SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

h Donald Sinclair ,; Shirley Thompson 3780 Linne Road,Tracy Page 3 of 4 average concentration of benzene in groundwater at your site has been approximately 380 micrograms per liter. Ninety percent destruction of this quantity would leave approximately 38 micrograms per liter behind, which is well over the MCL of 1.0, and therefore is not an acceptable cleanup goal for this site. 4. In the original June 2003 CAP, GTI proposed soil excavation as the best remedial alternative to target the remaining source of petroleum hydrocarbon contamination at this site. The Addendum changes the focus of the project from soil remediation to groundwater remediation. No explanation or justification for this change in focus was presented. In situ oxidation infusion remedial processes have been developed to target groundwater contamination (June 2003 CAP, section 2.4). Petroleum hydrocarbon contamination left in the vadose zone soil may continue to be a source of contamination leaching into the groundwater. 5. GTI proposes in the Addendum that a minimum of 20 sparge points would need to be installed as part of an in situ remediation effort, but they provided no explanation or supporting documentation for proposing this number. The subsurface lithology noted on the original boring logs should facilitate prediction of a radius of influence (ROI) for whichever oxidation process GTI is proposing, and if not, then a feasibility test must be conducted to demonstrate how many points would be needed to provide proper coverage. It has been the experience of SJCIEHD that the ROI of ozone infusion points can be up to 15 feet, realizing of course that GTI has not stated specifically that they are proposing ozone infusion. In addition, groundwater;contamination at this site has been limited to three of the shallow monitoring wells. 6. GTI has suggested in the Addendum that implementation of an in situ advanced oxidation remediation system could result in closure of this site in approximately one year's time. It has not been the experience of SJCIEHD that sites using this type of technology clean up that quickly., Ozone infusion is considered a long- term technology, one that is expensive to install but relatively cheap to maintain, and often remains in operation for;several years. In addition, following completion of whichever remediation technology you choose to implement, a is minimum of one.year of groundwater monitoring and sampling must be . I! completed. Based on the discrepancies between the original boring logs submitted to SJCIEHD and those submitted in the SCM, the vagueness of the Addendum as to specifically what type of in situ oxidation process GTI is proposing, the discrepancies between the volume , of soil contamination estimates in the February 2004 Report versus those in the Addendum (which in turn creates discrepancies in the cost estimates), the changing of .: remediation focus from soil to groundwater without explanation and without addressing the remaining soil contamination, among other things, SJCIEHD finds it very difficult to identify anything in the Addendum to approve. As the responsible party for this site, selection of a remedial option is up to you, but please be aware of the following: 1. If you select a remedial option that leaves 10% of the contamination behind, you will be required to continue groundwater monitoring for natural attenuation of the residual contaminants, potentialiy,for a significant period of time. 2. If you select an option that does riot target soil remediation you will be required to continue groundwater monitoring,°:for potentially a significant period of time, as i