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Geological Technics& Page 2 Groundwater Monitoring Report Project No 425 2 November 12,2001 ' • The predominant groundwater gradient direction for the intermediate depth aquifer ' is towards the east-northeast For the September 7, 2001 event the direction was calculated to be southeast and this is the second time this beanng has been recognized ' . Vertical groundwater gradients do exist at the site and range from 2 to 20 times the magnitude of the horizontal gradient At times the site has experienced both a negative and positive vertical gradient No clear trend has been recognized to account for these differences, but variations in community groundwater pumping and rainfall may be causal factors Thus, during low pumping demand, the vertical groundwater gradient would be expected to be upward, and the inverse would also be expected 2 Groundwater Contamination • Contaminant concentrations have decreased in all five wells that contained BTEX fand TPH-G during the .Tune, 2001 event The impacted soils in the vicinity of the former USTs were excavated in July 2001 The decrease may be reflective of the reduction of available mass to leach to groundwater Additional monitoring is required to determine contaminant trends o All of the deep-screened wells (MW-102, MW-105 MW-107 and MW-202) were non-detect for the event This is the fourth consecutive event for this condition o The domestic wells associated with the site were non-detect for all constituents ' 1.0 GROUNDWATER MONITORING ' 1.1 Hydrology of Site t1..1.1 Horizontal Groundwater Gradients Water Table Wells The average water table elevation at the site on September 7, 2001 was 72 24 feet above mean sea level This represents a decrease of 0 25 feet since the June 2001 monitoring event The water table groundwater gradient was 0 0017 ft/ft flowing N08°W A review of ' the groundwater gradients shows that the dominant groundwater flow during 2000 & 2001 was to the north-northeast with the slope ranging from 0 0015 up to 0 0044 ft/ft Table 1 of Appendix A summarizes the water table groundwater gradients and levels to date, and ' Figure 2A illustrates the September 7, 2001 groundwater direction and gradient Intermediate & Deep Wells The average groundwater elevation in the intermediate depth wells (MW-102, MW-105 & MW-107) for September was 71 97 feet above mean sea level and the intermediate depth groundwater gradient was 0 016 ft/ft flowing S48°E