The U.S. Army Fort Irwin National Training Center (NTC), approximately 35 miles north-northeast of Barstow, California, obtains all of its potable water supply from three groundwater basins (Irwin, Langford, and Bicycle Basins) within the NTC boundaries. In these basins, groundwater withdrawals exceed natural recharge, resulting in water-level declines. However, managed aquifer recharge using treated wastewater has offset water-level declines in Irwin Basin. Additionally, localized water-quality changes have occurred in some parts of Irwin Basin as a result of human activities (for example, wastewater disposal practices, landscape irrigation, and (or) leaking pipes). As part of a research study in cooperation with the U.S. Environmental Protection Agency (EPA) and the U.S. Army, the U.S. Geological Survey (USGS) collected eight electrical resistivity tomography (ERT) surveys on irrigated fields in the Irwin Basin in July 2019 and February 2020. The ERT geophysical technique injects direct-current electricity with known voltage and current into the earth using a series of electrodes and measures the resulting resistivity. This technique is generally limited to investigations of aquifer properties that are less than 100 meters below land surface.

The U.S. Army Fort Irwin National Training Center (NTC), approximately 35 miles north-northeast of Barstow, California, obtains all of its potable water supply from three groundwater basins (Irwin, Langford, and Bicycle Basins) within the NTC boundaries. In these basins, groundwater withdrawals exceed natural recharge, resulting in water-level declines. However, managed aquifer recharge using treated wastewater has offset water-level declines in Irwin Basin. Additionally, localized water-quality changes have occurred in some parts of Irwin Basin as a result of human activities (for example, wastewater disposal practices, landscape irrigation, and (or) leaking pipes). As part of a research study in cooperation with the U.S. Environmental Protection Agency (EPA) and the U.S. Army, the U.S. Geological Survey (USGS) collected eight electrical resistivity tomography (ERT) surveys on five irrigated fields in Irwin Basin in July 2019 and February 2020. The ERT geophysical technique injects direct-current electricity with known voltage and current into the earth using a series of electrodes and measures the resulting resistivity. This technique is generally limited to investigations of aquifer properties that are less than 100 meters below land surface.

The U.S. Army Fort Irwin National Training Center (NTC), approximately 35 miles north-northeast of Barstow, California, obtains all of its potable water supply from three groundwater basins (Irwin, Langford, and Bicycle Basins) within the NTC boundaries. In these basins, groundwater withdrawals exceed natural recharge, resulting in water-level declines. However, managed aquifer recharge using treated wastewater has offset water-level declines in Irwin Basin. Additionally, localized water-quality changes have occurred in some parts of Irwin Basin as a result of human activities (for example, wastewater disposal practices, landscape irrigation, and (or) leaking pipes). As part of a research study in cooperation with the U.S. Environmental Protection Agency (EPA) and the U.S. Army, the U.S. Geological Survey (USGS) collected eight electrical resistivity tomography (ERT) surveys on five irrigated fields in Irwin Basin in July 2019 and February 2020. The ERT geophysical technique injects direct-current electricity with known voltage and current into the earth using a series of electrodes and measures the resulting resistivity. This technique is generally limited to investigations of aquifer properties that are less than 100 meters below land surface.

The U.S. Army Fort Irwin National Training Center (NTC), approximately 35 mi north-northeast of Barstow, California, covers approximately 1,177 square miles, and is comprised of ten groundwater basins, three of which have been subdivided into subbasins on the basis of additional hydrologic testing. Since the early 1990s, the U.S. Geological Survey (USGS) has been studying water resources issues at Fort Irwin. One issue of concern is the potential effect of groundwater development resulting from planned training expansion and infrastructure at the NTC on natural springs and seeps, an important water source for wildlife. In 2010, the USGS entered into cooperative agreements with the U.S. Army to complete studies of groundwater resources focusing primarily on undeveloped basins within the NTC. Electrical resistivity data were collected in 2015 and 2017 at three groups of springs in undeveloped basins in order to quantify the spatial extent of groundwater associated with each spring and to detect hydrologic change over this two year time period. In 2017, electrical resistivity data were also collected at the airstrip on Bicycle Lake (a dry lakebed) to provide insight on ground failures and data regarding the depth of the known surface cracks and macropolygon features.

The U.S. Army Fort Irwin National Training Center (NTC), approximately 35 mi north-northeast of Barstow, California, covers approximately 1,177 square miles, and is comprised of ten groundwater basins, three of which have been subdivided into subbasins on the basis of additional hydrologic testing. Since the early 1990s, the U.S. Geological Survey (USGS) has been studying water resources issues at Fort Irwin. One issue of concern is the potential effect of groundwater development resulting from planned training expansion and infrastructure at the NTC on natural springs and seeps, an important water source for wildlife. In 2010, the USGS entered into cooperative agreements with the U.S. Army to complete studies of groundwater resources focusing primarily on undeveloped basins within the NTC. Electrical resistivity data were collected in 2015 and 2017 at three groups of springs in undeveloped basins in order to quantify the spatial extent of groundwater associated with each spring and to detect hydrologic change over this two year time period. In 2017, electrical resistivity data were also collected at the airstrip on Bicycle Lake (a dry lakebed) to provide insight on ground failures and data regarding the depth of the known surface cracks and macropolygon features.

