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Blended groundwaters having an influent concentration of approxi- <br /> mately 20 ppm were used to conduct pilot tests. Pilot tests were <br /> performed with a bench-scale ion exchange system similar to the system <br /> designed for MCTC. The tests were performed to determine the chromium <br /> removal capabilities of the ion exchange resins and to determine the <br /> system's run length prior to bed exhaustion. The data collected from <br /> the pilot tests were used as a basis to predict the operating character- <br /> istics of the actual chromium removal system. Figure 1 graphically <br /> illustrates the hexavalent chromium treatment system effluent concen- <br /> tration as a function of system throughput for various treatment system <br /> influent chromium concentrations. The horizontal dashed line at a <br /> concentration of 50 ug/l or parts per billion (ppb) represents the <br /> maximum hexavalent chromium concentration limit allowed for discharge. <br /> The 20 ppm curve shown on Figure 1 was determined directly from the <br /> laboratory data obtained using the 20 ppm blended groundwaters. The <br /> calculation of system throughput at breakthrough at a more likely <br /> groundwater influent concentration of 10 mg/l hexavalent chromium is <br /> presented in Table 3. The 30, 10, 5 and 1 ppm curves were developed <br /> based on the 20 ppm laboratory data curve. <br /> All of the curves shown on Figure 1 have a similar shape indicating <br /> that the system will behave in a predictable manner for varied influent <br /> concentrations. The treatment system total chromium effluent concen- <br /> tration is approximately 15 ppb for the first half of the run. The <br /> 15 ppb concentration is well below the 50 ppb limit allowed for <br /> discharge. As the treatment run continues, the effluent hexavalent <br /> chromium concentration begins to increase. The hexavalent chromium <br /> effluent concentration continues to increase as the run progresses until <br /> the concentration reaches the 50 ppb breakthrough limit allowed for <br /> discharge. <br /> Storm Water Performance <br /> Storm water runoff will enter the treatment plant during the rainy <br /> season starting in the fall of 1987. The float controls in the flow <br /> equalization basin allow for the preferential treatment of storm water <br /> 4 <br />