SITE INFORMATION AND CORRESPONDENCE

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Example 1• specific cria for shutting down individual extraction wells, including the number of Excerpt from a Conceptual Model consecutive monitoring events where cleanup levels must be achieved for attainment at a .. PCE concentrations in excess of 2,500 ug/L have particular well and consideration of potential persisted in shallow well MW-12S since the remedial contaminant rebound investigation,despite pumping from the underlying but adjacent deep extraction well EW-2. This persistence may indicate the possible presence of a continuing PCE process monitoring levels or other milestones source(NAPL or soil contamination)near MW-12S. that will indicate when individual components Furthermore,little drawdown is noted at MW-12S, of the above-ground treatment process can be despite pumping from EW-2. The lack of draw down at removed MW-12S due to pumping at EW-2 calls into question the ability of EW-2 to capture the PCE in the shallow zone in Revise Goals Over Time As Appropriate the vicinity of MW-12S and may indicate that EW-2 is in a low conductivity zone or that a low conductivity layer There are many reasons to consider revising goals of separates EW-2 and MW-12S.... the P&T system over time, some of which are Data Gaps: highlighted in Exhibit 2. presence of a continuing PCE source degree of capture near MW-12S Because the site-specific conceptual model evolves, periodic review of system goals should occur on a Considerations for the Site-Wide Exit Strategy: regular basis,perhaps once every 5 years. For contain shallow ground water near MW-12S by Superfund sites,this review of system goals could be pumping(short term) done with the Five Year Review process. In some characterize and then remove or contain the federal and state programs,a change in the site continuing PCE source decision document may be needed prior to changing the goals. Include Metrics For Evaluating System Performance C. EVALUATING PERFORMANCE AND EFFECTIVENESS OF THE P&T SYSTEM To help determine whether or not the system goals are achieved,each goal should include metrics (i.e., performance standards that can be measured). For Evaluation of P&T system performance should example,a goal of"ground water containment' is include evaluation of the subsurface perforniance, vague unless stated in conjunction with specific metrics offered by the extraction system,and evaluation of the such as gradients, drawdowns,or ground water above-ground performance, offered by the treatment elevations ("water levels") that must be achieved at specific locations. Similarly, metrics for"ground water Exhibit 2 cleanup"might include specific milestones for mass Some Reasons To Modify Goals of the removal,peak concentration reduction, and/or plume P&T System area reduction that must be achieved within specified time periods or at specified locations. revised regulatory framework Clearly Indicate When Some or All of the P&T new treatment technologies or strategies System Can Be Discontinued operating experience suggests existing goals are unrealistic and will not be met To provide a viable exit strategy for the P&T system or some of its components,the following details or costs are greater than originally anticipated metrics should be specified as part of the system goals: changes in plume extent • contaminants of concern (CDCs)being addressed by the P&T system, which may be a discovery of additional and/or continuing sources of subset of the COCs for the entire site contamination,such as soil contamination or NAPL • cleanup levels that must be achieved for each changes in land use or ground water production near specific COC addressed by the P&T system the system 3