AWWA QTC98358

In 1990, the Town of Hopkinton, MA, instituted feed of a polyphosphate sequestrant in two of its five wells to address colored water complaints caused by source water iron and manganese. Failure to meet the lead and copper Action Levels and continuing intermittent red water prompted Hopkinton to seek an alternative treatment strategy. After analysis of the water qualitites of the different wells, scales on some lead service lines, operation patterns, location of lead service lines, and distribution system configuration, a combination of sodium silicate (with chlorination) and sodium hydroxide addition at different wells were investigated. The alkalinity of the water was sufficient that a product with a ratio of 1.6 was preferable to the more widely used "TypeN" (3.22 ratio). Overall, the treatment change reduced 90th Percentile lead and copper levels by at least 90%, enabling compliance with the Lead and Copper Rule. Two major operational problems were encountered during the study, loss of pump suction and feed system clogging during winter months. Redesign of the feed system and the reduction of solids content of the silicate chemical by the manufacturer solved the two problems. This study showed that simultaneous overall corrosion control and sequestration of iron and manganese is possible for many small water systems with multiple wells and entry points, without the adverse consequences to drinking water and wastewater associated with polyphosphate addition. The aesthetic quality of the drinking water was equal or superior to prior treatment. The higher pH and silicate combination is also more compatible with protecting A-C and cement-lined pipes.

Product Details

Published:

01/01/1998

ISBN(s):

0898679796

Number of Pages:

14

File Size:

1 file , 250 KB