Site observational work plan for the UMTRA project site at Shiprock, New Mexico

The site observational work plan (SOWP) for the Shiprock, New Mexico, Uranium Mill Tailings Remedial Action (UMTRA) Project Site is the initial document for developing site-specific activities to achieve regulatory compliance in the UMTRA Ground Water Project. The regulatory framework used to select the proposed ground water compliance strategies is presented along with a discussion of the relationship of this SOWP to other UMTRA Ground Water Project programmatic documents. The Shiprock site consists of two, interconnected hydrogeologic systems: the terrace system and the floodplain system. Separate compliance strategies are proposed for these two systems. The compliance strategy for the terrace aquifer is no remediation with the application of supplemental standards based on classification of the terrace aquifer as having Class III (limited-use) ground water. The compliance strategy for the floodplain aquifer is active remediation using a subsurface biological barrier. These strategies were selected by applying site-specific data to the compliance framework developed in the UMTRA Ground Water programmatic environmental impact statement (PEIS) (DOE, 1994a). The site conceptual model indicates that milling-related contamination has impacted the ground water in the terrace and floodplain aquifers. Ground water occurs in both aquifers in alluvium and in fractures in the underlying Cretaceous age Mancos Shale. A mound of ground water related to fluids from the milling operations is thought to exist in the terrace aquifer below the area where settling ponds were in use during the mill operations. Most of the water occurring in the floodplain aquifer is from recharge from the San Juan River