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.