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Mr. Richard Callistro September 21, 1994 <br /> San Joaquin County Capital Projects Page 2 <br /> Work Plan Preparation <br /> As requested in the June 27th EHD Memorandum, a work plan will be developed for EHD's <br /> review which will detail the proposed investigation scope and methodology. A special effort will <br /> be made to place this new effort in context with the previous work completed and to characterize <br /> the work as a final effort to resolve lingering uncertainties about the alleged current impact of <br /> the site. The work plan budget will include an allowance for WESTON staff to attend a meeting <br /> (if necessary) to gain EHD's approval and concurrence with the planned activities. <br /> Well Installation and Soil Samaline <br /> During WESTON's review of the site information to prepare this proposal, the installation of <br /> only one well was evaluated as a minimum cost approach. However, due to the historic pattern <br /> of groundwater contours beneath the site which show the apparent presence of a gradient trough <br /> below the former tank site, WESTON is recommending that two wells be installed as part of this <br /> additional investigation. The wells, generally intended to replace existing dry monitor wells <br /> MW-2 and MW-3, will be sited to sit within this apparent trough. Not only will these well <br /> locations provide a better grid for determining the groundwater contours under the site, but their <br /> location will also identify any lateral groundwater gradient along the suspected trough. If lateral <br /> migration is detected, the sample results from the monitor well in the downgradient location <br /> should reveal whether the former tank site is contributing any significant degradation of <br /> groundwater quality. These wells, to be identified as MW-2A and MW-3A, will be located near <br /> the existing MW-2 and MW-3 locations except displaced laterally along Sutter and Washington <br /> Streets as shown on Figure 1. <br /> During the installation of the two wells, WESTON proposes to take soil samples at 5 foot <br /> intervals between 30 feet below grade surface (bgs) and the water table, anticipated to be near <br /> 50 feet bgs. Samples at shallower depths are not necessary as sampling performed near the <br /> proposed well locations between 5 and 30 feet bgs during the original site investigation work did <br /> not show the presence of any hydrocarbon constituents. All samples will be field screened and <br /> those showing measurable hydrocarbon emissions will be submitted for laboratory analysis. In <br /> any case, a minimum of three samples from each boring will be analyzed to satisfy EHD's <br /> request for additional soil data. All submitted soil samples will be analyzed for total petroleum <br /> hydrocarbons gasoline (TPH-G) and diesel (TPH-D) fraction by EPA Method 8015-M and for <br /> BTEX compounds by EPA Method 8020. <br /> SMTROPOSAL�LLLSTROMP A � 11 <br />