### July 2010 EMPM Agenda and Abstracts

PRESENTER Time TOPIC Duration

Peck/Baris 9:00 am Welcome and Introduction 5 minutes
Michael Barrett, U.S. EPA Ian Kennedy, PMRA 9:05 am A Look at Prospec tive Ground-Water Monitoring Studies and their Utility for Developing Leaching
Models 35 minutes

Marty Williams, P.E.
Waterborne Environmental
Inc. 9:40 am Screening Approach es for Predicting Pesticide
Concentrations in Groundwater 35 minutes

10:15 am Break 10 minutes
David Valcore, Valcore Consulting Harold Thistle,
USDA 10:25 am Mechanistic Ground Spray Boom Drift Model Development 35 minutes

Nathan Snyder
Waterborne Environmental
Inc. 11:00 am Using Modern Watershed and Cropping Data as a Basis for Estimating Percentage Crop Treatment 35 minutes

Jack Barbash and Frank Voss, USGS 11:35 am Design and Testing of a Process-Based Groundwater Vulnerability Assessment (P-GWAVA) System for Predicting the Concentrations of Agrichemicals in
Ground Water Across the Conterminous United States Using Data from the National Water-Quality Assessment (NAWQA) Program 35 minutes

12:10 pm Lunch 80 minutes
Michael Winchell,
Stone Environmental Russell Jones, Bayer Cropscience 1:30 pm Comparison of Models for Estimating the Removal of Pesticides by Vegetative Buffer Strips 35 minutes

Marty Williams, P.E.
Waterborne Environmental
Inc. 2:05 pm Advances in Modeling Urban/Residential Pesticide
Runoff 35 minutes

2:40 pm Break 5 minutes
Nick Poletika, Dow Agrosciences 2:45 pm Spray Drift Exposure Refinements for Salmonid
Off-Channel Habitat 35 minutes

Mark Velleux, HydroQual, Inc 3:20 pm Spatially-Distributed Watershed Model for Chemical Exposure Assessment: Case Study of Antimicrobial Copper Uses in Urbanized Areas 35 minutes

Peck/Baris 3:55 PM Wrap-up, Next Meeting 5 minutes

Peck/Baris 4:00 PM AdjournmentA Look at Prospective Ground-Water Monitoring Studies and their Utility for Developing Pesticide Leaching Models

Ian Kennedy 1 , James Wolf 2 , and Michael Barrett 2

, 1 PMRA, Ottawa, Canada

2 USEPA, Washington, DC

The datasets from prospective groundwater (PGW) monitoring studi es, required by EPA for registration of pesticides thought likely to leach to groundwater are being used by EPA and Health Canada's Pest Management Re gulatory Agency (PMR A) to evaluate and develop ground-water exposure models. PM RA and OPP's Environmental Fate and Effects Division (EFED) examined and modeled a number of completed PGW study reports for the utility of the datasets for use in testing leaching models. A number of
factors have been identifie d which commonly limit the use of these data, including:

 Uncertainties in pesticide and degradate fate properties.

 Data censoring, or reporting/detection limits which are set too high to accurately establish breakthrough patterns with dept h for the pesticide or degradates.

 The conducting of studies under conditions where precipitation or irrigation for long periods were insufficient to promote ground water recharge - this is often associated with a high rate of soil- pore water sample collection failure.

 Temporal and spatial variability in the soil matrix is often high and the sampling frequency and sampling locations may be insufficient to track water and solute

movement.

 Study was ended before a complete breakthrough curve was observed.

Screening Approaches for Predicting Pesticide Concentrations in Groundwater Dazhi Mao, Marty Williams, Mark Chep lick, Amy Ritter, and Robert Morris Waterborne Environmental Inc., Leesburg, VA

The presentation compares three modeling a pproaches for estimati ng pesticide exposure in groundwater: SCIGROW, an empirical mode l derived from the results of controlled, field-scale groundwater monito ring studies; 2) PRZM-GW, an adaption of the Pesticide Root Zone Model (PRZM) to estimate pesticide concentra tions 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 th ree approaches to reproduce the re sults of prospective groundwater monitoring studies are compared.

