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AD <br /> the east quadrant, which is not in agreement with the location & <br /> levels of contamination recorded to date. Although it is possi- <br /> ble that additional measurements might show a shift to the west, <br /> the regional gradient is to the east, from the Delta area towards <br /> the center of the basin <br /> Although the removed UST' s appear to have been a major source of <br /> the contamination encountered at this location, the data obtained <br /> to date strongly supports our original belief that another as yet <br /> unidentified offsite source exists - most likely to the west or <br /> north of the property While we believe that further investi- <br /> gation will be needed to identify such possible source(s) or at <br /> least to establish a "zero" line to the northwest, we are not yet <br /> prepared to submit a comprehensive workplan to accomplish that <br /> task. Our current workload limits the time available to explore <br /> the various options available to conduct such an investigation <br /> Those options include additional soil gas vapor surveys, soil <br /> borings, hydropunch sampling, cone-penetrometer tools , or <br /> combinations of them It will be necessary to obtain City & <br /> County encroachment permits and tresspass agreements from private <br /> parties, and possible additional insurance coverage prior to <br /> doing any offsite work Until we have authority from our clients <br /> to proceed, and have sufficient time to conduct the investigation <br /> in a timely manner, we recommend that quarterly monitoring <br /> continue. The additional information obtained may assist in <br /> further defining any potential offsite sources <br /> Wila Hunter & Associates <br /> Apr 1 6, 1994 <br /> cc• nchez <br /> CVRWQCB <br /> / R • <br /> NO Bfi0 <br /> I <br /> 3 <br />