Document ID: EPA-HQ-OPP-2005-0004-0003
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2007-09-21T04:00Z

<!DOCTYPE html
     PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
     "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<!-- EPA Template version 3.2.1, 28 June 2006 -->
<head>
	<!-- #BeginEditable "doctitle" -->
	<title>Minutes of the January 11, 2005 Exposure Modeling Public Meeting | Pesticides | US EPA</title>
	<meta name="DC.description" content="pesticide, pesticides,Access to and information regarding simulation models to predict pesticide concentrations in surface and ground water for use in both human health and aquatic ecological exposure assessments.  Exposure modeling public meeting products." />
	<meta name="keywords" content="EPA,Environmental Protection Agency, OPP, pesticides, pesticide, office of pesticide programs, scigrow, geneec, first, water models, exposure modeling public meeting" />
  <!-- #EndEditable -->
	<!-- #BeginEditable "metaElements" -->
	<meta name="DC.title" content="Minutes of the January 11, 2005 Exposure Modeling Public Meeting | Pesticides | US EPA" />
	<meta name="DC.subject" content="EPA,Environmental Protection Agency, OPP, pesticides, pesticide, office of pesticide programs, scigrow, geneec, first, water models, exposure modeling public meeting" />
	<meta name="DC.type" content="" />
	<!-- For date metadata, use the format YYYY-MM-DD -->
	<meta name="DC.date.modified" content="2007-06-07" />
	<meta name="DC.date.created" content="" />
	<meta name="DC.date.reviewed" content="" />
  <!-- #EndEditable -->

	<meta name="DC.language" content="en" />
	<meta name="DC.Creator" content="US EPA, Office of Pesticide Programs" />
	<meta http-equiv="Content-Style-Type" content="text/css" />
	<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
	<link rel="schema.DC" href="http://purl.org/dc/elements/1.1/" />
	<link rel="meta" href="http://www.epa.gov/labels.rdf" type="application/rdf+xml" title="ICRA labels" />
	
	<style type="text/css" media="screen">@import 'http://www.epa.gov/epafiles/s/epa.css';</style>
	<style type="text/css" media="screen">@import 'http://www.epa.gov/opp00001/styles/opp_styles.css';</style>
	<!--[if lt IE 7]>
	<link rel="stylesheet" type="text/css" href="http://www.epa.gov/epafiles/s/ie.css" />
	<link rel="stylesheet" type="text/css" href="http://www.epa.gov/opp00001/styles/opp_ie_styles.css" />
<![endif]-->
	<link rel="stylesheet" type="text/css" media="print" href="http://www.epa.gov/epafiles/s/print.css" />
	<script type="text/javascript" src="http://www.epa.gov/epafiles/js/epa-core.js"></script>
	<script type="text/javascript" src="http://www.epa.gov/epafiles/js/extra.js"></script>
</head> 

<body>
<p class="skip"><a id="skiptop" href="#content" title="Jump to main content.">Jump to main content.</a></p>

<div id="header"> <!-- START EPA HEADER -->

	<div id="logo"><a href="http://www.epa.gov/" title="US EPA home page"><img src="http://www.epa.gov/epafiles/images/logo_epaseal.gif" alt="[logo] US EPA" width="100" height="110" /></a></div>

	<div id="areaname"> <!-- START AREA NAME -->
		<p><span class="epaAreaName">Pesticides: Science and Policy </span></p>
  </div> <!-- END AREA NAME -->

