Wash Down Areas

All commercial premises that have wash down areas or pads or other open concrete areas need to provide an interceptor and apply for a Trade Waste Consent. Examples of such premises are car wreckers, car yards, mechanical workshops, fuel stations, and vehicle/other wash facilities.

The Trade Waste Consent to discharge to the sewer may require operation controls to be in accordance with an approved Environmental Management Plan. Because the installation of the petrol and oil interceptor involves drainage alterations, a Building Consent is also required.

Unroofed washdown area

An open unprotected area of impervious paving would be acceptable up to a maximum of 150m2, providing any attached shelter had the roof water discharged to the stormwater system. The washdown area should be graded 1:40.

Roofed washdown area

These areas can be as extensive as Clutha District Council Consent requirements allow, providing an approved drainage and disposal system is incorporated.

Maintenance of interceptor

It is the occupier’s responsibility to ensure the petrol and oil interceptor is maintained in effective working order. The trap needs to be cleaned out at frequent intervals (this interval will depend on the business). If the trap is not maintained, the occupier may be liable for any costs of damages to the sewer and the Tradewaste consent may be withdrawn. The sludge is to be removed by an approved operator for treatment and disposal at an authorised waste processing plant. It is the occupier’s responsibility to maintain a cleaning record. This should be kept on your property and shown to an Environmental Health Officer or Trade Waste Officer if requested during an inspection.

The effluent from the wash down area must be of a character which is similar to domestic sewage. Council will consider this provision met if the average wash effluent contaminant concentration does not exceed the values below by more than 20%, except for pH where it shall be within the range of 6.5 – 9.0. This will be measured as a rolling average over the latest samples.

Where there is a treatment system in place the wastewater factors e.g., Total Suspended Solids, Biochemical Oxygen Demand etc monitored as part of the annual inspection may lead to a reduction of category e.g., from Conditional 4 to Conditional 3. Where the wastewater factors are below domestic sewage equivalent.

To reduce the cleaning frequency of the petrol and oil interceptor, it is in occupier’s interest to ensure minimal loading of the system. Some good housekeeping practices can help reduce pollutant levels and the cost of discharging trade wastewater including:

Adopt dry cleaning methods such as wiping up and sweeping spills rather than hosing. There are also absorbent packs available to soak up oil spills.
Ensure that all equipment is properly cleaned and maintained.
Do not pour oil down the drain. Ensure that adequate storage is provided for used oil and that a collection programme is arranged with an oil recycler.
Use quick break detergents, which help with oil separation.
Use cleaning products that have a pH of 6.10 at working concentration.

If the pad is not maintained, the occupier may be liable for any costs of damages to the sewer and the Trade Waste Consent may be withdrawn.

Legal requirements

Wash Down Information Brochure

If you want a copy of this information feel free to print this page or download our Wash Down Information Brochure: