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

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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

SLIMBRIDGE CASE STUDY, INFILTRATION REDUCTION

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AERIAL VIEW

A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19

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Slimbridge Cambridge

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SEWER NETWORK

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Longaston Lane SPS (7-8/s)

To Coaley STW

Ryalls Lane SPS (17l/s)

Slimbridge Cambridge

A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19

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INFILTRATION PROBLEM EMERGES 2013=>

A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19

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More flooding (sewer only)
Flow Monitoring
PRT Analysis
Groundwater Assessment

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INFILTRATION PROBLEM EMERGES 2013=> #1

A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19

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20.00

0.00 20.00 40.00 60.00 80.00 100.00 120.00 01-Dec-13 00:14 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 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 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 30-Mar-14 12:59

Longaston Lane SPS Wet Well Level - Winter 2013/14

Dec13 Apr14 Flood Level Flood Level

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PROBLEM SUMMARY

A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19

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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

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SURVEY FINDINGS

A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19

7 Tranche 1 (2013) - CCTV: Mainline Survey (dry): 6 Locations of visible infiltration 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)

Mainline PDAS/Private PDAS/Private

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PROBLEM AREAS

A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19

8 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

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A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19

9 Groundwater Hydraulic Constraint Gaps in Network

SOLUTIONS: INFILTRATION RISK TRIANGLE

(ALL 3 COMPONENTS FOR INFILTRATION RISK TO BE REALISED)

Risk: Flooding, Pollution, Non-Compliance

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NETWORK SEALING PRINCIPLES

A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19

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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

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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

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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
r 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

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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
r 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

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CUSTOMER

The nature of the work required increased level of customer management, a number
f 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

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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

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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 m2 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

A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19

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5 10 15 20 25 30 35 5 10 15 20 25 30 35

Drop Rate (mm) Time (Mins)

Section 0402-0503

Drop Rate (mm) 1st Cycle S1 Drop Rate (mm) 1st Cycle S2 5 10 15 20 25 30 35 5 10 15 20 25 30 35 40

Drop Rate (mm) Time (Mins)

Section DR7-DR8A

Drop Rate (mm) 1st Cycle S1 Drop Rate (mm) 1st Cycle S2 Drop Rate (mm) 2nd Cycle S1 Drop Rate (mm) 2nd Cycle S2

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TECHNIQUE APPRAISAL

Advantages

More efficient on PDaS networks
Reduced customer impact on PDaS networks
One set-up for multiple runs
Chambers and laterals sealed as part of pipe

sealing operation

System capacity is not reduced
Removal of need to top-hat connections
Installation times comparable, if not quicker, than

traditional methods

Repeatable process
Can be installed on pipes or chambers of any

shape

A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19

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Disadvantages

Increased potential of environmental risk
Increase in tanker requirements and

movements

Additional site surveys
Grout procurement lead times
Potential under-utilisation of grout leading to

wastage

Increased footprint of TMA set up
Increase in manhole entry requirements
Increase in flow control measures
Not favourable if voids or structural defects are

present

Not a structural solution

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RESULTS#1 (DRY WEATHER RESPONSE)

A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19

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8 10 12 14 16 18 20 22

Wet Well Level %age 24 Hr Duration

Longaston Lane SPS - Wet Well Levels Dry Days. Pre and Post Scheme

15-May-15 20-Jan-19

Midday Midnight Midnight 12 Pump Cycles (diurnal profile) 30 Pump Cycles (no diurnal profile)

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RESULTS#2 (STORM RESPONSE)

A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19

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Max wet well level – 29% since completion Short & spiky response (no long tails)

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RESULTS – CAUTION REQUIRED

A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19

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Dry Winter! Network Not Fully Tested
Ongoing Assessments: Return in AMP7 for:

➢

Water tests on flood grout sections

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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.

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DO YOU HAVE ANY QUESTIONS?

A5s/11536 – Slimbridge Infiltration Reduction. WWT Networks Conference 29/01/19