### 2

The maximum EDWCs for surface water and groundwater are listed in Table 1

. The PRZM/EXAMS model predicted that total coumaphos residue concentration s (coumaphos + coumaphoxon) in surface water are not likely to exceed 0.10 μ g coumaphos equivalent/L for the maximum peak concentration (acute) and 0.03 μ g coumaphos equivalent/L for the average concentration (chronic). For groundwater, no breakthrough of coumaphos into shallow groundwater was observed using 100

- year PRZM

- GW simulations. However, breakthroughs

w ere observed for coumaphoxon

, but predicted EDWCs were several orders of magnitude lower than the predicted values of SCIGROW model. SCIGROW modeling results for groundwater are listed in Table 1 . SCIGROW predicted total coumaphos residue concentration in groundwater is not likely to exceed 1.91E

- 03 μ g coumaphos equivalent/L for the maximum peak concentration (acute) and the average concentration (chronic).

Table 1. Maximum EDWCs for Drinking Water Sources for Coumaphos and Coumaphoxon

Source of Drinking

Water Estimated Drinking Water concentrati on (μg/L)

Acute Chronic Average

chronic

Coumaphos

Surface Water 1 0.10 0.05 0.03

Groundwater 2 1.91 x 10

- 03 1.91 x 10

- 03 1.91 x 10

- 03
Coumaphoxon

Surface Water 0.002 0 0

Groundwater

, 2 5.06 x 10

- 06 5.06 x 10

- 06 5.06 x 10

- 06
Coumaphos Equivalents (Coumaphos+Coumaphoxon)

Surface Water 0.102 0.05 0.03

Groundwater 1.91 x 10

- 03 1.91 x 10

- 03 1.91 x 10

- 03

1 EDWCs based on PRZM/EXAMS model

2 EDWCs derived from SCIGROW



### Introduction

Coumaphos (O

- [3

- chloro

- 4

- methyl

- 2

- oxo

- 2H

- 1

- benzopyran

- 7

- yl] O,O

- diethyl phosphorothioate) is an organophosphate insecticide/ acaricide

. Coumaphos can be applied by dip vat, aerosol can, dustbag, hand

- held duster, hand

- held sprayer, backrubber oiler, mechanical duster , shaker can, and squeeze applicator. Based on the above understanding of the uses and methods of application on animals, there is a potential for indirect exposure to coumaphos in the environment via dislodging of applied chemical from animal hides. Coum aphos is also registered for the control of insects, mites, and ticks on livestock and swine bedding, and for the control of varroa mites

and small hive beetles in bee hives. However, t he indoor use of coumaphos ( e.g. , to treat swine bedding) and the place ment of coumaphos

- treated strips in bee hives would not be considered in the drinking water assessment because they do not provide complete routes of exposure to surface waters or groundwater.

In an earlier assessment, the Environmental Fate and Effects D ivision (EFED) assumed that the disposal of biorem e diated coumaphos dip vat solution on non

- agricultural land would be a major exposure route to drinking water sources for human consumption. Since dried sludge generated in evaporation ponds containing bior emediated dip vat solution is discarded in a landfill by

### 3

USDA APHIS (US EPA, 2008) , EFED concludes that exposure via application of bioremediated spent dip vat solutions to land is not a n exposure pathway for drinking water sources . Therefore, the applica tion of bioremediated spent dip vat solutions to land is not included in modeling of

EDWCs in surface water and groundwater

.

However, during a rain event, a certain fraction of coumaphos wash

- off from treated cattle can

come contact into with and be adsorbed o nto manure as well as transported as runoff from Concentrated Animal Feeding Operations ( CAFOs ) and pasture/rangeland. In registrant

submitted wash

- off studies, fresh cow hides were treated with either Co

- Ral® 11.6% emulsifiable liquid (MRID 4251 2601) or Co

- Ral® 25% wettable powder (MRID 42512602) and then dried for 0.5, 3, or 24 hours. The wash

- off fraction was measured after hides had been soaked in water for 0.5, 1, 2, or 4 hours. Results of these studies indicate that wash

- off fraction

is in versely related to drying time and dependent upon the formulation ( Table 2 ) but not affected by soaking time (data not shown). Although not the most conservative, wash

- off fractions for

the 24

- hour drying time were used in this assessment because they rep resent a reasonable time frame after application for a treated cow to be caught in a rainstorm

.

Table 2 . Percent Wash

- Off for Different Formulations of Coumaphos at Different Drying Times (MRIDs 42512601 and 42512602)

Formulation (%) Drying Time (hrs) Wash

- Off

Fraction Comment

Emulsifiable powder/concentrate (11.6) 0.5 0.116 Represents formulation associated with maximum application rates for the U.S. with the exception of Texas (back rubbers and spray) 3 0.046

24 0.027

Wettable powder/flowable concentrate (25) 0.5 0.38 Represents formulation associated with maximum application rates for Texas (dip vat and spray) 3 0.21

24 0.02

Bolded values were used in EDWCs assessment



### To accurately characterize the potential environmental exposure pathways, selecting the appropriate livestock management system and various exposure pathway scenarios is necessary. Several scenarios were considered to estimate the application rate for coumaphos and potential exposure to coumaphos and coumaphoxon for s urface water and groundwater

. A pplication rates

for manure applied to land and runoff from rangeland are based on spray (Texas) or back rubber (rest of the U.S.) application on cattle. Table 3 provides application rates for various scenarios. Detailed descriptions and example calculations of application rates for coumaphos a re also provide d in Appendix A.

It is assumed that there are no surface water and groundwater intakes directly adjacent to CAFOs; therefore, runoff from CAFOs is not co nsidered for the drinking water assessment.

Since the estimated application rate of 0.0004 lbs a.i. /A f or runoff from rangeland is approximately 38 times lower than the application rate for couma p hos

- containing manure, the

EDWCs are based on a single application of the maximum coumaphos

- containing manure for land application

. In general, the recommended application rate of manure is based on the nutrient ( i.e.

, nitrogen, phosphorus and potassium ) requirement s for crop s

. For this assessment, the application rate for manur e applied to pasture and rangeland is based on a 250 lb total

### 4

nitrogen/acre / year requirement for growing warm season perennial grass in Texas (Stichles and

McFarland 1 

### )

.