The U.S. Army Fort Irwin National Training Center (NTC), approximately 35 mi north-northeast of Barstow, California, covers approximately 1,177 square miles, and is comprised of ten groundwater basins, three of which have been subdivided into subbasins on the basis of additional hydrologic testing. Since the early 1990s, the U.S. Geological Survey (USGS) has been studying water resources issues at Fort Irwin. One issue of concern is the potential effect of groundwater development resulting from planned training expansion and infrastructure at the NTC on natural springs and seeps, an important water source for wildlife. In 2010, the USGS entered into cooperative agreements with the U.S. Army to complete studies of groundwater resources focusing primarily on undeveloped basins within the NTC. Electrical resistivity data were collected in 2015 and 2017 at three groups of springs in undeveloped basins in order to quantify the spatial extent of groundwater associated with each spring and to detect hydrologic change over this two year time period. In 2017, electrical resistivity data were also collected at the airstrip on Bicycle Lake (a dry lakebed) to provide insight on ground failures and data regarding the depth of the known surface cracks and macropolygon features.

The U.S. Army Fort Irwin National Training Center (NTC), approximately 35 mi north-northeast of Barstow, California, covers approximately 1,177 square miles, and is comprised of ten groundwater basins, three of which have been subdivided into subbasins on the basis of additional hydrologic testing. Since the early 1990s, the U.S. Geological Survey (USGS) has been studying water resources issues at Fort Irwin. One issue of concern is the potential effect of groundwater development resulting from planned training expansion and infrastructure at the NTC on natural springs and seeps, an important water source for wildlife. In 2010, the USGS entered into cooperative agreements with the U.S. Army to complete studies of groundwater resources focusing primarily on undeveloped basins within the NTC. Electrical resistivity data were collected in 2015 and 2017 at three groups of springs in undeveloped basins in order to quantify the spatial extent of groundwater associated with each spring and to detect hydrologic change over this two year time period. In 2017, electrical resistivity data were also collected at the airstrip on Bicycle Lake (a dry lakebed) to provide insight on ground failures and data regarding the depth of the known surface cracks and macropolygon features.

The U.S. Army Fort Irwin National Training Center (NTC), approximately 35 mi north-northeast of Barstow, California, covers approximately 1,177 square miles, and is comprised of ten groundwater basins, three of which have been subdivided into subbasins on the basis of additional hydrologic testing. Since the early 1990s, the U.S. Geological Survey (USGS) has been studying water resources issues at Fort Irwin. One issue of concern is the potential effect of groundwater development resulting from planned training expansion and infrastructure at the NTC on natural springs and seeps, an important water source for wildlife. In 2010, the USGS entered into cooperative agreements with the U.S. Army to complete studies of groundwater resources focusing primarily on undeveloped basins within the NTC. Electrical resistivity data were collected in 2015 and 2017 at three groups of springs in undeveloped basins in order to quantify the spatial extent of groundwater associated with each spring and to detect hydrologic change over this two year time period. In 2017, electrical resistivity data were also collected at the airstrip on Bicycle Lake (a dry lakebed) to provide insight on ground failures and data regarding the depth of the known surface cracks and macropolygon features.

The U.S. Army Fort Irwin National Training Center (NTC), approximately 35 mi north-northeast of Barstow, California, covers approximately 1,177 square miles, and is comprised of ten groundwater basins, three of which have been subdivided into subbasins on the basis of additional hydrologic testing. Since the early 1990s, the U.S. Geological Survey (USGS) has been studying water resources issues at Fort Irwin. One issue of concern is the potential effect of groundwater development resulting from planned training expansion and infrastructure at the NTC on natural springs and seeps, an important water source for wildlife. In 2010, the USGS entered into cooperative agreements with the U.S. Army to complete studies of groundwater resources focusing primarily on undeveloped basins within the NTC. Electrical resistivity data were collected in 2015 and 2017 at three groups of springs in undeveloped basins in order to quantify the spatial extent of groundwater associated with each spring and to detect hydrologic change over this two year time period. In 2017, electrical resistivity data were also collected at the airstrip on Bicycle Lake (a dry lakebed) to provide insight on ground failures and data regarding the depth of the known surface cracks and macropolygon features.

The U.S. Army Fort Irwin National Training Center (NTC), approximately 35 mi north-northeast of Barstow, California, covers approximately 1,177 square miles, and is comprised of ten groundwater basins, three of which have been subdivided into subbasins on the basis of additional hydrologic testing. Since the early 1990s, the U.S. Geological Survey (USGS) has been studying water resources issues at Fort Irwin. One issue of concern is the potential effect of groundwater development resulting from planned training expansion and infrastructure at the NTC on natural springs and seeps, an important water source for wildlife. In 2010, the USGS entered into cooperative agreements with the U.S. Army to complete studies of groundwater resources focusing primarily on undeveloped basins within the NTC. Electrical resistivity data were collected in 2015 and 2017 at three groups of springs in undeveloped basins in order to quantify the spatial extent of groundwater associated with each spring and to detect hydrologic change over this two year time period. In 2017, electrical resistivity data were also collected at the airstrip on Bicycle Lake (a dry lakebed) to provide insight on ground failures and data regarding the depth of the known surface cracks and macropolygon features.