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<br />MWSI Project <br />Phase II Conjunctive Use Summary Report - DRAFT <br /> <br />August 22, 1995 <br /> <br />Table 8: Borrow Limit vs. Surface Water CapturelPumping Rate <br /> <br />NO NET AQUIFER DEPLETIONS <br />BORROW SURF ACE WATER PUMPING RATE <br />LIMIT CAPTURE REQUIRED (Acre-Feet) <br />80,000 51,500 91,500 <br />100,00 58,500 J 08,500 <br />120,000 63,400 123,400 <br />140,000 67,800 137,800 <br /> <br />300 YEAR AQUIFER LIFE <br />BORROW SURFACE WATER PUMPING RATE <br />LIMIT CAPTURE REQUIRED (Acre-Feet) <br />80,000 65,500 140,000 <br />100,00 73,000 155,000 <br />120,000 78AOO 175,000 <br />140,000 83,000 200,000 <br /> <br />A graph of Table 8 is presented as Figure 8, This figure shows limited gains in yield for <br />both no net depletions and a 300 year aquifer life as the borrow limit is increased to 140,000 <br />acre-feel. While gains are limited, the increase in pumping rate and hence the cost of the project <br />is substantial. Based upon this graph, it is likely that the borrow rate should not extend beyond <br />100,000 acre-feet since costs escalate rapidly with little gain in surface water capture. This <br />assumption should be re-evaluated in Phase 3 of this study when costs of the system are better <br />understood, <br /> <br />Figure 8 also shows the limited benefit of allowing aquifer declines. For an 80,000 acre- <br />foot borrow limit, the net gain in surface water capture for "no net aquifer depletion" versus a <br />300 year aquifer life is 14,000 acre-feet or a 27 percent gain. This gain is achieved with a 52 <br />percent increase in well/collection costs, and an estimated 40 percent increase in overall project <br />costs. The result is similar and slightly worse as the borrow limit increases. <br /> <br />Considering the marginal cost of this gain in surface water yield and the expressed <br />concerns of several providers regarding aquifer depletion, the recommendation is made to <br />consider a "no net aquifer depletion" approach to conjunctive use. The yield under this scenario <br />at a borrow limit of 100,000 acre-feet is about 60,000 acre-feel. This yield would include <br />supplies needed to offset exisling groundwater depletions as well as any "new yield" that would <br />remaIn. <br /> <br />57 <br />