	<!-- START SEARCH CONTROLS -->
	<form id="EPAsearch" method="get" action="http://nlquery.epa.gov/epasearch/epasearch">
		<!-- START AREA SPECIFIC LINKS AND SEARCH BOX  -->
		<!-- CHANGE links to point to your own recent additions and contact pages -->
		<!-- REMOVE recent additions link if your area doesn't have one -->
		<p><a href="http://cfpub.epa.gov/pesticides/recentadditions.cfm">Recent Additions</a> | <a href="http://www.epa.gov/pesticides/regulating/contacts.htm">Contact Us</a> 
			<span class="search"><strong>Search:</strong> 
			<input type="hidden" name="fld" value="gov/pesticides/science,oppfead1/trac/science,oppfead1/carat,oppfead1/cb/ppdc/,gov/scipoly/sap,oppad001,pesticides/antimicrobials,oppbppd1/biopesticides/regtools/guidelines,oppbead1/methods,oppbead1/labs,oppefed1/models,opptsfrs/home,gov/scipoly/oscpendo,gov/PR_Notices" />
			<input type="hidden" name="areaname" value="Pesticides: Science and Policy" />
			<input type="hidden" name="areacontacts" value="http://www.epa.gov/pesticides/science/contacts.htm" />
			<!-- AREA ADVANCED SEARCH URL HERE (OPTIONAL) -->
			<input type="hidden" name="areasearchurl" value="http://www.epa.gov/pesticides/search.htm" />
			<!-- THE REMAINING HIDDEN INPUTS ARE USED BY THE SEARCH ENGINE - DO NOT EDIT -->
			<input type="hidden" name="result_template" value="epafiles_default.xsl" />
 			<input type="hidden" name="filter" value="sample2filt.hts" />
			<input name="typeofsearch" id="EPAall" type="radio" value="epa"/><label for="EPAall">All EPA</label> 
			<input name="typeofsearch" id="Areaall" type="radio" value="area" checked="checked" /><label for="Areaall">This Area</label> 
			<input name="querytext" id="searchbox" value="" /> 
		  <input name="submit" id="searchbutton" type="submit" value="Go" /></span>
	  </p>
	</form> <!-- END SEARCH CONTROLS -->
		
	<ul> <!-- BEGIN BREADCRUMBS -->
		<li class="first">You are here: <a href="http://www.epa.gov/">EPA Home</a></li>
		<li><a href="http://www.epa.gov/pesticides/index.htm">Pesticides</a></li>		
		<!-- START AREA BREADCRUMBS -->
		<!-- #BeginEditable "breadcrumbs" -->		
		<li><a href="http://www.epa.gov/pesticides/science/index.htm">Science & Policy</a></li>
		<li><a href="http://www.epa.gov/pesticides/science/models_db.htm">Models 
            and Databases</a> </li>
		<li><a href="http://www.epa.gov/oppefed1/models/water/index.htm">Water Models		</a></li>
		<li><a href="http://www.epa.gov/oppefed1/models/water/emwg_top.htm">Exposure 		Modeling Public Meeting (EMPM) Information and Products</a></li>
		<li>Minutes of the January 11, 2005 Exposure Modeling Public Meeting</li>
    <!-- #EndEditable -->
		<!-- END AREA BREADCRUMBS -->
	</ul> <!-- END BREADCRUMBS -->

</div> <!-- END EPA HEADER -->

<hr class="skip" />

<p class="skip"><a id="pagecontents"></a><a id="pagetop"></a></p>
<div id="content"> <!-- BEGIN PAGE CONTENTS -->	<!-- EPA SITE-WIDE ANNOUNCEMENTS -->
	<!-- DO NOT REMOVE - this code is used for emergency messages -->
<!-- If this page is a Program Office or a Topics home page, CHANGE "sitewidec" TO "sitewideb" -->
	<p id="sitewidec"></p>

	<!-- BEGIN PAGE NAME -->
	<h1><!-- #BeginEditable "PageName" -->Minutes of the January 11, 2005 Exposure Modeling Public Meeting<!-- #EndEditable --></h1>
	<!-- END PAGE NAME -->

			<!-- BEGIN CONTENT AREA -->

			<!-- #BeginEditable "content" -->

<p><strong>On this Page</strong></p>

<ul>
<li><a href="#attendees">Attendees</a></li>
<li><a href="#welcome">Welcome and Introductions</a></li>
<li><a href="#old">Old Action Items</a></li>
<li><a href="#brief">Brief Updates</a></li>
<li><a href="#topics">Major Topics</a></li>
<li><a href="#wrap">Wrap up</a></li>
</ul>

