ARCHIVED REPORTS_XR0012656 - Laserfiche WebLink

Home Browse Search

sa;. �:M 2 Noun) lav '�5. 1991 :;I�11-1Vest. Inc.. water ieveis were rllcasured in the pre existing �s'el1S, le :measurements verified that groundwater flows in a south, soULhNvesteriy as a result ciirecLion. The gradient was toullol LO vary t of tidally induced water level fluctuations in the nearby Stockton deep water channel. �',,,,,.iusianG •;nd i��cemmcncitL i s The extent of the released gasoline appears to be limited both ar allY and �.vith depth. 'File maximum lateral extent of affected soil and groundwater is approximately 30 feet in a downgradienL direction from the tank (see €"igure l). The maximum concentrations encountered were at or near the groundwater surface, then decreased quickly with depth. The limiting factor for downward migration therefore was the presence of groundwater at a shallow depth. San Joaquin County's next required phase of work is the preparation of a Problem Assessment Report (PAR). ERM-West, Inc. understands that the County has requested Catellus Develop e ERM-West,Corporation submit it a P that by June 17, 1991 (copy of letter enc an initial step in addressing the request, the results of the latest fieldwork should be released to the Cnnnty. And at the same time, open discussions with the County regarding their zoncerns and potential clean-up dards for the site. Secondly, ERM-West, Inc. recommends that the County be approached about postponing the June 17th deadline, pending the removal of two additional underground storage tanks. If problems are encountered with r those tanks, one Problem Assessment Report addressing all three sites instead of three reports would be more cost effective. Well Cnstru tion Two monitoring wells were constructed by ERM-West, Inc. on April 12. 1991. The wells, labeled-.,%,nW-4 and MW-5 were located hydraulically downgradient from the tank site and within the tank site respectively (see Figure 1). The soil borings at c:ch location were drilled to 30 feet and sampled at 5 foot intervals. A portion of the sample at each depth interval was preserved for subsequent laboratory analyses. The remainder of the sampled soiI5 were used for classification according to the Unified Soil Classification System (see enclosed boring logs) and for preliminary screening by head space analysis. After the borings were advanced to a depth of 30 feet, they were completed flush - as monitoring wells. The wells were constructed of 2-inch diameter, threaded, Schedule 40 PVC. The well screen was set ata depth t erva30 feet l of approximately 10 to..15.feet..__The.-remainder of the boring, n r was filled with sand. At the ground surface both- vells were-covered-wit - - - -- traffic boxes.