Submittal of the Mixed Waste Landfill Five-Year Report, Sandia National Laboratories/New Mexico, EPA ID Number NM5890110518, January 2019

The Department of Energy/National Nuclear Security Administration (DOE/NNSA) and Sandia National Laboratories /New Mexico (SNL/NM) personnel submitted the Mixed Waste Landfill (MWL) Five-Year Report for the January 2014 through December 2017 reporting period to the New Mexico Environment Department (NMED) in accordance with the requirements of Section 4.8.2 of the MWL Long-Term Monitoring and Maintenance Plan (LTMMP). The LTMMP became effective on January 8, 2014 and the first Five-Year Report was due January 8, 2019. The MWL is a 2.6-acre Solid Waste Management Unit (SWMU 76) located in the north-central portion of SNL/NM Technical Area III that has undergone corrective action. As of March 13, 2016, the NMED February 2016 Final Order became effective, granting the Class 3 Permit Modification to reflect that the MWL is Corrective Action Complete with Controls and incorporating the LTMMP in Attachment M of the SNL RCRA Facility Operating Permit. The LTMMP defines all monitoring, inspection, maintenance/repair, and reporting requirements for the MWL. This first MWL Five-Year Report is comprised of seven chapters that include a summary of all monitoring and inspection results for the reporting period, Fate and Transport Model review and updates, an evaluation of remedy effectiveness, a reevaluation of excavation feasibility, summary and conclusions, and references. All supporting documentation is provided in four annexes. The primary purpose of the Five-Year Report is to evaluate the effectiveness of the selected remedy (i.e., the ET Cover) and the likelihood of contaminants reaching groundwater. The 2014 through 2017 monitoring, inspection, and maintenance results provide the empirical data necessary to establish current site conditions, evaluate the effectiveness of the ET Cover and associated controls, and reevaluate the likelihood of contaminants reaching groundwater. The measure of effectiveness is the protection of human health and the environment. Based upon four years of monitoring, inspection, and maintenance under the LTMMP, MWL site conditions have improved and continue to be protective of human health and the environment. ET Cover native vegetation has matured and additional best practice measures to reduce erosion and control site drainage have been completed. MWL multi-media monitoring results are consistent with historical data, no trigger levels were exceeded, and there were no indications of new releases or changing conditions that would increase the risk to site workers, the public, or increase the likelihood of contaminants reaching groundwater. The MWL ET Cover and associated remedy controls are in good condition and performing as designed. The inspection and maintenance results confirm the physical integrity of the ET Cover, site controls, and all monitoring networks. 652 pages