Wastewater Collection System Rehab The High Hurdle of Measurable Flow Reduction MWEA 2013 Annual Conference Gregory P. Kacvinsky, P.E. OHM Advisors OHM-ADVISORS.COM ARCHITECTS. ENGINEERS. PLANNERS.
Investing to Reduce Flows When alternatives are evaluated: Do we really understand all potential costs for each alternative? Measure Success or Identify Failures Identify System Problems Flow Metering How (and where) will we measure success? Do we really understand the cost efficiencies of all alternatives? Implement CIP Evaluation of Alternatives Modeling and Analysis
Why Do We Invest? Sewer pipes and manholes are deteriorating More stringent wet weather requirements at WWTP Documented SSOs, Consent Orders Desire to reduce bill to wastewater treatment authority (i.e. DWSD)
How Do We Invest? Source Removal (pipe/lateral rehab, manhole repair, replacement) Wet weather storage Transport and treat
Source Removal 101 How do you measure flow reduction success? Volume? Peak? Baseflow? Where do you measure flow reduction? WWTP? Collector sewer? Interceptor sewer? Measuring flow reduction at a regional level: hard to demonstrate Measuring flow reduction at a neighborhood level: easier to demonstrate Misconceptions on flow reduction from rehab
Source Removal 101 Important to set the goals and manage expectations before a source removal program What percentage of peak and baseflow do we need to reduce? Is one or the other more important? How much flow meter history do we have prior to rehab? What is the plan for post-rehab flow metering? Who will evaluate pre- vs. postrehab success? What method(s) will they use?
Case Studies in I/I Removal
Case Study Communities Municipalities tributary to key interceptors flowing into regional systems Individual communities pay bills to regional authority based on metered flows Wealth of flow data Total bills based on total measured flow volume Additional charges assessed for exceeding contractual peak flows Motivation to reduce I/I flows Dual pressures (local billing and MDEQ ACOs)
Example 1 Initiated sewer/manhole rehab program to reduce measured flows and wet weather peaks Rehab was performed in various neighborhoods, mostly older sewers Several years of pre-rehab flow meter data (continuous) About 2 years of post-rehab flow meter data
Example 1 Methods of Analysis Community predicted nearly 10 cfs reduction in wet weather design flow due to typical values for pipe lining and manhole rehab 13-15 miles of pipe rehabilitated ~600 laterals partially lined ~150 manholes rehabilitated Defect repairs (from smoke testing) Independent analysis Baseflow analysis Event RDII volume vs. rainfall Meter Correlation Antecedent Moisture Modeling
Baseflow (cfs) Example 1 Baseflow Analysis 12 WAT Community Flow Long-Term Baseflow Patterns (2007-2011) 11 10 9 8 7 6 5 8-Mar 27-Apr 16-Jun 5-Aug 24-Sep 13-Nov Date 2007 2008 2009 2010 2011
Total RDII Volume (thousand cubic feet) Example 1 RDII Volume v. Rainfall Total Community WAT Community Flow Total RDII Volume vs. Total Event Rainfall Pre- vs. Post-Rehab (May - September data only) 10000 1000 Pre-Rehab (2006-2008) 100 Post Rehab (2010-2011) 10 0 1 2 3 4 5 6 Total Event Rainfall (inches)
Total RDII Volume (thousand cubic feet) Example 1 RDII Volume v. Rainfall Subdistrict Analysis Flow Meter 1590 (WAT) Total RDII Volume vs. Total Event Rainfall 1000 Pre- vs. Post-Rehab (May - September data only) 100 Pre-Rehab (2007-2008) Post Rehab (2010-2011) 10 0 1 2 3 4 5 Total Event Rainfall (inches)
Correlation Factor 2011 2010 2009 2008 2007 2006 Example 1 Meter Correlation Meter correlation measures the wet weather response of a rehabilitated meter district against that of a control (non-rehabilitated) district 2.0 Correlation Multiplication Factor Correlation Additive Factor (baseflow adjustment in cfs) 1.5 1.0 0.5 0.0-0.5
