Sometimes environmental engineers are called upon to venture into areas of practice that are somewhat unknown or to make on-the-spot decisions and recommend immediate action.  This lecture reviews two crisis situations in which Dr. Logsdon made water treatment recommendations without the benefit of detailed engineering studies or research on the specific problem at hand.  It is instances such as these that challenge the engineer’s creative ability and the sum total of his or her experience.

Carrollton, Georgia
A waterborne disease outbreak with an estimated 13,000 cases caused by Cryptosporidium parvum took place in Carrollton, Georgia in January and early February of 1987.  The Centers for Disease Control investigated the outbreak and reported that Cryptosporidium oocysts had been found in filtered water.  The US EPA dispatched Dr. Logsdon to assist CDC in dealing with the outbreak.

A rapid literature review on Cryptosporidium revealed no treatability studies on the filtration of the oocysts, and the only studies of disinfection effects had shown disinfecting chemicals to be ineffective against Cryptosporidium.  It was judged that chlorination should not be counted on for effective treatment, leaving filtration as the only effective barrier to passage of the oocysts into treated water. However, extensive research had shown that by attaining very low filtered water turbidity, very high percentages of bacteria, soil particles, and viruses could be removed.  Dr. Logsdon’s own work had proven filtration could remove asbestos fibers and Giardia cysts.  Because most particles in water have a negative zeta potential, Dr. Logsdon theorized the oocysts were also likely to be negative at water treatment pH values and, therefore similarly behave. The key to effective treatment was attaining the lowest practical filtered water turbidity, preferably below 0.10 ntu.   

Investigation at the Carrollton plant found that the filters were sometimes stopped and then restarted without backwashing.  This was suspected to permit oocysts to pass through the plant.  Numerous operating changes were recommended and implemented. As a result, filtered water with turbidity lower than 0.10 ntu was consistently produced and further outbreaks avoided.

Salem, Oregon
In February, 1996 massive flooding occurred in the Cascade causing the turbidity of the North Santiam River to rise to about 100 ntu. This river supplies Salem, Oregon, which uses slow sand filters for treatment.  This level of turbidity could prematurely  plug the filters and cut off the drinking water for about 100,000 people.  Pretreatment of the water was necessary.

The slow sand filters were located on a very large island in the river and fed by because of the gradient of the river and the slope of the island.  Fortunately, a box culvert, a wide channel, and a large pond were also present on the island.  These were converted by  design for flow measurement, rapid mixing, flocculation, and sedimentation functions

Dr. Logsdon directed Salem’s public works crews in location of chemical feed points, construction of rock wing walls to promote flocculation, and flow measurement so chemical dosages could be set.  This “design-build” job was completed in one working day, and operating crews from Salem maintained this ad-hoc system for a number of weeks until the turbidity subsided.  Treatment was successful, with 90% reduction of turbidity by the end of the first day.  The slow sand filters did not clog prematurely and Salem’s water supply was not interrupted.
 

Both of these crisis situations were successfully resolved by creative application of engineering concepts and principles and by the willingness of everyone involved to take actions that seemed appropriate based on engineering principles, even in the absence of studies proving the recommended actions would work as intended.

Avoiding Waterborne Disease Outbreaks by Understanding Prior Outbreaks
In August, 2003 a massive electric power blackout occurred in the United States and Canada, affecting millions of people.   On Wednesday, August 20 the Traverse City Record Eagle printed an article entitled “Putting pieces together.”   This article included the following paragraph: “‘In order to have a big problem, you have to have three or four bad things happen all at the same time,’ said Hoff Stauffer, a power transmission consultant with Cambridge Energy Research Associates.”  A similar concept is generally applicable to waterborne disease outbreaks, as explained in this lecture.

Water utilities need to be aware of the circumstances that can cause waterborne outbreaks so they can be better prepared to prevent them.  Recently published papers have indicated that outbreaks may be related to prior episodes of heavy runoff, which can be an important factor.  However, waterborne outbreaks are generally associated with not just one problem or event, but with the coincidence of a combination of problems or events, a single one of which might not have caused a disease outbreak. This lecture reviews several outbreak case histories from the USA and Canada, showing how the occurrence of two or more events or problems in the same time frame could have led to the passage of pathogens into the drinking water and thus caused the outbreak of concern.

Because of this association of outbreaks with multiple problems, changes in source water quality may signal increased risk.   At treatment plants where filtered water quality varies widely and turbidity excursions occur, the risk to public health is greater.   Treatment plant operators who maintain optimized treatment and excellent filtered water quality in spite of source water quality changes should expect to be successful in preventing waterborne disease outbreaks among the general population in the communities they serve. 

Included are discussions of outbreaks of cryptosporidiosis at Talent, Oregon; Carrollton, Georgia; Milwaukee, Wisconsin; and North Battleford, Saskatchewan; outbreaks of giardiasis at Berlin, New Hampshire and in a small Colorado community; and the Walkerton, Ontario outbreak caused by E. coli.

Information presented in this lecture should help engineering students understand the concept that multiple factors tend to increase the risk of transmitting pathogens in public drinking water supplies.  This concept is the basis for the public health practice of employing multiple barriers for protection of source water and treatment of drinking water.