May 29, 2020 TECHNICAL MEMORANDUM CWMNW Arlington, OR Analysis of Leachate Management Practices for the Chemical Waste Management of the Northwest Facility in Arlington, OR Authors Arthur S. Rood, M.S., K-Spar, Inc Emily A. Caffrey, Ph.D., Radian Scientific, LLC Helen A. Grogan, Ph.D., Cascade Scientific, Inc. Colby D. Mangini, Ph.D., CHP, Paragon Scientific, LLC Principal Investigator John E. Till, Ph.D., Risk Assessment Corporation Submitted to Waste Management RAC Technical Memorandum No. 5 - CWMNW Arlington - 2020 This page is intentionally blank. 1. Executive Summary This technical memorandum provides a review of the radiation doses associated with the landfill leachate management methods and processes at the Chemical Waste Management of the Northwest’s (CWMNW) facility in Arlington, OR. Over time, precipitation that falls on the landfill surface and moisture that is entrained in the wastes moves by gravity through the waste mass – this is referred to as leachate. Leachate moves down by gravity through the waste mass, where it is intercepted by the primary liner and is then channeled by the leachate collection system to the leachate sumps where it is subsequently removed by dedicated pumps. The leachate is then pumped from the sumps via a hose and applied over the surface of three of the four landfill cells as a dust control measure. Over time, and depending on ambient weather conditions, the water phase in the leachate evaporates. CWMNW is located in an arid climate such that the application of leachate as dust control is the primary leachate management method. On days when leachate application to the landfill surface is not possible due to precipitation or snow cover, the leachate is pumped into a tanker truck that transports it to the on-site wastewater treatment plant (WWT-1) where it is offloaded into a storage tank for further treatment. Chemical flocculants are added to the leachate so that flocked solids precipitate to the base of the tank. The remaining liquid is passed through a carbon filter bed that removes most of the remaining contaminants and is then stored in a separate tank. Once the treated liquid passes confirmatory testing the liquids are pumped into one of two lined ponds. Periodically, the flocked solids and carbon filter media from WWT-1 are removed and disposed in the landfill. Leachate samples were taken from each of the four primary sumps on March 25-27, 2020. All samples were analyzed for naturally occurring radionuclides of the U-238 and Th-232 decay series, U-235, K-40, and tritium (H-3). These sampling results were used along with the volume of water and mass of disposed solids as the basis to determine the radionuclide concentrations in the wastes disposed in the landfill. The three exposure scenarios are considered in this review include: 1. Leachate applied as dust control on the surface of the landfill; 2. Disposal of the flocked solids and carbon filter media in the landfill; 3. Disposal of treated leachate in the evaporation ponds. Receptors reviewed include landfill workers that operate on the landfill in full personal protective equipment, a laboratory worker, and the nearest current resident, located approximately 10,700 feet (more than two miles) from the edge of the landfill. This review finds that radiological doses from the leachate management practices at CWMNW are extremely low and do not suggest that any changes are necessary to the current leachate management methods. The maximum annual effective dose to a landfill worker who was assumed to spend 30 minutes per day on the landfill surface for 250 days per year from these practices was 0.22 mrem. Annual effective doses to the nearest resident were less than 0.005 mrem. The dose to a landfill worker from the disposal of flocked solids and carbon filter media from WWT-1 was also extremely low at 0.001 mrem. For comparison purposes, the average annual radiation dose from natural sources alone in the United States for an individual is approximately 310 mrem per year (NCRP 2009). This disposal scenario for the leachate treatment wastes is extremely unlikely in that it assumes all leachate from the landfill is treated through WWT-1; however, only a small fraction of the leachate is actually treated by the system because most of it is applied to the landfill surface as dust R I S K A S S E S S M E N T C ORPORATION 2 CWMNW Arlington, OR control. Further, the doses calculated for leachate being applied as dust control and the doses calculated for flocked solids and carbon filter media disposal are not additive as each scenario is evaluated independently assuming all of the radionuclides in the leachate are processed via that scenario. The highest calculated effective dose attributed to the landfill worker (0.22 mrem yr-1) is orders of magnitude less than the 25 