping-bucket raingage with a data-collection platform ar d 

satellite telemetry (table 2). Rainfall data were recorded in 0.25 mm increments at 15-minute intervals for 

the period June 1991 through November 1993. These data were primarily used to provide near-real time 

notification of rainfall for collection of water-quality data. Because calibrations and comparisons to rainfrll 

data from nearby gages showed a variable, low bias in rainfall data collected at the site, these data we~e 

not used for quantitative hydrologic analysis.

Physical Properties of the Soil

Physical properties of the soil were determined from analyses of continuous cores collected April 24, 

1991, from two locations (MW1 and Cl, fig. 3 and table 2). Physical properties measured or estimated 

include wet and dry bulk density, volumetric water and air content, and soil texture. Wet bulk density was 

determined on soil clods immediately after collection. Dry bulk density and volumetric water content of 

soil clods were determined gravimetrically after oven drying for 24 hours at 105°C. Volumetric air content 

was estimated by difference assuming an average grain density of 2.65 g/cm3 . Soil texture was determined 

on dried, disaggregated soil samples. Sand content and sand fractions were measured by dry sievirg 

using methods of Matthes and others (1992). The silt and clay content were determined by use of a 

modification of the single withdrawal pipette method of Matthes and others (1992) (R.A. Ludlow, U.S. 

Geological Survey, written commun., 1993).

Chemical Properties of the Soil

The soil cores collected on April 24, 1991, were analyzed for organic carbon and selected pesticides 

and pesticide soil metabolites (table 3). Determinations of organic carbon content in soil samples we~e 

performed at Merkel Soils Laboratory at The Pennsylvania State University by use of the Modified Mebius 

method (Nelson and Sommers, 1982, p. 571-573). Determinations of herbicide residue concentrations in 

soil samples were performed at the USGS Organics Research Laboratory in Lawrence, Kans. The method 

used is described in Adams and Thurman (1991).

Water-Resources Investigations Report 96-40 ^2
77° 22'30 

40° 8'45

77° 21'30"

40° 7 "SO"

15 30 FEET

I I

0 2.5 5 METERS

MONITOR WELL MW3 

 LYSIMETER 

NESTLN3

' ';':- OCULVERTC2

LIMESTONE OUTCROP - 

'I \ I \ \ \ \ * xX

MONITORWELLMW2

LYSIMETER 

NESTLN2

 LYSIMETERNESTLN1

OCULVERTC1 MONITOR 

WELLMW1

Figure 3. Location of (A) field site and (B) rainfall, soil, and water-quality sampling sites near Newville, Pa.

Water-Resources Investigations Report 96-4062
Table 1 . Selected herbicides, fungicides, and insecticides applied to agricultural land in Pennsylvania

[Kg, kilogram; Kg/ha, kilogram per hectare; ug/L, microgram per liter; MCL, maximum contaminant level, the maximum 

permissible level of a contaminant in water which is delivered to any user of a public water system; HA, health advisory 

level; Rfd, reference dose; --, no data]

Common name

Alachlor

Atrazine

Bensulide

Bromoxynil

Butylate

Chlorimuron

Clomazone

Cyanazine

Dicamba

Diuron

EPIC

Fluazifop

Glyphosate

Hexazinone

Imazethapyr

Imazapyr amine salt

Linuron

Maleic Hydrazide

Metolachlor

Metribuzin

Metsulfuron

Paraquat

Pebulate

Prometon

Pronamide

Propachlor

Propazine

Quizalofap

Sethoxydim

Simazine

Terbacil

Trifluralin

2,4-D

2,4-D dimethylamine

Principal crops

Herbicides

Corn, soybeans, sorghum

Corn, sorghum

Vegetables

Corn, sorghum, small grains, alfalfa

Corn

Soybeans, corn

Soybeans

Corn, sorghum

Pasture, corn, alfalfa, small grains

Small grains, alfalfa

Corn, potatoes, alfalfa

Soybeans alfalfa

Corn, soybeans, small grains

Alfalfa

Soybeans

Soybeans

Soybeans, corn

Tobacco

Corn, soybeans, sorghum

Alfalfa, soybeans, potatoes

Small grains, pasture

Corn, soybeans, alfalfa

Tobacco, tomatoes

Noncropland only

Alfalfa

Corn, sorghum

Sorghum

Soybeans

Soybeans, alfalfa

Corn, alfalfa

Alfalfa

Soybeans, alfalfa, small grains

Pasture, corn, soybeans, small

grains, orchard

Corn, alfalfa

Annual use in 

Pennsylvania 

(Kg/1000)

230

730

3.4

.29

54

.60

.34

200

50

13

91

.32

240

11

--

-

27

-

640

5.9

-

41

8.2

-

-

1.0

Discontinued1

-

.22

50

1.5

1.2

64

-

Typical annual 

application 

rate 

(Kg/ha)

1.7-4.5

.2-3.4

6.2

.2 -.6

4.5 - 6.7

.009 -.013

.8-1.1

1.3-6.0

.1-.6

1.3-1.8

3.4 - 6.7

.1-.2

.2-5.0

.4-1.5

.07

.07

.3-1.1

~

1.3-3.4

.2-1.1

.01

.3-3.4

4.4

-

.5-1.5

2.5-4.0

-

.1-.6

.6-1.7

.3 -.4

.6 -.8

.2 - 2.2

.1-.6

Water-qualit/ 

standards 

for longterrr 

exposure

(ng/U

2 (MCL)

3 (MCL)

-

-

350 (HA)

-

~

1 (MCL)

200 (HA)

10 (HA)

25 (Rfd)

-

700 (HA)

200 (HA)

-

~

2 (Rfd)

4,000 (HA)

100 (HA)

200 (HA)

-

30 (HA)

-

100 (HA)

50 (HA)

90 (HA)

10 (HA)

~

-

4 (MCL)

90 (HA)

2(HA)

70 (MCL)

-

Water-Resources Investigations Report 96-4062
Table 1. Selected herbicides, fungicides, and insecticides applied to agricultural land in Pennsylvania Continued

[Kg, kilogram; Kg/ha, kilogram per hectare; ng/L, microgram per liter; MCL, maximum contaminant level, the maximun 

permissible level of a contaminant in water which is delivered to any user of a public water system; HA, health advisor^ 

level; Rfd, reference dose; --, no data]

Common name

Benomyl

Captan

Chlorothalonil

Dodine

Ferbam

Maneb

Metalaxyl

Metiram

Thiophanate

Insecticides

Acephate

Azinphos-methyl

Carbaryl

Carbofuran

Chlordane

Chlorpyrifos

4,4'-DDT

Diazinon

Dicofol

Dieldrin

Dimethoate

Endosulfan

Esfenvalerate

Fenvalerate

Lindane

Malathion

Methamidophos

Methomyl

Methyl parathion

Oxamyl

Parathion

Permethrin

Phorate

Phosmet

Phosphamidon

Principal crops

Fungicides

Orchards, Vegetables

Orchards, grapes, strawberries, tomatoes

Orchards, vegetables, potatoes

Orchards

Orchards, grapes

Vegetables

Tobacco, potatoes

Orchards

Orchards, strawberries

Tobacco, green beans

Orchards, vegetables, alfalfa

Orchard, grapes, vegetables, potatoes

Corn, alfalfa, orchards, potatoes, tobacco,

vegetables

Termite control

Alfalfa, corn, tobacco

Orchards, vegetables

Corn, vegetables

Apples, strawberries

Termite control

Alfalfa, orchards, vegetables

Orchards, vegetables

Corn, orchards, vegetables

Soy beans

Seed treatments, orchards

Corn, alfalfa, small grains, vegetables,

Vegetables, potatoes

Orchards, corn, alfalfa

Orchards, grapes, sweet corn

Apples, potatoes

Tobacco

Alfalfa, corn, vegetables

Corn, potatoes, soybeans

Orchards, potatoes, alfalfa

-

Annual use in

Pennsylvania

(Kg/1000)

6.6

9.8

42

11

13

19

1.2

47

13

.8

40

26

86

Discontinued

1974

320

Discontinued

1973

8.7

1.6

Discontinued

1974

14

15

2.7

.08

-

47

4.2

25

10

7.4

43

24

22

30

-

Typical annual

application

ratP i die

(Kg/ha)

-

2.2 - 11

2.8 - 17

.8 - 1.0

3.0 - 5.7

2.7 - 7.9

.1-.6

20

.8 - 1.9

.8-1.1

.4 - 2.2

.8 - 2.9

.3-2.6

-

.6 - 2.2

-

.6-1.1

1.7-2.2

-

.20-1.1

.8-1.5

.02 -.22

.1

-

1.1-2.2

1.1

.6-1.7

.4-1.7

.6 -.8

.6 - 2.2

.11 -.34

1.1-3.5

.7-4.0

-

Water-quality 

standards

for longterm

exposure

(HQ/L)

50 (Rfd)

130 (Rfd)

15 (Rfd)

-

-

5 (Rfd)

-

-

-

-

-

700 (HA)

40 (MCL)

2 (MCL)

20 (HA)

.1 (HA)

.6 (HA)

-

.05 (Rfd)

.2 (Rfd)

-

-

-

.2 (MCL)

100 (HA)

-

200 (HA)

2 (HA)

200 (MCL)

-

50 (Rfd)

-

-

-

' Registration revoked.

Water-Resources Investigations Report 96-4062
Table 2. Rainfall, ground-water level, water-quality, and soil sampling sites near Newville, Pa.

Site name

U.S. Geological Survey 

site identification number Data-collection activities at site

Rain gage 

MonitorWelll (MW1)

Monitor Well 2 (MW2) 

Monitor Well 3 (MW3)

Culvert 1 (CD with

3 trough and 5 disk lysimeters

Culvert 2 (C2) with

3 trough and 5 disk lysimeters

Lysimeter Nest 1 (LN1) with 3

tube lysimeters

Lysimeter Nest 2 (LN2) with 3

tube lysimeters

Lysimeter Nest 3 (LN3) with 3 

tube lysimeters

400828077214701 Rainfall volume and intensity

400829077214301 Soil physical and chemical properties; pesticides in water,

ground-water level, hydraulic conductivity, gravity yield

400827077214601 Water quality, including pesticides, field measurements of water

quality, and major ions, and hydraulic conductivity

400828077214801 Water quality, including pesticides, field measurements of water

quality, and major ions, ground-water level, hydraulic conductivity and gravity yield

400828077214501 Soil physical and chemical properties; pesticides in water from

one trough lysimeter

400827077214701 Pesticides in water from one trough lysimeter

400829077214501 Water quality, including pesticides and field measurements of

water quality from two tube lysimeters; pesticides in soil

400827077214501 Water quality, including pesticides and field measurements of

water quality from one tube lysimeter; pesticides in soil (no 

data were collected from this installation during the intensive monitoring period May through October 1991)

400828077214701 Water quality, including pesticides and field measurement? of

water quality from three tube lysimeters; pesticides in soil

10 Water-Resources Investigations Report 96-4062
Table 3. Chemical data collected at water-quality and soil sampling sites near Newville, Pa.

at 25°C, microSiemens per centimeter at 25 degrees Celsius; mg/L, milligram per liter; g/kg gram per kilogram; ^g/L, 

microgram per liter; |ug/kg, microgram per kilogram; --, not applicable; KS, USGS Organics Research Laboratory, Lawrence, Kans. 

PA, USGS District Laboratory, Lemoyne, Pa.; PSU, The Merkel Soils Laboratory Pennsylvania State Univ., University Park, Pa.]

Physical property or 

chemical constituent

Sample Watstore/ 

Medium Storetcode Analytical method Where Minimum

reporting . . level 1 analyzed

Alkalinity, in mg/L as CaCC>3

Specific conductance (|uS/cm at 25° C)

pH, in standard units

Organic Carbon (g/kg)

Alachlor (|ug/L)

Alachlor (^ig/kg)

Ametryn (^ig/L)

Ametryn (|ug/kg)

Atrazine (|ug/L)

Atrazine (|.ig/kg)

Cyanazine (|ug/L)

Cyanazine (|ug/kg)

Cyanazine amide (|ug/kg)

Deethylatrazine (|ug/L)

Deethylatrazine (|ug/kg)

Deethylcyanazine (^ig/kg)

Deethylcyanazine Amide (^ig/kg)

Deisopropylatrazine (ng/L)

Deisopropylatrazine (^ig/kg)

Metolachlor (|ug/L)

Metolachlor (|ug/kg)

Metribuzin (|ug/L)

Metribuzin (ng/kg)

Prometon (ng/L)

Prometon (^ig/kg)

Prometryn (|ug/L)

Prometryn (|ug/kg)

Propazine (|ug/L)

Propazine (|ug/kg)

Simazine (|ug/L)

Simazine (|ug/kg)

Terbutryn(|ug/L)

Terbutryn ((jg/kg)

Triazines (by immunoassay as atrazine)

2-Chloroacetanilide (^ig/kg)

2,6-Diethylaniline (|ug/kg)

Water

Water

Water

Soil

Water

Soil

Water

Soil

Water

Soil

Water

Soil

Soil

Water

Soil

Soil

Soil

Water

Soil

Water

Soil

Water

Soil

Water

Soil

Water

Soil

Water

Soil

Water

Soil

Water

Soil

Water

Soil

Soil

95430

90095

90400

00687

46342

04006

38401

78505

39632

39631

04004

04041

-

75981

-

-

-

75980

-

39415

04005

82630

04000

04037

82402

04036

78688

38535

82534

04035

04008

38888

38890

34757

-

-

Fishman and Friedman (1970,

p. 55-56)

Fishman and Friedman (1970,

p. 461-463)

Fishman and Friedman (1970,

p. 363-364)

Nelson and Sommers (1982,

p. 571 -573)

Thurman and others (1990)

Adams and Thurman (1991)

Thurman and others (1990)

Adams and Thurman (1991)

Thurman and others (1990)

Adams and Thurman (1991)

Thurman and others (1990)

Adams and Thurman (1991)

Adams and Thurman (1991)

Thurman and others (1990)

Adams and Thurman (1991)

Adams and Thurman (1991)

Adams and Thurman (1991)

Thurman and others (1990)

Adams and Thurman (1991)

Thurman and others (1990)

Adams and Thurman (1991)

Thurman and others (1990)

Adams and Thurman (1991)

Thurman and others (1990)

Adams and Thurman (1991)

Thurman and others (1990)

Adams and Thurman (1991)

Thurman and others (1990)

Adams and Thurman (1991)

Thurman and others (1990)

Adams and Thurman (1991)

Thurman and others (1990)

Adams and Thurman (1991)

Thurman and others (1991)

Adams and Thurman (1991)

Adams and Thurman (1991)

1

1

.1

.01

.05

.05

.05

.05

.05

.05

.05 -.20

.05

.05

.05

.05

.05

.05

.05

.05

.05

.05

.05

.05

.05

.05

.05

.05

.05

.05

.05

.05

.05

.05

.1

.05

.05

PA

PA

PA

PSU

KS

KS

KS

KS

KS

KS

KS

KS

KS

KS

KS

KS

KS

KS

KS

KS

KS

KS

KS

KS

KS

KS

KS

KS

KS

KS

KS

KS

KS

PA

KS

KS

1 Minimum reporting level is the smallest measured concentration of a constituent that may be reliably reported using a given analytical 

method.

Water-Resources Investigations Report 96-4062 11
Ground-Water Levels

Ground-water levels were measured in two wells, MW-1 and MW-3, both completed as open hc^es 

in bedrock. Ground-water levels in well MW-1 were measured to the nearest 3 mm for the period July 1991 

through November 1992 by use of a float system and graphical recorder. Ground-water levels in well 

MW-3 were recorded to the nearest 3 mm at 15-minute intervals for the period July 1991 through April 

1993 by use of a pressure transducer and data logger. Ground-water levels were used to calculate changes 

in ground-water storage over time, evaluate timing of recharge relative to periods of rainfall and 

snowmelt, and estimate the gravity yield of the aquifer.

Aquifer Properties

Estimates of the transmissivity of aquifer materials adjacent to the open intervals of monitor wells 

MW-2 and MW-3 were made on the basis of slug tests. The water-level recovery in each well after the 

addition and removal of a cylindrical slug was monitored by use of a pressure transducer and data logger. 

Slug-test data were analyzed by use of methods of Bouwer and Rice (1976) that assume (1) the raising or 

lowering of the water level is small relative to the aquifer thickness, (2) there are no significant gains or 

losses of water within the zone of fluctuation of water level, (3) frictional well losses are negligible, and 

(4) the aquifer is homogeneous and isotropic. Errors arising as a result of departures from assumption-^ 1 

through 3 probably are minimal whereas, substantial departures from the assumption of homogeneous 

and isotropic aquifer materials may lead to substantial errors that may render the estimates inappropriate 

for many applications. Therefore, the transmissivity estimates presented in the report are given to indicate 

a range of possible values at the field site.

The gravity yield of the aquifer was determined by use of methods of Olmsted and Hely (1962) that 

relates the measured rise in ground-water levels (net recharge) to precipitation from a brief period of 

rainfall or snowmelt. The method assumes (1) evapotranspiration or change in soil moisture is negligib1 *?, 

(2) recharge is uniformly distributed, and (3) discharge from the aquifer relative to recharge is negligible. 