<hr />

<h2 id="attendees">Attendees</h2>

<table class="table zebra" summary="Attendees">
<thead>
<tr><th scope="col">Name</th><th scope="col">Association</th></tr>
</thead>
<tbody>
<tr><td>Dirk Young </td><td>OPP/EFED</td></tr>
<tr><td>Betsy Behl </td><td>OPP/EFED</td></tr>
<tr><td>Ron Parker</td><td> OPP/EFED</td></tr>
<tr><td>Mark Corbin</td><td>OPP/EFED</td></tr>
<tr><td>Jim Lin</td><td>EPA/EFED</td></tr>
<tr><td>Nelson Thurman </td><td>EPA/EFED</td></tr>
<tr><td>R. David Jones</td><td>EPA/EFED</td></tr>
<tr><td>James Hetrick</td><td>OPP/EFED</td></tr>
<tr><td>Lucy Shanaman</td><td>OPP/EFED</td></tr>
<tr><td>Michael Barrett</td><td>OPP/EFED</td></tr>
<tr><td>Marietta Echeverria</td><td>OPP/EFED</td></tr>
<tr><td>Cheryl Sutton</td><td>OPP/EFED</td></tr>
<tr><td>Jim Wolf</td><td>OPP/EFED</td></tr>
<tr><td>Alex Clem</td><td>OPP/EFED</td></tr>
<tr><td>Mohammed A. Ruhman</td><td>OPP/EFED</td></tr>
<tr><td>Piyush Singh </td><td>DuPont</td></tr>
<tr><td>Mark Russell</td><td>DuPont</td></tr>
<tr><td>Kathy Carr</td><td>Monsanto</td></tr>
<tr><td>Mary Nett </td><td>WQC</td></tr>
<tr><td>Pat Havens </td><td>Dow</td></tr>
<tr><td>Russell Jones </td><td>Bayer</td></tr>
<tr><td>T. S. Ramanarayanan</td><td>Bayer</td></tr>
<tr><td>Paul Hendley </td><td>Syngenta</td></tr>
<tr><td>Wenlin Chen</td><td>Syngenta</td></tr>
<tr><td>Scott Jackson </td><td>BASF</td></tr>
<tr><td>Nasser Assaf</td><td>Valent</td></tr>
<tr><td>Mark Cheplick </td><td>Waterborne Environmental</td></tr>
<tr><td>Cathleen Hapeman</td><td>USDA/ARS</td></tr>
<tr><td>Tamara Estes</td><td>Stone Environmental</td></tr>
<tr><td>Adrian Wadley</td><td>Stone Environmental</td></tr>
<tr><td>David Sullivan</td><td>Sullivan Environmental</td></tr>
<tr><td>Shannon Yanocha</td><td>Cerexagri Inc.</td></tr>
<tr><td>Lizanne Avon</td><td>PMRA (Canada)</td></tr>
<tr><td>Stuart Cohen</td><td>ETS</td></tr>
<tr><td>Quingli Ma</td><td>ETS</td></tr>
<tr><td>Dave Valcore</td><td>Dow</td></tr>
<tr><td>Andy Newcombe</td><td>LFR-Recon</td></tr>
<tr><td>Don Wauchope</td><td>USDA ARS</td></tr>
<tr><td>Jack Barbash</td><td>USGS/NAWQA</td></tr>
<tr><td>John Troiano</td><td>DPR</td></tr>
<tr><td>Natalia Peranginangin</td><td>Syngenta</td></tr>
<tr><td>Tom Nolan</td><td>USGS/NAWQA</td></tr>
<tr><td>Nancy Ragsdale</td><td>USDA ARS</td></tr>
</tbody>
</table>

<p class="pagetop"><a href="#content">Top of page</a></p>
<hr />

<h2 id="welcome">Welcome and Introductions</h2>

<p>Ron Parker and Marietta Echeverria, co-chairs of the Water Quality Tech Team, will be coordinating and facilitating the EMWG meetings for this year. This meeting is focused primarily on groundwater and leaching models. Tier II groundwater modeling will be included for the first time the carbamate cumulative risk assessment.</p>

<p>As a reminder the FIFRA EMWG web site can be found at: 
<a href="http://www.epa.gov/oppefed1/models/water/emwg_top.htm"> http://www.epa.gov/oppefed1/models/water/emwg_top.htm</a>
</p>

<p class="pagetop"><a href="#content">Top of page</a></p>
<hr />

<h2 id="old">Old action items</h2>

	<ul>
	<li><p>Industry will hold its review of EXPRESS until the User's Manual is released 	and the revised version is made available on the ORD/CEAM website. A preliminary 	review has already been undertaken and a full review will follow release of revised 	EXPRESS manual and the software by EPA (ORD or OPP). </p></li>
	<li><p>ORD and EFED will agree whether the volatilization feature should be turned 	on in PRZM/EXPRESS and EFED to make an internal decision on whether to use a 	constant soil temperature.  <strong>Decision to be communicated over list server or 	via reporting at the next EMWG</strong>.  </p></li>
	<li><p>Russell Jones to mention EPA availability to attend Landscape and Mitigation 	2 group (starts 2005) at upcoming EEASG meeting in Europe to formally obtain an 	invitation.  - <strong>conversations are underway</strong>.</p></li>
	<li><p>EFED is working with a contractor to complete corrections of surface water 	modeling scenarios</p></li>
	<li><p>Terrestrial Field Dissipation Study document - <strong>almost done working 	out minor edits and working out the logistics for releasing the FR notices followed 	by a 60 day comment period</strong></p></li>
	</ul>

