Greensboro s Confirmation: Documenting I/I Reduction in North Buffalo Basin with Post Rehabilitation Flow Monitoring November 2017 Chris Nesbit, PE, BCEE, Meredith Miller, PE, CDM Smith and Robbie Bald, PE City of Greensboro October 2017
Agenda Flow Monitoring and Prioritization (2011) SSES and Rehabilitation (2013 2015) Post Rehabilitation Flow Monitoring Analysis (2016) Conclusions 2 2017 Kentucky-Tennessee Water Professionals Conference
Flow Monitoring and Prioritization (2011)
Performed Flow Monitoring Analysis in 2011 to Identify Areas with High I/I in the Upper North Buffalo Drainage Basin 4
Location of SSOs in the Study Area from 2006 to 2011 SSOs from 2006 to 2011 6 SSOs rainfall related 5
A Wet-Weather Flow Hydrograph Is Composed of Several Wastewater Flow Components Wastewater Flows are composed of: Base wastewater flow (BWWF) Groundwater Infiltration (GWI) Rain Dependent Infiltration/Inflow (RDI/I) FLOW TIME
Prioritizing Sewersheds Based on Peak and Volume of I/I Priority 1 - Sewersheds 1, 6, 9, 13, 14, 17, and 18 Priority 2 Sewersheds 2, 7, 8, 12, and 21 7
Of the 480,000 lf of sewer, 213,000 was recommended for CCTV inspection 136,000 lf in Priority 1 and 77,000 lf in Priority 2 8
SSES and Rehabilitation (2013 to 2015)
Perform SSES and Rehabilitation to Reduce I/I and Control SSOs Priority 1 Sewersheds (red) CCTV d 135,000 feet in 2012-2013 Rehabilitation in 2014-2015 Priority 2 Sewersheds (orange) CCTV d 70,000 feet in 2015-16 Rehabilitation in 2016-2017 Post Rehab Flow Monitoring of Priority 1 in March-April 2016 10
SSES Identified Various Structural & O&M Defects In the Sewersheds that would lead to I/I 11
Few Active Infiltration Defects Observed via CCTV Shows Need for Flow Monitoring to Document I/I Table1 Priority 1 Sewersheds, Number of CCTV Defects Sewershed Number of Structural Defects (#) Joint Surface Defects Structura Infiltratio Obstruction Cracks Fractures Broken Holes Deformed Collapsed Offset Damage (Sags) l Defects Deposits Roots n s Defects Inspected Sewershed 1 29 101 73 2 0 0 16 6 14 241 2 405 3 24 434 77 6 Sewershed 18 19 80 47 2 1 0 7 1 21 178 0 216 8 15 239 58 5 Sewershed 13 30 81 44 2 3 0 11 0 26 197 2 188 0 4 194 73 9 Sewershed 14 5 36 14 1 0 0 5 3 1 65 0 137 2 0 139 58 8 Sewershed 6 12 57 59 0 1 4 16 8 12 169 0 157 6 18 181 100 28 Sewershed 9 25 123 70 1 5 0 25 4 14 267 1 442 12 21 476 149 36 Sewershed 17 37 186 56 3 1 0 10 0 20 313 1 195 3 4 203 99 30 Number of Pipes with Other Total Number of Number of Operations and Maintenance Defects Total Number of O&M Total Number of Pipes Number of Pipes with No Defects 12
Comprehensive Rehabilitation Performed for Majority of Pipes in Priority 1 and 2 Sewersheds Priority 1 Sewersheds CCTV d 135,000 ft., Recommended Rehabilitation 112,000 ft. Recommended Rehabilitation Pipe Length (ft.) Percent of Total Length CIPP 31,170 28% Sliplining 59,960 51% Pipe Bursting 22,337 20% Open Cut 1,547 1% Total 112,014 100% Priority 2 Sewersheds - CCTV d 70,000 ft., Recommended Rehabilitation for 62,000 ft. Recommended Rehabilitation Pipe Length (ft.) Percent of Total Length CIPP 17,377 28% Sliplining 38,956 62% Pipe Bursting 4,046 6% Open Cut 491 1% Other Rehab Method 1 1,787 3% Total 62,657 100% 1 Other Rehab Methods include Heavy Cleaning and Re- CCTV, Point Repair Only, Lateral Rehabilitation Only. 13
