A recent inspection uncovered a high-risk blend of features, something we call the “golden combination” and it raises immediate concerns.
The set up includes:
- Soakaway drainage
- Located within a GWSPZ1 (Groundwater Source Protection Zone 1)
- No oil interceptors installed on site
There is a significant pollution risk associated with operating a site under these conditions.
Discharging to a Soakaway
A soakaway is a drainage system designed to allow water to infiltrate directly into the ground, intended for surface water only.
There is no treatment system, filtration system, or interception built into a standard soakaway. This means anything entering the system is discharged straight into the surrounding ground.
If contaminated water enters the system, for example, runoff containing oils, fuels, or toxic sediments, there is nothing to prevent those pollutants from migrating into the soil and underlying groundwater.
The Risk of GWSPZ
The risk is significantly elevated when a site is located within a Groundwater Source Protection Zone 1 (GWSPZ1).
These zones represent where water has a direct pathway to public drinking water abstraction points. If within a GWSPZ 1, the water can reach an abstraction point within 50 days, presenting a seriously high risk if pollution was to occur.
As the system discharges via soakaway drainage, it is therefore uncontrolled as there is limited natural attenuation before pollutants reach the receptor creating serious risk.
No Oil Interceptors
The liabilities mentioned above could be largely prevented by the installation of an oil interceptor.
Oil interceptors are designed to capture oil and pollutants before they enter the drainage system. Without them:
- Oils and fuels can flow freely into the soakaway
- Contaminants bypass any form of separation
- Pollution risk becomes immediate rather than theoretical
Even small, routine spills can accumulate over time, leading to significant environmental impact.
Why This Combination Matters
Individually, each of these elements presents a manageable risk if properly controlled.m However, when combined, they create a direct pollution pathway.
Contaminated surface water → no interception → soakaway → permeable ground → drinking water source
This is why we refer to it as the “golden combination” — a perfect storm of conditions for groundwater pollution.
What Should Be Done?
Sites operating under these conditions should take immediate steps to reduce risk;
- Install appropriate oil interceptors
- Review drainage arrangements and eliminate contaminated discharges to soakaways
- Consider rerouting to foul or treated systems where appropriate
A CCTV Survey would provide information on all these risks, in addition to remediation costs.