3 . Estimated Coumaphos Application Rates for Various Scenarios

Sources of a.i.

from Application Scenario Wash

- Off

Fraction Maximum Single

Application Rate (lb/A) Number of

Applications/

Year Maximum

Annual Application Rate (lb/A) Texas: Spray Application (42% flowable concentrate) CAFO manure applied to land a No incorporation of manure into soil

0.02 0.015 1 b 0.015 Incorporation of manure into soil within a day

0.02 0.009 1 b 0.009 Rest of U.S.: Back Rubber Application (11.6% emulsifiable concentration) CAFO manure applied to land a No incorporation of manure into soil

0.027 0.0092 1 b 0.0092

Incorporation of manure into soil within a day

0.027 0.0051 1 b 0.0051

AU = animal unit

a Application rate of coumaphos depends on nutrient management and application method of manure.

b Application rate can be split based on total nitrogen (TN) requirement during the growing season.



### Residues of Concern

The residues of concern (ROC) for human health risk assessment and for tolerance expression are coumaphos and its oxygen analog coumaphoxon (US EPA, 2007). A maximum conversion efficiency of coumaphos to coumaphoxon of 10.2% was derived from available data on photodegradation in water.

Input Parameters and Modeling Approach

A limited environmental fate database for coumaphos indicates that it is persistent ( DT 50 

### of >1

year in aerobic soil ) and slightly mobile to hardly mobile ( K oc 

### = 1874 to 1 0297 L/kg ) in soil according to the FAO classification of mobility in soil (FAO

, 200 0 )

. The major pathway of coumaphos degradation appears to be photodegradation in water (DT 50 

### of 33 hours). A major degradate, oxygen analog coumaphoxon, was detected in an aqueous photodegradation study at a

maximum of 10.2% of applied chemical

. Limited environmental fate data are available for coumaphoxon , which suggest s that it is not per sistent in the terrestrial environment (DT 50 

### of 0.49 to 2.27 days) , but it is mobile (K oc 

### = 198.4 L/kg) in soil according to FAO classification of mobility in soil (FAO

, 200 0 )

. Since the environmental fate data suggest that the fate behavior s of coumaphos and coumaphoxon differ in the environment, EDWCs were estimated independently

for these chemicals.

The EDWCs of coumaphos and coumaphoxon were generated using Tier II PRZM/EXAMS model for surface water and Tier I SCIGROW (Screening Concentr ation in Groundwater Program) for groundwater

. Pesticide Root Zone Model

- Ground Water model ( PRZM

- GW ) was also used for groundwater based on a recent EFED guidance document (US EPA, 2012a).

1 http:// agrilifeextension.tamu.edu/

### 5

Surface Water

The EDWCs were generated using EFED’s standard suite of models. Pesticide Root Zone Model (PRZM v3.12.2, May 12, 2005) and Exposure Analysis Modeling System (EXAMS v2.98.04.06, Apr. 25, 2005) . PRZM and EXAMS are simulation models coupled with the input shell PRZM/EXAMS (PE v5.0, Nov. 15, 2006) to gene rate EDWCs of coumaphos and its major degradate, coumaphoxon

, that may occur in surface water used as drinking water. The PRZM model simulates pesticide movement and transformation from crop application through soil residue processes. The EXAMS model simu lates pesticide loading via runoff and erosion assuming a standard watershed of 172.8 ha that drains into an adjacent standard drinking water

index reservoir with surface area of 5.26 ha and an average depth of 2.74 m. A more detailed description of the i ndex reservoir watershed can be found in Jones et al. , 1998. Standard percent cropped areas (PCA) were used for proposed uses as estimates of the extent of watershed on which crops are grown. The national default for non

- agricultural use (PCA of 1.0) was applied in this assessment according to the current PCA guidance (US EPA 2012b ).

Groundwater

Screening Concentration in Ground water (SCIGROW v2.3, Jul. 29, 2003) is a regression model used as a screening tool to estimate pesticide concentrations found in groundwater used as drinking water. The SCIGROW model and user’s manual may also be downloaded from the

EPA Water Models web

- page ( http://www.epa.gov/oppefed1/models/water/#scigrow ). P ercent Crop Areas (P CAs ) are not used with the SCIGROW model.

In addition, Tier 1 groundwater EDWCs for coumaphos and coumaphoxon, resulting from use as land farming

, were also derived using the PRZM

- GW model (Pesticide Root Zone Model for Groundwater, version 1.0 7 , August 31, 2012), with the GW

- GUI (Graphical User Interface,

version 1.0 7 , August 31, 2012). PRZM

- GW is a one

- dimensio nal, finite

- difference model that estimates the concentrations of pesticides in groundwater. It accounts for pesticide fate in the crop root zone by simulating pesticide transport and degradation through the soil profile after a pesticide is applied to an agricultural field. PRZM

- GW permits the assessment of multiple years of pesticide application (up to 100 years) on a single site. Six standard scenarios, each representing a different region known to be vulnerable to groundwater contaminations, are

avai lable for use with PRZM

- GW for risk assessment purposes. In PRZM

- GW simulations, each

of these standard scenarios was used. PRZM

- GW output values represent pesticide concentrations in a vulnerable groundwater supply that is located directly beneath a rura l agricultural field following many years of pesticide application. Descriptions of all executable versions of current models used in drinking water exposure can be obtained from the URL link : http: //www.epa.gov/oppefed1/models/water/

.

Input Parameters

A summary of the model input parameter values used in PRZM/EXAMS , SCIGROW, and

PRZM

- GW Models are in Table 4 , Table 5

, and Table 6

, respectively. Input parameters were

selected in accordance with EFED’s “ Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides ,” Version 2.1 ( USEPA, 2009 ) . S ample model

### 6

output files are located in Appendix C

. PRZM/EXAMS t ime series for coumaphos and coumaphoxon for the highest surface water EDWCs ( i.e.

, BSS Turf scenario) are also attached in Appendix C

.

Table 4

. PRZM/EXAMS I nput P arameter s for C oumaphos and C oumaphoxon

Parameter Value D ata Source Comments Coumaphos

Maximum A pplication

Rate ( lb a.i./A )
[ kg a.i./ha ] 0.015 [ 0. 0 17 ]

Estimated Appendix A and Table 2 Maximum application rate applied to TX

0.0092 [ 0.01 ] See Appendix A and Table 2 Maximum application rate applied to rest of U.S.

