From the Valley Courier:
The health department’s final report (pdf) provides a comprehensive look at the disease 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.
The 65-page report concludes that animal waste most likely contaminated a concrete in-ground water storage tank that had several holes and cracks. 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. 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. “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 7 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.