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1 QUARTERLY GROUNDWATER MQNG REPORT631 Pacific Avenue Stockton California Floating liquid hydrocarbons have been handbailed from well MW-3, on either a weekly or twice-monthly basis, from February 1991 to the present Thicknesses of liquid hydrocarbons in MW-3 measured during the past 12 months are listed in Table 1 Liquids removed from the three wells are temporarily stored on site in Department of Transportation-approved 55-gallon drums The liquids are disposed of, on a quarterly basis, by Crosby & Overton, Inc , of Oakland, California, a licensed hauler A vapor extraction pilot test was performed at the site from February 20, 1992 During the test, hydrocarbon vapors were December rawn from the subsurface, ' via vapor extraction wells VEW-1 and VEW-2, and the horizontal slotted piping run installed beneath the former product line locations The vapors were burned using a portable internal combustion engine The purpose of the pilot test was to determine efficiency parameters (i e , hydrocarbon vapor yield, combustion efficiency, etc ) that may be expected during possible subsequent vapor extraction at the site Results of the vapor extraction pilot test will be reported under separate cover ' Sufficient data does notx <, e ist at the present time to estimate zero lines for petroleum hydrocarbons in groundwater beneath the site Data obtained during subsurface investigations, UST removal, quarterly groundwater monitoring, and pilot testing J performed at the site will be used to form recommendations for further investigation ' and/or remediation alternatives ' 4.0 GROUNDWATER MONITORING 41 Groundwater ' On February 26, 1992, Emcon personnel collected measurements of depths to liquids in each of the three wells The measurements were collected according to the Emcon sampling procedures (SP) included in Appendix A A groundwater elevation hydrograph is included as Figure 3 Figure 4 is a contour map of the potentiometric surface of the shallow water-bearing zone on February 26, 1992 During the past 4 months, sine October 8, 1991, groundwater levels have risen 2 43, 2 44, and 2 48 feet in MW-1, MW-2, and MW-3, respectively Floating hydrocarbons were observed in MW-3 on February 26, 1992, at a thickness of 0 01 font The nrnr onr1%m-m+nr elevation in MW-3 was corrected for hydrocarbon suppression according to the formula noted in Table 1 On the basis of the February 26, 1992, measurements, the estimated direction of groundwater flow was to the northeast (Figure 4) at an estimated average gradient of 0 0014 ft/ft The previous estimated direction of groundwater flow was to the east on October 8, 1991 �j 90 020A QMR 2