SLIMBRIDGE CASE STUDY, INFILTRATION REDUCTION Case Study - PowerPoint PPT Presentation

SLIMBRIDGE CASE STUDY, INFILTRATION REDUCTION Case Study Presentation WWT – Networks Conference 2019 Client – Severn Trent Water Principle D&B Contractor – nmcn Mike Wood – Stantec & Severn Trent Steve Wood – nmcn Alex Finlyson - nmcn 29/01/19

AERIAL VIEW Cambridge Slimbridge A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19 2

SEWER NETWORK Ryalls Lane SPS (17l/s) Longaston Lane SPS (7-8/s) Cambridge Slimbridge To Coaley STW A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19 3

INFILTRATION PROBLEM EMERGES 2013=> • More flooding (sewer only) • Flow Monitoring • PRT Analysis • Groundwater Assessment A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19 4

Flood Level A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19 100.00 120.00 -20.00 20.00 40.00 60.00 80.00 0.00 01-Dec-13 00:14 Dec13 03-Dec-13 15:59 06-Dec-13 07:44 08-Dec-13 23:29 11-Dec-13 15:14 14-Dec-13 06:59 16-Dec-13 22:44 19-Dec-13 14:29 Longaston Lane SPS Wet Well Level - Winter 2013/14 22-Dec-13 06:14 24-Dec-13 21:59 27-Dec-13 13:44 30-Dec-13 05:29 01-Jan-14 21:14 04-Jan-14 12:59 07-Jan-14 04:44 09-Jan-14 20:29 12-Jan-14 12:14 15-Jan-14 03:59 INFILTRATION PROBLEM EMERGES 2013=> #1 17-Jan-14 19:44 20-Jan-14 11:29 23-Jan-14 03:14 25-Jan-14 18:59 28-Jan-14 10:44 31-Jan-14 02:29 02-Feb-14 18:14 05-Feb-14 09:59 08-Feb-14 01:44 10-Feb-14 17:29 13-Feb-14 09:14 16-Feb-14 00:59 18-Feb-14 16:44 21-Feb-14 08:29 24-Feb-14 00:14 26-Feb-14 15:59 01-Mar-14 07:44 03-Mar-14 23:29 06-Mar-14 15:14 09-Mar-14 06:59 11-Mar-14 22:44 14-Mar-14 14:29 17-Mar-14 06:14 19-Mar-14 21:59 22-Mar-14 13:44 25-Mar-14 05:29 27-Mar-14 21:14 Apr14 30-Mar-14 12:59 Flood Level 5

PROBLEM SUMMARY • Sewer Flooding ODI Penalties (£243k/annum) (2xInternal, 10xExternal) • Pollution Risk • Excessive Pump Run Times (Energy / Carbon) • High OPEX Costs (>£100k Tankers, winter 2013/14) • Reputation A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19 6

SURVEY FINDINGS Tranche 1 (2013) - CCTV: Mainline Survey (dry): 6 Locations of visible infiltration PDAS/Private PDAS/Private Mainline Tranche 2 (2016) - CCTV: Mainline + Property Drainage Surveys: 30 Locations of visible infiltration identified 29 lengths where high infiltration potential (Importance of Survey Extent & Timing) A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19 7

PROBLEM AREAS Catchment wide – no clusters 52%: ‘Mainline’ Public Sewer 48%:Property Drainage (PDAS / Private) Overall good structural condition 2xStructural = Grade 5 2xStructural = Grade 4 1xStructural = Grade 3 Remainder = Grade 1 or 2 A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19 8

SOLUTIONS: INFILTRATION RISK TRIANGLE (ALL 3 COMPONENTS FOR INFILTRATION RISK TO BE REALISED) Groundwater Risk: Flooding, Pollution, Non-Compliance Gaps in Hydraulic Network Constraint A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19 9

NETWORK SEALING PRINCIPLES • Modelling: 70% infiltration reduction to meet desired standards • Robust catchment approach:- Must address property drainage to meet targets System Sealing……move away from single pipe approach for robust solution & to avoid migration risk • Address data shortfall – Long term data requirements Solution • Data: New FM chamber at SPS, SPS signal updates (2 min polling) • Data: New groundwater borehole (linked to eSCADA telemetry) • (Leaktight) Infiltration Liners + (top hats) – 800m (conventional) • MH Sealing – Resin injection + spraying – 7No. • Flood Grouting – 600m + 21 MHs A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19 10

