Site Walkover Surveys

Our engineers have been out of the office completing multiple Site Walkover Surveys in recent weeks.  The surveys are completed as part of our Phase 1 Desk Study services, and form an integral part of our Phase 1 Desk Study reports.  The purpose of the survey is to basically see a site in the flesh, to identify potential sources of contamination that could impact land and the surrounding environment, such as Above Ground Storage Tanks (ASTs), Underground Storage Tanks (USTs), pipelines, chemical storage areas, general site use etc.

Our engineers complete a pro-forma questionnaire for each site and take photographs that help to inform our reports and ultimately the sites Conceptual Model.  As well as contamination sources, other relevant details such as off site use, site access, building layouts, evidence of staining/vegetation die back, hummocky ground that could indicate buried wastes, presence of drainage/oil interceptors, site topography etc is checked and recorded.

It is essential that a site walkover survey is completed to inform a Phase 1 Desk Study report, as for obvious reasons the report is not compliant with UK Best Practice and relevant guidance, such as the EA/Defra document “CLR11 Model Procedures for the Management of Land Contamination“.  You cannot risk assess a site properly without seeing it and reconciling it with features identified during the historical review of Ordnance Survey mapping, also completed as part of the Phase 1 reporting process.  Ultimately, a Phase 1 report not completed properly can lead to significant cost and time delays on projects as they move forward through the risk assessment process.

It is also a part of the job our consultants really enjoy doing, as it gets them out of the office and onto site.

We have completed site visits in recent weeks in rural Northumberland in the villages of Lucker and Amble, North Tyneside, Darlington, Ellesmere Port, Weardale and Blackburn.  Some photos from the visits are posted below.

img_5621 img_5627 img_5731 img_5713 img_5708 img_5674 img_5634 img_5633 img_5736 img_5741 img_5754 img_5605

Wear Rivers Trust

We have just delivered a package of work for the Wear Rivers Trust in County Durham.  Ecological improvement works are planned by the Trust in the Stanley Burn catchment area to create and improve habitats, to improve surface water quality and help fluvial flooding impacts. The work is being progressed under permitted development rights with the Environment Agency.

DBS undertook a detailed Phase 1 Desk Study appraisal of the wider area comprising over 25 hectares of land, focusing on six priority areas for the Trust.  From that work we established the sites initial Conceptual Model (CM), and identified potential risk areas where contamination could be present in the subsurface due to past historical industry, this primarily related to Coal Mining and the presence of a large historical landfill.

Risks to the environment through the mobilisation of historic contamination were considered, as well as risks to human health through the improvements works and end users of the sites.  In total, three areas were identified for further investigation comprising intrusive investigation; we designed a cost effective programme of works to identify if theoretical pollutant linkages identified at desk study stage were significant, or not.

As the improvement works comprised of the shallow excavation of near surface soils only, a ground investigation (GI) comprising Hand Dug Pitting with a thermally insulated (to protect against buried services) double handed shovel and draining tool was designed as a cost effective approach, the maximum target depth of the work was only 1.0m bgl.  Representative samples were taken representing near surface (topsoil and subsoil) and deeper deposits (Glacial Till) for chemical analysis in the laboratory.  Two DBS engineers worked together to investigate the site, the benefit of not using a machine or drilling rig for the work, as well as saving costs, also ensured that the surrounding areas of the nature reserves were not disturbed.

Following the GI, a Phase 2 interpretative Contaminated Land report was prepared for three individual sites amalgamated as one concise report, the report identified that all areas of the site chosen for further work were “suitable for use”, soils testing results were screened against Chartered Institute of Environmental Health and Land Quality Managements Suitable for Use Levels (S4ULs) for Public Open Space (Park) end use.  The report also advised on suitable disposal routes for any arising’s needing to be disposed of as part of the eventual improvement works.

The work provided the Trust with the confidence they needed in advance of large scale excavation works that all risks from contamination were controlled, and that the work could proceed safely.

Some photo’s from the GI are attached.

img_1740 img_1735 img_1742 img_1745 img_1757

 

New Housing Development

DBS were on site last week supervising a Phase 2 Geoenvironmental Ground Investigation on a development site proposed for residential housing.

The ground investigation comprised a combination of mechanically excavated trial pits to maximum depths of 4.5m bgl, with cable percussion boreholes to maximum depths of 10m bgl.  DBS designed the investigation to obtain information on ground conditions, site chemistry, and to refine the sites Conceptual Model.  The work was undertaken to provide geotechnical (in situ and laboratory) information to allow foundation solutions to be designed, and environmental samples for chemical analysis.  The work will also support planning condition discharge for the new development with regards to contaminated land and ground stability.

The exploratory holes were set out on a grid system using a hand held GPS pre-programmed with six figure grid references, and each exploratory hole location was checked with a Cable Avoidance Tool (CAT) to confirm the absence of buried services.  Our engineer then supervised the work, logging all arisings to BS/Eurocodes standards.

The excavator was hired in by the client, the drilling company was PB Drilling of Wigan.

Pictures of the GI in full swing are provided below.

2 4 3a 6a