Erection of a Dwelling, Hill Cliffe Road, Walton, Warrington, WA4
Case Study Reference: CS22-12-01
Planning Authority: Warrington Borough Council
Planning Reference: https://online.warrington.gov.uk/planning/index.html and https://online.warrington.gov.uk/planning/index.html?fa=getApplication&id=152110
Synopsis:
Given the sensitive nature of the development (residential) and the history of the site a contaminated land planning condition was attached to the decision notice for the proposed development.
The first stage of discharging the condition was to prepare a Phase I desk study report in order to determine if the site has the potential to be impacted by elevated levels of contamination, and to determine the source as well as the likelihood of the risk occurring.
A desk study determines what issues relating to historical contamination may affect the site, this is undertaken by reviewing the site history using a combination of O.S. maps, aerial, plates 
and street level imagery, a review of data held by regulatory bodies (Environment Agency, local authority, BGS etc.) as well as a site walkover survey.
The history of the site and surrounds were researched using a combination of Ordnance Survey (O.S.) maps, street level imagery and aerial plates, this revealed the site was developed prior to the first edition (1877) O.S. map with evidence of development circa 1899 and between 1949 and 1966.
A Mill Pond was noted on the first edition map 150m north west as well as a sand pit 230m west on the 1897 map.
Street level imagery confirmed the site was occupied by a garage associated with a dwelling.
The planning history of the site was reviewed as part of the desk based research and reports associated with any previous application were located and studied and no previous applications were noted.
The published geological maps identified the drift geology being the Shirdley Hill Sand Formation. Deposits of alluvium (potential slurce of ground gases) are present 63m west of the site. The bedrock was given as the Wilmslow Sandstone Formation.
Data provided by the Coal Authority indicated that the site is not within a “Development High Risk Area”.
A review of the BGS borehole database did not reveal any borehole sin close proximity to the site.
Data provided by regulatory bodies identified Mill Pond and sand pit identified on the O.S. maps as well as a canal to the north of the site.
The sensitivity of controlled waters was undertaken to determine if the site posed a risk to the nearby water bodies, this concluded that as the bedrock was a principal aquifer and the site was within a Source Protection Zone (III) the groundwater was of moderate risk and the groundwater was a credible receptor.
On completion of the desk based research a site reconnaissance visit was undertaken, this confirmed the site comprised part of 
the adjoining dwellings curtilage with evidence of the demolition of a building.
Once the walkover survey was completed a qualitative risk assessment was undertaken on the potential sources of contamination identified in the desk study report in order to determine if any warranted further investigation, this concluded that the potential for made ground on the site required further assessment.
The report concluded that either intrusive works or remediation in lieu of site investigation were required.
In order to reduce the uncertainties in respect to the development the site investigation was undertaken in
The proposed works were undertaken in January 2023 and comprised 5 trial pits on a 10m, non-targeted sampling grid. The site was unchanged from the December 2022 site visit.
The investigation confirmed the presence of made ground a
cross the site, chemical testing and subsequent assessment confirmed the made ground was impacted by elevated concentrations of arsenic, lead and PAH’s.
The conceptual model created in the Phase I report was refined and using the depth of made ground across the site proposals for remediation were tailored for each garden and landscaped area giving the most cost effective options.
The Phase I and Phase II reports were submitted (2023/00339/DISCON) to partly discharge the contaminated land planning condition. The reports were accepted and the condition partly discharged.
Once the recommendations had been approved the final part of the pre commencement condition (remediation strategy / implementation plan) was prepared, this provided the methodology of how the remediation will be undertaken as well as how the works will be inspected and validated. This was approved in June 2023 and the development could commence.