Discrete periods of rainfall or snowmelt between the months November and April were chosen for 

analysis because evapotranspiration rates are low and soils typically are at field capacity.

Subsurface-Water Quality

Subsurface water includes water sampled from depths between the unsaturated zone just beneath 

the soil surface and within the regional aquifer. A broad range of subsurface-water-sampling equipment 

suction (porous tube and disk) lysimeters and gravity (trough) lysimeters completed in soil materials, 

piezometers completed at the soil-bedrock contact, and monitor wells completed as open holes below the 

water table in bedrock was installed at the field site (table 2 and fig. 3). Diagrammatic cross-sections of 

equipment installation and sampling depths are shown in figure 4.

Specific conductance, pH, and alkalinity of water samples were measured according to US^S 

methods in Fishman and Friedman (1989). Triazine herbicides were analyzed by use of immunoasray 

methods (Thurman and others, 1990), and 13 herbicides were analyzed by use of gas chromatographymass spectrometry (GC/MS) methods (Thurman and others, 1990). The water-quality and chemical 

constituents determined on site, sample medium, citations of analytical methods, and the method 

reporting levels are summarized in table 3.

Because of dry, hot weather conditions that persisted through the intensive monitoring period from 

April through October 1991, water samples could not be collected from the disk-type suction lysimeters or 

piezometers and only a few samples could be obtained from gravity (trough) lysimeters and suction (tube) 

lysimeters installed at shallower depths. Also, sample volumes from suction lysimeters generally were 

insufficient for the desired field and laboratory measurements of water quality. Water samples of 120 mL 

or more in volume that were collected during the intensive monitoring period (from April through 

October 1991) were analyzed by use of the GC/MS method; few samples collected during this period were 

large enough to do additional analyses. Immunoassay analyses were performed on samples less than 

120 mL in volume collected during the intensive monitoring period and all samples collected after the

12 Water-Resources Investigations Report 96-4062
SILICON FLOUR 

BENTONITE

r , SOIL OR 

NATIVE FILL

EH BEDROCK

B

SLOPING TROUGH 

LYSIMETER

Figure 4. Completion methods for (A) nested tube lysimeters and piezometers and (B) disk and trough lysimeters 

installed in culverts.

Water-Resources Investigations Report 96-4062 13
intensive monitoring period. During the intensive monitoring period, field measurements of water quality 

were performed on samples with either insufficient volume for GC/MS analysis and samples with 

volumes greater than necessary for GC/MS analysis. After the intensive monitoring period, field 

measurements of water quality were performed routinely on any water samples that were more than 

40 mL.

Quality Assurance of Chemical Measurements

The principal sources of potential sample contamination were the lysimeter materials and samplecollection and processing equipment. A sample of the 200 mesh silica flour slurry used as a filter pack 

around suction lysimeters was analyzed and determined not to contain detectable quantities of pesticide?. 

All suction lysimeters (and sample hoses) installed at the site were composed of polytetrafluoroethylene 

a chemically resistant material with little tendency to sorb or desorb organic compounds. Deionized water 

rinses of suction lysimeters that followed normal sampling were free of any detectable crosscontamination from pesticides, indicating no measurable desorption of herbicides from the lysimeter". 

Deionized water equipment blanks also did not contain detectable concentrations of pesticides, indicating 

that sample-collection and processing equipment and sample bottles were not a source of contamination.

Acknowledgments

The USGS gratefully acknowledges the cooperation of Dan and Francis Mains and their families for 

providing the field site used for this water-resource investigation and for providing agricultural-practices 

information for the study area. The USGS is grateful to the Cumberland County Extension Agents for 

assistance in locating field sites. The USGS also is grateful for analytical work performed by student 

volunteers at the Organics Research Laboratory at the USGS district office in Lawrence, Kans., under the 

direction of E. Michael Thurman.

HYDROGEOLOGIC SETTING OF THE FIELD SITE

The field site is on an undulating upland surface that occupies the central axis of the Cumberland 

Valley. The hydrogeologic setting of the part of the Cumberland Valley that includes the field site has been 

described as a regolith-mantled carbonate-rock aquifer system (Chichester, 1991). Much of this upland 

area is in the Conodoguinet Creek watershed part of the Susquehanna River Basin. The upland area is 

partially dissected by mostly dry valleys and widely spaced spring-fed creeks. The maximum topographic 

relief is about 90 m. Dissolution of the carbonate bedrock that underlies much of the upland area has 

produced a karst landscape dotted with numerous closed depressions and sinkholes (Kochanov, 1989). 

This type of landscape has been called "doline karst" (White, 1988). The landscape is well drained, 

primarily by subsurface drainage. The nearest streams, Mount Rock Spring and Big Spring Creeks, are 

about 4.8 km from the field site (fig. 2).

Recharge to this aquifer system is distributed over much of the upland surface and dry valley?. 

Discharge from the aquifer system is to spring-fed creeks and to Conodoguinet Creek. Ground water is 

stored in regolith having intergranular porosity and consolidated carbonate rock having mostly secondary 

porosity including partings parallel to bedding and foliation, fractures, and dissolution openings. Groundwater levels in wells near the field site ranged from 3.4 to 43 m below the land surface with a 

potentiometric surface slope of 7 to 11 m/km in a northeasterly direction (Hippe and others, 1994).

Average annual precipitation for 62 years of record (beginning in 1929) is 986 mm at Shippensbur?;, 

Pa. (U.S. Department of Commerce, 1992), which is about 8 km southwest of the field site. On average, 

precipitation is evenly distributed throughout the year (fig 5). Precipitation typically is greater then 

potential evapotranspiration from October through April and less than potential evapotranspiration from 

May through September. This relation between precipitation and potential evapotranspiration results in 

large seasonal variation in soil moisture content, recharge rates, ground-water levels, and stream base 

flow. This relation may influence the types and quantities of pesticides that leach to ground water.

14 Water-Resources Investigations Report 96-4062
"BURNOFF" AND

PREPLAN! HERBICIDE

APPLICATIONS

PREEMERGENT

HERBICIDE 

APPLICATIONS

FOLIAR APPLICATIONS OF 

PESTICIDES

POSTEMERGENT

HERBICIDE 

APPLICATIONS

HERBICIDE 

APPLICATIONS TO 

WINTER ANNUALS

O N

EXPLANATION

AVERAGE PRECIPITATION 

.-Q AVERAGE POTENTIAL EVAPOTRANSPIRATION

Figure 5. Relation between precipitation, potential evapotranspiration, and pesticide application periods in 

southeast and south-central Pennsylvania.

Water-Resources Investigations Report 96-4062 15
The unsaturated and saturated zones at the field site are comprised of layers of soil and bedrock 

having different physical and chemical properties. These properties influence the environmental 

processing of agricultural pesticides applied at the site. For this report, the term "unsaturated zone" refer? 

to the interval of subsurface materials that extends from the land surface to the top of the regional aquifer; 

it may include one or more intervals of limited areal extent having intermittent perched water-table 

conditions. The unsaturated zone comprises an interval of soil and an additional interval of carbonate 

bedrock situated above the normal zone of fluctuation of the regional aquifer. The part of the unsaturated 

zone within carbonate bedrock commonly is called an intermediate vadose zone or epikarst. Because most 

methods for investigation in unsaturated media are not well suited to the intermediate vadose zone, onl1" 

the soil and regional aquifer were instrumented for this field study Therefore, hypotheses regarding 

hydrologic processes or contaminant behavior in the intermediate vadose zone are based on indirect 

observations made as part of this field study and concepts presented in recent karst literature (Williams, 

1983,1985; White, 1988; Field, 1989).

Soil

Soils in the central part of the Cumberland Valley are formed from fine-grained residuum weathered 

from the underlying carbonate bedrock. These soils are classified as fine-loamy mixed, mesic Ultic 

Hapludalfs and mapped as the Duffield-Hagerstown Association (Zarichansky, 1985). The soils are 

characterized as deep (generally greater than 1.5 m) moderate to well-drained silt loam on gentle to 

moderate slopes (Zarichansky, 1985, p. 7). The Duffield-Hagerstown Association underlies a large part of 

the prime agricultural land in southeastern and southcentral Pennsylvania. Soil cores and excavations of 

Duffield-Hagerstown Association soils at the field site indicate that the soil profile consists of a partial 

covering of plant litter underlain by a mineral soil with three prominent master horizons, designated Ap, 

B, and C.

The Ap horizon consists of 0 to 40 cm of grayish brown sandy loam with granular structure and 

numerous roots and burrows. Coarse fragments of quartzite and shaley limestone comprise less than 

10 percent of bulk volume (table 4). The Ap horizon is nearly absent on tops of limestone pinnacles wher? 

it has been removed by erosion and mechanical cultivation. Typical thickness of this horizon is about 

30cm.

The B horizon is 0 to 150 cm thick and consists of medium to light brown sandy and silty loam with 

a slightly sticky and slightly plastic texture. Soil structure is well developed and blocky, changing to 

weakly developed and platy at depth. Argillic material coats ped faces and large pores; many coatings are 

black. Abundant black (presumably hematite or goethite) concretions are distributed throughout soil pedz. 

Roots are less abundant in the B-horizon than in the Ap-horizon; most large roots are between peds in the 

upper, blocky part of horizon. Coarse fragments of quartzite or shaley limestone may exceed 20 percent of 

the bulk volume. Typical thickness of the B horizon is 75cm. The B horizon has a sharp or slightlv 

gradational contact with overlying A horizon and gradational contact with underlying C horizon.

The C horizon consists of 0 to over 1,000 cm of light brown, moderate yellowish-brown, and dark 

yellowish orange sandy and silt loam that is slightly sticky and slightly to moderately plastic. The C 

horizon is massive or sparsely layered with darkly stained clay films along widely spaced, mostly vertical 

subplanar fractures. This horizon generally lacks roots and burrows. Coarse fragments of quartzite and 

shaley limestone comprise less than 10 percent of the bulk volume. Typical thickness of the C horizon h 

300cm.

16 Water-Resources Investigations Report 96-406?
Table 4. Textural data for soil samples from monitor well MW1 and culvert C1 near Newville, Pa. 

[mm, millimeter; >, greater than; <, less than]

Percent of bulk weight

Depth 

interval 

(meters)

Weight percent of 

<2 mm fraction

Sand-sized fraction

SJ

£E 1 E

{0°

0^

Very coarse 

2.0-1. Omm

E

s!

§6

0 r

E 

E 

in

E S

3 0

dj in

2 0

E 

E 

in

C\J

o 

<D in

C C\J 

U- 0

fine Very 

25-0.062 0.1mm

?I

(0 O 

CO C,

E 

E * 

^- oo

*9 

^co 2c<j 

±i O 

CO 0

11

2?° 8?

Sand Silt Clay

Monitor well MW1

0-.30

.30 -.61

.61-1.2

1.2 1.8

1.8-2.4

2.4 - 3.0

3.0 - 3.7

3.7 - 4.3

4.3 - 4.9

4.9 - 5.5

5.5-6.1

6.1-6.7

6.7 - 7.3

9.1

1.3

16.3

.5

18.8

9.8

16.8

3.2

9.1

2.5

3.7

7.6

2.1

7.2

2.8

27.5

.5

12.2

16.6

14.0

12.0

22.6

30.2

6.6

16.3

8.8

21.2

2.2

7.3

5.9

11.9

14.9

24.8

16.0

25.2

14.8

28.6

20.7

5.8

10.6

3.3

9.9

11.6

6.6

15.5

12.7

15.8

13.9

14.9

18.5

18.6

6.3

12.9

23.2

4.4

6.1

7.6

12.5

7.2

14.0

11.9

9.7

13.7

12.1

4.9

9.5

14.0

5.2

28.8

13.5

14.6

12.5

16.4

8.6

18.8

14.0

11.6

26.2

61.4

45.6

54.2

52.9

51.7

74.1

71.3

74.2

82.3

88.4

81.4

79.3

52.0

20.4

39.8

15.2

29.4

12.3

6.9

4.2

10.6

3.8

5.1

7.0

3.2

25.2

6.4

12.7

9.5

17.0

11.7

7.8

5.8

11.2

4.1

3.8

7.3

8.9

19.4

70.4

46.9

70.5

53.4

70.5

83.9

88.0

77.4

91.3

90.9

85.1

86.9

54.5

22.4 7.1

40.3 12.9

18.2 11.3

29.5 17.1

15.1 14.4

7.6 8.6

5.0 7.0

10.9 11.6

4.2 4.5

5.2 3.9

7.3 7.6

3.5 9.6

25.7 19.8

Culvert C1

0-.30

.30 -.61

.61 - 1.2

1.2 1.8

1.8 - 2.4

2.4 - 3.0

3.0-3.7

3.7 - 4.3

4.3 - 4.9

4.9 - 5.5

5.5-5.9

7.2

30.1

17.9

15.6

1.5

8.6

5.9

1.2

.4

.9

1.9

12.7

16.4

10.2

18.0

19.7

8.1

25.8

3.9

2.4

2.8

16.5

16.6

11.3

15.8

9.0

26.1

5.3

11.8

11.9

3.8

18.0

22.1

13.1

3.5

17.8

9.5

17.4

9.5

11.1

6.7

6.2

2.0

12.9

11.0

7.8

10.7

8.3

12.5

16.5

11.7

19.0

9.8

12.7

9.1

9.9

12.5

12.2

14.5

9.9

24.5

15.1

26.4

11.8

22.9

15.4

63.3

51.5

66.7

59.3

85.6

63.9

75.5

67.9

34.0

58.4

76.0

20.1

7.1

6.4

12.2

4.9

10.9

7.2

14.6

35.4

21.0

10.5

7.3

5.7

6.2

9.1

7.8

14.3

10.4

16.1

29.9

19.5

11.3

70.4

81.6

84.6

74.8

87.1

72.5

81.3

69.0

34.4

59.2

77.9

21.7 7.9

10.2 8.2

7.8 7.6

14.4 10.8

5.0 7.9

11.9 15.7

7.7 11.1

14.8 16.3

35.5 30.0

21.2 19.7

10.7 11.5

Water-Resources Investigations Report 96-4062 17
The water content of soil samples collected in April 1991 (with soil-moisture conditions approaching 

field capacity) was about 32 percent in samples collected from near the soil surface and as high as50 percent in samples from deeper, clay-rich intervals (table 5). The moisture content of soil materials at 

the field site is substantial because of the soil thickness and the high soil-moisture retention. About 310 err 

of total soil moisture was present in the 730-cm thick profile at the location of monitor well MW1 at near 

field capacity. Much of the soil moisture above the C horizon of Duffield Series soils is plant-available; 

from 20 to 30 cm of water may be available from the change in volumetric soil-moisture content at matric 

potentials between 33 and 150 Kp (1/3 bar and 15 bars) (E.J. Ciolkosz, The Pennsylvania State University, 

written commun., 1991).

Organic material is present throughout the full thickness of soil materials at the site. The Ap horizor 

has the greatest percentage of organic carbon at 1.7 weight percent (table 5). Samples from the B and 

C horizons typically contained from 0.1 to 0.3-weight percent organic carbon with no apparent trend ir 

content of organic carbon with depth.

Table 5. Selected physical and chemical data for soil samples at the monitor well 

MW1 and culvert C1 near Newville, Pa.

[g/cm3 gram per cubic centimeter; --, not determined]

Physical or chemical measurement

Depth 

interval 

(meters)

Blow 

count 

(blows per 

0.15 meters 

penetration)

Recovery 

(volume 

percent)

Dry bulk 

density

(g/cm5)

Moisture 

content 

(weight 

percent)

Organic 

carbon 

(weight 

percent)

Monitor well MW1

0-.30

.30 -.61

.61 - 1.2

1.2-1.8

1.8-2.4

2.4 - 3.0

3.0 - 3.7

3.7 - 4.3

4.3 - 4.9

4.9 - 5.5

5.5 - 6.1

6.1 - 6.7

6.7 - 7.3

0-.30

.30 -.61

.61 - 1.2

1.2-1.8

1.8-2.4

2.4 - 3.0

3.0 - 3.7

3.7-4.3

4.3 - 4.9

4.9 - 5.5

5.5-5.9

2,3

4,6

2, 3, 6, 8

3, 3, 4, 5

3, 5, 7', 10

3, 5, 7, 7

4, 7, 7, 9

3, 6, 7, 10

3, 5, 5, 6

3, 3, 5, 7

3, 3, 5, 5

2, 2, 3, 4

3, 4, 6, 5

2,2

3,8

3, 5, 5, 8

3, 5, 6, 10

5, 8, 12, 16

6,7,9,12

4, 6, 8, 10

3, 3, 5, 6

3, 3, 3, 2

2, 4, 4, 6

3, 4, 50, -

92

92

73

73

96

'48

100

88

73

69

100

81

-

Culvert C1

58

58

81

81

92

100

100

-

71

54

84

1.53

1.74

1.71

1.65

1.73

1.53

1.61

1.65

1.37

1.61

1.60

1.47

1.27

1.44

1.63

1.59

1.58

1.59

1.60

1.57

1.38

1.04

1.67

1.45

35

32

33

35

37

35

37

37

40

46

44

47

46

33

31

33

27

40

39

43

42

51

50

49

1.7

.76

.20

.11

.14

.15

.092

.11

.14

.14

.12

.14

.14

1.7

.32

.19

.10

.10

.12

.13

.18

.33

.20

.17

Recovery decreased by obstruction of soil sampler by rock fragment.

