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WASTE DISCHARGE REQUIREMENTS ORDER NO. R5-2008-0148 -13- LAWRENCE LIVERMORE NATIONAL SECURITY, LLC AND THE U.S. DEPARTMENT OF ENERGY FOR LAWRENCE LIVERMORE NATIONAL LABORATORY SITE 300 SAN JOAQUIN AND ALAMEDA COUNTIES 55.The Discharger used the DLM to evaluate the potential for constituents, except VOCs, in cooling tower effluent to impact beneficial uses of underlying groundwater. The lowest appropriate water quality limits protective of beneficial uses of groundwater were selected for the model endpoints. By applying an attenuation factor of 10 for areas where groundwater is less than or equal to 30 feet bgs and an attenuation factor of 100 for areas where groundwater is greater than 30 feet bgs, the Discharger determined that all constituents detected in the cooling tower blowdown were lower than the DLM value, indicating the discharges are not predicted to negatively affect groundwater. However, the Regional Water Board has since concluded that salts do not attenuate; therefore, an attenuation factor of one (1) should be applied for salts. In response to this conclusion, the results of the Discharger's analyses reported in the 28 January 2005 report were revised to reflect an attenuation factor of 1 for salts as shown on Attachments 16 and 21, parts of this Order. Concentrations of conductivity (measured as SC), sulfate, sodium, and TDS in the cooling tower effluent exceed water quality goals. Concentrations of chloride were elevated as well and have the potential to exceed the water quality goal. Background concentrations of these five constituents in groundwater vary throughout the site and vary in the different hydrostratigrahic units. Concentrations observed in existing monitor wells upgradient of the percolation pits range from just below to significantly above the water quality goals (see Attachment 17). 56.For discharges of cooling tower effluent, this Order requires the Discharger to conduct a salinity evaluation and minimization plan; requires the Discharger to obtain additional effluent information; requires the Discharger to evaluate fate and transport of salt to ground water; and requires the Discharger to develop additional information on salinity in the source water and receiving water. If any cooling tower discharges to percolation pits have degraded groundwater, the Discharger will be required to monitor groundwater up and downgradient of those discharges and submit a feasibility study proposing remedial alternatives to restore beneficial uses of groundwater if it is determined by the Regional Water Board that the groundwater has been unreasonably degraded. The Discharger must include a proposal for implementing a source control program and best practicable technology (BPT) to reduce pollutants in the discharge. 57.This Order also requires the Discharger to monitor semi-annually wastewater discharged to each cooling tower percolation pit as described in MRP No. R5- 2008-0148.