Appropriate Assessment of Land Quality to support a Habitats Regulations Assessment by Delta-Simons
Shortlisted for Brownfield Awards Category 1 - Best Project Preparatory Work
The project completed by Delta-Simons in support of the G-Park Ashby development represents possibly the first detailed and fully Habitats Regulations Assessment (HRA) compliant risk assessment of contaminated land in the UK. The assessment facilitated planning permission for the relocation of a 1km stretch of a watercourse directly feeding, and within the Impact Risk Zone (IRZ) of, the River Mease Special Area for Conservation (SAC).
The success of this Appropriate Assessment demonstrates the value of a programme of work that was planned and conducted in close consultation with regulators and in accordance with best practice, with an innovative approach to risk assessment. The Assessment was successful in removing the statutory ecological objection to the planning application and facilitated development of a large brownfield site, whilst ensuring a sensitive waterbody will be protected (and indeed enhanced) with a high level of evidence.
Background
GLP applied for planning permission for the redevelopment of a 27 Ha. former UK Coal processing facility for a new warehouse and distribution centre. The proposed development required the diversion of a tributary of the River Mease into a newly constructed 1km watercourse around the Site perimeter.
The statutory ecological consultee initially objected to the planning application as they considered a Likely Significant Effect (LSE) could occur from release of contaminants into the River Mease SAC from the proposed river realignment. The proposed realignment underlay disused railway sidings and former processing infrastructure, and cut through a coal seam in the underlying bedrock, which raised concerns that the watercourse could be introduced to new sources of contamination. It was therefore agreed that an Appropriate Assessment would be completed, as required by the Habitats Regulations.
Aerial View of the Proposed Development Site
View of the existing, modified channel with low biodiversity
The Habitats Regulations have stringent requirements; they simply state that “the project should not be authorised unless it can show beyond reasonable scientific doubt it will not adversely affect the integrity of the SAC.” An Appropriate Assessment must also consider cumulative effects of other plans / projects on the SAC. These specific requirements necessitated design of a bespoke investigation and a novel approach to the subsequent contaminated land risk assessment to deliver the Appropriate Assessment.
Innovation & Best Practice
Traditional contaminated land risk assessment approaches for Part 2A or development purposes were not appropriate in this scenario. Furthermore, the Environment Agency (EA) ecological risk assessment framework (Ref. 1) , whilst useful, was not designed with the intention of demonstrating ‘absence of an adverse effect beyond reasonable scientific doubt’. Delta-Simons therefore developed a bespoke, logical and tiered approach to the risk assessment process.
The ultimate aim was to demonstrate no risk of adverse effect on the SAC from Site-sourced contamination, with particular focus on existing, identified pressures on the River Mease in the wider catchment.
The intrusive investigation incorporated the following elements:
▲ Targeted investigation competed to obtain baseline soil and groundwater quality data representative of the current watercourse location;
▲ Similarly targeted investigation to obtain representative soil and groundwater quality data for the proposed watercourse location (and elevation), hence facilitating a direct comparison and whether the proposed relocation would increase or decrease the contaminant loading to the watercourse without mitigation;
▲ Sampling and analysis to assess existing upstream water quality of the watercourse and current impact as it passed through the Site, focussing on contaminants that were already elevated in the receptor so making it more sensitive to any additional inputs from the diversion.
Ground Investigation Design Targeting both Current and Proposed River Channels
Compliance
Traditional contaminated land risk assessment approaches for Part 2A or development purposes were not appropriate in this scenario. Furthermore, the Environment Agency ecological risk assessment framework (Ref. 1), whilst useful, was not designed with the intention of demonstrating ‘absence of an adverse effect beyond reasonable scientific doubt’. Delta-Simons therefore developed a bespoke, logical and tiered approach to the risk assessment process.
It was important to efficiently eliminate contaminants that will not adversely affect the integrity of the River Mease SAC and focus attention on those contaminants that required further, detailed assessment. Whilst the ecological risk assessment framework is sound, appropriate screening criteria (which are endorsed as a general approach by the EA) for soils are very limited.
Published, authoritative ecological screening criteria derived from UK sources (i.e. the EA) are limited in terms of the number of contaminants covered and also in the ecological context. The Soil Screening Values (SSVs) that the EA has derived to date (Ref. 2) and (Ref. 3) are based on direct ecotoxicity – i.e. organisms and plants that come into direct contact with soil and, therefore, not directly applicable for the G-Park Ashby assessment, where the risk assessment needed to consider mobilisation of soil contamination into groundwater and subsequently migrating into the river. On this basis, the SSV methodology adopted by the EA was considered likely to be overly conservative, albeit not necessarily so for every contaminant, and Delta-Simons undertook a review of the ecotoxicological basis for the individual SSVs to determine appropriateness.
In the absence of SSVs for many contaminants, Delta-Simons adopted the following approach:
▲ Some contaminants should not be present in background concentrations (e.g. trichloroethene). Any elevated concentrations above laboratory detection limits were therefore to be considered in greater detail via site-specific risk assessment.
▲ Where contaminants are naturally occurring and would be detected by the laboratory, it was important to consider background concentrations and whether the contaminant in question was elevated with respect to this background. If the contaminant was at or below background concentrations, this was considered to represent sufficient scientific evidence that the contaminant would not adversely affect the River Mease SAC.
