Forecasting Total Dissolved Solids Concentrations of Groundwater from the Lower Colorado Water Supply Project

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The All-American Canal (AAC) in southern Imperial County, California, has historically been unlined, resulting in substantial losses to seepage. In 2006, the Imperial Irrigation District (IID), under a contract with the United States Bureau of Reclamation (Reclamation), initiated a project to build a concrete-lined canal parallel to 23 miles of the earthen AAC. Construction was completed in 2010 and was estimated to conserve about 67,000 acre-feet per year of seepage (U.S. Bureau of Reclamation, 1994).

map showing the location of the All-American Canal and study area boundary

Location of the "Forecasting Total Dissolved Solids Concentrations of Groundwater from the Lower Colorado Water Supply Project" study area in southeastern Imperial County, California. (Public domain.)

Reclamation operates the Lower Colorado Water Supply Project (LCWSP), a well field in the Imperial Sand Dunes Recreation Area along the AAC, to replace surface water that was diverted from the Colorado River for users in California that do not hold, or hold insufficient, Colorado River rights. Water pumped from the LCWSP is discharged into the AAC. The desired quality of water for acceptable discharge into the AAC is 879 ± 30 milligrams per liter or less of total dissolved solids (TDS) concentrations on an average annual flow-weighted basis (U.S. Bureau of Reclamation, 2004).

Use of the recently lined AAC has greatly reduced groundwater recharge from seepage. TDS concentrations in water from LCWSP wells likely will increase as the low-TDS component of groundwater associated with AAC seepage since 1940 declines and native, high-TDS groundwater becomes the dominant source.

 

 

 

Phase 1: Initial Characterization of the Groundwater System and Operation of a Hydrologic Monitoring Network

Objectives

The overall objectives of the study are to improve the understanding of the groundwater system in the vicinity of the LCWSP well field, and to estimate the impact of lining the AAC on groundwater levels and TDS concentrations in LCWSP wells up to the year 2070. The study will be completed in three phases:

  1. Phase 1 - Initial characterization of the groundwater system and establishment of a monitoring network;
  2. Phase 2 - Evaluation of the groundwater system and its relation to the water quality produced from the LCWSP wells, and;
  3. Phase 3 - Development and application of a numerical model to provide forecasts of water levels and TDS concentrations in water pumped from LCWSP wells.

Study Approach

The current study consists of three main elements to address objectives of the ongoing Phase 1 monitoring program:

  1. Collection of water-level data – depth to water is measured annually at 30 wells, and continuously at up to 10 wells, to determine changes to the regional water table;
  2. Collection of water-quality data – water from wells is sampled at 8 wells annually from a group of up to 24 wells, for physical properties, inorganic constituents, and isotopic tracers to evaluate sources of groundwater recharge and flow paths in the groundwater system;
  3. Collection of micro-gravity data – microgravity data will be measured annually at 33 stations to determine aquifer storage change, as well as a high-precision elevation survey of the land surface to assess whether subsidence has occurred.

These work elements and sites draw upon the initial hydrologic monitoring network established by USGS between 2009 to 2011 (Coes and others, 2015).

Relevance & Benefits

The basic data collected and information gained from the study will provide the cooperator and state and federal agencies with a current understanding of hydrologic and water-quality conditions near the All-American Canal.

Baseline monitoring data will help identify temporal changes and provide a foundation from which future groundwater elevation and TDS concentrations can be forecasted.

The study provides information on groundwater movement and quality along the United States-Mexico border to multiple stakeholders.

Current Activity

Operation of the hydrologic monitoring network established during Phase 1 is ongoing. Collection of groundwater, water quality, and micro-gravity data is planned thru FFY2021. New wells, as information is made available, are evaluated for inclusion into the monitoring network.

A USGS Scientific Investigations Report summarizing work completed for Phase 1 of the project, “Initial characterization of the groundwater system near the Lower Colorado Water Supply Project, Imperial Valley, California” is available for download at: https://doi.org/10.3133/sir20155102

 

Lower Colorado Monitoring Network

The Lower Colorado Monitoring Network is a series of groundwater-level and water-quality wells, as well as streamgages and micro-gravity sites. An interactive map displays the sites and provides links to the most current data.

Go to Data Map >>

 

References

Coes, A.L., Land, M., Densmore, J.N., Landrum, M., Beisner, K., Kennedy, J.R., Macy, J.P., Tillman, F., 2015. Initial Characterization of the Groundwater System near the Lower Colorado Water Supply Project, Imperial Valley, California. U.S. Geological Survey, Scientific Investigations Report 2015–5102, p 72.

U.S. Bureau of Reclamation, 1994, Final environmental impact statement/final environmental impact report—AllAmerican Canal Lining Project: U. S. Department of the Interior, Bureau of Reclamation, Lower Colorado River Region, Imperial Irrigation District, 176 p.

U.S. Bureau of Reclamation, 2004, Quality of project well field water to be exchanged, Amendment 1 to Contract among the United States, Imperial Irrigation District, and Coachella Valley Water District for exchange of water from the Lower Colorado Water Supply Project Well Field for Colorado River Water: U.S. Department of the Interior, Bureau of Reclamation, no. 2–07–30–W0277, dated April 26, 2004, 2 p.

A USGS Scientific Investigations Report summarizing work completed for Phase 1 of the project, “Initial characterization of the groundwater system near the Lower Colorado Water Supply Project, Imperial Valley, California” is available for download at: https://doi.org/10.3133/sir20155102

 

Lower Colorado Monitoring Network

The Lower Colorado Monitoring Network is a series of groundwater-level and water-quality wells, as well as streamgages and micro-gravity sites. An interactive map displays the sites and provides links to the most current data.
 

Go to Data Map >>