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0 <br /> ENV. <br /> A M f A ! C A <br /> Mr. Duane White <br /> California Department of Toxic Substances Control <br /> April 29, 2005 <br /> Page 2 of 3 <br /> PG&E and ENV America response: PG&E will use the mud-rotary method to install <br /> MW-27. <br /> 2. DTSC comments: The DTSC is concerned with the potential for downward migration <br /> of acenaphthene in groundwater to the C zone and recommended that PG&E consider <br /> installing a C-zone well at the location of MW-27. Otherwise, an adequate explanation <br /> needs .to be given as to why the C zone cannot be impacted by acenaphthene at this <br /> location. <br /> PG&E and ENV America response: PG&E will collect a discrete-depth grab <br /> groundwater sample from the C zone in the boring for installing well MW-27. The <br /> sample will be collected using a Hydropunch sampler or other equivalent method. The <br /> (filtered and unfiltered) grab groundwater sample will be analyzed for polycyclic <br /> aromatic hydrocarbons (PAHs). Turbidity measurements will be recorded for any <br /> unfiltered grab groundwater sample analyzed for PAHs. The need for installing a C- <br /> zone groundwater monitoring well in the vicinity of MW-27 will be evaluated based on <br /> the analytical results of the discrete-depth C-zone grab groundwater sample. Additional <br /> grab groundwater samples may be collected and/or additional laboratory analyses may <br /> be requested based on field observations. <br /> 3. DTSC comments: The DTSC recommended that new monitoring wells be developed <br /> by bailing, surging, and pumping. <br /> PG&E and ENV America response: The new monitoring well MW-27 will be <br /> developed by bailing, surging, and pumping. <br /> 4. DTSC comments: The DTSC was concerned with the depth limitation of peristaltic <br /> pumps for sampling the B-zone wells using the micropurging procedures and requested <br /> that PG&E verify the depths of pump intakes during groundwater monitoring. <br /> PG&E and ENV America response: The limitation on peristaltic pumps is the lift; the <br /> maximum lift for water is usually about 30 feet at atmospheric pressure. The intake (via <br /> tubing) of the pump can be lowered to the midway of the screened interval of a well as <br /> long as the depth to water (DTW) is less than about 30 feet bgs. <br /> The DTWs measured in the A-, B-, and C-zone monitoring wells at the Site typically <br /> range from about 25 feet to 32 feet below ground surface. The wells are sampled using <br /> a peristaltic pump when DTW is shallower than 30 feet bgs, with intake (tubing) <br /> lowered to approximately the midway of the screened interval. When DTW is deeper <br /> than 30 feet bgs, the wells are sampled using a submersible pump with pump intake <br /> lowered to approximately the midway of the screened interval. <br /> P 1PG&E\PGE-05-01 Stockton MW26R Investigationtresponse to DTSC on WP Mpr2005.doc <br />