18 Water-Resources Investigations Report 96-4062
Carbonate Bedrock

Bedrock beneath the site is part of the Shady Grove Formation of Upper Cambrian age. It is 

composed of grayish black, thinly bedded, micritic limestone with an estimated thickness of 244 to 305 m 

(Becher and Root, 1981). Bedding in outcrops of the Shady Grove and Stoufferstown Formations nearby 

the field site strike east-northeast and is nearly vertical. Foliation is parallel to bedding and quartz-fill?d 

fractures are common both parallel to and crosscutting bedding. Drilling logs and cuttings from three 

monitor wells completed at the site reveal extreme spatial differences in karstification of carbonate 

bedrock. Monitor well MW1 (total depth of 122 m below the land surface) yielded less than 0.03 L/s on 

completion and had no evidence of appreciable fractures or voids in the unsaturated interval or 

discernible water-bearing zones. Monitor well MW2 (total depth of 61 m) yielded about 0.1 L/s and had 

numerous fractures and small voids in the unsaturated zone and numerous, low yielding water-bearing 

zones from the regional water table to a depth of 46 m. Monitor well MW3 (total depth of 38.1 m) yielded 

about 1.3 L/s and had numerous fractures and small voids in the unsaturated zone and additional mudfilled voids and water-bearing zones; a 4 m thick cavernous void was encountered starting at 24 m belc-v 

the land surface. In well MW3, some water was encountered in bedrock at 12 m below the land surface. 

This was above the static water level of the regional aquifer, showing that a perched water-table aquifer 

was present in the shallow bedrock.

Estimates of gravity yield and hydraulic conductivity of the carbonate-rock aquifer at the site span 

one and two orders of magnitude, respectively. These estimates provide a very limited assessment of the 

actual spatial distribution of porosity and permeability in carbonate bedrock beneath the site. Estimates of 

the gravity yield for five storms from precipitation data from the National Oceanic and Atmospheric 

Administration (NOAA) weather station at Shippensburg, Pa., and ground-water levels from monitor well 

MW1 were analyzed by use of the methods of Olmsted and Healy (1962, p. 16). The average gravity yield 

for the five storms was 3.4 percent and ranged from 0.5 to 7 percent (table 6). On average, soils at the site 

have about 12 times the average water content of an equal thickness of the regional aquifer. The average 

hydraulic conductivity of the open interval was estimated from slug tests (fig. 6) by use of the methods of 

Bouwer and Rice (1976). A smaller diameter slug was used in monitor well MW2 to fit the reduced annular 

space from the presence of a dedicated submersible pump and discharge line in the well bore this is 

shown by the lesser initial water-level displacement of well MW2 relative to wells MW1 and MW3 in 

figure 6. The average hydraulic conductivities of the open intervals of monitor wells MW2 and MW3 were 

0.14 and 1.4 m/day, respectively. The water-level decline at well MW1 was small over the test pericd, 

showing a very low permeability. The response from this well was not suitable for determining hydraulic 

conductivity by use of the Bouwer and Rice method.

Table 6. Gravity yield of the regional aquifer for selected periods of recharge from 

precipitation near Newville, Pa.

n . .. .. Ground- Precipilalion . _ . . . .

.... . . .. water Gravity yield Recharge period quantity . . . . . .. ,. .', level rise (volume percent) (millimeters) . .... .

' (millimeters)

November 21-22,1991 39.6 576 6.9

March 6-7,1992 44.7 2,280 2.0

April 21-22,1992 55.4 1,030 5.4

March 4-5,1993 64.3 12,560 .51

March 13-24,1993 124 6,190 2.0

Water-Resources Investigations Report 96-4062 19
200 400 600 800 1,000 1,200 1,400

TIME AFTER SLUG INJECTION, IN SECONDS

Figure 6. Water-level response of slug introduction for monitor wells MW1, MW2, and MW3 near Newville, Pa.

Recharge Mechanisms

In this regolith-mantled karst terrain, recharge may follow multiple pathways from the land surface 

to the regional aquifer. The three recharge mechanisms that are of most interest to the transport of 

agricultural chemicals are areally-distributed recharge, topographically-enhanced recharge, and sinkhole 

recharge (fig. 7). Recharge and contaminant transport through soil and the intermediate vadose zone 

(epikarst) are described as they apply to leaching of agricultural pesticides by the three recharge 

mechanisms.

Areally-distributed recharge results from infiltration of rainfall and snow melt through soil 

materials on parts of the regolith-mantled karst landscape that neither generate nor receive appreciable 

overland flow. Areally-distributed recharge is the predominant form of recharge on soil-covered, flat o~ 

gently sloping upland areas. Because most of the soil types farmed in the carbonate terrains in 

southeastern and southcentral Pennsylvania are relatively free of subsurface zones that are limiting with 

respect to deeper percolation of water, the recharge rate is controlled by the permeability and moisture 

content of soil materials.

20 Water-Resources Investigations Report 96-406?
111

DC

10

I 15

LUm 

<£ 20

LU

LU

2

z 25

LU

DC 

LU

30

35

40

MW3

MW1

MJ JASOND 

1991

JFMAMJJASONDJFMA 

1992 1993

MJJASOND 

1991

JFMAMJJASONDJFMA

1992 1993

Figure 7. Ground-water levels at monitor wells near Newville, Pa., and precipitation at Shippensburg, Pa., 

May 1991 through April 1993.

Water-Resources Investigations Report 96-4062 21
Soil and climatic conditions are most conducive to areally-distributed recharge from December 

through April of most years (fig. 5). During this part of the year, the soil-moisture losses incurred over the 

growing season have been made up by additional rainfall, and soil hydraulic conductivities approach their 

maximum. In winter and early spring, areally-distributed recharge can be expected from rainfall or 

snowmelt for any period when soils are not frozen.

Soil concentrations of most pesticides applied during the growing season are relatively low during 

the winter and spring when conditions are favorable for areally-distributed recharge. Appreciable 

quantities of most herbicides, insecticides, and fungicides degrade or volatilize between the time of 

application and the winter months. The pesticides and their degradation products that are most likely to 

leach from areally-distributed recharge are those that are mobile in the soil environment and either (1) 

have long half lives, so that pesticides persist in the soil beyond the growing season, or (2) are applied after 

harvest or just prior to the growing season. Residual quantities of the more persistent pesticides and their 

degradation products may be retained in the soil at environmentally significant concentrations well after 

the application period, so that these compounds may leach to the regional aquifer by areally distributed 

recharge. Fall or early spring application of herbicides to control winter annual weeds is the most notable 

agricultural practice that may lead to high soil concentrations during the period when there is substantial 

areally-distributed recharge.

The undulating topography of most regolith-mantled karst landscapes contains numerous swales 

and closed depressions that receive appreciable quantities of local runoff from adjacent areas that are 

subject to topographically-enhanced recharge. The added water from local runoff causes soils in these 

areas to remain moist for a greater part of the year than soils on adjacent slopes. Therefore, recharge to the 

regional aquifer is likely to occur from rainfall or snowmelt in greater quantity and over a greater part of 

the year in these areas than on uplands and adjacent slopes.

Climatic conditions conducive to recharge in these topographically low areas may extend into the 

growing season. Pesticides and their degradation products having the greatest probability of leaching to 

ground water from topographically-enhanced recharge include those compounds that are mobile in the 

soil environment and (1) are applied in the fall; (2) are applied in the spring as burnoff, preplant, or 

preemergent treatments; or (3) have long soil half lives so that pesticides persist in the soil beyond the 

growing season. Fall applications of herbicides to control winter annual weeds and springtime 

applications of burnoff, preplant, and preemergent herbicides are agricultural practices that may lead tc 

high soil concentrations during the period when there is potential topographically-enhanced recharge.

Sinkholes and shafts are ubiquitous features throughout the carbonate valleys of southeastern and 

southcentral Pennsylvania. Because these features allow rapid recharge to the aquifer and bypass the soil 

matrix and intermediate vadose zone, they are potentially important pathways for recharge and 

contaminant transport. Recharge through sinkholes may occur any time local runoff is generated. 

Recharge through sinkholes may reach the regional aquifer within hours of rainfall or snowmelt and may 

include pesticides and their degradation products that are otherwise readily volatilized or degraded in the 

soil environment or, because of their low solubility, exhibit little mobility in soil materials. Recharge 

through sinkholes also may occur when soils are frozen. Sinkholes or shafts in the instrumented part of the 

field site are not evident. However, many are visible along strike of bedding within 500 m to the east and 

west of the instrumented area.

Because the carbonate bedrock that comprises the intermediate vadose zone is not uniformly 

permeable, a perched aquifer may develop in soils and the uppermost part of the intermediate vadose 

zone. Williams (1983,1985) and Field (1989) indicate that much of the recharge to mantled carbonate-rock 

aquifers is focused through sporadically distributed dissolutional openings (called shafts or subcutaneous 

drains) that breach the intermediate vadose zone. Perched ground water may move in a radial patterr 

toward shafts for considerable horizontal distances in the soil and epikarst prior to recharging the regional 

aquifer.

Most closed surface depressions coincide with dissolutional features that breach the intermediate 

vadose zone. Precipitation and runoff that collect in closed depressions may saturate soils and recharge the 

regional aquifer at various times of the year, including periods with high potential for evapotranspiration.

22 Water-Resources Investigations Report 96-406?
Recharge through closed depressions must first pass through the soil that covers these dissolutional 

features but may then be transported rapidly through the intermediate vadose zone (fig. 8). Sinkholes 

provide an even more direct connection between the land surface and the regional aquifer so that runcff 

into sinkholes is transported to the aquifer after minimal contact with the soil and intermediate vadose 

zone.

Because soils at the site are thick and have a large specific retention of soil moisture, the quantity of 

water contained in the soil is large relative to the average annual recharge through soils to the regional 

aquifer. Therefore, most diffuse recharge is stored for a time in the soil before transport to the regional 

aquifer. Soil moisture and water-soluble contaminants could reside there for several years, assuming 

conditions of diffuse recharge and uniform flow through the unsaturated zone. Depending on degradation 

rates and sorption to soil particles, concentrations of the more labile contaminants in soil water may b° 

greatly reduced prior to their transport to the regional aquifer. However, preferential flow paths in the sc; l 

(root casts, animal burrows, and interpedal surfaces) and in the intermediate vadose zone allow part of th° 

recharge to bypass the unsaturated materials and create a broad range of residence times.

Ground-water-level data provide some insights into recharge periods and recharge mechanisms. 

Over the study period, ground-water levels in the regional aquifer at the site ranged from 7.6 to 32 m 

below the land surface (fig. 8) or about 183 to 158 m above sea level. The rate of decline in ground-water 

levels during extended periods of dry weather was between 0.02 and 0.04 m/d. The initial rise in groundwater levels commonly lagged behind the onset of rainfall or snowmelt by a few hours; the highest 

ground-water levels were from 2 to 5 days later. Ground-water levels had a pronounced annual cycle th° 

highest levels were during March or April and the lowest levels were from November to as late as 

February. This cycle was the result of recharge to the regional aquifer from rainfall and snowmelt durirg 

November through April. However, recharge also was observed from rainfall during the summer and f?ll 

when there was a combination of high potential for evapotranspiration and dry soil conditions. The short 

lag time between the onset of precipitation and recharge to the regional aquifer and the occurrence of 

recharge during periods of high potential for evapotranspiration and dry soil conditions suggest that 

recharge occurs in part along preferential pathways in the unsaturated zone.

Chemical Measurements of Soils and Subsurface Water

Chemical measurements of soils and subsurface water at the field site near Newville, Pa., we~e 

evaluated to describe processes responsible for changes after pesticide applications made during the 1991 

growing season. In 1991, above average temperatures began in May about 7°C above normal ard 

remained about 3° above normal from June through August. Precipitation recorded at Shippensburg, Pa., 

for the period May through August (U.S. Department of Commerce, 1992) was 89 mm below average 

rainfall for 62 years of record. The above average temperature and below average precipitation during tl>0 

1991 growing season lead to a crop failure and negligible ground-water recharge during the intensive 

monitoring period. The chemical data collected during this period document (1) changes in pesticide 

concentrations in shallow soil samples caused by their application with subsequent drought condition s, 

and (2) little change in subsurface water quality because of a negligible ground-water recharge.

Pesticide Concentrations In Soils

Pesticide concentrations in soils were evaluated on the basis of their distribution with depth in th° 

soil profile and their change in concentration from April to August 1991. Measurable concentrations of 

three herbicide and two pesticide degradation products were present only in the top 0.6 m of the two 

continuous soil cores collected April 1991 prior to the planting season (table 7). Atrazine, simazin«, 

metolachlor, and deisopropylatrazine were present in the top 0.1 m of each soil core; concentrations of 

these compounds ranged from 3.3 to 15.9 ug/kg. Atrazine, deethylatrazine, and deisopropylatrazine also 

were present at a depth of 0.3 to 0.6 m in the soil core at monitor well MW1. The pesticides were tlv? 

residual carryover from simazine, atrazine, and metolachlor applied alfalfa grown in 1989 and corn grown 

in 1990 for weed control. Deethylatrazine is a soil metabolite of atrazine whereas deisopropylatrazine is a 

soil metabolite of both atrazine and simazine.

Water-Resources Investigations Report 96-4062 23
SINKHOLE 

RECHARGE

TOPOGRAPHICALLY 

ENHANCED RECHARGE

AREA I RECHARGE

CD

Figure 8. Unsaturated zone hydrogeologic features and recharge mechanisms in a regolith-mantled carbonate-rock 

terrain.

O 

-O

s
Table 7. Pesticides detected in soil samples from monitor well MW1 and culvert C1 near Newville, Pa., April

[All concentrations in micrograms per kilogram; <, less than the indicated minimum reporting level; --, not 

determined]

Sample 

depth interval 

(meters)

0-

.30

.61

1.2

1.8

2.4

3.0

3.7

4.3

4.9

5.5

6.1

6.7

0-

.30

.61

1.2

1.8

2.4

3.0

3.7

4.3

4.9

5.5

-.10

-.61

-1.2

-1.8

-2.4

-3.0

-3.7

-4.3

-4.9

-5.5

-6.1

-6.7

-7.3

-.10

-.61

-1.2

-1.8

-2.4

-3.0

-3.7

-4.3

-4.9

-5.5

-5.8

Atrazine

5.2

1.0

<.05

<.05

<.05

<.05

<.05

<.05

<.05

<.05

<.05

-

<.05

5.5

<.05

<.05

<.05

<.05

<.05

<.05

<.05

<.05

<.05

<.05

Pesticide

Metolachlor Simazine

15.8

<.05

<.05

<.05

<.05

<.05

<.05

<.05

<.05

<.05

<.05

--

<.05

6.8

<.05

<.05

<.05

<.05

<.05

<.()5

<.05

<.05

<.05

<.05

Monitor well MW1

15.7

<.05

<.05

<.05

<.05

<.05

<.05

<.05

<.05

<.05

<.05

-

<.05

Culvert C1

15.9

<.05

<.05

<.05

<.05

<.05

<.05

<.05

<.05

<.05

<.05

Deethylatrazine

1.3

2.0

<.05

<.05

<.05

<.05

<.05

<.05

<.05

<.05

<.05

--

<.05

<.05

<.05

<.05

<.05

<.05

<.05

<.05

<.05

<.05

<.05

<.05

Deisopropylatrazine

9.3

10.6

<.05

<.05

<.05

<.05

<.05

<.05

<.05

<.05

<.05

-

<.05

3.3

<.05

<.05

<.05

<.05

<.05

<.05

<.05

<.05

<.05

<.05

Water-Resources Investigations Report 96-4062 25
On May 29,1991, corn was planted at the field site and atrazine and metolachlor were applied w; th 

a boom sprayer at rates of 1.7 and 2.2 kg/ha, respectively. The application resulted in an initial, average 

soil concentration of about 1,100 ug/kg of atrazine and 1,500 ug/kg of metolachlor in the top 100 mm of 

soil (assuming the pesticide was uniformly distributed on the soil surface and the soil had an average dry 

bulk density of 1.5 g/cm3). Concentrations of atrazine and metolachlor in soil samples collected 6 days 

after application were lower than the average initial concentration (table 8). At this time, the concentration 

of deethylatrazine was higher than it was before application. However, the concentrations of simazine or 

deisopropylatrazine changed very little. Average concentrations of atrazine, deethylatrazine, and 

deisopropylatrazine decreased substantially from 6 to 84 days after application; concentrations of 

metolachlor and simazine decreased only slightly over the same time.

Table 8. Concentrations of pesticides detected in top 0.30 m of soil near Newville, Pa.

