Gordon Robb, technical director at SLR Consulting, outlines assess potential impacts of development on water dependant habitat.
In addition to other statutory duties, the Scottish Environment Protection Agency (Sepa) has a responsibility to safeguard abitats sustained by groundwater, known as groundwater dependent terrestrial ecosystems (GWDTE).
Development, and in particular ground excavation, which can effect groundwater flow paths and groundwater quality has the potential to impair areas of GWDTE which are protected by the EU water framework Directive.
Without appropriate design or mitigation, excavations can intercept the groundwater table and divert groundwater flows away from areas of GWDTE or construction activities can introduce materials such as concrete or aggregate that can alter local groundwater chemistry and directly or indirectly impair GWDTE.
Assessment approach
In order to assess potential risk to GWDTE, Sepa has issued guidance to developers and for their advisors.
Sepa requires, as a minimum, a phase 1 habitat survey to be undertaken and provided as part of a planning application. The survey is used to identify wetland types. If it suggests that GWDTE may be present at or near a site where excavation is proposed then a national vegetation classification (NVC) survey also needs to be provided.
Buffers of 100 metres and 250m around areas of GWDTE are proposed by Sepa for excavations up to 1m and greater than 1m respectively. If development within these buffers is proposed then a detailed qualitative / quantitative assessment is required. This should be used to assess whether the development proposals will impact on the GWDTE, whether mitigation measures can reduce the significance of impact or whether the development proposals need to change to ensure no impact on the GWDTE.
Application of EIA to assess areas of GWDTE
As part of an EIA, much information is gathered to assess baseline conditions at the site and in its immediate surrounds. Typically there is a lot of information that can be used to characterise the site's geology, hydrogeology and hydrology, all of which are relevant in assessing GWDTEs. In addition, many sites will also have much information which can be used to characterise with confidence the habitats at and adjacent to the site. These sources of information can be used together to develop a conceptual site model (CSM) to complete an initial assessment of the likely presence and sensitivity of GWDTE.
Screening using NVC mapping can be used to identify areas that are more likely to have wetland habitats sustained by groundwater, for example, NVC types M6, S11, W4, CG11 and U17. Combined with the CSM, the initial GWDTE assessment can be refined.
Where the potential presence of GWDTE is identified through hydrogeological conditions and NVC mapping, developers can either apply SEPA's recommended buffers and/or undertake further assessment to confirm whether that identified habitats are in fact sustained by groundwater or not.
This screening approach, which is embedded in EIA methodology, allows appropriate time and resource to be invested when assessing GWDTEs.
There are number of methods that can be used to assess further and in greater detail areas of potential GWDTE. SLR has combined interpretation and assessment by ecologists, geologists, hydrogeologists and geochemists very successfully to assess the ground conditions near areas of GWDTE, potential groundwater flow paths and water quality to accurately delineate the contribution of different water sources to areas of possible GWDTE.
In a number of instances, SLR has been able to confirm that the potential GWDTEs are in fact sustained by surface water rather than groundwater, thus removing potential development constraints.
The EIA approach to assessment of areas of potential GWDTE also allows appropriate mitigation measures to be identified to maintain or improve GWDTE. For example, measures that maintain existing surface water or groundwater flow paths can be identified and specified. An understanding of the site ecology and geochemistry recommendations can be used to ensure that aggregate or concrete used on site will not locally alter groundwater quality.
An EIA approach to site assessment provides a very useful screening and scoping tool to assess potential impacts of development on water dependant habitat. The combination of common EIA disciplines can quickly develop a CSM which can be used as a screening tool to identify where further assessment is required. The same disciplines can be used to design additional site investigation, assess findings and identify appropriate mitigation measures to safeguard areas of GWDTE and groundwater resources.