<p class="pagetop"><a href="#content">Top of page</a></p>
<hr />

<h2 id="brief">Brief updates</h2>

<p><strong>PRZM 3.12.2 Evaluation (J. Hetrick)</strong></p>

<p>The QA/QC process for PRZM 3.12.2 has examined four aspects:</p>

	<ol>
	<li><p>Curve number format change from 3 inputs to up to 30 inputs (M. Echeverria) 	 - seems to be working correctly.</p></li>

	<li><p>Irrigation subroutines  (Jim Wolf) - Initial investigation revealed that</p>

		<ol>
		<li><p>irrigation occurred everyday because the soil moisture critical value 		was set above field capacity,</p></li>
		<li><p>the first day of the simulation was always irrigated because of 			problems with initialization,</p></li>
		<li><p>foliar washoff occurred with under canopy irrigation. </p></li>
		</ol>

	<p> D. Young suggested code changes and ORD/Athens accepted and now it appears to 	be working properly.  <strong>PRZM 3.12.2 will be released upon the completion of 	EFED's QA/QC process.</strong></p>
	</li>

	<li><p>Volatilization (R.D. Jones) - Preliminary investigation suggests that 	volatilization works correctly for a constant 	temperature, but does not work for 	varying temperature daily.  For the volatilization routines dispersion coefficients 	and enthalpies of vaporization are also needed, <strong>RD Jones will draft 	guidance for EFED and will make recommendations to ORD/Athens.</strong></p></li>

	<li><p>The dates corresponding to the RUSLE parameters in EFED's standard scenarios 	is set up according to a calendar-year (i.e., staring on January 1<sup>st</sup>) 	versus a crop-year (i.e., starting with emergence date.  EFED is modifying standard 	scenarios so the dates are in the correct format.  <strong>EFED will post scenarios 	on website once they are corrected.</strong></p></li>
	</ol>

<p><strong>EXPRESS (R. Parker)</strong></p>

<p>The current version of EXPRESS is available on the Waterborne website. ORD will be posting it on the CEAM website in the next two weeks. Everyone is encouraged to download and test the EXPRESS shell and comments are welcomed.  <strong>There is a draft implementation plan for EXPRESS currently being reviewed.</strong></p>

<p><strong>Review of Public Comments on EFED's Modeling Scenarios (R. Parker)</strong></p>

<p>All individual scenarios have been corrected.  <strong>EFED will make corrected scenarios available.</strong>  N. Thurman is organizing the effort to resolve inconsistencies between scenarios through a contractor, the initial response document will be going onto docket in the very near future. EFED has separated out the scenarios which were designed specifically for the OP cumulative assessment from the other standard scenarios since the OP scenarios were developed from a different set of criteria.  <strong>Betsy will send out a list of OP scenarios to the Listserve.</strong></p>

<p><strong>Spray Drift Update (N. Birchfield)</strong></p>

<p>The mechanistic ground spray model is now available in AgDISP. Ron Parker can provide access details for contacting Harold Thistle to those who wish to get a copy  The implementation of AgDRIFT into EXPRESS is an agenda item for EFED's monthly conference call with ORD/Athens.</p>

<p><strong>The Spray Drift Task Force (Rama):</strong></p>

<p>The SDTF is supportive of the incorporation of the mechanistic ground spray model in AgDISP. They are working to simplify AgDRIFT license and making code available to EPA.  They will prepare a final SDTF version of AgDRFIT and seek agreement with EPA on future of regulatory drift modeling and assist in the resolution of Homeland Security issues with distribution of drift models. The SDTF identified the need for a process for version control; this is a universal challenge for all models and development.  It is critical for reproducibility. The SDTF will evaluate the mechanistic ground spray model, hopefully resolving some fundamental concerns with empirical parameters, validating the velocity equation, and comparing the model to US and European data. The SDTF plans on identifying upgrades to AgDISP and long term data needs working with EMWG . <strong>Future agenda item: have ORD present protocol for version control or version control in general.</strong></p>

