5/8/2012 10:18:00 AM Turbidity to increase in Grand Canyon drinking water through June Annual event not harmful to health
NPS photo/Michael Quinn
Water gushes forth directly out of the cliffs, cascading over moss and fern to form Bright Angel Creek. This giant spring provides drinking water for every visitor and resident within Grand Canyon National Park. The water is delivered to the South Rim via a pipeline buried beneath the North Kaibab Trail (installed 1965-1970).
GRAND CANYON, Ariz. - Each year in the spring (April - June), Grand Canyon National Park experiences an increase in turbidity in the drinking water. This increased turbidity is caused by snow melt, spring rains recharging the aquifer and increased water flows through the rock formations to Roaring Springs, the point of supply for the Grand Canyon National Park Public Water Supply System.
As water flows through the 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 exhaustively researched and evaluated for the past fifteen (15) years by the National Park Service, by independent laboratories, by the US Public Health Service, and by the Arizona Department of Environmental Quality (ADEQ).
The turbidity is caused by dissolved inorganic material such as silicates and calcium precipitates suspended in the water. The Roaring Springs Water Risk Assessment performed in August 1995 states: "Particle characterization testing...indicates 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 of the turbidity event. Although the dissolved inorganic material causes the water to be slightly cloudy, it is well below maximum contaminate levels established by the Environmental Protection Agency (EPA) and is not harmful to health.
Turbidity has no health effects but can interfere with the disinfection processes practiced at the Grand Canyon National Park and may provide a medium for microbial growth. For those reasons, we routinely increase the chlorine residual of the drinking water and increase our 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, usually by late June or early July.
Grand Canyon National Park operates a Public Water Supply System licensed and approved by the EPA and by the ADEQ. All potable water provided by the Public Water Supply 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.