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ARCADIS Mr. Roberto Cervantes <br /> October 21, 2011 <br /> groundwater monitoring wells contained elevated levels of TPH as gasoline, diesel, <br /> and motor oil. However, groundwater is polluted as deep as 150 feet bgs at nearby <br /> decommissioned fuel facilities. Therefore, CEMC needs to continue monitoring <br /> these wells and investigate the deeper groundwater zones at this site. In particular, <br /> deeper groundwater near MW-4 needs to be investigated because it is down- <br /> gradient of the suspected source area. <br /> Response to Comment#2 <br /> ARCADIS concurs with the RWQCB request for continued monitoring of MW-4 and <br /> proposes additional monitoring of TPH-GRO, TPH-DRO, and TPH-mo in the existing <br /> monitoring wells(MW-1, MW-2, MW-3, and MW-4) in conjunction with the SIR <br /> recommendation to install two additional monitoring wells (MW-5 and MW-6) <br /> adjacent to and downgradient of the elevated TPH levels detected in CPT-6. <br /> Furthermore, ARCADIS proposes to install a monitoring well (MW-7) in the vicinity of <br /> elevated soil and grab groundwater TPH levels detected in the 2001 environmental <br /> assessment conducted by Geologic Technics located in the central part of the site. <br /> As part of the CPT-UVOST investigation described above, ARCADIS advanced one <br /> CPT-UVOST soil boring (CPT-6-UVOST) and one geoprobe soil boring (CPT-6-GP) <br /> at CPT-6. Screening data indicate the potential presence of LNAPL from 13.5 feet <br /> bgs to 19.7 feet bgs and no indication of LNAPL from 19.7 feet bgs to the final <br /> borehole depth of 32 feet bgs. Additionally, TPH and BTEX were not detected in the <br /> soil sample collected from CPT-6-GP at 21.5 feet bgs (ARCADIS, 2011). <br /> Based on the analytical and screening data, it is unlikely that impacted groundwater <br /> observed at nearby decommissioned fuel facilities at depths of 150 feet bgs is <br /> associated with historical Site operations. Furthermore, a geophysical survey <br /> performed on the property did not identify buried structures, USTs, pipeline, or other <br /> potential subsurface anomalies within 3 to 4 feet bgs. Sanborn maps from 1950 and <br /> aerial photos from 1975 show the property paved with above ground piping and <br /> ASTs enclosed by secondary containment berms. However, ARCADIS recommends <br /> collecting three grab groundwater samples in the anticipated deeper sand zone <br /> (approximately 35 feet bgs)to assess potential deeper groundwater impacts, as <br /> discussed below. <br /> Page: <br /> 3/7 <br /> G.IProjectsICHEVRON1401 N.San Jose S(ITECHNICABRMCRRTCWesponse to RWOCB Comments doc <br />