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Decommissioning Plan Schwartzwalder Mine RML CO-369-06 Cotter Corporation (N.S.L.) 8 March 2017 into account uncertainty associated with sampling and analytical variability, this result is consistent with approximate equilibrium across U-238 decay products. 2.2 Historical Cleanup levels The ore transfer pad area was remediated under a cleanup standard of 5 picocuries of radium-226 per gram of surface soil (5 pCi/g). This standard applies to soil concentrations above background levels. In the Ore Sorter/Crusher Area and portions of the Old Ponds Area, the objective was to excavate contaminated soils such that remaining soils and rock were below 20 micro-roentgen per hour (µR/h), a gamma radiation exposure rate expected at that time to correspond to less than 5 pCi/g of Ra-226 in soil based on previous experience. The 5 pCi/g Ra-226 criterion was also used for remediation of the drying trenches. For each of these RML areas, the 5 pCi/g above background standard for soil Ra-226 was used because of its applicability to uranium processing operations (40 CRF 192.12, 6 CCR 1007-1 part 18). All of the above areas are considered to be successfully decommissioned (see Section 1.3)., The OWTP area structures and underlying soils (RML #2) and the NWTP IX equipment remain to be addressed with respect to release from license and termination of the RML. For RML #2, the CDPHE has indicated that a dose-based standard of 25 mrem/yr will be used to determine soil cleanup criteria (CDPHE, 2001b). For RML #4, no soil removal activities are expected with decommissioning activities limited to radiological surveys of the building surfaces and IX treatment system equipment. 2.3 Background Characteristics 2.3.1 Direct Gamma Exposure Monitoring The lithology and mineralogy of the opposing valley slopes at the Schwartzwalder Mine site are quite different. The sandstone, mudstone, and clay rock types of the east-northeast valley side, where the nearest feasible receptor resides, are associated with higher background gamma counts than the metamorphic gneiss and schist rock types of the west -northwest side, where the licensed facilities are located. This difference in lithology confounds the use of TLD measurements for background subtraction at this site. To quantify this problem Cotter proposed the placement of ten TLDs on the east-northeast side of the valley for a period of one year. This proposal was approved by the CDPHE and monitoring began on April 1, 1988 and was completed in 1989. The average annual background gamma dose rate for the ten locations studied was measured as 184 mrem (approximately equivalent to a gamma exposure rate of 21µR/h). 2.3.2 Soil Background Assessment Cotter performed assessments of local background radiological soil characteristics during cleanup activities at the ore transfer pad, and the results were reported in the OTP Release Report (Cotter, 1998). Given the natural geology around the mine, along with environmental gamma monitoring results, it is possible that background uranium and Ra-226 concentrations in soils at the mine site are higher than values reported near the OTP, but direct measures in this area have never been established. A reasonable approach for estimating background is to assume values reported for background soil samples taken in the vicinity of the ore transfer pad (approximately