SITE INFORMATION AND CORRESPONDENCE_FILE 1

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FILE COPY U � page 2 2701 N. Wilson Way, Stockton Conclusions by BEM that possible offsite sources may exist are unsupported with the current groundwater gradient data included in the report. In order to support offsite source conclusions, the potential source is typically upgradient of the site and soil and groundwater samples should provide data that supports the conclusion. Currently the groundwater gradient direction is tozwrds these offsite areas and no samples have been collected in these areas that support the conclusion that an off-site source exists. Additional data is required to complete the site characterization and support these conclusions. A municipal water supplier did not always supply the area surrounding this site (California Water Services). Many private domestic and irrigation wells were used to provide this area with its water needs. In order to evaluate the impact to and from these wells on the groundwater,you will need to conduct a Well/ Sensitive Receptor survey. Please contact California State Department of Water Resources (D)XR) at (916) 653-5791 to obtain the information to start your file search of wells in the area. PHS-EHD will sign the official request to conduct the search when the DWR form is submitted to our agency. In order to be able to better evaluate the contamination status of this site,the next two quarterly groundwater monitoring and sampling events are to include sampling of all of the monitoring wells and sample analyses for all of the petroleum hydrocarbons constituents associated with this site. Recent Department of Health Services Laboratory changes have provided for EPA Method 8260B to accurately analyze for TPH as gasoline, BTEX, and the oxygenates in one analyses. Please use this method or a combination of approved methods that provide TPH g and BTEX, as well as TBA, TAME, ETBE,MtBE,DIPE, and methanol and ethanol. Once two consecutive quarterly sampling events indicate that the oxygenate constituents are not present in the groundwater samples, the analyses for them may be discontinued if requested. Although PHS-EHD may not agree with BEMs conclusion that the site is fully characterized,we are not placing any restrictions on the pending implementation of the Remedial Action Plan. It is possible to complete your investigative process at the same time you begin your field testing of possible remedial alternatives that are required for this site. As an example, the deeper groundwater investigation required in the source area ("DP-4 &6") may have a short screened interval (5 feet) air sparge well placed. This well could provide repeated groundwater data to verify if the soil contamination detected at 120' and 125' bgs is impacting the groundwater. Alternately,this well could be constructed so that it may function as a air sparge well, if your feasibility study shows this to be the most cost effective method of remediation. You should contact the San Joaquin County Public Works Department at (209) 468-3037 to ascertain the requirements for placing soil borings/groundwater grab methods in the Wilson Way right of way. Typically this procedure has time and day limitations on it due to the high traffic on the roadway. It would be advisable to see if late night/very early morning-weekend drilling is nossiblP_