Post Rehabilitation Flow Monitoring Analysis
Goal: Document Reductions in Volume and Peak I/I for Pre to Post-Flow Monitoring Data Phase 1 Historic Meter Data 2015 and 2010 master plan flow monitoring data Phase 2 CDM Smith Sub-basin Meter Data 2011 and 2016 pre- and postrehabilitation flow monitoring data 15
Phase 1: Historic Flow Monitoring Data Flow Monitoring Data March 7, 2010 June 20, 2010 January 13, 2015 May 18, 2015 Incremental Areas in the 200,000 ft. 16
Preand Post- Rehab Basins Post Rehabilitation Master Plan Flow Monitors NB 16 - Control NB 20 - Pre and Post Rehabilitation Analysis 35% of pipe upstream of NB 20 was rehabilitated. Flow Monitor Total Upstrea m Pipe Length (ft.) Total Rehabili tated Pipe Length (ft.) Percent of Pipe Length Rehabili tated Upstrea m of Monitor Rehab NB 16 194,000 67,000 35% Control NB 20 100,000 0 0% 17
Post Rehabilitation 2016 CDM Smith Flow Monitoring Data Control FM 2 Flow Monitors Downstream of Rehabilitated Sewersheds: FM 9, FM 14, and FM 18 Preand Post- Rehab Basins Flow Monit or Total Upstream Pipe Length (ft.) Total Rehabilit ated Pipe Length (ft.) Percent of Pipe Length Rehabilit ated Upstrea m of Monitor Control FM 2 10,300 0 0% Rehab FM 9 62,100 41,846 67% Rehab FM 14 12,200 10,217 84% Rehab FM 18 16,500 13,664 83% 18
Hydrograph Decomposition was performed on Greensboro Flow Data to Determine the Portion of Flow Hydrograph Attributed to RDI/I Average Weekday Dry- Weather Flow = 0.024 mgd Peak Hour Flow Rate = 0.17 mgd Total RDI/I entering system on May 2 event upstream of Flow Monitor 2 = 110,500 gallons 19
R-Value is the Fraction of Rainfall over a Sewershed that Enters the Sanitary Sewer as RDI/I Table 1. Pre- Rehabilitation R-Values for the Phase 2 (CDM Smith) Flow Meters Pre- and Post-Rehab Basins Flow Monitor Total Upstream Sewered Area (ac) Pre-Rehabilitation R-value (%) 2/28/2011 3/6/2011 3/9/2011 3/23/2011 3/30/2011 4/16/2011 Control FM2 69 1.17% 4.16% 4.41% 0.71% 4.37% 0.52% Rehab FM9 407 4.66% 3.89% 6.37% 0.88% 4.41% 2.57% Rehab FM14 73 4.01% 5.16% 6.59% 1.69% 6.63% 2.92% Rehab FM18 105 3.60% 4.77% 6.16% 1.74% 6.42% 2.92% Table 2. Post - Rehabilitation R-Values for the Phase 2 (CDM Smith) Flow Meters Pre- and Post- Rehab Basins Flow Monitor Total Upstream Sewered Area (ac) Post-Rehabilitation R-value (%) 2/22/2016 3/27/2016 3/28/2016 4/22/2016 4/27/2016 5/2/2016 5/5/2026 5/12/2016 Control FM2 69 10.34% 0.75% 3.21% 1.34% 0.53% 2.85% 5.00% 3.89% Rehab FM9 407 6.19% 0.54% 2.51% 0.33% 0.25% 2.91% 5.09% 2.35% Rehab FM14 73 2.11% 0.52% 1.00% 0.53% 0.28% 0.97% 1.96% 1.16% Rehab 20 FM18 105 9.06% 1.11% 6.41% 0.94% 0.56% 2017 Annual NC AWWA-WEA 1.73% Conference 3.76% N/A1
