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Firestone Store#3573 400 North El Dorado Street, Stockton, California October 25, 1995 VES Quarterly Report and Request for Closure-4589 Page 3 of 14 • 3 0 DATA INTERPRETATION — SYSTEM PERFORMANCE EVALUATION All information generated from initial startup of the SVES on November 4, 1994, through the current system shutdown date of May 8, 1995, has been utilized to interpret and evaluate system performance 31 System Operation Data The system was operated at an air flow rate of 40-cubic feet per minute (cfm) since startup (with the exception of shutdown periods) Vacuum has been applied to both vapor extraction wells at this site The applied flow rate of 40-cfm produced a vacuum level at extraction point VE-1 of approximately 16 inches-of-water column, and a vacuum level at extraction point VE-2 of approximately 3 inches-of-water column The difference in vacuum levels ' is a result of the permeability difference between the finer grained native soils surrounding VE-1 and the coarser gravel backfill surrounding VE-2 ' Well VE-1 (in native soil) was the primary extraction point utilized throughout the operation of the SVES Well VE-1 was shut down and well VE-2 was used briefly on February 27, 1995 However, due to lower achievable vacuum levels within the gravel backfill, and the absence of VOCs within the vapor stream (determined by PID screening), use of VE-2 was discontinued and VE-1 was returned to service on the same day The absence of both TPH-G and BTEX within the VE-2 vapor stream ' (determined by analysis) is believed to be a result of remediation caused by operation of VE-1 during the previous two months ' 32 System Radius of Influence The five vacuum monitoring points (MW-1 through MW-5) surrounding the former ' UST area have been monitored periodically during system operation (Well Location Diagram, Appendix 7 3) All five monitoring points have been influenced by the vacuum levels generated at both extraction wells Vacuum levels have remained relatively consistent within each monitoring point over time Differing vacuum levels between the monitoring points are a reflection of differing point locations, soil types, and depths ' Vacuum levels for extraction well VE-1 and the monitoring points are tabled below and are reported in units of inches-of-water as read from standard Magnehelic dial ' gauges All readings were collected by Mr Walter Lubcke of Automated Environmental Services, Modesto, California Field documentation of all vacuum readings are included in Appendix 7 4 ' RYAN-MURPHY, INCORPORATED Denver Environmental Construction Management Los Augeks