The National Training Center (NTC) at US Army Fort Irwin, CA (Fort Irwin) has a stormwater collection system located near the Sleepy Hollow housing area that includes a stormwater catchment basin, controlled release of flood waters, and enhanced local infiltration by a drywell. The system was not performing to design standards and best management practices. To research wet-weather capture and aquifer recharge, the Environmental Protection Agency (EPA) contracted GeoSystems Analysis, Inc. (GSA) to supervise the drilling and installation of a vadose zone testing well (Test Well) and a groundwater monitoring well (Monitor Well) at the Sleepy Hollow drywell site at Fort Irwin. Additionally, GSA contracted Torrent Resources Inc. (Phoenix, AZ) (Torrent Resources) to upgrade the drywell site.

The Test Well was instrumented with water and air piezometers to allow testing of the infiltration capacity of the on-site basin fill deposits and derive hydraulic conductivity properties for these materials through intermediate and large-scale field testing and laboratory testing. Water piezometers were used to conduct borehole permeameter tests to provide an estimation of the saturated hydraulic conductivity (Ksat) at the testing intervals. Air piezometers were used to conduct atmospheric pressure wave testing, which measures the bulk air permeability of vadose zone sediments in the vicinity of the well. Air permeability estimates can then be converted to estimates of water permeability. A water level and temperature sensor was also installed in one of the water piezometers to measure the depth of perched groundwater.

The Monitor Well was drilled to depths reaching the groundwater table to monitor the performance of the new drywell system. The Monitor Well also included a shallow piezometer installed above a low-permeability fine-grained sediment layer. Water level and temperature sensors were installed to measure the depth to groundwater and depth of perched water above the fine-grained layers. In addition, soil water content, electrical conductivity, and temperature sensors were installed at various depths in the vadose zone to monitor advancement of wetting fronts.