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Creok9kal Technics kc. Page 4 ' Groundwater Monitoring Report Project No. 1030.2 September 29,2003 2.0 FINDINGS AND DISCUSSION ' Petroleum Hydrocarbons • MW-1 shows an increase in all analyzed constituents (excluding toluene). The increase ' in petroleum hydrocarbons detected in the groundwater is linked to the rise of groundwater elevations. o Residual LNAPL, encountering rising groundwater, is altering to a dissolved state. o Groundwater elevation has increased 2.88 feet over the last quarter, nearly two feet above the historical average. o The highest groundwater elevations have been recorded between June and August. This corresponds to the flood irrigation practices occurring north and east of the property. ' • A plot of TPH-G and Groundwater Elevation versus Time for MW-4 (Chart 2) shows that petroleum hydrocarbon concentrations increase with high groundwater elevations, further validating the results from MW-1. • MW-2, MW-3, MW-101 and the domestic well were non-detect for all analyzed constituents. Increased groundwater elevations do not impact the concentration of contaminants in these wells suggesting that there is no residual LNAPL near these wells. o MW-2, MW-3 and the domestic well have been non-detect for all analyzed constituents since January of 1997, the first monitoring event at the site. ' o MW-101 has been non-detect for all analyzed constituents since installation and initial testing in May of 2002. • TPH-G and BTEX constituents have only been detected in MW-1 and MW-4. Figure 4 is an interpretation of the extent of TPH-G at the site. Site Characteristics ' • The plume is defined vertically by MW-101 and laterally by MW-2 to the southeast and MW-3 to the southwest. ' • MW-4 appears to be located near the leading edge of the plume. • The clay layer at 19 feet bgs provides a significant barrier to vertical plume migration. • Groundwater slope is gradual (<0.005 ft/ft) which impedes the migration of the plume. • Vertical groundwater gradient is historically positive (upward) making vertical migration unlikely. This event shows a negative vertical groundwater gradient, believed to be an anomaly caused by flooding of adjacent fields or an error in depth-to-water ' measurements. Future monitoring events will clarify these unusual calculations.