AWWA WQTC60690

In order tostreamline the conversion of its 260 MGD system to chloramine in February 2004, the San Francisco Public Utilities Commission (SFPUC) and its consultantsdeveloped an integrated water chemistry and operational strategy. This strategy providedoperational guidelines to the SFPUC and its wholesale customers for starting up thechloramine disinfectant under a coordinated procedure designed to help smooth waterdemand variations, convert the system quickly, minimize taste and odor complaints, andmeet all regulatory requirements.Implementation of chloramine was driven by a need to reduce disinfectant byproductlevels coupled with difficulty maintaining adequate free chlorineresidual in San Francisco's distribution system. The ability to establish an initial steadystate chloramine residual was a primary concern due to the distribution system's longdetention times, aged pipeline distribution network, high chlorine demand from unfilteredsource water, and the potential for prolonged blending with chlorinated water inoversized reservoirs. This prompted the need for an integrated water chemistry andoperational strategy during initial chloramine implementation. The water chemistrystrategy was based in part on a detailed analysis of the complex distribution systemfeatures (multiple treated water reservoirs in series with detention times up to 30 days).Since the conversion was anticipated to take a few weeks, a multi-stage water chemistrystrategy was considered to facilitate a smooth transition during the conversion period tosteady-state operations: a higher chloramine residual and lower chlorine-to-ammoniaratio for the first 3 weeks, followed by a lower chloramine residual and a higher chlorine-to-ammonia ratio for steady-state operating conditions. The purpose of this strategy wastwofold: to initially supply more free ammonia to blend with chlorinated water in thedistribution system and reduce potential for tastes and odors; and, to apply a higherdose than ultimately desired at steady state to speed conversion in the distribution system.The strategy involved coordination with the 29 wholesale suburban customers in the BayArea served from the SFPUC regional system. The strategy was based on interviewswith senior SFPUC staff, water quality and hydraulic modeling, and an evaluation ofpump station, reservoir and booster chlorination operations. Travel time estimates wereused to coordinate the monitoring activities, and to plan pump station, reservoirdrawdown, and booster station shutdowns. Reservoir operating strategies to speed thechloramine conversion included sequential drawdown, deep cycling, and temporarilytaking some reservoirs off-line. Scheduled re-fill was coordinated with the 29 wholesalecustomers that draw water from the SFPUC system in order to spread the demand overseveral days. Includes tables, figures.

Product Details

Edition:

Vol. - No.

Published:

11/15/2004

Number of Pages:

12

File Size:

1 file , 8.1 MB