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Review of the Draft DDJC-Sharpe Natural Attenuation and Treatment Technology Investigation Work Plan DDJC-Sharpe Lathrop, California July 2005 GENERAL COMMENTS 1. The rationale behind the technologies selected for evaluation in the Natural Attenuation and Treatment Technology Investigation Work Plan (WP) for DDJC-Sharpe is not clearly presented in the WP. In a traditional CERCLA evaluation of remedial alternatives, technologies would be screened, assembled into alternatives, the alternatives would be screened, and a detailed analysis of alternatives would be conducted. All of these ste s would be presented in a Feasibility Study (FS) with a clear set of criteria to help the public understand why some alternatives were preferred over others. The WP discusses several technologies (e.g., zero valent iron nanoparticles) that have apparently been eliminated already from consideration, but the rationale for their elimination is discus ed only briefly and none of the backup information (e.g. cost) that would be presented in the FS are presented in this WP. Please present more detailed rationale for the selection of technologies evaluated in the WP or explain if further rationale will be presented in a future FS. This information would also be useful to evaluate future optimization of ariy alternative that is implemented. 2. A groundwater model to evaluate flow and contaminant fate and transport is under development and is discussed in more detail in the Response Completion Plan (RCP)I or DDJC-Sharpe, but the model is not discussed in the WP. Regulatory Agencies are involved in the development of the model and will depend on it for making future remedial decisions for DDJC-Sharpe. Please consider presenting a brief discussion of the groundwater model and how it will be used to select treatment technologies for DDJC . Sharpe. 3. It appears from information presented outside the WP (e.g., at Remedial Project Manager meetings) that the investigation of treatment technologies centers on the hot spots within the plumes and that monitored natural attenuation focuses on the extremities of the plumes that are beyond the facility boundary, but this strategy is not clearly presented i the WP. Both are important because adequate source control will be needed to shorten the time frame of the cleanup, and contaminant concentrations in the off-base portion of the plume may require more active remedies to prevent further migration beyond the facility boundary. Please provide additional information on how this investigation will address both source areas and the groundwater contaminants that have migrated beyond, the facility boundary. 1