SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

Shell Station (former) page 2 1267 Country Club Blvd, Stockton Work plan addendum comment 1. Depth of CPT-8. Based on CPT-6 data, the first substantial sand zone occurs from 40 to 47 feet bgs. The log of CPT-6 shows a gravely sand and sand at 69 to 75 feet bgs. Grab ground water samples were collected from CPT-6 in August 2003 at 41, 70, 85, and 92 feet bgs. Petroleum contamination was detected at all of these depths. Therefore, limiting the ground water sampling as shown in the Addendum to a maximum depth of 45 feet bgs, the known deeper sand zone contamination is not being investigated. Additional ground water investigation at all previous depths, and possibly deeper, is required. 2. Laboratory Analyses. The Addendum referred to borings/data from SB-2 and CPT-6. EHD has reviewed the data from these borings as discussed below and has determined that other contaminant analysis, in addition to the analytes listed in the Addendum, are required. • SB-2: Installed in April 1997 to a total depth of 36 feet bgs. Ground water grab samples showed TEPH at 25,000 ug/I, TPPH at 20,000 ug/I, 2-Methylnaphthalene at 390 ug/l, Benzene at 1,900 ug/l, MtBE at 360 ug/I, and 1,2-DCA at 51 ug/I. • CPT-6: Installed in August 2003 to a total depth of 92 feet bgs with grab ground water samples at 41 , 70, 85, and 92 feet bgs. Benzene levels increased with depth and was 5.2 ug/I at 92 feet bgs. Xylene and Ethylbenzene levels also increased with depth, with the highest concentration at 92 feet bgs. Both TEPH and TPPH had detectable levels at all depths investigated, mostly in the low 100 to 300 ug/I range. No MtBE data is available from CPT-6. • B-3: Installed in April 1995 directly in the waste oil UST pit with a ground water sample collected from 28 feet bgs. TEPH was detected at 23,000 ug/I and TPPH at 4,800 ug/l. Benzene was detected at 1,900 ug/l. No MtBE or other waste oil constituent data was included in the report submitted to EHD. 3. Boring type. EHD appreciates the concept of utilizing CPTs to 'screen' and identify the subsurface lithology. EHD expects the contamination detected at the depths sampled in the CPT to be confirmed and delineated by further investigation. At depths where contaminants are detected during CPT investigations, EHD requires the placement of a discrete monitoring well screen to collect repeatable ground water data. In the past Shell/Cambria has concluded that contaminants detected in ground water grab samples from CPTs were the product of smearing or dragging down of the contamination from above.