ARCHIVED REPORTS XR0010083 - Laserfiche WebLink

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t Field Methods Exploratory„Borings Five exploratory borings were drilled at the site (Figure 1) on April 25, 2000 Three additional borings were scheduled to be drilled, however these borings were postponed due to difficult drilling conditions and a field modification of the workplan approach Drilling permits were secured from the PHS EHD, and all utilities were cleared prior to doing the field work Representatives of the Westside Irrigation District and City of Tracy met Wright in the field and directed where boreholes should be placed On the day of drilling, the City of Tracy requested that due to the presence of two large sewer lines, not to drill any borings tentatively scheduled in that vicinity Five direct push borings were advanced at the available locations shown on Figure 1 The borings were drilled into the uppermost aquifer strata to the contact of, and into the underlying confining strata (referred to as the aquitard strata in previous reports) Moderate to severe flowing conditions were encountered in some boreholes which required drilling methods to be alternated between push and auger drilling depending upon the severity of the flowing conditions In severe flowing borehole conditions, some soil and groundwater samples could not be collected The boreholes were drilled with truck mounted hollowstem auger and/or direct push drilling equipment All drilling equipment and sampling tools were cleaned prior to arriving, between driving samples and before leaving the site The augers were advanced to the desired sampling depth interval, and a drive split spoon sampler were dnven ahead of the drill bit The sampler was then retrieved and dissembled, and the soil filled brass or .} acetate liners retained for chemical analysis, were sealed with Teflon® paper and plastic endcaps, Iabeled, logged onto chain-of-custody forms and place in a chilled ice chest on crushed ice Dnll cuttings were drummed and left on-site The boreholes were logged using the Unified Soil Classification System under the supervision of a registered geologist Additional lithologic information was collected to describe the subsurface geology Soil samples were field screened for presence of contaminants by checking for presence of odor and staining, and a photoionization meter was used for soil field vapor measurement use Soil samples were collected at minimum five-foot intervals, with additional samples collected at intervals of obvious contamination and at stratigraphic features of interest using field discretion Upon completion of the borehole drilling and collection of information, all boreholes were backfilled with cement grout, placed from the bottom to top of the borehole by trerme line Field Modification of Workplan The PHS EHD representative and field geologist discussed the sampling as the borehole drilling, sampling and borehole sealing progressed on April 25, 2000 Field observations during drilling indicated that contaminants were not widespread at the originally selected MW-9 and MW-3 locations, hence a modification to the field work and sampling was approved by FHS EHD in the field The modifications included the following, advancing five boreholes near the originally selected locations, returning to the site at a later date to mark utilities for borehole drilling and to search for additional possible contaminant sources both at the original tank pit and elsewhere, and a discussion with PHS EHD regarding a review of previous work and the revision of the workplan prior to returning to the field to • continue assessment Page 2