R98-72 AUTHORIZING AGREEMENT - Laserfiche WebLink

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,� � , WATERSHED MONITORING FOR THE LAKE DECATUR WATERSHED by Illinois State Water Survey BACKGROUND The Illinois State Water Survey has been conducting the Watershed Monitoring and Land Use Evaluation for Lake Decatur Watershed study since spring of 1993. This study is a result between the Ci of Decatur and the Illinois of the signing of a Letter of Commitment (LOC) ty Environmental Protection Agency. The LOC was initiated because of high nitrate concentrations in the city's public drinking water supply since 1979. The study's main goal has been to assist the City of Decatur in complying with the LOC by following three specific objectives: 1) Establishment of a watershed monitoring network that will quantify the amount of nitrate being contributed by tributaries upstream of Lake Decatur; 2) Develop a non-point source pollution model for the watershed that will simulate nitrate yields from different land use practices, which can be used to evaluate the impacts of BMPs on water quality; and 3) Analyze current land uses in the watershed and formulate alternative land managementpractices and mitigation projects to reduce the nitrate concentrations in Lake Decatur to acceptable drinking water levels. A major technical report was published in January 1996 (Demissie, et al., 1996. - ISWS Misc. Pub. 169). The report provides the background information on the watershed by reporting on the historical water quality problems in Lake Decatur, watershed physical characteristics, and land uses. A discussion of the sources and transformations of nitrogen, as well as a detailed hydrologic analysis of the watershed are included. The hydrologic and water quality monitoring data (May 1993 through April 1995) are presented and the mathematical modeling effort discusses the effects of best management practices on the nitrate loading into Lake Decatur. Subsequent one-year progress reports have been published in ISWS Contract Reports 602 (Keefer and Demissie, 1996) and 620 (Keefer, Demissie, Shaw, and Howard, 1997). The latest , publication (ISWS Contract Report 620) reports watershed monitoring data from May 1993 through April 1997. Watershed monitoring data for this current collection period (May 1997 through April 1998) is almost complete. Analysis and reporting of this data will be performed the summer of 1998. The watershed monitoring component of the study was established in May of 1993 and will be concluding in April 1998. Figure 1 shows the location of the stations that are being monitored throughout the watershed. In order to best evaluate any impending land management changes, continued monitoring in the watershed is highly recommended. A sixth year of 1