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2.2.7.6 Oxidation Reduction Potential <br /> Oxidation reduction(redox)potential is a measure of the relative tendency of a solution to accept or <br /> ` transfer electrons. The redox potential of a groundwater system depends on which electron acceptor is <br /> being reduced by microbes during BTEX oxidation. The redox potential for the site ranged from-112 to <br /> ` 126 millivolts(mV). The lowest redox potential was measured in well MW-2A,which,as expected, <br /> coincides with the highest BTEX concentration,low dissolved oxygen concentration,and elevated iron, <br /> sulfate, and methane concentrations, all of which are consistent with anaerobic biodegradation. <br /> 2.2.7 7 pH <br /> The pH ofa solution is the negative logarithm ofthe hydrogen ion concentration. Groundwater at the site <br /> is slightly acidic,ranging from 6.64 to 6.71. Microbes capable of degrading petroleum hydrocarbons <br /> ` generally prefer pH values in the 6 to 8 range. The pH ofgroundwater at the site is therefore suitable for <br /> microbial activity. <br /> 6. 2.2.7.8 Total Dissolved Solids and Salinity <br /> Total Dissolved Solids(TDS)concentrations at the site ranged from 0.78 to 1.44 grams per liter(g/L). <br /> The salinity ranged from 0.89 to 1.04 parts per trillion(ppt). This indicates that the groundwater from <br /> Lithologic Zones 3 and 4 at the site is slightly brackish and not desirable as drinking water. <br /> 2.2.8 Groundwater Use <br /> Indic area surrounding the site,deep groundwater is utilized as a drinking water source by the California <br /> Water Service Company(CWSC). The CWSC has three production wells(Wells 28,37,and 53)within <br /> 5,000 feet of the site. Wells 28 and 53 are downgradient of the site;however,these wells pump water <br /> 6. from a much lower aquifer. Well 28 is screened from 208 to 425 feet bgs and Well 53 is screened from <br /> 250 to 530 feet bgs. <br /> ` Groundwater from the Lithologic Zone 4 aquifer is not presentlybeing used as a source ofpotable water. <br /> The relatively low hydraulic conductivity and slightlybrackish conditions ofthis aquifer suggest that it is not <br /> ` likely that Lithologic Zone 4 water will be a future source of potable groundwater. <br /> 7 <br />