[All concentrations in micrograms per kilogram; <, less than the indicated minimum reporting level]

Sample 

location

Sample 

date Atrazine Metolachlor Simazine Deethylatrazine

Deisopropylatrazine

35 days prior to application

MW1

Cl

Near LN1

Near LN1

Near LN2

Near LN2

Near LN3

Near LN3

Near LN3

Near LN3

Average:

Near LN1

Near LN2

Near LN3

Near LN3

Near LN3

Near LN3

Average:

Near LN1

Near LN1

Near LN3

Near LN3

Near LN3

Near LN3

Average:

04/24/91

04/24/91

05/28/91

05/28/91

05/28/91

05/28/91

05/28/91

05/28/91

05/28/91

05/28/91

06/04/91

06/04/91

06/04/91

06/04/91

06/04/91

06/04/91

08/21/91

08/21/91

08/21/91

08/21/91

08/21/91

08/21/91

5.2

5.5

4.2

4.7

5.1

5.8

5.0

5.9

3.1

2.3

4.5

5.5

214

275

270

496

253

252

41

64

39.3

14.2

18.4

13

32

15.8

6.8

1 day prior to application

8.9

6.7

16.7

24.2

38.1

8.2

8.6

8.6

15

6 days after application

8.1

280

320

448

427

355

306

84 davs after application

227

289

303

201

361

207

265

15.7

15.9

12.9

15.0

13.8

26.5

13.1

13.2

8.3

9.6

14

<.05

11

19.7

11.7

23

16.3

14

7.6

19

13.7

4.9

4.8

13.6

10.6

1.3

<.05

1.4

1.6

1.1

1.7

2.0

2.9

<.05

<.05

1.4

1.2

4.1

14.4

10.4

39

16.8

14

3.2

4.9

2.6

1.4

2.3

2.0

2.7

9.3

3.3

<.05

5.5

4.4

13.0

8.5

6.6

<.05

<.05

4.8

5.8

<.05

9.1

<.05

17.6

9.9

7.1

5.2

9.2

3.6

1.7

<.05

2.9

3.8

26 Water-Resources Investigations Report 96-40^
Subsurface-Water Quality

Field measurements of water quality indicate spatial and temporal variation in the mineral content 

and alkalinity of soil-water samples. Water samples from depths of 1.2 and 3.7 m below the land surface 

from lysimeter LN1, in a gently sloping area of the field site (fig. 3), had lower average spec : fie 

conductance, pH, and alkalinity than samples collected at similar depths from lysimeters LN2 and U T 3, 

both in an adjacent swale (table 9). Water samples collected at various depths from lysimeters LN1 and 

LN3 indicate that average specific conductance and alkalinity decrease substantially and average pH 

decreases slightly with increasing depth below the land surface. However, on the basis of available dc +a, 

the apparent changes in mineral content and alkalinity with increasing depth in the soil profile and with 

topographic position cannot be explained.

The concentrations of major ions and dissolved organic carbon in ground water for monitor wells 

MW2 and MW3 changed little during the intensive monitoring period. The dissolved-solids concentration 

determined by sum of constituents of ground water from wells at the site ranged from 653 to 724 mg/L 

(table 10). Calcium and bicarbonate are the dominant dissolved ions in ground water, with lesser 

concentrations of dissolved chloride, nitrate, and magnesium. The saturation of water with respect to 

common rock-forming minerals calculated from the geochemical model WATEQ4F (Ball and others, 19?7) 

indicates that ground water is oversaturated with respect to quartz, undersaturated with respect to 

dolomite, and saturated to oversaturated with respect to calcite.

Water samples collected from the field site were analyzed for 11 herbicides and 6 herbicide soil 

metabolites listed in table 3. Only atrazine, metolachlor, prometon, simazine, deethylatrazine, and 

deisopropylatrazine were detected.

During the intensive monitoring period, water samples were collected and analyzed from lysimeter 

LN3 at 2.1 m below the land surface and from lysimeters LN1 and LN3 at 3.7 m below the land surface. 

Atrazine, simazine, deethylatrazine, and deisopropylatrazine were detected and metolachlor was not 

detected in all samples (table 11). However, metolachlor was detected in one water sample collected from a 

trough lysimeter (from Culvert Cl at 1.2 m below the land surface). Triazine pesticides that were measured 

by immunoassay methods in each water sample not analyzed by GC/MS methods, were present at 

concentrations ranging from the minimum reporting level of 0.1 to 4.0 ug/L.

Similar concentrations of triazine residue were measured in soil-water samples collected from 1.2 m 

below the land surface at the location of each of the lysimeter nests. Concentrations in soil-water samples 

at this depth typically were lower than concentrations in samples collected at greater depths. 

Concentrations of triazine herbicide residue decreased through the sampling period from lysimeter LN1 at 

3.7 m and lysimeter LN3 at 2.1 m; concentrations in water samples collected from the other lysimeters 

showed no observable systematic variation. The cause of these spatial and temporal changes in triaz'ne 

residue concentrations is not known.

Traces of atrazine, simazine, deethylatrazine, and deisopropylatrazine were measured in water 

samples from each of the monitor wells (table 12). Metolachlor was measured in water from wells MlVI 

and MW3, and prometon was measured in monitor wells MW2 and MW3. Concentrations of 

deethylatrazine were higher than the other pesticides measured; concentrations ranged from 0.38 to 

1.12 |^g/L. Concentrations of all detected pesticides except prometon decreased slightly in ground water 

during the intensive monitoring period. Because prometon is not applied to crop land, the presence of 

prometon in water from monitor wells at the field site suggests an outside source of contaminants. The 

source of prometon is not known. However, the other pesticides may be related to agricultural activities at 

or near the field site prior to 1991.

Climatic and ground-water-level data indicate a lack of substantial recharge during the intensVe 

monitoring period. Therefore, the observed subsurface-water quality can be assumed to be the result of 

environmental factors and agricultural activities prior to the monitoring period. Slight changes in 

concentrations over the intensive monitoring period were related to physical and chemical processes 

taking place within the unsaturated zone and aquifer system and not from changes related to recharge 

during the 1991 growing season.

Water-Resources Investigations Report 96-4062 27
Table 9. Field measurements of water quality for samples from lysimeters near 

Newville, Pa.

[jiS/cm, microsiemen per centimeter at 25 degrees Celsius; mg/L as CaCC^, milligram per 

liter as calcium carbonate; m, meters below land surface; --, not determined]

Sample 

location and depth 

below land 

surface

LN1 at 1.2 m

Average:

LN1 at 3.7 m

Average:

LN2atl.2m

Average:

LN3atl.2m

Average:

Sample 

date

04/02/92

04/10/92

04/22/92

05/11/92

06/09/92

06/19/92

07/07/92

08/18/92

09/05/92

10/06/92

11/10/92

08/09/91

08/12/91

02/26/92

04/02/92

04/10/92

04/22/92

05/11/92

06/09/92

06/16/92

07/07/92

08/05/92

08/18/92

09/04/92

10/06/92

11/10/92

11/18/92

05/11/92

06/09/92

06/16/92

07/07/92

08/05/92

08/18/92

04/10/92

04/22/92

05/11/92

06/09/92

06/16/92

07/07/92

08/05/92

08/18/92

09/04/92

10/06/92

11/10/92

11/18/92

Specific 

conductance

(nS/cm)

299

343

397

431

433

427

428

452

461

456

460

417

370

281

257

223

222

233

228

231

228

228

231

232

228

225

232

243

691

660

578

655

640

550

629

440

525

626

620

644

660

682

685

709

737

760

782

656

PH

7.2

7.2

6.8

6.0

6.1

7.0

6.0

5.7

6.3

6.2

6.2

6.4

7.1

7.0

6.5

5.4

6.2

6.2

4.9

5.3

5.0

4.7

4.7

5.1

6.0

4.9

5.2

6.5

5.7

7.2

7.6

7.9

7.8

7.5

7.6

7.6

6.8

7.7

7.4

8.0

7.9

6.9

6.7

7.2

7.4

6.9

6.9

6.9

7.2

Alkalinity 

(mg/L as 

CaCO3 )

26

33

25

18

19

15

13

11

16

13

17

19

-

2

7

4

4

3

2

2

1

-

2

7

2

3

10

4

121

118

89

93

98

78

100

79

84

107

93

93

95

104

95

104

111

120

125

101

28 Water-Resources Investigations Report 96-406?
Table 9. Field measurements of water quality for samples from lysimeters near 

Newville, Pa. Continued

[u.S/cm, microsiemen per centimeter at 25 degrees Celsius; mg/L as CaCO3 , milligram per 

liter as calcium carbonate; m, meters below land surface; --, not determined]

Sample 

location and depth 

below land 

surface

LN3 at 2.1 m

Average:

LN3 at 3.7 m

Average:

Sample 

date

08/09/91

08/12/91

09/10/91

02/26/92

04/02/92

04/10/92

04/22/92

05/11/92

06/09/92

06/16/92

07/07/92

08/05/92

08/18/92

09/04/92

10/06/92

11/10/92

11/18/92

08/09/91

02/26/92

04/02/92

04/10/92

04/22/92

05/11/92

06/09/92

06/16/92

07/07/92

08/05/92

08/18/92

09/04/92

10/06/92

11/10/92

11/18/92

Specific 

conductance 

(nS/cm)

540

510

550

386

374

385

381

--

347

339

337

332

317

318

317

305

312

378

870

490

364

313

321

292

286

278

272

266

267

270

261

273

274

340

pH

7.0

7.2

-

7.3

7.5

7.5

7.4

7.5

7.4

7.9

7.8

7.0

7.1

6.9

6.9

6.8

6.6

7.2

7.4

8.1

6.9

6.6

7.0

6.6

7.0

7.1

6.4

6.4

6.4

7.0

6.4

6.7

6.3

6.8

Alkalinity 

(mg/L as 

CaCO3 )

-

--

84

105

98

112

81

79

77

74

68

55

50

47

46

47

73

81

69

48

50

37

36

33

31

26

23

33

21

25

23

38

Water-Resources Investigations Report 96-4062 29
Table 10. Concentrations of major ions and dissolved organic carbon in ground water from monitor wells near 

Newville, Pa.

[mg/L, milligram per liter; meq/L, milliequivalents per liter; -- not applicable]

Monitor well MW2 Monitor well MW3

Constituent 07/19/91 10/31/91

mg/L meq/L mg/L

Calcium 150 7.5 150

Magnesium 8.3 .68 10

Sodium 11 .48 15

Potassium 3.1 .08 5.4

Sum of cations 8.74

Bicarbonate 346 5.7 394

Sulfate 27 .56 25

Nitrate1 48.7 .79 38.5

Chloride 50 1.4 53

Sum of anions 8.45

Silica 9.0 -- 9.4

Dissolved organic carbon .6 .9

Sum of constituents 653 700

1 Reported as nitrate (NO^ ).

meq/L

7.5

.82

.65

.14

9.11

6.5

.52

.62

1.5

9.14

-

-

-

Table 11. Concentrations of pesticides detected in water from lysimeters

[All concentrations in micrograms per liter; m, meters below 

minimum reporting level; --, not determined]

Sample

location and Sample 

depth below date Atrazine Metolachlor 

land surface

LN1 at 1.2 m 04/02/92 

04/10/92

04/22/92

05/11/92

06/09/92

06/16/92

07/07/92

08/18/92

09/05/92

LNlat2.1m 08/18/92

LNlat3.7m 08/09/91 0.40 <0.05

08/12/91 .56 <.05

08/15/91 .62 <.05

08/19/91 .52 <.05

08/20/91 .54 <.05

08/21/91 .56 <.05

08/21/91 .60 <.05

09/04/91

09/10/91

09/14/91

09/16/91

09/25/91 .30 <.05

10/07/91

10/11/91

land surface;

07/10/91

mg/L

160

7.1

19

3.0

--

359

27

53.2

82

-

8.6

.8

719

meq/L

8.0

.58

.83

.08

9.49

5.9

.56

.86

2.3

9.62

-

-

--

11/01/91

mg/L meq/L

160 8.0

6.9 .57

18 .78

2.9 .07

9.42

386 6.3

20 .42

57.6 .93

63 1.8

9.61

9.1

.9

724

near Newville, Pa.

<, concentration less than the indicated

Pesticide residue

Simazine

_

-

-

-

~

~

-

-

-

0.18

.20

.16

.14

.14

.14

.14

-

-

-

-

.08

-

-

Deethylatrazine

~~

-

~

-

-

-

-

-

-

0.90

1.06

1.02

1.30

.95

1.00

1.09

-

-

-

-

.75

-

-

Deisopropylatrazine

~

~

-

~

-

-

-

-

0.47

.49

.55

.60

.38

.53

.53

-

--

--

-

.25

-

-

Triazines by 

immunoassay

0.2 

.2

.1

.1

.4

.3

.1

.2

.2

.9

--

-

--

--

--

-

--

1.2

1.0

.8

.9

-

.7

.7

30 Water-Resources Investigations Report 96-4062
Table 11. Concentrations of pesticides detected in water from lysimeters near Newville, Pa. Continued

[All concentrations in micrograms per liter; m, meters below land surface; <, concentration less than the indicated 

minimum reporting level; --, not determined]

Sample 

location and 

depth below 

land surface

LN1 at 3.7 m

LN2atl.2m

LN2 at 3.7 m

LN3atl.2m

LN3 at 2.1 m

Pesticide residue

Sample

date Atrazine Metolachlor Simazine Deethy'- atrazme

10/18/91 -

10/31/91 -

11/14/91 -

11/22/91 -

12/02/91 -

12/03/91 - --

12/09/91

12/17/91 - -

01/09/92 - -

02/06/92 - --

02/26/92 -

04/02/92 -- -

04/10/92 -

04/22/92 -

05/11/92 _ _ _ -

06/09/92 - - --

06/19/92 -

07/07/92 -

08/18/92

09/05/92

04/02/92

04/10/92

04/22/92 - - -

05/11/92 -

06/09/92 -

06/16/92 -

07/07/92 -

08/05/92

08/18/92 - --

04/02/92

04/10/92 _ _ -

04/02/92 -

04/10/92 --

04/22/92 _ _ ~ -

05/11/92 -

06/09/92 -

06/16/92 -

07/07/92 -

08/05/92 - - -

08/18/92 -- -

09/04/92 -- - -

07/29/91 -

08/09/91 0.47 <0.05 0.34 0.84

08/12/91 .43 <.05 .32 .80

08/15/91 .52 <.05 .37 .97

08/19/91 .51 <.05 .36 .90

08/20/91 .58 <.05 .33 1.01

08/21/91 .56 <.05 .32 .97

09/14/91 -

09/16/91 --

09/25/91 .30 <.05 .23 .61

10/07/91 .31 <.05 .25 .62

10/11/91 .28 <.05 .22 .63

Deisopropyl- Triazines by 

atrazine immunoassay

.6

.6

.5

.4

.3

 .J

.3

_ 3

.4

 3

.3

.4

 4

 4

 4

.7

.7

4

.7

_ 7

.1

 1

.2

 2

 .3

.4

.1

.2

 4

0.2

.6

 2

.5

4

.3

.4

.4

_ 2

.3

 .J

.3

1.7

0.94 1.4

.88 1.3

1.31

.96

.97

.91

1.0

1.0

.58

.58

.58

Water-Resources Investigations Report 96-4062 31
Table 11. Concentrations of pesticides detected in water from lysimeters near Newville, Pa. Continued

[All concentrations in micrograms per liter; m, meters below land surface; <, concentration less than the indicated 

minimum reporting level; -, not determined]

Sample

location and Sample 

depth below date Atrazine Metolachlor 

land surface

LN3at2.1m 10/18/91 0.29 <0.05

11/14/91

11/22/91

12/02/91

12/03/91

12/09/91

12/17/91

01/09/92

02/06/92

02/26/92

04/02/92

04/10/92

04/22/92

05/11/92

06/09/92

06/16/92

07/07/92

08/05/92

08/18/92

09/04/92

LN3at3.7m 08/09/91 0.77 <0.05

09/14/91

04/02/92

04/10/92

04/22/92

05/11/92

06/09/92

06/16/92

07/07/92

08/05/92

08/18/92

09/04/92

Cl at 1.2m 10/07/91 <.05 .49

04/02/92

Cl at 2.1 m 04/02/92

C2 at 2.1m 06/09/92

Pesticide residue

_. . Deethyl- Deisopropyl- Simazme . . . K . ' atrazme atrazme

0.23 0.62 0.57

_

_ 

_ _

_ _ _

_ _

_ _

_ _ _

_ _

_

_ _

_

_ _

_

_ _

_ _

.. _

_ _

_ _

 _

0.19 0.96 0.74

_

_ _

_ _

- - . -

_ _

_ _

_

_ _

_ _

_

<.05 <.05 <.05

_ _

_

_

Triazines by 

immunoassay

-

.6

.7

.6

.8

.6

.7

.6

.5

.4

.5

.5

.4

.3

.6

.4

.3

.4

.5

.4

~

1.0

1.3

1.3

1.4

1.3

1.8

1.6

1.3

1.6

1.6

1.5

-

.1

1.0

4.0

Table 12. Pesticide concentrations in water from monitor wells near Newville, Pa.

