Animal waste contaminated one of Alamosa’s concrete in-ground water storage tanks that had several holes and cracks, causing last year’s deadly Salmonella outbreak in the Colorado town according to a new report. 

drinking_water_glass.jpgColorado’s Department of Public Health and Environment blames animal waste entering Alamosa’s public water supply as the reason why one person died, 442 were sickened, and the whole town was forced to depend upon state National Guard deliveries for drinking water when Salmonella contamination prevented the use of public water.

In a 65-page report released Wednesday, state health officials said a water sample collected during the outbreak indicated that water in the tank contained bacteria.

Additional site visits conducted in 2009 found animal footprints in the snow around the tank, and a photograph in July 2009 captured bird feces on a corner of the tank that was repaired at the time of the outbreak, the report states.

While these observations were made in 2009, they likely are representative of the animal activity that could have contaminated the water supply in the tank in 2008.

Overall, state health experts estimate that up to 1,300 people may have been ill in the town of 8,900. For about three weeks during the outbreak, Alamosa residents were advised to drink bottled water or boil their water, and many businesses temporarily closed.

The health department’s final report provides a comprehensive look at the Salmonella outbreak, the response to the outbreak, and the conclusion of the 18-month investigation into how the city’s drinking water became contaminated.  The investigation involved a detailed review of the water system; historical records; and interviews with city of Alamosa personnel, local health officials and responders to the outbreak.

”We believe the people in Alamosa deserve to know what happened, what was done about it and why it happened,” said Ron Falco, Safe Drinking Water program manager in the Water Quality Control Division at the department.

“We cannot say with absolute certainty where the Salmonella came from because the actual contamination event was not directly observed, and probably occurred at least seven to 10 days before the outbreak was reported,” Falco acknowledged. “But after weighing all the evidence, we believe that the most likely scenario is that contamination entered this in-ground storage tank.”

The city commissioned an inspection of the in-ground storage tank in July 1997 by a professional tank inspection company. That inspection report noted cracking and problems with the corners of the tank, and recommended routine inspections for the future. It appears that the tank continued to deteriorate into 2008.

The state did not know of the city’s 1997 inspection findings, and its own inspections did not focus on storage tanks and distribution piping.

Alamosa was granted a waiver from state requirements to disinfect its drinking water in 1974, so water being served to the public in Alamosa at the time of the outbreak was not chlorinated.

The investigation showed that only a small quantity of bird or animal feces contamination may have led to the salmonella outbreak. This kind of outbreak may have been very difficult to prevent in a system that did not chlorinate its water.

The state is continuing its review of all public drinking water systems with disinfection waivers, and has withdrawn 72 of them since the Alamosa outbreak. “This incident further underscores the long-accepted public health benefits associated with disinfecting drinking water,” said Falco. “Chlorine is a highly effective means of destroying bacteria such as Salmonella.”