INFRASTRUCTURE STRATEGY

9.4.1 Water quality and pollution risks for industrial premises and estates

Designing the drainage infrastructure for an industrial estate requires consideration of the two primary categories of pollution risk identified in the opening section of this chapter: incident risk management and contingency planning, and designing to capture and treat diffuse pollutants in runoff.

Details of pollution risk have been described elsewhere (e.g., Harper, 1987; D’Arcy

& Bayes, 1995). The diffuse nature of industrial estate pollution, with multiple sources, requires a best management practice approach, involving good housekeeping measures such as bunding oil and chemical tanks as well as provision of drainage infrastructure (SUDS features) to capture pollutants entrained in runoff (Campbell et al. 2004). An open drainage structure has great merit since it allows for easy inspection of drainage by management as well as statutory agencies, and allows for quick and effective damage-limitation responses in the event of traffic or other actions. Hydrocarbons are generally the contaminants most likely to exceed recommended limits in urban stream sediments (e.g., Wilson et  al. 2005). Various studies have independently demonstrated that soft engineering SUDS favour not just capture of diffuse pollutants, but provide degradation in situ (Horner et al. 1994; Napier et al. 2009; Leroy, 2016).

For hydrocarbons, that degradation reduces the cost of disposal when the accumulated sediment is eventually removed from the features (avoids likelihood of need for expensive disposal at an approved landfill site). Table 9.2 summarises how different drainage features can be important elements of a strategic approach to infrastructure provision when planning industrial and commercial developments.

A third category, usually addressed by guidance and best practice recommendations for building site construction, rather than the infrastructure itself, is the misconnection of process effluents into surface water drains. Typical errors include sewage as well as various wash waters and other effluents. Causes of pollution vary from structural errors in construction, to ad hoc steam cleaning of plant or vehicles. A shared steam cleaning area on an industrial estate would be an infrastructure option which could be a good way to ensure proper collection and treatment, or recycling, of wash waters, if designed and agreed in consultation with the local water utility for sewer connection. Use of mobile plant for irregular steam cleaning may still occur however, and in a conventional industrial estate served by a separate sewer system will result in pollution. A pipe free system, using SUDS techniques, should reduce risks of pollution by operators unaware of the different types of sewer on conventional premises. That is as important for commercial as for industrial premises.

9.4.2 Spatial application of SUDS

This refers to where the technology should be applied across a development. It is concerned with responsibilities, with ownership of sources of pollution and

Table 9.2 Usefulness (Good, Medium, Limited) of various types of drainage features for industrial/commercial premises and estates. FeatureContingency Plans for Major Incidents Diffuse Pollutant Capture*

Comments: 1.Pollutant degradation in situ 2. Storage capacity 3. High visibility drives cleaner practice Grass filter stripLimitedGood1 if not overloaded, 3 Grass swaleGoodMedium1,2,3 Large volume for incident management Under-drained swaleMedium/GoodMedium1,2,3 Less storage capacity at surface than a swale Permeable pavementLimited/ MediumGood1,2 May be difficult to access contaminant in event of an accident or spill, storage dependent on sub-base void space volume Gravel filter drainMediumMedium1,3 Limited storage, but slows release from source area if via a flow control structure Bioretention unitsLimitedMedium1,3 Visibility of bad practice disposal Green roofsLimitedMediumFor air pollution (e.g., factory unit air vent release) Green wallsLimitedLimited1? Green walls rooted in a filter drain may be good? Detention basinGoodMedium/Good1,2 Drain-down with facility to close outlet Retention pondGoodGood1,2 Quiescent water body for skimming oil after spill, long residence time. Oil boom deployment easy. Good for ‘polishing’ drainage quality routinely. Fire-water source. Oil interceptorsLimitedLimitedClose to high-risk installations, *pre-treatment for fuelling points, ideally outflow to foul sewer Silt trapsMediumLimitedIf not too close to at-risk installations, may be useful as pumping sumps for fire water Inspection chambersMedium/GoodLimitedA large chamber prior to drainage connection to public network is good for controlling outflow of drainage and fire-water, or pumping latter for safe disposal. High intensity filtration unitsLimitedRetrofit optionProvides ways to address existing chronic pollution Vortex separatorsLimitedRetrofit optionProvides ways to address existing chronic pollution *Treatment effectiveness – see International Stormwater BMP Database, [2016] accessed at www.bmpdatabase.org, and CIRIA (2015).

Drainage infrastructure for industrial and commercial premises 127 stormwater runoff, with contingency planning and risk management. It allows for policies by planning authorities and environmental regulators to require SUDS as source controls, for conveyance and for end-of-system.

9.4.2.1 At source and on site

It is necessary to have source control SUDS at each unit on an industrial estate, to allow capture of pollutants as close to source as possible, and within the remit of site management, for each of the premises on the estate. This allows for management at each site to see and act upon incidents, as well as ensure maintenance is undertaken for the site’s own drainage infrastructure. It also establishes responsibility for each site owner/operator (consistent with the polluter pays principle). Public sector (or private estate managers) should only be responsible for off-site drainage, including SUDS features.

All premises are not alike and the Maryland stormwater manual (Maryland, 2009) identified stormwater hotspots, defined as

‘a land-use or activity that generates higher concentrations of hydrocarbons, trace metals or toxicants than are found in typical stormwater runoff, based on monitoring studies.’

