IEMA Are Suds the Answer for Drainage

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IEMA -Are Suds the Answer for Drainage?

• Risk Based Approach
• to the Impact of
• Road Drainage
• on
• Hydrogeology

Geological Survey of Ireland, 12th December 2007
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Introduction

• Principle
• Suds and Road Drainage
• GSI \ EPA \ DOE Guidance
• Implementation of procedure
• Risk from accidental spillage
• Routine runoff Assessment Criteria
• Application of the Assessment Criteria
• Additional Criteria
• Procedure Flow Chart
• Practical Example

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Principle

• Utilise concept of aquifer vulnerability and
  source protection to assist the initial
  assessment of all proposed developments upon the
  groundwater environment, in the context of roads
• Source - Road
• Path - Substrate
• Receptor - Aquifer Vulnerability

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Suds and Road Drainage

• Suds Components commonly used in road drainage
• Components commonly used in Road Drainage
• Filter Drains
• Swales / Open Channels
• Attenuation ponds
• Infiltration basins
• Soakaways
• Sustainable
• Offers choice of open and closed systems

Typical Filter Drain
Typical Attenuation Pond
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GSI \ EPA \ DOE

• Risk and Risk Management
• Hazard
• Potential of contaminant loading
• Vulnerability
• Likelihood of contamination if a contaminant
  event occurs
• Consequences
• Depends on the Value of the groundwater

DOE, EPA, GSI, (1999). Groundwater protection
schemes
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GSI \ EPA \ DOE

• Groundwater Protection Responses matrix
• Available for each activity or group of
  activities
• Landfills
• Organic Land spreading
• Single Houses

DOE, EPA, GSI, (1999). Groundwater protection
schemes

• No Protection Response matrix for roads

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Implementation of Procedure

• To classify the risk arising from Road Runoff, a
  procedure for assessing the risk from runoff was
  implemented
• Risk of accidental spillage assessed
• Method of scoring Risk associated with road
  runoff
• Risk from routine runoff
• Risk scoring
• Additional Criteria assessed
• Positive Hydrostatic pressure
• Public water supply
• Karst Features
• Flow chart
• Practical Example

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Risk from Accidental Spillage

• Assessment of the risk of an acute pollution
  impact - HA 216 / 06
• Risk expressed as annual probability
• Guideline probability gt 1 acceptable
• May be less for SACs etc.
• Inputs
• RL Length of road
• AADT Annual Average Traffic Daily Flows
• HGV percentage of Heavy Goods Vehicles
• SS Spillage rates UK data
• Ppol Probability for a given accident of
  serious pollution occurring UK data
• Output
• Pacc Probability of a spillage
• Pacc RL x SS x ( AADT x 365 x 10-9)x(HGV /
  100)
• Pinc The probability of a spillage accident
  with an associated risk of a serious pollution
  incident occurring
• Pinc Pacc x Pol

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Routine Runoff risk scoring

• For routine runoff the factors attributed to the
  risk from road runoff are attributed a risk
  weighting HA 216 / 06

Source
Pathway
Degree of Risk X Weighting Risk Score
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Criteria 1 Traffic Density

• It is believed that heavy travelled roads such as
  motorways and multilane highways (AADT gt30,000)
  produce higher concentration of pollutants than
  roads located in rural areas (Barrett et al,
  1998)
• Therefore for this assessment the risk associated
  with runoff has been categorised into three
  levels
• Low Risk AADT lt 15,000
• Medium Risk AADT 15,000 50,000
• High Risk AADT gt 50,000

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Criteria 2 Rainfall

• The larger the rainfall, the larger the runoff
  however the longer the antecedent period, the
  more pollutant, therefore
• Two rainfall components
• Volume
• Low Risk lt 740mm
• Medium Risk 740-1060mm
• High Risk gt 1060mm
• Intensity in one hour for 1 in 100 year
• Low Risk lt 35mm
• Medium Risk 35-47mm
• High Risk gt 47mm

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Criteria 3 Soakaway Geometry

• Applies to soakaways and linear draina gefeatures
  such as filter drains and open ditches
• Risk depends on the directness of path and
  distribution of pollutant
• Therefore soakaway geometry categories
• Low Risk Linear feature
• Medium Risk Shallow Soakaway
• High Risk Single point serving high road area

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Criteria 4 Unsaturated Zone

• Considerable depths to water table can allow for
  attenuation of the pollutant
• Therefore the risk associated with depth of
  unsaturated zone has been assessed as depth to
  water table of
• Low Risk gt15m
• Medium Risk 15 5m
• High Risk lt 5m

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Criteria 5 Flow type

• Intergranular flow offers maximum opportunity for
  beneficial interaction between migrating fluids
  where as fissures by there definition offer
  direct paths to the water table
• Therefore for this assessments the risk
  associated with Flow type has been classified as
• Low Risk - Unconsolidated or Non fractured
  consolidated flow
• Medium Risk - Consolidated deposits
• High Risk - Heavily consolidated deposits,
  igneous and metamorphic rocks

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Criteria 6 Effective Grain Size

• Finer materials provide the greatest moisture
  storage and the longest delay in migration from
  the surface to the water table.
• Therefore the risk has been classified by the
  effective grain size encountered
• Low Risk Fine sand below
• Medium Risk Coarse sand
• High Risk Very Coarse sand above

