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Mr. Theodore I. Wittmayer, Attorney at Law January 27, 1993 <br /> Stone Brothers and Associates Page 4 <br /> 2. Soil Investigation <br /> The proposed soil investigation scope consists of soil sampling from the soil boring o er the <br /> former UST site and soil sampling from the two monitoring well borings. Thus, two of the <br /> borings will be located near the former UST site (Area 1) and one will be located near the <br /> former gasoline dispenser and boring B-9 (Area 2). <br /> The lateral extent of hydrocarbon impact to soil has been well defined in Area 1 but the vertical <br /> extent there has not been well defined. Soil samples from the boring through the concrete slab <br /> and from the monitoring well boring in Area 1 should adequately define the depth extent of <br /> hydrocarbon impact in this area because the monitoring well boring will include soil field <br /> screening and analysis of soil samples to approximately 60 feet below the ground surf ce, the <br /> expected depth to groundwater. <br /> The amended work plan does not propose an approach for defining the lateral extent of <br /> hydrocarbon presence in Area 2. Although the proposed Area 2 monitoring well boring will be <br /> sampled at 5 foot intervals down to groundwater, this will not adequately define the lateral/ <br /> extent. The work plan should include step-out borings which will define a boun in the <br /> subsurface beyond which hydrocarbons are not detectable. This approach will provide enough <br /> data to determine the approximate volume of hydrocarbon impacted soil. <br /> 3. Groundwater Investigation <br /> The work plan amendment proposes to install and sample two groundwater monitoring wells, <br /> one in Area 1 and the other in Area 2. Samples from these wells should provide an indication <br /> of the extent of hydrocarbon impact to groundwater in those specific locations. <br /> Although the two wells will provide important groundwater quality data in the two potential <br /> hydrocarbon source areas, the groundwater investigation should include the installation and <br /> sampling of additional monitoring wells. The State of California Leaking Underground Fuel <br /> /Tank (LUFT) Field Manual, which provides guidance for UST site investigations, states that at <br /> least three and preferably four wells should be installed on a site to adequately d termine <br /> grouter quality and to define the local groundwater flow direction. <br /> It is WESTON's opinion that the two monitoring wells proposed by EAI will not provide <br /> adequate groundwater quality and flow direction information to satisfy the data requirements of <br /> this groundwater investigation. Each proposed well location is a potentio hydrocarbon source <br /> area, therefore if there is a hydrocarbon impact to groundwater from th9se sources, placing wells <br /> in those areas does not provide information on the downgradient laterld extent of the impact nor <br /> does it provide any data on the upgradient, background water quality. The downgradie t lateral <br /> extent data is required to determine the size of the hydrocarbon plume (if pres nt while the <br /> STKC%RMS%WrrMYRLwr <br />