Guidance for architects, and developers on flood risk, drainage and phase 1 contaminated land reports is summarised below with links to the key summary documents.
Planning legislation and guidance places the responsibility on developers and/or landowners to secure a safe development with respect to contamination. The Council’s duty is to ensure that owners and developers carry out the necessary investigations and formulate proposals for dealing with any contamination in a responsible and effective manner.
The contaminated land assessment procedure will identify the potential for contamination and identify possible areas that may require remedial works in order to make a site ‘suitable for use‘. The investigation is usually split into three phases, although not every site will require each phase to be carried out. The investigations should be carried out in accordance with established procedures such as (but not limited to):
The Phase I Preliminary Risk Assessment (also known as a desk study) is the collection of information in order that the ‘conceptual model’ can be established. The study should document the site history and identify all potentially contaminative land uses.
The conclusions of the report should contain recommendations as to whether the site is, or can be made suitable for its proposed use, and also any proposals for progression to Phase II, if required.
Note that Cheshire East do not accept the submission of a HomeCheck Report or similar in lieu of a Phase I Preliminary Risk Assessment. These reports are written for conveyancing purposes and do not fulfil the requirements of a Phase I assessment.
Phase II Ground Investigation
A ground investigation is an onsite survey of the actual ground conditions at the site. The purpose of this is to prove (or disprove) the presence of possible contaminant linkages, mainly through the sampling of soil and groundwater and also through ground gas monitoring where necessary. The results of these investigations should determine whether any contamination exists and if so, if it is sufficiently elevated to pose a potential risk to health. Investigations also focus on the presence of pathways, which can include groundwater, and an assessment of the actual and proposed land uses.
Phase III – Remediation Strategy / Verification Report
The remediation phase of the process is split into two sections. Firstly, the Remediation Strategy is a document detailing the objectives, methodology and procedures for the proposed remediation works. This must be submitted for approval by the Council before any works commence and is usually a requirement of a standard contaminated land condition.
Secondly, following completion of the works, a Verification Report must be submitted demonstrating that the works have been carried out satisfactorily and the remediation targets have been achieved.
Cheshire East state that a Phase 1 assessment should include a walkover survey which means assessing the site and identifying any visual evidence of sources of contamination (oil tanks, staining or ash/made ground).
Cheshire East Council
Most floods in Cheshire East have come from rivers, surface water run-off and sewers. There have been few problems caused by groundwater flooding.
If you are making a planning application, Cheshire East advise to check your Site’s flood risk. Remember to check both the flood risk from rivers or the sea and the flood risk from surface water for a full picture of risk at your location.
A Flood Risk Assessment (FRA) will be required for development proposals of 1 hectare or greater in Flood Zone 1 and for all proposals for new development located in Flood Zones 2 and 3 as designated by the Environment Agency. An FRA will also be required for any development other than minor development in a designated critical drainage area which has been notified to the Local Planning Authority by the Environment Agency.
The FRA should identify and assess the risks of all forms of flooding to and from the development and demonstrate how these flood risks will be managed, taking climate change into account. The FRA should identify opportunities to reduce the probability and consequences of flooding.
The Environment Agency’s Flood Map is the main dataset for predicting the location and extent of fluvial flooding through Cheshire East. This is supported by the Weaver Gowy and the Upper Mersey CFMPs and a number of detailed hydraulic river modelling reports which provide further detail on flooding mechanisms.
As of August 2013 (when Cheshire East’s SFRA was published) 1,800 residential properties had been identified to be within Flood Zone 3. The towns with the most properties at risk include Congleton, Crewe and Alsager with 223, 176 and 173 residential properties respectively. Like the Flood Zones, these counts include the properties that may be protected, to some extent, by flood defences.
Surface water flooding
Surface water flooding, in the context of the Cheshire East SFRA, includes:
Surface water flooding can occur anywhere where ground levels and profiles tend to cause surface water to flow and accumulate. However, there are certain locations where the probability and consequence of these mechanisms are more prominent due to the complex hydraulic interactions in the urban environment. Urban watercourse connectivity, sewer capacity, and the location and condition of highway gullies all have a major role to play in surface water flood risk.
CEC published the Cheshire East Level 1 Surface Water Management Plan (SWMP) in July 2012. The strategic review of flood risk across the study area indicated that the overall level of surface water flood risk was moderate. Although the general classification of risk across the study area is moderate, there were a number of locations where flooding posed a high risk to people and/or property. 55 individual Risk Areas were identified where the level of risk is considered to be high enough to warrant further investigation.
Canal flood risk
There are six canals running through Cheshire East as illustrated. The Canal and Rivers Trust are responsible for the care and enhancement of all five canals, including:
Cheshire East District Council
Cheshire East advise that your FRA should include the design of surface water management systems including Sustainable Drainage Systems (SUDs) and address the requirement for safe access to and from the development in areas at risk of flooding. This can also be produced as a separate report, such as in GeoSmart’s SuDSmart Pro report and in further detailed drainage design.
All new buildings need separate connections to foul and storm water sewers. If an application proposes to connect a development to the existing drainage system, then details of the existing system should be shown on the application drawing(s). It should be noted that in most circumstances surface water is not permitted to be connected to the public foul sewers.
Where connection to the mains sewer is not practical, then the foul/non-mains drainage assessment will be required to demonstrate why the development cannot connect to the public mains sewer system and show that the alternative means of disposal are satisfactory.
If the proposed development results in any changes/replacement to the existing system or the creation of a new system, scale plans of the new foul drainage arrangements will also need to be provided.
Cheshire East District Council
Groundwater flooding is caused by the emergence of water from beneath the ground, either at point or diffuse locations. The occurrence of groundwater flooding is usually local and unlike flooding from rivers and the sea, does not generally pose a significant risk to life due to the slow rate at which the water level rises. However, groundwater flooding can cause significant damage to property, especially in urban areas, and can pose further risks to the environment and ground stability.
The Environment Agency’s CFMPs do not consider groundwater flooding to be a significant issue in Cheshire East’s administrative boundary, as there is little historic evidence to suggest that groundwater flooding is an issue worth further investigation. Development within areas susceptible to groundwater flooding will generally not be suited to SuDS and proposals for infiltration drainage; however, this is dependent on a detailed site investigation and risk assessment.
The Environment Agency’s national dataset, Areas Susceptible to Groundwater Flooding (AStGWF), provides the main dataset used to assess the future risk of groundwater flooding. The AStGWF map uses four susceptible categories to show proportion of each 1km grid square where geological and hydrogeological conditions show that groundwater might emerge. It does not show the likelihood of groundwater flooding occurring. The map shows that the probability of groundwater flooding is very high in Nantwich, and parts of Crewe and Knutsford. The probability of future groundwater flooding tends to be lower in the north east of the study area. There could however be localised problems, which will not be identified on the strategic map.