A Ratio of RDI/I Peak Flow Rate to Peak Rainfall Rate was used to Determine Impact of Rehab on Reducing Peak RDI/I Flows Table 1. Pre- Rehabilitation Peak Flow Ratios for the Phase 2 (CDM Smith) Flow Meters Pre- and Post-Rehab Basins Flow Monitor Total Upstream Sewered Area (ac) Pre-Rehabilitation Peak Flow Ratio (GPD/AC/in/hr) 2/28/2011 3/6/2011 3/9/2011 3/23/2011 3/30/2011 4/16/2011 Control FM2 69 4,141 9,802 4,289 1,337 8,789 13,410 Rehab FM9 407 5,635 6,554 8,003 2,271 7,039 17,825 Rehab FM14 73 8,174 12,502 11,488 3,914 14,397 35,338 Rehab FM18 105 9,399 19,735 16,322 3,025 14,604 39,945 Table 2. Post-Rehabilitation Peak Flow Ratios for the Phase 2 (CDM Smith) Flow Meters Pre- and Post- Rehab Basins Flow Monitor Total Upstream Sewered Area (ac) 2/22/201 6 3/27/201 6 Post-Rehabilitation Peak Flow Ratio (GPD/AC/in/hr) 3/28/201 6 4/22/201 6 4/27/201 6 5/2/2016 5/5/2026 5/12/201 6 Control FM2 69 9,511 4,314 8,816 4,451 2,272 3,851 6,896 2,068 Rehab FM9 407 3,981 1,554 3,744 1,375 1,284 3,308 5,277 1,344 Rehab FM14 73 1,574 919 2,408 1,030 976 1,123 2,667 702 Rehab 21 FM18 105 6,118 3,716 14,479 3,091 3,143 2017 Annual 4,288 NC AWWA-WEA 7,344 Conference N/A 1
Linear Regression Analysis is Used to Compare the Pre- and Post Rehabilitation Monitoring Volume of RDII (R-Value) Sewershed NB20 vs. Control NB16 3.0% 2010 2015 R Value for Sewershed NB20 2.5% 2.0% 1.5% 1.0% y = 0.6053x R² = 0.9322 y = 0.2852x R² = 0.9051 0.5% 0.0% 0.0% 1.0% 2.0% 3.0% 4.0% 5.0% 6.0% 7.0% 8.0% R Value for Control NB16 22
Historic Meter Data Rehabilitated Basin RDI/I Volume NB20 RDI/I Peak Flow NB20 Control Basin NB16 NB16 Percent of Pipe Length Rehabilitated Upstream of Monitor 35% 35% 23 Pre-Rehabilitation Slope 0.61 0.62 Post-Rehabilitation Slope 0.29 0.38 Percent I/I Reduction 53% 39% R Value for Sewershed NB20 3.0% 2.5% 2.0% 1.5% 1.0% 0.5% Volume of RDII (R-Value) Sewershed NB20 vs. Control NB16 2010 2015 y = 0.6053x R² = 0.9322 y = 0.2852x R² = 0.9051 0.0% 0.0% 1.0% 2.0% 3.0% 4.0% 5.0% 6.0% 7.0% 8.0% R Value for Control NB16 Peak Flow Ratio (gpd/ac/in/hr) for Sewershed NB 20 6,000 5,000 4,000 3,000 2,000 1,000 0 y = 0.6219x R² = 0.7941 Peak RDII NB20 vs. Control NB16 2010 2015 y = 0.3801x R² = 0.8558 0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000 Peak Flow Ratio (gpd/ac/in/hr) for Control NB16
CDM Smith Post Rehabilitation Analysis Results FM 9 R Value for Sewershed FM9 8.0% 7.0% 6.0% 5.0% 4.0% 3.0% 2.0% 1.0% y = 1.2236x R² = 0.4213 Volume of RDII (R-Value) Sewershed FM9 vs. Control FM2 2011 2016 y = 0.6896x R² = 0.8733 0.0% 0.0% 2.0% 4.0% 6.0% 8.0% 10.0% 12.0% R Value for Control FM2 Peak Flow Ratio (gpd/ac/in/hr) for Sewershed FM9 24 20,000 18,000 16,000 14,000 12,000 10,000 8,000 6,000 4,000 2,000 0 Peak RDII FM9 vs. Control FM2 2011 2016 y = 0.4975x R² = 0.6779 y = 1.0905x R² = 0.7552 0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 Peak Flow Ratio (gpd/ac/in/hr) for Control FM2 RDI/I Volume Rehabilitated Basin FM9 FM9 Control Basin FM2 FM2 Percent of Pipe Length Rehabilitated Upstream of Monitor RDI/I Peak Flow 67% 67% Pre-Rehabilitation Slope 1.22 1.09 Post-Rehabilitation Slope 0.69 0.50 Percent I/I Reduction 44% 54%
