In 2019 VHE were awarded the latest contract from Clyde Gateway to remediate Chromium impacted ground within the Shawfield area of Glasgow.
The appointment followed successful works carried out on Phase 1 during 2013/14 and also two phases of product trail works at the site during 2016 and 2017.
The project was part of a greater scheme within the area to remediate Chromite Ore Processing Residue (COPR) from the former J&J Whites Chemical Works, which had been used to backfill disused clay pits in the area. The main environment issue of COPR was the presence of hexavalent Chromium (CrVI). The scheme, designed by consultants Aecom, saw reducing agents injected into the ground to convert the mobile and toxic CrVI into the more immobile and less toxic Cr III.
VHE’s works followed two periods of product trails on site to determine the best form of reducing agent to be used. It was concluded that two forms of Calcium Polysulphide were to be used. Where concentration was at the highest (at least an order of magnitude higher than Phase 1) pre-treatment of the ground was undertaken by injecting another reagent to partly act as a catalyst to the reduction reaction.
It was anticipated that over 2 million litres of solution would be injected into the saturated zone of the 2.5ha site via 4,750 injection points. Each injection point drilled a steel tube into the ground up to a depth of 7m on triangular grid pattern. A pre-set volume of solution was delivered through the tube at 200mm vertical intervals, removing the injection rod from the ground at the same time ready to be installed in the next location.
The injected solution was batched on-site and delivered to the point of injection via a sealed system. Up to 8 injection teams worked simultaneously to achieve the works within a 30 week programme.
The works involved the close control and presentation of thousands of data sets and records to verify the works undertaken followed by a groundwater monitoring regime of the area to assess the successfulness of the works in reducing the concentration of CrVI within the groundwater.