Some business customers discharge not only general sewage, but also substances defined as “trade wastewater” under Hunter Water’s Customer Contract.
These customers, which range from cafes and restaurants to large industrial or commercial businesses, must attain a Trade Waste Agreement from Hunter Water prior to discharging any wastewater to sewer.
There are several different Trade Waste Agreement types used by Hunter Water depending on the business type and the strength and volume of the wastewater discharged to the sewerage system.
Each Trade Wastewater Agreement type has a different trade waste fee structure that reflects the risk posed by a trade wastewater customer and the costs associated with treating their wastewater. These fees are in addition to the general sewer charges.
For a complete list of current prices see our Trade Waste Fees Guide.
Under the terms of a Trade Waste Agreement, customers pay for the mass of contaminants that they are allowed to discharge to the sewer. To determine this mass, a trade waste charging formula utilises the concentration and volume of the trade waste. The volumetric component of this formula is based on an assessed Trade Waste Discharge Factor (TWDF).
Understanding the Trade Waste Discharge Factor (TWDF)
A TWDF is calculated as the percentage of metered water consumption discharged as trade waste. Generally the TWDF will differ from the Sewer Discharge Factor (SDF) because the total discharge to the sewerage system may not all be trade waste. The TWDF is applied as a specific percentage (eg 38%), and is outlined in the Trade Waste Agreement.
The TWDF can be determined in a number of ways, including:
- It may be a condition of the trade waste agreement to install in-line flow monitoring equipment which continuously measures flow. This is one of the most accurate means for measuring the total flow of trade waste to sewer, and provides the necessary evidence to support a specific TWDF being applied. However, the disadvantage is that measuring equipment can be expensive for customers to install and maintain.
- When pumping to sewer, a flow measuring meter may be required and these readings will be used as the discharged trade waste volume to sewer.
- Flow monitoring devices may be required to be installed for a short period of time to assess the average flow to sewer over time. This is then converted to a percentage of metered water consumption.
- An agreed assessment of the TWDF may also be applied when the discharger can justify the site flow reduction to sewer.
- Benchmarking other comparable customer outlets may also be used to determine the volume discharged to sewer.
The approach taken to determine a TWDF depends on a number of factors, including the cost to the customer of installing flow monitoring equipment, the variability of trade waste flows to sewer over time, available information on estimated discharge volumes for the particular type of enterprise, the ease of installing temporary flow meters and the relative costs and benefits of other measures.
Hunter Water has processes in place to address situations where customers do not agree with the TWDF that has been applied to their property, and any necessary adjustments are made once supporting documentation has been verified.