SITE INFORMATION AND CORRESPONDENCE

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0 Bert E. Van Voris - 2 - 17 September 2004 Supervising Engineer years its discharge to the LTU. Regional Board letter dated 26 May 2004 concurred with the Conceptual Compliance Plan and commented as to what type of information would be needed to support a project to implement the plan. Most of my comments pertain to the proposed offsite discharge and continued use of the reservoir, however some concern the ongoing and proposed continuation of the LTU discharge and its impact to soil and shallow groundwater. In the Introduction of the RWD's technical report, Musco indicates it seeks to have the Regional Board replace Order No. R5-2002-0148 and related orders (presumably C&A Order No. R5-2002-0149 and the TSO) with WDRs that implement the proposed project. In its 29 July 2004 letter,Musco reiterates two outstanding requests to the Regional Board: Request 1. Extend by one year the 6 September 2004 deadline for full compliance with Effluent Limitation C.1 of the WDRs,which sets numerical limits for total dissolved solids (TDS), sodium, and chloride of 2047, 597, and 601 mg/L, respectively. Comment: Values for TDS, sodium, and chloride in Effluent Limitation C.1 were based on a statistical analysis of concentration data from Musco's onsite industrial supply well. Specifically,the values equal the average of values in a limited sample plus two standard deviations (i.e., 95% confidence limit). Musco believed that Effluent Limitation C.1 specified a higher quality than necessary to prevent degradation of shallow groundwater potentially affected by its discharge. The time schedule in the CAO for Effluent Limitation C.1 recognized Musco's inability to immediately comply but required in the interim that Musco progressively meet increasingly stringent effluent limitations until it fully complied by 6 September 2004. Musco received additional opportunity to characterize background groundwater quality to be used to review the reasonableness of and, if appropriate, adjust the concentrations of Effluent Limitation C.l. The 26 May 2004 Regional Board letter stated that data submitted to date indicate Effluent Limitation C.1 is not adequately protective of water quality and recommended Musco withdraw the extension request and instead submit a RWD describing a discharge that implements best practicable treatment and control for salt. While the concentrations of TDS and sodium in Musco's discharge have decreased due to several salinity source control measures, self-monitoring reports for January through June 2004 indicate that over 90% of the values reported for discharge TDS and sodium exceed the limitations of 2,045 and 597 mg/L, respectively. During this period, the average TDS and sodium concentrations were 3,390 and 784 mg/L, respectively. Recent self-monitoring reports indicate that the discharge to the pond consistently exhibits IDS concentrations of below the 2,000 mg/L, while the discharge from the reservoir does not (due largely to the concentrating effects of evaporation). The RWD/RWR states Musco requires three to five years to fully implement the proposed project. The RWD identifies target concentration ranges for effluent inorganic dissolved solids (900 to 1,100 mg/L), sodium (284 mg/L), and chloride (204 mg/L)—values considerably lower than Effluent Limitation C.1 that would be achieved within 18 to 24 months. As these limitations require technology that Effluent Limitation C.1 may not have required, an extension to achieve the more stringent treatment is reasonable.