SITE INFORMATION AND CORRESPONDENCE

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Mr. Chuck Cannel September 7, 1994 a ~ Page 2 Quarterly Monitoring Results and Discussion The general groundwater flow across the site is to the south with an average hydraulic gradient of approximately 0.006. Water-level data are listed in Table 1. Table 2 shows past h and present hydraulic gradients and groundwater flow directions. Figure 1 illustrates II groundwater contours and the groundwater flow direction. Well W-211 was not used for contouring, as this well is completed in a deeperzone than the other wells. Well W-2A was not used in contouring because this well contained only a small amount of water that likely has collected in the end cap and is not represen ative of the water table surface. i The current southerly flow direction andgradie t of 0.006 are within the ranges previously reported. On June 23, 1994, the depth-to-water ranged from 62.07 feet to 64.91 feet. Water-Ievels in the monitoring wells decreased an average of 2.43 feet between March 22, 1994, and June 23, 1994 with the exception of ell-2A. Well-2A, which has been dry since August 1993, registered a water-level at -20.30 feet. This indicates a positive change in the water-level since the last measurement. The reason for this change is unclear. The next quarter's water-level measurements will be used to verify this change. Current and historical analytical results are sumn arized in Table 3. The complete laboratory reports, including chain-of-custody documentation, for the quarterly sampling are presented f in Exhibit A. Benzene and TPH-G were detected in wells W-2A and W-3. The detection limits for benzene and TPH-G are 0.3 and 10 micro'-rams per liter (pg/l), respectively. i Status of Site Remediation This section provides a description of the remediation system and discusses the effectiveness of the remediation system operation. Description. The remediation system at ARCO Station 434 consists of a groundwater extraction and treatment system (GWETS) 'and soil vapor extraction and treatment system (SVETS). The GWETS consists of one groundwater extraction well (E-1) with a designed pumping capacity of I Gallon per minute. T eatment of the extracted groundwater is accomplished with two granular activated carbon vessels, each having 1,000-pound capacity. Groundwater is extracted from the well via a submersible pump. Discharge of the treated groundwater is to the City industrial sewer system under Wastewater Discharge Permit No. 151 issued by the City of Lodi Public Works D partment. Installation and start-up of the GWETS occurred in October 1992. The GWETS was shut down on April 19, 1993, due to nondetectable concentrations of hydrocarbons in he water. I , I Use or disclosure of data contained on this sheet is subject to the restriction specified at the beginning of this document. i Ii 1318\RE PO R T SLYD 94 QTR.R PT 4 3