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4.Environmental Analysis V obtained, if available, from DWR, San Joaquin County Environ mal Health Department, Stanislaus County, and the former property owners :'Crroundwater wells that will not remain in operation shall be properly destroyed and removed in accordance with the DWR Well Standards and, depending on the location, under permit and inspection ` from either the Stanislaus County Department of Environmental Health or San Joaquin County as per the San Joaquin County Development Title, Section 9-1115.5(e). The well destruction shall be designed to create a sanitary seal that would not conduct vertical water flow in the event that the well is truncated or damaged during mining operations. Impact Significance After Mitigation: Mitigation for this impact ensures that unused or abandoned wells would be properly destroyed and that water quality impacts .. associated with truncated or undiscovered, open wells would be less than significant. Impact 4.8.4: Groundwater extraction associated with the proposed project could lower groundwater levels beyond the project boundaries,lower local or regional groundwater levels that are below the current pumping depths of existing private or municipal groundwater supply wells.This would be a less-than-significant impact. .� The proposed project would require water for aggregate processing,dust control, and landscaping.The city of Tracy, as well as other local municipal, agricultural, and industrial operations relies on groundwater as either a primary water supply or to supplement surface water entitlements obtained from state and federal water projects. Local pumping wells (those within approximately two miles)are currently extracting groundwater from the similar aquifers,and consequently, increased pumping within this system could lower local groundwater levels and reduce or eliminate available groundwater for other local users. Adverse impacts of a significant decline in groundwater levels are realized when the groundwater level is lowered below the level of the down-well pump or in some cases,below the depth of the wells. Groundwater Impact Analysis Groundwater extraction data for the agricultural wells within the proposed project area indicate that between 1997 and 2003, agricultural uses on the former properties required an average of approximately 570 acre-feet of groundwater.The former agricultural operations extracted groundwater from the Barnes Well,the A&L property well, and the Costa Ranch domestic well.9 The estimated water demand for the proposed aggregate mining operations would range between 3.8 and 8.9 million gallons of water per day(mgd)depending on production quantities. Under normal operations,the project applicant would generate the majority of its water supply from surface water decanted and recycled within a series of proposed silt settlement(siltation)ponds.10 9 This average groundwater pumping volume combines a seven-year average groundwater withdraw rate of 95 ac- ft/yr from the Burnes No.2 Well,a seven-year average withdrawal rate of 474 ac-ft/yr from the A&L No. I Well and annual withdrawal rate of 1 ac-ft/yr from the Costa Property domestic well with partial agricultural use. 10 Once a silt pond is excavated,permeable aggregate material would be exposed on the bottom of the pond.Because of the high permeability of the underlying aggregate material,water entering the pond would seep vertically into the underlying gravels.The seepage would continue until the fine-grained silts discharged into the pond begin to r settle into the pore spaces of the aggregate.As the fine-grained sediments accumulate,the pond bottom becomes less permeable and the infiltration volumes and rates reduce. RMC Pacific Vernalis Quarry Mining and Reclamation Project 4.8-26 ESA 1203015 Draft Environmental Impact Report May 20013