Watershed group’s study confirms high arsenic levels in Uncompahgre River

Uncompahgre River Valley looking south

From email from the Uncompahgre Watershed Partnership (Tanya Ishikawa):

Watershed group’s study confirms high arsenic levels in Uncompahgre River
Uncompahgre Watershed Partnership releases sediment release study results

RIDGWAY, COLO.– A recently released study by the Uncompahgre Watershed Partnership (UWP) confirmed that arsenic levels in the Uncompahgre River in Ouray County continue to exceed state water quality standards for human health. Though not a direct source of drinking water for homes and businesses in Ouray, Ridgway, Loghill and other downstream neighborhoods, the river is used for agriculture and recreation and may be connected to underground sources that feed nearby wells.

UWP Board Member Dennis Murphy, who volunteered on the study, will make a presentation of the report’s findings to the Ouray County Board of Commissioners on Tuesday, Jan. 30. The nonprofit watershed group has secured $1,000 from the county and $500 from Ridgway to partially fund a followup hydrodam sediment release study, and has discussed the possibility of collaborating with the county on a study of well water on properties along the Uncompahgre River between Ouray and Ridgway.

The Uncompahgre River is known to have relatively high concentrations of several heavy metals such as manganese, aluminum and iron, since it has many tributaries that pass through both naturally high mineral content in the mountains as well as minerals exposed by past mining activity. The water flowing through the river between Red Mountain Pass and Ridgway Reservoir turns various shades of green, yellow and orange at different times throughout the year, due to human-caused and natural events that increase the flows of heavy metals.

For years, the Ouray County government has fielded calls from concerned people when the river’s color was brightest. One annual event that elicits such a public response is the sluicing of the Ouray Hydrodam, when a gate at the bottom of the dam is opened to release sediment from the reservoir. The sediment flows into and builds up in the reservoir each year, and must be released to improve operations. This release, usually once a year, sends an orange plume down the river.

“The hydrodam has a storage capacity of less than one acre-foot, which fills quickly with sediment and precipitated metals from the inflow. The annual sluice event releases accumulated sediment and metals in hours rather than slowly, over the period of a year,” said Murphy, a retired Bureau of Land Management hydrologist.

Some community members have wondered if the plume with its higher concentrations of metals has negative impacts on the Uncompahgre River. Last March, UWP studied the plume by taking water and sediment samples before, during and after the dam release at three locations along the river by a group of volunteers with hydrology expertise, led by UWP Project Manager Agnieszka Przeszlowska.

Analysis of the sampling data showed that the water and sediment released from the hydrodam raised water levels in the river for a short period. The stream flow in the Uncompahgre River near Ouray increased from 141 cfs (cubic feet per second) to 174 cfs for less than 30 minutes. Downstream near Ridgway, the streamflow peaked at 170 cfs for approximately three hours and 30 minutes, only 2 cfs higher from the 168 cfs peak the previous day.

During the release, measurements showed substantially raised total metal concentrations, including manganese, aluminum, arsenic, cadmium, copper, iron, lead, nickel, selenium, silver, and zinc. All metal concentrations met aquatic life standards and most metals met human health standards, according to state water quality criteria.

However, both manganese and arsenic were at unsafe levels. The release is not suspected to be an original source of the manganese and arsenic concentrations, so UWP recommends additional study to better understand sources and concentrations within the watershed.

Manganese exceeded water safety standards before, during, and after the release at the sampling location below the dam, but attained levels within safety standards at the other two sampling locations at certain times around the release. No drinking water sources including wells are located near the dam, and the overall manganese concentrations were considered relatively benign.

However, the arsenic concentrations, which exceeded the human-health criterion before, during and after the sediment release at all three sampling locations, are considered more of a concern. “The EPA classifies arsenic as a Class A carcinogen, meaning it may pose the highest risk of cancer. This classification results in a very low human-health standard (0.02 microgram per liter of total arsenic),” according to the report produced for UWP by Ashley Bembenek and Julia Nave of Alpine Environmental Consultants in Crested Butte.

The arsenic concentrations are not new in the Uncompahgre River near Ouray and Ridgway, which have occasionally exceeded the human-health and raw water supply criteria in other measurements taken over the past 15 years.

The UWP study did not directly investigate the potential effect of the sediment release on public water supplies. The raw source waters for local utilities are all upstream from the Uncompahgre River and do not receive any flows from the releases. While those supplies would be unaffected by the sediment release, wells in the area may be affected. They were not studied in 2017, but plans are being considered to study them in 2018.

Murphy concluded, “This initial study was conducted under significant time, labor, and financial constraints, so did not provide as complete a picture as we had hoped. However, using what we learned from this study will be beneficial to better design future studies and monitor potential water quality issues in the Upper Uncompahgre Valley. As an example, the metal arsenic, a class A carcinogen, shows to be elevated at times in the Uncompahgre River. Sampling the water quality of domestic wells in the valley bottom, that may be pumping water connected to the river, might expose some potential health issues previously undetected.”

As far as the health impacts of arsenic on recreational users of the Uncompahgre River, the Colorado Department of Public Health and Environment put out an advisory after the 2015 Gold King Mine spill into the Animas River, stating that it “does not anticipate adverse health effects from exposure to contaminants detected in the sediment during typical recreational activities or through incidental contact with the sediment.”

The CDPHE recommends prudent public health practices when coming into contact with sediment and surface water containing heavy metals: 1. Don’t drink untreated water from the river. 2. Wash hands thoroughly with soap and water after contact. 3. Avoid contact in areas where there is visible discoloration in sediment or river water. 4. Wash clothes after contact. 5. Supervise young children to make sure they follow these recommendations.

The full report on the Ouray Hydrodam Sediment Release is available online at: http://www.uncompahgrewatershed.org/2017-hydrodam-sediment-release-study-report/

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