July Incident
BACKGROUND
Hawkesbury City Council
1. Hawkesbury City Council (ABN 54 659 038 834) (HCC) owns and operates a sewage treatment plant at Fairey Road, South Windsor, NSW. This sewage treatment plant is known as South Windsor Sewage Treatment Plant (the Premises).
2. HCC holds Environment Protection Licence 3306 (EPL) for the Premises allowing HCC to carry out sewage treatment. A copy of the EPL as at July 2015 can be found at Tab A.
3. The EPL includes condition O1.1 which provides:
O1.1 Licensed activities must be carried out in a competent manner.
This includes:
a) the processing, handling, movement and storage of materials and substances used to carry out the activity; and
b) the treatment, storage, processing, reprocessing, transport and disposal of waste generated by the activity.
The Premises
4. The Premises are located at the southern end of Fairey Road, South Windsor. They are bordered to the north, west and south by the Windsor Downs Nature Reserve (the Nature Reserve), and to the east by agricultural land and private residences.
5. A map showing the location of the Premises and the Nature Reserve (the Map) is at Tab B. The blue line on the Map represents the boundary of the Premises.
The WAS Balance Tank, Decant Pit and Sludge Lagoon
6. The areas of and plant at the Premises that are most relevant to this incident are the Waste Activated Sludge (WAS) Balance Tank, the Decant Pit adjacent to the WAS Balance Tank, the Macerator Pit, the Sludge Lagoon, the Stormwater Collection Pit and the Stormwater Discharge Pit.
7. These areas are marked on the Map as follows:
a. "A" - the Sludge Lagoon;
b. "B" - the WAS Balance Tank;
c. "'C" - the Decant Pit
d. "D" - the Macerator Pit;
e. "E" - the Stormwater Collection Pit; and
f. "F" - the Stormwater Discharge Pit.
8. There are two biological reactors at the Premises used to treat sewage sludge and wastewater. Activated sewage sludge is used and produced as part of this treatment.
9. As part of the process, excess sludge, known as waste activated sludge, is periodically wasted (pumped) from the biological reactors to the WAS Balance Tank. The sewage sludge settles in the WAS Balance Tank, which allows separation of sludge from supernatant liquid.
10. There is a floating decant system in the WAS Balance Tank which automatically directs the supernatant liquid from the WAS Balance Tank to the Sludge Lagoon when the supernatant liquid reaches a pre-set level of about 5.4m-5.8m. The start and stop levels for decanting are set by the operator and monitored by a radar level sensor connected to the supervisory control and data acquisition (SCADA) system at the Premises. The SCADA system is a system for remote monitoring and control that operates with coded signals over communication channels. It can be used via a computer screen to start and stop pumps to which it is connected, and to view details related to sensors and alarms at the Premises.
11. There is also a turbidity sensor floating in the WAS Balance Tank to measure the clarity of the supernatant liquid in the WAS Balance Tank. The decant system automatically directs supernatant liquid to the Sludge Lagoon only when the turbidity of the supernatant liquid is below a specified threshold, namely 0.18 to 0.2 %. When the turbidity is above this threshold, the automatic decant valve closes and decanting ceases. When the decanting is to take place, the automatic outlet valve opens and supernatant liquid flows through piping, via the Decant Pit, to the Sludge Lagoon. This process occurs automatically based on the SCADA setting set by the operator.
12. The WAS Balance Tank also has a manual decant facility. This facility can be used to decant the supernatant liquid manually when the floating decant system or automated decant valve is out of operation due to maintenance or failure.
13. The solids from the WAS Balance Tank are piped into the Macerator Pit and then into the centrifuge within the sludge dewatering facility for dewatering. Biosolids are then taken offsite by a licenced contractor for beneficial use and/or landfill.
14. If the sewage sludge or supernatant liquid in the WAS Balance Tank fills up to a high level, it overflows via an emergency overflow pipe. The overflow pipe feeds underground into a T intersection, where it joins the decant line. During normal operations, the overflow pipe transfers WAS Balance Tank overflow via the T intersection piping to the Sludge Lagoon.