[All concentrations are in micrograms per liter; <, less than; --, not determined]

Pesticide

Sample Sample

location date Atrazine Metolachlor Simazine

MW1 06/04/91 0.32 0.06 0.07

MW2 06/04/91 .64 <.05 .39

07/10/91 .64 <.05 .44

08/12/91 .56 <.05 .29

10/31/91 .30 <.05 .14

MW3 07/10/91 .56 .07 .26

11/01/91 .50 .05 .20

Deethyl- Deisopropylatrazine atrazine Prometon

0.38 0.12 <0.05

1.12 .79 .09

1.11 .77 .10

.87 .53 .12

.55 .29 .14

.84 .44 .13

.58 .30 .17

Triazines by

immunoassay

0.6

1.5

1.4

1.5

-

1.2

-

32 Water-Resources Investigations Report 96-4062
SIMULATION OF PESTICIDE FATE AND TRANSPORT

The digital-computer model selected to evaluate pesticide leaching potentials in agricultural 

carbonate terrains of Pennsylvania was the pesticide component (LEACHP) of the Leaching Estimation 

and Chemistry Model (LEACHM) by Hutson and Wagenet (1992). LEACHP is process-based model of 

water and solute movement and chemical reactions in soils. Fates of pesticides were compared at the end 

of a simulated 2-year period by use of the model. Model estimates included the percentages of pesticid°s 

remaining undissolved on the soil surface, residuals in the soil profile, losses by a combination of 

evaporation and volatilization, losses by degradation, and losses by leaching. The modeling approach is 

based on the assumption that pesticides will reach ground water in the same relative proportions that they 

leach from the top 2 m of soil, thereby enabling ranking of potentials for pesticide leaching to ground 

water. Modeling results are discussed in terms of their possible implications for the development of 

agricultural best-management practices.

A brief discussion of the configuration of the screening model, modeled soil hydrology, moc^el 

processes used to calculate pesticide transport, and simplifications used in the modeling approach follows.

Configuration of the Screening Model

Hutson and Wagenet (1992) documented the LEACHP digital computer model. A simplified 

flowchart of the LEACHP model, as configured for this study, is shown in figure 9. Soils data from the field 

site, temperature and precipitation data from the Shippensburg, Pa., NOAA station (U.S. Department of 

Commerce, 1993), and pan evaporation data from the Landisville, Pa., NOAA station (U.S. Department of 

Commerce, 1992) were used to simulate transport of 66 pesticides through the top 2 m of a typical 

agricultural carbonate soil during a typical 2-year period. Agricultural carbonate areas of Pennsylvaria 

currently use 62 of the 66 pesticides. The discontinued insecticides chlordane, DDT, and dieldrin and the 

discontinued fungicide benomyl were used in Pennsylvania agriculture and were included in the 

simulations for comparative purposes. Each year of the 2-year simulation used climatic data from the 19?2 

calendar year, a year of near-normal annual precipitation. Precipitation measured at the Shippensburg, 

Pa., gage during 1992 was 103.1 cm, or 4.6 cm greater than the 30-year average precipitation measured 

during the period 1951-80 (U.S. Department of Commerce, 1993). The model simulated a pesticide 

application made on May 16 for each of 2 years at a rate of 1.12 kg/ha.

Assumptions and Simplifications

The modeling approach in this report employed several assumptions and simplifications regarding 

climatic conditions, soil properties, pesticide properties, and reaction types and kinetics. Some of the most 

significant assumptions and simplifications used in the LEACHP model, as configured for this repo-t, 

include:

1. Physical and chemical properties of pesticides are in some instances estimated (as

discussed in Wauchope and others, 1992). Significant errors in estimated organic carbon 

partition coefficients and pesticide degradation rates (on the basis of estimated half lives) 

affect pesticide leachability rankings.

2. The simulations used near annual-average climatic conditions. Excessively dry or wet 

years may produce different model results.

3. Algorithms describing water and solute movement in the screening model assume 

homogeneous conditions within model layers, an assumption that is not representative 

of most soil environments in mantled karst terrains. Specifically, focused recharge and 

preferential flow of water and solutes were not simulated.

4. Only the top 2 m of soil were simulated, the model assumes that pesticides will reach 

ground water in the same relative proportions that they leach through the top 2 m of soil.

5. Complex pesticide transformation and degradation processes, including

biotransformation, chemical hydrolysis, photolysis, and oxidation-reduction reactions 

are combined into the pesticide degradation rate value for each model layer.

Water-Resources Investigations Report 96-4062 33
LEACHP initializes all arrays and variables, then transfers control to MAINP, 

the effective main program, from which the following subroutines are called:

READP Reads data file.

- YES RETPRED Retentiyity and conductivity parameters from 

sand, silt, clay, bulk density regression.

WATDAT Calculates water retentivity and hydraulic conductivity data for the 

soil hydrological constants used, and prints in tabular form.

End of 

last day?

-YES- END

NO

POTET Calculates daily potential evaporation from pan evaporation.

i

-YES- Add pesticide and partition between 

gas, solution, and solid phases

Time = 1 day?

-YESNO

I

TSTEP Calculates the length of the time step (At) according to 

expected water flux density or specified limits.

ETRANS Potential evaporation for the time step assuming 

sinusoidal change during the day.

WATFLO Finite difference solution of soil water flow equation

using appropriate upper boundary and specified lower 

boundary condition.

SOLP Finite difference solution of convection-dispersion 

I equation, including volatilization.

Mass balance

checks, cumulative,

and profile totals

- YES CADATE Calendar days from day number.

STAT Pesticide distribution center of mass, percentiles. 

OUTP Print mass balance components and profile data.

Figure 9. Flowchart for LEACHP digital computer model logic and options used to simulate water and pesticide 

transport and chemical reactions in soils.

34 Water-Resources Investigations Report 96-4062
6. A uniform application rate of 1.12 kg/ha (approximately 1 pound/acre) was used, 

although there is a broad range of pesticide application rates based on desired selectivity 

of the product, formulation, application method, crop, soil conditions, and climatic 

conditions.

7. An application date of May 16 was used, although actual application dates for the many 

pesticides tested vary depending on their use, crop, soil conditions, and climatic 

conditions.

Soil Hydrology

The screening model used physical and chemical data from the uppermost 2 m of soil at monitor 

well MW-1 (tables 4 and 5). Each of 20 vertical layers, 100-mm thick were initialized with a volumetric 

water content of 0.3, an arbitrary value that lies between soil field capacity and saturation. Model 

algorithms used methods of Rawls and Brakensiek (1985) to describe soil-moisture retention and 

Campbell's (1974) equation to calculate hydraulic conductivities for each model layer as a function of 

volumetric water content. Then the transient flux of water through the unsaturated zone and the rate of 

water evaporation from the soil surface are then estimated by a finite-difference approximation of 

Richard's equation:

80 8 |~T^ sn*. 8H , TT ,._ ^

where 0 is volumetric water fraction of the soil (unitless) 

H is hydraulic head (length), 

K is hydraulic conductivity (length per time), 

f is time,

z is depth (length positive upwards), and 

U is sink term representing water lost per unit time by transpiration (I/time).

The subroutines POTET and ETRANS (fig. 9) estimated evapotranspiration from user-input 

evaporation potentials and estimated flux of water across the soil water and atmosphere interface. The 

screening model was configured without crop simulations and approximated from pan evaporation data 

in the subroutine POTET. The fraction of evaporation lost during a day varies sinusoidally as a function of 

daily temperature. The subroutine ETRANS approximates the evapotranspiration lost by the following 

formula:

[cos27c(t.-0.3) -cos27c(U-0.3)1

f = - -^ , (2)

where f is evapotranspiration lost during a daily 12 hour period,

t1 is 0.3 day (0712 hours), and

t2 is 0.8 day (1912 hours).

The model estimated drainage to below 2-m of soil depth was 57 cm of water per year, or about 55 

percent of the annual precipitation inputs using climatic data from the 1992 calendar year. Evaporative 

losses were about 45 percent of precipitation inputs. The simulated recharge rate was appreciably higher 

than the 41 percent of annual precipitation estimated for the carbonate-rock terrain of the Conodoguinet 

Creek Basin for a 5-year period (Becher and Root, 1981). However, the simulated recharge rate was nearly 

identical to the 53 percent of annual precipitation estimated at an agricultural field site in a carbonate 

terrain of Lancaster County for a 6-year period (Hall and Risser, 1993).

Water-Resources Investigations Report 96-4062 35
Pesticide Transport

The pesticide properties database of Wauchope and others (1992) was the chief source of pesticide 

input used for the simulations. The pesticide properties are summarized in tables 13-15. The subroutine 

SOLP (fig. 9) models solute transport by use of the following general convection/dispersion equation:

5c, _

(3)

where z is soil depth (length),

0 is saturated soil volumetric water content (unitless),

p is soil bulk density (mass per volume)

q is macroscopic water flux (volume per time),

D(Q, q) is an apparent diffusion coefficient (length squared per time),

CL is concentration in the liquid phase (mass per volume), and

(j> is a term to account for sources and sinks.

Volatilization in SOLP is calculated according to the following equation:

J = -Ksoii C L - <4>

where J is total diffusive flux of chemical from the soil-liquid to the atmosphere [mass/(time x length

squared)], 

KSOJI is overall mass transfer coefficient for diffusion across the soil-water/atmosphere interface

(length per time), and 

CL is concentration of chemical in soil water (mass per length cubed).

The following equation assumes pesticide sorption is linear:

c s = KdcL , (5)

where cs is concentration of the chemical in the sorbed phase (mass chemical/mass soil),

Kd is partition coefficient (volume per mass) calculated from the organic carbon partition

coefficient Koc times the fraction of organic carbon in the soil, and 

CL is concentration in solution (mass per volume).

Pesticide degradation coefficients [kdeg, mass/(time in days)] for layers 1 through 10 in the uppermost 

1 m of the model were calculated from estimated field half lives, assuming first-order decay, according to 

the following formula:

i A °-693 kdeg = . . (6) half life in days

Pesticide degradation rates are commonly assumed to decrease with decreasing soil carbon content 

at depth (Buyanovsky and others, 1993, p. 65). By use of this assumption, degradation coefficients for the 1 

to 2 m depth of the model were reduced in proportion to the average carbon content of the soil. The 

average organic carbon content of layers 11 through 20 was 0.12 approximately 16 percent of the average 

organic carbon content of 0.76 in layers 1 through 10. Therefore, pesticide degradation coefficients for 

layers 11 through 20 were calculated by multiplication of the coefficients for layer 1 through 10 by 0.16.

36 Water-Resources Investigations Report 96-4062
Table 13. Physical and chemical properties of herbicides

[data are from Wauchope and others (1992); g/m3, gram per cubic meter; mg/dm3, milligram 

per cubic decimeter; L/kg, liter per kilogram]

Common name

Alachlor

Atrazine

Bensulide

Bromoxynil octanate

Butylate

Chlorimuron-Ethyl

Clomazone

Cyanazine

Dicamba salt

Diuron

EPTC

Flua zif op -p -butyl

Glyphosate

Hexazinone

Imazapyr

Linuron

Maleic hydrazide

Metolachlor

Metribuzin

Metsulfuron-methyl

Paraquat

Pebulate

Prometon

Pronamide

Propachlor

Propazine

Quizalofop-ethyl

Sethoxydim

Simazine

Terbacil

Trifluralin

2,4 D acid

Gram 

molecular 

weight

269.77

215.69

397.54

403.0

217.4

414.8

239.7

240.7

221.04

233.1

189.32

383.4

169.1

252.3

261.3

249.11

150.2

283.80

214.3

381.4

257.2

203.36

225.3

256.13

211.69

229.7

372.8

327.5

201.66

216.7

335.28

221.04

Solubility in 

water 

(g/m3 )

240

33

5.6

0.08

44

1,200

1,100

170

400,000

42

344

2

900,000

33,000

11,000

75

400,000

530

1220

9,500

620,000

100

720

15

613

8.6

0.31

4,390

6.2

710

0.3

890

Vapor 

density 

(mg/dm3 )

2.04 EA

3.35 E-6

1.72 E-5

1.04 E^

1.52 E-l

8.92 E-ll

1.74E^

2.08 E-8

8.92 E-ll

8.66 E-7

3.46 E+l

5.15 E-6

6.83 E-ll

2.72 E-6

1.13 E-6

2.28 E^

6.06 E-ll

4.78 E^

1.15 EA

5.13 E-ll

1.04 E-10

9.77 E-2

9.37 E-5

1.17E-3

2.61 E-4

1.62 E-6

6.02 E-6

2.82 E-6

2.39 E-7

3.61 E-6

1.99 E-4

9.46 E-5

Organic 

carbon 

partition 

coefficient 

(L/kg)

170

100

1,000

10,000

400

110

300

190

2

480

200

5,700

24,000

54

100

400

20

200

60

35

1,000,000

430

150

800

80

154

510

100

130

55

8,000

20

Degradation 

rate constant 

(days' 1 )

4.62 E-2

1.1 5 E-2

5.77 E-3

9.90 E-2

5.33 E-2

1.73 E-2

2.88 E-2

1.95 E-2

4.95 E-2

7.70 E-3

1.15 E-l

4.62 E-2

1.47 E-2

7.70 E-3

7.70 E-3

1.1 5 E-2

2.31 E-2

7.70 E-3

1.73 E-2

2.31 E-2

6.93 E-l

4.95 E-2

1.38 E-3

1.1 5 E-2

1.15 E-l

5.13 E-3

1.15 E-2

1.38 E-l

1.15 E-2

5.77 E-3

1.1 5 E-2

6.93 E-2

Sensitivity Analysis of the Model

A sensitivity analysis determined which variables most influence pesticide leaching within a broad 

range of pesticide and soil-properties data values (table 16). The analysis used the top three layers of the 

model. The chemical properties of atrazine were used in the sensitivity analysis of soil properties, and r 

pesticide application rate of 1.12 kg/ha or about 112 mg/m2 .

Increases in the organic-carbon fraction of the soil caused moderate decreases in simulated pesticide 

concentrations in leachate (fig. 10). However, concentrations of pesticide leachate were relatively 

insensitive to a broad range of soil textures.

Water-Resources Investigations Report 96-4062 37
g

=1 Q

0.2 0.3 0.4 0.5 0.6 

SOIL CLAY FRACTION

0.2 0.3 0.4 0.5 

SOIL SILT FRACTION

0.00 0.01 0.02 0.03 0.04 0.05 0.08 0.07 0.08 0.09 0.10 

SOIL ORGANIC CARBON FRATION

Figure 10. Model sensitivity to variation in soil properties.

Table 14. Physical and chemical properties of fungicides

[data are from Wauchope and others (1992); g/m3, gram per cubic meter; mg/dm3, milligram 

per cubic decimeter; L/kg, liter per kilogram; >, greater than]

Common name

Benomyl

Captan

Chlorothalonil

Dodine Acetate Salt

Ferbam

Maneb

Metalaxyl

Metiram

Thiophanate-Methyl

Gram

molecular 

weight

290.3

300.61

265.92

287.44

416.50

265.29

279.3

1,088.7

342.40

Solubility

in water 

(g/m3 )

2.0

5.1

.6

700

120

6

8,400

.1

3.5

Vapor

density 

(mg/dm3 )

1.56 E-9

1.33 E-6

1.43 E-2

1.51 E-6

2.18 EA

1.07E-11

8.44 E-5

4.39 E-10

1.84 E-6

Organic

carbon

partition 

coefficient

(L/kg)

1,900

200

1,380

100,000

300

>2,000

50

500,000

1,830

Degradation

rate constant 

(days' 1 )

1.03 E-2

2.77 E-l

2.31 E-2

3.46 E-2

4.07 E-2

9.90 E-3

9.90 E-3

3.46 E-2

6.93 E-2

38 Water-Resources Investigations Report 96-4062
2 2

0.001 0.01 01 1 10 100 1.000 10000100.000 1.000.000 

LOG OF SOLUBILITY, IN GRAMS PER METER CUBED

10'" 10'' 10* 10* 10~ 10"B 10~ 10"* 10 3 10'2 10' 1 10' 

LOG OF VAPOR DENSITY IN MILLIGRAMS PER DECIMETER CUBED

10 100 1,000 10,000 100,000 1,000,000 

LOG OF ORGANIC CARBON PARTITION COEFFICIENT

0.001 001 01 

LOG OF DEGRADATION RATE, IN DAYS

Figure 11. Model sensitivity to variation in pesticide properties.

Changes in pesticide solubility, vapor density, organic carbon partition coefficient, and degradatior 

rate each affected the modeled pesticide concentration in leachate. The organic carbon partition coefficient 

(Koc) and the pesticide degradation rate constant were the pesticide properties having the largest effect or 

leachate concentrations. Leachate concentrations decreased sharply as Koc's increase from 1 to 1,OOC 

(fig. 11), at which point the pesticide concentrations in leachate approached zero. Concentrations of 

pesticide present in leachate also decreased sharply as degradation rates increased from 0.0001 (half life of 

greater than 4,000 days) to 0.1 per day (half life of less than 1 day; fig. 11). Pesticide solubility affected 

pesticide concentrations in leachate in a nonlinear manner (fig. 11). The greatest relative changes ir 

leachate concentrations occurred for water solubilities from 0 to 1 gm/m3 . The test range of vapor 

densities also produced a nonlinear response in leachate concentrations. Leachate concentrations were 

insensitive to vapor densities of less than l.OE-5 mg/dm3 but decreased sharply with vapor densities 

greater than from l.OE"5 to l.OE'2 mg/dm3 (fig. 11).

