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Proposal <br />Comprehensive Water Distribution System Audit <br />~ <br />As an example, for a tmcer concentration, of 50,000 <br />mg/L, and a trocer flow rate of 0.01 gpm, and a <br />downstream tracer concentration of 5.0 mg/l, the process <br />flow rate is calculated as, <br />0.05 x 50,000 =(Q + 0.05) x 5.0 <br />500=5Q+0.05 <br />0 =100.01 gpm <br />Theseledionofthetraceriscritical. Thetracercannatread <br />with any of the ather compounds i n the process flow for the <br />procedure to be accurate. Additianally,itisdesirobletouse <br />a tracer that is not present in the process flow, because the <br />need for o bockground sample upstream of the point of <br />traceraddition iseliminoted. <br />Mizing in fhe pipeline is imporfant. The basic assumptian is <br />thatthe tracer will be uniformly mixed with the process flow <br />so that the downstream tracer roncentmtion measured is on <br />occurate indication ofthe adual downstream concentration. <br />The rate of tracer oddition must be known with good accurary <br />for this method to be used. The rate of tracer addition is <br />usually determined bytiming the draw down in the calibrated <br />tracer cantainer. for this reason a groduated rylinder is <br />usually used as the container. The metering pump must <br />pump at a constant rate, therefore, multiple volume readings <br />are token on the mlibrated container. <br />Transfer Standard <br />The use of a transfer standard to calibrate flow meters is <br />relatively common place; however, it is important to <br />document that the transfer standard is properly mlibrated. <br />Transfer standards used for flow meter calibration usually <br />include either clamp-on ultrasonic meters or pitat tubes. If <br />used mrredly, either instrument can function adequatelyas <br />a transfer standnrd. A rypical transfer standard installation <br />isshown in Figure 5. <br />It is important that the recommendations for proving an <br />undisturbed flow path both upstream and downstream of <br />Carter -Burgess <br />the transfer standord be fol lowed. Additional Iy, the transfer <br />standard should 6e calibrated before gaing to the field, and <br />after being used in the field. <br />For pitat tubes, the assumptian that the averoge flow in the <br />pipe is being measured is impodant. Pipes exhibit a <br />parabolic velocity profile, and multiple measurements are <br />required to obtain accurote results. <br />Aker evaluating each meter's installatian, the Corter 8 <br />Burgess Team will use the in situ calibration procedure that <br />is mast appropriate for each meter. <br />Leak Detection <br />The location of leaks in the distribution system can be very <br />challenging. One of the most common ways to locate leaks <br />is to use geophones and listen for leaks in the system. This <br />procedure is generally quite precise, and it will pravide <br />some relative indication of the size of the leak. However, <br />the procedure is best employed when the approximate <br />location of the leak is known. For a distribution system <br />wide study the ezclusive use af sonic detection methods is <br />generally cost prohibitive. <br />Fortunately, there are some steps that con be taken to narrow <br />down the areasto be investigated. In most cities the night- <br />time water consumptian for residentiaVcommercial uses is <br />quitesmall,especiallybetween2amond4am. Duringthis <br />ti me, portions of the distribution system can be isolated and <br />water elevations in the elevated tanks monitoied. falling <br />water elevotions are an indication of possible leoks. <br />18 <br />