15. A photograph showing the overflow pipe (coloured blue) is at Tab C.
16. The Decant Pit is a pit adjacent to the WAS Balance Tank that houses pipes and fittings for the flow of supernatant liquid from the WAS Balance Tank to the Sludge Lagoon as part of the decant process. The Decant Pit is a concrete pit that provides access to the decant pipes and fittings for maintenance purposes.
17. The dimensions of the inside of the Decant Pit are 1.89 metres by 1.87 metres, with a height of about 0.85 metres. The volume capacity of the Decant Pit is approximately 3 cubic metres (or 3,000 litres).
18. There is a sump on the floor of the Decant Pit which connects, via ag piping, to stormwater. The sump is 300mm by 300mm in size, and 50mm deep. The floor of the Decant Pit angles at a fall of 50mm towards the sump. A photograph showing the sump in the Decant Pit is at Tab D.
19. A schematic showing the Decant Pit is at Tab E. Photographs showing the Decant Pit are at Tab F.
20. Prior to 2013, waste activated sludge from both biological reactors was pumped into the Sludge Lagoon daily for additional stabilisation and thickening, before being pumped to a mobile beltpress or a hired centrifuge for dewatering.
21. HCC now utilise a newer sludge dewatering facility, so waste activated sludge is now pumped from the bioreactors to the WAS Balance Tank and then to the sludge dewatering facility, and can, if necessary, be diverted into the Sludge Lagoon as required.
22. The Sludge Lagoon now receives supernatant liquid from the WAS Balance Tank as well as centrate liquid from the biosolids dewatering process of the centrifuge dewatering facility. The Sludge Lagoon also contains historical (pre-2013) sewage sludge.
23. Prior to the overflow incident, the Sludge Lagoon contained about 4,700 cubic metres of sewage sludge.
24. There is a weir attached to the Sludge Lagoon. Supernatant liquid and centrate that is pumped into the Sludge Lagoon settles, and the upper less turbid supernatant liquid layer flows into the weir. From the weir, the supernatant liquid drains into biological reactors 1 and 2 at the Premises for treatment.
25. A photograph of the weir in the Sludge Lagoon is at Tab G.
26. A schematic showing the location of the WAS Balance Tank, the Decant Pit, the Sludge Lagoon, the Sludge Lagoon weir and biological reactor 2 is at Tab H. Decision to clean the Sludge Lagoon
27. Sometime prior to 16 July 2015, HCC staff decided that the level of supernatant liquid in the Sludge Lagoon should be lowered to enable the removal of the solid sludge material in the bottom of the Sludge Lagoon. HCC planned to pump out approximately one metre of supernatant liquid floating over the settled sludge in the Sludge Lagoon prior to commencing removal of the settled sludge.
28. HCC Wastewater Supervisor, Michael Stewart, discussed how to pump out the Sludge Lagoon with HCC Waste Manager, Ramiz Younan, and HCC Engineer Krishnan Thiyagaraja. It was decided that the best way to lower the level of supernatant liquid in the Sludge Lagoon was to firstly remove some piping in the Decant Pit, connect a flexible hose to the pipe through which supernatant liquid decants from the WAS Balance Tank to redirect it to the Sludge Lagoon weir (and then into the biological reactors), and then to pump the supernatant liquid from the Sludge Lagoon into the WAS Balance Tank.
Thursday 16 July 2015
29. On Thursday 16 July 2015, HCC Operator in Charge, Joshua Hawke, and three other HCC employees, under the direction of the HCC Engineer Krishnan Thiyagaraja, modified the pipework in the Decant Pit. A section of the pipework in the Decant Pit was removed and a temporary flexible pipe was attached to one end of the pipework. The temporary flexible pipe was extended around the Sludge Lagoon and into the Sludge Lagoon weir. The other end of the pipework in the Decant Pit was left uncapped and remained open.
30. The open pipe was not capped.
31. These modifications directed decant from the WAS Balance Tank around the Sludge Lagoon, into the Sludge Lagoon weir and back into the treatment processes. In normal operations, decant from the WAS Balance Tank is piped into the Sludge Lagoon.
