SITE INFORMATION AND CORRESPONDENCE_FILE 2

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Mr. Denis L. Brown *awl 1W. Page 2 of 3 2494 E. Fremont Street 23 July 2008 Stockton, CA In the CAP, CRA proposed cleanup levels based on Regional Water Quality Control Board (RWQCB) environmental screening levels (ESI-s), the region of origin not specified. The Central Valley Regional Water Quality Control Board (CVRWQCB) does not accept any numerical cleanup levels except the water quality objectives (WQOs) of the Central Valley Basin Plan. Sites can be closed with contaminant concentrations above the WQOs if cleanup of the site has been conducted to a point that the contaminants can no longer pose a significant threat to human health, the environment or to groundwater, and it can be shown that the contaminant plume is stable and shrinking and will continue to decline to background conditions within a reasonable time frame. Therefore, the EHD cannot accept the proposed cleanup levels. To remediate the contaminants on the site, CRA evaluated monitored natural attenuation (MNA), groundwater extraction (GWE), soil vapor extraction (SVE) with air sparging (AS), multi- phase extraction (MPE), and insitu chemical oxidation (ISCO). The EHD concurs with CRA that MNA is likely to be too slow a process to employ effectively on your site. The reported point of comparison of the remaining methods was based primarily on construction, operation, maintenance and monitoring costs, with ISCO being the least expensive option. The technical justification for favoring ISCO was a bit vague, and seemed to rest on site geological heterogeneities that for some reason were less favorable to GWE, SVE with AS, and MPE, but which could be overcome by ISCO. This technical justification is not adequate, virtually all sites in San Joaquin County are heterogeneous, but the various technologies considered have been utilized, both successfully and unsuccessfully, depending on the site specific characteristics. Due to the upgradient location of the former ARCO station site and the apparent high contaminant mass on that site, the EHD believes that ISCO may be the preferred technology, but notes that ISCO is not universally applicable to all sites. The report on the evaluations of the technologies considered should be revised to present the technical basis on which ISCO was selected with enough detail so that the EHD can properly consider and concur with the selected technology. The EHD believes that in addition to the costs noted above, the technical evaluation report for each of the technologies considered should include a discussion of the interaction of the site hydrogeology, contaminants and, in the case of ISCO, any injected chemicals. One fundamental piece of information would be the mass of contaminants that would be addressed by each technology. Intuitively, the estimated cost effectiveness of each method would include an evaluation of the cost per unit mass of contaminants abated and the overall effect on plume control and achieving a low-risk status for the site. Available guidance documents for evaluation of ISCO technology notes that bench scale tests (BST) are not standardized, so the EHD will not comment on the methodology; however, in order for the CVRWQCB to evaluate the BST results with regard to potentially requiring a report of waste discharge or issuing waste discharge requirements (WDRs), the work plan proposed in the CAP will need to be revised to include the following in addition to what was proposed in the work plan portion of the CAP: • The stoichiometry or chemical equations with concentration in moles off all expected intermediate and end products from the reaction between the injectant and the soil and the groundwater. • For oxidizing conditions analysis for total and dissolved iron, total dissolved solids (TDS), major anions (chloride, sulfate, nitrate, and fluoride), chemical oxygen demand (COD), and expected breakdown products from the interaction between the injectant, chemicals of concern (COCs) and soil. CAP and WP Comment Letter 0708