Environmental Science & Engineering Magazine22 | March 2012

Wastewater Infrastructure

city’s south end. This is an area of Sud-bury that municipal engineers were par-ticularly concerned about, given the ageof the system (servicing began in 1960),the number of lift stations and force mainsdue to the rolling topography of the area,and the proximity of Nepahwin Lake.

The scope of the I&I study includedobtaining an understanding of the collec-tion system, monitoring of sewage flows,performing an assessment and analysis ofthe collection system, and developing aplan for remediation of the sewers. Thestudy began in the spring of 2009 withrainfall and sewer flow monitoring. Re-porting was completed by the end of 2011.

At the onset of the study, the Lo-EllenPark Area sanitary sewage system con-sisted of four sewage lift stations and as-sociated force mains, 13 km of sanitarysewers and 243 maintenance holes. RVAprepared mapping of the collection sys-tem in the study area, complete with trib-utary areas for each lift station, populationand demand information, and routing ofeach sewer.

In the summer of 2009, the City com-pleted a trunk sewage rock tunnel in thisarea, which allowed for the decommis-sioning of two lift stations. However, thesources of I&I in the collection systemwere not alleviated by the trunk sewer, sothe principal driver behind the study re-mained.

Assessment and analysisSix Hach Sigma 910 portable flow

The City of Greater Sudbury inOntario is reviewing options toincrease the operation effi-ciency of the various waste-

water treatment plants within its area.One facet of the wastewater treatmentsystem that has come under greaterscrutiny is the collection system. TheCity is concerned that a significantamount of water is entering the sewersfrom outside sources (e.g., rainwater andgroundwater), all of which flows to theCity’s 10 wastewater treatment plants.

In addition, capacity constraints in thecollection network at times overwhelm thesystem and cause localized flooding andthe need to discharge to the environment.

The City engaged R.V. Anderson As-sociates Ltd. (RVA) to complete an inflowand infiltration (I&I) study on the waste-water collection system in Lo-Ellen Park,which is a primarily residential area in the

monitors and submerged area/velocitysensors were used to monitor sewageflows. The monitors were installed inMarch 2009 and removed from service inearly February 2010. During the courseof the study, the City commissioned apermanent flow meter, hence one of theportable meters was relocated in order tomeasure flows in another region of thestudy area. Also, a portable AmericanSigma data-logging rain gauge was set upin a central location to collect rainfalldata for the study area. Flow monitor andrain gauge data was recorded at 15-minute intervals.

Flow monitors were equipped with re-mote communications by means of TelogRU-33 recording telemetry units. Theseunits were directly connected to theSigma flow monitors, and logged data asit was being collected. The telemetryunits would call the Internet serviceprovider at regular 12-hour intervals, viamobile telephone service, and report thedata recorded.

The website would then update therecords of the data channel for that instru-ment. Essentially, this equipment allowedstaff to verify the various data channels(e.g., flow depth, velocity, battery life,etc.) from their office, rather than makingsite visits. Field visits were made to eachsite roughly once per month to downloaddata manually, to perform a visual checkon the installation, and to change batter-ies if required.

Sigma flow monitors and Telogrecording telemetry units duringstudy.

Probe and band in sewer.

I&I study reveals several issues with Sudbury’swastewater collection system By Robert G. Langlois

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ES&E Mar2012_4_2012 12-04-09 9:30 PM Page 22

March 2012 | 23www.esemag.com

Wastewater Infrastructure

Raw data was collected from the flowmonitors and rain gauge and processedonce the study period was complete.Generally, flow was observed to increasein the sanitary sewers when rain oc-curred. Typically, peak flows in the sew-ers occurred roughly two hours after peakrainfall, but not all monitors reported ob-servable increases for every rain event.However, the observed increases insewage flow were typical of infiltration.