32. Photographs showing the inside of the Decant Pit with attached temporary flexible pipe are at Tab I.
33. In order to pump supernatant liquid from the Sludge Lagoon into the WAS Balance Tank, HCC staff used a pump on a pontoon within the lagoon (the Lagoon Pump). Photographs of the Sludge Lagoon and the Lagoon Pump are at Tab J. Friday 17 July 2015
34. On Friday 17 July 2015, the HCC Engineer directed the HCC Wastewater Supervisor to cap the open pipe in the Decant Pit. The HCC Wastewater Supervisor did not cap the open pipe as he was not aware that the sump in the Decant Pit connected to stormwater.
Saturday 18 July 2015
35. At about 10:30-11:00am on Saturday 18 July 2015, HCC Wastewater Supervisor Michael Stewart switched the Lagoon Pump from the automatic setting to the manual setting and turned it on, in order to pump out supernatant liquid from the Sludge Lagoon into the WAS Balance Tank. 36. At 10:49am the WAS Balance Tank began filling with supernatant liquid from the Sludge Lagoon.
37. Mr Stewart left the Premises at about 1:30pm on Saturday 17 July 2015 without turning the Lagoon Pump off. He was the last HCC staff member to leave the Premises on 18 July 2015.
38. As a result, the Lagoon Pump continued pumping and the water level in the Sludge Lagoon dropped to the level of the sewage sludge. The Lagoon Pump then began to pump sewage sludge into the WAS Balance Tank.
39. The automatic decant system within the WAS Balance Tank decanted supernatant to the Sludge Lagoon weir from about 2:54pm on Saturday 18 July 2015 until about 1:17pm on Sunday 19 July 2015. From about 1:17pm on Sunday 19 July 2015, the decant valve closed as the turbidity exceeded the threshold.
40. SCADA screenshots/printouts showing the liquid level in the WAS Balance Tank from Saturday 18 July 2015 to Monday 20 July 2015 are at Tab K.
41. The WAS Balance Tank then continued to fill until the emergency overflow level was reached at about 5:22pm on Saturday 18 July 2015.
42. At about 5:22pm, sewage sludge overflowed from the WAS Balance Tank through the overflow pipe. During normal operations, the overflow pipe discharges via T intersection piping into the Sludge Lagoon, however on 18 July 2015, the overflow flowed through the pipework in two directions, to the Sludge Lagoon and into the Decant Pit. The overflow flowed into the Decant Pit through the uncapped open pipe.
43. The open pipe should have been capped either during the set-up of the temporary flexible pipe arrangement in the Decant Pit on 16 July 2015, or after the HCC Engineer instructed the HCC Wastewater Supervisor to cap the pipe on 17 July 2015, but it was not capped. Photographs showing the pipe which was not capped at the time of the incident are at Tab I.
44. The sewage sludge drained from the Decant Pit through the sump via underground ag piping into the Stormwater Collection Pit located at the rear of the WAS Balance Tank. From there the sewage sludge flowed via underground piping into the Stormwater Discharge Pit.
45. The sewage sludge filled the Stormwater Discharge Pit, then overflowed out of the pit and across the Premises, following the natural contours of the land. Photographs showing the Stormwater Discharge Pit as at 22 July 2015 are at Tab L.
46. The sewage sludge flowed through bushland located at the rear of the Premises and onto an internal service road leading to the Premises western gate. The point at which the sewage sludge flowed onto the internal service road is marked 'G' on the Map.
47. At the western gate, the sewage sludge pooled for approximately 10-15 metres along the fence line, and flowed through a 15-20 metre section of the gate and fence onto the fire trail. The western gate is marked 'H' on the Map.
48. The fire trail runs parallel to the fence line of the Premises between the Premises and the Nature Reserve.
49. The sewage sludge then flowed through the Nature Reserve until it reached Rifle Range Road approximately 50 metres from the Premises boundary. It then flowed through a culvert under Rifle Range Road, and further into the Nature Reserve.
50. The sewage sludge then entered an ephemeral creek in the Nature Reserve and followed the bed of that creek downstream. Sewage sludge flowed approximately 400 metres down the ephemeral creek.
