SITE INFORMATION AND CORRESPONDENCE

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Mr. Harlan Knoll, R.E.H.S. December 30, 2005 Page 2 Figure 3a is a map showing the approximate potentiometric surface for the six monitoring wells on October 30, 2005 and Figure 4a is that for December 05, 2005. The overall potentiometric surface configurations was domed centering in the vicinity of monitoring well MW-3 as has been the case for the quarterly monitoring events. MW-3 is adjacent to the former remedial excavation boundary as shown on previous consultants' reports. The monitoring wells were installed in 1990 and the former excavation occurred in 1996. MW-3 is at the center of the groundwater mound that has been persistent over the last several years and may be in hydraulic connection with the former excavation backfill. This doming may be the result of higher permeability backfill used to backfill the excavation. MW-3 is also near the center of the triangle formed by monitoring wells MW-1, MW-2, and MW-4. The potentiometric surface for this well triangle for October 30, 2005 is shown in Figure 3b and for December 05, 2005 in Figure 4b. Monitoring of the water levels and the potentiometric surface for the well triangle formed by monitoring wells MW-1, MW-2, and MW-4 independent of the domed center at MW-3 dampens the effect of the higher water level at MW-3. Monitoring well MW-4 is about 75 feet from Thornton Municipal Well No. 2; MW-1 is at a distance of about 113 feet and MW-2 is about 157 feet distant. If there is a water level response in these wells from the pumping of Thornton Municipal Well No. 2, monitoring well MW-4 should respond more than the more distant wells MW-1 and MW-2. Drawdown in these wells, particularly MW-4, should result in the potentiometric surface direction rotating toward the Municipal pumping well and the potentiometric surface gradient steepening toward the Municipal pumping well. Submersible pressure transducer/data logger combinations were placed in monitoring wells MW- 1, MW-2, and MW-4 and a barometer was placed in the vicinity on Wednesday, November 30, 2005. These devices were set to record total pressure (overlying water plus the atmospheric pressure and their variations, regardless of the cause) every 20 minutes for a five day period extending through Monday, December 05, 2005. The pressure data recorded by the pressure transducer/data logger combinations are presented in Figure 5. The top graph is the response of the barometer and clearly shows the atmospheric response to the low front of the winter storm of December 1, 2005 and the diurnal pressure response on subsequent days. The three lower graphs are the response recorded by the pressure transducer/data logger combinations set out in monitoring wells MW-1, MW-2, and MW-4. On each of these graphs, the black line (lower line to the left and higher line to the right) portrays the direct total pressure recorded, calibrated to the water surface elevation at the time of transducer removal. H 2 OGEOL A GROUND WATER CONSULTANCY