Nick Poletikaa

Brian Breta

Mike Winchellb

a Dow AgroSciencs LLC

b Stone Environmental, Inc.

1
Background

 Pronamide (propyzamide) is a soil-applied herbicide 

registered for use on numerous crops to control a wide 

variety of weeds.

 It is difficult to pass an FQPA dietary risk assessment 

due to a cancer endpoint attributed to total residues of 

concern (parent + multiple metabolites) and modeled 

30-year average drinking water exposure estimates that 

range from 10.8 to 105 μg L-1for surface water sources.

 Regulatory approval of use on leaf lettuce cannot be 

granted unless exposure can be shown to be negligible.

2
Proposed Methodology for An 

Alternative to Monitoring

 California is primary market for pronamide, with most 

of that use occurring in the Central Coastal valleys.

 Preliminary review of source water protection reports 

indicated that coastal California production areas were 

unlikely to have agriculture listed as potential sources 

of contaminants by Community Water Systems (CWS)

 Propose that existing public records and data sets can 

be used to document potential for pronamide 

contamination of surface water sources on the central 

California coast from use on lettuce

3
Presentation of Sensitive Drinking 

Water Information

 US EPA has a policy on sensitive drinking water 

information (US EPA, 2005; US GAO, 2006) that we 

will follow using an approach consistent with the one 

EPA is considering for sharing information products 

with a wide public audience that is based on the 

concept of drinking water indicators (Cooter et al., 

2011)

 Example: Watershed Boundary Dataset subwatershed

HUC12 drainage areas , 160,000 estimated for US (Laitta

et al., 2004)

 We use this as our indicator

4
Data Sources

 UC Extension list of coastal counties with historical lettuce 

productiona

 Historical CWS intake locations pre-9/11/2001

 Safe Drinking Water Information System (SDWIS)

 UC Davis Drinking Water Source Assessment and Protection 

Program and On-Line Mapping Tools

 USGS NHD Flowline, Waterbody, and HUC12 data

 Cal EPA/Department of Pesticide Regulation Pesticide Use 

Reports (PUR) 2007-2009 average use in a section

 Google Earth (for place names)

 Internet search: Google (for reports to customers and contacts)

 Employees at CWS 

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a Contra Costa, Monterey, San Benito, San Luis Obispo, Santa Barbara, Santa Clara, Santa Cruz
Procedure

 Start with historical intake locations and PUR data

 Check against current SDWIS active CWS list

 Three categories

 No longer active: remove from list

 Remain active: check for accuracy (NHD, Google Earth)

 New active CWS not on historical list: investigate location 

(NHD, Google Earth, Google, employees)

 After locations of all current intakes are found, then 

examine for exposure potential based on use and 

NHDFlowline Hydro Net flow direction

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Procedure – Decision Tree for 

Location

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If Use in 

County, 

Compare 

Historic to 

Current 

SDWIS

Currently 

Active

Historic –

Check 

Location

New – Find 

Location No Longer 

Active (Done)

Ground Truth, if

Necessary
8

Example of No Use 

in County
9

Example of Currently Active Accurate 

Historical Intake Location in County 

Represented by HUC12 Indicator with 

Use in County (1-Mile Sections)
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Example of Information 

Obtained from Google 

Search for New Location

SLO Co. Master Water Plan

“Lopez Reservoir provides 

supplies to ... Grover Beach ...
Procedure – Decision Tree for 

Exposure Potential

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Intake 

Locations

SW Hydrologic 

Connection

Upstream from 

Use Sites* 

(Done)

Downstream 

from Use Sites 

No SW 

Hydrologic 

Connection 

(Done)

Ground Truth, if

Necessary

*And with protected conveyance if water transported.
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Example of No SW 

Hydrologic Connection 

from Google Search

SLO Co. Master Water Plan

“Lopez Reservoir provides 

supplies to ... Grover Beach ... via 

the Lopez pipeline system.
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Example of No SW 

Hydrologic Connection 

from Map
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Example of SW Hydrologic 

Connection with Location 

Upstream from Use Sites
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Many CWS Receive Water 

from Remote Sources
Results for 223 Locations Evaluated: None 

with Exposure Potential

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Lines of Evidence Used to Make Determination (% of Total Number of Sites)

Not Active Internet Map Ground Truth

5.4 26.9 55.6 12.1
Review of 223 Active Intakes 

Suggests a Consistent Pattern

17

Photo credit: Rohm and Haas/DAS
Implication of Different EDWC Assumptions for 

Dietary Risk

 No exposure potential for drinking water sourced from 

surface water suggests that the SCI-GROW estimated 

drinking water concentration (EDWC) can be used for 

dietary risk assessment.

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EDWC Exposure 

Estimation 

Method

EDWC from 

Lettuce Use

(μg/L)

Dietary 

Exposure

(mg/kg/day)

Anticipated 

Cancer Risk

PRZM/EXAMS 64.1a 0.001359b 4 x 10-5

SCI-GROW 0.699 0.000026 6.78 x 10-7

No water

(food only)

0 0.000012 3.14 x 10-7

a Surface water 30-year mean exposure (EFED).

b EDWC + HED dietary exposure estimate.
Conclusions and Recommendations

 Zero exposure potential from surface water from the lines 

of evidence evaluated

 Approach could be extended to other areas of California 

(PUR for actual use) and other regions with western 

irrigated agriculture (CDL or CLU for potential use)

 Routine updates needed to demonstrate no change has 

occurred

 A significant amount of work was involved to address the 

new sites without sensitive location data available to the 

public.

 Suggest that EPA/USGS conduct future similar analyses, 

when appropriate, as they have access to the sensitive 

location data

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Acknowledgements

 Olivier de Cirugeda Helle, Dow AgroSciences – GIS 

and internet searches

 Kay Mercer, KMI – Ground truthing

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References

 Cooter, W, Everett, K, Chrest, D, Rineer, J, Bergenroth, B, Anzzolin, A. 

2011. Examples of Cross-Program Approaches for Sharing Drinking 

Water Indicators. ESRI International User Conference, San Diego, CA, 

July 11-15, 2011. Paper Number 3063.

 Laitta, M, Legleiter, K, Hanson, K. 2004. The National Watershed 

Boundary Dataset. HydroLine, Summer 2004, p. 1. ESRI Water 

Resources Group. 

http://www.esri.com/library/newsletters/hydroline/hydroline_summer2004.pdf.

 U.S. EPA. 2005. Policy to Manage Access to Sensitive Drinking WaterRelated Information. Office of Water, Michael Shapiro, Deputy 

Assistant Administrator, April 5, 2005, Washington, DC.

 U.S. GAO. 2006. Information Sharing: The Federal Government Needs 

to Establish Policies and Processes for Sharing Terrorism-Related and 

Sensitive but Unclassified Information. GAO-06-385. U.S. Government 

Accountability Office, Washington, DC.

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