mrem yr–1 recommended dose limit by the American National Standards Institute (ANSI 2009) for unrestricted release of soils from land containing Technologically Enhanced Naturally Occurring Radioactive Materials (TENORM), and the 100 mrem yr-1 public dose limit set by the Nuclear Regulatory Commission in 10 CFR § 20.1301. This page is intentionally blank. R I S K A S S E S S M E N T C ORPORATION 2 CWMNW Arlington, OR 1. Introduction This technical memorandum provides a review of the doses associated with the landfill leachate management methods and processes at the Chemical Waste Management of the Northwest’s (CWMNW) facility in Arlington, OR. This review of the doses associated with the leachate management practices has been completed using the March 2020 radioanalytical results of landfill leachate sampling conducted at the request of Oregon Department of Energy. Potential exposure pathways for radionuclides in the leachate are identified and potential doses to landfill employees and the public are evaluated. The CWMNW landfill is located about 11 km south of the Columbia River. Landfill Unit L- 14 is located is on the west side of the facility. Figure 1-1 shows the location of Landfill Unit L-14, the nearest CWMNW building with employees onsite (the CWMNW Laboratory), the nearest resident, and the meteorological station. Figure 1-1. Location CWMNW, Landfill Unit L-14, the nearest CWMNW facility (CWMNW Laboratory), nearest resident, and the meteorological station. Analysis of the Leachate Management Practices 3 at CWMNW 1.1. CWMNW Leachate Management System Landfill Unit L-14 at CWMNW is a double lined Subtitle C design landfill with 4 lined leachate collection sumps that consist of a primary sump, secondary leak detection sump and tertiary leak detection sump collecting leachate from the current 86,490 m2 (21 acres) landfill. The landfill is divided into four cells with each cell designed to drain into a sump (Figure 1-2). Figure 1-2. Landfill Unit L-14 showing the four cells (L-14 cell 1, L-14 cell 2, L-14 cell 3, and L- 14 cell 4), the sumps (S1, S2, S3, and S4), evaporations ponds (Pond-A and Pond-B), and nearby monitoring wells in the Selah formation. Water infiltrates the landfill surface due to precipitation and to a lesser extent from using leachate for dust control by applying it to the top surface of the landfill. Those liquids filter that down through the entire waste mass and are conveyed by the primary liner to the leachate collection sumps at the base of the landfill. Leachate spraying is not expected to result in a large amount of water infiltration because spraying only occurs when evaporation is high. An alternate leachate management practice is utilized during periods of precipitation when leachate cannot be applied. An overview of the two leachate management practices is given in Figure 1-3. R I S K A S S E S S M E N T C ORPORATION 4 CWMNW Arlington, OR Leachate Spray System - Primary L-14 cell 1 L-14 cell 2 L-14 cell 3 L-14 cell 4 Sump Sump Sump Sump Wastewater Evaporation Storage Treatment Pond-A and Tank Plant Pond-B Water only sent to wastewater treatment Chemical flocculants plant during periods of added, particulates rain/snow and snow settle to base cover on landfill Solids/Filter media sent to landfill Figure 1-3. Overview of leachate management at CWMNW. When leachate is used for dust control, the leachate is pumped from the sumps via a hose and sprayed over the surface of the landfill where it evaporates. CWMNW is located in an arid climate which has 109 inches of dry pan evaporation per year. The spraying process continues until the area is adequately wetted. The approximate area of a single spray is illustrated in Figure 1-4. Once the area is adequately wetted, the sprayer is repositioned to a new location and the process repeated. Spraying is performed in areas of no disposal activity, mainly across cells L-14 cell 1, L-14 cell 2, and L-14 cell 3. Annually, the use of leachate for dust control will be distributed over all three cells. Analysis of the Leachate Management Practices 5 at CWMNW Figure 1-4. Google Earth view of the eastern portion of landfill L-14 showing the wetted spray area (dark grey regions) with the sprayer moving north to three other locations. Runoff from the spray operations is collected using the landfill internal stormwater collection system and sent to a separate lined stormwater pond at the north end of the current landfill. The calculated area of the southern wetted region is 337 m2. An alternative leachate management practice is used when evapotranspiration is poor. On days where precipitation is occurring, or the ground is covered with snow, the leachate is pumped into a tanker truck that transports the leachate to the wastewater treatment plant-1 (WWT-1) where it is offloaded into a storage tank.