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Comments on Focused Gro Awater - 2 - • 19 October 2007 <br /> Extraction Test — DDJC Sharpe <br /> COMMENTS ON RECOMMENDATIONS: <br /> 1. Groundwater extraction from MW418C appears to be more effective than from EWC3. <br /> Regional Water Board staff concurs with the recommendation not to resume extraction <br /> from EWC3, and to begin extraction from MW418C after the third quarter rebound period. <br /> 2. URS concluded that groundwater extraction from MW437C removes TCE from a portion <br /> of the water bearing zone that extraction from EWCC1 does not remove. However, the <br /> recommendation to cycle extraction over 6-month periods between the two wells would <br /> have the effect of reducing the total mass of TCE removed each year from the aquifer. <br /> Therefore, Regional Water Board staff does not concur with the recommendation. DDJC <br /> should proceed with planned further investigation at P-5A as this may help identify the <br /> source of TCE observed in MW437C. DDJC should resume extraction from EWCC1, <br /> and consider concurrent extraction from MW437C; this may increase the total TCE mass <br /> removal rate. <br /> 3. Regional Water Board staff concurs with DDJC's recommendation to complete model <br /> runs for development of recommendations that would optimize extraction rates and <br /> potentially identify locations for additional extraction wells. <br /> OTHER COMMENTS: <br /> 1. In Section 2.0.3, there is a typographical error in the screen interval description for <br /> monitoring well MW437C. <br /> 2. In Section 2.2.1, last sentence, there appears to be a typographical error in the <br /> designation of the rebound monitoring well. <br /> 3. The meaning of Section 3.2.4.2 is confusing and should be clarified, especially the last <br /> two sentences. <br /> If you have any questions, please contact me at (916) 464-4675, or by email at <br /> jbrownell@waterboards.ca.gov. <br /> ?James R. Brownell, M.S., P.G. <br /> Engineering Geologist <br /> Federal Facilities Cleanup Unit <br /> cc: Mr. Michael Work, US EPA Region 9 (San Francisco) <br /> Mr. Peter MacNicholl, DTSC Region 1 (Sacramento) <br /> Ms. Diane Hinson, San Joaquin County Environmental Health Department (Stockton) <br /> Mr. Michael Thomas, URS (Sacramento) <br /> Ms. Sara Dwight, TechLaw, Inc (Sacramento) <br /> Mr. Rich Howard, TechLaw, Inc (Sacramento) <br />