SITE INFORMATION AND CORRESPONDENCE FILE 1

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620 West Charter Way Page 2 of 3 MW-9 at 20 and 30 feet bsg, in CPT-3 at 40.5 feet bsg, and in CPT-4 at 73 feet bsg; minor concentrations of benzene and xylenes were detected in CPT-5 at 95 and 100 feet bsg. CPT-5 soil samples at 85 and 90 feet bsg were not impacted. The low concentrations of the limited suite of analytes detected at 95 and 100 feet bsg in CPT-5 may indicate that the samples were collected near the margin of the plume. EHD will not require any deeper soil investigation at this time. • CETI states that the lateral extent of impacted soil has been delineated, but does not cite the data to demonstrate this conclusion. EHD reviewed a portion of the data, noting that MW-9 soil was intensely impacted at 20 and 30 feet bsg, but no data exists west or north of MW-9, and no post-remediation data has been collected. MW-7 soil was also impacted at 21 and 31 feet bsg, but post-remedial CPT-3 data starts at 40 feet bsg. Impacted groundwater from CPT-9 does not exclude the possibility of impacted soil at that location. Thus, the northern extent of impacted soil is not delineated. Confirmation borings should be advanced to collect soil data to demonstrate the effectiveness of the soil vapor extraction, and to obtain a current mass estimate for sorbed contaminants. • EHD does not concur with CETI's position that the vertical extent of impacted groundwater has been demonstrated. CPT-5 is the deepest boring with total depth at 97 feet bsg. Groundwater samples collected at 80.5 and 84 feet bsg were non- detect for COCs; however, at 91 feet bsg, high concentrations of TPH-g and benzene were detected. Another groundwater sample, collected at total depth of 97 feet bsg, was found to be non-detect. The inconsistent data from the deeper groundwater samples from CPT-4 and CPT-5 suggest that the sand interval from approximately 76 to 87 feet bsg is at or near the vertical margin of impacted groundwater. A short-screen well set in the sand should collect data sufficient to demonstrate this point. Please install such a well near CPT-5 to monitor this potential contaminant migration pathway and potentially delineate the vertical extent of the dissolved plume. EHD approves the advancement of the two proposed CPT borings across Charter Way and the two proposed CPT borings to the east-northeast on the adjacent property (location of the Best Western Motel) to further assess the lateral extent of petroleum hydrocarbon contamination in soil and groundwater. Please submit a work plan to EHD by September 1, 2005, for the advancement of these four borings that includes technical justification for the location, depth, and sampling targets of these borings. EHD also approves the reduction in sampling schedule for monitoring wells MW-1, MW 3, MW-5, and MW-6, from quarterly to annually; however, EHD believes groundwater samples collected from MW-4 and MW-10 should be analyzed semiannually instead of