Simulated Pesticide Fate and Transport

Digital simulations were used to classify and rank the leaching potential for the 66 pesticides 

(herbicides, fungicides, and insecticides). Pesticides were classified as a small leaching potential if less 

than 0.1 mg/m2 (about 0.1 percent of the initial application) of pesticide leached from the top 2 m of soil 

during the 2-year simulation period, and less than 0.1 mg/m2 of pesticide residual remained in the soil 

profile. Pesticides were classified as having a medium leaching potential if less than 0.1 mg/m2 o(

Water-Resources Investigations Report 96-4062 39
Table 15. Physical and chemical properties of insecticides

[data are from Wauchope and others (1992); g/m3, gram per cubic meter; mg/dm3, milligram per cubic 

decimeter; L/kg, liter per kilogram]

Common name

Acephate

Azinphos-methyl

Carbaryl

Carbofuran

Chlordane

Chlorpyrifos

4,4'-DDT

Diazinon

Dicofol

Dieldron

Dimethoate

Endosulfan

Esfenvalerate

Fenvalerate

Lindane

Malathion

Methamidophos

Methomyl

Methyl parathion

Oxamyl

Parathion

Permethrin

Phorate

Phosmet

Phosphamidon

Gram 

molecular 

weight

183.16

317.33

201.23

221.25

409.80

350.62

354.49

304.3

370.51

380.91

229.28

406.91

419.9

419.9

290.85

330.3

141.13

162.2

263.21

219.3

291.27

391.30

260.38

317.33

299.7

Solubility in water 

(g/m3)

818,000

29

120

351

:.056

.4

'.056

60

.8

'.186

39,800

.32

.002

.002

7

130

1,000,000

58,000

60

282,000

24

.006

22

20

1,000,000

Vapor 

density 

(mg/dm3 )

1.68 E-5

3.42 E-6

1.30 E-5

7.14 E-6

2.20 E-4

3.21 E-4

'1.90 E-4

9.82 E-4

7.97 E-5

'3.67 E-6

3.08 E-4

3.73 E-6

2.49 E-7

2.49 E-7

5.16 E-4

1.43 E-4

6.10 E-3

4.36 E-4

2.12 E-5

2.72 E-4

7.83 E-5

2.73 E-7

8.96 E-4

8.36 E-6

2.66 E-4

Organic 

carbon 

partition 

coefficient 

(L/kg)

2

1,000

300

22

238,000

6,070

2 240,000

1,000

5,000

312,000

20

12,400

5,300

5,300

1,100

1,800

5

72

5,100

25

5,000

100,000

1,000

820

7

Degradation 

rate constant (days' 1 )

2.31 E-l

6.93 E-2

6.93 E-2

1.38 E-2

2 1.98 E-4

2.31 E-2

2 1.80E-4

1.73 E-2

1.54 E-2

3 7.98 E-4

9.90 E-2

1.38 E-2

1.98 E-2

1.98 E-2

1.73 E-3

6.93 E-l

1.15 E-l

2.31 E-2

1.38 E-l

1.73 E-l

4.95 E-2

2.31 E-2

1.15 E-2

3.64 E-2

4.07 E-2

'Brown and Myers, 1992. 

2Jury and others, 1987. 

-\Jury and Ghodrati, 1989.

Table 16. Properties of soils and pesticides used in model sensitivity analysis and relative effect on 

simulated pesticide leaching

[gm/m3, grams per cubic meter; mg/dm3, milligrams per cubic decimeter]

Value

Soil clay fraction (percent) 

Soil silt fraction (percent) 

Soil organic carbon fraction (percent) 

Pesticide solubility (gm/m ) 

Pesticide vapor density (mg/dm3 ) 

Pesticide organic-carbon partition coefficient 

Pesticide degradation rate constant, in days

Range

Oto75 

Oto75 

OtolO 

0 to 1.0 E+06 

l.OE-lltol.OE+01 

l.OE+OOtol.OE+06 

6.93E-01tol.73E-04

Effect on 

simulated 

pesticide 

leaching

Small 

Small 

Medium 

Medium 

Medium 

Very large 

Very large

40 Water-Resources Investigations Report 96-4C62
pesticide leached from the top 2 m of soil during the 2-year simulation period, and 0.1 mg/m2 or more c( 

pesticide residual remained in the soil profile. Pesticides were classified as having a large potential for 

leaching to ground water if pesticide concentrations of 0.1 mg/m2 or more were present in leachate.

Relative potentials for pesticide leaching to ground water were ranked within each group. Pesticides 

within each small and medium group were ranked by use of the maximum depth of penetration of th° 

pesticide in soil, as indicated by the relative depths of the 99th percentile of cumulative pesticid0 

breakthrough. Pesticides in the large leaching-potential group were ranked according to the leachat0 

concentrations; larger masses indicate of greater leaching potentials. Among pesticides in the larg° 

leaching-potential groups, when ties occurred, the pesticide with the larger residual mass in the soil profil0 

was assigned the larger leaching potential. If ties also occurred in the soil profile residual values, th° 

pesticide with the greater penetration depth in soils was assigned the larger leaching potential

Herbicides

Degradation or a combination of volatilization and evaporation are the primary environmental fate? 

of 29 of the 32 herbicides for the simulated 2-year period. Three herbicides bensulide, paraquat, and 

prometon were primarily retained in the soil profile as a result of rather low vapor densities and low 

degradation rates, however, of these three compounds, only prometon leached under the modeled 

conditions (table 17). A percentage of 18 herbicides was retained in the soil profile at the end of th° 

simulated 2-year period. From 0.1 to 4.1 percent of seven of these compounds leached beyond th° 

maximum depth of 2,000 mm and were assigned a large leaching potential. On the basis of the screening 

model, 11 herbicides were assigned a medium leaching potential, and 14 a small leaching potential.

On the basis of the screening model, seven of the eight agricultural herbicides (alachlor, atrazine. 

cyanazine, dicamba, glyphosate, metolachlor, and 2,4-D) most used in Pennsylvania (applications greater 

than 50,000 kg/yr from Gianessi and Puffer, 1991) are primarily lost from soils by degradation. Butylate. 

the other high-use herbicide, is primarily lost by volatilization and evaporation. Of the high-uso 

herbicides, only atrazine was given a large leaching potential. Glyphosate and metolachlor were given a 

moderate leaching potential; the other five most-used herbicides were given a small leaching potential.

Prometon is the only herbicide with a class I human toxicity rating and a large leaching potential 

based on the screening model. Prometon is used for long-acting, nonselective control of vegetation on 

noncropland. Usage data for prometon in Pennsylvania is not available. The other herbicides given a class 

I human toxicity rating are lost from soils by degradation (2,4-D) or a combination of volatilization and 

evaporation (trifluralin).

Fungicides

Degradation or volatilization and evaporation are the primary environmental fates of the nin° 

fungicides for the simulated 2-year period. Chlorothalonil was lost primarily from volatilization and 

evaporation, and the other fungicides were lost primarily from degradation (table 18). A percentage cf 

four fungicides was retained in the soil profile at the end of the simulated 2-year period. Of these, only th° 

fungicide metalaxyl was present in leachate beyond the maximum depth of 2,000 mm. Metalaxyl wa* 

given a large leaching potential, three other fungicides were given a medium leaching potential, and five 

fungicides were give a small leaching potential based on the screening model.

Metiram and chlorothalonil are the most used fungicides on agricultural land in Pennsylvania; they 

are lost from soils by degradation and a combination of volatilization and evaporation, respectively, based 

on the screening model. Metiram was given a moderate leaching potential and chlorothalonil was given a 

small leaching potential. Metalaxyl, the only fungicide given a large leaching potential, has an estimated 

annual use in Pennsylvania of 1,200 Kg on potato and tobacco crops (Gianessi and Puffer, 1992a).

Chlorothalonil and dodine are the only fungicides with class I human toxicity ratings-evaluated 

with the model. Model calculations indicate that these fungicides have a relatively low leaching potential.

Water-Resources Investigations Report 96-4062 41
Table 17. Fate of herbicides after simulated 2-year period, evaluation of leaching potentials, and human toxicity cla~s 

[mg/m2 , milligrams per square meter; mm, millimeter; S, small; M, medium; L, large; <, less than; >, greater than]

Pesticide

Alachlor

Atrazine

Bensulide

Bromoxynil octanate

Butylate

Chlorimuron ethyl

Clomazone

Cyanazine

Dicamba salt

Diuron

EPIC

Fluazifop-P-butyl

Glyphosate

Hexazinone

Imazapyr

Linuron

Maleic hydrazide

Metolachlor

Metribuzin

Metsulfuron methyl

Paraquat

Pebulate

Prometon

Pronamide

Propachlor

Propazine

Quizalofop ethyl

Sethoxydim

Simazine

Terbacil

Trifluralin

2,4D acid

Remaining 

undissolved 

on soil 

surface 

(percent 

of applied))

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

Remaining Lost by 

in soil volatilization 

profile and evaporation 

(in percent (percent of 

of applied) applied)

0

3

80

0

0

1

<1

0

0

9

0

0

2

0

0

4

<1

8

1

<1

76

0

57

36

0

18

4

0

<1

15

0

0

5

<1

18

99

87

0

42

0

0

<1

87

7

0

35

<1

5

0

11

2

0

0

87

2

49

6

2

32

0

78

3

99

2

Lost by 

degradation 

(percent of 

applied)

95

96

2

<1

13

99

58

100

100

91

13

93

98

65

99

91

99

81

96

99

24

13

40

15

94

79

64

100

21

80

1

98

Lost by 

leaching 

(percent of 

applied)/ 

(mg/m2)

0

<!/.!

0

0

0

0

0

0

0

0

0

0

0

0

0

0

<l/.2

0

<!/.!

<!/.!

0

0

<l/.6

0

0

<l/.2

0

0

0

2/4.1

0

0

Maximum 

depth of 

leaching 

(mm)

670

>2,000

360

0

750

1300

450

600

2,000

380

0

180

130

0

0

390

>2,000

860

>2,000

>2,000

99

440

>2,000

400

0

>2,000

330

0

1,300

>2,000

200

1,900

Group by 

leaching 

potential

S

L

M

S

S

M

M

S

S

M

S

S

M

S

S

M

L

M

L

L

M

S

L

M

S

L

M

S

M

L

S

S

Rank by 

leaching 

potential

21

5

7

28.5

20

15

17

22

18

10

28.5

25

14

28.5

28.5

12

4

11

5

6

8

23

2

9

28.5

3

13

28.5

16

1

24

19

Human 

toxicit' 

class 1

II

III

III

n

m

m

m

n, iii

in

in

in

IV

m

IV

IV

m

IV

HI

m

IV

n

in

i

IV

in

IV

in

in

IV

IV

i, n, in

i,m

From Sine (1993). See appendixes I and 2.

Insecticides

Degradation or volatilization and evaporation are the primary environmental fates of 21 of the 25 

insecticides for the simulated 2-year period. Four insecticides dieldrin, esfenvalerate, fenvalerate, and 

permethrin were primarily retained in the soil profile as a result of rather low vapor densities and lo^v 

degradation rates (table 19). None of the four insecticides retained in the soil profile leached to greater than 

180 mm during the simulated 2-year period. A percentage of nine insecticides were retained in the soil 

profile at the end of the simulation period. However, only one insecticide, carbofuran, leached beyond tl^ 

maximum depth of 2,000 mm; it was the only insecticide assigned a large leaching potential. Ten 

insecticides were assigned a medium leaching potential, and 14 a small leaching potential based on th° 

screening model.

42 Water-Resources Investigations Report 96-40/2
Table 18. Fate of fungicides after simulated 2-year period, evaluation of leaching potentials, and human toxicity class

[mg/m2, milligrams per square meter; mm, millimeter; S, small; M, medium; L, large; I, most toxic, IV, least toxic; <, les^ 

than; >, greater than]

Fungicide

Benomyl

Captan

Chlorothalonil

Dodine acetate salt

Ferbam

Maneb

Metalaxyl

Metiram

Thiophanate methyl

Remaining 

undissolved

on soil

surface

(percent

of applied))

0

0

0

0

0

0

0

23

0

Remaining

in soil

profile

(in percent

of applied)

5

0

0

0

0

6

5

5

0

Lost by

volatilization

and evaporation

(percent of

applied)

0

1

98

<1

5

0

2

0

2

Lost by

degradation

(percent of

applied)

95

99

2

99

95

94

92

72

98

Lost by

leaching

(percent of

applied)/

(mg/m2)

0

0

0

0

0

0

<1

0

0

Maximum

depth of

leaching

(mm)

220

0

970

99

450

210

>2,000

99

220

Group by

leaching

potential

M

S

S

S

S

M

L

M

S

Rank by

leaching

potential

4

9

5

8

6

2

1

3

7

Human

toxicity

class 1

IV

IV

I, II

I

IV

IV

HI

IV

IV

1 From Sine (1993). See appendixes 1 and 2.

Five of the six agricultural insecticides (carbaryl, carbofuran, malathion, methomyl, and parathior) 

most used in Pennsylvania (applications greater than 25,000 kg/yr from Gianessi and Puffer, 1992b) are 

primarily lost from soils by degradation based on the screening model. Chlorpyrifos, the other high-use 

insecticide, is primarily lost by volatilization and evaporation. Of the high-use insecticides, onlv 

carbofuran was assigned a large leaching potential. Methomyl was assigned a medium leaching potential, 

and the four other high-use insecticides were assigned a small leaching potential.

Twelve insecticides had formulations with a class I human toxicity rating. Four of these insecticides 

were high-use compounds. Carbofuran was applied to about 8 percent of the corn and 13 percent of trie 

potatoes planted in Pennsylvania during 1991 and ranked second only to chlorpyrifos in total annual 

insecticide use on agronomic crops in the state (Gianessi and Puffer, 1992b). Carbaryl, methomyl, and 

parathion also are high-use insecticides with a class I human toxicity rating; however, they have small and 

medium leaching potentials based on the screening model.

Relation of Pesticide Use and Model-Derived Leaching Potentials 

to Pesticides Detected in Ground Water

Ground-water quality data collected in southeastern and south-central Pennsylvania by the USGS 

between 1983 and 1993 were primarily analyzed for triazine and amid herbicides and selected so; l 

metabolites. Ground-water-quality data for most of the fungicides and insecticides and several of tri^ 

herbicides used in Pennsylvania (Jacoby, 1992) does not exist. Pesticide leaching potentials from the model 

simulations are compared to those pesticides detected in samples collected and analyzed by the USGS in 

table 20. These comparisons are qualitative, and any relations in the data must be interpreted with caution, 

because it is not known what pesticides have or have not been applied on land in the recharge areas to th? 

wells.

The compounds detected with greater frequency in ground-water samples collected and analyzed 

by the USGS are high-use herbicides (alachlor, atrazine, and metolachlor), soil metabolites of high-use 

herbicides (deethylatrazine, deisopropylatrazine, and diethylaniline), and triazine herbicides of lessor c** 

unknown use (simazine and prometon). The detected compounds span the range of leaching potential 

groups and are ranked from the second highest leaching potential (prometon) to a tie for the lowect 

leaching potential (EPTC) of the herbicides evaluated using the model simulations. The principal 

environmental fates of the compounds detected based on model simulations include losses from the soil 

by volatilization and evaporation (EPTC, pebulate, and simazine), by degradation (alachlor, atrazine,

Water-Resources Investigations Report 96-4062
Table 19. Fate of insecticides after simulated 2-year period, evaluation of leaching potentials, and 

human toxicity class

[mg/m2 , milligrams per square meter; S, small; M, medium; L, large; I, most toxic, IV, least toxic; <, less than; >, greater 

than]

Insecticide

Acephate

Azinphos-methyl

Carbaryl

Carbofuran

Chlordane

Chlorpyrifos

4,4'-DDT

Diazinon

Dicofol

Dieldrin

Dimethoate

Endosulfan

Esfenvalerate

Fenvalerate

Lindane

Malathion

Methamidophos

Methomyl

Methyl parathion

Oxamyl

Parathion

Permethrin

Phorate

Phosmet

Phosphamidon

Remaining 

undissolved 

on soil 

surface 

(percent 

of applied))

0

0

0

0

0

0

0

0

0

0

0

0

93

93

0

0

0

0

0

0

0

90

0

0

0

Remaining 

in soil 

profile 

(in percent 

of applied)

0

0

0

2

<1

0

<1

0

2

50

0

3

1

1

12

0

0

<1

0

0

0

<1

3

0

0

Lost by 

volatilization 

and evaporation 

(percent of 

applied)

0

0

0

<1

0

99

99

23

27

35

7

23

5

5

76

3

48

10

1

6

17

5

25

5

6

Lost by 

degradation 

(percent of 

applied)

100

100

100

97

99

1

0

77

71

15

93

74

1

1

12

97

52

89

99

94

83

4

72

95

94

Lost by 

leaching 

(percent of 

applied)/ 

(mg/m2)

0

0

0

<1/1.6

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

Maximum 

depth of 

leaching 

(mm)

0

280

450

>2,000

180

190

99

280

190

180

0

150

150

150

320

0

0

1,500

0

0

190

99

280

290

1,900

Group by 

leaching 

potential

S

S

S

L

M

S

S

S

M

M

S

M

M

M

M

S

S

M

S

S

S

M

M

S

S

Rank by 

leaching 

potential

22.5

17

14

1

8

18

11.5

16

6

2

22.5

5

9.5

9.5

3

22.5

22.5

7

22.5

22.5

19

11.5

4

15

13

Human 

toxicit' 

class 1

m

I

i, n, m

i, ii

ii

n, in

n

n,m

n,m

i

n

i

ii

ii

n

in

i

I, IV

i

i

i

n, in

i

n

i

'From Sine (1993). See appendixes 1 and 2.

cyanazine, linuron, metolachlor, and propazine), and retention in the soil (prometon). According to the 

simulation, three of the compounds detected (atrazine, prometon, and propazine) were expected to lea-"h 

to ground water. However, five of the compounds detected in ground water (alachlor, cyanazine, EPTC, 

pebulate, and simazine) were not expected to leach to ground water.

