LOWER WEST PEACE SUBDIVISION GROUNDWATER MITIGATION

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Phillip Dixon
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1 LOWER WEST PEACE SUBDIVISION GROUNDWATER MITIGATION Nick VanderKwaak Bob Gammer 28 October

2 Groundwater Seepage Since 2008 BC Hydro has worked with the Town and residents to mitigate basement seepage issues in LWP subdivision, and now proposes to complete and make permanent the existing groundwater pumping system. Background High river levels in the Peace River during winter freeze-up induce a rise in the groundwater levels below the LWPRS High groundwater levels lead to seepage along the basement walls and floors of up to 30 of 150 properties located in the LWPRS Groundwater seepage events have occurred 4 times in the 38 years since the Bennett Dam was constructed - in 1982, 1992, 2005, & 2008 As a result of the 2005 event Town of Peace River, Alberta Environment & BC Hydro commissioned the first groundwater study by P Machibroda. An ice consolidation event at the Town in January 2008 resulted in unusually high river and groundwater levels for the January-March 2008 period.

Background High river levels in the Peace River during winter freeze-up induce a rise in the groundwater levels below the LWPRS High groundwater levels lead to seepage along the basement walls and

3 Background cont d homeowners in Lower West Peace reported water issues, 10 of which had water enter the living space. BC Hydro provided funding to mitigate the impact of high groundwater levels. This included sump pump installations in 35 basements, dehumidifiers, furniture moving, storage, incremental costs to the Town Committed to being part of the permanent solution to the high groundwater problem Retained P Machibroda Engineering to drill and test 9 dewatering wells Retained LandLink Consulting to work with residents dewatering wells drilled and tested; 2 storm-drain pump outs installed higher-capacity dewatering wells drilled and tested

This included sump pump installations in 35 basements, dehumidifiers, furniture moving, storage, incremental costs to the Town Committed to being part of the permanent

4 Background cont d 2011/12 New groundwater dewatering model developed and calibrated by Schlumberger Water Services Increased confidence that a ground water pumping scheme will work to keep basements dry, and Concept designs completed and costs estimated. Concluded that ground water pumping system can be constructed at reasonable cost. Costs of seepage mitigation and wells: $1.1 Million to date 2013 Groundwater pumping and properties (purchase/covenants) alternatives considered Groundwater pumping identified as preferred alternative. Costs of project planning and engineering $300k.

Concluded that ground water pumping system can be constructed at reasonable cost. Costs of seepage mitigation and wells: $1.

5 Lower West Peace River 2009 Dewatering Wells 2010 Large Capacity Dewatering Wells Storm Sewer Pumping Stations

6 Technical Update The following slides were prepared by Schlumberger Water Services

Town of Peace River Heart River Peace River

9 Finding Groundwater Control Solutions for the LWPRS through Numerical Modeling The Problem: From winter Freeze-up Development of an extensive river ice cover with thickness of several meters. The water below the ice cover is slowed down because of the friction imparted by the base of the ice cover Schlumberger. All rights reserved. To maintain river flow, a reduction in velocity leads to an increase in the river section, and therefore to higher river levels. The significant ice thickness also contributes to a higher river level.

The water below the ice cover is slowed down because of the friction imparted by the base of the ice cover. 2012 Schlumberger.

10 Finding Groundwater Control Solutions for the LWPRS through Numerical Modeling to Groundwater Seepage The riverbed and the alluvial deposits underlying the subdivision are hydraulically connected The increase in river level leads to an increase in groundwater levels within the alluvial aquifer 2012 Schlumberger. All rights reserved.

subdivision are hydraulically connected The increase in river level leads to an

11 Finding Groundwater Control Solutions for the LWPRS through Numerical Modeling Groundwater Seepage Control The Options Sumps Slurry cut-off wall Dewatering wells French drains 2012 Schlumberger. All rights reserved.

Control The Options Sumps Slurry cut-off wall

12 Finding Groundwater Control Solutions for the LWPRS through Numerical Modeling Conceptual model Groundwater Modeling 2012 Schlumberger. All rights reserved. Construction Numerical model Calibration Prediction What if... Scenario A Scenario B

Simulation Day 1 Day 10 Groundwater elevation

Prediction: Wells versus Drains 18 wells

20 Finding Groundwater Control Solutions for the LWPRS through Numerical Modeling Assessment of groundwater control options 2012 Schlumberger. All rights reserved. Criteria Slurry Wall Wells French Drains Effectiveness of groundwater control Ease of maintenance Temporary damage to roads and underground utilities Disruption to traffic during construction Environmental risk High but dewatering wells are still needed; feasibility not demonstrated Low and involving onsite disruption Very limited damage Very limited Potential damage to dyke integrity High High and requiring minimal on-site disruption Limited damage during drilling, higher potential for damage during pipe installation Limited to moderate disruption No risk High Intermediate and requiring minimal on-site disruption Intermediate damage during drilling, higher potential for damage during pipe installation Moderate disruption Potential for subsidence Cost Highest Lowest Higher

Environmental risk High but dewatering wells are still needed; feasibility not demonstrated Low and involving onsite disruption Very limited damage Very limited Potential damage to dyke integrity

21 Outfall Concept Design 21

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28 Project Plan 2013/14 Establish formal agreement with Town of Peace River Update LWP residents Publish a design-build RFP Seek permits and regulatory approvals Finalize well layout and pump specifications Seek input to final design BCH internal approval of Implementation phase 2014/15 Operate existing wells and pumps as needed during winter Construction summer 2014 or 2015 Start of operation and monitoring Project costs: Overall project estimated to cost $5-6 Million including about $2 Million for construction.

29 Permitting Requirements Water Act (Alberta) The current permit (Permit No ) will cover the proposed 18 wells and outfall structure (expires July 31, 2015). Once there is a design with the final locations of the infrastructure (wells, piping etc ) Public Lands Act (Alberta) License of occupation for outfall (60 days, if required) Navigable Waters Protection Act (Canada) Notification/Review (90 days) Fisheries and Oceans Canada No Notifications or approvals required

30 Summary BC Hydro proposes to complete the existing groundwater pumping system, to meet it s commitment in 2008 to be part of the overall solution to basement seepage in the LWP subdivision With Town Council agreement, BC Hydro will proceed with the project.

31 Requested Council Resolution 1. The Town agrees with BC Hydro that an acceptable solution for Lower West Peace subdivision basement seepage is a system of dewatering wells including an outfall to Peace River. 2. The Town intends to enter into a formal agreement with BC Hydro, with BC Hydro regarded as a partner 3. The Town will participate in the solution and cooperate with BC Hydro by providing at no charge: Permission to install and operate the proposed system on Town property Design reviews, permits and inspections Joint engagement with residents and other stakeholders Assistance with establishing piping alignment and working around existing infrastructure and rights of way, and facilitating co-location of equipment where appropriate. 31

5.0 OVERVIEW OF FLOOD DAMAGE REDUCTION MEASURES

5.0 OVERVIEW OF FLOOD DAMAGE REDUCTION MEASURES Flood damage reduction consists of two basic techniques structural and non-structural. Structural methods modify the flood and take the flood away from people