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�- - Upgradient Environmental Consultants --. April 30, 199$ ;; 32 Mr. Ken Gillies Gillies Trucking P. O. Box 8303 Stockton, CA 95208 Subject: Report of l st Quarter Monitoring ies Trucking Yard 893 Newton Road tockton, CA As you requested, groundwater monitoring for the first quarter of 1998 was performed by Upgradient Environmental on April 28, 1-998. This is the only activity that we performed during the quarter. Upon arrival at the site, the monitoring wells were opened and allowed to equalize with atmospheric pressure. Wells GT-5 and GT-6 were under unusally high pressure, which blew the well caps out of the weil box when the locks were removed. Two weIis were not opened: GT-2 could not be located, as a result of road grading activity since our last visit to the site in 1997, and GT-9, which is located on the neighboring property, could not be accessed because of a locked gate. Water depth was measured with a Solinst water level meter. The depth averaged8 feet, which is the shallowest it has been since Upgradient began monitoring the site in (Table 1). At this depth, the water level is 28 feet above the screened interval in GT-1, GT-2, and GT-3 and 7 feet above the screen in GT-5, GT-6, and GT-9. Because of this, and because no gasoline odor was detectable on the water level probe, no samples were collected for laboratory analysis. Figure k shows the groundwater flow direction determined from the #bur monitored wells. The flow patter« is different from what we have seen in previous quarters, although this may be partly due to the lack of data from GT-2 and GT-9. The map shows a sharp, south-north trending bend in the gradient lines in the vicinity of the former UST cavity. North of the cavity, the gradient lines imply flow to the northeast. South of the cavity, the lines imply flow to the northwest. Overall, flow is northward toward your drinking water well, with a gradient of 0.00625 ft/ft. This is opposite to the general direction that we have observed in previous quarters, although the gradient was northward in the very first monitoring event(September 1994). Although groundwater gradients do commonly fluctuate to a degree, gradients do not usually reverse completely except where they are driven either by human activities (e- g. agricultural pumping) or by inflow to or outflow from nearby major streams. In this case, such a reversal would account for the presence of contamination in the borings and wells both north and south of the UST cavity. Stockton: P.O. Box 8002, Stockton, CA 95208 (209) 772-3620 Cameron Park: 3369 Kimberly Road, Cameron Park, CA 95682 (916) 677-3055