Laserfiche WebLink
<br />MWSI Project <br />Phase II Conjunctive Use Summary Report - DRAFT <br /> <br />August 22, 1995 <br /> <br />Alternatively, the additional surface water supplies obtainable under a conjunctive use <br />plan could be temporarily stored in aquifers and used to produce additional firm yield which can <br />be made available to the metropolitan area. Under this latter approach, conjunctive use is similar <br />to new reservoir construction except that the additional storage space is achieved by using the <br />storage capacity of aquifers, <br /> <br />There are sufficient groundwater supplies available within and/or adjacent to the <br />metropolitan area to greatly increase the efficiency of use of divertible surface supplies from <br />surface supply systems under a conjunctive use approach. There are, however, concerns <br />regarding the depletion of these non-tributary aquifers over time, and decisions must be made <br />regarding acceptable rates of long term depletion. Groundwater management goals can range <br />from depletions at one percent per year, the maximum allowable under Colorado Statute, to no <br />long-term depletion, which can be accomplished only through aquifer recharge, Within this <br />range of choices, aquifer depletion rates could be controlled and managed as pan of the design of <br />a conjunctive use plan, thereby determining a design life for the aquifers included in the system, <br />For example, specifYing a depletion rate of 0.2 percent per year would pip the system for a 500- <br />year life. <br /> <br />A key component to an optimal conjunctive use plan is the use of unused surface water to <br />replenish the groundwater in the aquifers, In this case, the aquifers can act as an underground <br />storage reservoir which would be depleted in time of drought and recharged in times of excess <br />supply from surface water sources. <br /> <br />While groundwater recharge is occurring at numerous locations throughout the United <br />States, deep aquifer recharge using wells is relatively new in Colorado. Pilot programs <br />recharging the Arapahoe aquifer of the Denver Basin have been underway for several years with <br />promising results on a pilot scale as described in a previous section, It is possible that that <br />groundwater recharge (including injection, storage and recovery) of the Denver Basin aquifers <br />could be viable on a larger scale and could be used in a conjunctive use program. Some <br />unresolved technical issues remain, however, including the feasibility ofrecharging other Denver <br />Basin aquifers and of recharging relatively large volumes of water into extensive areas of the <br />Denver Basin aquifers over the long term. Additional research and expanded pilot studies are <br />recommended to determine the feasibility of recharge, both physically and economically. These <br />studies need to determine if high rates ofrecharge can be sustained over long periods of time and <br />should continue to evaluate the effects of recharge on well productivity, Reduced productivity <br />and increased well redevelopment costs could significantly affect the economics of a conjunctive <br />use program. <br /> <br />Another factor which could affect the feasibility of recharge for conjunctive use is the <br />size and continuity of the groundwater/recharge area panicipating in a conjunctive use plan. If <br />the recharge area is relatively small and is adjoined by non-panicipating areas with high rates of <br />groundwater depletion, the recharged waters may not be physically available for recovery or may <br /> <br />29 <br />