SITE INFORMATION AND CORRESPONDENCE

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5. Experience with diesel recovery attempts from the exploratory pit indicates the lateral flow of free- phase diesel in the vadose zone at the release site is inhibited. After a few months of product removal from the pit,no measurable thickness of diesel remained nor did diesel appear in the bottom of the pit for the several months after that the pit remained open. While diesel was not present in the pit,a diesel thickness of nearly seven inches was measured in a Geoprobe boring installed during December, 1996, approximately 25 feet from the pit. 6. The lateral extent of dissolved hydrocarbons in groundwater was nearly found during the Geoprobe investigation performed in December 1996. The groundwater monitoring program proposed herein will provide additional information regarding the lateral movement,if any,of contaminated groundwater. T The utility pipelines exposed during trenching had not been backfilled with gravel and,therefore,it is unlikely that buried utilities create a preferred pathway for subsurface flow of free-phase diesel away from the leak area. 8. Previous surveys to locate water supply wells in the area found no domestic groundwater wells within a minimum of'/2 mile of the site. 9. The LOF complex covers nearly 175 acres and the diesel plume,if present,is nearly centered in LOF's property. As such,LOF limits the use of the shallow groundwater aquifer in a large area surrounding the release site. 10. The release site is within an industrial complex. Much of the property surrounding the site is also used for industrial purposes. Shallow groundwater in the area is of generally low quality. Deeper aquifers in the area have been impacted by chemical releases from the former Occidental Chemical Company facility located adjacent to the LOF complex. 11. LOF desires to collect additional information on the groundwater and diesel plume characteristics at the release site before any further product recovery is considered. Proposed Modifications to Approved Scope of Work Because of the unanticipated site conditions mentioned,LOF proposes that the diesel recovery described in the Work Plan dated June 23, 1997, and as modified in the Work Plan Addendum dated May 11, 1998,not be conducted at this time. It is anticipated that the need for active diesel recovery can be evaluated at the time of plant closure, based on the results of the proposed groundwater and diesel plume monitoring described in this letter. Installation of an Additional Monitor Well LOF proposes to complete the section of the approved Work Plan regarding the installation of monitor wells MW-1, MW-2,and MW-3 (Section 4.0—Subsections 4.1 through 4.7, inclusive). In addition, a fourth monitor well(MW-4)is proposed. The additional monitor well will be installed near the location of the former diesel leak. The proposed monitor well MW-4 location is shown in an attached figure. It is proposed that MW-4 be drilled, constructed,developed and surveyed as described in the Work Plan for MW-1,MW-2, and MW-3 with the exception that MW-4 will be constructed of 4- inch diameter PVC. The intended primary use of MW-4 will be to monitor the thickness of the diesel product at that location. If diesel product is encountered at the location proposed for MW- 4, groundwater sample collection from the well for laboratory analysis will not be conducted during the initial phase of monitor well installation or during subsequent quarterly monitoring(as described below). Proposed Monitoring Program In lieu of active diesel recovery at the site,LOF proposes a groundwater and free-phase diesel monitoring program. The monitoring program and associated reporting will document the lateral extent of the dissolved diesel plume,the thickness of free phase diesel in the approximate center of the plume,the groundwater gradient at the site,and the potential for natural attenuation of the plume due to intrinsic bioremediation. N� �.• tY CONDOR