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Oil Spill, Haverfordwest

The property was constructed from block and render approximately 8 years ago and has not had any extensions added. The property includes a large lounge, kitchen and dining room on the ground floor and bedrooms on the first floor. A double garage is located to the south and a conservatory is attached to the western elevation of the dwelling. A block paved driveway leads from the road side to a detached double garage. The garden consists predominantly of lawn with an area of patio to the west of the house.

The householder arranged for a delivery of Kerosene heating oil in late September 2012. Whilst filling the Aboveground Storage Tank (AST) the operative noticed a split in the side of the AST and stopped the oil transfer;

Based on the level of the identified splits and the volume of oil remaining within both the original and storage tanks, an estimate of 100-300L of kerosene lost to ground was presented.

Kerosene contamination to soils surrounding the AST was noted within a lawn and patio area

Objective

The aim was to ensure that the householders could remain in the property while removing the risks posed by contaminated soils and return amenities to the dwelling.

The remediation strategy was undertaken within one phase. This involved preparation works, mas excavation and reinstatement following a phase of validation by an Environmental Consultant.

Methodology

Environmental Damage Management (EDM) mobilised to site following instruction to undertake an initial site investigation identifying significant kerosene contamination in near surface soils beneath the failed AST located within a storage area of the lawn.

A series of soil bores, trial pits and probe holes were advanced to delineate an area of 10.08m2 of kerosene impaction material.

At the start of remediation work, the failed AST was drained of residual kerosene which was stored within a temporary vessel, fencing was removed and LPG gas cylinders set aside to allow for access.

EDM proceeded to excavate and remove a total of 15.7 tonnes of kerosene contaminated material from the spill origin to a maximum depth of 1.05 meters below ground level (mbgl)  

The excavation exposed the foundations of the third party, external dividing wall. Slightly elevated Volatile Organic Compounds (VOC) were recorded using a Photo Ionisation Detector (PID) and therefore residual contamination at these foundations were treated with a single application of chemical oxidant (RegenOx).

Following successful validation, the remediated area was backfilled and reinstated to its original condition, this included finishing the excavated area with compacted aggregate to supports the AST plinth.

This remediation strategy was chosen as the most cost effective option because demolition, excavation and reinstatement works could be undertaken quickly limiting disturbance to the home owner.

Validation

On completion of the remedial works, the excavation was validated with the attendance of an EDM Environmental Consultant. A total of 3 no soil samples (VS-1 to VS-3) were obtained from the base and sides of the excavation and were submitted for analysis to an accredited laboratory.

Analysis confirmed that all soil samples were within remediation target values.

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