Number of Applications 1 Assumed, however, a pplication rate can be split based on total nitrogen requirement during the growing season. Depth of Incorporation (inches) 0 and 8 http://ohioline.osu.edu/agf

fact/0208.html C ommon practices for application of manure Method of Application Ground application Applied as manure Spray Drift 0 Applied with manure spreader Application Efficiency 1.0 Assumed

Scenario and Application Date (day

- month) PA Turf , 15

- 10

FL Turf , 15

- 10

BSS Turf , 15

- 10 Based on PRZM/EXAMS

Scenarios Assumed manure applied during

dormant season

Molecular Mass (g/mol) 362.5 US EPA 2007

---

Vapor Pressure (Torr) 1.0 x 10

- 07 US EPA 2007

--- Henry’s Law Constant (atm m3/mol) 2.62 x 10

- 07 Estimated ==

Solubility in Water (mg/L) 20 US EPA 2007

---
Hydrolysis t 1/2 at pH 7.0 (days) 0 Not Available Considered stable to hydrolysis @ pH 7.0 Aquatic Photolysis t 1/2 (days) 1.38 MRID 42764101

MRID 43103901 Coumaphoxon is a major

degradate (10.2%)

Aerobic Soil

Metabolism t 1/2 (d ays ) 0 MRID 40518701 Considered stable

Aerobic Aquatic

Metabolism t 1/2 (d ays ) 0

--- Input parameter guidance (USEPA, 2009)

Soil Partitioning

Coefficient (K

oc ; ml/ g o ) 5904 MRID 45721401 Represent s average K Foc from 4

soils

Wetted in? No

--- Assumed Percent Crop Area (Decimal) 1.0 US EPA 2012b Recommended PCA for non

agricultural uses Coumaphoxon

Maximum A pplication

Rate ( lb a.i./A )
[ kg a.i./ha ] 0. 0015 [ 0. 0 017 ] Estimated 1

---

Number of Applications 1 Assumed Based on application rate of coumaphos Depth of Incorporation (inches) 0 Assumed

---

### 7

Table 4

. PRZM/EXAMS I nput P arameter s for C oumaphos and C oumaphoxon

Parameter Value D ata Source Comments

Method of Application Not applicable

--- Degradation product of coumaphos

Scenario and Application Date (day

- month) BSS Turf, 15

- 10 Based on PRZM/EXAMS

Scenarios Assumed manure applied during

dormant season

Molecular Mass (g/mol) 346.7 EPISUITE Estimated value

Vapor Pressure (Torr) 7.68 x 10

- 08 EPISUITE Estimated value Henry’s Law Constant (atm m3/mol) 1.10 x 10

- 09 EPISUITE Estimated value

Solubility in Water (mg/L) 31.6 EPISUITE 4.1 Estimated value

Hydrolysis t 1/2 at pH 7.0 (days) 0 Not available Assumed stable

Aquatic Photolysis t 1/2 (days) 0 Not available Assumed stable

Aerobic Soil

Metabolism DT 50 (d ays ) 4.1 MRID 48705501 90 th percentile upper confidence

bound on the mean half

- life of coumaphoxon Aerobic Aquatic

Metabolism t 1/2 (d ays ) 8. 2 2

--- 2X of Aerobic Soil Metabolism

DT 50 (days) Soil Partitioning

Coefficient (K

oc ; ml/g

oc ) 198.4 EPISUITE 4.1 Estimated value

Percent Crop Area (Decimal) 1.0 US EPA 2012c Recommended PCA for non

agricultural uses

1 Coumaphos application rate (0. 015 lb a.i/A) x [(0.102, the maximum conversion rate from aquatic photolytic degradation of coumaphos to coumaphoxon in laboratory studies) x (0.96, the molecular weight ratio of coumaphos to coumaphoxon)]

2 In the absence of a aerobic aquatic metabolism study, 2X of aerobic soil metabolism DT 50 value was m ultiplied by 2 according to “ Guidance for selecting input parameters in modeling for environmental fate and transport of pesticides. ” Version 2.1 October 22, 2009.



### Table 5 . SCI

- GROW (v2.3) Input Parameter Values for Coumaphos and Coumap h oxon

Parameter Value Data Source Comments

Coumaphos

Maximum Application Rate (lbs a.i./acre) [kg a.i./ha] 0. 015 [0.017] Table 2 ---

Number of

A pplications 1 Table 4

---

K Foc (mL/g) 1870 MRID 45721401 Since there is a threefold difference in observed values, the lowest non

- sand

K FOC value used.

Aerobic S oil

M etabolism DT 50 (days) 0 MRID 45118631 Stable

Coumaphoxon

Maximum A pplication 0. 0015 (0. 0017 ) Table 4

---

### 8

Table 5 . SCI

- GROW (v2.3) Input Parameter Values for Coumaphos and Coumap h oxon

Parameter Value Data Source Comments

Rate lb a.i./A (kg a.i./ha)

Number of

A pplications 1 Table 4

---

K
oc (mL/g) 198.4 EPISUITE 4.1 Estimated value

Aerobic soil metabolism (DT 50 ) d 4.1 MRID 48705501 90 th percentile upper confidence bound

on the mean half

- life of coumaphoxon



### Table 6 . PRZM

- GW (v 1. 7 ) Input Parameter Values for Coumaphos and Coumap h oxon

Parameters Value Data Source Comment s Coumaphos Application Method Ground Table 4

--- Application Rate (lbs. a.i./acre) [kg a.i. /ha] 0. 015 [0. 017 ] Table 2

---

Application Frequency 1 Table 4

---

Hydrolysis (DT 50 ) (days) S table

--- No study

Aerobic soil metabolism (DT 50 ) ( d ays) 1095 1 MRID 45118631 Stable. Assumed 3X of duration of study

K
oc 5904 L/ Kg MRID 46808411 Average K Foc 2

Coumaphoxon
Application Method Ground Table 4

--- Application Rate (lbs. a.i./acre) [kg/ha] 0. 0015 [0. 0017 ] Table 2

---

Application Frequency 1 Table 4

---

Hydrolysis (DT 50 ) ( d ays) 0 Not available Assumed stable 2

Aerobic soil metabolism (DT 50 ) ( d ays) 4.1 2 MRID 48705501 90 th percentile upper confidence bound

on the mean half

- life of coumaphoxon

K
oc 198.4 EPISUITE 4.1 Estimated value

1 Model requires a numerical value for DT 50 was estimated using the NAFTA degradation kinetics procedure and did not have a recommendation for modeling (Figure 1, Appendix B). In addition, the estimated Single First Order (SFO) DT 50 of 2761 days is well beyond the duration of study. Therefore, 3x of duration ( i.e.

