Research Opportunities for Studies of Contaminant Transport in Fluvial Systems at the TIMS Branch - Steed Pond System, Savannah River Site

A workshop to identify the scientific issues associated with contamination in riparian, fluvial, and hyporheic systems was held in March 2003 at the Savannah River Site (SRS). The workshop examined the general scientific remediation challenges and research opportunities in such systems and on Tims Branch - Steed Pond, a specific uranium- and heavy-metal-contaminated riparian system at SRS. A diverse group of scientists representing a wide range of scientific disciplines came from academia, national laboratories, and research centers to develop recommendations for future ERSD research opportunities. There was agreement among the workshop participants that riparian, fluvial, and hyporheic systems represent a unique opportunity to advance science and to enable progress on DOE's environmental cleanup of contaminated sites. The participants at this workshop documented both the critical need and the great promise for research on hydrological and biogeochemical processes controlling contaminant transport and fate in contaminated surface and near-surface systems. The approach of the workshop was to assess the Tims Branch - Steed Pond system at the SRS as an appropriate site to identify research needs that support potential remediation strategies

Development of a Vertical Recirculation Well System for the A/M Area of the Savannah River Site

The objective of this work is to examine and develop a remediation scenario to provide long term hydraulic control and remediation of the dissolved chlorinated solvent plume within the Western and Southern Sectors of the A/M Area. This scope includes the development and siting of a remediation system that will contain the 500 part per billion trichloroethylene isoconcentration contour within each sector

TECHNICAL EVALUATION OF TEMPORAL GROUNDWATER MONITORING VARIABILITY IN MW66 AND NEARBY WELLS, PADUCAH GASEOUS DIFFUSION PLANT

Evaluation of disposal records, soil data, and spatial/temporal groundwater data from the Paducah Gaseous Diffusion Plant (PGDP) Solid Waste Management Unit (SWMU) 7 indicate that the peak contaminant concentrations measured in monitoring well (MW) 66 result from the influence of the regional PGDP NW Plume, and does not support the presence of significant vertical transport from local contaminant sources in SWMU 7. This updated evaluation supports the 2006 conceptualization which suggested the high and low concentrations in MW66 represent different flow conditions (i.e., local versus regional influences). Incorporation of the additional lines of evidence from data collected since 2006 provide the basis to link high contaminant concentrations in MW66 (peaks) to the regional 'Northwest Plume' and to the upgradient source, specifically, the C400 Building Area. The conceptual model was further refined to demonstrate that groundwater and the various contaminant plumes respond to complex site conditions in predictable ways. This type of conceptualization bounds the expected system behavior and supports development of environmental cleanup strategies, providing a basis to support decisions even if it is not feasible to completely characterize all of the 'complexities' present in the system. We recommend that the site carefully consider the potential impacts to groundwater and contaminant plume migration as they plan and implement onsite production operations, remediation efforts, and reconfiguration activities. For example, this conceptual model suggests that rerouting drainage water, constructing ponds or basin, reconfiguring cooling water systems, capping sites, decommissioning buildings, fixing (or not fixing) water leaks, and other similar actions will potentially have a 'direct' impact on the groundwater contaminant plumes. Our conclusion that the peak concentrations in MW66 are linked to the regional PGDP NW Plume does not imply that there TCE is not present in SWMU 7. The available soil and groundwater data indicate that the some of the waste disposed in this facility contacted and/or were contaminated by TCE. In our assessment, the relatively small amount of TCE associated with SWMU 7 is not contributing detectable TCE to the groundwater and does not represent a significant threat to the environment, particularly in an area where remediation and/or management of TCE in the NW plume will be required for an extended timeframe. If determined to be necessary by the PGDP team and regulators, additional TCE characterization or cleanup activities could be performed. Consistent with the limited quantity of TCE in SWMU 7, we identify a range of low cost approaches for such activities (e.g., soil gas surveys for characterization or SVE for remediation). We hope that this information is useful to the Paducah team and to their regulators and stakeholders to develop a robust environmental management path to address the groundwater and soil contamination associated with the burial ground areas

INDEPENDENT TECHNICAL REVIEW OF THE FOCUSED FEASIBILITY STUDY AND PROPOSED PLAN FOR DESIGNATED SOLID WASTE MANAGEMENT UNITS CONTRIBUTING TO THE SOUTHWEST GROUNDWATER PLUME AT THE PADUCAH GASEOUS DIFFUSION PLANT

The U. S. Department of Energy (DOE) is currently developing a Proposed Plan (PP) for remediation of designated sources of chlorinated solvents that contribute contamination to the Southwest (SW) Groundwater Plume at the Paducah Gaseous Diffusion Plant (PGDP), in Paducah, KY. The principal contaminants in the SW Plume are trichloroethene (TCE) and other volatile organic compounds (VOCs); these industrial solvents were used and disposed in various facilities and locations at PGDP. In the SW plume area, residual TCE sources are primarily in the fine-grained sediments of the Upper Continental Recharge System (UCRS), a partially saturated zone that delivers contaminants downward into the coarse-grained Regional Gravel Aquifer (RGA). The RGA serves as the significant lateral groundwater transport pathway for the plume. In the SW Plume area, the four main contributing TCE source units are: (1) Solid Waste Management Unit (SWMU) 1 / Oil Landfarm; (2) C-720 Building TCE Northeast Spill Site (SWMU 211A); (3) C-720 Building TCE Southeast Spill Site (SWMU 211B); and (4) C-747 Contaminated Burial Yard (SWMU 4). The PP presents the Preferred Alternatives for remediation of VOCs in the UCRS at the Oil Landfarm and the C-720 Building spill sites. The basis for the PP is documented in a Focused Feasibility Study (FFS) (DOE, 2011) and a Site Investigation Report (SI) (DOE, 2007). The SW plume is currently within the boundaries of PGDP (i.e., does not extend off-site). Nonetheless, reasonable mitigation of the multiple contaminant sources contributing to the SW plume is one of the necessary components identified in the PGDP End State Vision (DOE, 2005). Because of the importance of the proposed actions DOE assembled an Independent Technical Review (ITR) team to provide input and assistance in finalizing the PP