AWWA WQTC62373

In November 2000 the Washington Aqueduct (WA), the water treatmentprovider to the District of Columbia, switched its disinfectant from chlorine tochloramines in order to reduce disinfection byproducts (DBP). This disinfection changeproved successful as total trihalomethanes and halo acetic acids decreased considerablyin the distribution system, which is operated by the District of Columbia Water & SewerAuthority (DCWASA). However, accompanying this change was an increase in 90thpercentile lead compliance levels from 12 parts per billion (ppb) to 70 ppb.DCWASA conducted lead profiles that showed average peak concentrations up to150 ppb in homes with lead service lines. (Giani, Edwards, et al. - 2004). Review of theprofiles indicated that the majority of the lead was dissolved coming from the leadservice lines. In Spring 2004, a desktop study and several pipeloop research projects evaluateddifferent corrosion control options and identified orthophosphate as the most optimalcorrosion control treatment. In June 2004, orthophosphate was added to an isolatedsection of DC's distribution system and studied. Several lead profiles were conductedalong with routine water quality field monitoring during that time.In August 2004, the Washington Aqueduct began adding orthophosphate in theform of phosphoric acid at its treatment plants. Entry point residuals were slowlyincreased over a two-week time frame to 3.5 mg/L as PO₄. Over the next 12 months,WASA studied the formation of lead phosphate and the stability of the phosphate scale inthe distribution system through the data collected from lead profiles.This paper discusses the results of the research conducted prior to and after thestart of orthophosphate corrosion control. Specifically this paper describes proceduresand results from laboratory circulation loops and lead profiles conducted at residentialhomes with lead service lines in relation to the lead concentrations being released, thetype of lead being released (i.e. dissolved Lead-II or particulate Lead-IV), and the amountof time for the orthophosphate to properly passivate the lead in the service lines. Includes 3 references, figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2005

Number of Pages:

16

File Size:

1 file , 400 KB