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RECEIVED <br />t = Time to Groundwater FEB 2 5 2016 <br />z = Depth to Groundwater <br />k = hydraulic conductivity ENVIRONMENTAL <br />HEALTH RF.RARTMENT <br />• Depth to Groundwater reference - <br />Groundwater is encountered at 4 feet below ground surface (bgs) in <br />MW-36WA and 5 feet bgs in wells MW -68A and MW -63A. The <br />majority of the wells at the site show that groundwater varies <br />widely between 4 and 12 feet bgs, and the occurrence of <br />groundwater at 4-5 feet bgs is observed in more than one location. <br />This, combined with projected water levels using the cross sections <br />and expected seasonal fluctuations in the water table, suggests that <br />4 feet bgs is an appropriate depth -to -groundwater value for <br />calculations aimed at a real worst case scenario approach. <br />• Hydraulic Conductivity (k) reference — <br />Pumping tests data were provided for wells MW -28A, MW -29A, <br />MW -18A, and MW-3OA. It is noted that these wells are located <br />north of the secondary containment berm for the tank farm. Cross <br />section information shows that the upper unit (primarily fine- <br />grained materials) is laterally continuous across much of the site to <br />a depth of at least 4 feet bgs. The hydraulic conductivity values are <br />based on an average value calculated from multiple units, which <br />are laterally continuous across the entire site and extend to a depth <br />of at least 50-70 feet bgs. <br />Based on drawdown and recovery test results, Neumann and Theis <br />equations are used to obtain Transmissivity, Hydraulic <br />Conductivity, and Specific Yield values for these four wells. <br />Hydraulic Conductivity values range from 11 ft/day to 97 feet per <br />day. For the Time to Groundwater calculation, a value of 26 ft/day <br />was used, which is the calculated estimate for the ground beneath <br />the site, based on the Distance -Drawdown method. This value is <br />chosen instead of the maximum hydraulic conductivity because the <br />pumping tests provide enough information to reasonably <br />approximate actual flow velocities, instead of using theoretical <br />maximums due to uncertainty. <br />ERM 5-2 110870\CHEVRON\SPCC - JULY 2010 <br />