SITE INFORMATION AND CORRESPONDENCE

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Mr. Jim Lancaster 14 August 2002 Woolsey Oil, Inc 2 The Report states a correlation exists between seasonal rising groundwater levels and lower contaminant concentrations. The Report also states that after two quarters of upward gradients between the two aquifers, there now exists a downward vertical gradient between the upper and lower aquifers. The Report requests a discussion with Regional Board staff concerning the need to install an additional downgradient well to characterize the extent of the MtBE plume. The Report states it is arguable that MW -10 consistently provides downgradient coverage. Comments 1. The downgradient lateral extent of the MtBE plume must be determined. The Report states that Regional Board staff agreed, in a letter dated 11 September 2000, that a new downgradient well west of MW -10 (located south and slightly east of the site) was not needed, unless the groundwater gradient changed or contaminant concentrations increased. Both of these conditions have occurred at the site. The groundwater gradient has changed at the site, making MW -10 a cross gradient well at best. The January 2002 groundwater contour map shows a southwesterly groundwater flow direction, away from monitoring well MW -10. This is the most noticeable shift reported since monitoring began at this site. The April groundwater contour map shows a south -southwesterly groundwater flow direction, also away from MW -10. Prior to 2002, the reported groundwater flow direction varied by quarter (Table 1). The 2002 groundwater contour figures and Table 1 show groundwater flow directions of: • southeast, 2 quarters; • south-southeast, 4 quarters; • south, 16 quarters; • south-southwest, 2 quarters; and • southwest, 1 quarter. The majority (16 of 25 quarters) of the time, groundwater is flowing south. The July 2002 groundwater contour map shows a southeasterly groundwater flow direction towards MW -10. Groundwater concentrations of MtBE are increasing at MW -3 (southernmost onsite downgradient well), and are now (July 2002) at their highest levels (190 gg/L) since MtBE analysis began in April 2000. The MtBE groundwater plume contours shape consistently shows an elongation that appears to have a southwest -oriented axis, suggesting movement towards the southwest and through MW -3. We also disagree with the statement in the Report that the location of the 932A -C Victor Road building makes an investigation west of MW -10 impractical. The main issue appears to be that several recreational vehicles stored on the parking lot around the building would have to be moved to investigate the property. In a phone call to Regional Board staff on 16 July 2002, GZA requested clarification whether an additional downgradient monitoring well was needed to investigate the MtBE plume. We responded that an investigation could involve either installing a new downgradient monitoring well, or analyzing several grab groundwater samples using direct push methods, to delineate the MtBE plume and evaluate the need for a new monitoring well.