AWWA WQTC62508

AWWA WQTC62508 Balancing Source Water Quality and Quantity During Drought
Conference Proceeding by American Water Works Association, 11/01/2005

Moss, Linda R.

More info

Full Description

A drought cycle began in Salt Lake City in 1999 and persisted through 2004. In 1999, the reserves in the UpperReservoir were drawn down to provide drinking water. It was anticipated that runoffwould happen again sometime in the foreseeable future and fill it back up. The next fouryears did not see much in the way of runoff. The decision was made in 2000 tominimally utilize Parleys Treatment Plant and purchase water from neighboring utilitiesthat had more storage. The flow through volumes in the Lower Reservoir went from20,000 acre-ft to less than 5,000 acre-ft annually. The Upper Reservoir did not fill untilthe spring of 2005 after a heavy winter. No water was released andvery little was treated from the Lower Reservoir during 2000 through 2004. Very smallreleases were made from the Upper to the Lower Reservoir to provide what wasabsolutely necessary for treatment during 2000 to 2004. The Lower Reservoir became anessentially closed system, and water quality problems started to occur in 2002. In late October of 2002 Parleys Treatment Plant was called upon to produce water afterbeing off for about nine months. The algae counts in the raw waterwere about 202,000,000/100L. The predominant organism was Oocystus Gigal. Whilethis organism is not a taste and odor problem, it forms a slime coating which made it verydifficult to coagulate and remove in the treatment process. Good floc appeared to formjust fine. Then the floc broke up across the sedimentation basin, and unfilterable waterresulted at the end. Eventually, 60 mg/L of ferric chloride produced a settleable andfilterable floc. The normal dose for the treatment plant was 5-10 mg/L. This incidentprompted a closer look at what had been happening to water quality on the reservoirduring the drought. In general, DO decreased and TDS increased as the reservoir annual flow throughamounts decreased. This paper discusses improvements due to measures that were taken during the summer of 2004. Includes figures.