<p class="pagetop"><a href="#content">Top of page</a></p>
<hr />

<h2 id="topics">Major Topics</h2>

<p><strong>PRZM Diary - Silk Purse or Sow's Ear? Comparing the Predicted Occurrence of Atrazine in the Vadose Zone (PRZM3) with Observed Detections in Shallow Ground Water Across the United States (NAWQA) (J. Barbash, USGS)</strong></p>

<p>The purpose of this study was to examine the extent to which a process model can predict the concentrations of pesticide in ground water using national-scale data only.  The approach consisted of maximizing the incorporation of current process understanding.</p>

<p>The bottom line was that there was poor agreement between PRZM predictions and observations and major concerns related to the importance of compartment size were identified.</p>

<p>PRZM3 is a 1-dimensional, dynamic, compartmental code that simulates water flux, transport and transformations of solutes and degradates in the root zone.  The main advantages of PRZM are that it accounts for broad range of processes and has been widely used and tested.  Some disadvantages of PRZM include poor documentation, large dependency on compartment size, and problems with irrigation. Preferential flow is not modeled in PRZM ("Tipping Bucket" Model).</p>

<p>The sites were selected from the Agricultural Land-Use Studies conducted for NAWQA 1993-1998.  Networks with 10 or more sites were chosen, distances from fields vary dramatically, and a large proportion of the sites are irrigated.</p>

<p>Soil properties were derived from STATSGO data averaged over depth.  Although this was not a satisfying approach, it was considered the only nationally available data.  Degradation was assumed constant with depth.  Wilting point and field capacity were calculated according to the USDA's/ROSETTA program. The crucial element in PRZM is the difference between field capacity and wilting point and not the absolute values.</p>
<p>For all wells, uniform emergence, maturation and harvest date were simulated.   This was considered "best available data within time constraints". The investigators welcome better data sources as they become available.  Comment: SWAT modelers use heat units to set the dates cropping dates.</p>

<p>A uniform atrazine use intensity (application rate) was assumed per site. Intensity was varied by county using NCFAP/ USDA and Ag Census data. Atrazine hydrodynamic dispersion was simulated through numerical dispersion alone (PRZM). This was considered a limitation.  </p>

<p>Soil properties were averaged over 1.5 m whereas flow and concentration were modeled to 1.0 m.  Compared monitoring wells are sampled at water table.  No calibration other than compartment size was performed.</p>

<p>Comparisons between observed and predicted were a function of compartment size.  Where a compartment size of 1 cm resulted in no model output.  Up to 30 cm is necessary to get results.  This was considered an incredibly unsatisfying approach. Russell Jones reported that this was inappropriate given the history of PRZM.  Many other questions were asked including the period of modeling and the importance of looking at the predicted hydrology before worrying about the chemical. Based on the problems they saw, they abandoned further work on PRZM.  They are not planning on publishing this aspect of the work.</p>

<p>It was pointed out that residual atrazine in groundwater is not necessarily associated with this year's application but is more likely to be an accumulation from several years. <strong>Please send additional comments to Jack</strong></p>

<p>Comparisons between prediction and observations concentrations (1254 sites) were poorly correlated.  One sample measurement was compared to one simulation (flow weighted average for 5 years); not accounting for temporal variability.  Detection frequencies were also poorly correlated.</p>

<p>The authors concluded that the study demonstrates the infeasibility of constructing modeling system utilizing national-scale data sources. They encountered considerable difficulties with PRZM including: counter-intuitive dependence of predicted concentration on compartment size, poor documentation and difficult error diagnosis.  The results showed limited agreement between observed and simulated concentrations.</p>

<p><strong>Comparison of LEACHM and PRZM Modeling to Field Data: Effect of Evaporation Simulation on Water Balance and Pesticide Movement (J. Triano, CDPR)</strong></p>

<p>John Troiano presented work from himself, Frank Spurlock and Murray Clayton at CA DPR on water balance.  CA is concerned about ET because of the importance of irrigation in the state and the dependence of irrigation on ET estimates.</p>

<p>LEACHM handles irrigation/evaporation on fine sub-daily time steps. They agreed that FAO-56 methodology makes an optimum benchmark for bare soil irrigation.  Their J. E. Q 1993 presentation (vol 22: 290-298) was the source of the field data -irrigation was set in reference to Et0 values using Rainbird sprinklers. They view irrigation need as 133% of crop ET (to account for spatial inhomogeneity in irrigation).</p>

