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Work Plan-Pilot Testing Page 3 Cutter Lumber Site • Project No. 102.3 � October 30,2001 I similarities due to the common geologic and hydrologic features and to similar characteristics of the contaminant plumes. Since the early 1990's groundwater levels in this part of Stockton have risen at least 10 feet. This fact in conjunction with the known distribution of gasoline reveals that much of contaminant mass lies well below the groundwater surface. Unfortunately, this deeper groundwater contamination is not likely to be efficiently mitigated by the simple vapor extraction. We suggest that vapor extraction can be an important part of a remedial I ' action plan, but will not be useful in remediating hydrocarbon contamination situated more than a short distance beneath the groundwater surface. Air sparging to introduce oxygen into the subsurface and mobilize contaminants may address the deep ' contamination plume. Injected air will encourage the growth of aerobic bacteria and should also help to mobilize light hydrocarbons. As these mobilized hydrocarbons move through and up the water column, down gradient vapor extraction wells may be used to ' extract the mobilized hydrocarbons. One drawback of this remedial method is that the vapor extraction and the air sparging may both tend to generate a local rise in the level of groundwater. Hydrocarbons may tend to migrate "down-hill" radially away from this ' localized groundwater "mound". Prior work at the Manna Pro site suggests, however, that this effect is small and is unlucky to materially expand the lateral extent of the gasoline-impacted zone. 1.3.2 Scope of Work I ' The tasks described in this Work Plan encompass the following principal elements. ' • Conduct a water well survey to identify all groundwater production wells located within 2,000 feet of the point of release. • Construct a pilot vapor extraction system / air sparge system (VES/AS). One new ' vapor extraction and one new air sparge well will be drilled and constructed. The vapor extraction well will be 4 inches and diameter and drilled to a total depth of 40 feet. The air sparge well will be completed to 50 feet below grade. The air sparge ' will be constructed as an attempt to mobilize deeper hydrocarbons to the groundwater surface where they may then be removed and destroyed by vapor extraction. The air- sparging test will be conducted in conjunction with the pilot vapor extraction work ' mentioned above. • Operate the pilot vapor extraction / air sparge system. This test will entail 10 days of VES operation and 7 days of AS operation. Air will be injected into the sparge well ' with a compressor, and gasoline-laden vapors will be extracted from the VE well with a blower / ring compressor. Air samples will be collected and the efficiency of the VES and VES/AS systems will be calculated based on parameters measured from the VE well and nearby groundwater monitoring wells that are currently in existence. 2937 Veneman Ave.,#13240 Geo-Phase Environmental Inc. Phone(209)569-0293 Modesto,CA 95356 Fax(209)569-0295 1