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Mr. Curtis Fujii - 2 - 22 June 2001 2. Success of the proposed corrective action will depend on all landfill gas being captured. The corrective action plan should include a landfill gas monitoring system designed to demonstrate that the gas extraction system is working. 3. The EFS presents one preferred corrective action system, effectively precluding discussion of other alternatives. The EFSs should be revised to present the range of remediation techniques considered with a statement of relative effectiveness and costs. 4. The Board encourages the use of artificial recharge as part of a corrective action to prevent depletion of the groundwater resource. However, we are concerned that planned placement of recharge area will split the plume and cause the northeast part of the plume to move away from the site. Therefore, the location of recharge area should be moved to prevent this or propose some other system to control the northward movement of PCE contaminated plume. 5. Model simulations indicate that the proposed plan will decrease PCE and TCE levels below the drinking water standard of 5 ug/1 within five years. As noted above the standard in California for VOCs is non-detect based on Title 27, Section 20420(k)(6). Please rerun the model and estimate the time to reach non-detect for VOCs. 6. The model is not clear whether it includes the deeper groundwater that has been impacted in northern portion of the plume. Please demonstrate that the model and remediation system is designed to cover the entire plume. 7. Any corrective action plan must include a water quality-monitoring program to demonstrate the effectiveness of the corrective action program. At a minimum the program should include existing monitor wells and the following new wells: a. a well cluster east of MW-14, to monitor declining PCE levels at 145 and 175 feet; b. a well near boring ARL-IA, screened to monitor concentrations at 145 feet; c. a well near boring ARL-3A, to monitor concentrations at 140 feet; d. a well cluster near boring ARL-3B,to monitor concentrations at 140 and 180 feet e. and one or more additional wells adjacentt to the recharge area. 8. Progress toward cleanup should be re-assessed semi-annually. If TCE or PCE concentrations fail to decrease over any one year time period or if chlorinated solvent contamination cannot be contained within the present area of contaminated groundwater, a revised plan will be required. Please submit an amendment to the EFS addressing the issues noted above and a work plan time schedule by 31 July 2001. If you have any questions,please call me at(916) 255-3814. ROSS D. ATKINSON Associate Engineering Geologist