<p>DPR showed that compartment size was key and the fit for Bromide data improved with 100 instead of 20 segments.  This is influenced by depth of modeling as expected. Research  also looked at influence of timing of irrigation due to the way LEACHM handles irrigation during the day. </p>

<p>PRZM parameterized to be same as LEACHM but with extraction depths of 15 and 30.  Since it is a daily record, PRZM fits are temporarily offset and the first day of irrigation provides a lot of recharge.  PRZM predicts (much) more drainage than LEACHM and fit for bromide was better for LEACHM than PRZM (which moved it further)   </p>

<p>Under winter rain studies PRZM did better at predicting transport without irrigation at 160 days. The issue appears to link to the amount of water applied. It would be instructive to compare PEARL, MACRO for these data sets. </p>

<p>Irrigation regimes on atrazine suggests LEACHM does better than PRZM at low/medium percolation but questions exist at high percolation.  Group pointed out that the alternative evaluation is that the over prediction of transport explains why PRZM over predicts transports (and is therefore a suitable regulatory leaching model).</p>

<p>John feels LEACHM FAO did better on evaporation since it handles both up and down water movement.  Some of this data from LEACHM matches findings from TDR studies.</p>
<p>Considerable discussion covered some fundamental questions on soil hydrology.</p>

<p><strong>Root Zone Water Quality Model (RZWQM): Brief Overview and Case Study (D. Wauchope, S. Cohen, Q. Ma)</strong></p>

<p>Development of RZWQM began in 1985 for upgrading nutrient capabilities and hydrologic modeling.  The pesticides processes were originally considered overly complex and detailed.  RZWQM was revised in 1998 to simplify pesticide processes and to upgrade the user interface.  </p>

<p>RZWQM is executed on a variable time-step with water balance, solute transport, heat transport etc. all solved sub-hourly.  Pesticide processes include a parent - daughter - granddaughter transformation pathway, and multiple options for soil sorption kinetics.</p>

<p>There is currently a standalone version as well as a modularized link with OMS(?).  Additional crop models (CRES-MAZE) are available.  Simulated preferential flow via macropores has been well validated.  ARS will support RZWQM if EPA decides to use this model for pesticide registration.  The fundamental need is for vetted scenarios.</p>

<p><strong>Use of RZWQM to Model Pesticide Leaching in Soil and to Ground Water: Sorption Kinetics, Solute Transport & Field Testing (D. Wauchope, S. Cohen and Q. Ma)</strong></p>

<p>Don introduced the RZWQM topic by giving some history and discussing some novel work (e.g. wheel track study in watershed Z). They are adding another crop model option and feel the macropore element does a good job; however, the erosion routine is still in need of refinement.  The OMS will be used to "preserve" the RZWQM code.  Laj Ahuja feels that if EPA adopts the model USDA will provide training and help but if code changes are needed.  Don believes that a key step will be the creation of agreed RZWQM scenarios that will be needed if we are to be effective with RZWQM.</p>

<p>Quingli Ma made a detailed RZWQM presentation (backed up by a handout including an extensive bibliography) and this also generated a lot of interest.  Generally the model performance was good but additional guidance and collections of data are needed for several of the parameters. </p>

<p>Part 1: Distinguishing Features of RZWQM</p>

<p>Distinguishing features of RZWQM include options for modeling solute sorption, macropore flow, links with extensive databases and the ability to model a wide range of agronomic practices.  Solute sorption can be modeled with a linear-equilibrium adsorption model, a non-linear (Freundlich) equilibrium adsorption model or a two-site equilibrium-kinetic sorption model. Macropore flow is simulated in cylindrical holes, planar cracks and includes absorption of water and chemicals to macropore walls. RZWQM is linked to many databases including USDA-ARS soil physical and hydraulic properties database, NRCS soil Pedon database, STATSGO, USDA-ARS PPD, and several crop growth databases.  Major management practices simulated with RZWQM are tillage operations, fertilizer and pesticide application, planting and harvesting, and irrigation applications.</p>

<p>Part 2: Evaluation of RZWQM </p>

<p>Study-1 (Ma et al, 1996. Soil Sci. 161:646-655)</p>

<p>The study was designed to compare instantaneous equilibrium and equilibrium-kinetic sorption models for simulating leaching of pesticides. Atrazine and fenamiphos was applied to soil cores in the lab. Simulated rainfall was applied at 5cm/h for 2 h and leachate and runoff were collected continuously.  Breakthrough curves for simulated (using equilibrium kinetics and instantaneous equilibrium with average K<sub>oc</sub> and optimized K<sub>oc</sub> by minimizing RMSE) and observed data were compared.  Optimized K<sub>oc</sub> resulted in best prediction.</p>

