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WASTE DISCHARGE REQUIREMENTS ORDER NO. R5-2008-0148 -5- <br /> LAWRENCE LIVERMORE NATIONAL SECURITY, LLC AND <br /> THE U.S. DEPARTMENT OF ENERGY FOR <br /> LAWRENCE LIVERMORE NATIONAL LABORATORY SITE 300 <br /> SAN JOAQUIN AND ALAMEDA COUNTIES <br /> 17.Nitrate is a groundwater constituent that may result from natural and <br /> anthropogenic sources. The CERCLA investigations have identified both <br /> natural and anthropogenic sources of nitrate at Site 300 including the <br /> geology, historic releases associated with explosive compounds, and septic <br /> systems. Multiple independent data sets, including nitrogen and oxygen <br /> isotopes of nitrate and excess dissolved nitrogen, indicate trat nitrate is <br /> naturally denitrifying in the confined regions of the bedrock aquifers at Site <br /> 300. <br /> 18.CERCLA investigation and/or remediation occurring in areas where the <br /> Discharger has determined that septic systems may be impacting <br /> groundwater are: <br /> a) Building 812 — Remedial Investigation/Feasibility Study and pilot study for <br /> treatment of uranium, volatile organic compounds (VOCs), explosive <br /> compounds, nitrate and perchlorate. <br /> b) Building 834 — Active remediation for VOCs and diesel, treated nitrate- <br /> bearing groundwater is misted to the air. <br /> c) Building 850 — Pilot study targeting perchlorate remediation, which will <br /> denitrify nitrate as an added benefit. <br /> d) Building 899 — Monitored natural attenuation for TCE, perchlorate, tritium <br /> and nitrate. Nitrate concentrations above the MCL are limited to one well <br /> which is in the vicinity of the septic system leach field. <br /> 19.Site 300 operates a nontransient, noncommunity drinking water system under <br /> a permit issued by the California Department of Public Health. Groundwater <br /> is pumped from two-onsite supply wells (Well 20 [primary] and Well18 <br /> [backup]). Well 20 is screened between 425 and 475 feet bgs and Well 18 is <br /> screened between 387 and 517 feet bgs. Both are screened in the regional <br /> aquifer, the Tertiary Neroly Lower Blue Sandstone (Tnbsl). The water is <br /> chlorinated in the distribution system and is monitored to assure that drinking <br /> water standards are met. Analyses of nitrate concentrations in the <br /> groundwater from these wells consistently have been below the detection limit <br /> for nitrate of 0.5 mg/L, indicating that natural and anthropogenic nitrate <br /> sources are not degrading the regional aquifer. <br /> 20.Regional Water Board staff concludes that some localized degradation of <br /> groundwater from the nitrate associated with domestic waste in septic system <br /> discharges has occurred in the past and may still be occurring. Issuance of <br /> this Order and the associated MRP provides a means to monitor the impacts <br /> that the septic systems may have caused to groundwater, and will help the <br /> Regional Water Board ascertain whether continued use of these systems will <br />