AWWA WQTC58971

In search of a less labor intensive and costly solution to the problem of losing disinfectant residual, the Southern California Water Company - Southwest District (District) implemented a study to investigate the long-term effect of polyphosphate based corrosion inhibitors on disinfection residuals, hydraulics, and water quality. The major objectives of this study were to: determine the relationship between the application of the polyphosphate blend and chlorine residual level; determine the effect of the addition of the polyphosphate blend on biofilm accumulation within the distribution system; determine if customer complaints due to color were reduced after the addition of the polyphosphate blend; and, determine if customer complaints due to taste, odor and particles were reduced after the addition of the polyphosphate blend. The addition of the polyphosphate blend started on November 6, 1998, in a small, isolated area of the distribution system less than 1 mi2 and was expanded on June 17, 1999 to approximately 3.6 mi2 in size. Pipe diameters in the study area vary from 4 to 12 inches in diameter and material composition is approximately 50% unlined cast iron, 25% cement-lined cast iron and 25% asbestos cement pipe. The study area is approximately 80% residential and 20% commercial and light industrial facilities and is representative of the rest of the distribution system. The polyphosphate blend was initially added to one groundwater source and then expanded to five more groundwater sources and one surface water connection. In November of 2002, two more groundwater sources and one surface water source were added. The addition of at least two more groundwater sources to this program is planned for the end of this year or the beginning of next year. Currently, the polyphosphate blend is added to five groundwater sources and two surface water connections. Each source is disinfected with a chloramine dose of 1.2 to 2.5 mg/L. The chloramines are formed by combining free chlorine with natural ammonia in the well water, or by adding a 19% strength ammonium hydroxide solution at a Cl2 to NH4-N ratio of 5:1 to chlorinated water. Dosing of the polyphosphate blend is set according to the following: 1 mg/L per mg/L of iron and manganese plus all divalent metals, 1 mg/L per 200 mg/L of hardness measured as CaCO3, plus 0.15-0.3 mg/L for residual and corrosion control. At all sites the polyphosphate blend solution is injected after the chlorine and/or ammonia addition at the plant effluent line. To evaluate the study objectives, water quality constituents are currently collected at seven distribution sites, which are representative of the plant sites. In addition to the seven primary locations, water quality samples are also collected from the wells and up to 25 other locations within the distribution system. This paper summarizes and discusses results obtained from one specific area of the distribution system as described before. All the water sources for this area are treated with the polyphosphate blend, and water quality data from this area has been collected since June of 1998. Includes 16 references, tables, figures.