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Mr Terry Tarditi April 17, 2001 Page 4 Overall, TPH-G concentrations in all four wells have decreased since April 1999, especially in MW-2 TPH-G concentrations in MW-3, however, remain elevated MTBE concentrations remain low to below method reporting limits in wells MW-2 and MW-3, and have increased in MW-4 MTBE concentrations in well MW-1 increased from December 1995 to April 2000, where they began to level off The groundwater flow direction and constituent concentration levels detected in the monitoring wells indicate constituent migration in a southwest direction Constituent concentration levels in the up-gradient well, MW-2, have decreased over time In summary, benzene, TPH-G and MTBE concentrations have peaked and are decreasing in MW-1, which is located adjacent to the former UST area The benzene plume configuration has not changed significantly over time, but additional monitoring wells are recommended to define the south and southwest limits MTBE concentrations have increased in MW-4 at a greater rate than in the downgradient well MW-3 ! The following documents are enclosed with this letter Figure 1 Site Map Figure 2 Groundwater Elevation Contour Map,January 19, 2001 Figure 3 Groundwater Constituent and Isoconcentration Map, January 19, 2001 Figure 4 Rose Diagram of Groundwater Flow Direction Figure 5 Benzene Concentrations over Time Figure h TPH-G concentrations over Time Figure 7 MTBE Concentrations over Time Table 1 Historical Groundwater Elevation Data Table 2 Groundwater Flow Direction and Gradient Table 3 Groundwater Analytical Data Table 4 Comparison of Groundwater Analytical Results with Previous Sampling Event Attachment A Field Data Sheets Attachment B Laboratory Analytical Reports • Use or duclosure of data continued on this sheet is subject to the restrtctton specified at the beginning of this document 04/17/01P\16000\16271\Repons\1st01gtr doe