Annual turbidity in water caused by spring snow melt at Grand Canyon

Annual turbidity in water caused by spring snow melt at Grand Canyon
Date: April 8, 2013
Contact: Maureen Oltrogge, 928-638-7779

Grand Canyon, Ariz. - Each year in the spring (April - June) water turbidity increases in the drinking water within Grand Canyon National Park. This increased turbidity is caused by snow melt and spring rains recharging the aquifer, as well as by increased water flows through rock formations to the point of supply for Grand Canyon National Park's water supply system supplied from Roaring Springs. As water flows through these rock formations, very small particles of inorganic material are dissolved from the rock and are held in suspension in the water. This suspended inorganic material is too small to be removed by the centrifugal separation process used at Roaring Springs and remains in the potable water. These particles of dissolved rock and minerals appear in the potable water as a slight tint or a noticeable cloudiness. The extent of the turbidity is directly proportional to the amount of snowmelt and rainwater that flows through the rock formations.

This annual turbidity event has been researched and evaluated by the National Park Service, independent laboratories, the U.S. Public Health Service, and by the Arizona Department of Environmental Quality. The turbidity is caused by dissolved inorganic material such as silicates and calcium precipitates suspended in the water. A Roaring Springs Water Risk Assessment performed states: "Particle characterization testing though the use of electron microscopy and energy dispersive spectrometry indicate that the turbidity are comprised of silicon, aluminum, oxygen, potassium, magnesium, calcium, and iron. This indicates that the particles are from common sedimentary rock". No organic materials have been identified during these investigations. Although this dissolved inorganic material causes the water to be slightly cloudy, the dissolved material is well below maximum contaminate levels established by the Environmental Protection Agency and is not harmful to health.

Turbidity has no health effects but can interfere with the disinfection processes practiced at Grand Canyon National Park and may provide a medium for microbial growth. For those reasons, The National Park Service routinely increase the chlorine residual of the drinking water and increase microbiological water sampling and testing throughout this spring period of increased turbidity to insure that the drinking water is adequately disinfected. The increased chlorine dosage and the enhanced microbiological monitoring and testing is maintained until the turbidity drops to the normal values of less than 1.0 NTU (Nephelometric Turbidity Unit - used to measure the extent or degree of cloudiness), usually by late June or early July.

The National Park Service operates the public water supply system within Grand Canyon National Park. The system is licensed and approved by the Environmental Protection Agency and by the Arizona Department of Environmental Quality. All potable water provided by this system must meet Federal and State of Arizona standards at all times. Although this turbidity can cause cloudiness in the potable water, it does not create a health risk to the public.

For additional information, please contact Dave Welborn, Utility Systems Supervisor, Grand Canyon National Park at 928-638-3019 or 928-638-7673 or by email at Thomas_Welborn@nps.gov.