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Quarterly Report - July and October 1999 Former ARCO MINI-MART I4511 Pacific Avenue, Stockton, California I1.0. INTRODUCTION AND SCOPE OF WORK 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 was to monitor the ground water monitoring well network on the site This report documents collection and analysis of 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, prepared by AGE, dated 22 December 1998 Data from previous ground water monitoring events are included in the tables of this report I2.0. PROCEDURES 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) I sites I2 1 MONITORING WELL PURGE PROCEDURES I On 08 July and 27 October 1999, a Solinst water level meter was used to measure the depth to ground water in monitoring wells MW1 through MW7 and vapor well VW1 After depth to ground water measurements, a minimum of 3 standing water casing volumes of water was purged from each well to be sampled using a PVC submersible two-stage pump On 08 July 1999 and 27 October 1999 approximately 15 and 12 gallons of water respectively were removed from vapor well VW 1, 25 gallons of water were removed from well MW 1, 20 gallons from wells M W 2 and M W 3 On 08 July 1999 approximateiy 12 gallons water were removed from wells M W 4 and MW5, 10 gallons water removed from well MW6 and MW7 On 27 October 1999 approximately 10 gallons water were removed from wells MW6 and MW7 Temperature, pH and conductivity of purged ground water were measured at 3-gallon or 5-gallon intervals, as appropriate fol each well, using an ICM and Hydac water analyzer The field data and field sheel5 are included in Appendix A Purged water was temporarily stored on-site in 55-gallon DOT-approved H-17 storage drums pending proper disposal 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 IAdvanced GeoEnvironmenta!Inc I