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<br />MWSI Project <br />Phase II Conjunctive Use Summary Report - DRAFT <br /> <br />August 22, 1995 <br /> <br />. There is a potential for mircobiota growth near the well bore due to the <br />ammonium concentration in the groundwater. This problem can be handled <br />through a residual disinfectant in the recharge water and pumping the well to <br />waste before recharge, <br /> <br />. There is a significant reduction in trihalomethanes (THM) and total organic <br />carbon (TOC) concentration in the recharge water. This is important as the EP A <br />may reduce the maximwn THM contaminate level for municipal water supplies, <br />There was a concern with respect to THMs due to the injection of chlorinated <br />water, The THMs are removed by absorption upon aquifer materials or biological <br />processes, <br /> <br />. CH2M reports that Well A-6 exhibited an increase in well efficiency after the <br />initial injection cycle with subsequent small reductions in efficiency after the <br />initial cycle, The increase in efficiency is attributable to a flow reversal through <br />the well screens which is similar to developing the well, In the third injection <br />cycle the well experienced an improvement in its hydraulic condition which was <br />thought to be the result of hydraulic fracturing of the aquifer. <br /> <br />Data and information from both studies indicates that mixing of injected and native <br />waters occurs during the injection/recovery cycles. Centennial's water quality information <br />suggests that pumping-phase water quality trends from the injected to the native water quality <br />over the pumping cycle, <br /> <br />Recharge Projects Elsewhere <br /> <br />Groundwater injection and recovery projects have been established in Utah, Nevada, <br />Florida, California, Texas, Washington, Virginia, and in foreign countries (Payne, 1995). The <br />earlier projects developed in these other states were established in 1985 to 1987. Other projects <br />were started in ]990 to 1993. The projects involve injection and recovery into unconfined, semi- <br />confined, and confined aquifers, The Willows and Centennial projects have the lowest values <br />for transmissivity and specific capacity when compared to projects in these other states. Projects <br />in these other states have the benefit of better aquifer properties when compared to the Denver <br />Basin aquifers, These better aquifer properties result in higher injection and recovery rates and <br />more favorable well hydraulics, Wells in Florida can inject and recover groundwater at several <br />thousand gallons per minute. A review of case studies shows that the injection and recovery <br />projects established to date have been successful and have not been burdened with problematic <br />well hydraulic or water quality problems, <br /> <br />Assessment of Recharge Potential <br /> <br />From our review of the Centennial and Willows injection and recovery projects, and our <br />meetings and discussions with the participants in these projects, we conclude that injection, <br />storage and recovery projects in ,the Arapahoe aquifer are viable. The unknowns at this time <br /> <br />15 <br />