BACKGROUND • Flood grouting involves the two-part pouring of silicate solutions to form a soil-grout- matrix, a sandstone like material around the pipe to prevent infiltration and exfiltration • Technique first trialled in the UK in the 1990’s by Thames Water, but is largely used in Europe and North America • Technique owned by Sanipor GmbH but licensed in the UK to Onsite Ltd A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19 11

TECHNIQUE • Suitability assessment carried out • Control levels established • Section isolated, cleaned and inspected • Water test carried out to determine leakage rate of the section • Section flooded with S1 up to the control level • Hydrostatic pressure ensures the liquid is injected through any cracks or gaps in the sewer and saturates the surrounding soil against ground water pressure • S1 is pumped out leaving the surrounding subsoil saturated • Section is flushed and flooded with the S2 component • S1 and S2 react with soil particles achieving water tightness • S2 is pumped out following final settlement check and system cleaned • Post water test carried out if required • The result is 99% water tightness to EN1610 A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19 12

RISK ASSESSMENT • Further surveys and detailed catchment appreciation were required • Contingency plans for grout loss into voids, groundwater and adjacent water courses were established • Other risks were identified such as the blocking of gullies or traps on the network • Additional downstream flow controls put into place • Vehicle movement plan developed to deal with narrow village roads A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19 13

CUSTOMER • The nature of the work required increased level of customer management, a number of forums were held prior to the works. • Owing to a large part of the works taking place in private land, individual consultation was held with each resident ahead of the works where access would be required. • Feedback from site suggested that the residents showed a keen interest in the technique and were very accommodating. A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19 14

MONITORING • Prior to works the system volume was established to enable to site teams to monitor drop levels at the point of installation in the manhole • This allowed for contingency plan trigger points to be determined based on acceptable loss rates A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19 15

INSPECTION & TESTING • Following mixing of S1 & S2, the drop rate of S2 is measured to determine the leakage rate against the standard set out in EN1610 (0.3 litres per m 2 of system surface) • Initial test results carried out on site have demonstrated that no lengths exceeded the allowable rate • Site based testing is backed up by initial catchment data demonstrating a reduction in pump start cycles Section 0402-0503 Section DR7-DR8A Time (Mins) Time (Mins) 0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35 40 0 0 5 5 Drop Rate (mm) 10 Drop Rate (mm) 10 15 15 20 20 25 25 30 30 35 35 Drop Rate (mm) 1st Cycle S1 Drop Rate (mm) 1st Cycle S2 Drop Rate (mm) 1st Cycle S1 Drop Rate (mm) 1st Cycle S2 Drop Rate (mm) 2nd Cycle S1 Drop Rate (mm) 2nd Cycle S2 A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19 16

TECHNIQUE APPRAISAL Disadvantages Advantages • More efficient on PDaS networks • Increased potential of environmental risk • Reduced customer impact on PDaS networks • Increase in tanker requirements and • One set-up for multiple runs movements • Chambers and laterals sealed as part of pipe • Additional site surveys • Grout procurement lead times sealing operation • System capacity is not reduced • Potential under-utilisation of grout leading to • Removal of need to top-hat connections wastage • Installation times comparable, if not quicker, than • Increased footprint of TMA set up • Increase in manhole entry requirements traditional methods • Repeatable process • Increase in flow control measures • Can be installed on pipes or chambers of any • Not favourable if voids or structural defects are present shape • Not a structural solution A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19 17

RESULTS#1 (DRY WEATHER RESPONSE) Longaston Lane SPS - Wet Well Levels Dry Days. Pre and Post Scheme 22 20 18 Wet Well Level %age 16 14 12 10 Midnight Midnight Midday 8 24 Hr Duration 12 Pump Cycles (diurnal profile) 30 Pump Cycles (no diurnal profile) 15-May-15 20-Jan-19 A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19 18

RESULTS#2 (STORM RESPONSE) Max wet well level – 29% since completion Short & spiky response (no long tails) A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19 19

RESULTS – CAUTION REQUIRED • Dry Winter! Network Not Fully Tested • Ongoing Assessments: Return in AMP7 for: ➢ Water tests on flood grout sections ➢ Revisit liners to check for shrinkage / failure ➢ Revisit dig down repairs to check for settlement ➢ Inspect MHs for water-tightness • Assess longer term deterioration of network. PRTs now referenced vs groundwater level from BH data. A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19 20