, 3 x 365 day) of aerobic soil metabolism study was used in the modeling

2 EFED input parameter guidance http://www.epa.gov/oppefed1/models/water/przm_gw/wqtt_przm_gw_input_guidance.htm



### Results

Drinking water e stimated coumaphos concentrations in surface water and groundwater are

summarized in Table s 6 and 7

. Sample o utput from model runs are provided in Appendix C

.

### 9

PRZM/EXAMS model concentrations (μg/L) represent untreated surface water concentrations.

The SCIGROW and PRZM

- GW concentrations represent groundwater concentration s that might be expected in shallow unconfined aquifers under sandy soils. All scenarios run in PRZM

- GW required the use of an extended weather file, which allows the user to run the sim ulation for up to 100 years in order to observe breakthrough into shallow groundwater

. N o breakthrough of coumaphos in shallow groundwater was observed using 100

- year PRZM

- GW simulations. However, b reakthroughs were observed for coumaphoxon for four scenar ios ( Table 7 )

.

The simulated concentrations provided in this assessment are conservative estimates of concentrations in drinking water. If dietary risks require refinement, higher

- tiered, crop

- specific

and location

- specific models and modeling scenarios can be used.

Table 6

. Maximum EDWCs Based on Manure Containing Coumaphos and its Degradate Coumaphoxon application

Drinking Water Source Crop Scenario 1

- in

- 10 year

acute (μg/L) 1

- in

- 10 year

chronic (μg/L) 30

- year annual

average (μg/L) Coumaphos

Non

- incorporated Manure

Surface Water 1 BSS Turf 0.10 0.05 0.03

FL Turf 0.05 0.03 0.02

PA Turf 0.08 0.05 0.03 Incorporated Manure 2

BSS Turf 0.01 0 0

Groundwater Generic Scenario 3 1.91 x 10

- 03 1.91 x 10

- 03 1.91 x 10

- 03
Coumaphoxon

Surface Water BSS Turf 0.002 0 0

Groundwater GenericScenario 3 5.04 x 10

- 06 5.04 x 10

- 06 5.04 x 10

- 06

1 EDWCs generated using PRZM/EXAMS model

2 EDWCs were generated for the highest non

- incorporated scenario (BSS turf) for surface water

3 EDWCs generated using SCIGROW model and can be considered for both acute and chronic values



### Table 7 . PRZM

- GW EDWCs Based on Manure Containing Coumaphos and its Degradate Coumaphoxon

Application Rate and Frequency Scenario 1 Highest Daily Value ( μ g/L) Post

Breakthrough Average ( μ g/L) Average Simulation

Breakthrough Time (days)

0.015 lbs a.i./A x 1 application 

### Coumaphos

FL Citrus 0.185 2 Not Reported Incomplete

FL Potato 3.22 x 10

- 06 2 Not Reported Incomplete
GA peanut 2.74 x 10

- 06 2 Not Reported Incomplete

NC Cotton 0.038 2 Not Reported Incomplete

Delmarva sweet corn 0.003 2 Not Reported Incomplete

WI corn 4.98 x 10

- 04 2 Not Reported Incomplete 

### Coumaphoxon

0.0015 lbs a.i./A x 1 application FL Citrus 5.02 x 10

- 12 4.78 x 10

- 12 30012

FL potato 0 2 0 2 Incomplete
GA peanut 9.14 x 10

- 18 2 Not Reported Incomplete

NC cotton 2.65 x 10

- 17 2.61 x 10

- 17 29441

Delmarva sweet corn 2.02 x 10

- 16 1.77 x 10

- 16 24107

### 10

Table 7 . PRZM

- GW EDWCs Based on Manure Containing Coumaphos and its Degradate Coumaphoxon

Application Rate and Frequency Scenario 1 Highest Daily Value ( μ g/L) Post

Breakthrough Average ( μ g/L) Average Simulation

Breakthrough Time (days)

WI corn 2.49 x 10

- 14 2 Not Reported Incomplete

1 These scenarios are regional vulnerable sites for groundwater evaluation.

2 Since there is no breakthrough with 100

- yr PZRM

- GW simulation, the reported values are not reliable.



### Monitoring Data

There w ere no national

- scale or state monitoring data available for this assessment.

Drinking Water Treatment
There is no available information on the drinking water treatment effects on coumaphos and coumaphoxon.

Uncertainties

The main uncertainty associated with this drinking water asse ssment is the lack of acceptable environmental fate data for coumaphos and its degradate coumaphoxon. Limited data are available for coumaphos and its degradate, coumaphoxon. Supplemental photodegradation in water data (MRID 42764101 and 42764102) indicat e that the maximum coumaphoxon concentration at any sampling time was 10.2% of coumaphos application rate. This conversion rate was used to estimate a coumaphoxon application rate.

In addition, there is an additional uncertainty related to the e stimated DT 50 

### value, which is approximately 7X higher than the duration of the aerobic soil metabolism study and 15 to 23X higher than the reported field dissipation half

- lives. Groundwater concentrations were based on

3X of the duration of the aerobic soi l metabolism study.

In this drinking water assessment, EFED attempted to locate the best available data/models for estimating coumaphos and its degradate, coumaphoxon

, residues in drinking water sources

, CAFO manure applied to land, and potential runoff from rangeland. EFED used wash

- off

fractions for the 24

- hour drying time in this assessment because they represent a reasonable time frame after application for a treated cow to be caught in a rainstorm. Potential exposure could be higher or lower depending on CAFO operations such as : indoor versus outdoor facilit ies

, number of cattle treated/day, and other variables associated with manure management for crop production as well as weather conditions. Un certainty associated with each of these individual components could potentially dictate higher or lower E DW Cs.

### 11 References

ASAE. 2005. Manure Production and Characteristics. ASAE Standard D384.1 FEB 03.American Society of Agricultural Engineers. St. Joseph, MI

FAO 2000. Appendix 2. Parameters of pesticides that influence processes in the soil 

### . In FAO

Information Division Edi torial Group (Ed.), Pesticide Disposal Series 8. Assessing Soil Contamination. A reference Manual, Rome: Food and Agricultural Organization of the

United Nations. Available at http://www.fa o.org/DOCREP/003/X2570E/X2570E06.htm (Accessed April 10, 2013).



### USDA. 2008. Agricultural Waste Management Field Handbook, Part 651. Natural Resources Conservation Services, U.S. Department of Agriculture, Washington, D.C.