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Criteria 7 Lithology

• Significant clay minerals and organic content
  offer increased potential for beneficial
  attenuation
• Therefore the risk associated with runoff has
  been categorised into three levels
• Low Risk gt 15 Clay minerals
• Medium Risk 15ltClay mineralsgt1
• High Risk lt 1 Clay minerals

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Application

• Using the above stated criteria and testing
  regime, a risk score is establish based on
  weighting and score
• Low 1
• Medium 2
• High 3
• Taking the final Risk Score
• Low Risk of Impact lt 150
• Medium Risk of Impact 150 250
• High Risk of Impact gt 250
• Using this rational
• Low risk minimal mitigation required
• Medium risk further consideration of particular
  situation is required
• High risk consider sealed system

X Weighting Risk Score
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Additional Criteria

• Positive Hydrostatic pressure and the path of
  least resistance
• Public drinking water supply / Source Protection
• Karst Features

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Positive Hydrostatic Pressure

• Occurs where ground water is naturally above
  level of pathway
• Where the direction of flow is into the receiving
  pathway, the risk of groundwater pollution is
  naturally mitigated as pollutant follows path of
  least resistance

Road Runoff
Water table
Positive Hydrostatic Pressure
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Public Drinking water supply

• Source Protection Zones
• Each locations requires case by case examination
  of the location of road run off in relation to
  ground water extraction point.
• Guidance
• Inner Protection Area
• 300m fixed radius (GSI)
• 50 day travel time, minimum 50m radius (HA216/06)
• Outer Protection Area
• Outer protection Zone 1000m (GSI)
• 400 day travel time (HA216/06)

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Karst Features

• Assessment of vicinity to works from GSI
  Groundwater Vulnerability mapping
• Assessment of specific features from available
  Ground Investigation information

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Procedure Flow chart
REGIONALLY IMPORTANT AQUIFER Point of Discharge
(Base) Drain / Ditch / Filter Drain
Conventional Drainage
GSI Assessment
Low / Moderate Vulnerability
lt 3m Low k Subsoil
From BH Logs / EW-MLA series
Continuous Hydrostatic Pressure
Competent Rock (RQD gt 40) and confirmed by on
site inspection
Conventional Drainage
Yes
Additional Criteria
Conventional Drainage
No
Distance from Karst, Sinkhole, Fault
HA216/06 Method
Low Risk Score lt 150
Conventional Drainage
Sealed Drainage
High Risk Score gt 250
YES
Conventional Drainage
Distance from Public / Private Water Supply
Medium Risk Score 150 - 250
2m of Low k subsoil below drainage level above
aquifer
Condition Satisfied?
Sealed Drainage
Sealed Drainage
NO
From BH Logs / EW-MLA series
Lined Interceptor Drain
Lined Filter Drain
Sealed Drainage

• May consist of compacted clay
• base with bentonite mix

to be confirmed on site by BRE Digest 365 or
similar approved every 250m or as agreed with
the DSR (Low k lt 10-5m/s Lambe Whitman, 1979)
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Practical Example

• Initial Assessment
• rock gravels within 3m of drainage
• ? Sealed Drainage required

• Secondary Assessment
• groundwater level between 0.9m 2.5m depth
• below drainage level therefore no continuous
  hydrostatic pressure

• Risk Assessment
• Score 190
• Medium Risk, examine material over aquifer
  insufficient buffer ? SEALED

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References

• DMRB-UK,9 (2006). Design Manual for roads and
  bridges Enviromental Assesment Vol11. Sec. 3
  Environmental Assessment Techniques Part 10 (HA
  216/06)
• DMRB-NRA (1996). Design Manual for roads and
  bridges Geotechnics and drainage Vol4. Sec. 3.
  Part 3 HD 33/96 (NRA Erratum June 2001)
• DOE, EPA, GSI, (1999). Groundwater protection
  schemes
• M. Breun, P.Johnston, M.K.Quinn et al.(2006),
  Impact of Assessment of highway Drainage on
  surface water quality
• Ciria (2007). The Suds Manual, CIRIA Report C697
• TW Lambe, RV Whitman (1979), Soil mechanics, John
  Wiley Sons

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Summary

• Risk Based Approach to the Impact of Road
  Drainage on Hydrogeology
• Suds and Road Drainage
• GSI \ EPA \ DOE Procedure
• Implementation of procedure
• Risk from accidental spillage
• Routine runoff Assessment Criteria
• Application of the Assessment Criteria
• Additional Criteria

• This paper is presented as a concept paper and
  due diligence should be exercised when addressing
  any issues contained within this presentation.
  Expert opinion should always be sought. Although
  every effort has been made to ensure that the
  accuracy of the material contained in this
  presentation, complete accuracy cannot be
  guaranteed. RPS Consulting Engineers accept no
  responsibility whatsoever for loss or damage
  occasioned or claimed to have been occasioned, in
  part or full, as a consequence of an person
  acting or refraining from action, as a result of
  a matter contained in this presentation.

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IEMA -Are Suds the Answer for Drainage?

• Thank You

Geological Survey of Ireland, 12th December 2007