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' Work Plan Page 3 Former Manna Pro Site Project No 207 3 August 16, 1999 ' existing well boxes in preparation for their replacement In addition, all well caps and locks were replaced with new ones Based on the most recent available quarterly monitoring event conducted by Azure Environmental, It appears the groundwater is impacted by gasoline with little or no ' residual diesel fuel The contaminant plume is stable and except for a small area under EI Dorado Street, the plume appears to be contained within the Property boundaries ' 1.3 Proposed Scope of Work The goal of the work described herein is to develop new engineering data which will be ' used in conjunction with existing data, as the basis of a Feasibility Study to identify the most feasible and cost effective method to adequately mitigate the residual soil and groundwater contamination at the former Manna Pro facility The Feasibility Study will ' compare several alternatives for remedial action and determine which methods should be used to generate the final Remedial Action Plan (RAP) Concurrently, additional work is being proposed to further characterize the distribution of hydrocarbons contained in ' groundwater below 50 feet, and to determine the location of any water production wells which may exist within 2000 feet of the point of release This work, described in the following sections is proposed pursuant to a directive of the San Joaquin County PHS/EHD dated June 23, 1999 The following two sub-sections discuss the guiding concepts of the tasks being proposed by this Work Plan, and introduce the mayor elements of the work that will be needed to accomplish the stated goals 1.3.1 Conceptual Basis Past work performed by Groundwater Technology Inc (GTI) documented pilot level field testing of a remedial concept involving simultaneous vapor extraction and groundwater pumping This work provides much of the basis for additional work needed to complete the pilot testing for a feasibility study The GTI work demonstrates that while subsurface soils are relatively impermeable, vapor extraction at the Manna Pro site is feasible if vapor extraction wells are installed relevantly close to each other The purpose of groundwater pumping proposed in the GTI report was to control the down-gradient spread of the contaminant plum and to draw down groundwater to increase the vadose zone exposed to the vapor extraction well The limitations on pumping rates achievable, due to the poor permeability of the shallow clay aquifer, suggest that groundwater "pump and treat" would be ineffective in remediating the hydrocarbon contamination and may also ineffective in plume capturing or lowering groundwater to make vapor extraction more effective These factors, in conjunction with the costs involved in pumping and Iwaste treatment & disposal, make this technology unattractive 2937 Veneman Ave,#B240 Geo-Phase Environmental Inc Phone(209)569-0293 Modesto,CA 95356 Fax(209)569-0295