Abstract
Determining hydraulic connections and travel times between recharge facilities and production wells has become increasingly important for permitting and operating managed aquifer recharge (MAR) sites, a water supply strategy that transfers surface water into aquifers for storage and later extraction. This knowledge is critical for examining water quality changes and assessing the potential for future contamination. Deliberate tracer experiments are the best method for determining travel times and identifying preferential flow paths between recharge sites over the time scales of weeks to a few years. This paper compares the results of two deliberate tracer experiments at Kraemer Basin, Orange County, CA, USA. Results from the first experiment, which was conducted in October 1998, showed that a region of highly transmissive sedimentary material extends down gradient from the basin for more than 3 km [1]. Mean groundwater velocities were determined to be approximately 2 km/year in this region based on the arrival time of the tracer center of mass. A second experiment was initiated in January 2008 to determine if travel times from this basin to monitoring and production wells changed during the past decade in response to new recharge conditions. Results indicate that flow near Kraemer Basin was stable, and travel times to most wells determined during both experiments agree within the experimental uncertainty.
Highlights
Groundwater has been a primary source of potable and irrigation water for centuries
Lesser quality sources can become a larger portion of the recharge water at managed aquifer recharge (MAR) operations because the availability of higher quality water such as imported water from remote watersheds is limited and may shrink due to shifts in climate and the diversion of this water to other uses such as maintaining riparian ecosystems
SF6 formed a rising bubble plume that only partially dissolved in the water column; an unknown quantity of tracer was released into the recharge water
Summary
Groundwater has been a primary source of potable and irrigation water for centuries. During the last 50 years, the soaring demand for freshwater has placed unprecedented stresses upon many aquifers throughout the world; many aquifers are in overdraft. Because the available water for the recharge operation can be of lesser quality than the local groundwater supply, there is the potential to degrade the existing aquifer. Even in cases where the recharge water may be of a higher quality, it may have a different geochemical character (e.g., redox state) than the ambient groundwater and the potential exists for mobilization of intrinsic constituents, such as arsenic. For these reasons, it is vital to understand the fate and transport of potential contaminants near MAR sites. From this understanding can cost effective and appropriate regulations be developed
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