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i i Mr. Gordon Lee Boggs April 25, 1989 j Page 4 r 1 Installation of Proposed Groundwater Monitoring Wells i i 1. The Regional Board suggested an additional monitoring well on the southeast corner of the Kettleman Lane-Hutchins Street intersection. ARCO and Brown and Caldwell believe the proposed monitoring well at the Save Mart on the northeast corner of that intersection along with existing monitoring wells on the southwest corner (well W-5) and adjacent to Municipal Well 12 (well W-4) will be sufficient to define the southeastern extent of the plume. 2. The Regional Board requested vapor meter readings of the soil samples collected from the off-site monitoring well borehkoles. ARCO agrees to this. The p e -� - _ _ -Regional- Board - also -requested-- the�uInsaturated�'sail—Barri le nearest the ` ' groundwater surface be collected . for laboratory analysis for benzene, ethylbenzene, toluene, and xylene (BETX) and for total petroleum hydrocarbons (TPH). ARCO agrees to have the soil sample in question analyzed for BETX and TPH (gasoline range) and also intends to have the sample collected from 5 feet above that sample submitted for laboratory analysis for BETX and TPH (gasoline range). 3. The Regional Board requested monthly sampling for BETX and TPH of monitoring wells W-2, W-2A, and W 2B to determine with more certainty that hydrocarbons exist in groundwater at 80 feet below grade. Only monitoring well W-2B is screened at this depth. ARCO agrees to begin monthly sampling of well W 2B for BETX. 4. Monitoring well W-1 has been difficult to purge and sample. To be assured of collecting representative data, ARCO proposes to replace monitoring well W-1 (total depth 65 feet below ground surface) with a 70-foot deep monitoring well. The proposed replacement well will be immediately adjacent to well W-1 and will be drilled, constructed, developed, s�mpied, and surveyed as described for the other additional monitoring wells in Brown and Caldwell's work plan. Well W-1 will be .drilled out using a truck-mounted drilling rig equipped with hollow-stem augers. The borehole will then be backfilled with a bentonite/cement slurry placed by tremie pipe. Groundwater Extraction Well Brown and Caldwell would like to address two of the Regional Board's comments which we feel do not accurately reflect conditions at the site. 1. ARCO last had free product removed from monitoring wells W-2 and W-3 in July 1988. Brown and Caldwell measures water levels in all existing monitoring wells with an electronic oil-water interface probe on a biweekly basis. No free product has been detected in any monitor well since August 1988. BROWN AND CALDWELL 723 5 STREET SACRAMENTO,CALIFORNIA 95814-7092•(916)444-0123