Study Description and Setup

The polyphosphate-blend-addition pilot study began in November 1998, in a less than 1 mi2 isolated area of the distribution system. The District expanded the study in June 1999 to about a 3.6 mi2 area. Pipes in the study area vary from 4 to 12 in. in diameter and are approximately 50 percent unlined cast iron, 25 percent cement-lined cast iron, and 25 percent asbestos-cement pipe. The study area, comprised of approximately 80 percent residential and 20 percent commercial and light industrial facilities, is representative of the rest of the distribution system.
Polyphosphate-blend solution was added at the effluent of five groundwater plants and at a treated surface water connection from Metropolitan Water District of Southern California. Each water Source was disinfected using chloramines at a concentration of 2.5 to 4.0 mg/L total chlorine.
The polyphosphate-blend dose varied based on water quality parameters. It was dispensed at a rate of 1 mg/L per 1 mg/L of iron (Fe), manganese (Mn), and all divalent metals, plus 1 mg/L per 200 mg/L of hardness measured as calcium carbonate (CaC03) and 0.15-0.3 mg/L for polyphosphate-blend residual and corrosion control. In all cases, thc polyphosphate-blend solution was injected after the chlorine and ammonia addition in the plant effluent line.
To evaluate changes in water quality, a number of parameters (Table 1) were measured regularly at five primary distribution system locations, each representing one of the plants. The same parameters were also monitored at each of the groundwater wells and 25 other locations within the distribution system. At each of the distribution system monitoring sites, orthophosphate was measured weekly, and heterotrophic plate counts (HPC) and total coliforms were monitored monthly, to determine bacterial activity. Background data -were collected three weeks prior to the startup of the pilot study at four of the five primary distribution system locations.