Appendix 2B Test Basins and Monitoring Data Used for Model Evaluation for SAM

One of the elements of environmental model development is comparison of model outputs (in the case of SAM, estimated pesticide concentrations in water) to measured data (in this case, monitoring data) (USEPA CREM, 2009). To be useful in evaluating how well SAM estimates pesticide concentrations in water, the monitoring data need to be sampled sufficiently to capture the day-to-day, seasonal, and yearly variations in pesticide concentrations in water (see USEPA OPP, 2010b, 2011, and 2012 for a more in-depth discussion). The extent to which monitoring data adequately reflect short-term variability in pesticide concentrations in water depend on how frequently samples are collected and whether the sampling was targeted to pesticide use areas and times of the year in which pesticides have been sampled. As the interval between sampling events increases, the likelihood of capturing short duration/daily peaks in pesticide concentrations decreases.

USEPA OPP focused on three test basin areas - the Mark Twain Lake (MO) basin, the Scioto River (OH) basin and the White River/East Fork (IN) basin - for initial model evaluations. These three basins contain multiple monitoring sites, predominantly for atrazine, with multiple years of sampling and sampling frequencies that range from weekly to daily. The data predominantly come from two atrazine monitoring studies conducted by Syngenta Crop Protection: the Atrazine Ecological Exposure Monitoring Program (AEEMP) and the Atrazine Monitoring Program (AMP) for drinking water.

The AEEMP, which monitored headwater streams in areas expected to be vulnerable to atrazine runoff, is one of the few monitoring studies that include daily sampling for pesticide concentrations in water (USEPA OPP, 2009a). The AMP study included weekly sampling for atrazine during the likely use season (USEPA OPP, 2011, 2012). These two data sets, which covered a range of watershed sizes and water body types (headwater streams to larger streams and rivers, reservoirs and other impoundments), were used to do preliminary evaluations of SAM. Details on these studies, as well as the data themselves, can be obtained through USEPA OPP's Atrazine Information page (http://www.epa.gov/oppsrrd1/reregistration/atrazine/).

The Catalog tab provides a summary of the monitoring study, watershed area, and maximum annual concentrations measured for each year of the study. The tabs that follow (listed in the Catalog tab) each provide measured concentrations from the monitoring studies, a graph plotting the concentrations over time (chemograph), and, in the case of the AEEMP sites, ancillary data on daily precipitation and stream flow.

USEPA OPP is looking for additional intensively-sampled data for other pesticides in order to expand the evaluation to a broader range of pesticide uses and properties. These will be included in expanded model development plans.Figure 1: Location of Test Basin Areas for SAM Model Development and Evaluation.

Figure 2: AEEMP and AMP Monitoring Sites in the Mark Twain (MO) Test Basin Area.Figure 3: AEEMP and AMP Monitoring Sites in the Scioto River (OH) Test Basin Area.

Figure 4: AEEMP and AMP Monitoring Sites in the White River (IN) Test Basin Area.