ACO Technologies plc: Martin Fairley – Research DirectorHR Wallingford: Bridget Woods Ballard – Principal Engineer

Commercial sites and the delivery of sustainable drainage

Content

• Commercial Urban application of SuDS – challenges

• Importance of stakeholder group – supermarket sector example

• Use of ‘hypothetical model’, objectives, results

• Recent academic studies

• Future sustainable drainage strategies for the commercial sector?

• Research imperatives

Commercial urban sites: challenges & opportunitiesChallenges:

•Existing dense urban infrastructure

•Limited infiltration (soils, contamination)

•Single property – drainage approved but not adopted

•Stormwater ‘intensive’

Opportunities:

•9000+ UK sites (larger grocery retail)

•Top 3 combined turnover >£112bn

•53p in every £1 spent is on food and beverage

•Commercial objectives & CSR

•Part of the community – sustainability leadership?

Impact of parking?

• Tippecanoe County, Indiana: parking lots make up more than 6.57% of the total urban footprint

• ≈ 75% commercial

• area of parking lots exceeded the area of parks in the city limits by a factor of three

The environmental and economic costs of sprawling parking lots in the United States: Amélie Y. Davis a,c, Bryan C. Pijanowski a, , Kimberly Robinsona, Bernard Engel b∗

Commercial car park characteristics• Increase runoff and contaminant loadings to freshwater systems

• Contribute to urban heat island effect

• Biologically inert

• Maintenance sealant (PAH) impacts

Development of a ‘hypothetical’ model

Model constraints & objectives

Design constraints:

• Zero infiltration

• 1:60 gradient across site

• Minimum 2 treatment stages

• 1:100 year event managed on-site

Objective:

•To test SuDS in ‘commercial’ context

•To review potential economic/affordability implications

•To look at delivery and modelling challenges

•To engage the supermarket ‘giants’ in the debate

•To promote the consideration of future design options

Future: explore potential for retro-fit

The Draft National Standards / BS 8582Infiltration, where possible

InterceptionNo runoff for 5mm rainfall

Peak flow control1:1 year to greenfield/pre-development rate 1:100 year to greenfield/pre-development rate

Volume control1:100 year 6 hour to greenfield/pre-development volume

Water qualityMinimum 2 treatment components for commercial sites

Interception delivery

Infiltration

Rainwater harvesting (Y/D < 0.9, BS8515)

Green roof

Permeable pavement

Vegetated systems

>50%

Assumptions?

4 X rule – vegetated surfaces

2+ X rule – PP + infiltration

1 X rule – PP no infiltration, green roof

Volume control delivery

Further infiltration

Further rainwater harvesting

Tight control of runoff volume exceeding greenfield/pre-development (LTS)

(2 l/s/ha max)

Conveyance to minimalist vegetated SuDSBenefits

•No loss of parking spaces

•Conventional car park surface construction

Limitations

•Non-compliant Interception?

•Treatment sufficiency?

Satisfying ‘interception’ rule

Benefits

•Conventional car park surface construction

•Compliant solution

Limitations

•Loss of parking spaces - £2000 / space / week

•Additional landscape maintenance

Permeable sub-base

Benefits

Conventional car park surface construction

•No loss of car park spaces

•Compliant solution

Limitations

•Interception compliance?

•Cost?

Modelling challenges

• Interception

• Treatment

• Complexity of multiple level flow controls, storage minimisation and optimisation

Urban runoff contaminants: what are of concern ?

• A Minimum Data Set of Water Quality Parameters to Assess and Compare Treatment Efficiency of Stormwater Facilities

Simon Toft Ingvertsen,* Marina Bergen Jensen, and Jakob Magid

How are they most effectively controlled?…Results showed that about 99% of road-associated particles

(number concentrations) are smaller than 20 μm.Characteristics of road sediment fractionated particles captured from paved surfaces, surface run-off and detention basinsM. Kayhanian , E.R. ⁎McKenzie 1, J.E. Leatherbarrow 2, T.M. Young (2012)

•Fine particles play major roles in controlling the fate of metals

•In the US, most quality criteria for metals are in the dissolved form

•Drying process important for XOC’s

•Combined aerobic / anaerobic zones for nutrients

•Treatment train – that integrates sedimentation and filtration, probably most effective (with some redundancy for robust control)

•Is it more cost effective to treat small events, and discharge larger ones without?

•Need for design to minimise re-suspension of particulates

Conclusions

• Compliance with draft Standards not significantly more costly ‘provided that Interception can be met in an affordable way’

• Where even very limited infiltration can be mobilised, subsurface storage could potentially be used to facilitate disposal of 5mm

• Green roof crucial to Interception delivery

• Detailing and modelling skills key to minimising impact of drainage requirements where space is valuable

• R&D into understanding and appropriately mitigating environmental risk associated with runoff from commercial car parking would be of great value

• And this requires understanding of the efficiency of vegetated components and proprietary products in treating likely pollution levels