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`w. 'we Central Valley Construction - 2 - 18 July 2001 12565 South Manthey Road, Lathrop Based on the investigation activities completed to date, JCA submitted a Workplan to remediate contaminated soil and monitor groundwater contamination at the site. The Workplan includes the following elements: • Excavate contaminated soil to the extent detectable using a photo ionization detector, and collect confirmation soil samples for lab analyses. • Aerate contaminated soils on-site under air permit from the San Joaquin Valley Air Pollution Control District. • Complete three borings to minimum depth of 35 feet, and convert the borings into groundwater monitoring wells. Monitor and sample the wells for TPHd,TPHg,BTEX, and fuel oxygenates. • Submit an investigation report to document soil removal, sampling activities, and well installation. Staff finds that the Workplan does not follow the typical investigation and corrective action procedures.For example,you have not defined the lateral or vertical extent of contamination, and are relying on the excavation work to complete this definition. The current depth to water is approximately 18 feet, and it will be difficult to determine soil contamination below the water table. It is unknown what the historical low groundwater level has been, and the vertical extent of contamination will not be defined by excavation activities. Prior to site closure, complete lateral and vertical definition of soil and groundwater contamination will be required. However,based on your willingness to complete corrective action,we will consider your Workplan as the soil remediation plan. The Workplan is approved with the following additions: • All soil sampling and assessment work is to be completed following the enclosed Tri-Regional Recommendations for Preliminary Investigation and Evaluation of Underground Tank Sites. The reporting format must follow Appendix A of the Tri-Regional Recommendations. • Complete a well receptor survey within 2,000 feet of the site, and submit well construction details for on-site DW-1. • Start soil sampling and logging for the three borings at 5 feet instead of 10 feet. • The monitoring well screen interval should not exceed 20 feet in length. • Include DW-1 in quarterly monitoring. • Additional investigation will be required at the former AGT to determine the extent of contamination identified by GTI. Within 60 days of completing monitoring well installation and sampling, submit a report of findings to the County and this office documenting the site characterization and remediation activities. Please call me at (916)255-3115 at least five business days prior to any site work to schedule a field inspection appointment. Marty Hartzell Associate Engineering Geologist cc: Ms. Margaret Lagorio, San Joaquin County Public Health Services, Stockton Mr. John Cummings, John Cummings&Associates, Fremont