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1I2 0 GE OL q DEC � �005 A GROUND CONSULTANCY ENVIRONAIE N,I HEALTH • WATER PERMI fISERVICE5 Mr Harlan Knoll, R.E.H.S November 28,2005 Senior Registered Environmental Health Specialist San Joaquin County Environmental Health Department 304 E Weber Avenue, Third Floor Stockton, CA 95202-2708 RE Fourth Quarter 2005 Groundwater Monitoring Report- Former Donna Gardner Property, 26056/26080 North Thornton Road, Thornton, CA Dear Mr. Knoll, This Fourth Quarter, 2005 Groundwater Monitoring Report is submitted by H2OGEOL on behalf of R B Construction, Inc for the former Donna Gardner Property, located at 26056126080 North Thornton Road in Thornton. The site Iocation is shown on Figure 1 Diagrammatic site area features and former features and the locations of the monitoring wells are shown in Figure 2 10 POTENTIOMETRIC SURFACE The depth to water in each monitoring well was measured on October 19, 2005 between 11 13 and 11.32 hours Depths to water were measured to +/- 0 01 feet using a Solmst Model water level meter The depths to water were converted to potentiometric surface elevation by subtracting the measured depths to water from the casing top elevations reported in the September 29, 2003 groundwater monitoring report submitted by Environmental Restoration Services. The depth to water, casing top elevations, and potentiometric surface elevations are presented in Table 1 All available water level measurements from 1990 through 2000 are summarized in Attachment C and from 2001 through the present measurement set are summarized in Attachment D in Table D 1 Table 2 lists the slope (gradient)and direction of gradient of the potentiometnc surface for the triangles with a well at each apex for these water level measurements. Potentiometric surface slope (gradient)and direction of gradient from 2004 and 2005 are summarized in Attachment D in Table D2, Figure 3 is a map showing the approximate potentiometric surface for the six monitoring wells on October 19, 2005 The potentiometric surface was domed centering in the vicinity of monitoring well MW-3 (Figure 3) MW-3 is adjacent to the former remedial excavation boundary 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 P 0 Box 2165 ■ Livermore, California 94551-2165 ■ (925)373-9211