Flow (cfs) Rain (in/hr) Flow (cfs) Rain (in/hr) Flow (cfs) Rain (in/hr) Example 1 Continuous Modeling 20.0 0 Observed 18.0 Modeled Continuous modeling reveals that there is no systematic under- or over-prediction when using pre-rehab calibrated model against postrehab conditions 16.0 Rain 1 This suggests NO CHANGE in wet weather response 14.0 2 12.0 10.0 8.0 3 18.0 Post-rehab validation 0 20.0 0 6.0 4 8/19 8/20 8/21 8/22 8/23 8/24 Pre-rehab calibration 16.0 14.0 Observed Modeled Rain 1 18.0 16.0 14.0 Observed Modeled 1 Rain 12.0 2 2 12.0 10.0 8.0 Model predicts RDII Volume to within 1% of observed 6.0 4 3/4 3/5 3/6 3/7 3/8 3/9 3 10.0 8.0 Model underpredicts observed RDII volume by 2.5% 6.0 4 3/20 3/21 3/22 3/23 3/24 3/25 3/26 3/27 3
Example 1 Findings Rehab did not have a measureable impact on peaks or volumes Rehab effort was scattered, and difficult to measure success on a community level No positive economic benefit (quarterly bills not reduced) Estimates used for flow reduction from rehab activities may be flawed
Example 2 Bloomfield Orchards Subdivision (Auburn Hills) ~450-500 homes Footing drain disconnection for every home Several years of pre-rehab flow meter data (continuous) About 3 years of post-rehab flow meter data
Example 2 Methods of Analysis Independent analysis (County) Baseflow analysis Event RDII volume vs. rainfall Meter correlation Continuous modeling
Baseflow (cfs) Example 2 Baseflow Analysis 0.45 Bloomfield Orchards Subdivision Long-Term Baseflow Patterns (2000-2006) 0.40 0.35 0.30 0.25 0.20 0.15 0.10 2000 2001 2002 2003 2004 2005 2006 0.05 1-Mar 20-Apr 9-Jun 29-Jul 17-Sep 6-Nov Date
Total RDII Volume (thousand cubic feet) Example 2 RDII Volume v. Rainfall Bloomfield Orchards Subdivision Total RDII Volume vs. Total Event Rainfall Pre- vs. Post-Rehab (May - September data only) 100 2000-2001 10 2005-2006 1 0 0.5 1 1.5 2 2.5 3 Total Event Rainfall (inches)
Flow (cfs) Rain (in/hhr) Flow (cfs) Rain (in/hr) Example 2 Continuous Modeling 3.0 0 2.5 Observed 0 2.5 2.0 Observed Modeled Rain 1 2.0 1.5 Modeled Rain 1 1.5 2 1.0 2 1.0 0.5 3 0.5 3 Post-rehab validation 0.0 2.5 4 9/10 9/10 9/10 9/10 9/10 9/11 9/11 9/11 Pre-rehab calibration 2.0 1.5 1.0 Observed Modeled Rain 0 1 2 0.0 4 5/10 5/11 2.5 5/11 5/12 5/12 5/13 2.0 1.5 1.0 Observed Modeled Rain 0 1 2 0.5 3 0.5 3 0.0 4 8/2 8/2 8/3 8/3 8/4 8/4 0.0 4 6/21 6/21 6/22 6/22 6/23 6/23
Example 2 Findings Rehab had a significant impact on measured flows and volumes Success is easier to measure when rehabilitation occurs aggressively over entire metered district
Example 3 Aggressive sewer, manhole, lateral rehab over 3-year period $15-$16 million investment 2 years of pre-rehab flow meter data (continuous) 12 months of post-rehab flow meter data Post-rehab data is 2012-2013 (historically-dry conditions)
Example 3 Methods of Analysis Local analysis Model calibration to 2012 storms (July and August) Analysis shows significant reduction in wet weather flows Independent analysis (Regional Authority) Baseflow analysis Event RDII volume vs. rainfall Continuous Modeling
Example 3 Baseflow Analysis (>25% reduction) 16.00 Community Master Meter 7-day minimum flows (BASEFLOW) 2006-2013 14.00 12.00 10.00 8.00 6.00 4.00 2.00 Pre-Rehab Post-Rehab 0.00 Sep-06 Mar-07 Sep-07 Mar-08 Sep-08 Mar-09 Sep-09 Mar-10 Aug-10 Feb-11 Aug-11 Feb-12 Aug-12 Feb-13 Aug-13
Example 3 Baseflow Analysis (non-rehab district, >20% reduction) 0.800 Control District (No Rehab) 7-day minimum flows (BASEFLOW) 2006-2013 0.750 0.700 0.650 0.600 0.550 0.500 0.450 0.400 0.350 0.300 Jan-07 Jul-07 Jan-08 Jul-08 Dec-08 Jun-09 Dec-09 Jun-10 Dec-10 Jun-11 Dec-11 Jun-12 Dec-12 Jun-13
Total RDII Volume (thousand cubic feet) Example 3 RDII Volume v. Rainfall Community Master Meter Total RDII Volume vs. Total Event Rainfall Pre- vs. Post-Rehab (April - October data only) 10000 2006-2009 1000 2011-2012 100 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 Total Event Rainfall (inches)
