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PUBLIC HtALTH SERVICES <br /> SAN JOAQUIN COUNTY '''= Oc <br /> ENVIRONMENTAL HEALTH DIVISION <br /> Karen Furst, M.D., M.P.H., Health Officer <br /> 304 East Weber Avenue, Third Floor • Stockton, CA 9520 -=J / 1 � <br /> 0 <br /> 209/468-3420 <br /> APR 10 2[000 <br /> HAROLD 6 DENA KNOWLES ROEK BROTHERS <br /> C/O PATRICK RIDDLE DON ROEK <br /> 7574 SHORELINE DR PO BOX 30038 <br /> STOCKTON CA 95219 STOCKTON CA 95213-0038 <br /> RE: ROEK PROPERTY WORKPLAN SITE CODE:9031 <br /> 102 SOUTH WILSON WAY <br /> STOCKTON CA <br /> On April 5, 2000 representatives from San Joaquin County Public Health Services Environmental Health <br /> Division(PHS/EHD),the Central Valley Regional Water Quality Control Board—Region 5 (CVRWQCB), <br /> both the former and current owners of the site described above, legal counsel and site consultant met to <br /> discuss the September 17, 1999 "Workplan for Remedial Effectiveness/Case Closure Evaluation" <br /> submitted by Ground Zero Analysis Inc. (GZA). In response PHS/EHD provides the following comments. <br /> PHS/EHD has performed a comprehensive review of existing site data and at this time recognizes that <br /> concentrations of fuel related hydrocarbons in groundwater remain at significant levels exceeding <br /> California Primary Maximum Contaminant Levels (MCL's) after several months of active engineered <br /> remediation efforts. Review of the 0 Quarter Monitoring Event Report (QMER) of 1999 and the 1" <br /> QMER of 2000 verifies the need to perforce additional site characterization including exploratory borings <br /> to evaluate the effectiveness of the recent Soil Vapor Extraction (SVE) remediation efforts to date. Case <br /> closure was discussed at the meeting and both the CVRWQCB and PHS/EHD agree that site closure at this <br /> time is premature. <br /> Rising groundwater has drown most monitoring wells for this site as depth to water is now above the <br /> screened interval in wells MW-3 through MW-12, and vapor extraction wells VW-1 and VW-4. Data <br /> quality from drown wells should be considered less representative as the height of the water column <br /> increases inside the well particularly in monitor wells with exceptionally long screened intervals where an <br /> averaging or dilution effect can be significant in artificially lowering the observed hydrocarbon <br /> concentration. In addition the rising groundwater can diminish remediation effectiveness since less well <br /> screen is exposed above the water table. PHS/EHD will provide directives to the responsible party <br /> focusing on subsurface high hydraulic conductivity preferential flow paths (if present) decreasing the <br /> length of monitor well screened intervals to more accurately estimate contaminant mass flux at this site. <br /> The September 17, 1999 "Workplan for Remedial Effectiveness/Case Closure Evaluation" has been <br /> approved with the following conditions. An addendum to the workplan is required. <br /> Quarterly groundwater monitoring shall continue until notified in written format from PHS/EHD. <br /> Remedial effectiveness confirmation boreholes must extend to 100' below ground surface or greater if <br /> needed and be continuously logged to total depth. The construction of well screen intervals should be <br /> supported by continuous cores to avoid bridging high and low conductivity lithologic units or creating <br /> potential vertical conduits. A contingency to complete these boreholes to new monitor or soil vapor <br /> extraction wells should be included in the addendum to the workplan when submitted. PHS/EHD and the <br /> CVRWQCB recommends destruction and replacement of MW-13 with multi-level cluster wells. <br /> A Division of San Joaquin County Health Care Services <br />