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Phase II Environmental Site Assessment Multi-Modal Station Stockton,San Joaquin County,California Page 23 5.3 GROUNDWATER ELEVATION • Groundwater elevations were calculated for the surveyed detection and perimeter bonngs by subtracting the depth to groundwater measurements from the surveyed reference elevation associated with each of the borings that were surveyed The groundwater elevations indicate an east to northeast groundwater gradient In general, the groundwater elevations and groundwater gradient are consistent with groundwater information from nearby sites Groundwater elevation contours for the site are depicted in Figure 14, Appendix A 5 4 ADDITIONAL INVESTIGATION During drilling activities in the northwestern portion of 730 E Channel Street, two metal plate caps were observed in the concrete paved surface These plate caps were removed and a 4-inch metal pipe and V/4- Inch metal pipe associated with at least one UST were discovered The cap was removed from the 13/4- inch pipe and a stick was lowered into the pipe to determine if any product remained in the UST The bottom four to six inches of the stick were covered with a fluid exhibiting a petroleum odor when it was removed The depth to the bottom of the UST was approximately seven feet bgs A sample was obtained to identify the product in the UST A piece of%-mch PVC screen was lowered into the UST and plastic tubing with a check valve was used to retrieve a liquid sample (BK4-730-TK1S) for product identification After collection of the sample and removal of the PVC screen from the UST, it was noted that the bottom six inches of the screen were partially coated by a black sludge The product sample was collected in one VOA container The sample was labeled, chilled with ice, and transported by courier under chain-of-custody procedures to Excelchem for identification The laboratory analytical results are presented in Table 11 and indicate the product is diesel fuel Laboratory data sheets and the chain-of- custody form are included in Appendix F Table I I —Analytical Results for UST Product Sample 730 E. Channel Street Constituents Benzene m,p-Xylene 1,2,4-Tnmethylbenzene Naphthalene TPH-D Analytical Method—. 8260B 8260E 8260H 8260B 9015m Reporting Limiter 0 5µg/L 0 5µg11. 0 5µg/L 0 5µg/L 50µg/L Sample ID Date BK4-730-TKI S 9/11/02 52 140 140 62 12,000 pg/L=micrograms per liter=parts per million=ppm While drilling detection boring DBK4-730-13 Inside the building adjacent to the vehicle maintenance bays at an existing concrete patch in the floor at 730 E Channel Street on Block 4, the drilling rig met refusal at 1 5 ft bgs A '/4-inch steel strap located Immediately beneath the concrete surface was determined to be the cause of refusal, and a black substance with a hydrocarbon odor was discovered at approximately 15 feet bgs Additionally, an approximately four to six-inch diameter pipe was observed extending northward from the patch DBK4-730-13 was relocated off of the patch approximately one foot away from this location Further investigation of the patch included the removal of a one-foot by one-foot section of the concrete patch with a jackhammer to uncover a concrete vault with a concrete divider down the center The vault was filled with soil that had no odor or visual indications of contamination at the surface A hand auger was used to attempt to sample the black grease-like substance encountered at approximately 1 5 bgs The hand auger was advanced until the tip of the auger encountered the black substance and a strong hydrocarbon odor was noted emanating from the hole An insufficient amount of material was recovered . with a 2-inch sampling sleeve, as the sleeve met refusal at a depth of 20 inches The recovered material was taken from the end of the sleeve and packed into a four-ounce glass jar for analysis Efforts were � 1 i f CONDOR