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Ms. Kerry Sullivan April 8, 1992 Page 11 Page 4.6 - 10 No diversion from the Mokelumne River (i.e., under appropriate right) was assumed,since it has not been established(by the applicant or the State Division of Water Rights) that there is water C183 available for appropriation in sufficient quantity and frequency to be of any significance to the lakes'water supply needs. Portions of the property are riparian. Riparian users have a correlative right to use natural flow and can store up to 30-days' need. Page 4.6- 12 The water balance calculations show the make-up water requirementto be in the range of 200 to 400 acre-feet during the iate summer and early fall of these dry years. In order to meet the water needs of the project, as presently planned, this water would be obtained either from groundwater pumping, from summer diversions from the Mokelumne River under riparian right (see following discussion),or from a combination of these two sources. This amount of water, if obtained entirely from the Mokelumne River, could represent a diversion of as much as 10 to 15 C184 percent of the summer streamflow in the river. Indications from the Department of Water Resources (DWR) are that no summer diversions are likely to be permissible for environmental reasons (Cassel, 1991). If obtained from groundwater, it would be equal to twice to three times the present amount of groundwater withdrawal, and would exceed the estimated local recharge of the aquifer, adding to the existing overdraft conditions in the area. Obtaining a portion of the required make-up from both sources would lessen the magnitude of the individual impacts on the river and on the aquifer. The plan is to fill the lakes from natural runoff in Jahant Slough and excess flows in the Mokelumne River (pursuant to riparian and aoorooriative rights, once obtained) during the winter and spring runoff. Groundwater pumping will be confined to necessity and will be within recognized water rights and much less than would occur if the property was irrigated similarly to the adjacent farms. Page 4.6 - 17 Mitigation 4.6-2 The applicant should apply for and obtain an appropriative water right permit for the increased storage of runoff from Jahant Slough or from diversion of runoff from the Mokelumne River.. This C185 will include the completion of any studies, as required by the State Division of Water Rights, including determination of the availability of such water in Jahant Slough and the lower reaches of Mokelumne River for appropriation. We will apply for such permits. Page 4.6 - 18 Mitigation 4.6-3(a) Dry season diversion of water from the Mokelumne River for irrigation, under claim of riparian right, should be limited to an amount determined to not adversely affect instream flow requirements or the existing water users. Prior to final map approval, the applicant should complete an inventory of existing water uses and instream flow requirements during the summer C186 to deterrr'ne the amount of water available for summer diversion, and the applicant's equitable share of such water. This',nventory should focus on summerflow allocations and environmental LII-L%