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Mr Chuck Carmel • December 6, 1993 Page 2 Quarterly Sampling Results and Discussion Emcon's field notes and the analytical report from the quarterly groundwater sampling are contained in Exhibit A Exhibit B presents the water-level data for this site Exhibit C summarizes historical groundwater flow direction and gradient data for this site Figure 1 shows the water-level elevations for each well and the contours of equal water-level elevation for August 5, 1993 Figure 2 shows BTEX and TPH-G concentrations for each well sampled The general, groundwater flow direction is to the northeast under a hydraulic gradient of 0 002 Water-level elevations have decreased an average of 161 feet since the last quarterly monitoring (April 29, 1993) The TPH-G and BTEX concentrations detected iii the samples collected this quarter are generally consistent with previously reported results Concentrations of TPH-G in the samples from wells E-1 I and BHD-1 are higher than previously detected The samples from E-3, E-6, E-7, and E-12 contained one or more of the constituents at concentrations lower than previously detected The samples from off-site wells PRA, PR-2, and BHD-2 did not contain detectable concentrations of hydrocarbons, indicating that off-site migration is being contained by the GWES The hydrocarbon concentrations detected in BHD-1 are thought to be attributed to the Chevron station across the street from the ARCO site Chevron's well MW-I is located approximately 30 feet to the north of well BHD-1 and near Chevron's former UST location Samples from MW-1 generally contain sirridar TPH-G and BTEX concentrations to those in BHD-1 Status of Site Remediation This section provides a description of the remediation system and discusses the operation of the remediation system for the thud quarter 1993 Description. The remediation system at ARCO Station 2133 consists of a GWES The GWES consists of one groundwater extraction well with a designed pumping capacity of 15 gallons per minute (gpm) There is no treatment of the extracted groundwater prior to discharge to the sanitary sewer as per the City of Stockton wastewater discharge permit issued for this site The system is sampled monthly to ensure the discharge is within permitted limits The analytical results are included in Exhibit D Groundwater is extracted from the well via a submersible pump Installation and start-up of a free product recovery system occurred in 1934 After the free product was recovered, the system was modified for use as 12M"J�Ev43YIRLMKzsveo93QrM Rrr Q��srsrau