17Aug / 2016
Some of the GGS team spent the day performing investigative ground work (having sought permission – of course) at a former landfill site in Greater Manchester. This practice exercise sought to assess the composition of the landfill through the use of trial pits and forensic soil analysis. It also uncovered some unlikely treasures.
Project: Investigative ground work at a former landfill site
Where: Greater Manchester
When: July 2016
Why: Investigative ground work exercise/to see what could be found!
Why does investigative ground work take place?
An essential part of ground investigation is trial pitting. It is essential for the determination of site conditions through informing on soil strata and composition, groundwater conditions and permeability. This information, coupled with continuous ground gas monitoring data, enables GGS to provide a well informed and accurate prediction of all sub-surface gas behaviours.
There are plans to build a large number of residential homes on the site under investigation, therefore the source-pathway-receptors that could potentially affect construction need to be identified. The intelligence acquired through ground investigation empowers GGS to recommend appropriate remediation and mitigation strategies, that once applied allow for safe development.
What happens during this type of work?
Investigative ground work first requires digging ‘trial pits’ – holes in the ground with a 1 metre wide top edge and a length of 4 metres. A JCB digs up soil horizons no deeper than 4 – 4.5 metres, with engineers staying 1 metre back from the edge at all times.
The remaining landfill is dug into, with the content being placed to one side of the trial pit, and representative samples taken of what was uncovered. A bag of material weighing approximately 10kg is collected and filtered through over a length of tarp. Different categories of matter are extracted and weighed using a newton scale to assess the composition of the landfill. After evaluating the overall weight, all that remains is ashy waste and inert soils.
Forensic analysis of the soil then takes place to ascertain the total organic carbon content (TOC) so the site can be graded. Moderate to high organic materials produce more gas, resulting in elevated carbon dioxide and methane levels. The trial pits all had different characteristics and compositions depending where on the site they were dug. Most contained ash and clinker as the main waste products, which are typical of a landfill from the 1960s. One trial pit also had a very potent hydrocarbon odour, suggesting the presence of petroleum, possibly from a nearby petrol station.
What was found during the trial pit exercise?
Despite this not being the real intention of the dig, the work yielded some unlikely treasures. These caused surprise and some laughter, but ultimately made us consider the nature of landfill and how long it really takes for objects to degrade.
We found at the site:
- A Horlicks jar
The most exciting finds were:
- A copy of Woman’s Own from 8th October 1960
- An old fashioned lighter
How can GGS help establish safe conditions on my site?
GGS combines a holistic understanding of the legacy of landfill activities with sound knowledge of current regulatory requirements (including Part 2A and Greenhouse Gas Emissions). Our innovative continuous monitoring technologies allow for the comprehensive collection of site data, leading to accurate and reliable assessments. Our market leading services give our clients reliable, cost-effective services that deliver trusted recommendations and confidence in future developments.
Find out more about GGS’ landfill services here.