51. The overflow travelled approximately 500-600 metres in total from the Premises Western Gate into the Nature Reserve.
52. The yellow line on the Map at Tab B shows the approximate path of the overflow from Rifle Range Road into the Nature Reserve to the west.
53. A map prepared by HCC showing the path of the overflow is at Tab M.
54. Photographs taken on Wednesday 22 July 2015 are attached as follows:
a. Tab N - One photograph showing some sewage sludge on the Premises internal service road.
b. Tab O - Four photographs showing sewage sludge along the Premises western boundary fence line and leading through the western gate onto the fire trail.
c. Tab P - Four photographs showing sewage sludge and turbid water on the fire trail.
d. Tab Q - Five photographs showing sewage sludge and turbid water in the ephemeral creek in the Nature Reserve.
55. A screenshot/printout from the HCC SCADA system showing the level of sewage sludge in the WAS Balance Tank from 18 to 20 July 2015 is at Tab R.
Sunday 19 July 2015
56. From 6:00am until about 7:30am on Sunday 19 July 2015, two HCC on call employees were working at the Premises.
57. One of the employees checked the SCADA alarms. There were no SCADA alarm messages on 19 July 2015.
58. The employees walked or drove around the Premises, but did not notice the overflow.
59. The employees were not aware that the overflow level had been reached in the WAS Balance Tank and were not aware that the pump in the Sludge Lagoon was operating.
Monday 20 July 2015
60. On Monday 20 July 2015, the HCC Operator in Charge, Joshua Hawke, arrived at work and checked the SCADA. The SCADA showed that the WAS Balance Tank had reached the emergency overflow level and was not decanting.
61. Mr Hawke instructed HCC Wastewater Operator Matthew Haines to go and check the WAS Balance Tank. Mr Haines noticed that the level in the Sludge Lagoon was very low and that the pump was running in the Sludge Lagoon. He notified Mr Hawke and turned off the Lagoon Pump at about 7:08am.
62. When the Lagoon Pump was turned off, the Decant Pit was half full. Mr Hawke opened the decant valve on the WAS Balance Tank manually via the SCADA.
63. Mr Hawke then pumped out and hosed down the Decant Pit.
64. HCC staff did not become aware that sewage sludge had discharged off the Premises until a telephone call was received from a member of the public at approximately 12pm on Monday 20 July 2015. That person reported a sewage spill on land adjoining the Premises.
65. After receiving the report from the member of the public, HCC Wastewater Supervisor Mr Stewart investigated the report and identified that sewage sludge from the WAS Balance Tank had overflowed into the Decant Pit, through stormwater piping, out onto the back bush portion of the Premises and onto adjoining land.
66. At 12:45pm, HCC staff notified the EPA of the overflow via the Environment Line. HCC staff also subsequently notified Penrith local Public Health Unit, the WorkCover Authority of NSW, Hawkesbury City Council Regulatory Services Branch, Fire and Rescue NSW and the National Parks and Wildlife Service.
67. At about 1:30pm, the sewage sludge flow was stemmed at the Premises boundary to prevent further overflow into the Nature Reserve. HCC staff dug a channel in the road on the Premises in an attempt to divert and contain the flow of sewage sludge to a path along the fence line within the Premises. HCC staff also put hay bales along the fence line to prevent sewage sludge continuing to leave the Premises.
68. HCC staff organised for a sullage tanker from Premier Pump Out to assist with the clean-up, and an estimated 20,000 litres of mixed water and sewage sludge was sucked up into the tanker on 20 July 2015 and disposed of at the Premises treatment plant.
69. On the afternoon of 20 July 2015, HCC arranged for Transpacific Industrial Services staff to attend the Premises to assess the overflow at the Premises and in the Nature Reserve and to provide advice on the clean-up.
Volume and content of overflow
70. Approximately 543,840 litres of sewage sludge discharged out of the Stormwater Discharge Pit as a result of the overflow. Of this, approximately 78,125 litres of sewage sludge remained on the grounds of the Premises.
71. Approximately 465,715 litres of sewage sludge flowed off the Premises onto the fire trail and into the Nature Reserve, including into the ephemeral creek, as a result of the overflow.
