Hydraulic Modeling to Develop a Repeat Sampling Plan for Upstream and Downstream Locations Under the Revised Total Coliform Rule

摘要

The Philadelphia Water Department maintains and operates a distributionrnsystem which serves a population of approximately 1.6 million people nearly 275rnmillion gallons of water each day. This distribution system contains over 3,100rnmiles of water main and is divided up into 13 different pressure districts.rnOverall system water quality is tracked using 87 dedicated grab samplingrnstations spread throughout the city. Using these stations an average of 480rnsamples are collected per month for the presence of coliform bacteria and E. colirnfor compliance with the Total Coliform Rule (TCR).rnUnder the Revised Total Coliform Rule (Revised TCR), utilities may bernrequired to submit a sampling plan detailing their upstream and downstreamrnsampling locations for repeat sampling in the event of a total coliform or E. colirnpositive result. The existing requirement is to collect repeat samples within 5rnupstream and 5 downstream service connections. It is expected that the RevisedrnTCR will give States the flexibility to approve water systems who have the abilityrnto develop system specific, efficient, and effective repeat sampling plans.rnUpstream and downstream sites listed in these revised sampling plans may bernallowed to extend past the 5 service connection limit of the 1989 TCR. Upstreamrnand downstream sites may also be allowed to be deviated from on the actual dayrnof repeat sampling if it is the case that the system is not in routine operation.rnThis presentation will detail PWD’s efforts to develop the basis for itsrnupstream and downstream repeat sampling plan by the time the Revised TCRrngoes into effect. This will be accomplished by:rn1.Creating a GIS layer of all of our grab sampling locations. This layerrnwill identify the buildings which house each dedicated grab samplingrnlocation, as well as the building’s service connection. This will allowrnus to determine precisely which main is feeding each samplingrnlocation.rn2.Identifying average day flow patterns in the mains surrounding eachrnof our dedicated grab sampling locations. This will be accomplishedrnby running PWD’s InfoWater hydraulic model and analyzing thernsurrounding mains for their flow directions, as well as any reversals inrntheir flow directions over the average 24 hour day.rn3.Testing out the feasibility of editing and re-running the hydraulicrnmodel the day of repeat sampling. This would be useful for daysrnwhen we believe that flow directions in the mains surrounding arnparticular site may be different from that of the average day. Thesernflow direction changes could be caused by a variety of reasons. Thesernreasons include known valve closures (construction, small mainrnbreaks), large main breaks requiring lengthy repairs, reservoirs beingrntaken in and out of service for repairs, and other major operationalrnchanges from routine operation.