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last e-mail • • Page 2 of 4 <br /> From: Vicki McCartney [EH] [mailto:vmccartney@sjcehd.com] <br /> Sent: Wednesday, February 16, 2005 2:06 PM <br /> To: gforsythe@secor.com <br /> Cc: Nuel Henderson [EH] <br /> Subject: Chevron Station #92033 at 508 Charter Way, Stockton, CA <br /> George, <br /> Nuel Henderson and I would like to meet at 11 o'clock on March 22, 2005, in Room 307 of <br /> the Cheadle Building located at 304 East Weber Avenue in Stockton, California, if this time <br /> is convenient for you. The following are some of the issues we would like to discuss <br /> concerning the Site Conceptual Model(SCM) for Chevron Station #92033 at 508 Charter <br /> Way, Stockton, CA, and future work for this site. <br /> 1. Appendix H, titled Groundwater Mass Balance Calculations, gives an area for the <br /> impacted soil, but no map is presented to illustrate the area. <br /> 2. Groundwater mass balance calculation concerns include: <br /> o Grain density is too low to need to multiply by porosity. (The unit weight of <br /> soil is extremely low for most soil types (62.9 pounds). San Joaquin <br /> County Environmental Health Department(EHD) believes using 100 or <br /> 110 pounds per cubic foot would be more appropriate. <br /> o Impacted soil in the saturated zone is ignored, but this impacted soil is <br /> probably significant and most likely is contributing to the groundwater <br /> contamination. <br /> o Secor's estimates for dissolved contaminant masses appear to be off by a <br /> factor of one thousand. Dissolved contaminant masses should be 0.63 <br /> pounds instead of 631.7 pounds for gasoline; 0.0165 pounds instead of <br /> 16.5 pounds for diesel; 0.069 pounds instead of 68.7 pounds for benzene, <br /> and 0.081 pounds instead of 81.1 pounds for MTBE. <br /> 3. Impacted soil and groundwater are not vertically delineated; however, Secor does <br /> not address this in Section 9 of the SCM. Instead Secor proposes <br /> to advance eight soil borings to a depth of approximately 30 feet below surface <br /> grade (bsg) to target unsaturated soil from approximately 8 to 21 feet bsg, <br /> and convert three borings into monitoring wells. Secor does not give an <br /> explanation for the boring locations and depths. It is documented that soil is <br /> known to be impacted to depths of at least 35 feet bsg so it is unclear why these <br /> borings are being advanced to only 30 feet bsg. Secor proposes to collect grab <br /> groundwater samples from each boring, even the borings that will be converted <br /> into monitoring wells. Secor does not indicate what analyses will be performed on <br /> the groundwater samples. <br /> 4. It is unclear why soil samples will be analyzed for different analyses based on <br /> where the soil samples are collected and it is unclear why soil samples will be <br /> analyzed for Title 22 metals. <br /> 5. The recent increase of MTBE concentrations in MW-2 over the past year needs to <br /> be investigated. <br /> 6. Secor should evaluate different interim remediation methods at this site. <br /> 7. A sensitive receptor survey is still needed for this site. <br /> Vicki McCartney,REHS <br /> San Joaquin County <br /> Environmental Health Department <br /> 304 E.Weber Avenue <br /> Stockton,CA 95202-2708 <br /> Phone: (209)468-3456 <br /> Fax: (209)468-3433 <br /> E-mail: vmccartney@sjcehd.com <br /> -----Original Message----- <br /> 2/22/2005 <br />