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Mr. Curt Richards - 2 - • 9 June 2008 . M Olin Chlor Alkali Products July 2005. Jim Brownell indicated that if Pioneer continued to utilize AP-2 as a water supply well during the third quarter of 2007, the Regional Water Board would require construction of a monitoring well on the Facility property. On 30 April 2007, Secor, on behalf of Pioneer, submitted a letter requesting eight revisions to MRP No. R5-2007-0804. The requested revisions are summarized below: 1. Reduce frequency of general constituents analyses. 2. Remove dissolved iron from the required general constituents list. 3. Reduce frequency of volatile organic compound (VOC) analyses of groundwater samples from Upper and Middle Horizon monitoring wells. 4. Reduce frequency of VOC analyses of groundwater samples from the Homestead, Reed, and Medina domestic wells. 5. Discontinue sampling of industrial supply wells AP-1, Banta #1, and Banta #2. 6. Abandon monitoring wells MW-4, MW-5, and MW-8. 7. Reduce the frequency of depth to groundwater measurements in the Upper and Middle Horizon monitoring wells. 8. Reduce the frequency of required groundwater monitoring reports. In a letter dated 29 May 2007, the Regional Water Board approved Pioneer's 16 March 2007 work plan proposing to abandon monitoring wells MW-4, MW-5, and MW-8. (On 6 June 2007, the Regional Water Board reissued the letter to correct an inadvertent monitoring well reference error.) Wells MW-4, MW-5, and MW-8 were no longer needed for the continued monitoring of the Upper Horizon groundwater beneath the Facility. Monitoring wells MW-1 , MW-2, and MW-7 would be sufficient for future onsite monitoring of these horizons. On 22 June 2007, Pioneer notified Regional Water Board staff by electronic mail that it planed to replace the Pombo domestic well rather than install a wellhead treatment system. In the 2 February 2007 cover letter to MRP No. R5-2007-0804, the Regional Water Board had required Pioneer to prepare a work plan for design, construction, operation, and maintenance of a wellhead treatment system for the Pombo domestic well by 15 March 2007. On 10 July 2007, Regional Water Board staff issued a draft MRP and explanation cover letter to Pioneer. The five items discussed during the 6 March 2007 meeting were incorporated into the draft MRP. Also, some of the eight revisions that Secor requested in the 30 April 2007 letter were incorporated into the draft MRP. The Regional Board cover letter explained how it addressed each of the eight revision requests. A summary of the response to each request is presented below. 1 . The following parameters were collected on a semiannual frequency for two years.- chloride, ears:chloride, sodium, total organic carbon, total dissolved solids, nitrate, nitrite, sulfate, sulfite, total iron, dissolved iron, ferrous iron, and total alkalinity. Pioneer proposed to continue semiannual monitoring of chloride and sodium, and to monitor the remaining parameters annually. The Regional Water Board incorporated those changes into the draft MRP.