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New West Petroleum #1003 • 3 - 3 April 2008 Lodi, San Joaquin County and discharged to the storm sewers under an existing NPDES general permit. Five additional groundwater extraction wells (enclosed Figure 4) would be placed in an arc around the front of the MTBE plume in aquifer zones A and B. Based on previous pump tests, an effective extraction radius of influence would prevent further migration of the MTBE plume while reducing offsite MTBE concentrations in groundwater. The necessary flow rate calculated for each extraction well would be approximately 10 gallons per minute (gpm) to capture the entire MTBE plume, while the maximum flow rate possible using the 3" submersible pumps is 20 gpm. The FS proposes that horizontal boring methods be used to reduce the impacts to neighboring properties from conventional trenching. The estimated cost for the expanded GWP&T remedy is $600,000 for four years of operation and two years of post-treatment groundwater monitoring. Recent bids from subcontractors for all alternatives were included in the appendices of the FS. The FS recommends implementing the expanded GWP&T system as a proven effective treatment that also provides hydraulic control for the MTBE plume. Comments: 1) The FS fulfills the CAO requirement in Order Nos. 12 and 13, and is accepted. 2) 1 concur to expanding the current interim GWP&T, which has effectively reduced groundwater concentrations on site, and when properly designed and site conditions are favorable, is a proven technology for mass reduction while providing protection to sensitive receptors through hydraulic control of an aquifer. Proceed to develop the plans and specifications for the GWP&T to be submitted in the Final Remediation Plan (FRP) as required in CAO Order#15. The FRP, which is due by 1 August 2008, is discussed in my letter dated 6 February 2008, which responded to CSI's request for a functional equivalent to the FRP. 3) While the table of WQGs is correct in listing individual limits, I would caution you to not use it as the regulatory approved cleanup levels. The table does not include all of the applicable WQGs for each COPC listed. In fact, the Regional Water Quality Control Board, Central Valley Region has promulgated WQGs listed in the August 2007 A Compilation of Water Quality Goals, which are available from the Internet on our website at http://www.waterboards.ca.gov/centraIva]ley/water issues/water quality standards limits 4) Also available at the above web address is the April 2004 Beneficial Use Protective Water Quality Limits for Components of Petroleum-Based Fuels that include WQGs for TPHg, which is a COPC. Note that MTBE, at 5 ug/L, is the lowest applicable WQG for that COPC, as stated in the FS.