In order to
streamline the conversion of its 260 MGD system to chloramine in February 2004, the San Francisco Public Utilities Commission (SFPUC) and its consultants
developed an integrated water chemistry and operational strategy. This strategy provided
operational guidelines to the SFPUC and its wholesale customers for starting up the
chloramine disinfectant under a coordinated procedure designed to help smooth water
demand variations, convert the system quickly, minimize taste and odor complaints, and
meet all regulatory requirements.
Implementation of chloramine was driven by a need to reduce disinfectant byproduct
levels coupled with difficulty maintaining adequate free chlorine
residual in San Francisco's distribution system. The ability to establish an initial steady
state chloramine residual was a primary concern due to the distribution system's long
detention times, aged pipeline distribution network, high chlorine demand from unfiltered
source water, and the potential for prolonged blending with chlorinated water in
oversized reservoirs. This prompted the need for an integrated water chemistry and
operational strategy during initial chloramine implementation. The water chemistry
strategy was based in part on a detailed analysis of the complex distribution system
features (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 chemistry
strategy was considered to facilitate a smooth transition during the conversion period to
steady-state operations: a higher chloramine residual and lower chlorine-to-ammonia
ratio 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 was
twofold: to initially supply more free ammonia to blend with chlorinated water in the
distribution system and reduce potential for tastes and odors; and, to apply a higher
dose 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 Bay
Area served from the SFPUC regional system. The strategy was based on interviews
with senior SFPUC staff, water quality and hydraulic modeling, and an evaluation of
pump station, reservoir and booster chlorination operations. Travel time estimates were
used to coordinate the monitoring activities, and to plan pump station, reservoir
drawdown, and booster station shutdowns. Reservoir operating strategies to speed the
chloramine conversion included sequential drawdown, deep cycling, and temporarily
taking some reservoirs off-line. Scheduled re-fill was coordinated with the 29 wholesale
customers that draw water from the SFPUC system in order to spread the demand over
several days. Includes tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 12 |
| Published : | 11/15/2004 |