Table 9.3, modified from the Maryland guidance identifies some hotspots likely to occur on industrial/commercial premises. To protect groundwater resources, runoff from hotspots cannot be allowed to infiltrate, and a greater level of stormwater treatment is required at hotspot sites. Hotspots are contrasted with lower risk urban areas such as residential streets and rural highways, residential properties, office developments, and non-industrial rooftops.

Table 9.3 Some identified stormwater hotspots on industrial/commercial premises.

Hotspot Comments

Outdoor storage of scrap materials Risks of oil, PCBs, PAHs, toxic metals, and other pollutants

Recycling facilities Depends on materials on site Vehicle fuelling stations Oil interceptors

Vehicle service & maintenance facilities Sealed sumps, indoor activities preferable Vehicle & equipment cleaning facilities Oil-detergent mixes, solvents

Fleet storage areas (bus, truck etc.) Hydrocarbons

Commercial parking lots Hydrocarbons

Industrial sites with outdoor storage of potential pollutants

Raw materials, products and by-products, wastes

Outdoor loading/unloading areas Solids and liquids, foods and other degradable materials, not just toxic substances

Council depots Local authority road sweepers, refuse trucks, fuel, maintenance work & cleaning

Marinas and hull paining/

refurbishment areas

Detergent, anti-fouling paints, fuelling points Source: Aadapted from Maryland, 2009.

9.4.2.2 Conveyance swales or drains

The range of pollutants being transported in and around industrial estates also warrants use of open, passive treatment features such as grass swales or filter drains for conveyance to a final SUDS feature. Typically, the conveyance features for the drainage will be alongside the access roads in an estate. A road tanker accident could occur away from the destination premises, and a roadside intervention feature such as a swale or filter drain allows for local pollution prevention action to isolate and contain spills. The technology will also provide a secondary treatment function after the source/site controls. Swales also allow visible pollution incidents such as oil or dyes, or toxic effects on vegetation, to be easily seen and hence dealt with.

9.4.2.3 Regional (whole estate) features

It is impractical, unjustifiable, and probably undesirable to require a stormwater wetland or retention pond for every factory or other premises on an industrial estate.

In normal circumstances a final retention pond, if protected from excessive loading by source controls and road side swales as above, would produce river quality drainage even from an industrial estate (D’Arcy et al. 2007). And if and when a major incident occurred, the end-of-system retention pond or wetland would also allow management of a catastrophic pollution accident (e.g., a major sludge or oil leak).

Considering an estate or business park as a whole, the above application of the technology within and across the estate constitutes a ‘treatment train’ of successive stormwater management measures. In practice a ‘treatment web’ may be a more appropriate description of the drainage features; some in series, but not all in a single strand.

9.4.3 Treatment capability

For an entire estate, or an extensive factory such as an automobile assembly plant, cable manufacture, or a brewery, this is a function of two different considerations:

(a) the collective master plan overview of the treatment impact of an overall scheme, which aims to produce river quality drainage from the development as a whole

(b) the type of treatment processes that are present in any single SUDS component of the development infrastructure.

The first category (a) is the sum of the second, (b). Treatment capability is concerned with how a feature will capture pollutants entrained in stormwater runoff, and also the fate of pollutants in the SUDS features. It is also important to consider what proportion of the pollutant load in the runoff will be treated by the feature, and how much by-passes it, if any? The essence of a best practice approach is that environmental protection should be achieved if units with known and demonstrable performance are designed on the basis of the pollutants likely to be

Drainage infrastructure for industrial and commercial premises 129 present in runoff from the catchment, and are constructed and installed correctly, and maintained.

Pollutant capture may be by sedimentation, filtration, adsorption, or storage.

Biodegradation and decomposition may be achieved by ultraviolet light and microbes, and pollutant uptake can occur in vegetation and, for some substances, in the food chain. Treatment processes and factors affecting the removal of various pollutants have been considered in various studies and guidance publications, for example, Horner et al. (1994), Campbell et al. (2004), Ellis et al. (2013), and CIRIA (2015).

The fate of pollutants may involve biodegradation in the water column (e.g., in a retention pond), or in aerobic soils in a swale or detention basin, or on microbial films on stone media in permeable pavements and filter drains, as well as on stems of higher plants. Degradation may occur on the surface of vegetation exposed to ultraviolet light, or on hard surfaces such as permeable pavement (less likely to be washed off by sheet flow into drainage systems than conventional pavement).

The treatment capabilities and fate of pollutants are important for maintenance considerations and disposal costs of accumulated material in SUDS, as are sediment storage capacities within a SUDS feature (Napier et al. 2009).

A treatment train of measures allows for sequential capture of pollutants in successive features across a development; sometimes within premises, certainly from the source control at each of the premises, through to a regional pond or wetland. The different pollutant capture and/or degradation properties of various types of features can be considered in selecting features for use in such a treatment train. The cumulative removal of pollutants from runoff across a development will enhance the biodiversity and amenity value of any end-of-system feature such as a pond or wetland.

A stormwater management train, by contrast seeks to include all aspects of stormwater management needs; flood risk as well as pollution risk. It may seek merely flow attenuation at source for roof runoff, some treatment for driveway runoff, as well as provision of treatment for street runoff and/or perhaps end-of-pipe features providing flood risk management functions too, with due allowance for exceedence flows to move across a development without damage. It incorporates the aspirations of the treatment train in a broader context, rather than simply for example allowing high flows of possibly cleaner runoff to by-pass treatment features, but possibly still present a local flooding risk.

9.5 DISCUSSION