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last e-mail • • Page 1 of 3 <br /> s <br /> Vicki McCartney [EH] <br /> From: Vicki McCartney [EH] <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 the Cheadle Building <br /> located at 304 East Weber Avenue in Stockton, California, if this time is convenient for you. The following are <br /> some of the issues we would like to discuss concerning the Site Conceptual Model(SCM) for Chevron Station <br /> #92033 at 508 Charter Way, Stockton, CA, and future work for this site. <br /> 1. Appendix H, titled Groundwater Mass Balance Calculations, gives an area for the impacted soil, but no <br /> 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 soil is extremely low for <br /> most soil types (62.9 pounds). San Joaquin County Environmental Health Department <br /> (EHD) believes using 100 or 110 pounds per cubic foot would be more appropriate. <br /> o Impacted soil in the saturated zone is ignored, but this impacted soil is probably significant and most <br /> likely is contributing to the groundwater contamination. <br /> o Secor's estimates for dissolved contaminant masses appear to be off by a factor of one thousand. <br /> Dissolved contaminant masses should be 0.63 pounds instead of 631.7 pounds for gasoline; 0.0165 <br /> pounds instead of 16.5 pounds for diesel; 0.069 pounds instead of 68.7 pounds for benzene, and <br /> 0.081 pounds instead of 81.1 pounds for MTBE. <br /> 3. Impacted soil and groundwater are not vertically delineated, however, Secor does not address this in <br /> Section 9 of the SCM. Instead Secor proposes to advance eight soil borings to a depth of approximately <br /> 30 feet below surface 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 explanation for the boring <br /> locations and depths. It is documented that soil is known to be impacted to depths of at least 35 feet bsg <br /> so it is unclear why these 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 into monitoring wells. <br /> Secor does not indicate what analyses will be performed on the groundwater samples. <br /> 4. It is unclear why soil samples will be analyzed for different analyses based on where the soil samples are <br /> collected and it is unclear why soil samples will be analyzed for Title 22 metals. <br /> 5. The recent increase of MTBE concentrations in MW-2 over the past year needs to 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 /> From: George Forsythe [mailto:gforsythe@secor.com] <br /> Sent: Tuesday, February 15, 2005 11:39 AM <br /> 2/16/2005 <br />