Pressure washing an industrial yard can create a pollution problem because water used to remove dirt may also collect oil, fuel, grease, sediment and other contaminants. If that washwater reaches a surface water drain, it may travel directly into the environment rather than through sewage treatment.
For an industrial estate manager in England, the main question is not simply whether the yard can be washed. It is where the resulting water will go and whether it can be contained, recovered or lawfully discharged.
Surface drains versus foul drainage
Industrial yards often contain several types of drainage. Their appearance at ground level does not necessarily reveal where they lead.
A surface water drain normally carries rainwater away from roofs, roads and hardstanding. Depending on the drainage arrangement, it may discharge into a watercourse, soakaway or another part of the surface water network.
Foul drainage carries wastewater towards sewage treatment. Some premises have combined drainage, while others have separate systems serving different areas.
This distinction is important because contaminated industrial washwater should not enter surface drainage intended for clean runoff.
In its pollution prevention guidance for businesses, the Environment Agency explains the need to identify drainage routes and prevent contaminated water from entering the environment. The guidance specifically includes yard cleaning among activities that may produce contaminated water.
A site drainage plan should identify:
- The gullies, channels and drains serving the washing area.
- Whether each drain carries surface water, foul water or combined flows.
- The direction of flow and the destination beyond the site boundary.
- Any connections shared with neighbouring industrial units.
Where the drainage arrangement is unknown, a survey may be needed before work is planned. Assuming that an external drain connects to the foul sewer can lead to the wrong disposal decision.
How surface residues change washwater handling
Industrial pressure washing does not create the same type of wastewater on every site. The characteristics of the deposits being removed matter as much as the quantity of water used.
A relatively clean paved circulation area may produce mainly suspended dirt and grit. A loading bay, maintenance yard or vehicle parking area may contain hydrocarbons, grease and material released from equipment.
Other areas may have process residues, chemical deposits or substances associated with stored goods. Cleaning products introduced during washing can further change the composition of the water.
Several factors affect how washwater should be managed:
- Oil and fuel: Residues may be mobilised and carried towards drains.
- Silt and grit: Pressure washing can move accumulated solids into channels and pipework.
- Grease: Concentrated deposits may require controlled removal rather than being washed towards drainage.
- Cleaning chemicals: Their presence may influence treatment requirements and the suitability of an intended disposal route.
Where grease or other concentrated residues are present, removing the bulk deposits before pressure washing can reduce the amount entering the washwater. The cleaning method must also account for any chemical products used and how the resulting liquid and solids will be collected. Increasing water pressure alone does not resolve the disposal problem.
Capture, authorised discharge or off-site removal
Once contamination and drainage routes are understood, the next decision is how to prevent the washwater from escaping into an unsuitable outlet.
Temporary containment may be used to keep water within the cleaning area while it is collected. Depending on site conditions, recovery equipment can then transfer the collected liquid into suitable storage or treatment arrangements.
The lawful destination must be established separately from the cleaning method.
In England, contaminated washwater may be managed through an appropriate contained treatment or reuse system, an authorised foul or combined sewer discharge, or collection for removal by a registered waste carrier.
Discharge into a foul or combined sewer is not automatically permitted merely because the drain connects to sewage treatment. The relevant sewerage undertaker’s permission may be required, including trade effluent consent where applicable.
An existing oil separator does not necessarily make a discharge acceptable. Separator suitability depends on its design, maintenance, the substances present and the destination of the water. Detergents can also interfere with separation.
What to establish before washing begins
The estate manager should first identify the surfaces requiring treatment, the likely contaminants and the drainage arrangements. This provides the basis for selecting an appropriate cleaning and recovery approach.
Where several businesses share a yard, the assessment should include neighbouring drainage connections and activities that may introduce further contamination during the work.
For industrial pressure washing, practical scope decisions include which areas can be isolated, where collected water can be held and how the intended destination will be authorised.
The key distinction is between removing contamination from the paving and transferring that contamination elsewhere. Effective yard cleaning needs to achieve the first without causing the second.
