FIELD DOCUMENTS - Laserfiche WebLink

Home Browse Search

L & M OPERABLE UNIT- FIRST QUARTER 2012 SITE STATUS, REMEDIAL SUMMARY, AND GROUNDWATER MONITORING REPORT Introduction April 30, 2012 I:\Tidewater\TW Stockton (P2A)\QMRs\2012\1Q12\1Q12 QSSR QRSR QMR Stockton_FINAL.doc 1.3 Environmental investigations began at the Site in 1989 and quarterly monitoring and sampling activities were initiated in 2002. Stantec (formerly SECOR International Inc.) was retained in late 2002 for environmental consulting services at the Site. A summary of previous investigations is included in Appendix B. 1.2 REGIONAL GEOLOGY/HYDROGEOLOGY The shallow groundwater bearing zone (A-Zone) primarily extends from the ground surface to depths ranging from approximately 25 ft bgs to 40 ft bgs. Subsurface material in the shallow zone predominantly consists of silts, silty sands, and silty gravels from four to 10 ft bgs, and then organic clays, clays, high permeability silts, and lenses of silty sands and poorly graded sands to depths ranging from 25 to 40 ft bgs. The shallow zone is generally underlain by low permeability silts and clays (with an occasional, thin, silty sand or poorly graded sand lens) of highly variable thickness. A deeper groundwater bearing zone (B-Zone) is encountered at a depth of approximately 42 ft bgs and extends to approximately 50 ft bgs. Subsurface material in the B-zone consists of poorly graded sands and silty sands. Below 50 ft bgs, clay and silt with some imbedded sand is encountered and extends to a depth of approximately 64 ft bgs, underlain by sands and silty sands of varying moisture extending to a depth of approximately 73 ft bgs. Clay is encountered below the sands to an approximate depth of 84 ft bgs, underlain by a sand/silty sand layer extending to approximately 92 ft bgs. This stratum is a water-bearing zone identified as the C-Zone. Below this sand layer, imbedded clays and silts are encountered to a depth of approximately 115 ft bgs, underlain by a sand/silty sand layer with some imbedded clay to a depth of approximately 130 ft bgs. This stratum is designated as the D-Zone. Clay and silt is encountered below this sand layer to a total depth explored of 140 ft bgs. Groundwater beneath the Site is influenced by the Stockton Channel to the north and the Mormon Slough to the south. The regional groundwater flow direction for the shallow and deeper groundwater bearing zones is generally to the east-northeast.