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<br />Attachment I <br /> <br />CHATFIELD RESERVOIR STORAGE REALLOCATION <br />WATER QUALITY ANALYSIS ALTERNATIVES <br /> <br />Meetings of the water quality workgroup have investigated a range of approaches to <br />determining the impact of reallocation on various water quality parameters. The existing <br />model has been determined to be inadequate to characterize future changes in volume or <br />operations. A one-dimensional model, LAKE2K could be used to address some <br />parameters but would not be effective for all. The use of two- and three-dimensional <br />models (CE-QUAL- W2 or Environmental Fluid Dynamics Code [EFDC]) could be used <br />to address most of the questions; however, their costs under the current budget and time <br />frame appear to be prohibitive. <br /> <br />Water quality concerns have focused on three main issues: nutrients/algae (including <br />phosphorus and dissolved oxygen), metals mobility, and E. coli bacteria. Tetra Tech <br />proposes the following approaches to addressing these three concerns. Although <br />volumetric changes are considered through these approaches, detailed evaluation of <br />operations are not. Operational influences are expected to be most influential under <br />"critical" conditions, and these conditions will be evaluated using the proposed <br />approaches. <br /> <br />Metals Mobility <br /> <br />The mobility of metals within Chatfield Reservoir could be addressed in the absence of a <br />dynamic model using a three step approach. First Tetra Tech would use existing <br />bathymetric data, stage-storage relationships, and existing monitoring data to estimate the <br />anoxic lake volume and the bottom surface area of the lake that it covers under the <br />existing condition as well as conditions simulating the increased storage scenario. The <br />maximum volume in the lake would represent the "worst-case" scenario. The second step <br />would involve a literature review and identify metals flux rates from typical lake bottoms <br />under anoxic conditions. In the final step, Tetra Tech would apply the flux rate(s) to the <br />entire anoxic bottom surface area to predict an overall internal metals loading from the <br />lake bottom. The loading and the lake volume would be used to estimate surface water <br />concentrations. <br /> <br />Assumption: The only thing that changes between the current and future scenarios is the <br />size of the anoxic zone and the lake volume. <br /> <br />Limitation: The approach does not fully address the dynamics of the system, however it <br />evaluates the most probable mechanism for metals influence under the proposed scenario. <br /> <br />Cost: Approximately $12,000 <br />