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CONTROLLING GROUNDWATER ON CONSTRUCTION SITES

Dr Martin PreenePreene Groundwater ConsultingJune 2014

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SYNOPSIS

• Good and bad examples of water management

• Surface water management

• Groundwater control

• Environmental impacts from water management

• Conclusion

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PRACTICE PROFILE

Preene Groundwater Consulting is the Professional Practice of Dr Martin Preene and provides specialist advice and design services in the fields of dewatering, groundwater engineering and hydrogeology to clients worldwide

Dr Martin Preene has more than 25 years’ experience on projects worldwide in the investigation, design, installation and operation of groundwater control and dewatering systems. He is widely published on dewatering and groundwater control and is the author of the UK industry guidance on dewatering (CIRIA Report C515 Groundwater Control Design and Practice) as well as a dewatering text book (Groundwater Lowering in Construction: A Practical Guide to Dewatering)

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GOOD CONTROL OF GROUNDWATER

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POOR CONTROL OF GROUNDWATER

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SURFACE WATER CONTROL

Groundwater control alone cannot keep an excavation dry. Surface water must also be controlled

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SURFACE WATER CONTROL

• Source control- intercept run-off before it reaches the excavation- prevent unnecessary generation of water in the excavation- collect water as soon as it reaches the work area (or before!)

• Water collection - French drains to intercept run off- collector drains and sumps- pumping systems (keep it simple!)

• Water treatment- solids removal (settlement tanks, Siltbusters)

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GROUNDWATER CONTROL BY EXCLUSION

Cut-off walls penetrate into underlying low permeability stratum

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GROUNDWATER CONTROL BY PUMPING

Common Techniques

• Sump Pumping• Wellpoints• Deepwells• Ejector wells

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SUMP PUMPING

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WELLPOINTS

From CIRIA Report C515 (2000): Groundwater Control: Design and Practice

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DEEPWELLS

From CIRIA Report C515 (2000): Groundwater Control: Design and Practice

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EJECTOR WELLS

From CIRIA Report C515 (2000): Groundwater Control: Design and Practice

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RANGE OF APPLICATION OF PUMPING METHODS

Amount of lowering of groundwater level

Low permeability (silts) High permeability (gravels)

From CIRIA Report C515 (2000): Groundwater Control: Design and Practice

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Water management on construction sites can have a range of impacts:Impact 1: Abstraction

- e.g. settlement, impact on water sources and water quality

Impact 2: Pathways for groundwater flow- e.g. increased risk of aquifer pollution

Impact 3: Barriers to groundwater flow- e.g. changes in groundwater level

Impact 4: Discharges to groundwater- e.g. risk of fuel spills, etc

Impact 5: Discharge to surface water- e.g. risk of pollution of surface waters

ENVIRONMENTAL IMPACTS

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IMPACTS FROM ABSTRACTION

Effect on groundwater quality• Pumping from dewatering systems changes natural hydraulic gradients

and velocities• This can cause the migration of plumes of polluted water associated with

contaminated sites

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Distortion of structure in uniform soil conditions

IMPACTS FROM ABSTRACTION – SETTLEMENT

Distortion of structure due to change in soil conditions

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CONCLUSION

• Effective management of surface water and groundwater can be crucial for construction projects

• Groundwater can be controlled by pumping methods and exclusion methods

• Technology needs to be carefully selected

• Environmental impacts including ground settlement and movement of contaminated groundwater

• With suitable planning and design these challenges can be overcome

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CONTROLLING WATER ON CONSTRUCTION SITES

Dr Martin PreenePreene Groundwater ConsultingJune 2014