The necessary chemical and physical properties of the soil metabolites of atrazine 

(deisopropylatrazine and deethylatrazine), simazine (deisopropylatrazine), and alachlor (diethylanaline) 

detected in ground water were not known such that their environmental fate could be simulated with the 

LEACHP model. The toxicity of these soil metabolites also was not known.

The model simulations would not have predicted the leaching of several compounds that have be°n 

detected with some frequency in ground water from agricultural carbonate rock terrains of southeastern 

and south-central Pennsylvania. The poor predictive capability of the model could be an indication that 

either (1) the processes by which some or all of the detected pesticides leach to ground water in these karst 

areas were not accurately represented by the LEACHP model as it was configured for these simulations, or 

(2) one or more of the pesticide or soil variables used as input to the model are substantially different frm 

actual field conditions.

44 Water-Resources Investigations Report 96-4062
Table 20. Pesticides detected in ground water from selected wells, lysimeters, and springs in southeastern and 

south-central Pennsylvania, 1983 through 1993

[; S, small leaching potential; M, medium leaching potential; L, large leaching potential; NR, not rated; --, not 

analyzed]

Pesticide

Alachlor

Atrazine

Bromacil

Cyanazine

Deethylatrazine

Deisopropylatrazine

Diethylanaline

EPTC

Linuron

Metolachlor

Pebulate

Pendimethalin

Prometon

Propazine

Simazine

Tebuthiuron

Estimated 

leaching 

potential from 

the model 

simulation

S

L

NR

S

NR

NR

NR

S

M

M

S

NR

L

L

M

NR

Percentage 

of 28 sites 

sampled in 

1983 with 

detects1

12

41

--

0

-

--

-

--

-

7

--

-

-

0

0

-

Percentage 

of 1 1 sites 

sampled in 

1 989 with 

detects2

9

82

--

0

82

64

-

0

~

45

~

~

-

0

0

-

Percentage 

of 7 sites 

sampled as 

part of this 

study with

detects

0

86

--

0

86

86

0

--

-

43

~

-

29

0

86

-

Percentage 

of 37 sites 

sampled in 

1991 with 

detects3

3

43

-

0

81

22

-

-

-

11

-

-

24

3

22

-

Percentage 

of 30 sites 

sampled in 

1993 with 

detects4

27

93

3

3

77

-

3

7

3

77

7

3

77

0

37

3

From Fishel and Lietman (1986).

2 From D.JK. Wangsness (U.S. Geological Survey, written commun., 1990). 

3 From Durlin and Schaffstall (1993). 

4From B.D. Lindsey (U.S. Geological Survey, written commun., 1994).

For this report, the LEACHP model was configured to represent pesticide fate and transport in a 

uniform flow field through the subsurface with both vertical downward infiltration and deep percolatior. 

Although the model simulations provide quantitative estimates of pesticide fate, it may be most useful fcr 

a qualitative understanding of how the combined soil and pesticide properties may influence pesticide 

leaching through agricultural soils in the carbonate rock terrains of southeastern and south-central 

Pennsylvania. As configured, quantitative estimates from the model could systematically underpredict the 

depth of movement and net pesticide losses from nonuniform subsurface flow and leaching from highly 

structured soils. The model may not be appropriate for prediction of even the presence or absence of 

pesticides in ground water in areas where focused recharge through karst features is an important proces > 

or where lateral flow associated with the development of locally perched aquifers is appreciable.

The LEACHP model, as configured for this report, simulated pesticide sorption and degradation by 

use of a single organic carbon partition coefficient and degradation rate constant for each pesticide to 

represent a multitude of soil processes. The model assumes that (1) sorption processes can be described by 

a linear relation, and (2) degradation processes can be described by a first order equation and a decreased 

degradation rate at depth in the soil. The sensitivity analysis presented earlier in the report demonstrated 

that of the variables evaluated, the organic-carbon partition coefficient and pesticide degradation rate had 

the largest relative effect on pesticide leaching (table 16). However, it is unknown if the degradation-rate 

constants used in the model simulations are close to actual degradation rates or that the actual sorption 

and degradation processes are represented properly by the relations used in the model. Degradation-rate 

constants probably are the least certain of the model input variables used in these model simulations 

(Wauchope and others, 1992).

Water-Resources Investigations Report 96-4062 45
Predictive capability of a screening model could be improved (1) by use of locally derived pesticid0 

properties data, (2) an improved representation of processes that control ground-water recharge and 

pesticide transport in areas with regolith-mantled karst landscapes, and (3) additional ground-water 

monitoring data for leachable pesticides in areas of known use.

Implications for the Development of Agricultural Best-Management Practices

Ground-water quality data collected from USGS studies and results of the model simulations 

provide information that could be significant for the development of agricultural best-managemert 

practices in carbonate-rock areas of southeastern and south-central Pennsylvania Three general findings 

follow.

1. The pesticides detected in ground water from the agricultural, carbonate-rock terrains of southeastern 

and south-central Pennsylvania, include compounds with a broad range of ground-water leaching 

potentials and environmental fates. Related findings include:

Although the pesticides detected included those compounds assigned large, medium, 

and small ground-water leaching potentials, the pesticides detected with the greatest 

frequency generally had medium or large leaching potentials and high use on agricultural 

land relative to most other compounds evaluated.

The pesticides detected include compounds that are lost from the soil primarily by 

each of the environmental processes simulated by the model, so that the occurrence of 

these compounds in ground water can not be attributed to the action of just one pesticide 

property or environmental process.

Current water-quality data probably best represent pesticide occurrence of only those 

chemicals that are ubiquitous in use on major crops. A more thorough evaluation of the 

use and limitations of pesticide screening models needs additional water-quality data. 

Available data do not include analyses for several high-use compounds and compounds 

with large or moderate leaching potentials.

Addition of pesticide-use data in recharge areas to wells and springs sampled could 

provide useful comparisons of pesticide use and the presence or absence of pesticides in 

ground water. This approach is essential for evaluating the leaching potentials of lessor 

used pesticides and pesticides with much of their total use limited to either small 

geographic areas or minor crops.

2. Use of area specific estimates of variables describing pesticide-soil interactions, specifically sorption 

and degradation, and additional characterization of pesticide transport pathways through regolithmantled karst areas may improve the predictive capability of pesticide screening models in the carbonaterock terrains of southeastern and south-central Pennsylvania. Related findings include:

The pesticide properties used to describe pesticide-soil interactions and degradation 

rates in the screening model were compiled from field studies conducted at many 

locations throughout the United States, or in many cases they were estimated from 

properties of similar compounds (Wauchope and others, 1992). The existing pesticideproperties data may not be representative of the climate, soils, and pesticide- application 

practices in southeastern and south-central Pennsylvania.

The screening model assumes uniform one dimensional flow and transport through 

the unsaturated zone. Significant departures from this assumption in areas underlain by 

regolith-mantled carbonate rocks is evident, including focused recharge, preferential flow 

paths in structured soils, radial flow to shafts, and runoff into sinkholes.

46 Water-Resources Investigations Report 96-4062
3. Model simulations indicate that many pesticides used in Pennsylvania are degraded in the soil 

environment. The compounds formed from the partial degradation of pesticides could be a substantial par 1 

of all pesticide residues present in ground water. Related findings include:

Pesticide degradation products are among the most frequently detected pesticide 

residues in ground water in southeastern and south-central Pennsylvania (Durlin and 

Schaffstall, 1993; Hippe and others, 1994; B.D. Lindsey, U.S. Geological Survey, written 

commun., 1994) and in the United States (Jacoby, 1992).

For many pesticides, the principal sequences of degradation reactions have not been 

elucidated, and the various degradation products have not been fully characterized with 

respect to their physical and chemical properties, their stability in soil and ground water, 

and their effects on human-health and the environment (Somasundaram and Coats, 1991).

Degradation products of some pesticides have larger solubilities and higher vapor 

pressures than the parent compounds, giving them greater mobility in water and in the 

atmosphere (Somasundaram and Coates, 1991). Large changes in mobility or toxicity to 

plants, animals, and humans can cause some pesticide degradation products to impose an 

environmental or human health hazard greater than the parent compounds.

SUMMARY AND CONCLUSIONS

Because karst areas have a demonstrated susceptibility to ground-water contamination, ar 

improved understanding of the processes that control ground-water recharge and leaching of pesticides 

through soils may aid in developing agricultural practices that minimize adverse effects on ground-water 

quality.

The study area, a 4.5-hectare field site, is situated in a regolith-mantled carbonate-rock terrain 

typical of the carbonate-rock terrains in southeastern and south-central Pennsylvania. Unsaturated 

materials at the field site consist of an upper vadose zone composed of soils formed from weathering of 

limestone bedrock and an intermediate vadose zone composed of karstified limestone. Soils are absent or 

scattered bedrock pinnacles and are more than 12 m thick in other areas of the site. Organic carbon content 

of soil materials is about 1.7 percent in the Ap-horizon and from 0.1 to 0.3 percent throughout the full 

thickness of the B- and C-horizons.

Because soils at the site are thick with a large specific retention of soil moisture, the quantity of water 

contained in the soil is large relative to the average annual recharge through soils to the regional aquifer. 

From assumptions of diffuse recharge and uniform flow through the unsaturated zone, it was determined 

that soil moisture and water-soluble contaminants would generally have a residence time of several years 

However, preferential flow paths in the soil (root casts, animal burrows, and interpedal surfaces) and ir 

the intermediate vadose zone allow part of the recharge to bypass most of the unsaturated material? 

creating a broad range of residence times.

Ground-water levels in the field site had a pronounced annual cycle; the highest levels occurred 

during March or April and the lowest levels between November and February. The initial rise in groundwater levels commonly lagged behind the onset of rainfall or snowmelt by a few hours. The highest 

ground-water levels occur from 2 to 5 days later. Recharge from rainfall occurred during the summer and 

fall even when there was a combination of high potential for evapotranspiration and dry soil conditions 

The short lag between the onset of precipitation and recharge to the regional aquifer and the occurrence of 

recharge during periods of high potential for evapotranspiration and dry soil conditions suggest that 

recharge occurs in part along preferential pathways in the unsaturated zone.

Recharge through sinkholes and other preferential flow paths to the regional aquifer within hours of 

rainfall or snowmelt may include contaminants that are otherwise readily degraded in the soil 

environment and contaminants that, because of their low solubility, exhibit little mobility in soil materials. 

For example, at the field site, atrazine, metolachlor, simazine, and the atrazine soil metabolites 

deethylatrazine and deisopropylatrazine were at concentrations above the minimum reporting level of 

0.05 M-g/L in just the upper 0.6 m of bulk soil samples collected from land surface to a depth of 7.3 m.

Water-Resources Investigations Report 96-4062 47
However, concentrations of atrazine, simazine, and atrazine soil metabolites were detected in water 

samples from lysimeters installed in soil material at depths of 1.2, 2.1, and 3.7 m and from monitor weUs 

completed in the regional aquifer.

Data collected to characterize the field site were used to configure a pesticide screening model. 

Model simulations indicate that most field-applied pesticides have a tendency to volatilize to the 

atmosphere, accumulate in soils, degrade in the subsurface environment, or leach to ground water. Model 

results were used to rank the leaching potentials of a total of 66 herbicides, fungicides, and insecticid°s. 

Model results suggested that 18 of the 32 herbicides, 4 of the 9 fungicides, and 11 of the 25 insecticides have 

a moderate to large potential for leaching to ground water. Pesticides given a large or moderate potential 

to leach to ground water span a broad range of total use on agricultural land in Pennsylvania and have a 

wide range of toxicities to humans.

A comparison with available pesticide monitoring data suggests that the presence of pesticides in 

Pennsylvania's ground water may be under-reported. Monitoring data do not exist for more than twothirds of the pesticide compounds currently used in Pennsylvania. Many of these compounds have a large 

or moderate potential for leaching to ground water.

Comprehensive monitoring for pesticides and pesticide-degradation products in ground water 

downgradient of areas of pesticide use improved characterization of the physical properties of 

agricultural, carbonate soils, and improved management models developed from process-oriented 

research would facilitate development of effective pesticide best-management practices.

REFERENCES CITED

Adams, C.D., and Thurman, E.M., 1991, Formation and transport of deethylatrazine in the soil and vadose 

zone: Journal of Environmental Quality, v. 20, p. 540-547.

Ball, J.W., Nordstrom, O.K., and Zachman, D.W., 1987, WATEQ4F - A personal computer FORTRAN 

translation of the geochemical model WATEQ2 with revised data base: U.S. Geological Survey OpenFile Report 87-50,108 p.

Becher, A.E., and Root, S.I., 1981, Groundwater and geology of the Cumberland Valley, Cumberland 

County, Pennsylvania: Pennsylvania Geological Survey, 4th ser., Water Resource Report 50, 95 p.

Belluck, D.A., Benjamin, S.L., and Dawson, T., 1991, Groundwater contamination by atrazine and its 

metabolites: Risk assessment, policy, and legal implications, in Somasundaram, L., and Coats, J.R., 

eds., Pesticide transformation products: Washington, D.C., American Chemical Society, ACS 

Symposium Series 459, 305 p.

Bouwer, Herman, and Rice, R.C., 1976, A slug test for determining hydraulic conductivity of unconfiried 

aquifers with completely or partially penetrating wells: Water Resources Research, v. 12, p. 423-428.

Brown, L.R., 1987, State of the world, Chapter 7 - Sustaining world agriculture: New York, N.Y., W.W. 

Norton and Co., 268 p.

Brown, J.R., and Myers, V., eds., 1992, Handbook of RCRA ground-water monitoring constituents chemical 

physical properties: Washington, D.C., U.S. Environmental Protection Agency, 40 CFR Part 2M, 

Appendix 9, number PB92-233287, 268 p.

Buyanovsky, G.A., Gajda, A.M., Kremer, R.J., and Pieczonka, G.J., 1993, Effect of soil depth on carbofuran 

and aldicarb degradation, in Luxmoore, ed., 1993, Sorption and degradation of pesticides in so; ls: 

Madison, Wis., Soil Science Society of America, Inc., Special publication number 32, p. 65-71

Campbell, G., 1974, A simple method for determining unsaturated conductivity from moisture retention 

data: Soil Science, v. 117, p. 311-314.

Chambers, R.D., ed., 1993, The Perm State Agronomy Guide 1993-94: University Park, Pa., Pennsylvania 

State University, College of Agriculture.

48 Water-Resources Investigations Report 96-4062
REFERENCES CITED-Continued

Chichester, D.C., 1991, Conceptual hydrogeologic framework of a regolith-mantled carbonate system, 

Cumberland Valley, Pennsylvania: Geology in the South Mountain Area, Pennsylvania, 56th Annual 

Field Conference of Pennsylvania Geologists Guidebook, p. 95-107.

Durlin, R.R., and Schaffstall, W.P., 1993, Water resources data for Pennsylvania, water year 1992-volume 

2: U.S. Geological Survey Water-Data Report PA-92-2,342 p.

Field, M.S., 1989, The fate and transport of chemical contaminants in karst terranes: U.S. Envrionmental 

Protection Agency Report EPA/600/D-90/001,14 p.

Fishel, D.K., and Lietman, P.L., 1986, Occurrence of nitrate and herbicides in ground water in the upper 

Conestoga River Basin, Pennsylvania: U.S. Geological Survey Water-Resources Investigations Report 

85-4202, 8 p.

Fishman, M.J., and Friedman, L.C., eds., 1970, Methods for determination of inorganic substances in water 

and fluvial sediments: U.S. Geological Survey Techniques of Water-Resources Investigations, book 5, 

chap. Al, 545 p.

Furtick, W.R., 1993, Uncontrolled pests or adequate food?, in Goldfarb, T.D., ed., Taking sides: Guilford, 

Conn., Dushkin Publishing Company, p. 180-187.

Gates, J.P., 1988, Tracing the evolution of organic/sustainable agriculture, a selected and annotated 

bibliography: Beltsville, Md., U.S. Department of Agriculture, Bibliographies and Literature of 

Agriculture Number Publication Number 72.

Garner, W.Y., Honeycutt, R.C., and Nigg, H.N., eds., 1986, Evaluation of pesticides in ground water: ACS 

Symposium Series 315, Washington, D.C., American Chemical Society, 558 p.

