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The 1 gpm pumping rate and 2-week cycle estimate can be used to estimate the decline in <br /> groundwater TPH-g concentration that could be attained in the first year of operation. <br /> Considering the decline of 8% in the TPH-g concentration after 32,625 gallons of <br /> pumping and dividing the anticipated annual cumulative pumping volume by 32,625 <br /> yields the number of 8% decline cycles that could be achieved in 1 year: <br /> 250,000 gallons-32,625 gallons=7.66 cycles. Rounding the number of cycles <br /> up to 8 and projecting an 8% concentration decline during each cycle,we can predict that <br /> by the end of one year the TPH-g concentration might decline to approximately 9,000 <br /> µg/1. This means that the operation would likely require 2 or more years to complete. <br /> The third negative result of the test is the fact that the combined TCE/PCE concentration <br /> actually increased during the test, rather than decreasing like TPH-g and BTEX. This <br /> suggests that VM-2 is located in the central portion of a subsurface gasoline plume and <br /> over time began to pull the margin(s) of the plume inward(which is in accord with <br /> geological data from previously collected soil and groundwater samples). However,the <br /> results also suggest that the well is located nearer a margin of a chlorinated hydrocarbon <br /> plume and began to pull the more concentrated center of that plume toward the well <br /> during the test. If so, then chlorinated hydrocarbon concentrations will not decline in <br /> concert with gasoline concentrations and the results of the test cannot be used to predict <br /> when the site would be remediated to an acceptable level. In fact, groundwater extraction <br /> could actually exacerbate the chlorinated hydrocarbon contamination problem at Valley <br /> Motors. <br /> 5.0 RECOMMENDATIONS <br /> Although the test demonstrated that groundwater extraction is somewhat effective in <br /> reducing the gasoline impact to groundwater, we do not feel that it would be wise to <br /> recommend proceeding to full-scale remediation at this time because of the threat posed <br /> by the potential chlorinated hydrocarbon plume. Potential sources of trichloroethane, <br /> perchloroethane, and other chlorinated hydrocarbons are located west(upgradient)of <br /> �j Valley Motors. The proper course of action would be to perform additional investigation <br /> ��"` to determine whether a separate chlorinated plume exists, ap its extent, identify its �t/�0 <br /> source, and determine t e esponsi e Pa'i-ly'beTore oder remediation at Valley Motors <br /> takes place. That would make it possible to assess the risk that groundwater extraction at �t <br /> Valley Motors might cause that plume to migrate. It would also make it easier to monitor —� <br /> such a plume and avoid liability for any migration that might occur. However,before <br /> investigation of potential sources of chlorinated hydrocarbons could take place, it would <br /> be necessary to secure funding from the State UST Cleanup Fund or another source to <br /> insure that Valley Motors does not bare the cost of investigating someone else's <br /> contamination. <br /> If political, financial, or other considerations preclude further investigation, then we Z <br /> recommend a meeting with SJC/EHD, the Regional Water Quality Control Bow 0 <br /> the State US Cleanup Fund to discuss cleanup standards for fuel hydrocarbons. In <br /> l M <br /> 6 <br />