<p>Study-2 (Ma et al, 2004. Soil Sci. Soc. Am. J. 68: 1491-1500)</p>

<p>RZWQM was used to model the fate of acetochlor and terbuthylazine in the field on a clay loam.  There was good correlation between observed and predicted soil water content across four seasons.  Macropore flow was not simulated.  The equilibrium-kinetics sorption model does a better job predicting pesticide mass in the soil profile and pesticide concentration in soil than the instantaneous equilibrium model.</p>

<p>Study-3 (Ahuja et al, 1996. Pestic. Sci. 48:101-108)</p>
<p>RZWQM was used to model cyanazine and metribuzin in the field on a loamy sand soil.  There was good correlation between measured and predicted concentrations in the soil profile. </p>

<p>Study-4 (Ma et al, 2004. Pest Magmt. Sci. 60: 240-252)</p>

<p>This study examined the effect of soil pH on adsorption coefficients and leaching in a sandy soil.  For certain chemicals environmentally relevant ranges in pH (pH = 4-9) can have a large effect on K<sub>oc</sub> and pesticide leaching.</p>

<p>Study-5 (Malone et al, 2004. Pest Magmt. Sci. 60:277-285)</p>

<p>This study examined the effect of macropore flow and on herbicide leaching.  Excellent correlation, even at a small time-step (hourly), between observed and predicted average cumulative percolate was reported.  Model calibration was performed (see reference for details).</p>

<p>The presenters concluded that RZWQM satisfactorily simulates pesticide fate and transport in soil under a wide range of conditions.  Several unique features makes RZWQM a superior tool for better predictions of pesticide leaching in soil, which in turn provides basis for ground water risk assessment.  Additional guidance and collection of data are needed for several of the input parameters.</p>

<p><strong>Groundwater Modeling for the Carbamate Cumulative Assessment (N. Thurman, D. Young)</strong></p>

<p>A case study of the n-methyl carbamate cumulative risk assessment will be presented to the FIFRA SAP on 2/16-2/18/05 in Crystal City.  More info available at 
<a href="http://www.epa.gov/scipoly/sap">www.epa.gov/scipoly/sap</a>.  The portion of the SAP dealing with drinking water exposure will be on February 17<sup>th</sup>.  There will be four panelists for water exposure, who are still being screened.</p>

<p>The surface water assessment takes advantage of the same approach that was used in the OP cumulative risk assessment.  Ground water is a new, important route of exposure being addressed for carbamates.  Three models, LEACHM, RZWQM, PRZM, will all be presented to the SAP.  The plan is to compare the models with field data for the two carbamates for which there are PGW studies. EFED is considering the European (depth?) and Canadian method (depth?) for converting result from these leaching models to ground water exposure estimates.</p>

<p>Questions to the SAP: </p>

	<ol>
	<li><p>The approach for selecting SW scenarios is based on vulnerability to 	cumulative exposure of carbamates.  A similar approach is being proposed for GW 	scenarios.  Is this reasonable?  Also, is using the integration at the bottom of a 	plane of a leaching model to estimate GE exposure reasonable?</p></li>
	<li><p>Gain feedback from SAP on the relative strengths and weaknesses of each 	model.</p></li>
	<li><p>Gain feedback on conceptual models for co-occurrence of carbamates in GW.  	The conceptual models consist of the use of different pesticides in different 	years, the use of different pesticides for different pests in the same year/ 	season, and the use of different pesticides in adjacent fields. </p></li>
	</ol>

<p><strong>User-friendly CXTFIT2 Model to Estimate Setback Distances (T. Estes)</strong></p>

<p>This applies to aquatic herbicides and the need to estimate the impact of dispersion and degradation so that a "set back" distance from CWS intakes can be calculated for compounds where there is a possibility of exceeding a DW LOC.</p>

<p>General Problem:</p>

	<ul>
	<li><p>Concerns for direct application of a pesticide to a pre-determined treatment 	area</p></li>
	<li><p>Application is in concentrations</p></li>
	<li><p>Dispersion and transport occurs</p></li>
	<li><p>If treatment does not result in an exceedence of a LOC - no problem</p></li>
	<li><p>If above, there is a problem; and there is an DW intake you may need a set-	back</p></li>
	</ul>