CDM Smith Post Rehabilitation Analysis Results - FM 14 R Value for Sewershed FM14 7.0% 6.0% 5.0% 4.0% 3.0% 2.0% 1.0% y = 1.4986x R² = 0.6992 Volume of RDII (R-Value) Sewershed FM14 vs. Control FM2 2011 2016 y = 0.2579x R² = 0.7503 Peak Flow Ratio (gpd/ac/in/hr) for Sewershed FM14 0.0% 0.0% 2.0% 4.0% 6.0% 8.0% 10.0% 12.0% 25 40,000 35,000 30,000 25,000 20,000 15,000 10,000 5,000 0 R Value for Control FM2 Peak RDII FM14 vs. Control FM2 2011 2016 y = 0.2555x R² = 0.6718 y = 2.0777x R² = 0.8182 0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 Peak Flow Ratio (gpd/ac/in/hr) for Control FM2 RDI/I Volume RDI/I Peak Flow FM14 Rehabilitated Basin FM14 Control Basin FM2 FM2 Percent of Pipe Length Rehabilitated Upstream of Monitor 84% 84% Pre-Rehabilitation Slope 1.50 2.08 Post-Rehabilitation Slope 0.26 0.26 Percent I/I Reduction 2017 Annual NC AWWA-WEA 83% Conference 88%
CDM Smith Post Rehabilitation Analysis Results FM 18 R Value for Sewershed FM18 Peak Flow Ratio (gpd/ac/in/hr) for Sewershed FM18 26 10.0% 9.0% 8.0% 7.0% 6.0% 5.0% 4.0% 3.0% 2.0% 1.0% 45,000 40,000 35,000 30,000 25,000 20,000 15,000 10,000 5,000 0 y = 1.4145x R² = 0.6822 Volume of RDII (R-Value) Sewershed FM18 vs. Control FM2 2011 2016 Peak RDII FM18 vs. Control FM2 2011 2016 y = 0.9176x R² = 0.81 0.0% 0.0% 2.0% 4.0% 6.0% 8.0% 10.0% 12.0% R Value for Control FM2 y = 2.4852x R² = 0.856 y = 1.0575x R² = 0.6466 0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 Peak Flow Ratio (gpd/ac/in/hr) for Control FM2 RDI/I Volume Rehabilitated Basin FM18 Control Basin FM2 FM2 Percent of Pipe Length Rehabilitated Upstream of Monitor RDI/I Peak Flow FM18 83% 83% Pre-Rehabilitation Slope 1.41 2.49 Post-Rehabilitation Slope 0.92 1.06 Percent I/I Reduction 35% 57%
The City of Greensboro was able to Achieve a 35 88 % Reduction in I/I Entering Their Collection System by Performing Comprehensive Rehabilitation Rehabilitated Basin RDI/I Volume RDI/I Peak Flow RDI/I Volume RDI/I Peak Flow RDI/I Volume RDI/I Peak Flow RDI/I Volume RDI/I Peak Flow FM9 FM9 FM14 FM14 FM18 FM18 NB20 NB20 Control Basin FM2 FM2 FM2 FM2 FM2 FM2 NB16 NB16 Percent of Pipe Length Rehabilitated Upstream of Monitor 67% 67% 84% 84% 83% 83% 35% 35% Pre-Rehabilitation Slope 1.22 1.09 1.50 2.08 1.41 2.49 0.61 0.62 Post-Rehabilitation Slope 0.69 0.50 0.26 0.26 0.92 1.06 0.29 0.38 Percent I/I Reduction 27 44% 54% 83% 88% 35% 57% 53% 39%
Conclusions
Conclusions Flow monitoring of small sewersheds (15,000 35,000 lf range) prioritizes areas for comprehensive rehabilitation to reduce I/I. Post rehabilitation flow monitoring of rehabilitated sewersheds is necessary to effectively document I/I reduction. The key to effective post rehabilitation flow monitoring is to monitor a control area where no rehabilitation is performed and use linear regression analysis. Greensboro documented reductions in peak flow from 39% to 88% and reductions in I/I volume from 35% to 83%. No obvious correlation as to why some mini-basins achieved higher percentage reductions in I/I. 29
Conclusions Although monitoring the sub-basin where rehabilitation is performed is ideal, monitors of a larger basin area can be utilized as long as a significant percentage (in this case 35%) of the footage upstream was rehabilitated. 30
November 2017 Contact Us Chris Nesbit NesbitCM@cdmsmith.com October 2017