Total RDII Volume (thousand cubic feet) Example 3 RDII Volume v. Rainfall Control District (No Rehab) Total RDII Volume vs. Total Event Rainfall Pre- vs. Post-Rehab (April - October data only) 1000 2006-2009 100 10 2011-2012 1 0 1 2 3 4 5 6 Total Event Rainfall (inches)
Example 3 Continuous Modeling 2012 data show a nudging of the needle to reduced peaks and volumes 2013 data (only 3 storms) show similar response to prerehab conditions
Example 3 Findings Early data suggests little to no flow reduction (peak and baseflow) More data needed to confirm this hypothesis (meter data through 2013 would be ideal) Success is easier to measure when rehabilitation occurs aggressively over entire metered district
Limits of Source Removal Chasing I/I is difficult. This is what we re learning by observing numerous City-wide efforts at I/I reduction: Problems migrate to next downstream defect Sanitary sewer acts as an unofficial dewatering pipe for groundwater in developed areas ENTIRE system (Pipes, MHs and laterals) needs to be rehabilitated to have a measurable impact (VERY EXPENSIVE)
Cumulative Capital Expense (USD) Wet Weather Alternatives $1,000,000 $900,000 $800,000 $700,000 Storage Cost Curve Inflow Source Removal Manhole Rehab Private I/I Sources (FDD) Cost to remove 0.40 cfs of private sources (e.g. FDD) = $897,600 Cost to store 0.40 cfs = $122,000 $600,000 $500,000 Cost to Construct 10.6 MG to store excess peak flow (43 cfs) = $12.2 M $400,000 $300,000 $200,000 $100,000 Cost to remove 0.96 cfs of direct inflow sources = $40,000 Cost to store 0.96 cfs = $294,000 Cost to remove 0.81 cfs of manhole sources = $365,000 Cost to store 0.81 cfs = $250,000 $0 0 0.5 1 1.5 2 2.5 Notes Cumulative Peak Flow Removed (cfs) 1. Flow removal based on SSES report estimates 2. Assumes a flow removal of 4 gpm per home at $10,000 cost per home 0.4
Economics of System Rehab Rehabilitation may be sought for the wrong reasons. It is ultimately about: Structural integrity of pipes and manholes Adding 20+ years to pipe longevity through lining Lower O&M costs through reduced frequency of emergency repairs
Literature Review Reviewed specific programs across the country Read technical/academic papers on wet weather flows in wastewater collection systems
Municipal Experience Urbana-Champaign Sanitary District (UCSD), IL Naperville, IL Concord, MA Various municipalities, Oakland County, MI
European Communities Dresden University Study (2007) Study of communities in UK, Germany, Switzerland
European Communities Non-sanitary flows are the norm in separate wastewater collection systems (30%-50% of total sewer flows are typical) Typically, about 5% to 10% of total I/I can be cost-effectively removed Aggressive rehabilitation programs have mixed results. Often, only complete rehab programs can nudge the needle
Key Takeaways Many communities have invested in significant rehabilitation programs with little to no measureable peak or volume reduction Flow meter data is often the weakest link flow metering should be extended well beyond rehab period for statistically-meaningful data The key benefit of sewer rehabilitation may be structural (extending the life of the asset)
Financial-Driven Decisions What is the economic impact of reduced baseflows or peaks? Present value? What is the most economically-efficient way to reduce I/I? Is a regional solution possible (i.e. storage or conveyance)? Local rate payers ultimately will expect the most cost-effective solution
Recommended Steps Know the goals - set appropriate hurdles Establish a reliable and long-term metering program (extend beyond rehab period) Fully vet the wet weather control options at your disposal Don t overpromise Asset Management Plans great opportunity to put these steps to the test
Questions Contact info: Gregory P. Kacvinsky, P.E. OHM Advisors greg.kacvinsky@ohm-advisors.com OHM-ADVISORS.COM ARCHITECTS. ENGINEERS. PLANNERS.