APPLICATIONS OF AN ELECTROMAGNETIC BOREHOLE FLOWMETER FOR HYDROLOGIC CHARACTERIZATION

Electromagnetic borehole flowmeter (EBF) surveys are effective for accurately measuring the vertical groundwater-flow distribution in wells under ambient (static) and dynamic (e.g., pumping-induced) test conditions. Ambient EBF surveys are useful for determining the representativeness of well water samples for hydrochemical characterization, while dynamic EBF surveys are commonly used for determining the vertical distribution of relative hydraulic conductivity within the well-screen section.

Monitoring wells with very low or no ambient vertical flow conditions are generally assumed to be more viable for the detection and monitoring of groundwater contaminants. To demonstrate this type of application, an EBF ambient survey was conducted at a well site used for monitoring a technetium-99 contaminant plume at the Hanford Site. The observed technetium-99 concentration for this well (41 pCi/L) is two to three orders-of–magnitude lower than observed concentrations at surrounding monitoring well facilities. An EBF ambient well survey conducted within the saturated well-screen interval at this well location indicated an upward, in-well vertical flow rate ranging up to 0.30 L/min. This observed upward flow supports a conceptual model where deeper relatively uncontaminated groundwater is flowing upward within the well and discharging to more shallow, overlying contaminated groundwater near the top of the well-screen section.

Dynamic EBF surveys determine the lateral in-flow distribution within the well-screen section during pumping. From this lateral in-flow distribution, the vertical distribution of relative horizontal hydraulic conductivity within the surrounding aquifer can be inferred. This type of characterization information is important for the design and deployment of in situ treatment technologies within heterogeneous aquifer systems. At several treatability test sites, dynamic EBF vertical flow profiles have been used to evaluate formation heterogeneities and assess their potential impact on testing and deployment of the planned technology demonstrations. These data, along with other hydrogeologic characterization information, were used to develop a detailed site specific conceptual model of site hydrogeologic conditions.