10. Treating effluents best available techniques (BAT)

BAT for treating effluents at onshore oil and gas sites.

You should recycle effluent streams, wherever practical, to minimise the amount of:

• fresh water you need to use
• effluent you need to treat

Examples of likely effluent streams include:

• produced water
• flowback fluid
• well cellar fluids
• contaminated rainwater collected in secondary or tertiary containment facilities
• accumulated water drained from crude oil storage vessels
• other process effluents
• water used during cleaning or maintenance activities

The Environment Agency considers the BREF document Common waste water and waste gas treatment and management systems in the chemical sector to be BAT for treating effluents from onshore oil and gas operations.

To identify the appropriate BAT for your effluents you will need to work out the following:

• the expected volume and composition of effluent streams
• the temperature and pH of effluent streams
• whether any effluent streams are chemically incompatible with other effluent streams
• whether any of the effluent streams are odorous

You must include this information in your permit application along with a description of the treatment techniques you have selected.

You must design your waste water treatment and storage facilities to handle abnormal volumes of waste water. You should consider the likelihood and impacts of:

• artesian conditions in an aquifer - which means that the groundwater is pressurised, causing a high volume of water to be generated on site
• heavy rainfall
• an elevated groundwater table