Salinity Trends in a Groundwater System Supplemented by 50 Years of Imported Colorado River Water

The Indio subbasin of the Coachella Valley is a desert
area of
southern California where a growing population depends primarily on
groundwater for drinking and agricultural uses. The aquifer system
has been supplemented with Colorado River water through managed recharge
and widespread irrigation since the mid-20th century. We use a combination
of geochemical modeling and trend analysis to identify changes in
total dissolved solids through time, elucidate the sources of dissolved
solids, and quantify the extent of contributions from those sources
throughout the Indio subbasin. We conclude that recharged Colorado
River water is the primary source and driver of increasing salinity,
particularly in areas immediately downgradient from the recharge locations
and in the eastern part of the subbasin away from the recharge ponds
due to irrigation using imported water. Other contributions of dissolved
solids to groundwater resources include geothermal waters, wastewater
effluent, and agricultural return flow, although their effects are
more localized. This study presents a broadly applicable framework
for identifying sources of dissolved solids in groundwater wells and
salinity trends at a regional scale in a large data set.