Mechanistic Ground Spray B oom Drift Model Development
David L. Valcore 1 , Harold W. Thistle 2 , P. C. H. Miller 3 , and Clare Butler-Ellis 3

1 Valcore Consulting

2 USDA-USFS

3 Silsoe Applic. Unit, The Arable Group, UK

A number of high quality spray drift datasets exist internationally that have provided empirical drift deposition curves for spray dr ift risk exposure assessments to sensitive areas. Existing agricultural ground spray drift deposition models are empirical. There is aneed for more accurate drift predictions to greater distances than the typical 30-100
meters or even the 300 meter distance av ailable from the EPA AgDRIFT model. A multi-phase international effort to develop a robust mechanistic ground boom spray drift model is underway to address the need to evaluate mitigation options that modify application parameters including spray boom and nozzle type, meteor ology and low drift technologies. An updated random walk multi-nozzle spray deposition drift model developed by Silsoe Spray Application Unit, UK was chosen as the basis of current efforts. Initial comparisons of this mode l with EPA’s accepted Sp ray Drift Task Force
data have been made and show that the m odel can successfully predict ground deposits up to 200 meters downwind, and potentially beyond. Preliminary sensitivity analysis of the key parameters in the model algorithms will be discussed. A brief summary of development status, current insights, research and verification plans will also be presented, including benefits expected for drift risk assessments, drift mitigation options, and support of EPA’s Drift Reduction Technology program.

Using Modern Watershed and Cropping Data as a Basis for Estimating Percentage Crop Treatment Nathan J. Snyder 1 , Joshua J. Amos 1 , Peggy S. Lee 1 , and Aldos C. Barefoot 2

1 Waterborne Environmental Inc. Leesburg, VA

2 DuPont Crop Protection, Newark, DE

Distributing pesticide use data or determini ng percent of crop treatm ent 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 collecti on resolution (i.e. CRD/c ounty/zipcode data distributed to a small watershed), spatially accurate cropping estimates are required. The use of modern watershed and cropping info rmation (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 la rge watersheds (8-digit Hydrologic Unit Codes), and 2) concerns with scale and uncertainty of crop distribution within watersheds. Regional PCAs were an interim st ep 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 re gional PCAs, updates to watersheds and crop coverages have become available. Concerns with limitations in PCAs for individual crops for development of prot ective residue values for drin king water assessments can be addressed through the recently available data . It is appropriate to move beyond an interim step and improve drinking water estim ates using cropping and pesticide use data distributed through PCA adjusted EEC s in actual drinking watersheds.Design and Testing of a Process-Based Groundwater Vulnerability Assessment (PGWAVA) System for Predicting the Concentrations of Agrichemicals in Ground Water

Across the Conterminous United States Usin g Data from the National Water-Quality Assessment (NAWQA) Program
Jack E. Barbash and Frank D. Voss

U.S. Geological Survey, Tacoma, WA

Over the past two decades, many tools have been employed to predict the likelihood of detecting surface-derived contaminants in groun d water. Statistical relations have been used at large spatial scales to predict contaminant occurrence from various site-based parameters. At such scales, however, process- based simulations of the transport and fate of the compounds of interest have been re latively uncommon. This presentation will describe an approach that (1) employs a geographic information system to provide spatially-structured data input to a pr ocess-based vadose-zone model (PRZM or RZWQM) for any location in the conterminous United States, (2) simulates the transport and fate of pesticides, pesticide transfor mation products and nitrate to estimate their
concentrations in the vadose zone beneath ea ch selected location, and (3) compares the simulated concentrations with those measured in shallow ground water sampled from over 1,900 wells across the Nation between 1992 and 2007 by the U.S. Geological Survey’s National Water-Quality Assessment (NAWQA) program.

Comparison of Models for Estimating the Removal of Pesticides by Vegetative Buffer Strips
Michael Winchell 1 , Russell Jones 2 , and Tammara Estes 1

