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Draft OU-1 ROD Memorandum -2- 4 June 1993 DDRW, Tracy that WDRs will be issued for OU-1 . The following sections of the Draft ROD must be modified to accurately reflect existing or pending permitted discharges: Declaration, Description of the Remedy Section 2.3.2, History of Regulatory Activities, page 2-5 Section 4.2. 1, Scope of OU-1, page 4-2 Section 7.3.2.2, Compliance with ARARs, page 7-11 Section 10.4.6, Action-Specific ARARs, page 10-3 2. Effluent Limits. Effluent treatment standards are discussed in Sections 4.2.5 to 4.2.7 and are listed in Table 4.2-3. The effluent treatment standards listed in Table 4.2.3 do not differentiate between daily maximum and monthly median concentrations. These effluent limitations established for the OU-1 WDRs must be consistent with the effluent performance standards in the ROD. Because the RWD for OU-1 was not submitted until 15 May 1993, we cannot prepare and adopt the WDRs prior to finalization of the ROD. Therefore, the effluent limits listed in Table 4.2-3 in the ROD must be revised to reflect the following concentrations: Maximum Daily Monthly Median Constituent Units Concentration Concentration Carbon Tetrachloride (CCL4) µg/l 1.0 0.5 Chloroform Ag/l 1.0 0.5 1,1-Dichloroethene (DCE) Ag/1 1.0 0.5 Dieldrin µg/l background background Tetrachloroethene (PCE) Ag/1 1.0 0.5 Trichloroethene (TCE) µg/1 1.0 0.5 Total Volatile Organic Ag/1 5.0 1 .0 Constituents (VOCs) In general , non-detect (ND) levels have been established for the VOCs for the effluent limit for the monthly median concentration because use of best- practicable treatment technology (BPT) with the selected treatment technology of air stripping will meet these concentrations. The effluent limits for the daily maximum concentration of 1.0 µg/1 for each individual constituent and of 5 µg/l for Total VOCs are established to accommodate potential operational excursions and is not based on any Primary Maximum Contaminant Level (MCL) . Because dieldrin is not naturally occurring but is found in the ground water both on- and off-site and because dieldrin was established as a constituent of concern as part of the health based risk assessment, effluent limits must be established for the discharge of the treated ground water from OU-1. However, the dieldrin concentrations found in ground water may or may not be attributable to waste disposal activities at DDRW, Tracy. The site-wide remedial investigation (RI) should determine whether DDRW, Tracy is a responsible party for the dieldrin ground water contamination. Therefore, until it is known that DDRW, Tracy is a responsible party, the appropriate effluent limitation should be established at background concentrations. Currently, pesticides are found in very low concentrations in the influent to the IRM. These concentrations are not significant enough in excess of