US EPA, 2013 a . Drinking Water Assessment for Registration Review of Coumaphos. Environmental Fate and Effects Division, Office of Chemical Safety and Pollution Prevention. U. S. Environmental Protection Agency.(DP 409560)

US EPA, 2013b. Revised Drinking Water Assessme nt for Registration Review of Coumaphos. Environmental Fate and Effects Division, Office of Chemical Safety and Pollution Prevention. U. S. Environmental Protection Agency.(DP 409560)

US EPA. 2012a. Memorandum: Approval of PRZM

- GW for use of Drinking Water Exposure Assessment. Environmental Fate and Effects Division, Office of Chemical Safety and Pollution Prevention. U. S. Environmental Protection Agency.

US EPA. 2012b . Memorandum: NAFTA Guidance for Evaluati ng and Calculating Degradation

Kinetics in Environmental Media. Environmental Fate and Effects Division, Office of Chemical Safety and Pollution Prevention. U. S. Environmental Protection Agency.

US EPA. 2012c

. Development and Use of Percent Cropped Area and Percent Turf Area Adjustment Factors i n Drinking Water Exposure Assessments: 2012 Update http://www.epa.gov/oppefed1/models/water/pca_adjustment_dwa.html

US EPA, 2009. Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides, Version II. U. S. Environmental Protection Agency. Washington, D.C. http://www.epa.go v/oppefed1/models/water/

US EPA. 2007. Coumaphos: Human Health Risk Assessment for Proposed Use on Honey and Honeycomb. PC Code: 036501; Petition Number: 2E6504; DP Number: D315769.

US EPA. 2008. Memorandum: EFED Response to Comments for Coumaphos Registration Review Regarding Data Needed to Refine Ecological Risk Assessment Environmental Fate and Effects Division, Office of Chemical Safety and Pollution Prevention. U. S. Environmental Protection Agency (DP Barcode D347373).

### 12

US EPA, 2000. Reregistr ation Eligibility Decision Addendum and FQPA Tolerance Reassessment Progress Report: Coumaphos. Office of Prevention, Pesticides, and Toxic

Substances. United States Environmental Protection Agency. EPA 738

- R

- 00

- 010

.

US EPA. 1998. Coum a phos

- EFED Reply to Registrant’s Rebuttal. Office of Prevention,
Pesticides and Toxic Substances, DP Barcodes D230394 and D239676

US EPA. 1994

. Coumaphos (36501) Reregistration Case No. 0018. Product and Residue Chemistry Chapters for the Coumaphos Reregistration Eligibil ity Decision (RED)

Document. DP Barcode D207352

.

### 13 Appendix A

The maximum single application rate ( i.e. , 0.027 lb a.i./animal for dip vat 2 

### ) and the maximum annual application rate ( i.e. , 0.063 lb

a.i./animal for spray 3 

### ) for cattle are for the end

- use product Co

- Ral ® Flowable Insecticide (EPA Reg. no. 11556

- 98). U se of this product is restricted to employees of the USDA

- APHIS who are enrolled in the USDA

- APHIS cholinesterase monitoring program 

### . The

USDA’s Cattle Fever Tick Eradication Program (CFTEP) uses this product solely in Texas. As a result, these maximum application

rates were used to assess exposures in drinking water sources in Texas only. The next highest maximum single application rate ( i.e.

, 0.01 lb a.i./A for dust or spray 4 

### ) and maximum annual application rate for cattle ( i.e. , 0.05 lb a.i./animal for back rubbers 5 

### ) were used

to assess exposures in drinking water sources in the rest of the United States.



## Table A

- 1. Application Information for Regis tered Uses of Coumaphos: Cattle a,b,c

Use Application

Method/ Equipment Form.

(% a.i.) Maximum Single

Application Rate Annual

Number of Applications Minimum

Application

Interval (Days) Maximum

Annual Application

Rate d
(lb a.i./animal) Comments

(lb a.i./ animal) (lb a.i./

gal)

Beef/range/ feeder cattle; dairy cattle Back rubbers EC (11.6) 0.00829 (avg.; est.) 0.0762 3.5 (avg.) NS or AS 0.029 --

Back rubbers EC (6.2) 0.00829 (avg.; est.) 0.0385 6 or NS 10 or NS 0.050 Represents maximum annual application rate for the U.S. with the exception of

Texas

Dip vat FC (42) 0.027 (est.) 0.0255 e 2 10 0.054 EPA Reg No. 11556

- 98; use restricted to employees of the USDA

- APHIS Represents maximum annual application

rate for Texas

Dust Dust (1) 0.01 3 (avg.) NS 0.03 Represents maximum single application rate for the U.S. with the exception of

Texas

Dust Dust (1) 0.0013 3 (avg.) 10 or 14 0.0039

-- Dust Dust (1) 0.000625 3 (avg.) 1 0.0019

--

2 2 applications @ 0.027 lb a.i./animal = 0.054 lb a.i./animal/yr for dip vat

3 3 applications @ 0.021 lb a.i./animal = 0.063 lb a.i./animal/yr for spray

4 3 applications @ 0.01 l b a.i./animal = 0.03 lb a.i./animal/yr for spray or dust

5 6 applications @ 0.00829 lb a.i./animal = 0.05 lb a.i./animal/yr for back rubbers

### 14



## Table A

- 1. Application Information for Regis tered Uses of Coumaphos: Cattle a,b,c

Use Application

Method/ Equipment Form.

(% a.i.) Maximum Single

Application Rate Annual

Number of Applications Minimum

Application

Interval (Days) Maximum

Annual Application

Rate d
(lb a.i./animal) Comments

(lb a.i./ animal) (lb a.i./

gal)

Spray FC (42) 0.021 (est.) 0.021 3 (avg.) 10 0.063 EPA Reg No. 11556

- 98; use restricted to employees of the USDA

- APHIS Represents maximum single application

rate for Texas

Spray EC (6.2) 0.01 (est.) 0.01 3 (avg.) 10 0.03 Represents maximum single application rate for the U.S. with the exception of

Texas

Spray EC (11.6) 0.00978 (est.) 0.00978 3 (avg.) AS 0.029 --

Ear Tag IM (20) 0.00625 3 (avg.) NS 0.019

--

AS = as needed; avg. = average; est. = estimated (by BEAD); NS = not specified; EM = emulsifiable concentrate; FC = flowable concentrate; Form. = formulation; IM = impregnated material; Max. = Maximum; Min. = Minimum; NA = not applicable; RTU = ready to us e

a label data report (Label Use Information System report; LUIS) dated September 13, 2007

b application information for maximum single and annual rates in BOLD

c estimated/average values provided by BEAD

d not specified on label; calculated based on maxi mum single application rate and maximum annual number of applications

e 0.306% suspension

### 15

In registrant

- submitted wash

- off studies, fresh cow hides were treated with either Co

- Ral® 11.6% emulsifiable liquid (MRID 42512601) or Co

- Ral® 25% wetta ble powder (MRID 42512602) and then dried for 0.5, 3, or 24 hours. The wash

- off fraction was measured after hides had been soaked in water for 0.5, 1, 1, or 4 hours. Results of these studies indicate that

wash

- off fraction is inversely related to drying time and dependent upon the formulation ( Table

A

- 2 ) but not affected by soaking time (data not shown). Although not the most conservative,

wash

- off fractions for the 24

- hour drying time were used in this assessment because they represent a reasonable time frame after application for a treated cow to be caught in a rainstorm.

