Ruddlesden geotechnical


Groundwater/ Controlled Waters Risk Assessments

The risks of contamination to the water environment (controlled waters) are commonly considered in conjunction with those to human health, often to satisfy a planning requirement.

In common with human health risk assessments, controlled waters risk assessments initially comprise a desk-based preliminary risk assessment, to produce the initial conceptual site model (CSM) and identify the source-pathway-receptor linkages, often followed by an intrusive investigation, to allow a qualitative risk assessment to be made.

Depending on the findings of the qualitative assessment, Ruddlesden can undertake a quantitative controlled waters risk assessment (also known as a P20 assessment), using borehole, laboratoryand hydraulic data to model the anticipated levels of contamination at controlled waters receptors and to derive on-site remedial targets.

Case Study

P20 Groundwater Risk Assessment Demonstrates No Remediation Required

At a former engineering works near Exeter, elevated levels of polyaromatic hydrocarbons (PAH) and total petroleum hydrocarbons (TPH) were recorded in both the soil and groundwater beneath the site.

As screening criteria had been exceeded in the groundwater beneath the site for these contaminants, further assessment was required to ascertain whether the recorded levels of contaminants beneath the site could migrate to off-site receptors, e.g. to a nearby river, and cause unacceptable levels of pollution to the water environment.

Remedial targets were calculated using the Environment Agency’s Remedial Targets Worksheet (P20 assessment). In this instance, the recorded values were below the calculated remedial targets and the risk assessment demonstrated that unacceptable pollution was unlikely to occur to controlled waters, as the levels of contaminants on-site were modelled to have diluted by natural attenuation and dispersion processes before reaching the receptor.

No further assessment or remedial works were considered to be necessary. This was agreed with and accepted by the Environment Agency.

  • AGS
  • Constructionline
  • CSCS
  • SMAS
  • ECFC trust