1. Trial Cap – Post Sand cap A Trial Capping Project for Contaminated Dredged Material from the Port of Tyne, UK – A Learning Experience! Chris Vivian, Silvana Birchenough, Jon Rees and Andy Birchenough - The Centre for Environment, Fisheries & Aquaculture Science (Cefas), Lowestoft, UK

2. Port of Tyne – The Problem In 2003, 160 000 m 3 contaminated sediment identified as needing removal to facilitate efficient port functioning. Sediments at the Port of Tyne were contaminated with TBT, heavy metals including Cd, Cu, Hg, Pb and Zn and PAHs. Metals mainly from historic mining sources in the Tyne catchment, TBT from dry docks and PAHs from industry. There are limited solutions for the removal and disposal of the material that are both environmentally sound and economically viable in this highly urban estuary. Trial capping project for 60,000m 3 (=94,000t) sediment from 3 wharves was agreed.

3. Newcastle City Council Neptune Quay A&P (Tyne) Ltd Wallsend Dry Docks Swan Hunter (Tyneside) Ltd Slipway Ends a b c d Dredging Sites – Tyne Estuary

4. Objectives of the Trial The sea-disposal and capping trial was designed to meet the following objectives set by the licensing authority: No loss of contaminated material during transport to the capping site; Minimal loss of contaminated material during the dredging operation; Minimal contaminant loss to the water column by short- term monitoring during the placement and capping operation; Minimal disturbance of contaminated material during the placement of the cap material; Placement of adequate thickness of capping material over the whole volume of the deposited contaminated material; Long-term maintenance of the integrity and efficacy of the cap assured by monitoring and cap maintenance when required;

5. Work plan Characterisation of material:  Chemical – TBT/DBT, metals, PCBs, PAHs, ∑ HCs, TOC, elutriate test  Physical – PSA, % dry matter, geotechnical analysis Dredging method – backhoe with lid Selection of capping area – within existing Souter Point disposal site Type of disposal – split hopper barge Cap design – level bottom capping with 1.5 m cap made up of 135,000t silt and sand Monitoring plan

6. Capping trial disposal site Dredge site Capping Trial Disposal Site Souter Point disposal site is about 4 miles off the NE coast. Maximum depth is approximately 48 m. Relatively weak tides – max 20 cm/s springs and 10 cm/s neaps. Ebb and flow tides predominantly in a near north-south direction with a residual flow to the south. Capping trial disposal site - CDM targeted at 200 x 200 m box with cap intended to cover 300 x 300 m box.

7. Monitoring/Assessment Seabed topographySediment structureBenthic biotaSediment quality AGDS Sidescan Multibeam Photograph SPI Microbial Epifauna Meiofauna Macrofauna Trace organics Contaminants PSA Sub-bottom Profiler Water quality Water analysis

8. Dredging & Split Hopper Barge

9. Placement of CDM and capping material CDM Placement: 160 barge loads between 13 th Dec 2004 and 20 th Mar 2005 Only 1 barge load outside target zone – by 20 metres Period prolonged due to adverse weather Contributed to spread of thin layers of CDM Dumped CDM settled rapidly – 35 minutes to settle out Only low water column SPM levels reached site boundary Capping material placement: After 100,000 m 3 silt deposited by 11 th April 2005, multibeam survey found it had been widely dispersed - ~70% lost outside target area Silt deposition suspended and 90,000 m 3 sand deposited DEFRA /CEFAS agreed that a 0.6m sand cap was adequate after sediment re-suspension modelling Multibeam surveys not useful for defining limit of area needing capping due to limited resolution but adequate for cap thickness However, SPI was very effective at detecting thin layers of CDM

10. Cap Thickness Total sand and silt cap East West section through cap North south section through cap

11. Risk Assessment of Cap Cap thickness – median 0.2 – 0.25 m (max 1.0 m) – but ? up to 0.45m allowing for errors in bathymetric data Cap thickness significantly <1.5m Cap thickness was very patchy Thin layers of CDM spread well beyond target area Single Severe storm A series of small storms Trawling or other human activity exposing cap Facts about the cap Factors likely to effect cap integrity 3 small storms enough to erode cap (3 x 15 cm) More cap material needed to be placed Findings of Risk Assessment Additional material added June 2006

12. The cost of the trial and monitoring was approximately £3.2 million. Post-dredge sediment analyses showed significant TBT and metal contamination remained below the dredged depths but navigational access to the berths was available. Final trial monitoring was undertaken in September 2007 and bathymetry in May 2008 to ensure that the objectives of the sea disposal had been met. After licence expiry, an MOU was agreed between the Port of Tyne, Defra and the Marine and Fisheries Agency covering ongoing monitoring and maintenance of the cap thickness to ensure a minimum of 0.6 m sand cap at all times. Overall Result

13. Lessons Learned – 1 Cap design: Silt capping material can be hard to distinguish from CDM so use silt cautiously for capping Where practical, use of a containment dyke should be considered to prevent spread of the CDM Prior to licensing, ensure that enough suitable capping material is available for short and long-term needs Disposal Operations: Possible to place CDM accurately in 50 m water depth. Prolonged exposure of CDM prior to capping likely allowed the wide spread of thin layers of CDM detected by SPI. Need to minimise prolonged exposure of CDM prior to capping However, only small volumes of CDM moved from where it was placed - largely due to the very cohesive CDM and to the way it was dredged and dumped that largely maintained its cohesive nature.

14. Lessons Learned – 2 Monitoring: Range of monitoring methods used was appropriate but could be refined Monitoring should preferably be undertaken in good weather To ensure the best data quality, multi-beam bathymetry and sub- bottom profiling instrumentation needs to be state-of-the-art. SPI was invaluable in detecting thin layers of CDM. More extensive use is recommended in future to provide better data on thin layers. Additional/improved ways of determining cap thickness are needed. Need for an explicit agreement at the time of licence issue on the principles of the minimum long-term monitoring programme. Licensing Issues: Needs to be clear agreement on actions, protocols and deadlines to avoid any misunderstandings or delays.

15. Lessons Learned – 3 Licensing (continued): Clear agreement needed on responsibility for monitoring, mitigation and remediation in short and long-term before any licence is issued. All future projects should be considered within an overall sediment or dredged material management strategy for the area concerned e.g. an estuary and not in isolation i.e. no piecemeal projects. Research: Although the trial has been considered a qualified success, further studies are required to provide to assess its long-term success Better monitoring techniques needed e.g. for cap thickness. Liability: An unambiguous agreement on who takes on responsibility for long- term liabilities arising from a project should be put in place before any licence is issued.

16. For more information:  Chris Vivian (chris.vivian@cefas.co.uk)chris.vivian@cefas.co.uk  Silvana Birchenough (Silvana.Birchenough@cefas.co.uk)Silvana.Birchenough@cefas.co.uk  Jon Rees (Jon.Rees@cefas.co.uk)Jon.Rees@cefas.co.uk  Andrew Birchenough (Andrew.Birchenough@cefas.co.uk)Andrew.Birchenough@cefas.co.uk  Report ‘The First UK Offshore Contaminated Dredged Material Capping Trial: Lessons Learned’ at: http://archive.defra.gov.uk/environment/marine/d ocuments/legislation/cms-tynecappingtrial.pdf http://archive.defra.gov.uk/environment/marine/d ocuments/legislation/cms-tynecappingtrial.pdf