72. The sewage sludge that overflowed from the WAS Balance Tank and ultimately off the Premises into the Nature Reserve was partially digested sewage sludge containing an average solids concentration of 2%.
73. Sewage sludge in the WAS Balance Tank typically had the following characteristics:
a. Biological oxygen demand - 1,210mg/L.
b. Faecal coliforms - 16,000cfu /100ml.
c. Ammonia Nitrogen-42mg/L.
d. pH-7.2.
e. Total Phosphorus - 190mg/L.
f. Total Nitrogen - 430mg/L
74. HCC took samples from 20 July 2015 until 21 August 2015 on the Nature Reserve at. two locations; one upstream in the ephemeral creek, and one downstream in the ephemeral creek.
75. EPA Officer Rebecca Whiteside took eleven samples from five locations within and near the Nature Reserve on 22 July 2015.
Clean-up
76. HCC contracted Transpacific Industrial Services to carry out the clean-up of the sewage sludge on the Nature Reserve following the incident. Transpacific staff attended the Premises and the site of the overflow in the Nature Reserve on Monday 20 July 2015.
77. Between 21 July and 5 August 2015, Transpacific Industrial Services staff carried out clean-up work at the Premises and within the Nature Reserve. This clean-up work involved manual removal of sewage sludge, excavation of sewage sludge, and collection of sewage sludge, stormwater and hose down water using sucker trucks.
78. Between Tuesday 21 July and Friday 31 July 2015, Transpacific collected approximately 1,073,000L of sewage sludge, hose down water and stormwater from within the Nature Reserve. This material and water was discharged into the Premises treatment system for retreatment.
79. On 6-7 August 2015, rain simulation on the affected areas in the Nature Reserve was carried out by the NSW National Parks and Wildlife Service.
80. On 14-18 September 2015, Transpacific Industrial Services spread bark over the affected area.
81. Photographs showing the clean-up of the sewage sludge in the Nature Reserve are at Tab S.
82. HCC spent approximately $293,000 on the clean-up of the overflow.
CAUSE OF THE OVERFLOW
Pipe in Decant Pit uncapped
83. HCC failed to cap the open pipe in the Decant Pit after the modification of the pipework in the pit on 16 July 2015.
84. The HCC Engineer instructed the HCC Wastewater Supervisor to cap the pipe on Friday 17 July 2015. The Wastewater Supervisor did not cap the pipe as he considered that the pipe should be left open to act as an emergency overflow pipe back to the sludge lagoon in the Decant Pit if needed. No procedure in place to check modifications to Decant Pit pipework
85. The modifications to the Decant Pit pipework were not recorded.
86. The changes made to the pipework in the Decant Pit were made after verbal discussions only. There was no procedure in place regarding carrying out the modifications. There was also no written procedure in place to check that the modifications had been done appropriately, however the HCC Engineer was instructed to check the modifications during initial consultation to verify they were carried out correctly, and did carry out a check of the modifications and give verbal instructions in relation to the capping of the pipe on Friday 17 July 2015.
Unmarked stormwater outlet at bottom of Decant Pit
87. The sump connected to stormwater at the bottom of the Decant Pit was not marked or otherwise identified as being connected to stormwater. HCC Staff not adequately trained regarding stormwater
88. HCC operational staff working at the Premises were not trained in relation to the stormwater drainage system at the Premises.
89. HCC Engineer Mr Thiyagaraja was aware of the existence of the stormwater drainage system at the Premises as he supervised the construction of the dewatering system. Other HCC staff, including the Operator in Charge and Wastewater Supervisor, were not aware that the sump at the bottom of the Decant Pit was connected to stormwater, and as such were not aware of the consequences of leaving the pipe in the Decant Pit uncapped.
90. Aside from the HCC Engineer and HCC Manager of Waste Management, HCC operational staff were not aware that the Stormwater Discharge Pit was connected to the Decant Pit.
Stormwater drains and outlets not signposted and no official stormwater diagram
91. The stormwater drains and outlets at the Premises were not signposted or otherwise identified as being connected to stormwater, and some HCC staff, including the Operator in Charge, were not aware of any official stormwater diagram being available to staff.
