Filling stations and the risk to soil and groundwater
Fuel distribution points can pose a serious threat to the environment, particularly to soil and groundwater.
The main sources of contamination at filling stations are leaking underground tanks and pipelines, spills during unloading, and faulty separators. The danger is that a leak is invisible from the surface and can continue for months, which is why such sites are covered by groundwater monitoring imposed through administrative decisions.
Filling stations are an unavoidable part of the landscape and there is little point arguing about their necessity. It is worth looking at them from the perspective of what happens below ground level, because that is where the problem lies.
Where contamination comes from
- Leaking underground tanks — corrosion, construction defects, mechanical damage during earthworks.
- Process pipelines and connections — the most common place for slow, long-running leaks.
- Spills during unloading — the transfer from a road tanker is the most sensitive moment in operation.
- Faulty oil separators — passing contaminants into stormwater drainage and on into the ground.
- Historical legacy — stations with a long history may be contaminated by installations decommissioned decades ago.
Why a leak is hard to notice
Fuels are lighter than water, so after passing through the unsaturated zone they accumulate on the water table and spread with the direction of flow. Nothing shows at the surface. The shortfall in the fuel balance is often small enough to fall within measurement tolerance, while the contamination steadily grows.
The later the response after an uncontrolled spill, the wider the contamination — and clean-up cost depends mainly on the volume of contaminated soil, not on how much product entered it.
What monitoring such a site involves
- a network of piezometers following the direction of groundwater flow, with points upgradient and downgradient,
- cyclical water sampling and determination of petroleum substances,
- soil contamination testing around tanks, dispensers and the unloading point,
- assessment of installation tightness and separator performance,
- reporting in line with the scope of the administrative decision.
When remediation is needed
If testing shows exceedances of the permissible content of risk-causing substances, the site must be cleaned up. At filling stations this usually means methods that work in place — biological treatment and in situ oxidation — because the site normally stays in operation and cannot be excavated.
We gained our experience in this field working with fuel groups; the Best Contractor HSSE Performance 2011 award from Royal Dutch Shell related precisely to work at Shell filling stations. See soil remediation and awards and references.
Frequently asked questions
The scope of monitoring follows from the administrative decisions issued for the specific site rather than from a single rule covering all stations. In practice most fuel distribution sites are covered, given the nature of the substances stored.
Indirectly — through groundwater monitoring from piezometers around the site and soil testing in the tank area. A fuel balance is often insufficient, because a slow leak falls within measurement tolerance.
In many cases yes. In situ methods — biological treatment and oxidation — are delivered through injection boreholes without excavation, so the site can stay in operation. The type and extent of contamination decide.
Need a quote for testing or remediation?
Describe the site and the planned investment — we will prepare a free quote and advise which scope of testing the regulations require.