Determining the fate and transport of septic-tank effluent in the southern area of Warren subbasin, California

Science Center Objects

Residents and businesses in Yucca Valley, CA rely currently on septic tanks to treat their wastewater. The local water district, Hi-Desert Water District (HDWD), is planning to construct a sewer system and wastewater treatment plant, initially serving the West, Midwest, Mideast, Northeast, and East hydrogeologic units of the Warren subbasin.

Map of study area, Yucca Valley, California.

Map of study area, Yucca Valley, California. (Public domain.)

HDWD may be required to expand the sewer system to include the area south of the West, Midwest, Mideast, and East hydrogeologic units, referred to in this study as the South hydrogeologic unit. However, this area has not been developed for water supply and consequently has not been well characterized hydrogeologically and the effects of septic-tank effluent discharge on the groundwater system are unknown.

The objectives of this study are to: (1) assess the hydrogeology of the South hydrogeologic unit of the Warren subbasin; (2) identify the vertical distribution of nitrogen species in the unsaturated zone within the south hydrogeologic unit; (3) determine the need for the proposed sewer system; and (4) develop water-management strategies that control nitrate concentrations.

Specific tasks will be: (1) review of existing data (2) collect geophysical data, (3) installation of saturated- and unsaturated-zone monitoring sites, (4) collection of aquifer test data and monitoring and sampling of proposed and existing of saturated- and unsaturated-zone monitoring sites, (5) extending an existing groundwater-flow and solute-transport model to include the South hydrogeologic unit of the subbasin, and (6) preparation of an data report and an interpretive report.