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w Quarterly Report - December 1998 Former ARCO MINI-MART 4511 Pacific Avenue, Stockton, California 1.0. INTRODUCTION AND SCOPE OF WORK Add At the request of Mr. Art Wyatt, Advanced GeoEnvironmental, Inc. (AGE) has prepared this Quarterly Report for the site located at 4511 Pacific Avenue, Stockton, California (the site). The scope of work this quarter was to monitor the ground water monitoring well network on the site. This report documents collection and analysis of grab ground water samples and the results of ground water measurements. The site setting is illustrated in Figure 1. Structures, monitoring well and soil boring locations are illustrated in Figure 2. The site history and a description of previous work performed at the site were detailed in the Quarterly Report-March 1996 dated 30 April 1996,prepared by AGE. Findings from the latest soil and grab ground water sampling event were detailed in Quarterly Report-June 1998, t- prepared by AGE, dated 22 December 1998. Data from previous ground water monitoring events are included in the tables of this report. 2.0. PROCEDURES w� Field procedures were performed in accordance with Central Valley Regional Water Quality Control Board (CVRWQCB) and San Joaquin County Public Health Services - Environmental Health �. Division (PHS-EHD) guidelines for subsurface investigations of underground storage tank- (UST) sites. 2.1. MONITORING WELL PURGE PROCEDURES �.. On 31 December 1998, a Solinst water level meter was used to measure the depth to ground water in monitoring wells MW 1 through MW7 and vapor well VW L i— After depth to ground water measurements,a minimum of 3 well volumes of water was purged from y each well to be sampled using a PVC submersible two-stage pump. Approximately 16 gallons of water were removed from vapor well VW 1; 22 gallons of water were removed from wells MW 1 and MW3; 25 gallons from well MW2; 12 gallons water were removed from well MW6 and MW7; and 13 gallons of water were removed from wells MW4 and MW5. Temperature, pH and conductivity of purged ground water were measured at 2-gallon or '/z well-volume intervals, as appropriate for each well, using an ICM water analyzer. The field data and field sheets are included in Appendix A. Purged water was temporarily stored on-site in 55-gallon DOT-approved 14-17 storage drums. Following purging, the depth to ground water was measured to ensure that a minimum of 80% well- volume recharge had been achieved prior to sampling. Advanced GeoEnvlronmental Inc.