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77 s 1 IRONMENTAL INC. HORIZON EN Specialists In Site Assessment,Remedial Testing,Desigq.and Operation October 28, 1999 Mr. Joe Aldridge Ultramar Inc. 525 West Third Street Hanford, California 93230 Subject: Quarterly Groundwater Monitoring Report Third 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 third 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 (Figure 2). Groundwater Monitoring Depth-to-groundwater measurements were obtained from all the monitoring wells by Doulos Environmental Company (Doulos) on August 30, 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 MW-1 through MW-9 and vapor extraction wells VW-1 and VW-4. A groundwater sample was not collected from monitoring well MW-4 because the wellhead appears to have been paved over. Groundwater samples were not collected from vapor wells VW-2, VW-3, VW_5 and- -- 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 County Public Health Services 1 Environmental Health Division (SJCPHSIEHD), the groundwater samples were analyzed for Total Petroleum Hydrocarbons as gasoline (TPHg); the volatile aromatics benzene, toluene, ethylbenzene and 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 (805)589-8389 • FAX(805)589-1456