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Former Beacon Station No 12419 March 24,2003 Stockton California Groundwater Groundwater Monitoring Report ~ laboratory (ELAP No 2236) located in Davis, California The samples were analyzed for total petroleum hydrocarbons as gasoline (TPHg), the volatile aromatic compounds benzene, toluene, ethylbenzene and total xylenes (BTEX), and the fuel oxygenate methyl-t-butyl ether (MTBE) by Environmental Protection Agency (EPA) Method 8260B Groundwater Monitoring Results Depth-to-groundwater measurements were subtracted from the surveyed TOC elevations to calculate groundwater elevations Groundwater elevation data were used to construct a groundwater contour map as shown on Figure 2 The groundwater flow direction was variable across the site but generally trended to the southeast Groundwater gradients ranged from approximately 0 001 to 0 003 Groundwater analytical results are summarized in Table 1 Benzene concentration data from this sampling event were used to construct a benzene iso concentration map as shown on Figure 3 Copies of the laboratory data sheets and chain-of-custody documents are included as Attachment C GeoTracker Electronic Data Delivera6Ies The analytical electronic data deliverable (EDD) is uploaded by Kiff The groundwater well measurement file EDD (GEO_WELL) for this quarterly monitoring event has been uploaded by Horizon The GEO_WELL file upload confirmation sheet is contained in Attachment E Recommendations Horizon recommends continued quarterly monitoring be erfa rmed to evaluate trends in the groundwater gradient and concentrations of dissolved hydrocarbons The Problem Assessment Report/Corrective Action Plan (PAR/CAP) for the site submitted in March 2002 has been approved by the San Joaquin Country Environmental Health Department (SJCEHD) Horizon has submitted a Remedial Action Plan (RAP) to the SJCEHD which describes the proposed remedial system installations Approval of RAP is pending The proposed remediation system plans are complete and Horizon is in the process of obtaining the necessary permits from the San Joaquin County Building Department It was proposed in the fourth quarter 2002 that the sampling frequency of monitoring well MW-7, MW-11, air sparge well AS-2 and AS-3 be decreased to a semi-annual (first and third quarters) schedule, and monitoring wells MW-1 through MW-5 and air sparge AS-1 be decreased to an annual schedule (first quarter) The remaining monitoring wells MW-6 and MW-8 through MW-10 would continue to be sampled on a quarterly schedule It is proposed that the quarterly monitoring schedule take effect starting the first quarter of 2003 Horizon requests approval of the proposed changes to the monitoring program 419gmrQ103 Project No 1419 46 2 HORIZON ENVIRONMENTAL INC.