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Ms. Nancy Bishop - 2 - 25 September 2007 Questions that remain unanswered by the 2002 pilot study are the following: Is HRC effective with the higher concentrations of constituents found in the injection area, and is HRC also effective with the low concentrations of pollutants found off-site?. The proposed modifications of the pilot study are designed to answer these questions. Modifications to the Pilot Study Two injection grids are proposed using HRC-X°, which is the same basic formulation as HRC, but more viscous. This formulation is expected to further slow the release of electrons, extending the product's active period in the subsurface. One injection grid is proposed in the northwest portion, consisting of 21 injection points aligned in two parallel rows. This injection grid will partially overlap the 2002 HRC application area. A new intergrid well, MW-6R, and a new downgradient monitoring well, MW-7 were installed on 27 an 28 August 2007, and the damaged existing well, MW-6, was destroyed with Regional Water Quality Control Board, Central Valley Region (Regional Water Board) staff concurrence and under the oversight of San Joaquin County Environmental Health Department. The second injection grid is also proposed as 21 injection points aligned in two parallel rows. It is proposed in the right-of-way of Welty Road, across the diffuse portion of the plume. Existing monitoring well MW-5 is about 30 feet downgradient of this injection grid. In both of the injection grids, HRC-Xa will be injected into shallow groundwater between 24 and 48 feet below ground surface (bgs), at the rate of about four pounds of HRC-X°per linear foot. The new monitoring wells are screened between about 25 and 45 feet bgs, as are the existing monitoring wells. Monitoring Progam Western Farm Service has been monitoring the extent of constituents in groundwater and the effectiveness of the 2002 pilot study under the terms of Monitoring and Reporting Program (MRP) No. R5-2003-0815. This MRP is being revised to accommodate the pilot study modifications. A draft MRP is attached for your review and comment. Conditional Concurrence of Pilot Study Modifications Regional Water Board staff conditionally concur with the proposed pilot study modifications. WFS shall complete the following tasks: • For new monitoring wells MW-7 and MW-6R, provide copies of drilling permits, boring logs and as-built construction diagrams. • For MW-6, provide a copy of the well destruction permit. • Within 30 days preceeding HRC-X0 injection, obtain pre-project groundwater samples from MW-2, MW-4, MW-5, MW-6R, and MW-7. These samples shall be analyzed for nitrate, ammonium, alkalinity, total dissolved solids, sodium, chloride, sulfate, methane, dissolved iron and dissolved manganese. Within 60 days preceeding the HRC-X® injection, these wells shall be sampled for volatile organic compounds and 1,2,3-TCP. • Comply with the attached draft Monitoring and Reporting Program until the Executive Officer issues a final Monitoring and Reporting Program.