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SWSI Phase 2 Technical Roundtable <br />Water Conservation and Efficiency <br />There should be lesser environmental impacts than new water storage <br />development, unless a reduction in return flows impacts the environment more <br />than new storage development. <br />Water and wastewater treatment, distribution, collection, capital, and operations <br />and maintenance costs may be reduced. <br />Return flows from over-irrigation may be of a reduced water quality than the <br />original water quality of the water diverted for M&I use. <br />Some of the issues involved in evaluating the net available water supply produced <br />from M&I water conservation are: <br />M&I direct flow water rights cannot be stored or carried over for drought periods <br />(absent a change of use proceeding in water court), thus conserving water and <br />reducing the demand on direct f low rights may not create reliable supply to meet <br />new demands (for example for new growth.) <br />CU water rights, such as transbasin, non-tributary, groundwater, or CU <br />agricultural transfers, on the other hand, can be stored. If the overall demands on <br />CU supplies can be reduced, the "saved" water can be used to meet the demands of <br />new growth, improve reliability or both, if adequate storage is available to carry <br />over the conserved water for use in drought periods. <br />Many MB~I water users have substantial transf erred agricultural rights that provide <br />for the diversion of the entire historical amount of irrigation use as long as CU is <br />not increased and historical return flows are maintained. In these instances, <br />wastewater returns and return flows from lawn irrigation have been quantified and <br />may be used to maintain historical return flows such that historical CU is not <br />increased. In some cases, conservation that results in reduced volumes of <br />wastewater or lawn return flows can require M&I users to acquire additional water <br />supplies to maintain these historical returns if sufficient effluent is not available. <br />These additional water supplies may be of a lower quality and theref ore less <br />expensive than the water produced through conservation. <br />Augmentation plans can be developed that account f or wastewater and lawn return <br />flows, and only require that the M&I CU be replaced. As a result, conservation <br />would not result in an increase in supply unless the MB~I CU is reduced, such as <br />through the reduction in total irrigated areas of lawn or conversion of lawn to <br />lower water using landscape. The assumed CU may be decreed in an augmentation <br />plan and as a result, any attempt to use conserved water could require a re-opening <br />of the augmentation decree to re-quantify CU. This action would likely be costly <br />and could present a high level of risk to the water provider. M&I landscape <br />irrigation return flows, in addition to satisfying downstream rights, also creates <br />delayed return flows than can have instream and riparian environmental benefits, <br />and maintains aquifers f or domestic and irrigation wells. <br />~• ~ <br />DRAFT <br />12 <br />S:IMEETINGSITECHNICAL ROUNDTABLEITRT MEETING - SPECIFICIWATER EFFICIENCYISWSI WATER EFFICIENCY TRT BRIEFING.DOC <br />