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HORIZON ENVIRONMENTAL INC. Specialists in Site Assessment,Remedial Testing,Design and Operation rr January 10, 2000 Mr. Joe Aldridge Ultramar Inc, 525 West Third Street Hanford, California 93230 Subject: Quarterly Groundwater Monitoring Report Fourth Quarter- 1999 Beacon Station No. 474 3443 East Main Street, Stockton, California Mr. Aldridge: Horizon Environmental Inc. (Horizon) has prepared this Quarterly Groundwater Monitoring Report which presents results for the fourth quarter 1999 monitoring activity for the above- referenced site (Figure 1). There are currently nine groundwater-monitoring wells (MW-1 through MW-9) and six vapor. extraction wells (VW-1 through VW-6) associated with this . site. All of the wells are located onsite, except for wells MW-4 and MW-5, which are offsite groundwater monitoring wells located within nearby street right-of-ways (Figure 2). Groundwater Monitoring Depth-to-groundwater measurements were obtained from all the monitoring wells by Doulos Environmental Company (Doulos) on December 10, 1999 (see Table 1). Static groundwater levels were reported as being measured from the top-of-casing (T.O.C.) of each well and recorded to the nearest 0.01-foot. Water level measurements were subtracted from reference elevations as reported by previous consultants to obtain water elevations, as listed in Table 1. Ultramar Inc. (Ultramar) Field Procedures are presented as Attachment A with this report. Doulos Sampling Information Sheets are included as Attachment B. Historical groundwater data as reported by previous consultants is included as Attachment D. Groundwater samples were collected from monitoring wells MWA, MW-2, MW-3, MW-5 through MW-9, and vapor extraction wells VW-1 and VW-4 on December 10, 1999. A groundwater sample was not collected from monitoring well MW-4 because the wellhead appears to have been paved over by the City of Stockton. Groundwater samples were not collected from vapor wells VW-2, VW-3, VW-5 and VW-6 because these wells are screened _ above the water table. Collected samples were submitted under chain-of-custody (COC) to Kiff Analytical (Kiff), a California Department of Health Services-certified analytical laboratory (ELAN No. 2236) located in Davis, California. As requested by the San Joaquin SCounty Public Health Services / Environmental Health Division (SJCPHS/EHD), the groundwater samples were analyzed for Total Petroleum Hydrocarbons as gasoline (TPHg); 5011 Golden Foothill Parkway,Suite 7 . EI Dorado Hills,CA 95762 • (916)939-2170 . FAX (916)939-2172 P.O.Box 5283 • Bakersfield.CA 93388 9 (805)589-8389 • FAX(805)589-1456