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1 <br /> ARCADIS Ms. Kathryn Dominic ' <br /> August 24, 2010 <br /> trend of decreasing concentrations with depth. At sampling locations HA-2, HA-4, ' <br /> HA-5, and HA-6, the 3-foot sampling results are one to two orders of magnitude <br /> lower than the 1-foot sampling results. ' <br /> As stated previously, the maximum detected concentration of 620 mg/kg is well <br /> below the ESL of 2,200 mg/kg and the 95% UCL concentration of 417 mg/kg is lower ' <br /> than the ESL of 450 mg/kg. These comparisons demonstrate that current soil <br /> conditions do not pose an environmental or human health risk. <br /> Only two of the six soil samples collected from 3 feet bgs slightly exceeded the <br /> original CAO cleanup goal of 50 mg/kg (HA-1 98 mg/kg; HA-3 74 mg/kg). <br /> Groundwater ' <br /> The groundwater beneath the biotreatment beds has not been affected by TPH-d (or , <br /> TPH-mo). Groundwater is encountered at approximately 12 to 15 feet bgs at the Site. <br /> As shown in Figure 3, groundwater sampling results at wells MW-01A, MW-04A, <br /> MW-05A, and MW-26A indicate that TPH-d was not detected above the reporting , <br /> limit in samples collected during the March 2010 sampling event. The biotreatment <br /> beds have been in place for 16 years; however, TPH-d has not been detected in the ' <br /> four wells during the past six to seven years in the groundwater samples. <br /> Recommendations ' <br /> No further remedial actions are recommended for the biotreatment beds at the Site. <br /> ARCADIS further recommends that the RWQCB rescind the CAO based on the ' <br /> summary of analytical results and the premise that the biotreatment beds have <br /> achieved the substantive requirements of the CAO No. 92-707. <br /> 1 <br /> I <br /> Page: <br /> 10/12 ' <br />