In addition to the flow and rain moni-toring, smoke testing was carried out onroughly 20 km of sewer and service lat-erals of the Lo-Ellen Park area. This test-ing involves forcing vaporized liquidsmoke into the sanitary sewer systemwith a portable high-powered fan. Theobjective of this portion of the investiga-tion was to confirm sewer configurationand identify I&I sources, as flow moni-toring alone does not provide a completepicture.

Typically, smoke is visible as it emitsfrom all openings into the sanitary sewersystem, such as roof vents and mainte-nance holes. However, occasionallysmoke is visible coming from pointswhere the sanitary system should not beconnected — such as roof downspouts orstorm sewer catch basins.

A media release was first issued toresidents advising them of the plannedwork, and a public open house washosted by the City to answer questions.Testing was carried out over a five-dayperiod in October 2009. In general, re-sults of the smoke testing indicated therewere no combined sewer, roof leader orfoundation drain connections. The testingdid provide information on one possible“indirect” connection, open cleanouts inlawns and possible sags in the sewer sys-tem. Five maintenance holes were iden-tified as possible heavy water inflowsources.

As part of the investigation, the Cityprovided footage of the closed-circuit tel-evision (CCTV) inspection performed onall the sewers in the Lo-Ellen Park area.RVA completed a review of the videosprovided by the City’s pre-selected serv-ice provider. CCTV was not completed inareas immediately upstream of lift sta-tions, at inaccessible maintenance holes,or where monitoring devices were in-stalled.

The CCTV investigation provided

qualitative information pertaining to thesewers in the area, which are composedof vitrified clay (VC), asbestos cement(AC) transite pipe, concrete andpolyvinyl chloride (PVC) pipe. In gen-eral, the older sections of pipe are in theworst shape. Many of the segments of VCand concrete pipe are beyond their usefullife. VC joints have separated and infil-tration is apparent, or some gaskets haveslipped off the concrete pipes. For the re-mainder of the pipes there are many

dented segments, sags or pipes “out ofround,” but pipe integrity is generallygood.

Plan for remediationRVA’s investigation of the sanitary

system in the Lo-Ellen Park area re-vealed that the system does not experi-ence high dry-weather infiltration, butdoes exhibit higher than average flowduring storm events. Normally, high re-sponse to storm events is due to inflow,

continued overleaf...

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Environmental Science & Engineering Magazine24 | March 2012

Wastewater Infrastructure

which is not generally occurring in theLo-Ellen area. Accordingly, infiltrationobserved in the sanitary sewer is likelyfrom groundwater from sources such aspipe joints and cracks, or at older brickmaintenance holes.

Other sources are weeping tile connec-tions to the sanitary service laterals, whichcould also be contributing through jointsand cracks. While the smoke testing didnot reveal direct weeping tile connections,homeowners have noted anecdotally that

their weeping tiles run to the sanitary sys-tem during rain events and spring runoff.

The study made the following addi-tional recommendations.• Disconnect water “blowoffs” (i.e., direct connections to sanitary sewers)• Educate the public about lot grading• Remove VC piping where replacement is warranted• Seal all brick and block maintenance holes• Add inserts to structures in road low points

• Implement open-grate storm maintenance-hole covers at road low points to help alleviate flooding of roads caused by catch basins frozen in under snow banks.

The CCTV videos showed pipes withan accumulation/buildup of grease in thearea of the 10 restaurants and two schoolsin the study area. RVA recommended thegrease should be cleaned from the pipesand sources addressed.

In addition, RVA recommended thatthe City educate residents of low-lyingareas about its new Preventative Plumb-ing Subsidy Program and encouragethem to implement this disconnectionprogram. For homes that do not haveweeping tile connections to the sanitarylaterals, RVA recommended the City en-courage residents to place the sump dis-charge outside the home to grade and notto laundry tubs or other sanitary sewerconnections.

Robert G. Langlois, P.Eng., is with R.V. Anderson Associates.

E-mail: rlanglois@rvanderson.com

Smoke machine.Smoke testing was carried out onroughly 20 km of sewer and servicelaterals of the Lo-Ellen Park area.

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