<p>Concentration is a function of basic dispersion/convection equations.<br />	
Conditions for Setback Estimation<br />
Treatment Area Assumptions (Kennedy and Mahoney, 2002):</p>

	<ul>
	<li><p>Since it is a 1-D; only the length of the application area is considered</p>	</li>
	<li><p>Index Reservoir: L = 640/82 = 7.8</p></li>
	<li><p>Treatment length: 360 m; water flow rate 2.28 m/d, dispersion rate 43.2 	m2/day; for a <4 acre treatment area</p></li>
	</ul>

<p>Questions to be answered:</p>

	<ul>
	<li><p>Model is very sensitive to flow rate.  What are appropriate flow rates for 	specific application areas or waterbody sizes?</p></li>
	<li><p>What are appropriate dispersion rates?</p></li>
	<li><p>Should water body size be correlated with treatment area?</p></li>
	<li><p>How do CXTFIT2 results compare to observed concentrations?</p></li>
	<li><p>How are half-lifes to be determined?</p></li>
	</ul>

<p>Limitations of original model:</p>

	<ul>
	<li><p>Not designed for setbacks</p></li>
	<li><p>Can only be run for one set of parameters at a time</p></li>
	<li><p>Output is not user-friendly</p></li>
	</ul>

<p>Development of Setback:</p>

	<ul>
	<li><p>Runs CXTFIT2 iteratively for a range of water flow rates, dispersion rates 	and pesticide half-lives for a fixed application length and treatment 	concentrations</p></li>
	<li><p>Allows user to specify LOC and it calculate the necessary set-back</p></li>
	</ul>

<p>Proposed future enhancements:</p>

	<ul>
	<li><p>Ability to generate concentrations at a specific setback for range of flow 	rates, dispersion rates, and half-lives</p></li>
	<li><p>Ability to store output for each simulation for iterative runs if requested 	by user</p></li>
	<li><p>Better user-interface</p></li>
	<li><p>Built-in standard scenarios</p></li>
	</ul>

<p>The SETBACK module is a tool for convenient use of CXTFIT2 and it runs them interactively.  This model is available via Tammy Estes.</p>

<p class="pagetop"><a href="#content">Top of page</a></p>
<hr />

<h2 id="wrap">Wrap-up: Next Meeting</h2>

<p>This next meeting will be held on April 11, 2005.</p>

<p class="pagetop"><a href="#content">Top of page</a></p>
<hr />

      <!-- #EndEditable --> 

</div> <!-- END CONTENT -->

<hr class="skip" />

<div id="area-nav"> <!-- BEGIN LEFT SIDEBAR NAVIGATION -->
	<h3 class="skip">Local Navigation</h3>
	<ul>
		<li><a href="http://www.epa.gov/pesticides/">Pesticides Home</a><hr /></li>
		<li><a href="http://www.epa.gov/pesticides/science/index.htm">Science & Policy Home</a></li>
		<li><a href="http://www.epa.gov/pesticides/science/committees.htm">Advisory Committees</a></li>
		<li><a href="http://www.epa.gov/pesticides/science/policies.htm">Policy & Guidance</a></li>
		<li><a href="http://www.epa.gov/pesticides/science/guidelines.htm">Test Guidelines</a></li>
		<li><a href="http://www.epa.gov/pesticides/science/models_db.htm">Models & Databases</a></li>
		<li><a href="http://www.epa.gov/oppbead1/labs/index.htm">Laboratories</a></li>
		<li><a href="http://www.epa.gov/oppbead1/methods/index.htm">Analytical Methods Procedures</a></li>
	</ul>
</div> <!-- END LEFT SIDEBAR NAVIGATION -->

<hr class="skip" />

<div id="footer"> <!-- BEGIN FOOTER -->
	<ul id="globalfooter">
		<li><a href="http://www.epa.gov/">EPA Home</a></li>
		<li><a href="http://www.epa.gov/epafiles/usenotice.htm">Privacy and Security Notice</a></li> 
		<!-- BEGIN AREA COMMENTS LINK -->
		<!-- CHANGE link to point to your own contact page -->
		<li class="last"><a href="http://www.epa.gov/pesticides/science/contacts.htm">Contact Us</a></li>
		<!-- END AREA COMMENTS LINK -->
	</ul>

</div> <!-- END FOOTER -->

<p class="skip"><a id="skipbot" href="#content" title="Jump to main content.">Jump to main content.</a></p>
</body>
</html>