Water screening values: misunderstood or misused

Things to watch out for in Geoenvironmental Appraisals & Remediation Strategies.

Drinking water standards (DWS’s) refer to the concentration & quality of water at a consumers tap. There are surface water DWS’s and groundwater DWS’s, depending on the source of water abstracted. DWS’s can be a useful critical concentration in detailed risk assessments considering dilution, dispersion and attenuation along a migration pathway. BUT these are not default land quality remedial targets, and there are very few scenarios where a DWS should be applied directly to a soil leachate value.

Environmental Quality Standards (EQS’s) apply to surface water features.  The values are derived based on each chemical toxicological effect on the surface water ecology such as fisheries or invertebrate. EQS values are usually based on an annual average concentration and pH and water hardness are important site-specific data needed to apply the correct EQS value.  EQS values have no relevance to groundwater, unless perhaps the groundwater is acting as a pathway, discharging directly to a surface water.

Understanding water-based screening values and applying these appropriately in land quality assessments is essential. These are not interchangeable values, where the lowest is simply applied. A conservative approach might seem like a useful and quick way to gain Regulatory agreement, but it will ultimately lead to unsustainable remediation, excessive project costs and mid-delivery reassessment of end criteria when it becomes blindingly obvious that the soil leachate value is never going to comply with the DWS or EQS (Hart Environmental are asked for support in this scenario a lot!).

Understanding the conceptual site model is critical. Detailed quantitative risk assessment is not always required, but it is an important part of land quality assessments when deciding on remedial targets.

Hart Environmental are frequently asked about managing groundwater, either as a longer-term abstraction or short-term dewatering. When it comes to groundwater there are two main considerations.

  1. Protecting groundwater as a resource – do you need a permit to abstract water?
  2. Protecting the environment – do you need a permit to discharge the water?

There are exclusions and exemptions that cover a range of situations, but it is not always straight forward, and it cannot be assumed that construction-based activities or short-term activities are automatically exempt or indeed that a permit is always required.

The decision whether your project meets one or more of these exclusions and exemptions, must be determined by the project team and the decision process needs to be clear and transparent. There are extremely long delays obtaining permits, so any delays in understanding and assessing the water management regime can cause significant delays in delivering the project.

Hart Environmental regularly work collaboratively supporting project teams, if you have a project and would like our advice, send an email to liz@hart-environmental.co.uk, and we would be happy to help.