Assessing the Feasibility of Artificial Recharge and Storage and the Effectiveness and Sustainability of Insitu Arsenic Removal in the Antelope Valley, California

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Project Update - 8/2/2011: Water having an arsenic concentration of 30 micrograms per liter was infiltrated from a test pond beginning in December, 2010. After water moved downward through the unsaturated zone, arsenic concentrations in Lysimeters as deep as 110 ft beneath the pond were about 2 micrograms per liter. Laboratory column experiments show similar changes in arsenic concentrations in column discharges.

Scientists placing speciality equipment in monitoring wells

Speciality equipment placed in monitoring wells measure water flow-rate through the unsaturated zone

(Public domain.)

Groundwater pumpage for agricultural and municipal supply has resulted in water-level declines of more than 200 ft in some parts of the Antelope Valley groundwater basin and land subsidence of more than 6 ft in some areas. Future urban growth, increased agricultural demand, and limits on the supply of imported water will continue to increase the demand for groundwater. The Antelope Valley East Kern Water Agency (AVEK), the Los Angeles County Department of Public Works (LACDPW), and the city of Palmdale are considering artificial recharge to supplement local groundwater and meet future demand at North Buttes, Westside, and Amargosa Creek project areas in the Lancaster subbasin of the Antelope Valley groundwater basin. In addition to artificial recharge of imported water, the water agencies are considering using recharge through the unsaturated zone to remove arsenic from local groundwater. Previous work by the USGS has shown that naturally occurring alumina, iron, and manganese oxides on the surfaces of mineral grains sorb arsenic as water infiltrates through the unsaturated zone. If successful, arsenic removal through sorption in the unsaturated zone would augment local supply and represent a savings of between 45 and 65 million dollars in arsenic treatment costs over the life of the project compared to sorption on conventional media. Prior to implementing full-scale artificial recharge and storage programs at the proposed artificial-recharge and storage sites the following questions need to be answered for each site. Is the site suitable for this artificial recharge? That is, what is the anticipated recharge rate, are there near-surface geologic layers that will prevent water from reaching the water table, is there sufficient storage volume, can the water be extracted economically, and what is the in-situ water quality. At sites where in-situ arsenic removal is being considered, additional questions need to be answered. Such as, how will recharging the groundwater basin with high-arsenic groundwater affect the water quality of the aquifer and the extracted water? What is the effectiveness, sustainability, and long-term impact on the unsaturated zone of in-situ arsenic removal?

The objectives of this study are to: 1) determine if the proposed sites in the Antelope Valley groundwater basin are suitable for artificial recharge and storage; 2) determine the effects of artificial recharge on water levels and water quality at the proposed sites; and 3) determine the effectiveness and sustainability of in-situ arsenic removal in the unsaturated zone at selected sites.

Group of people standing in dry grasses and dirt

Scientists and engineers meet to discuss preliminary arsenic removal results at the test pond in Antelope Valley

(Public domain.)

The proposed study will augment the water supply of the rapidly growing Antelope Valley area through the more efficient use of available water resources. The study will provide information on: 1) artificial recharge of water infiltrated from ponds, 2) the infiltration of high-arsenic water from ponds through thick unsaturated zones to recharge underlying aquifers, and 3) the fate and transport of arsenic in unsaturated alluvial deposits. The proposed study addresses USGS science strategy directions “A Water Census of the United States” and “The Role of Environment in Human Health”.

The study objectives will be met by a two-phase study approach at each site. The first phase will evaluate the feasibility of the site for artificial recharge and storage using existing or readily collected data. If the Phase 1 results indicate that artificial recharge may be feasible, a pilot-scale artificial-recharge project will be implemented to evaluate the feasibility of artificial recharge via surface spreading. High-arsenic groundwater from nearby wells will be used for the pilot-scale project at the North Buttes site to determine the effectiveness and sustainability of in-situ arsenic removal by alumina, iron, and manganese oxides on unsaturated materials.