Gianessi, L.P., and Puffer, C.A., 1991, Herbicide use in the United States: Washington, D.C., Resources for 

the Future, December 1990, (revised April 1991), 128 p.

___ 1992a, Fungicide use in U.S. Crop Production: Washington, D.C., Resources for the Future, August 

1992.

___ 1992b, Insecticide use in U.S. Crop Production: Washington, D.C., Resources for the Future, 

November 1992.

Goss, D.W., 1992, Screening procedure for soils and pesticides for potential water-quality impacts: Weed 

Technology, v. 6, p. 701-708.

Goss, D.W., and Wauchope, R.D., 1991, The SCS/ARS/CES pesticide properties database - II using with 

soils data in a screening procedure: Proceedings of the Third National Pesticide Research Conference 

of the Virginia Water Resources Research Institute, Richmond, Virginia, p. 471-493.

Grant, S.A., Jabro, J.D., Fritton, D.D., and Baker, D.E., 1991, A stochastic model of infiltration which 

simulates "macropore" soil water flow: Water Resources Research v. 27, no.7, pp. 1439-1446.

Green, R.E., Schneider, R.C., Gavinda, R.T., and Miles, C.J., 1993, Utility of sorption and degradation 

parameters from the literature for site-specific pesticide impact assessments, in Luxmoore, ed., 1993, 

Sorption and degradation of pesticides in soils: Madison, Wis., Soil Science Society of America, Inc., 

Special publication number 32, p. 65-71.

Hammond, A.L., ed., 1992, World Resources: New York, N.Y., World Resources Institute and United 

Nations Environment Programme, Oxford University Press, 385 p.

Hall, D.W., and Risser, D.W., 1993, Effects of agricultural nutrient management on nitrogen fate and 

transport in Lancaster County, Pennsylvania: Water Resources Bulletin WARBAQ, Vol. 29, No. 1, p 

55-76.

Water-Resources Investigations Report 96-4062 49
REFERENCES CITED-Continued

Hippe, D.J., Witt, E.G., Ill, Baumbach, G.E., Brightbill, R.A., Giovannitti, R.M., and Char, S.J., 1992, 

Assessment of herbicide contamination of water resources in Cumberland and Lancaster Counties, 

Pennsylvania using enzyme-linked immunosorbent assay methods: abs., Proceedings of the 

Geological Society of America 1992 Northeastern Section Meeting.

Hippe, D.J., Witt, E.C, III, and Giovannitti, R.M., 1994, Hydrogeology, herbicides and nutrients in ground 

water and springs and relations of water quality to land use and agricultural practices near Carlisle, 

Pennsylvania: U.S. Geological Survey Water-Resources Investigation Report 93-4172,66 p.

Hutsen, J.L., and Wagenet, R.J., 1992, LEACHM: Leaching estimation and chemistry model: Ithica, N.Y., 

Dept. of Soil, Crop, and Atmospheric Sciences, Cornell University, Research Series no. 92.3.

___1993, A pragmatic field-scale approach for modeling pesticides: Journal of Environmental Quality, 

v. 22, p. 494-499.

Jabro, J.D., and Fritton, D.D., 1990, Simulation of water flow from a percolation test hole in layered soil: Soil 

Science Society of America Journal, v. 54, p. 1,214-1,218.

Jabro, J.D., Lotse, E.G., Simmons, K.E., and Baker, D.E., 1991, A field study of macropore flow under 

saturated conditons using a bromide tracer: Journal of Soil and Water Conservation, v. 46, no. 5, 

p. 376-380.

Jacoby, H., ed., 1992, Pesticides in ground water database: a compilation of monitoring studies: 1971 -1991 

national summary: Washington, D.C., U.S. Environmental Protection Agency report number EPA 

734-12-92-001, U.S. Government Printing Office report number 1993-348-066:80183.

Jury, W.A., Farmer, W.J., and Spencer, W.F., 1984a, Behavior assessment model for trace organics in soil - 

II. Chemical classification and parameter sensitivity: Journal of Environmental Quality, v. 13, no. 4, 

p. 567-572.

Jury, W.A., Spencer, W.F., and Farmer, W.J., 1983, Behavior assessment model for trace organics in soil - I. 

Model description: Journal of Environmental Quality, v. 12, no. 4, p. 558-564.

___1984b, Behavior assessment model for trace organics in soil - III. Application of screening model: 

Journal of Environmental Quality, v. 13, no. 4, p. 573-579.

___1984c, Behavior assessment model for trace organics in soil - IV. Review of experimental evidence: 

Journal of Environmental Quality, v. 13, no. 4, p. 580-586.

Jury, W.A., Focht, D.D., and Farmer, W.J., 1987, Evaluation of pesticide groundwater pollution potential 

from standard indices of soil-chemical adsorption and biodegradation: Journal of Environmental 

Quality, v. 16, no. 4, p. 422-428.

Jury, W.A., and Ghodrati, 1989, Overview of Organic Chemical Environmental Fate and Transport 

Modeling Approaches, in Sawhney, B.L., and Brown, K., eds., Reactions and Movement of Organic 

Chemicals in Soils: Madison, Wis., Soil Science Society of America publication number 22,474 p.

Kastenburg, W.E., and Yeh, H.C., 1993, Assessing public exposure to pesticide-contaminated ground water: 

Ground Water, v. 31, no. 5, p. 746-752.

Kellogg, R.L., Maizel, M.S., and Goss, D.W., 1992, Agricultural chemical use and ground water quality: U.S. 

Department of Agriculture Cooperative State Research Service under agreement no. 91-38813-69-6.

Kochanov, W.E., 1989, Sinkholes and karst-related features of Cumberland County, Pennsylvania: 

Pennsylvania Geological Survey, Open File Report 8902,9 p., 9 maps.

Leonard, R.A., Knisel, D.A., and Still, D.A., 1987, GLEAMS - ground water loading effects of agricultural 

management systems: Transactions of the ASAE, v. 30, no. 5, p. 1,403-1,418.

50 Water-Resources Investigations Report 96-4062
REFERENCES CITED-Continued

Lietman, P.L., and Hall, D.W., 1991, Herbicides in surface and ground water of agricultural carbonate 

valleys, Lancaster County, Pennsylvania, in Weigmann, D.L., ed., Pesticides in the next decade: the 

challenges ahead: Proceedings of the Third National Research Conference on Pesticides, November 

8-9,1990, Virginia Water Resources Research Center, Blacksburg, Va., p. 38-56.

Lietman, P.L., Ward, J.R., and Behrendt, T.E., 1983, Effects of specific land uses in nonpoint sources o* 

suspended sediment, nutrients and herbicides-Pequea Creek basin, Pennsylvania 1979-80: U.S. 

Geological Survey Water-Resources Investigations Report 83-4113, 88 p.

Logan, T.J., 1990, Agricultural best management practices and groundwater protection: Journal of Soil and 

Water Conservation, March-April issue, p. 201-206.

Mackay, D., 1991, Multimedia environmental models - the fugacity approach: Chelsea, Mich., Lewis 

Publishers, Inc., 257 p.

Mackay, D., and Stiver, W.H., 1991, Predictability and environmental chemistry Chapter 8, Grover, R., and 

Lessna, A.J., eds., Environmental chemistry of herbicides, volume II: Boca Raton, Fla., CRC Press.

Matthes, W.J., Jr., Sholar, C.J., and George, J.R., 1992, Quality-assurance plan for the analysis of fluvial 

sediment by laboratories of the U.S. Geological Survey: U.S. Geological Survey Open-File 

Report 91-467, 31 p.

Mullins, J.A., Carsel, R.F., Scarbrough, J.E., and Ivery, A.M., 1993, PRZM2, A model for predicting pesticide 

fate in the crop root zone and unsaturated soil zones 2.0: Washington, D.C., U.S. Environmental 

Protection Agency, EPA/600/R-93/046.

Nelson, D.W., and Sommers, L.E., 1982, Total carbon, organic carbon, and organic matter, in Page, A.L., 

Miller, R.H., and Keeney, D.R., eds., Methods of soil analysis part 2-Chemical and microbiological 

properties second edition: American Society of Agronomy, Inc. and Soil Science Society of America, 

Inc., Madison, Wis., 1,159 p.

Olmsted, F.H., and Hely, A.G., 1962, Relation between ground water and surface water in Brandywine 

Creek basin Pennsylvania: U.S. Geological Survey Professional Paper 417-A, * p.

Pennsylvania State University, 1991, The agronomy guide 1991-1992: The Pennsylvania State University 

College of Agriculture, University Park, Pa., 159 p.

Pimentel, D., 1987, Is Silent Spring behind us?, in Marco, G.J., Hollingworth, R.M., and Durham, W., eds., 

Silent Spring Revisited: York, Pa., American Chemical Society, Maple Press Inc., 

ISBN 0-8412-0981-2, 214 p.

Rao, P.S.C., Hornsby, A.G., and Jessup, R.E., 1985, Indices for ranking the potential for pesticide 

contamination of ground water: Jacksonville Beach, Fla., Soil and Crop Science Society of Florid? 

Proceedings Volume 44.

Rawls, W.J., and Brakensiek, D.L., 1985, Agricultural management effects on soils water retention, ir 

DeCoursey, D.G., ed., Proceedings of the 1983 Natural Resources Modeling Symposium: U.S. 

Department of Agriculture, Agricultural Research Service, ARS-30,532 p.

Rutledge, A.T., and Helgesen, J.O., 1989, Use of a simplified transport model for pesticides in the 

unsaturated zone, in Mallard, G.E., and Ragone, S.E., eds., U.S. Geological Survey Toxic Substances 

Hydrology Program proceedings of a technical meeting, Phoenix, Ariz., September 26-30, 1988, 

U.S. Geological Survey Water-Resources Investigations Report 88-4220, p. 523-530.

Sine, Charlotte, ed., 1993, Farm Chemicals Handbook: Willoughby, Ohio, Meister Publishing Company.

Thurman, E.M., Meyer, M., Pomes, M., Perry, C.A., and Schwab, A.P., 1990, Enzyme-linked 

immunosorbent assay compared with gas chromatography/mass spectrometry for the 

determination of triazine herbicides in water: Journal of Analytical Chemistry, v. 62, p. 2,043-2,048.

Water-Resources Investigations Report 96-4062 51
REFERENCES CITED--Continued

U.S. Department of Commerce, 1992, Climatological data annual summary Pennsylvania: National 

Climatic Data Center, Asheville, N.C.

___1993, Climatological data annual summary Pennsylvania: National Climatic Data Center, Asheville,

N.C.

U.S. Environmental Protection Agency, 1986, Quality Criteria for water: USEPA-40015-86-001, 256 p.

___1991, Drinking water regulations and health advisories: U.S. Environmental Protection Agency, 

Office of Water, Washington, D.C., 10 p.

Ward, J.R., 1987, Surface-water quality in Pequea Creek basin, Pennsylvania 1977-1979: U.S. Geological 

Survey Water-Resources Investigation Report, 85-4250,66 p.

Wauchope, R.D., 1992, Environmental risk assessment of pesticides: Improving simulation model 

credibility: Weed Technology, v. 6, p. 753-759.

Wauchope, R.D., Buttler, T.M., Hornsby, A.G., Augustin-Beckers, P.W.M., and Burt, J.P., 1992, The 

SCS/ARS/CES pesticide properties database for environmental decision-making: Reviews of 

Environmental Contamination and Toxicology, v. 123, p. 1-164.

White, W.B., 1988, Geomorphology and hydrology of karst terrains: New York, Oxford University Press, 

464 p.

Williams, P.W., 1983, The role of the subcutaneous zone in karst hydrology: Journal of Hydrology, v. 61, 

p. 45-67.

___ 1985, Subcutaneous hydrology and the development of doline and cockpit karst: Zeitschrift fur 

Geomorphologie, v. 29, p. 463-482.

Wolf, E.C., 1987, Chapter 8 - Raising agricultural productivity, in Brown, L.R., ed., State of the world: New 

York, N.Y., W.W. Norton and Co., 268 p.

Zarichansky, J., 1985, Soil survey of Cumberland and Perry Counties, Pennsylvania: U.S. Department of 

Agriculture, Soil Conservation Service, 226 p.

52 Water-Resources Investigations Report 96-4062
APPENDIXES

Water-Resources Investigations Report 96-4062 53
Appendix 1. Pesticide human toxicity categories (from Sine, 1993)

Toxicity (Human)

The AAPCO1 has adopted these regulatory principles relating to the determination of highly toxic 

materials:

"Highly Toxic: An economic poison which, when it falls within any of the following categories when 

tested on laboratory animals (mice, rats, and rabbits), is highly toxic to man within the meaning of there 

principles: "(a) Oral toxicity: Those which produce death in half or more than half the animals of any 

species at a dosage of 50 milligrams at a single dose, or less, per kilogram of body weight when 

administered orally to 10 or more such animals of each species.

"(b) Toxicity on inhalation: Those which produce death in half or more than half of the animals of 

any species at a dosage of 200 parts or less by volume of the gas or vapor per million parts by volume of air 

when administered by continuous inhalation for one hour or less to ten or more animals of each specios, 

provided such concentrations is likely to be encountered by man when the economic poison is used in any 

reasonable foreseeable manner.

"(c) Toxicity by skin absorption: Those which produce death in half or more than half of the animals 

(rabbits only) test at a dosage of 200 milligrams or less per kilogram of body weight when administered by 

continuous contact with the bare skin for 24 hours or less to 10 or more animals. Provided, however, th at 

an enforcement official may exempt any economic poison which meets the above standard but which is 

not in fact highly toxic to man, from these principles with respect to economic poisons highly toxic to men, 

and may after hearing designate as highly toxic to man any economic poison which experience has shown 

to be so in fact."

Hazard 

indicators

Oral LDs

Inhalation LDs

Dermal LDs

Eye Effects

Skin Effects

1

up to and including 

0.2 mg/ liter

up to and including 

0.2 mg/ liter

up to and including 

200 mg/kg

Corrosive; corneal 

opacity not reversible within 7 days

Corrosive

II

from 50 thru 500 

mg/kg

from 0.2 thru 2 

mg/ liter

from 200 thru 2,000

Corneal opacity 

reversible within 7 

days; irritation persisting for 7 days

Severe irritation at 72 

hours

III

from 500 thru 5,000 

mg/kg

from 2.0 thru 20 

mg/ liter

from 2000 thru 20,000

No corneal opacity; 

irritation reversible 

within 7 days

Moderate irritation at 

72 hours

IV

greater than 5,000 

mg/kg

greater than 20 

mg/ liter

greater than 20,000

No irritation

Mild or slight irritation at 72 hours

1 Association of American Pesticide Control Officials, Inc.

54 Water-Resources Investigations Report 96-4062
Toxicity Categories

The USEPA has published regulations for use of human hazard signal words on pesticide labels: 

Signal words assigned by levels of toxicity

(A) Toxicity Category I

All pesticide products meeting the criteria of Toxicity Category I shall bear on the front panel the 

signal word "Danger." In addition, if the product was assigned to Toxicity Category I on the basis of ite 

oral, inhalation, or dermal toxicity (as distinct from skin and eye local effects), the work "Poison" shall 

appear in red on a background of distinctly contrasting color and the skull and crossbones shall appear in 

immediate proximity to the word "Poison."

(B) Toxicity Category II

All pesticide product meeting the criteria of Toxicity Category II shall bear on the front panel the 

signal word "Warning."

(C) Toxicity Category HI

All pesticide products meeting the criteria of Toxicity Category III shall bear on the front panel th° 

signal word "Caution."

(D) Toxicity Category IV

All pesticide products meeting the criteria of Toxicity Category IV shall bear on the front panel th° 

single word "Caution."

(E) Use of signal words

Use of signal word(s) associated with a higher Toxicity Category is not permitted except when th e 

Agency determines that such labeling is necessary to prevent unreasonable adverse effects.

Water-Resources Investigations Report 96-4062 55
Appendix 2. Risk assessment

Risk assessments are beyond the scope of this report, however, human- toxicity data from Sine (1993; 

appendix 1) have been included on tables 18-20 to provide a preliminary indication of relative hazards to 

human health. Effective pesticide management strategies will address the presence of pesticide residues in 

water, soil, air, biota, and vegetation, and will consider the effects of pesticide use on humans, animals 

(Sine, 1993, p. E14- E17), birds, fish, and bees (Sine, 1993, p. E18-E20), and other non-target animals, insectr. 

and plants. Toxicity of herbicides to rats and rabbits is discussed in Perm State Cooperative Extension 

Agrichemical Fact Sheet 2a, toxicity of fungicides is discussed in Fact Sheet 2b, and toxicity of pesticides is 

discussed in Fact Sheet 2c, all by Dr. Winand K. Hock, Professor of Plant Pathology at Perm State. A "mey 

affect" pesticide list for endangered species is in Sine (1993, p. D13), and includes several pesticides 

currently used in agricultural, carbonate terrains of Pennsylvania, including acephate, azinphos-methyl, 

carbofuran, chlorpyrifos, endosulfan, fenvalerate, parathion, permethrin, phorate, and trifluralin. An 

example of a risk assessment for pesticides in ground water was published by Kastenburg and Yeh (199?).

56 Water-Resources Investigations Report 96-^062