No abstract

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83). Supplemental InformationConcentrations of chemical constituents in water are given in milligrams per liter (mg/L).

No abstract

The San Juan River is a vital source of water for drinking, irrigation, and recreational use for individuals in the arid Four Corners Region, much of which encompasses the Navajo Nation. The Navajo Nation Environmental Protection Agency (NNEPA) discovered elevated concentrations of aluminum, arsenic, and lead in surface water samples from routine monitoring of the San Juan River. Tributaries, most of which are ephemeral, that flow into the San Juan River may be contributing elevated concentrations of aluminum, arsenic, and lead. These metals could come from local oil drilling operations, abandoned uranium mines and mills, agricultural land, natural gas power plants, geology and erosion, illegal dumping of waste, and other sources. In cooperation with the NNEPA, the U.S. Geological Survey (USGS) is working to determine which tributaries are contributing aluminum, arsenic, and lead to the San Juan River, as well as the relative contributions from anthropogenic and natural sources. Thirty-four tributaries and numerous sites on the San Juan River, from Navajo Dam, NM to Mexican Hat, UT are being sampled routinely for surface water and sediments by scientists at the NNEPA and the USGS. Surface water samples are being analyzed for major ions and trace metals, and sediment mineralogy is being analyzed using a scanning electron microscope (SEM) at the University of New Mexico. Water chemistry and sediment mineralogy data analysis is ongoing. Results from a February 2021 baseflow synoptic survey of the San Juan River, and from tributary samples collected in July 2021, show concentrations of aluminum as high as 3.77x10 6 parts per billion (ppb), above the Environmental Protection Agency (EPA) suggested goal for aluminum of 200 ppb. Arsenic results were as high as 27 ppb, above the EPA maximum contaminant level (MCL) for arsenic of 10 ppb. Lead results were as high as 218 ppb, above the EPA MCL for lead of 15 ppb. SEM analysis of sediments collected in August 2021 show a large amount of aluminum in tributary sediments. Arsenic and lead have not been found in SEM analysis, which could be due to their low concentrations, or desorption from sediments. To better determine the effect of tributary chemistry on the San Juan River, USGS scientists are beginning to use aerial imaging to model streamflow so that metal loads can be calculated. Determining the relative contributions of metals to the San Juan River is vital to the public for recreational use, for water managers in the region, and for future scientific inquiry.

The Gold King Mine Release of August 5, 2015 mobilized three million gallons of water and sediment into a tributary of the Animas River, which flows south from Colorado into New Mexico. The Animas enters the San Juan River at Farmington, New Mexico, the sixth largest city in the state and one of several communities that rely on the Animas and San Juan rivers for drinking water and (or) crop irrigation. Mines such as the Gold King are sources of metals and acidity to streams of the area, leading to concerns regarding the effects of the release on water quality. Potential problem constituents such as lead and arsenic (among others) were analyzed in surface water and sediment samples collected by the U.S. Geological Survey (USGS) in August 2015. Surface-water samples collected from the San Juan River at Farmington on August 8, 2015 (a time when the orange color indicative of the release was observed) had concentrations in whole water (unfiltered) samples of 552 µg/L lead and 26.3 µg/L arsenic. The concentrations of lead and arsenic were above the lead action level of 15 µg/L and the maximum contaminant level of 10 µg/L for arsenic, as set by the U.S. Environmental Protection Agency for drinking water. In contrast, the dissolved concentrations (0.45 µm filter) of these elements at the same site and time (lead <0.04 µg/L and arsenic 0.23 µg/L) were about two to three orders of magnitude below drinking-water standards and three to 5 orders of magnitude below the whole water sample concentrations. At the San Juan River at Farmington streamgage, located approximately two river miles downstream from the Animas River at Farmington streamgage, concentrations measured in whole water samples collected 4 hours after the samples on the Animas River ranged from 122 µg/L for lead, and 7.89 µg/L for arsenic. These concentrations were likely affected by dilution from the San Juan River which had discharge on August 8, 2015 of about 1,300 cfs, whereas discharge on the Animas River at Farmington was about 800 cfs.Based on the results for total and dissolved water samples, constituents of concern generally were associated with particulates in the water. Bed sediment samples collected from the Animas River at Farmington on August 12, 2015 had lead concentrations ranging from 33.0 to 179 mg/kg and arsenic concentrations ranging from 3 to 11 mg/kg (n =4). Concentrations of these constituents in bed sediments were generally lower at the San Juan River at Farmington, similar to the trend in water-quality data for the same sites. Concern related to suspended particulates and bed sediment in these rivers continues months after the release. Continuous monitoring of pH, temperature, specific conductance, and turbidity is expected to help to understand the current geochemical interactions in the rivers. Additionally, water-quality sampling during snowmelt and storm events will provide valuable information about sediment and metal mobility during high-discharge events in the Animas and San Juan Rivers.