Nonpoint‐source pollution from agriculture can cause the degradation of groundwater and surface water. Some studies conducted in Coastal Plain aquifers have shown NO−3 removal from groundwater due to assimilation by vegetation or denitrification before discharge to a stream is significant; relatively few have been conducted on other physiographic and geological regions within the Chesapeake Bay watershed. This study was conducted at the boundary of the Valley and Ridge and Appalachian Plateau physiographic provinces to understand how the hydrological and geochemical conditions in this region effect the transport and removal of NO−3. The groundwater flow system at the farm studied, located at the base of a valley, is influenced by one groundwater flow component parallel to the axis of the valley and a second flowing perpendicular to the axis having been recharged from topographic highs along the sides of the valley. The axis‐perpendicular component is transporting NO−3 and Cl− applied as fertilizers and manure on an upgradient field and also Cl− from salting of an adjacent road to the study site. The relatively nutrient‐free water from the axis‐parallel component dilutes NO−3 and Cl− concentrations at the site from seasonal averages of 11 mg N/L and 90 mg Cl/L to levels <0.4 mg N/L and 1 mg Cl/L, respectively. Some evidence exists for NO−3 removal from groundwater <3 m belowground; however, it is difficult to confirm the removal process with dilution dominating the system.

Our review suggests several reliable predictors of bipolar episodes. Knowledge of these factors has significant clinical implications and could aid in treatment and prevention strategies. However, further research is clearly needed to address the limitations of the existing research and to increase our understanding of predictors of relapse, with the intent of improving quality of life and preventing episodes in patients with bipolar disorder.

In 1983, high-level radioactive waste repository performance requirements related to groundwater travel time were defined by NRC subsystem regulation 10 CFR 60.113. Although the DOE is not presently attempting to demonstrate compliance with that regulation, understanding of the prevalence of fast paths in the boundwater flow system remains a critical element of any safety analyses for a potential repository system at Yucca Mountain, Nevada. Therefore, this analysis was performed to allow comparison of fast-path flow against the criteria set forth in the regulation. Models developed to describe the conditions for initiation, propagation, and sustainability of rapid groundwater movement in both the unsaturated and saturated zones will form part of the technical basis for total-system analyses to assess site viability and site licensability.This study is an enhancement of previous groundwater travel time analyses. In it the authors attempt to define the appropriate conceptual model for assessing fast-path flow. The conceptual model thus allows disequilibrium flow in the fractures and in the matrix. This conceptual model also allows for spatial and temporal variability of infiltration from the ground surface. In addition, the natural heterogeneity in hydrologic properties and the uncertainty in the values for those properties is expected to play an important role in allowing controlling rapid movement of groundwater. Because of this uncertainty in the distribution of rock properties, a probabilistic approach has been used in the unsaturated zone. Geostatistical simulation techniques, constrained by a geologic framework model, are used to create multiple realizations of the unsaturated domain. Numerical modeling of steady-state groundwater flow in these heterogeneous, two-dimensional domains is accomplished using the TOUGH2 code. A particle tracking method is used to simulate the advective and dispersive movement of groundwater in the simulated flow field and to calculate travel times from the repository to the water table. Numerical modeling of steady-state groundwater flow in the saturated zone is performed within a deterministic, three-dimensional model domain representing the upper 250 m of the saturated zone. Advective and dispersive transport are simulated by particle tracking from the water table to the five km limit of the accessible environment.The results of the groundwater flow modeling provide insights into the implications of the conceptual models employed, the sensitivity of modeling results to specific parameters and assumptions, and distributions of groundwater travel time for a set of base case calcu1,ations. Values of matrix saturation simulated by the unsaturated flow modeling compare favorably with measured matrix saturations from boreholes near the modeled cross-sections. Particle travel times in the unsaturated zone are particularly sensitive to infiltration rates, fracture-matrix connectivity, and fracture frequency. Increased infiltration rate, in concert with reduced fracturematrix co...