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5 GROUND WATER INVESTIGATION RESULTS <br /> 5.1 GEOLOGIC FINDINGS <br /> As referenced in above and in previous reports, the geology beneath the site is <br /> dominated by Quaternary Age alluvial sediments of the ancestral Stanislaus River, <br /> derived from granitic parent material. Borings at the site indicate near surface is <br /> comprised of silty sand to sandy silt material with shallow lenses of clean sand and <br /> r sandy gravels at depth. Both borings encountered sand at depth (greater than 35 feet) <br /> and MW-10 encountered a laterally discontinuous sandy gravel/gravelly sand layer at 5 <br /> to 20 feet. Sand encountered was composed of poorly sorted fine to coarse grained sand <br /> f <br /> material. <br /> First encountered ground water while drilling at MW-10 was found in the shallow <br /> gravel layer at 15 feet below ground surface. This level was considered to be perched as <br /> the confining silt/clay layer below was dry and ground water receded to 23 ft after <br /> drilling. The first encountered ground water in MW-11 exhibited semi-confined aquifer <br /> behavior. First encountered ground water while drilling was 26 feet bgs which came up <br /> to 21.2 feet bgs after drilling. <br /> 5.2 GROUND WATER FINDINGS <br /> Ground water elevations at the site range from 79.35 to 84.31 ft. Ground water <br /> elevation is presented in Table 5. Ground water flow is influenced by mounding near <br /> MW-1, refer to Figure 2. Ground water mounding produces an increase in elevation <br /> near monitoring wells MW-1 and MW-3. Ground water flow is radial at a gradient <br /> between wells MW-11 and MW-6 calculated at 0.00187 ft/ft. <br /> Analytical parameters results are provided in Table 3. For the parameters Total <br /> Dissolved Solids, Bicarbonate as CaCo3, and Chloride results were elevated from MW- <br /> 10 relative to MW-11. TDS exceeds California and Federal Secondary Drinking Water <br /> Standard Maximum Contaminant Levels (MCL) in both wells and the duplicate. The <br /> MW-10 chloride result at 220 mg/L is elevated but still below the secondary MCL of 250 <br /> mg/L. <br /> City o RRiverbank Wastewater Treatment Plant Monitoring Well Installation <br /> DE Protect No 109 06 May 2006 <br /> 14 Rev.0 <br />