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HORIZON ENVIRONMENTAL INC. r Specialists in Site Assessment,Remedial Testing, Design and Operation i January 4, 2002 Mr. Joe Aldridge Ultramar Inc. 685 West Third Street Hanford, California 93230 Subject: Quarterly Groundwater Monitoring Report Fourth Quarter 2001 Beacon Station No, 12474 3440 East Main Street, Stockton, California Mr. Aldridge: Horizon Environmental Inc. (Horizon) has prepared this report which documents fourth quarter 2001 groundwater monitoring at the subject site located in San Joaquin County as shown on Figure 1. There are currently 12 groundwater monitoring wells (MW-1 through MW-12), seven vapor extraction wells (VW-1 through VW-7) and one air sparge well (AS- 1) associated with this site. The wells are located on site, except for monitoring wells MW- 4 and MW-5, which are located on East Main Street and Broadway right-of-ways north of the site (Figure 2). Groundwater Monitoring Groundwater monitoring activities were conducted by Horizon on the third and fourth of December 2001 according to Horizon Field Methods and Procedures (Attachment A). Monitoring activities included measurement of static groundwater level, purging groundwater from the wells, collection of groundwater samples, and preparation and delivery of the samples to the analytical laboratory. The depth to groundwater was measured to the nearest 0.01 foot from the top-of-casing (TOC) in monitoring wells MW-1 through MW-10 and MW-12, vapor extraction wells VW- 1 and VW-4, and air sparge well AS-1. Monitoring well MW-11 and vapor extraction wells VW-2, VW-3 and VW-5 through VW-7 were dry. The physical parameters conductivity, pH and temperature were monitored with field instrumentation during the purging process. The visual characteristics of turbidity, the presence of free product or sheen, and the obvious olfactory characteristics of the groundwater were also noted during the purging process. Field groundwater monitoring well purge data are included on Horizon Monitoring Well Data sheets. Groundwater samples were collected from groundwater monitoring wells MW-1 through MW-10, MW-12, vapor extraction wells VW-1 and VW-4, and air sparge well AS-1. The �• samples were submitted, under chain-of-custody documentation, to Kiff Analytical LLC 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 • (661) 589-8389 - FAX (661) 589-1456