Table A

- 2 . Percent Wash

- Off for Different Formulations of Coumaphos at Different Drying Times (MRIDs 42512601 and 42512602)

Formulation (%) Drying Time (hrs) Wash

- Off Fraction a

Emulsifiable powder/concentrate (11.6) 0.5 0.116

3 0.046

24 0.027

Wettable powder/flowable concentrate (42) 0.5 0.38

3 0.21

24 0.20

a Bolded values were used in the aquatic exposure assessment



### To accurately characterize the potential environmental exposure pathways, selecting the appropriate livestock management system and various exposure pathway scenarios is necessary.

T wo scenarios were considered to estimate the application rate of coumaphos for drinking water

assessment. The fol lowing scenarios and example calculations of application rates are based on spray application on cattle. Table A

- 3 provides application rates for various scenarios.

Table A

- 3 . Estimated Coumaphos Application Rates for Various Scenarios

Sources of a.i. from Application Scenario Wash

- Off

Fraction Maximum Single

Application Rate (lb/A) Number of

Applications/

Year Maximum

Annual Application Rate (lb/A) Texas: Spray Application (42% flowable concentrate) CAFO manure applied to land a No incorporation of manure into soil

0.02 0.015 1 b 0.015 Incorporation of manure into soil within a day

0.02 0.009 1 b 0.009 Runoff from range land 0.02 0.00013 3 0.0004 Rest of U.S.: Back Rubber Application (11.6% emulsifiable concentration) CAFO manure applied to land a No incorporation of manure into soil

0.027 0.0092 1 b 0.0092

Incorporation of manure into soil within a day

0.027 0.0051 1 b 0.0051 Runoff from range land 0.027 0.0001 3 0.0003

AU = animal unit

a Application rate of coumaphos depends on nutrient management and application method of manure.

b Application rate can be split based on total nitrogen (TN) requirement during the growing season.

### 16

Example Calculation: Manure from CAFOs (Concentrated Animal Feeding Operation)

Manure is a valuable soil amendment/organic fertilizer for any farming operation and has been used for centuries to supply needed nutrients for crop growth. Manure not only supplies many beneficial nutrients for crop production, but could also be a potent ial source for pesticides that

are embedded into manure from wash

- off from treated livestock. Application rate of coumaphos was estimated based on dry weight of manure application for crop production. The following steps were used to calculate the applica tion rate of coumaphos.

Example Calculations: Manure from CAFOs (Concentrated Animal Feeding Operation

Step 1 : Total dry weight of manure (DM)/AU(animal unit) /year

DM = 8.5 lb solid in manure [ASAE, 2003] /AU x 365 days = 3103 lb dry manure/AU/year or 1.55 tons/AU/year

Step 2 : Active ingredient in manure (AM) lb a.i./AU

AM = (A x F x S x W x PA) lb a.i./AU/year

Where: A = application rate: 0.021 lb/AU for spray application ( Table A

- 1 ) F = frequency of application: 3/AU/year ( Table A

- 1 )

S = # of stocking/year: 4 (Based on 90

- 120 days stocking period for cattle in feedlot 6 

### )

W = wash

- off fraction: 0.02 (Texas; coumaphos formulations restricted to APHIS) or 0.027 (for non

- restricted coumaphos formulations; rest of the U.S.) ( MRIDs 42512601

and 425126 02) PA = potential fraction of coumaphos washed off of cattle during a rain event that can come into contact with and adsorb to manure: 0.36 (assumed based on EPISUITE estimate for adsorption into sludge)

Sample calculation is based on Co

- Ral ® Flowable Insecticide: AM = (0.021 x 3 x 4 x 0.02 x 0.36) = 0.0018 a.i. lb/AU

Step 3 : Active ingredient in manure (lb a.i./ton)

(0.0018 lb a.i./1.55 ton manure) = 0.0012 lbs a.i./ton dry manure

Step 4: Total nitrogen production (TN) per animal (lbs TN/ AU/year)

TN = (N x L x V x D) lbs TN/AU/year

Where: N = nitrogen content in manure per AU (TN lb/AU) (ASABE, 2003)

6 http :// www.epa.gov/agriculture/ag101/beefproducts.html

### 17

L = average fraction of N retained during storage and handling: 0.5 (Table 11.5, USDA, 2008). The range of N retention varies from 40 to 60 for arid region and 55 to 70 in humid region. V= Fraction of N loss due to volatilization: 0.1 (based on next day incorporation into soil after application in warm wet soil condition) to 0.5 (based on no incorporation for seven days into soil) (Table 11.6, USDA, 2006). The range of volatility loss varies from 50 percent in warn dry soil to 10 percent in cool wet soil. In addition, volatility loss may also depend on method of manure application (i.e. 5% and 25% volatilization loss from injection and sprinkling methods respectively. Since there is an inverse relationship between volatilization loss and application rate o f manure, the highest and lowest volatilization rate was considered to calculate application rate of coumaphos. D = 365 of days /year

Sample calculation: TN = (0.34 x 0.5 x 0.5 x 365) = 31 lbs TN in manure/AU/year [For no incorporation for seven days under warm dry soil scenario]

Step 5 : Total N in manure (lb/ton manure)

(31 lbs TN/1.55 ton manure) = 20 lbs TN/ton manure/AU

Step 6: Application rate of manure (ton/acre)

In general, the application rate of manure is based on TN recommendation for cro p types. For example, 250 lb TN/acre per year requires for growing warm season perennial grass in Texas 7



### .

Sample calculation: (250 lbs TN/acre) x (1 ton Manure /20 lbs TN) 12.5 tons manure/acre require for growing perennial grass in Texas

Step 7: Appli cation rate of active ingredient (lb/acre)

(0.0012 lbs a.i/ton) x (12.5 tons manure/acre) = 0.015 lbs a.i./acre

Therefore, the application rate of 0.015 lbs a.i/A is based on 2% coumaphos wash

- off from

treated cattle.