▲ As one line of evidence, Delta-Simons reviewed international ecotoxicological GAC, albeit incorporating a review of limitations and how applicable the method of derivation was to the UK / EA approach.
▲ The risk assessment incorporated consideration of specific EA conservation objectives for the River Mease SAC, which in terms of chemistry focussed on phosphate and ammonium / nitrate and incorporated a review of existing EA water quality data for the wider catchment.
The tiered approach to the contamination assessment is summarised in the flow chart below:
Robust, Sustainable & Defensible Solution
The tiered approach of the Assessment enabled the majority of contaminants to be rapidly dismissed as not being of concern. In particular, an absence of contamination associated with historical Site activities, such as trackside fuel spillages or application of pesticides / herbicides, was demonstrated, and such sources could therefore be discounted from posing a risk to the SAC.
The laboratory data identified elevated nitrogen in both oxidised and reduced forms in groundwater and surface water. The presence of this nutrient was important due to the eutrophic nature of downstream sections of the River Mease SAC. The dataset obtained allowed understanding of the source of nitrogen and transformation / behaviour through the Site. Furthermore, it was possible to demonstrate with confidence the absence of an on-Site source for nitrogen compounds, and to identify agricultural sources within the immediate vicinity and via a small tributary impacted with reduced nitrogen.
Nitrogen Cycling in Groundwater through the Site – Influx of Reduced Nitrogen from Tributary and Farmland and Oxidation Downgradient
Elevated phosphate recorded in surface water in the existing watercourse was able to be attributed to the confluence of a tributary with off-site agricultural fertiliser application identified as the distinct source. Without a carefully thought out sampling strategy, such an input from an off-site source would not have been possible to prove with the level of confidence required by the Habitats Regulations.
Elevated concentrations of arsenic, lead, zinc, naphthalene, fluoranthene and pyrene were recorded in bedrock in proximity to the on-site coal seam, consistent with the presence of coal in the sample. As such, noting that the proposed Brook diversion earthworks would result in the coal seam being exposed in the face/base of the Brook channel, it was considered logical to conclude that this would present a potential risk to surface water quality and hence the SAC and represent a LSE without mitigation.
The investigation also identified elevated selenium in groundwater in Coal Measures bedrock in proximity to the coal seam that would be exposed in the bed of the new river course. Consequently, release of selenium and potentially other metals from bedrock could result in an LSE without mitigation.
Selenium Concentrations in Groundwater Along the Proposed River Course Identifying Increase Coincident with Coal Seam
Cost Effectiveness
The design of the investigation and risk assessment was such that, in one phase of work, it was possible to demonstrate the absence of an adverse effect from the historical use of the Site beyond reasonable scientific doubt. The project did however confirm an LSE associated with exposure of a coal seam within the riverbed diversion and potential release of metals and PAHs into the watercourse.
The earthworks for the watercourse diversion were re-designed to mitigate risk from the coal seam outcrop by overdigging the channel excavation by 2m local to the seam and filling the void created with impermeable clay to prevent future direct contact with surface water and thus protect the SAC from risk of adverse effect. This was the only remedial measure identified as necessary.
The efficient process of achieving the high level of proof required to achieve Habitats Regulations objectives in a single phase of works prevented delay of commencement and confidence that the proposed river diversion could provide environmental betterment with improved habitat and without deterioration to water quality.
Engagement
Delta-Simons and GLC engaged in extensive consultations with Northwest Leicestershire District Council and their statutory ecology consultant (responsible for all aspects associated with the River Mease SAC). The regulators – the Council, their ecological consultant, the EA and Natural England had no experience of dealing with a contaminated land investigation to assess potentially adverse effects on a SAC. Therefore, it was important to explain the proposed approach in great detail and agree a practical but thorough process for the design and scope of both the investigation and complex risk assessment process that would achieve the requisite level of proof regarding potentially adverse effects.
The key regulator, the ecological consultant, was not conversant with the contaminated land discipline; we therefore ensured communication of the issues was handled in a simple and non technical manner. Furthermore, both Natural England and the Environment Agency were consulted on various technical aspects within their areas of expertise and approved all elements of the work completed, including investigation design and risk assessment process.
The final report produced by Delta-Simons was approved in short order, with only minor queries by the local authority, their statutory ecologist and the Environment Agency.
Environmental, Economic & Social Benefits
It was essential for the tributary of the River Mease (that currently meanders through the centre of the Site) to be diverted to enable redevelopment of this strategically important 27Ha brownfield site within the so called ‘golden triangle’ for UK logistics. The Site had been derelict since 2004 and if the diversion could not be accomplished, the Site would have been blighted as an economic resource.
However, the need to demonstrate that the diversion would not pose an environmental risk downstream was also paramount, given the sensitivity of the high-quality habitat that is already at unfavourable status due to chemical contamination (nutrients). The obligation placed on the developer by the Habitats Regulations, to ensure absence of adverse impact to the River Mease SAC, is therefore an onerous level of proof – well beyond what is typically required for a contaminated land risk assessment, but justified and supported by case law.
The successful risk assessment process removed the planning objection and permission was granted for the logistics development to proceed. The diversion of the watercourse provides the opportunity to place the river in a higher quality channel, to create more favourable habitat for key species including Spined Loach, Bullhead and Otters, all identified in the SAC designation. The development will also result in a £30m investment in the Site to create the new business and natural environment and potentially create up to 990 new jobs once completed.