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The presentation compares three modeling approaches for estimating pesticide exposure in ground water: SCIGROW, an empirical model derived from the results of controlled, field-scale groundwater monitoring studies; 2) PRZM-GW, an adaption of the Pesticide Root Zone Model (PRZM) to estimate pesticide concentrations in shallow ground water; and PRZM-ADAM, the linkage of PRZM to an aquifer dispersion and advection model based on Darcy's law to estimate concentrations in ground water. The methodology and the ability of all three approaches to reproduce the results of prospective groundwater monitoring studies are compared.

Distributing pesticide use data or determining percent of crop treatment is dependent on estimates of cropping information. If an attempt is made to distribute sales or use data to a geographic area smaller than the collection resolution (i.e. CRD/county/zipcode data distributed to a small watershed), spatially accurate cropping estimates are required. The use of modern watershed and cropping information (and a comparison to traditional county level data) will be presented through a case study. Examples of improvement to the traditional regional PCA values currently being used for drinking water modeling will be discussed. Two areas of the USEPA regional PCA methodology will be evaluated 1) Regional default PCAs developed from large watersheds (8-digit Hydrologic Unit Codes), and 2) concerns with scale and uncertainty of crop distribution within watersheds. Regional PCAs were an interim step in moving from national PCAs to PCAs developed from actual drinking watersheds. In the 10-years since the 1999 SAP review and seven years since the development of regional PCAs, updates to watersheds and crop coverages have become available. Concerns with limitations in PCAs for individual crops for development of protective residue values for drinking water assessments can be addressed through the recently available data. It is appropriate to move beyond an interim step and improve drinking water estimates using cropping and pesticide use data distributed through PCA adjusted EECs in actual drinking watersheds.

The US Environmental Protection Agency's (USEPA's) Storm Water Management Model (SWMM) is widely used for urban water management and water quality analysis. The model is limited in its ability to simulate pesticides because of a general lack of knowledge of washoff coefficients values for hard surface runoff and the inability to specify discrete pesticide applications. USEPA's Pesticide Root Zone Model (PRZM) was developed to simulate pesticide runoff and leaching in agricultural environments and is limited in its ability to urban drainage features. Recent enhancements have been to both models to overcome these deficiencies. Pesticide and water runoff predictions from both models are compared.

A weight-of-evidence analysis is being conducted to identify major sources of pesticide loadings to the Sacramento River, San Joaquin River, and Bay-Delta estuary. The objective of this analysis is to improve decision making and optimize resource spending across a number of federal, state, and regional water quality programs.

As part of this project, a series of modeling scenarios were developed to compute the edge-of-field loading for 20 pesticides in the agricultural realm. An underlying challenge in this effort was to properly represent 3,500,000+ pesticide applications, on 100+ different crops and land uses, account for California’s unique management practices, and account for spatial-temporal climate effects in the period 2000 – 2008.

Using a geographic information system a super-agricultural land use layer was create to represent all potential pesticide use sites for the period of interest. In turn, this agricultural super layer was combined with the spatial component of the CA PUR , the PLSS sections, soils from the detailed soil survey and area of influence for selected CIMIS weather stations to determine all unique combinations (of chemical, soil and crop) that needed to be modeled and processed at the catchment level.

In this poster presentation we will provide insight in assumptions, methods, data sets, and modeling results to handle fast volumes of information required to compute edge-of-field pesticide loadings and determine co-occurrence with sensitive species in the spatial-temporal area of interest.

In order to meet USEPA federally listed threatened and endangered species spatial data requirements, the Generic Endangered Species Task Force (GESTF) was formed to develop a series of four spatial datasets that represent potential pesticide use sites. This poster describes the development and datasets that represent terrestrial use sites (crop, forestry and turf); an accompanying poster describes the aquatic use sites dataset. To generate the terrestrial use sites datasets, a GIS was used to compile US Department of Agriculture (USDA) National Agriculture Statistics Service Cropland Data Layer (NASS CDL) data for the 2009 growing season into a seamless dataset covering the continental United States. From this dataset, each CDL pixel was assigned to one of the GESTF’s use site classes according to strictly defined and documented methods. Forestry use sites were further refined using data from state level GAP Program databases. Potential pesticide use site area summaries were generated for each of the over 2.5 million NHDPlus catchment and upstream watersheds, allowing for ready integration of the use site data with existing NHDPlus data and tools. In order to maximize transparency and reproducibility, extensive metadata conforming to Federal Geographic Data Committee (FGDC) standards was generated for each use site dataset and, to the extent appropriate, project documentation and Quality Assurance / Quality Control were conducted following USEPA Good Laboratory Practices (GLP) guidelines.

In order to meet USEPA federally listed threatened and endangered species spatial data requirements, the Generic Endangered Species Task Force (GESTF) was formed to develop a series of four spatial datasets that represent potential pesticide use sites. This poster describes the development and dataset representing potential aquatic use sites; an accompanying poster describes the terrestrial use sites (crop, forestry and turf) datasets. National Hydrography Dataset Plus (NHDPlus) data covering the continental United States was used as the basis for developing the aquatic use sites dataset. Because flowing water bodies that are narrower than approximately 300’ are represented as lines in the NHDPlus data, all lines were ‘expanded’ using a Geographic Information System (GIS) to create a spatial dataset containing an area attribute for each water body. The width of each flowline was estimated using the average annual flow provided in the NHDPlus data along with assumptions about the width-depth ratio, and the resulting widths were categorized into predetermined width classes that were used to represent the water body widths. Overlapping confluences of varying size streams were processed using a hierarchical scheme so that larger streams and rivers took precedence over smaller water bodies. The resulting data were clipped to retain the ponds, lakes and large rivers that existed in the source NHDPlus data, and to ensure that no overlap existed when all surface water features were combined into a single spatial layer. In order to maximize transparency and reproducibility, extensive metadata conforming to Federal Geographic Data Committee (FGDC) standards was generated for each use site dataset and, to the extent appropriate, project documentation and Quality Assurance / Quality Control were conducted following USEPA Good Laboratory Practices (GLP) guidelines.

An analysis in California was undertaken to quantify the potential economic impact to agriculture in terms of revenue resulting from no spray setbacks of pesticides from urban / residential land use. The setback distances were proposed in the report, “Pesticides in the Air – Kids at Risk: Petition to EPA to Protect Children From Pesticide Drift”, submitted on October 13, 2009 by Earthjustice and Farmworker Justice on behalf of United Farmworkers et al. The report is concerned with the transport of organophosphate & carbamate pesticides from target agricultural fields by evaporation and atmospheric volitization and recommends 60’ (ground applications) and 300’ (aerial application) set backs from non-target sites like urban / residential land use types to reduce bystander exposure from spray drift.

Using medium resolution land cover in a Geographic Information System (GIS), two counties in California, Kern and Butte counties, were identified as falling in the upper distribution of counties with respect to the interaction of agriculture within 60’ and 300’ of urban / residential land use. High resolution (field scale) cropping spatial data & crop-specific production and value data were then used to calculate the acreage and dollar value for crops with the potential for pesticide application in the 60’ and 300’ buffers.

The additional economic impact of completely removing a field from production was calculated when at least 25% of the field was within the pesticide no spray set back. Total field retirement may be more economically viable than partial removal in some scenarios. The results indicated a significantly greater economic impact when entire fields were removed entirely from production. The calculated acreage and dollar values were compared with values reported in annual county agricultural crop reports, and the results are presented. This study highlights the importance of understanding the magnitude and degree to which no spray set backs impact the agricultural economy.