Hunter Valley Flood Mitigation Scheme Update on drain clearing works - PDF document

Hunter Valley Flood Mitigation Scheme Update on drain clearing works in the Williamtown area. Thanks for the opportunity to update the Community Reference Group on drain clearing works as part of the Hunter Valley Flood Mitigation Scheme. 1

2 As a brief reminder the Hunter Valley Flood Mitigation Scheme has a number of assets in the Williamtown area. Drains include the Tilligerry Creek Drain, 10 foot, 14 foot, Dawson’s Drains and the Ring Drain. In addition there is the Ring Levee and a number of floodgates on Tilligerry Creek and the Ring Drain. There is a lot more drainage infrastructure in the area that is not part of the Scheme. The areas in green are the areas of drain that were identified as requiring clearing. 2

3 Drain clearing works were completed in April 2018, in part due to weather conditions. 3.8 Km of the Tilligerry Creek was cleared. 3

4 Photos of the machines in operation 4

Before After 5 Photos of drains before and after 5

Before After 6 6

7 As part of the work sampling was undertaken in 2016 for planning purposes. 11 sites were sampled in total, across Tilligerry creek, RAAF Drain, 10 Foot Drain and Dawsons Drain. Samples were taken for PFHxS and PFOS combined concentrations. Results showed that water < veg < soil < sediment Results have been previously provided to the CRG. 7

5 monitoring sites 2 sites on Ring Drain • 1 reference site • 1 site below Dawsons and 14 foot 2 sites on Tilligerry Creek 1 reference site on Moors Drain 1 additional site on Tilligerry established during works 8 Then in 2018 5 monitoring sites were established. 3 sites on drains where works were to take place. And 2 reference sites. Sites were sampled in Feb 2018 prior to works commencing. Then 2 weeks after works, 1 month and again 2 months after works. Additional sampling was done during works at one site to assess the effectiveness of sediment curtains. 8

Monitoring Surface water samples from the drains Pre-works February 2018 Two weeks after works 3 May 2018 One month after works 30 May 2018 Two months after works 26 June 2018 Additional site was established on Tilligerry Creek sampled 9 March 2018 9 9

Results – pre-works levels across the 5 sites Combined PFOS + PFHxS (micro grams per litre) 10 Pre works sampling was undertaken at Tilligerry Creek, Moors drain and Ring Drain in February 2018. Ring Drain 1 - 0.005 Ring Drain 2 – 0.34 Moors Drain 3 – 0.09 Tilligerry Creek 4 – 0.025 Tilligerry Creek 6 – 0.025 10

Results – Tilligerry Creek Combined PFOS + PFHxS (micro grams per litre) Results are similar to levels previously recorded max 0.2 ug/L 11 Tilligerry Creek and Moors Drain were sampled pre-works, during works, 2 weeks post works, 1 month post works and two months post for the combined PFOS + PFHxS in surface water. 11

Results – Tilligerry Creek Combined PFOS + PFHxS (micro grams per litre) Results for these sites are below the levels previously recorded for Tilligerry Creek max 0.2 ug/L 12 Additional sampling was undertaken during works. In response to a request from commercial fishers to look at levels during works we sampled at a works site, sampling above and below the sediment curtain. Site 6 was sampled prior to works commencing, and we established site 5 during works sampled on 9 March 2018. And then sampled 1 month and 2 months after works were completed. 12

Reference site – no works done Results – Moors Drain Combined PFOS + PFHxS (micro grams per litre) Results are similar to levels previously recorded max 1.7 and 1.2 ug/L 13 Tilligerry Creek and Moors Drain were sampled pre-works, during works, 2 weeks post works, 1 month post works and two months post for the combined PFOS + PFHxS in surface water. 13

Results – Moors Drain Rainfall and PFOS + PFHxS levels 14 In trying to explain the results for Moors Drain I compared the fortnightly running rainfall total against the levels recorded in the drain. 14

15 Drain clearing remaining includes a small section of the lower length of Tilligerry Creek, and 10 foot and Dawsons Drains. Subject to obtaining landholder agreement works could recommence in spring this year. 15

Questions 16 16