How to get the best quality sports pitches
By Alex Vickers, Turftrax Ltd
Brownfield sites are commonly developed into sports pitches either via Section 106 agreement clauses or as part of wider regeneration programmes. This can present real challenges if sustainable, quality surfaces are to be established. The most obvious challenge is dealing with any contaminated land issues present on the site. This creates complications associated with any cut and fill, grading and drainage works that could potentially expose any contaminants to sensitive receptors. Clearly, in such situations, expertise in contaminated land remediation should be sought.
Risks associated with such land can be high, not only to users, but also to those working the sites and, in financial terms, to the owners. It is important to understand the nature of any such risks before any works are carried out, both in respect to health and safety and also in respect to liability for possible pollution or exposure of sensitive receivers to the source of possibly hazardous materials.
Once such material is exposed at the surface, a real risk of exposure to sensitive users is created, potentially leading to a site that was previously classed as uncontaminated, becoming classed as contaminated, with all the associated costs that will bring. For this reason it is important not to disturb any suspected sites and to get expert advice from a specialist Contaminated Land Consultancy where there is any doubt.
If you suspect a site may contain contaminants, then samples from both the topsoil (top 25 mm) and the suspect layer should be taken and sent for analysis at a certified laboratory for a standard contamination test which will cover both metals and organic contaminants. This should be done very carefully using protective equipment, if required. Again, it is sensible to take expert advice on this though this can be very expensive.
Interpretation of the results can be tricky, however the Environment Agency have published Soil Guideline Values (SGV's) contaminant concentrations for certain contaminants which will help you decide whether your site is a potential source of contamination. These can be found at: www.environment-agency.gov.uk
These only cover a few of the potentially harmful substances that can be found in land, but they are a good start. One issue in respect to sports fields is that the risk assessments carried out to produce the SGV's do not cover this end use (they typically cover residential use with and without growing vegetables, allotments and commercial / industrial use). A private consultancy company, WS Atkins, have developed an additional risk assessment model that now covers more contaminants and also provides SGV's for parks and playing fields.
This model is only available commercially from Atkins however, (http://www.atrisksoil.co.uk/). Even with this information it still only covers human health and not risks to property, water courses or protected habitats. It will only help you to establish if your site is a potential source of contamination.
Whether a site can be classed as contaminated not only depends on the contaminants in the soil, it also depends on whether it poses a significant risk of causing significant harm to people, their property, water courses or protected environments/habitats.
To establish this you need to establish whether there is a source of contaminants (hence the sampling and the use of SGV's), a plausible pathway and a sensitive receptor. If you have all these things then your site may well be contaminated, but that will be for the Local Authority or, in some cases, the Environment Agency to decide.
In the first instance, your Local Authority should be your first port of call if you need to take things further, and they will be able to recommend suitable specialist companies to assist you. It cannot be emphasised enough that if you have concerns about contamination on a site you already own or one you are considering purchasing, then you must get expert advice. Mistakes in this area can be very expensive and can also be dangerous.
In doing this, however, it is vital not to lose sight of the required end use of your site and the characteristics required to ensure the sports pitches produced are not only fit for purpose, but are also sustainable for those who will be left to manage them. Frequently, a traditional, hard civil engineering approach results in pitches that have certain engineering characteristics such as stability, surface evenness and a backbone of land drains, but leaves a lot to be desired in terms of creating an environment to support a living sward of grass and to provide the required playability for the sports in question.
One approach to dealing with sites that have some contamination issues is the careful mapping of the areas affected. This will allow sensible planning of the sports facilities such that the location of the pitches can be optimised to ensure that they are placed in the least sensitive areas. In some cases, it may not be possible to place less sensitive uses such as car parks over the contaminated areas, therefore the methods used to construct or improve the sports pitches need to be adjusted to ensure the users and wider environment are protected from any contamination and that costs are minimised. Figure 1 shows the results of an Electro-Magnetic Inductance (EMI) survey of existing amenity land built over an old sewage works.
