### Refinements to the USEPA Tier 2 Drinking Water Risk Assessment Guidance: Addressing atypical use patterns Nathan Snyder Aldos Barefoot

EMPM – September 20, 2011

# Summary

• Tier 2 Exposure Modeling • Surface Water PRZM/EXAMS (Standard Scenarios using PE5) • Index reservoir (Drinking Water Exposure) • Foliar Processes, Application Methods, Crop Season Representation • Overview of current USEPA policy on using Percent Crop Area (PCA) factors in Human Health Risk Assessments • Limitations in procedure for areas outside of the continental United States (PR/HI) • Options for refinements • Mixed major/minor use PCA values in combined watershed EEC determination • Higher resolution land- use data • Focused watershed assessments
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# Current Practice

• Clear rules and standard practices for selecting environmental fate inputs • Modeler (registrant or USEPA) judgment in selection of scenarios, interpretation of label, assignment of scenarios to primary use areas or 

### regions • Core models allow for representation of most label use requirements • Examples come from USEPA assessments and 

### proposed refinements and label changes

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## Considerations in Model



# Parameterization

• Mixed Application Types • Foliar, soil applied... • Multiple Crop Seasons per year • Crop Rotations • Runoff and Spray Buffers • Biphasic, metabolites, or other atypical environmental fate conditions • Label language preventing use when rain is forecast • Multiple crops in watersheds • PCA and drinking water watersheds

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# Application Representation

• PRZM allows for variable CAM within a single simulation • Assuming seed treatment, incorporated, wetted-in, shank applications to occur as soil applied or foliar applications overestimates exposure • Many products have foliar uses, following pre- and at-plant applications (possibly at higher rates) • Use labels provide application guidance including methods, rates, timing (intervals) • PE5 can handle variable intervals and rates, but only one CAM type

# Sensitivity of CAM Selection

• Example 2 kg/ha (at plant), followed by 2 @ 1 kg/ha on 7- day intervals • 1 - in- 10 Year Annual Maximum Peak values: • 204 ppb (PE5 all cam 2) versus 172 ppb (PRZM/EXAMS CAM 4 then 2)

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# Crop Scenarios

• Soil, Crop, 

### Weather defined by Scenario • Currently there are standard and extra 

### scenarios created for special assessments

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# Crop Scenarios

• Conditions requiring additional (or modified) 

### scenarios • Crop rotations • Multiple seasons 

### • Representation of multiple seasons without also 

### adding cropping periods lead to over estimates of EECs

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# Modified Crop Scenarios

• Triple cropped Lettuce in California • Tomato/Cucumber rotation (double cropped) in Florida • Washoff, plant decay rate, and application timing in crop season

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# Drinking Water Assessments

• PRZM/EXAMS Predictions adjusted by Percent 

### Crop Areas (PCA) for determining Estimated Drinking Water Concentrations (EDWC) • Established National (87%), Major Crop (20% – 57%), Combined Major Crop (46% - 83%), and 

### Regional PCA (7% - 87%) available

10• National PCA Adjustment Factors • 8- Digit HUCs intersected with County level Crop (1997 and 1992 USDA Census of Agriculture) all agriculture • PCA Adjustment Factors for Major Crops • Same as above, but cropping specific to target crops • Available for Corn, Wheat, Soybeans and Cotton • Method developed to combine EECs if use is on several major crops with similar or different timing • Regional PCA Adjustment Factors • Same methodology but identified highest PCA in each of 18 regions • Updates Coming.... 

# PCA Values

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## Other States/Territories and Minor



# Crops
• Specialty Crops grown in areas outside of the “lower 48” – Puerto Rico and Hawaii • Products labeled for uses other than Corn, Wheat, Soybeans, or Cotton considered minor • Applying PCA methodology leads to excessively 

### conservative assessments • Approach using PCA methodology and conservative representation of land - use in regions of concern can lead to improved 

### assessments

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# Puerto Rico – Modeling and Cropping

• One Scenario (PR Coffee), FL Surrogates used 

### in other cases, with PR Weather

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# Puerto Rico - PCA
• PCA of 100% due to lack of an established value • Watershed Boundaries are available at 8- , 10- , 12- Digit Resolution • Census of Agriculture data available for municipalities • Smaller unit than typical US counties

