ARCHIVED REPORTS_XR0011832 - Laserfiche WebLink

Home Browse Search

Subsurface Investigation and Well Installation Report ARCO Facility No 6100 Tracy, California Page 6 Laboratory Analysis Soil and groundwater samples collected during the investigation were forwarded to Sequoia Analytical Laboratories (ELAP # 1624) for chemical analysis Strict chain-of- custody procedures were followed from the time the samples were collected until the time the samples were delivered to the laboratory The samples were analyzed for TPHG and BTEX using DHS/LUFT methods, and for MTBE, tertiary butyl alcohol (TBA), di- isopropyl ether (DIPE), tertiary amyl methyl ether (TAME), ethyl tertiary butyl ether (ETBE), ethanol, 1,2 dichloroethane (1,2 DCA), and ethylene dibromide (EDB) using USEPA Method 8260B Select samples were additionally analyzed for methanol using USEPA Method 8015 Modified A composite sample of the drill cuttings was collected and additionally analyzed for total lead using USEPA Method 6010 Soil analytical results are presented in Table 1, and Certified Analytical Reports with chain-of-custody documentation are presented in Appendix F RESULTS OF THE INVESTIGATION Site Geolo2y and Hydrogeology The geology beneath the site is primarily silt, with discontinuous zones of clay Caliche . is present within much of the silt and clay Non-native fill material consisting of clay and silt were generally encountered from the ground surface to depths of approximately 5 to 10 feet bgs Sand, clay, and gravel mixtures with thicknesses of approximately 0 5 to 2 feet were encountered in all borings at depths ranging from approximately 14 to 22 feet bgs A sand layer, approximately 3 to 4 feet in thickness, was encountered at depths ranging from approximately 48 to 63 feet in all borings Approximately 15 feet of silty sand and sand were encountered in all borings at depths ranging from approximately 68 to 92 feet bgs Zones of cementation were encountered between 80 and 90 feet in all of the soil borings The sandy layers encountered at 48 feet and at 80 feet bgs appear to be laterally continuous across the site Interpreted geologic relationships are illustrated on cross sections A to A' (Figure 3) and B to B' (Figure 4) The downhole electrical logging methods were successful in distinguishing sand and silty sand lithologies from silt and clay Silty sand and sand layers are displayed on the geophysical log as zones of higher resistivity deflecting from a generally consistent baseline of silt and clay Silt, clay, and caliche cannot be distinguished using the geophysical log Following a meeting with representatives of CRWQCB and SJCPHS in January 2001, a Delta geologist searched the area around the site to locate outcropping bedrock The purpose of the search was to identify the strike and dip direction of bedrock in the vicinity of the site Delta postulated that bedded sediment beneath the site would likely M dip in the same direction as local sedimentary bedrock The nearest sandstone outcrops were found approximately 1 mile west of the site Bedding in the outcrop was measured P 1ARCO\61001REPORTS16I00-well install report doc