SITE INFORMATION AND CORRESPONDENCE

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Mr. Brian Miller • - 2 - • 2 June 2006 observed in all of the carbon-based amendments. Zero valent iron began degrading the nitrate and chlorinated organic compounds within the first week, and degrading the sulfate within the first month. Ammonium concentrations increased in the zero valent iron treatment. Pilot Study Proposal and Revisions Applying the results of the treatability study, in the Pilot Test Work Plan Western Farm Service proposed a one-year in-situ pilot study to compare two zero valent iron amendments: zero valent iron without amendments in one application area; and ERCTM' which is zero valent iron combined with a slow-release carbon source, in an adjacent application area. Following a 1 February 2006 meeting between Ms. Carolyn Kneiblher of GeoSyntec Consultants and Regional Water Board staff, GeoSyntec provided an 8 March 2006 Memorandum that provided additional information on the EHCTm amendment. Regional Water Board staff is concerned about the generation of ammonium in the bench test that evaluated zero valent iron. Ammonium is a constituent of concern at the site, as are chlorinated compounds such as 1,2,3-TCP. In the area of the proposed pilot tests, extraction/monitoring well E-1 has contained 1,200 mg/I of ammonium, 250 mg/I of nitrate (as nitrogen) and 95 ug/I of 1,2,3-TCP. The bench test with zero valent iron clearly showed that iron rapidly degraded 1,2,3-TCP and other chlorinated compounds, but it also converted nitrate to ammonium. Whereas the bench tests with carbon amendments did not conclusively remove chlorinated compounds, they did remove nitrate without an increase in ammonium, and the carbon amendments additionally appeared to accelerate the removal of ammonium. In response to a 22 March 2006 telephone conversation whith Ms. Kneiblher during which Regional Water Board staff expressed concern about ammonium increases resulting from zero valent iron reactions, GeoSyntec provided a revised injection layout plan in the 25 April 2006 Semi-Annual Monitoring Report. For reference, this revised layout is attached to this letter as Figure 1. The revised injection layout plan proposes to conduct the pilot test exclusively with EHCTM, and to not conduct the pilot test proposed with unamended zero valent iron. The EHC'm injection area is expanded laterally to encompass the area formerly proposed for unamended zero valent iron. The EH CTM will be mixed as an aqueous slurry and hydraulically injected into the A-zone using Direct Push Technology through cone-penetrometer test rods. The application area will consist of two rows of about seven injection points each, spaced about five feet apart. GeoSyntec estimates that about 2,600 pounds of EHCT will be placed in the treatment area. Pilot Study Monitoring Wells Two pilot study performance monitoring wells (PM-1 and PM-2) will be installed about 10 and 20 feet downgradient of the proposed injection area. The work plan for the construction of these wells is contained within the Pilot Study Work Plan, and the placement of the wells is shown on the attached Figure 1. Existing monitoring wells located nearby in the A-zone are MW-8, about 70 feet downgradient of the treatment areas, and E-1, about 10 feet upgradient of one end of the injection area.