Phase 1 Environmental Risk Assessments (desk studies) are now routinely required by regulatory bodies as part of the Planning process when development is proposed, in order to formulate an initial Conceptual Site Model (CSM). This forms the basis for an appropriate and relevant intrusive ground investigation which addresses contaminants specifically potentially relevant to the site, identified pathways and receptors. A thorough understanding of the site, via a CSM is critical to the appropriate and comprehensive investigation of a site.
Geological, mining and historical desk studies are also commonly required, in isolation, to provide background information on other aspects of a site, such as potential foundation solutions and construction risks.
Ground Engineering offers a comprehensive Phase I Desk Study service, to include historical, geotechnical, geoenvironmental and mining aspects as required. These can be undertaken as a separate phase of work, often as part of pre-purchase due diligence assessments and presented in a stand alone report, or can be integrated into a comprehensive combined geotechnical and geoenvironmental investigation report. The scope of each desk study is tailored to the needs of each specific client and project, the aims and objectives, programme and budget.
Using a combination of extensive in-house databases, publications and directories, specialist researchers and web-databases, Ground Engineering is able to offer a fast turnaround option on desk studies as and when required by its clients in order to meet modern development/due diligence programmes.
In particular, Ground Engineering has extensive in-house records relevant to development in the London, Peterborough and Milton Keynes areas, including;
- Widespread historical map coverage
- Large scale geological maps and plans
- Extensive in-house borehole database
- Bomb damage plans
- Aerial photographs
- Publications and directories
CASE STUDY – PHASE 1 DESK STUDY
The Ice House
The importance of good desk study information into the background history of any site prior to the commencement of works is vitally important. During a recent redevelopment of a site in London, through comprehensive desk study researches, the likely presence of a Victorian ice house was identified before subsequently being investigated intrusively.
Before to the introduction of refrigerators in the early 20th Centaury, ice was harvested in Norway and transported to London, ready for distribution throughout the capital. Prior to this distribution, the large blocks of ice, typically 150kg in size, were unloaded from wharfs and stored in large icehouses, often containing deep underground icewells.
From a review of the historical mapping for the site, no structure was recorded in1862 but by the time of the 1871 map, a clearly defined circular structure known as the ice house was present. However, by the time of the 1894-96 map the area associated with the site was covered with a rectangular building of similar dimension but now not named. It was from further research undertaken after the review of the historical maps which provided additional anecdotal evidence of an icehouse to compliment the single entry on a single map. This evidence included reports that an icewell was reported to have been constructed in 1863, and was noted at the time to have been “very big”, with nominal dimensions of 12.5m (41 feet) across and eventually 30m (100 feet) deep.
Given that the structure could be at least 30m deep from the existing ground level, this posed a significant risk to any future development of the site. At the time of the investigation, the previous use of the property had been as a car-wash, and from site inspection there were some clearly defined circular walls still in evidence. From measurements taken on site of these walls and through subsequent calculation, it was considered that these would have formed part of the internal structure of the previous icewell.
In order to confirm the information identified during the researches, the subsequent phase of the intrusive investigation not only included excavated pits to identify the presence any existing walls associated with the icewell, but also the extent of the structure both vertically and horizontally. Boreholes drilled outside of the icewell footprint recorded near surface undisturbed London clay, typical of the anticipated geology; however boreholes drilled locally near to these but within the footprint returned very different ground conditions. Once below ground, the brick built walls of the icewell were still in place and within the icewell footprint itself, over 14m of loose saturated ash and made ground were recorded. Below this deep, poor made ground the icewell terminated in a solid floor which, once broken through, identified competent undisturbed London Clay to depth.
Although the final depth of the icewell was closer to 30 feet rather than the suggested 30 m, this still posed a significant geotechnical issue, not least because of the local poor quality made ground and near vicinity of a major London Underground station. Final ground solution for the redevelopment of the site called for the use of a piled foundation, which in turn necessitated deep investigative boreholes to prove ground conditions on account for the potential loss of skin friction from piles located near to the icewell walls. However without the prior knowledge of the presence of the icewell, it is entirely possible that all boreholes could have been located outside of its footprint, and in turn these would only have identified the near surface undisturbed London Clay deposits resulting in a very different ground solution.