Licence conditions for pollution studies and reduction program


Licence conditions for pollution studies and reduction programs

Licence number: 4197
Title: Pollution Reduction Study 9 - Assessment of Effluent Discharge Quality to Determine if Limits Should be Reduced
Start date: 01 Jan 2021
Licence Condition
Background The limits for Ammonia and Total Nitrogen in Condition L3.4 are considered interim limits.  The EPA had originally proposed limits less than these based on the design of the new sewage treatment plant and limits applied to similar design plants. The licensee argued that the limits would be unachievable in certain circumstances.  At the time of developing the licence for the new sewage treatment plant the EPA advised that it intended to review the limits after 5 years of monitoring of the new plant (around 2026). Based on monitoring of actual plant performance, the EPA advised that it will consider whether it is appropriate to reduce the 100 percentiles of Ammonia and Total Nitrogen.  During this process the EPA intends to review the limits compared to similar plants such as Stroud and Hallidays Point.  Deliverables By 31 July 2026 the licensee must supply the EPA report that assesses the first five years of monitoring data for the newly installed Dungog Sewage Treatment Plant, once it has been brought into regular operation.  The report must provide all data obtained for Point 9 for the pollutant parameters ammonia and total nitrogen in the form of an Excel table, which includes for each day of sampling a comment as to whether a sludge lagoon was being dewatered at the time of the sampling and if greater than 10 mm of rain has been recorded at Dungog in the 24 hours prior to the sample being taken.  Where any sample exceeds an ammonia concentration of 2 mg/L or a total nitrogen concentration of 10 mg/L a comment must be included in the table as to the reason, or most likely reason, why these concentrations were exceeded.  The report must undertake an statistical assessment of the dataset and provide the 50 percentile, 90 percentile and 100 percentile results for the pollutant parameters ammonia and total nitrogen.  The report must provide commentary on the results obtained and draw conclusions on what should be appropriate ammonia and total nitrogen limits for effluent quality at Point 9.