Example Calculation: Cattle Grazing in Rangeland

Runoff of washed

- off coumaphos from treated cattle could be a major contributor from treated cattle grazing on rangeland. Application rate was estimated from runoff contribution based on

wash

- off of coumaphos and animals stocking rat e per acre.

7 Stichles and McFarland, http://agrilifeextension.tamu.edu/

### 18

Application Rate (AR) of active Ingredient (lbs/Acre) AR = (A x F x C x W)

Where: A = application rate: 0.021 lb/AU (spray application) F = frequency of application: 3 (spray application) C = # of AU in pasture/land: 0.3 was based on 800 lbs cattle (Pratt and Rasmaussan, 2001). There is an inverse relationship between weight of cattle and number of AU in pasture/land. Numbers of AU on pasture land also depends on the size of cattle and forage production.

W = wash

- off fraction: 0.02 (Texas) or 0.027 (rest of the U.S.) ( MRIDs 42512601 and 42512602)

Sample calculation: AR = (0.021 x 3 x 0.3 x 0.02) = 0.0004 lb s /A

### 19 Appendix B

Figure 1. Aerobic Soil Degradation Kinetics (MRID 48705501)

### 20 Appendix C

- Model Outputs

Surface Water

Sample PRZM/EXAMS Output

stored as TX_M02_D.out

Chemical: Coumaphos

PRZM environment: TurfBSS.txt, modified Wedday, 31 July 2013 at 14:00:27

EXAMS environment: ir298.exv,modified Tueday, 26 August 2008 at 06:14:08

Metfile: w13958.dvf, modified Tueday, 26 August 2008 at 06:14:44

Water segment concentrations (ppb)

Year Peak 96 hr 21 Day 60 Day 90 Day Yearly

1961 0.01 0.01 0.00 0.00 0.00 0.00

1962 0.02 0.02 0.01 0.01 0.01 0.00

1963 0.02 0.02 0.02 0.01 0.01 0.01

1964 0.07 0.06 0.05 0.04 0.03 0.02

1965 0.06 0.06 0.05 0.04 0.04 0.03

1966 0.05 0.04 0.04 0.04 0.03 0.03

1967 0.06 0.06 0.05 0.04 0.04 0.03

1968 0.05 0.05 0.04 0.04 0.04 0.04

1969 0.04 0.04 0.04 0.04 0.03 0.03

1970 0.06 0.06 0.05 0.04 0.04 0.03

1971 0.03 0.03 0.03 0.03 0.03 0.03

1972 0.05 0.04 0.04 0.03 0.03 0.03

1973 0.06 0.06 0.05 0.04 0.04 0.03

1974 0.11 0.10 0.08 0.05 0.04 0.03

1975 0.08 0.07 0.06 0.05 0.05 0.05

1976 0.07 0.07 0.06 0.05 0.05 0.04

1977 0.05 0.05 0.05 0.04 0.04 0.04

1978 0.08 0.08 0.06 0.05 0.04 0.04

1979 0.10 0.10 0.08 0.06 0.06 0.05

1980 0.06 0.06 0.06 0.05 0.05 0.05

1981 0.15 0.14 0.11 0.08 0.08 0.06

1982 0.08 0.08 0.07 0.06 0.06 0.06

1983 0.05 0.05 0.05 0.05 0.05 0.05

1984 0.05 0.05 0.04 0.04 0.04 0.04

1985 0.05 0.05 0.04 0.04 0.04 0.04

1986 0.06 0.05 0.05 0.04 0.04 0.04

1987 0.06 0.06 0.05 0.05 0.04 0.04

1988 0.04 0.04 0.04 0.04 0.04 0.03

1989 0.04 0.03 0.03 0.03 0.03 0.03

1990 0.06 0.05 0.04 0.04 0.03 0.03

### 21

Sorted results

Prob. Peak 96 hr 21 Day 60 Day 90 Day Yearly

0.03 0.15 0.14 0.11 0.08 0.08 0.06

0.06 0.11 0.10 0.08 0.06 0.06 0.06

0.10 0.10 0.10 0.08 0.06 0.06 0.05

0.13 0.08 0.08 0.07 0.05 0.05 0.05

0.16 0.08 0.08 0.06 0.05 0.05 0.05

0.19 0.08 0.07 0.06 0.05 0.05 0.05

0.23 0.07 0.07 0.06 0.05 0.05 0.04

0.26 0.07 0.06 0.06 0.05 0.04 0.04

0.29 0.06 0.06 0.05 0.05 0.04 0.04

0.32 0.06 0.06 0.05 0.05 0.04 0.04

0.35 0.06 0.06 0.05 0.04 0.04 0.04

0.39 0.06 0.06 0.05 0.04 0.04 0.04

0.42 0.06 0.06 0.05 0.04 0.04 0.04

0.45 0.06 0.06 0.05 0.04 0.04 0.04

0.48 0.06 0.05 0.05 0.04 0.04 0.03

0.52 0.06 0.05 0.05 0.04 0.04 0.03

0.55 0.05 0.05 0.05 0.04 0.04 0.03

0.58 0.05 0.05 0.04 0.04 0.04 0.03

0.61 0.05 0.05 0.04 0.04 0.04 0.03

0.65 0.05 0.05 0.04 0.04 0.04 0.03

0.68 0.05 0.05 0.04 0.04 0.03 0.03

0.71 0.05 0.04 0.04 0.04 0.03 0.03

0.74 0.05 0.04 0.04 0.04 0.03 0.03

0.77 0.04 0.04 0.04 0.04 0.03 0.03

0.81 0.04 0.04 0.04 0.03 0.03 0.03

0.84 0.04 0.03 0.03 0.03 0.03 0.03

0.87 0.03 0.03 0.03 0.03 0.03 0.02

0.90 0.02 0.02 0.02 0.01 0.01 0.01

0.94 0.02 0.02 0.01 0.01 0.01 0.00

0.97 0.01 0.01 0.00 0.00 0.00 0.00

0.1 0.10 0.09 0.08 0.06 0.06 0.05

Average of yearly

averages: 0.03

Inputs generated by pe5.pl

- Novemeber 2006

Data used for this run:

