Old Meldrum Case Study
Project Title
Old Meldrum Depot Remediation
Site
The site was used as a depot for a company working with agricultural chemicals for over 20 years until it closed in 2003. Chemicals stored at the site included pesticides and fertilisers. In addition there was a chemical soakaway on the site for disposal of dilute pesticide residues from crop sprayers, use of which ceased in 1989. Up until 1965 the site was operated as a railway station for ~40 years. The site is approximately 1.46 ha and is bounded by a small surface watercourse, modern domestic housing, a bus dismantling yard and an embanked main road.
Contamination
The site investigation revealed areas of both hydrocarbon and serious pesticide contamination. The main pesticides of concern were DDT (insecticide), trifluralin (herbicide), Pendimethalin (herbicide) and aldrin (insecticide). The risk assessment demonstrated moderate risk to receptors (groundwater and occupants of domestic houses with top soil laid gardens). Risk was low-moderate for site users as pesticide operators wore specified PPE.
Remediation
After study of the contaminant regimes and their locations various lab trials were conducted to determine the optimum method(s).
- Moderate TPH contamination - Biopiles with pH adjustment using lime. Additions of fertiliser and bespoke microbial culture.
Pesticide soakaway and surrounds, including extracted groundwater - Bioremediation using a bunded lasagne layer treatment, this consisted of compost inoculated with microbes, mixed with sawdust and the contaminated soil, this mixture was laid out within a bund, then covered with permeable Terram, then sand on top of that, then the next layer of compost/sawdust/soil and so on. The contaminated groundwater was introduced to the system as irrigation; this water was also circulated below ultra violet lamps to accelerate degradation of trifluralin.
- Silt from rock washings from soakaway - Due to very high level of contamination this small volume of material was consigned to hazardous landfill.
- An area of the yard contaminated with >65 mg/kg total DDT - Ex-situ chemical oxidation treatment using Fenton's Reagent.
Benefits
A 65-90 % reduction in contaminant concentration was achieved, depending on the specific contaminant. SEPA was satisfied with the reduction of risk of contamination of a burn from surface water draining from the site. The land was subsequently sold for industrial use after agreement from the local authority.