The scan clearly identified the extent of the old works and, when validated by targeted soil sampling and analysis, allowed different approaches to be taken to reconstructing and improving the sports fields on the site.
The EMI survey allowed the engineers to avoid designing any pitch construction works that would have penetrated the clean cap over the contaminants below (concentrated in the darker wedge shaped patch shown in Figure 1). The approach in this case was to import clean topsoil to build up levels in the main rugby pitch and training grid, thereby allowing the pitch to be graded level and then drained without cutting into the contaminated layers.
To use this approach on all 4 pitches on the site would have been prohibitive in respect to cost, however the scan allowed the extent of contamination to be mapped and the remaining pitches were relocated off the contaminated area and graded and drained in the existing, clean natural soil. This allowed three pitches to be improved for less than one third the cost of reconstructing them all on the same basis as the rugby pitch.
Very often, when pitches are constructed on brownfield sites they are either built directly in the engineering cap (many sites do not have a restoration cap), producing very low quality pitches that drain badly and have insufficient air-filled porosity to support a healthy sward, or built on very thin layers of free-draining material above the compacted engineering cap. In such situations it is possible for very little play (especially in respect to winter sports) to take place even up to 3 years post-construction.
Avoiding this is relatively simple by carefully selecting the capping material. Obtaining the cheapest top-soil or soil forming material may make economic sense at the time, but the cost of reconstructing failed sports pitches years later can be very significant. Clearly, an engineered cap must meet its primary purpose of isolating the material below the cap. Therefore, rather than risk the integrity of that material, it is better to add at least enough topsoil material to allow a drainage system to be installed safely. A minimum depth of 500mm for a lateral drainage system is required. Shallow drains are very inefficient and generally a poor use of money.
By carefully designing drains it might be possible to use lower quality soil material for most of the build-up and then have a thinner layer of better quality material that will drain effectively as a result of the supplementary drainage. An example of this is shown in Figure 2.
In this case, a shallow depth of free-draining sports rootzone material is placed over a network of shallow, close centred slits filled with the same rootzone material. This creates a much deeper effective drainage depth due to the hydraulic connection between the material in the slits and the material in the surface layer. In this case, the engineering cap must be deep enough to allow lateral drains and slits to be installed (over 700 mm depth), but the results can be first class.
A key drawback to the use of very free-draining materials is, however, the effect this has on water requirements and nutrient requirements. Typical specifications for top-level pitches have drainage requirements in the region of 150 mm hr. The inevitable consequence of this is the use of sand for construction and the need for intensive irrigation to maintain turf vigour and surface stability. High drainage rates result in nutrient leaching from the sand material and a need for frequent fertilisation.
The costs of this can be very high indeed. At a time when efficient water use is required (despite the recent bad weather), this approach cannot be sustainable in any situation outside of high level sport. To this end, the use of suitable natural soil and the creation of deep profiles over engineering caps may be a more effective solution in the long term. Though initially expensive, deep profiles and careful soil management can create excellent pitches with drainage enhanced by a sufficient depth of soil that allows a large enough hydraulic head to build up in the soil pore network to push water from the pores at the base of the profile.
Where funds are more limited, and the quality of the material available for construction is poor, then careful design of surface shape on pitches, and the use of composted green waste can accelerate the development of good soil structure within the restoration cap, which ultimately can create good pitches that have a much lower water and nutrient requirement but, at the same time, still perform well, albeit with a lower carrying capacity.
In conclusion, careful planning can result in significant savings in construction costs and in the long-term sustainable performance of sports pitches constructed on brown field sites. Unfortunately, all too often the pitches are built with little thought to their long-term use, sustainability or minimum performance requirements. This either leads to expensive remediation work and pitches that are still compromised by their initial construction, or worse, to pitches that are of no use to their community at all. This undermines a developer's reputation and may limit the value of the sporting legacy left from the regeneration of such sites.