Output File: TX_M02_D

Metfile: w13958.dvf

### 22

PRZM

scenario: TurfBSS.txt

EXAMS

environm

ent file: ir298.exv

Chemical

Name: Coumaphos

Descripti

on Variable

Name Value Units Comments

Molecula r weight mwt 362.5 g/mol

Henry's

Law

Const. henry 2.62E

- 09 atm

- m^3/mol

Vapor

Pressure vapr 1.00E

- 07 torr

Solubility sol 20 mg/L

Kd Kd mg/L

Koc Koc 5904 mg/L

Photolysi

s half

- life kdp 1.38 days Half

- life

Aerobic Aquatic

Metabolis

m kbacw 0 days Halfife

Anaerobi c Aquatic

Metabolis

m kbacs 0 days Halfife

Aerobic

Soil

Metabolis

m asm 0 days Halfife

Hydrolysi

s: pH 7 0 days Half

- life

Method: CAM 1 integer See PRZM manual

Incorpora

tion Depth: DEPI cm

Applicati

on Rate: TAPP 0.017 kg/ha

Applicati

on Efficienc

y: APPEFF 1 fraction

Spray

Drift DRFT 0 fraction of application rate applied to pond

Applicati

on Date Date 15

- 10 dd/mm or dd/mmm or dd

- mm or dd

- mmm

Record

17: FILTRA

IPSCND 1

UPTKF

### 23 PRZM/EXAMS Time Series

Ground water

Sample SCIGROW Outputs

SCIGROW VERSION 2.3

ENVIRONMENTAL FATE AND EFFECTS DIVISION

OFFICE OF PESTICIDE PROGRAMS

U.S. ENVIRONMENTAL PROTECTION AGENCY

SCREENING MODEL
FOR AQUATIC PESTICIDE EXPOSURE

SciGrow version 2.3 chemical:Coumaphos time is 5/22/2014 10:25: 9

------------------------------------------------------------------------ Application Number of Total Use Koc Soil Aerobic rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism (days)

------------------------------------------------------------------------ 0.015 1.0 0.015 1.87E+03 1095.0

------------------------------- -----------------------------------------

groundwater screening cond (ppb) = 1.91E

- 03

************************************************************************

SciGrow version 2.3

chemical: Coumaphoxon time is 5/22/2014 10:27:30

------------------------ ------------------------------------------------ Application Number of Total Use Koc Soil Aerobic rate (lb/acre) applications (lb/acre/yr) (ml/g) metabolism (days)

------------------------------------------------------------------- ----- 0.002 1.0 0.002 1.98E+02 4.1

------------------------------------------------------------------------

groundwater screening cond (ppb) = 5.04E

- 06

************************************************************************

### 24 Sample PRZM

- GW Outputs

Groundwater Analysis for Coumaphos and the Florida Citrus

- FL Central Ridge, Polk County

- (Tampa) Met File (12842.Dvf)

- Astatula Sand, Hrgb A Scenario

Estimated groundwater concentrations and breakthrough times for Coumaphos are presented in

Table 1 for the Florida Citrus

- FL Central Ridge, Polk County

- (Tampa) Met File (12842.dvf)

- Astatula sand, hrgb A groundwater scenario. A graphical presentation of the daily concentrations in the aquifer is presented in Figure 1. These values were generated with the PRZM

- GW (Version 1.07). Critical input values for the model are summarized in Tables 2 and 3.

Table 1. Groundwater Results for Coumaphos and the Flor ida Citrus

- FL Central Ridge, Polk County

- (Tampa) Met File (12842.dvf)

- Astatula sand, hrgb A Scenario.

Peak Concentration (ppb) 0.185

Post

- Breakthrough Mean Concentration (ppb) Incomplete

Entire Simulation Mean Concentration (ppb) 0.0476

Avera ge Breakthrough Time (days) Incomplete

Throughputs 0.6034609

Table 2. Chemical Properties for Groundwater Modeling of Coumaphos.

Koc (ml/g) 5905

Surface Soil Half Life (days) 1095

Hydrolysis Half Life (days) 0

Diffusion Coefficint Air (cm2/day) 0.0

Henry's Constant 0.0

Enthalpy (kcal/mol) 0.0

Table 3. Pesticide application scheme used for Coumaphos. This application scheme was applied every year of the simulation.

Application Date

(Month/Day) Application Method Application Rate

(kg/ha)

10/15 Ground application with mass

distribution increasing proportionally with depth to 4 cm 0.017

### 25

Figure 1. Aquifer Breakthrough Curve for Coumaphos and the Florida Citrus

- FL Central Ridge, Polk County

- (Tampa) Met File (12842.Dvf)

- Astatula Sand, Hrgb A Scenario

Groundwater Analysis for Coumapho xon and the Florida Citrus

- FL Central Ridge, Polk County

- (Tampa) Met File (12842.Dvf)

- Astatula Sand, Hrgb A Scenario

Estimated groundwater concentrations and breakthrough times for Coumaphos are presented in

Table 1 for the Florida Citrus

- FL Central Ridge, Polk County

- (Tampa) Met File (12842.dvf)

- Astatula sand, hrgb A groundwater scenario. A graphical presentation of the daily concentrations in the aquifer is presented in Figure 1. These values were generated with the PRZM

- GW (Version 1.07). Critical input values for the model are summarized in Tables 2 and 3.

Table 1. Groundwater Results for Coumaphos and the Florida Citrus

- FL Central Ridge, Polk County

- (Tampa) Met File (12842.dvf)

- Astatula sa nd, hrgb A Scenario.

Peak Concentration (ppb) 5.02E

- 12

Post

- Breakthrough Mean Concentration (ppb) 4.78E

- 12

Entire Simulation Mean Concentration (ppb) 2.49E

- 12

Average Breakthrough Time (days) 30012.66

Throughputs 1.204892

Table 2. Chemical Properties for Groundwater Modeling of Coumaphos.

Koc (ml/g) 2922

Surface Soil Half Life (days) 4.1

### 26

Hydrolysis Half Life (days) 0

Diffusion Coefficint Air (cm2/day) 0.0

Henry's Constant 0.0

Enthalpy (kcal/mol) 0.0

Table 3. Pesticide application scheme used for Coumaphos. This application scheme was applied every year of the simulation.

Application Days

Relative to Emergence Date (01/01) Application Method Application Rate

(kg/ha)

0 Ground application with mass

distribution increasing proportionally with depth to 4 cm 0.0017

Figure 1. Aquifer Breakthrough Curve for Coumaphos and the Florida Citrus

- FL Central Ridge, Polk County

- (Tampa) Met File (12842.Dvf)

- Astatula Sand, Hrgb A Scenario