Effect of the Paradox Valley Unit on the dissolved-solids load of the Dolores River near Bedrock, Colorado, 1988-2001

Abstract

Discharge of brine with an average dissolvedsolids concentration of about 256,000 milligrams per liter from alluvium in Paradox Valley, a collapsed salt anticline, substantially increases the dissolved-solids load of the Dolores River. In 1996, the Bureau of Reclamation began operation of the Paradox Valley Unit, a series of brine-withdrawal wells completed in alluvium along the Dolores River and a deep-injection well for the brine, to decrease flow of brine into the river. This report presents the findings of a study to determine the effectiveness of the Paradox Valley Unit from 1988 through September 2001. Differences in dissolved-solids load of the Dolores River between two gaging stations, one upstream and one downstream from the Paradox Valley Unit, indicate that an average dissolved-solids load of about 313 tons per day (an annual average of about 115,000 tons) was contributed by brine inflow to the Dolores River before operation of the Paradox Valley Unit began in July 1996. By September 30, 2001, the dissolved-solids load contributed by brine had declined to an average of about 29 tons per daya decrease of about 90 percent. This decrease might have been facilitated by a decrease in precipitation and streamflow into the Paradox Valley during the last few years of the assessed period.

High-resolution mapping of the freshwater–brine interface using deterministic and Bayesian inversion of airborne electromagnetic data at Paradox Valley, USA

“…The removal of salt resulted in subsequent collapse of the overlying materials and the development of a topographic depression along the axis of the anticline (Withington 1955). Groundwater dissolution of the Paradox Formation salt has also led to the development of a highly concentrated sodium-chloride-dominated brine plume, where groundwater TDS concentrations can exceed 250 g/L (Watts 2000;Chafin 2003). The Dolores River, which crosses the axis of the Paradox Valley as it flows north towards the Colorado River, acts as a natural groundwater discharge location and experiences substantial increases in salinity as it intercepts the Paradox brine.…”

“…Paradox Valley is one of several collapsed saltcored anticlines characteristic of the region (Shoemaker et al 1958;Cater and Craig 1970;Sugiura and Kitcho 1981;Gutiérrez 2004), where the intrusive salt core lies near the land surface and has been exposed to active groundwater circulation, leading to salt dissolution, land surface collapse, and the development of shallow brine. Historically, more than 100,000 metric tons of salt per year discharged to the Dolores River from the groundwater brine plume underlying Paradox Valley, making the valley one of the most concentrated salinity sources in the CRB (Watts 2000;Chafin 2003;Mast 2017).…”

Substantial Declines in Salinity Observed Across the Upper Colorado River Basin During the 20th Century, 1929–2019

“…To address these challenges, the Colorado River Basin Salinity Control Forum was established in 1973 (Colorado River Basin Salinity Control Forum [CRBSCF], 2014) to enhance and protect the quality of water in the Colorado River for use in the United States and Mexico, in accordance with the 1972 Clean Water Act and the Salinity Control Act of 1974 (U.S. Bureau of Reclamation, 2017). To reduce or prevent salinity loading to streams, the Salinity Control Forum implements a variety of salinity-control measures, such as well fields designed to intercept brine from entering rivers (Chafin, 2003), improved irrigation infrastructure, vegetation management, land retirement, canal lining, and water-efficient irrigation systems that reduce surface runoff and infiltration through saline soils (Anning et al, 2010). To inform their mitigation strategies, previous studies have investigated dissolved-solids sources (Miller et al, 2017), transport processes (Cadaret et al, 2016;Rumsey et al, 2017), and the effectiveness of salinity-control efforts (Schaffrath, 2012;Thiros, 2017).…”