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ARCO Products Company <br /> Page 2 <br /> Analysis of groundwater samples from MW1 and MWS , using EPA method 8260 for <br /> oxygenates requested by PHS/EHD , was performed on the samples collected <br /> November 18, 1997 , with only MTBE being detected. MW1 and MW5 are the <br /> historically highest concentration wells with regard to petroleum hydrocarbon <br /> concentrations. Oxygenates , including MTBE are not necessarily found in the wells with <br /> the highest petroleum hydrocarbon concentration . After the installation of new <br /> monitoring wells on and off site , PHS/EHD will require additional analysis of <br /> groundwater samples for oxygenates using EPA method 8260. <br /> The quality assurance and quality control (QA/QC) data from the laboratory for EPA <br /> method 8260 for the groundwater samples collected November 18 , 1998 and analyzed <br /> on December 1 , 1997 was not included in the February 5 , 1998 quarterly report, please <br /> submit these QA/QC data sheets immediately. Also please note that the detection limit <br /> for MTBE was raised using EPA method 8020 for those samples, so the results were <br /> reported as non detect. If the detection limit must be raised , then the samples should <br /> be analyzed using EPA method 8260 . <br /> Since the vapor extraction wells at this site are constructed with a larger slotted screen <br /> and the annulus is filled with pea gravel , PHS/EHD will not require further groundwater <br /> sampling of these wells . <br /> The destruction of MW3 , the installation of monitoring wells which will intersect the <br /> groundwater interface , the vertical definition of on site soil and groundwater <br /> contamination in the area of the former UST's and piping/dispenser area discussed <br /> above , and the installation of air sparge and vapor extraction wells should be addressed <br /> in a work plan to be submitted to PHS/EHD by August 10, 1998. <br /> If you have any questions contact me at (209) 468-3449 . <br /> Donna Heran , REHS , Director <br /> Environmental Health Division <br /> Margaret Lagorio , Supervising REHS <br /> Site Mitigation Unit <br /> c: CVRWQCB - Mark List <br /> Pinnacle Environmental Solutions - Mark Capps <br />