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# PCA for Puerto Rico

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# Hawaii – Modeling and Cropping

• No existing scenarios 

### • Use FIRST or Surrogates with HI Weather

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# Hawaii - PCA
• PCA of 100% due to lack of an established value • Watershed Boundaries are available • Census of Agriculture data available for Counties (Islands)

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# Hawaii – Drinking Water Supplies

• Hawaii has 128 Public Water Supplies, 10 use Surface Water as their source

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## State/Local Source Water Assessment



# Information

• Specific PCA calculations difficult (Modern Land - use data limited and specific intake locations PCA determination not within current USEPA Methodology) • Pragmatic review of local information and target crops reveal PCA resulting in a failing assessment not realistic • Example Descriptions: • “The upstream watersheds for the sources lies within a Forest Preserve which is non-agricultural ” • “To further complicate the network, water can be shared from all 3 WTFs, Several Reservoirs were identified but individual sources were not, however the combining of the Maui hydrology reports reveal that nearly all of the upstream land from the intakes is in conservation and non agricultural uses. “ • “The stream is in government owned non agriculture land.” • “Map 13 (Water Resource Associates 2004). The ALUM - Maui map (ALUM 1980) does not appear to show any agriculture in the upstream watershed of the Iao stream. “
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## Drinking Water Assessment Tiered



# Process
• Run all EPA scenarios applicable to product • Adjust using National PCA (highest predicted scenario) • Adjust using Regional PCA 

### (regionally assigned scenario) • In regions with any uses 

### exceeding level of concern, explore refined approach
2122 

# Applying PCAs in Tier 2 Assessments

# PCA Calculation

9/15/2011 23

# Crop PCA

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# Regional Refinement

25• A process to combine localized knowledge of drinking water supplies and labeled crops should enable the development of conservative yet refined PCA values • Use actual watersheds used for drinking water rather than surrogate HUC-8 watersheds • Use publically available source information • NHDPlus catchments can be used to hide specific LAT/LON of intakes while providing needed watersheds to produce refined PCAs • Use spatially distributed cropping data rather than “All Agriculture” at a county scale • Additional scenarios/weather stations to address regional concerns • Represent distribution and timing of applications where diverse land use exists in watersheds
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# Options for Tier 3

### • USEPA Assessment utilized county level NASS Census of Agriculture from 1997 (or 1992 if missing) • Used “Cropped Area” for default and “Corn”, “Soybean”, “Cotton”, or “Wheat” for major crops 

### • Distributed county acreage to HUC-8 Watersheds • Did not utilize minor crop data • Cropland Data Layer (CDL) now seamless for 

### Continental US

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# Landuse

# NASS CDL Data

28• CDL offers a complete spatial view at a 56m resolution • CDL has 130 classes, including some from the NLCD • Census of Agriculture is summarized at a county resolution • Includes only agricultural areas • Includes >200 crop categories • A comparison of the 2 NASS sources is needed to identify groupings needed for detailed PCA calculations 29 

## CDL versus Census 

## of Agriculture• County review of CDL versus Census of Agriculture • Neither dataset is perfect (omissions, border effects, incorrect categorizations, under/over reporting, crop damage)

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# CDL versus Census of Agriculture31 

# Watershed Assessment

• Summarize CDL for each Watershed • Accuracy assessment of Counties • Conservative CDL groupings based on County Census of Agriculture • Determine PCA for relevant crop groups • Use as basis for scenario creation (intersect with soils) or watershed modeling

# Conclusions
• Within framework of Tier 2, options exist for improving the representation of crop protection 

### products • Label language accurately represented • If multi -cropping is typical in a region, scenarios should be created to represent cropping practices • Refinements to regional PCA values for minor crops following methodology like mixed major crops

32• USEPA PCA methodologies can be applied to Puerto Rico • Hawaii is an example where an analysis of limited surface water source assessments can be used • Tier 3 analysis can add refinements not possible in currently established guidance • Refined use pattern representation (and real drinking water watershed PCA or modeling) • Additional soil, weather, environmental fate representation (spatial modeling) • Probabilistic approaches for key parameters • Use of focused monitoring data 33



# Conclusions