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SOURCE - Winter 2016

www.ca-nv-awwa.org 11 “No coliforms have been detected; turbidities are less than 1 NTU.” chlorination with the on-board chlorine dosing pump. The chlorine addition process, however, requires planning and is relatively slow. It can take several hours to break point 1,000 feet for an eight-inch main. Operating costs are dependent on the sediment loading of the pipe and the resulting number of filters required per mile of pipe flushed. Other factors that affect operating costs include the fuel costs to power the truck’s pump and the savings from not having to replace the water previously discharged through conventional flushing. In order to be effective, the zero discharge truck requires the use of unidirectional flushing, but, unlike with conventional unidirectional flushing, the source of the water does not necessarily need to be clean. (Ed. Note: An illustration of a typical flushing operation is shown in the Table of Contents.) Per NO-DES and SJWC’s own standing operating procedures, the truck is disinfected only when it is not in use for more than 30 days. During operation, the truck is continuously disinfected by the chlorinated water from the distribution system passing through it.  After flushing, the water is returned to the distribution system as a matter of standard operating procedure, but no water is discharged to the storm drain other than when folding the hoses at the end of the day and emptying the filter vessels to decrease weight. This amounts to approximately 500 gallons between hoses and filters. We take a weekly coliform sample on the filtered effluent being returned to the distribution system and have not had a detect in six months of use. We are working on studying biofilm removal, pre- and post- flushing dissolved metals, and filter waste hazardous wastes characterization.   Whether or not a utility decides to use a zero discharge flushing truck, it should be able to address internal and external questions on the need for flushing, the frequency at which its distribution system should be flushed, and the effectiveness of the flushing program in maintaining water quality. To that end, SJWC is cooperating with other utilities on developing a study to document pre- and post-flushing water quality, the effectiveness of zero discharge flushing in removing biofilm and controlling nitrification in water mains, and the required flushing frequency of its distribution system to proactively improve water quality. There is currently no formal permitting in District 17 (Santa Clara County) of the California Water Resources Control Board Division of Drinking Water (DDW) for the zero discharge truck. However, it is possible that, as other utilities bring on-line this or similar flushing trucks, DDW may require a formal permit application and impose distribution or treatment licensing requirements. The DDW District 17 Engineer has reviewed SJWC’s Standard Operating Procedure for the flushing truck and conducted a field inspection to see the truck in operation, and SJWC is required to provide DDW with copies of its monthly flushing log sheets. SJWC is also preparing a report on the use of the flushing truck, coliform detections associated with flushing, customer feedback, chlorine residual data, turbidity data, and the velocities maintained during flushing as well as an overall evaluation of the system. It should be noted that no coliforms have been detected as of this writing, and that turbidities post-flushing in the mains are always much less than one NTU. —Francois Rodigari, San Jose Water Company S OPERATIONS The conversation starts here In Brown and Caldwell’s online 1Water series, water leaders are talking about new technologies, inter-agency collaboration and non-traditional approaches to secure this precious resource for generations to come. Join the conversation, and share your insights at bc1Water.com


SOURCE - Winter 2016
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