Lagoon Pump not turned off
92. HCC did not have any procedures in place to ensure that the Lagoon Pump was turned off at the end of the working day on Saturday 18 July 2015.
No overflow alarm on WAS Balance Tank
93. At the time of the overflow, there were no alarms on the WAS Balance Tank, including to indicate that sewage sludge had reached the emergency overflow level and/or was overflowing.
94. At the time of the overflow, there was a sensor installed in the WAS Balance Tank that indicated the level of sewage sludge in the tank, however this sensor was not alarmed.
95. A screenshot/printout from the SCADA system showing the level of sewage sludge in the WAS Balance Tank from 18 to 20 July 2015 is attached above at Tab L.
No thorough end of shift / weekend inspections
96. At the time of the overflow, HCC employees did not carry out thorough inspections of the Premises at the end of shifts or on weekends.
ENVIRONMENTAL HARM
Likely harm to the environment
97. The overflow of sewage sludge from the Premises into the ephemeral watercourse in the Nature Reserve resulted in likely temporary significant harm to the aquatic environment of the watercourse for a distance of approximately 400m downstream of the point at which the sewage sludge overflow intersected the watercourse (the Inflow Point). There is no evidence of actual harm to the aquatic environment.
98. The likely harm to the aquatic environment of the watercourse includes:
a. degrading the water quality of the unnamed watercourse for approximately 400 metres downstream of the Inflow Point;
b. exposing resident aquatic animals and plants in the receiving waters to a highly organically rich material with a high potential to deoxygenate waters;
c. the smothering effects on sediment dwelling organisms due to the deposition of thick sludge layers; and
d. elimination of watercourse aquatic animals and plants due to necessary clean-up activities involving complete pump-out of sludge affected pools.
99. Direct adverse physical effects on aquatic life in the unnamed watercourse in the Nature Reserve was likely to be of a relatively short duration spanning a few weeks. The removal of the majority of deposited sewage sludge solids from the watercourse line and ponded areas in the weeks after the overflow is likely to have eliminated the likelihood of ongoing smothering effects of the deposited sludge material on aquatic life.
100. Any unrecovered component of the nutrient rich sewage sludge could continue to act as a nutrient pool that may lead to excessive plant and algal growth in the pools of the unnamed watercourse in future seasons.
101. The report of Dr Moreno Julli on environmental harm dated 14 July 2016 is at Tab T.
Public health risk
102. The discharge of sewage sludge from the Premises resulted in a potential risk to public health to people exposed to the spill.
103. On Friday 24 July 2015, a member of the public contacted the EPA to report concerns about the risk to public health noting the accessibility of the overflow site to the public. HCC staff then installed sign tape to restrict access to the overflow site in the Nature Reserve. A photograph showing the installed sign tape is at Tab U.
REMEDIAL ACTION
104. HCC has taken the following steps to prevent a recurrence of the overflow incident:
a. The HCC Wastewater Supervisor, Operator in Charge and other HCC staff at the Premises have been instructed that the open pipe in the Decant Pit must be capped when the pipework inside the Decant Pit has been modified or dismantled and when undertaking the process of pumping into the WAS Balance Tank from the Sludge Lagoon.
b. Earthen bunding has been installed at the Premises to contain any future spills on site and pipework has been installed in association with the bunding to direct any spillage to one of several areas on site including the Sludge Lagoon or the bypass pond.
c. Employees have been given a written instruction that, before carrying out any work not covered by a safe work method statement, the procedure for that work must be documented and signed off by the Operator in Charge, the Wastewater Supervisor and the Engineer, and a toolbox talk in relation to the procedure must be held with all relevant staff.
d. Employees are required to fill in a daily checklist at the start of shift, which is signed off each Monday morning by the Operator in Charge, Wastewater Supervisor and Engineer.
PRIOR REGULATORY HISTORY
105. Hawkesbury City Council has no prior convictions for environmental offences.
EARLY GUILTY PLEA
106. Hawkesbury City Council entered a plea of guilty at the earliest opportunity.
COOPERATION
107. Hawkesbury City Council has fully co-operated with the Prosecutor in its investigation of these offences and in the preparation of this matter for hearing to date including reaching an agreed position on this Statement of Facts.