ARCHIVED REPORTS XR0002745 - Laserfiche WebLink

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u> . page 2, 16 Harding Way The PAR presents the results of further site assessment, including an analysis of the extent of the total petroleum hydrocarbon impact at this site, a summary of the feasibility tests that have been completed, an evaluation of other possible remediation methods, and SECOR's recommended remediation method(s) believed best to mitigate the contamination emanating from the site Assessment activities in June 2002 included the installation of two additional deep monitoring wells, DMW-2 and DMW-3, two shallow monitoring wells, MW-10 and MWA 1, and one extraction well, EW-2 These wells were located down and cross gradient to the site The only detections of contamination in soil was MtBE, detected at depths from 30-55 feet bsg in various borings, at a maximum concentration of 13 parts per million (ppm) in the 50-foot bsg sample from DMW-3 Analytical results of groundwater samples collected from the wells following development were consistent with site trends Contaminant concentrations in the shallow wells down gradient, near MW-6, were high, the concentrations in the deep wells were low, similar to onsite well DMW-1 Shallow monitoring wells MW-10 and MW-11, located furthest down and cross gradient to the site, had minor detections of toluene and xylenes only SECOR concluded that the results of these assessment activities indicate that the vertical and lateral extent of the soil contamination has been fully delineated, and that the down and cross gradient extent of the groundwater contamination has been defined, except for a detection of 12 ppb MtBE in cross gradient well MW-5 SECOR estimated the mass of contaminants remaining in the groundwater at 1,432 gallons SJCIEHD recommends further evaluation of the vertical extent of contaminant impact to groundwater following the completion of several more rounds of quarterly monitoring In the PAR, SECOR recommends a combination of groundwater extraction (GWE) and soil vapor extraction (SVE) as potentially the most effective strategy for remediation of the contamination and for control of the off-site migration of the plume Based on capture zones and effective radius of influences calculated from the feasibility testing, SECOR proposes to install five additional GWE wells and one additional SVE well A total of seven wells will be used for GWE and nine will be used for SVE Additional recovery wells will be installed in the future if evaluation of the system operations indicates it would be necessary for more complete mitigation of the problem The PAR also suggests that air sparging may be introduced in the future as an enhancement to the GWE and SVE systems, but feasibility testing would have to be completed to properly design such a modification to the system The PAR states that one purpose of remediation at this site is to reduce contaminant concentrations to below remediation goals, but does not state what those goals are Under the Porter-Cologne Act,waters of the State of California include both surface and groundwaters Water quality goals for waters of the State in the Central Valley can be found in "A Compilation of Water Quality Goals" (Central Valley RWQCB, August 2000) and "Fourth Edition of the Water Quality Control Plan (Basin Plan)for the Sacramento River and San Joaquin River Basins" (Central Valley RWQCB, September 1998) Both of these documents are available on the RWQCB website at www swrcb ca govlrwgcb5 As stated in the Basin Plan, unless otherwise designated by the RWQCB, all • groundwaters in the Region are considered as suitable or potentially suitable, at a minimum, for municipal and domestic water supply, agricultural supply, industrial service