Sanitary Sewer. Infiltration & Inflow (I/I) Study. Presented by:

Transcription

1 Sanitary Sewer Infiltration & Inflow (I/I) Study City of Beatrice, Nebraska IAWEA Collection System Specialty Conference Presented by: Brian Mulinix, P.E. March 10, 2011

2 Discussion Topics Definition of Infiltration & Inflow Criteria for Evaluating Background and Current System Review & Discussion of Results What Has Been Done Planning Your System Study

3 Infiltration Definition Enters sewer system from ground Defective pipes, joints and connections, manhole walls Expect year-round, but influenced by groundwater fluctuations Broken Pipe Tree Root Bad Joint

4 Inflow Definition Enters sewer system as direct connection Sump pumps, roof leaders, foundation/surface drains Roof Leader Not linked to groundwater levels Misalignment Creek Inlet

5 Infiltration/Inflow Illustration

6 Evaluation Criteria

7 Infiltration Evaluation Criteria Population Based 1991 EPA criteria Non-excessive 130 gal/capita/day Sum of domestic base-flow & infiltration over 7-14 day average at high groundwater levels

8 Infiltration Evaluation Criteria (cont.) Sewer Based Developed from Federal grant programs Leakage quantified as gal/day/inch-diameter- mile Non-excessive < 1,500 gpd/idm, but as high 10,000 gpd/idm Standardized units for ranking or prioritizing subsystems for further study

9 Inflow Evaluation Criteria Population Based 1991 EPA criteria Non-excessive 275 gal/capita/day total daily average storm flow Regardless, considered excessive if sewer collection system or treatment plant experiences hydraulic overload

10 Inflow Evaluation Criteria (cont.) Rainfall / Inflow Volume Relationship Massachusetts Department of Environmental Protection Total inflow volume correlated to total rainfall produced from the storm No threshold; expressed as gal/lineal foot sewer Inflow Severity, used to prioritize subsystems for evaluation

11 Background of System

12 Background City of Beatrice 12,600 population Sewers date back to ,000 lineal feet sewer 570,000 lineal feet sewer Seven lift stations, six inverted siphons I/I Problems exhibited and studied early s Extreme WWTP Hydraulic Overloading

13 Drainage Basin Map D E C B A

14 Lid of Manhole D8 lifted off from rim due to excessive flow during a July 17, 2008 storm. Evidence of significant flow discharged from manhole. Located on a gravity sewer downstream of L.S. #1. Excessive Storm Events

15 Direct Connections Discovered Water flowing from river Flow entering Manhole D11 directly from river. Overflow pipe effluent flap valve was closed and completely submerged in river.

16 Equipment Evaluated Lease versus Purchase Consider length of study Regular maintenance Flow Monitor ISCO 2150 Area Velocity Meter Rain Logging ISCO 674 Rain Gauge

17 Installation Considerations

18 Discussion of Results

19 Basin D Infiltration Rate: 166 gpm Criteria: 234 gpcd 941 gpd/idm

20 Sub-Basin D 20 Infiltration Rate: 68 gpm Criteria: 345 gpcd 3,661 gpd/idm

21 Basin E Infiltration Rate: 99 gpm Criteria: 202 gpcd 1,904 gpd/idm

22 Basin D Inflow 1-yr Storm: 0.33 Mgal Aver. Storm: 358 gpcd Severity: 2.1 gal/lf

23 Sub-Basin D 20 Inflow 1-yr Storm: 0.20 Mgal Aver. Storm: 632 gpcd Severity: 14.0 gal/lf

24 Basin E Inflow 1-yr Storm: 0.33 Mgal Aver. Storm: 283 gpcd Severity: 4.4 gal/lf

25 Results Summary Basin C E D D 20 Area (acres) ,420 Population 4,687 1,067 2, Length (lf) 89,700 52, ,000 14,300 IDM Infiltration (120 gpcd, 1,500-3,000 gpd/idm) gpcd gpd/idm 1,741 1, ,661 Inflow (275 gpcd) gpcd gal/lf

26 Basin E1-E5 Evaluations Basin I.D. E1 E2 E3 E4 E5 Population Length (lf) 2,580 6,200 12,900 17,700 12,800 IDM Infiltration (120 gpcd, 1,500-3,000 gpd/idm) gpcd E3 gpd/idm 2,478 3, Inflow (275 gpcd) gpcd 1, gal/lf E4 E2 E5 E1

27 Basin C1-C5 Evaluations Basin C1 C2 C3 C4 C5 Population ,397 1,142 Length (lf) 20,131 17,412 8,755 25,099 18,332 IDM Infiltration (120 gpcd, 1,500-3,000 gpd/idm) gpcd gpd/idm 4,287 1,231 2, Inflow (275 gpcd) gpcd gal/lf C3 C1 C5 C4 C2

28 Continued Basin C Evaluations C1a C1c C2a C2b Population 628 3,259 1,397 1,142 Length (lf) 10,828 61,491 10,152 7,260 IDM C1c Infiltration (120 gpcd, 1,500-3,000 gpd/idm) gpcd C1a gpd/idm 6, , Inflow (275 gpcd) gpcd gal/lf C2b C2a

29 What About a 2-inch Rain Event? Create 800,000 gallons $ extra cost Backups: $15,000? NPDES permit violation? SRF requires I/I Minimization Hydraulic sizing considerations for future expansions/replacements

30 Impacts of Infiltration/Inflow Lift Stations Additional Sewer Maintenance Influent Headworks Equipment Wear/Tear RBC Building Flooding Potential for Sewer Backups NPDES permit

31 Realized Benefits Eliminated tremendous WWTP flows Excluded large percentage of City for detailed investigation Avoided unneeded capital expansions/replacements

32 Follow-Up Activities Re-implement flap gate maintenance Selected Basins Smoke testing Camera inspection Basin B Monitoring Anticipate selective repairs at manholes or short sewer segments Budget Sensitive

33 Planning Your I/I Study Determine your system needs: Objectives Personnel resources, schedule Available budget Available budget Divide into 10,000 LF sub-basins Identify known issues Sanitary sewer map Be patient!

34 Questions Brian Mulinix, P.E. (402)

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37 gallon/capita/day Basin C Basin D Basin E gpd/idm Basin C Basin D Basin E

38 Rehabilitation Solutions Disconnect inflow sources Sewer line Sliplining Cured-in-place-pipe Spirally wound pipe Segmental lining On-line replacement Spot Repair Manhole Replacement Chemical grouting Structural lining Coating systems Lateral Removal/replacement Lining External grouting

39 Physical Evaluations Smoke testing Dyed water testing Closed circuit television inspection Sewer scanner and evaluation technology Sonar technology Man-entry inspection Manhole inspection