1 Stone Environmental, Montpelier, VT

2 Bayer CropScience, Stilwell, KS

Vegetated buffer areas established between agri cultural fields and r eceiving waters have long been recommended as a best manage ment practice to reduce the amount of sediment, nutrients, and pesticides enteri ng water bodies and re cently intensively managed vegetated filter strips have been mandated as label requirements for plant protection products in both Europe and North America. Also recently, models have been developed to predict the amount of active i ngredients and their metabolites removed from runoff flowing through these strips . This presentation reviews th e features of five models (APEX, PRZM, REMM, SWAT, and VFSMOD-WQ ) which can be used to predict the reduction in pesticide loss in runoff pa ssing through a vegetative buffer strip. The predictions from four of these models are compared using three common data sets, one from Europe and the other two from the Unit ed States. The conditions modeled include a range of soils properties, slope s, rainfall events, and pesticide sorption characteristics. All four models predic ted significant reductions of pesticid es in the buffer consistent with the observed reductions, providing strong support for the use of these models as tools for estimating buffer effectiveness. A sensitiv ity analysis was conduc ted with the four models to determine the effects of input parameter uncertainty on the predictions of pesticide reduction in the buffer.Advances in Modeling Urban/Residential Pesticide Runoff Marty Williams, Amy Ritter, Me gan White, and Mark Cheplick Waterborne Environmental Inc., Leesburg, VA

The U.S. Environmental Protection Agency 's (USEPA's) Storm Water Management Model (SWMM) is widely used for urban wa ter 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 fo r hard surface runoff and the inability to specify discrete pesticide applications. USEPA's Pesticide Root Zone Model (PRZM) was developed to simulate pesticide runoff a nd leaching in agricultural environments and is limited in its ability to urban drainage f eatures. Recent enhancements have been to both
models to overcome these deficiencies. Pestic ide and water runoff predictions from both models are compared.

Spray Drift Exposure Refinements for Salmonid Off-Channel Habitat
Nick Poletika 1 , Rick Reiss 2 , Steve Cryer 1 , and Stever Cramer 3

1 Dow AgroSciences LLC

2 Exponent, Inc

3 Cramer Fish Sciences

Off-channel stream habitat is viewed by th e National Marine Fisheries Service as the habitat type in which Pacific Coast threaten ed/endangered salmonids are most vulnerable to adverse impacts from spray drift residues re sulting from applications of agricultural pesticides. Data describing the water body characteristics of off-channel habitat associated with agricultural landscapes were collected and used to conduct refined spray drift and aquatic dissipation modeling. Fl owing water was found to be a key characteristic influencing exposure magnitude and duration in off-cha nnel stream features relevant to agricultural settings. Based on advanced technical m odeling approaches and representative, best available measurement data, time-varying exposure assessments for the three main types of important off-channel habitat (side channels, alcoves, and backwater pools) were completed for durations consistent with acute toxicity testing. The exposure assessments were compared to screening-level exposure predictions assuming typical off-channel habitat is repres ented by shallow static water bodies.

Spatially-Distributed Watershed Model fo r Chemical Exposure Assessment: Case Study of Antimicrobial Copper Uses in Urbanized Areas

Mark Velleux, Paul Paquin, Aar on Redman, and Robert Santore HydroQual, Inc.

Copper is used as an antimicrobial agent in building materials such as algae-resistant shingles and treated wood. In urbanized area s, copper-containing bu ilding materials may be present in roofs, wood decks, wood fen ces, and utility poles installed in densely clustered and widely dispersed locations across the landscape. Releases from these materials may pose risks to aquatic a nd terrestrial organisms. The TREX (T wodimensional R unoff E rosion and Ex port) watershed model was used to simulate spatiallydistributed copper releases, runoff, and estim ated exposure concentr ations in surfacewater, soil, and sediment for an urbanized setting. Setting desi gn was based on typical housing densities and upper-end copper use patt erns in building materials to provide a representative “worst-case” scenario with respec t to spatial distributi ons and variability of copper sources at the watershed scale. Copper release rates from bu ilding materials were
defined as functions of surface area and rainfall using meas urements from manufacturers or other field study results. The model require s data to define watershed boundaries, the stream network, land surface elevations, soils, land use, physical processes that control runoff and soil and sediment transport, as well as rainfall. Data were obtained from standard sources including the U.S. Geol ogical Survey, Natural Resource Conservation Service, National Weather Service, and Ce nsus Bureau. The watershed area was 21.4
km 2 . The model grid was defined at a 90 me ter resolution and includes 2,558 cells. Simulations were performed for a 10-year period with 772 storms defined using 15- minute rainfall data. Results were analyzed in terms of the frequency with which modeled exposure concentrations exceeded benchmarks for water, sediment or soil. Surface water
benchmarks were determined with the biot ic ligand model (BLM) for copper. Simulated copper exposures from algae-resistant shingles were relatively low and did not result in exceedances in any media. Simulated exposures from treated wood were larger than those for shingles and resulted in two water quality benchmark exceedances (i.e. 2 days in 10 years).