Laserfiche WebLink
i <br /> I <br /> I <br /> Shallow boreholes B-1 through B-5 were advanced to three feet. The borehole B-6 was <br /> advanced to about 30 feet and continuously logged using the Unified Soil Classification System <br /> under the supervision of a professional geologist. Additional lithologic information was <br /> collected as needed to describe the subsurface geology. Soil samples were field screened with a <br /> portable photoionization detector(Minirae 200 PID meter) for petroleum fuel hydrocarbon vapor <br /> and also visually checked for staining. Upon completion of the borehole drilling and collection <br /> of water samples, the boreholes were backfilled with grout, placed from the bottom to top of the <br /> borehole per the permit requirements. <br /> All soil cuttings, decontamination water and sample tubes and other consumable items used in <br /> sampling were placed in labeled 55-gallon closed top drum. The cleanup and grout mixing water <br /> was stored in a closed top drum and solids were placed in an open top drum; both drums are <br /> stored at the Client-specified location(Boyd Service Center). i <br /> 3.2_ _ Field Modifications of the Work Plan for Soil Sampling <br /> Once the shallow drilling was completed along the pipeline, one boring was advanced in the <br /> former tank pit. One soil sample was collected at a depth of 9 feet within the tank pit backfill <br /> and additional soil samples collected at five-foot intervals thereafter until refusal. The work plan <br /> had initially planned for groundwater sampling and a field discussion with the EDH <br /> representative indicated that a groundwater sample was desired. However the estimated depth to <br /> groundwater was over 70 feet and may be as deep as 120 feet in this area, and beyond the depth <br /> capability of the GeoProbe drill rig. Boring B-6 in the former tank pit was advanced to a depth <br /> of 30 feet below grade where the driller called a refusal to advance the drill bit/sampler, and the <br /> boring was terminated. Wright and EHD agreed to review the soil data presented in this report <br /> and then determine a course of action regarding the need to advance a deep boring to <br /> groundwater. <br /> 4.0 Brief Conceptual Site Model and Subsurface Conditions <br /> The project site is located at the Tracy Municipal Airport near the northwestern edge of the San <br /> Joaquin Valley. Holocene alluvial fan deposits eroded and dissected by streams draining from <br /> the nearby Coast Range Hills to the northwest underlie the area. Surfical soils in the airport <br /> region are mapped by the U. S. Department of Agriculture as Capay-Stomar-Zacharias soil <br /> association moderately well drained and moderately fine textured and may contain gravel <br /> forming on alluvial fans, interfan basins and stream terraces. Capey soils are mapped as having <br /> moderately slow permeability. The underlying alluvium generally consists of weakly <br /> consolidated and irregularly interbedded sand, silt and clay deposits. These subsurface alluvial <br /> strata may be of variable lateral and vertical continuity and extent. <br /> Very large groundwater aquifers underlie the Tracy Airport region. These aquifers can produce <br /> very large quantities of agricultural and municipal drinking water. There are no groundwater <br /> flow information for the airport vicinity, however regional groundwater flow is estimated to flow <br /> to the west and northwest in the airport region. Historic pumping has drawn down the <br /> Page 3 of 7 <br /> i <br />