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STATE 0 CALIFORNIA <br /> CALIFORNIA REGIONAL WATER QUALITY CONTROL BOARD— <br /> GEORGE DEUKMEJIAN,Governor <br /> CENTRAL VALLEY REGION <br /> 3443 ROUTIER ROAD yes <br /> SACRAMENTO,CA 95827-3098 <br /> 6 March 1990 <br /> Mr. David Whitridge <br /> Wilson, Hoslett & Whitridge <br /> Attorneys at Law <br /> 504 Bank of Stockton Building <br /> 311 East Main Street <br /> Stockton, CA 95202 <br /> RALPH HAYES & SON, INC. , PROPERTY, 10765 WEST CLOVER ROAD, TRACY - GROUND WATER <br /> MONITORING REPORTS <br /> We have reviewed the ground water monitoring reports prepared by WHF <br /> Environmental Consultants, Inc. , (WHF) which you submitted for this site. Three <br /> ground water monitoring wells were installed in November 1987 to evaluate the <br /> potential impact on ground water from a petroleum hydrocarbon spill which <br /> reportedly occurred during removal of underground storage tanks at this site. <br /> According to the WHF reports, the analytical r=esults for samples obtained from <br /> the monitoring wells indicate that no contamination of ground water has occurred. <br /> Based on our review of the information provided, the investigations performed <br /> do not provide sufficient data to reasonably draw this conclusion. Analytical <br /> results for a sample of ground water obtained from the excavation at the time <br /> the tanks were removed showed 20 parts per billion (ppb) benzene, 50 ppb xylene, <br /> and 3,900 ppb motor oil . From the information provided. it is not possible to <br /> determine whether this pollution resulted from the reported spill which occurred <br /> during the tank removal , or from previous leakage from one of the underground <br /> storage tanks. <br /> According to the reports, the gradient of ground water flow at this site has <br /> changed over time. It does not appear that any of the samples obtained from the <br /> monitoring wells during the course of the investigations were representative of <br /> conditions downgradient from the tank area. In addition the reported detection <br /> limit for the samples obtained. from the wells were too high to reasonably <br /> conclude that ground water was not impacted by petroleum hydrocarbons. <br /> Based on the information provided, staff cannot concur that either leakage from <br /> the tanks or the reported spill of petroleum hydrocarbons did not impact ground <br /> water at this site. Therefore, it will be necessary investigate ground water <br /> quality in the verified downgradient direction from the former underground <br /> storage tanks. This investigation should include but may not be limited to: <br /> 1. Verification of the ground water gradient at the site; <br /> 2. Two rounds of ground water analytical samples with appropriate lab <br /> detection limits, following approved chain-of-custody procedures. <br />