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When do bacteria in our surface waters present a public health risk?

Submitted by June 28, 2011 10:05 am

thumnail

I have to admit that, as I write this, I do not have an answer to the question that I just posed. I must also admit that this question has plagued me for some time and without training in public health issues, I feel ill-equipped to draw conclusions. Thus, I am writing about it here in an attempt to unpack this complicated issue. I will discuss the facts about bacteria in our watershed and general public health implications, allowing you to draw your own conclusions.

Fact #1: Escherichia coli (E. coli) bacteria are members of a group of bacteria known as fecal coliforms. These bacteria originate in the intestines of warm-blooded animals. The presence of E. coli in surface waters means that the water has been contaminated by fecal material. Bacteria is naturally present in surface waters at low concentrations. At high concentrations, it indicates that something in the watershed is contributing excess bacteria: agricultural runoff, domestic sewage contamination, wastewater treatment plants, septic systems,or runoff from areas heavily contaminated with pet waste. While high concentrations suggest a problem, E. coli is not really the thing to be concerned about. Only a few strains of E. coli cause illness in humans. Because it is impossible to test for every possible disease-causing organism, E. coli is used as an indicator–if E. coli is present in surface waters it means that more harmful microbes could also be present, like Cryptosporidium, Giardia, Shigella, and norovirus. These are known water-borne pathogens and present a very clear risk to the health of humans that come into contact with that water. Diseases acquired from contact with contaminated water can cause gastrointestinal illness, skin, ear, respiratory, eye, neurologic, and wound infections. The most commonly reported symptoms are stomach cramps, diarrhea, nausea, vomiting, and low-grade fever.

The USEPA’s recreational water quality standard for E. coli is 235 Colony-Forming Units (CFU) per 100 milliliters. This standard corresponds to approximately 8 incidences of gastrointestinal illnesse per 1000 swimmers. Because of the risk to public health, when bacteria concentrations exceed this standard, beaches and swimming areas are closed to the public until bacteria concentrations come down to safe levels again.

Fact #2: Neither Watson Lake or Granite Creek are currently “impaired” for E. coli bacteria. However, it is considered a pollutant of concern. Past testing by Prescott Creeks and ADEQ has revealed consistently high levels of bacteria in Granite Creek and its tributaries (not so much Watson Lake), especially after precipitation events (see the image gallery on the “first flush“).

Fact #3: Because E. coli levels frequently exceed the state’s surface water quality standard, Granite Creek is expected to be listed by the EPA in 2012 as impaired for bacteria. This will be in addition to Granite Creek’s current impairment for low dissolved oxygen and Watson Lake’s current impairment for high nutrients and high pH (2004). Granite Creek is also expected to be listed for nutrients in 2012. With pathogens being the 2nd leading cause of water quality impairment around the US (sediment being the first), it looks like our very own waterways will be joining the ranks of many others around the nation.

Fact #4: Granite Creek and its tributaries are Waters of the U.S., meaning that they are protected by the federal Clean Water Act and are held to a “fishable/swimmable” water quality standard, i.e.; water quality in our creeks and lakes should support safe recreation and the protection and propogration of fish, shellfish, and wildlife. So even though our creeks are dry part of the year and, when they do flow, they don’t provide the best places for swimming and wading, the water should be safe enough for us to do so if we wish.

We know that people get in the creeks, if only anectodally. We have 9 named creeks that flow through Prescott, roughly 1800 private property owners bordering those creeks, and numerous trails that provide access to the creeks. People come into contact with the creeks all the time–it may be hard to estimate numbers, but I think it would be hard to dispute this fact.

Armed with this information, I’ll pose the question again: in the Granite Creek Watershed, where there are no official swimming areas and our creeks are dry for part of the year, do high bacteria levels present a public health risk? I am beginning to think that the answer to this question is ‘yes.’

What do you think?