Trenchless Technology

NOV 2018

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W W W.T R E N C H L E S S T EC H N O LO GY.C O M 47 Initially, the City focused on rehabil - itation and repair of public sewers to address the I/I issue. Pre-construction flow meters were installed in the spring 2014 to quantify sewer flows prior to rehabilitation efforts. The $6.25 mil - lion Phase I Rehabilitation Program, initiated in Flow Meter areas FM3 and FM12, consisted of the following: • Lining of approximately 57,400 ft of mainline sewer pipe; • Spot replacement of collapsed sew- er pipe in 75 locations; • Service lateral connection lining of approximately 1,445 service later- als; and • Lining and rehabilitation of ap - proximately 340 manholes. Following the completion of con- struction work, a post-construction flow metering program was conducted in spring 2016 utilizing the same tem- porary flow meters in FM3 and FM12 that had been used prior to construc- tion. Using this flow meter data, to- gether with pre-construction metering results and data from the permanent flow meters, allowed the project team to determine the extraneous flow re- moved because of rehabilitation ef- forts on the public sewer system. As can be seen in Figure 1, the average dry weather flow in FM3- North during the nighttime hours, when approximately 90 percent of the flow is from infiltra- tion, was reduced from 0.36 mgd in spring 2014 prior to rehabilitation, to 0.28 mgd in spring 2016 after reha- bilitation. This equates to a 22 percent reduction of base infiltration because of rehabilitation of the public system only. As such, the goal of 50 percent I/I removal could not be achieved by simply rehabilitating the public sewer system. As result, the City decided to embark on a comprehensive rehabilita- tion approach that would address both public and private I/I sources. Based on local knowledge of the system, it was stipulated that sump pumps were likely the most common private inflow source in the City along with roof leaders and driveway drains. The first step in the identification and removal of private inflow sources was the initiation of a Sump Pump Amnes- ty Program (SPAP) to encourage partic- ipation. In addition, the City amended local ordinances that provided for enforcement of illegal discharges of unpolluted water into the City sewer system. The amendments required building owners to redirect any illicit sources from the sewer system. These sources included, but were not limited to, sump pumps, roof drains (gutter downspouts), yard drains, driveway drains and patio drains. Following a multi-year private in- flow removal program, an analysis was conducted by comparing similar rain events occurring before and after private inflow sources were removed in FM3. A storm event that occurred on Sept . 30, 2015, lasting 11.5 hours (from 3 a.m. to 2:30 p.m.), and pro - ducing 1.74 in. of rain was used for estimating the I / I prior to removal of private sources. A storm event that occurred on Oct . 9, 2016, lasting 14.5 hours (from 6 a.m. to 8:30 p.m.) and producing 1.70 in. of rain was used for estimating the I / I after removal of pri- vate sources. The peak flow observed as a result of the rainfall in 2015 was 3.73 mgd, while the peak flow due to rainfall in 2016, following the remov- al of 258 private inflow sources, was 2.13 mgd. This equates to a 43 percent reduction in inflow as a result of the private inflow removal program. The results of this project indicated that the implementation of a compre- hensive rehabilitation program of the public sewer collection can remove as much as 22 percent of infiltration. Furthermore, an aggressive and dili- gent private inflow identification and removal program, if successful , can remove as much as 43 percent of the private inflow within a particular flow meter area. The combination of these two programs focusing on public and private inflow sources could remove up to 65 percent of the extraneous flow in a sewer collection system. In conclusion, the City was able to achieve the goal of 50 percent I/I reduc- tion by addressing both the public and private sources of I/I. The public sourc- es were primarily removed by lining all mainline sewers; lining all service lat- eral connections from the main to the first joint; lining all manholes rehabili- tation of sewer lines by CIPP lining , lin- ing of manholes and grouting of service lateral connections. The private sources were primarily removed through the Sump Pump Amnesty Program. Nicholas J. Rystrom, P.E., is with the City of Revere, Massachusetts. Jonathan E. Kunay, P.E., is with CDM Smith, Boston. Ahmad Habibian, Ph.D, P.E., is with CDM Smith, Fairfax, Virginia. Figure 1. Infiltration Removal in FM3-North from Comprehensive Rehabilitation of the Public System

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