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+- 406gical Technics inc. �"� \'"'{ Page 8 Interim Remedial Action Plan Project No.622.2 March 28,2005 A chain of custody document, listing all samples collected and their intended analyses, will accompany the samples from the field to the laboratory, thereby providing a means to track the movement of the samples and ensure their integrity. 3.1.3.2 Water Monitoring/Sampling Procedure The extraction wells will be sampled at startup and monthly thereafter at the well head using disposable bailers so that individual well concentrations can be measured. Water samples will also be obtained from the carbon system lead/intermediate vessel effluents on a monthly basis (or more often if sewer discharge permit requires). Water samples will be collected into 40-m1 VOA vials, preserved with hydrochloric acid, while minimizing sample aeration during transfer of the sample. All samples will be checked for headspace bubbles, labeled, inserted into foam holders and placed into a cooled ice chest for transport to a state certified laboratory. k. The sampling technician will wear disposable gloves while collecting all samples. The samples will be analyzed at Excelchem in Roseville, California for the following: • BTEX by EPA method 8260; reporting limits of 0.5 ptg/l V • TPH-G by EPA method 8260; reporting limits of 50 µg/1 • MTBE by EPA Method 8260; reporting limit of 0.5 [tg/l • TBA by EPA Method 8260; reporting limit of 5.0 �tg/1 A chain of custody document, listing all samples collected and their intended analyses, will .,. accompany the samples from the field to the laboratory, thereby providing a means to track the movement of the samples and ensure their integrity. .. 3.2 Plume Control In Figure 5 the plume is shown as having a contaminated core with a lobe that extends from the core to the right (northeast) that is the predominant down gradient direction. The depth of the lobe occurs in a sand layer of varying thickness that has been recorded in the core location and the down gradient location of wells MW-5 and MW-6. The sand layer is present at 4. approximately 38 — 48 feet bgs and acts as a preferential pathway for off site contaminant transport (refer to Figure 3 for lithology). w- Installing a traditional groundwater pump and treat system would address this issue by controlling the spread of the MTBE plume through the sand layer. The following sections detail the methods to achieve hydraulic control of the on site plume and prevent further �-- dispersion of the contaminants. 3.2.1. Extraction Well +r Existing extraction well EW-1 is screened from 37 — 50 feet bgs which intercepts the sand layer described above. During the pilot test extraction rates of up to 11 gpm were achieved