Tracking the Sources of Metals in the San Juan River on the Navajo Nation

From a U.S. Geological Survey fact sheet of 2021 (version 1.1, July 2021), describing a project then beginning.

The San Juan River is a major water source for communities in the Four Corners region — Colorado, Arizona, New Mexico and Utah — and a vital source of water for the Navajo Nation. The Navajo Nation Environmental Protection Agency (NNEPA) samples surface water on the Nation from time to time, and has found some elements above its surface water standards, the upper limits for drinking or other uses.

The study area: the San Juan River Basin, the river and its tributaries, and the Navajo Nation chapters in and around it. Base from the U.S. Geological Survey's The National Map. Credit: U.S. Geological Survey.

Metals of concern

"Constituents of concern" are substances that could be harmful in large enough amounts. In the San Juan River they include metals such as arsenic, lead and aluminum, which can come from nature or from human activity and can affect the health of people, plants and animals.

Possible sources include:

• the Animas River, a natural source because of the rocks it flows through, and because of hard-rock mining at its headwaters;
• oil and gas development, coal mining and coal-fired power plants;
• towns and cities, and illegal dumping;
• abandoned uranium mines and mills;
• overgrazed land;
• the natural geology;
• leaching from underground farm return flows.

A geologic source. Photograph by Johanna M. Blake, U.S. Geological Survey.

Drainage from hard-rock mining. Photograph by Johanna M. Blake, U.S. Geological Survey.

Standards

Concentrations are total (unfiltered) unless marked * (dissolved, filtered). µg/L, micrograms per litre; NCNS, no current numerical standard.

• Arsenic: long-term exposure above the MCL can damage skin, cause circulatory problems and may raise the risk of cancer.
• Lead: long-term exposure can delay infants' and children's physical or mental development, and cause kidney problems or high blood pressure in adults. The lead action level tells water users to check how corrosive their water is; lead comes from pipes or from erosion of natural deposits.
• Aluminum: high levels discolour water. Its secondary MCL is a goal so that color, taste and smell are unaffected; it is not a health threat.

The MCL is the highest level of a contaminant allowed in drinking water; below it there is no known or expected health risk. "Acid-soluble" aluminum is what passes a 0.45-micrometre filter after the sample is acidified to pH 1.5–2.0 with nitric acid.

A milligram per litre is 1 part per million — like 1 minute in 2 years, or 4 drops in a 55-gallon drum. A microgram per litre is 1 part per billion — 1 second in nearly 32 years, or 1 drop in a tanker truck.

The project

The USGS is working with the NNEPA to identify which tributaries, in the reach through the Navajo Nation, bring metals and trace elements into the San Juan River, and how much each natural and human source contributes. With local community members, they chose tributaries for sampling equipment. The three-year project, begun in spring 2021, will compare the chemical signatures of water in the major tributaries to find where metals above safe levels may be entering the river. The results will serve the Navajo Nation, drinking water managers, irrigation districts, scientists and the public.

How:

• Background. Compile published data on the chemistry of rocks, sediment and water — including geologic maps and historical streamflow and water-quality records — to identify possible sources and gaps. Comparing the chemistry of the inputs helps tell their contributions apart.
• Sampling. Collect and analyse water and suspended sediment in the river and its tributaries. Sediment chemistry gages combine a water sampler, a suspended-sediment trap and a pressure transducer that senses when water is in the channel; a bed-material sampler collects sediment from the channel bottom, and a probe records water quality such as pH.
• Streamflow. Measure flow where it is unknown. USGS streamgages can send near-real-time flow and water-quality data; where one cannot be installed, drones (unmanned aircraft systems) collect data to calculate channel dimensions, which with water levels from the sediment gages give streamflow. Flow multiplied by metal concentration gives the metal load each tributary carries.

A USGS streamgage can deliver near-real-time streamflow and sometimes water-quality data. Photograph by Jeb Brown, U.S. Geological Survey.

Where a streamgage cannot be installed, a drone can collect data to calculate channel dimensions. Photograph by Jeb Brown, U.S. Geological Survey.

A water-quality probe used to measure properties such as pH. Photograph by Leslie Gordon, U.S. Geological Survey.

Sources

• Blake, J.M., Chavarria, S.B., and Matherne, A.-M., 2021, Tracking the source of metals to the San Juan River (ver. 1.1, July 2021): U.S. Geological Survey Fact Sheet 2021–3029. https://doi.org/10.3133/fs20213029
• The standards come from the Navajo Nation Environmental Protection Agency (written communication, 2015) and the U.S. Environmental Protection Agency's drinking water regulations (2021).
• The map, table and photographs are taken from the fact sheet's PDF. Its eleven photographs of source areas from the Navajo Nation EPA and its two stock images, all used with permission, are not reproduced.
• Rewritten in hubnx's own words.