It was proposed to construct a new production facility within a larger manufacturing site in West Sussex. The site was located in a very sensitive location with regards to the underlying aquifer and a nearby potable groundwater abstraction.
The preliminary contamination risk assessment carried out identified a number of potential contamination sources relating to the surrounding manufacturing works. Due to the requirement for a significant number of piles to be bored as part of the construction of the proposed facility the Environment Agency were concerned about the potential risks to controlled water posed by the site as it currently stood, as well as by how that level of risk may be affected by the proposed development works.
An initial ground investigation was carried out comprising a series of shallow window sampler boreholes across the site to investigate the potential for shallow contamination and the risk from ground gases, along with a pair of deeper cable percussion boreholes to provide information on the chalk aquifer at depth. Standpipes were installed within both the shallow and deeper boreholes to allow monitoring of ground gases and ground water.
The preliminary set of monitoring results suggested that there may have been some localised shallow ground water contamination in part of the site. In view of these findings a second phase of investigation works was carried out which comprised further shallow sampling targeted at the location of the suspected area of contamination and another pair of deep boreholes to assess the potential impact to the groundwater at depth.
Following an extended period of groundwater monitoring we were able to show that the groundwater within the chalk aquifer at depth appeared to be present in semi-artesian conditions beneath a layer of structureless chalk and alluvium and that, whilst some minor contamination was present within the shallow aquifer, it was not in danger of migrating downwards.
A series of test piles were bored and further groundwater monitoring was carried out both prior to, during and after the completion of the piling. This testing helped to inform the piling works risk assessment which concluded that the piling works were which the Environment Agency approved, allowing construction works to commence.
Groundwater monitoring was carried out before and during the main piling works to confirm that the boring was not having an unacceptable impact on the underlying aquifer. Following completion of the piling works two more further of monitoring were carried out and a completion report was provided which enable the Environment Agency to discharge the planning conditions relating contamination assessment works at the site.