North East File Collection - NEFC

Key Points
Background
Marine Licences
Maintenance Dredging - Clean or Dirty?
OSPAR Convention
PAHs
Cumulative Actions
Rate of disposal
UKD Orca
Contamination
Sampling of Riverbed
Sampling December 2018
Sampling August 2019
Sampling in 26th November 2020?????
Sampling 13th October 2021
Sediment Explorer of Key Sediment Templates
Polycyclic Aromatic Hydrocarbon Sediment

Key Points

PD Teesports disposal at sea license(MLA/2015/00088) issued in 2015, was incorrectly issued for one tenth of material actually dumped at sea and only corrected with variation 6 in 2022
Opinions of the safety of disposal at sea states the incorrect quantities of material
The dredged material disposed of at sea is many 100s of times above notification level for polycyclic aromatic hydrocarbons
UKD Orca disposed of 5% of annual dredge in 10 days rather than 18 days, almost double rate of disposal at sea
UKD Orca dredge occurred at the same time as the marine die-off occurred in late September and early October 2021
Why was sampling carried out one year early immediately after UKD Orca dredge, i.e. many sample were below level where river is usually dredged
Sampling in October 2021 showed PAHs had in general increased compared to November 2020 (of 176 measurements 152 increased by upto 22times), but no similar increase seen in metal concentration (of 64 measurements only 34 had increased by at most 4 times and some had decreased to 10%)
This suggests that an event with a large release of hydrocarbons happened prior to 13th October 2021

Background

The River Tees is a major port for the UK and so by act of parliament the statutory harbour authority (SHA) has a legal obligation to keep the river channels clear to allow navigation. The SHA is now PD Ports, the company that owns and operates Teesport. The act of parliament gives the SHA permission to carry out maintenance dredging but does not give the SHA permission to dispose of the dredged material at sea. PD Ports has to apply for marine licenses from the Marine Management Organisation to dispose of the dredged material at sea.

Maintenance dredging covers dredging which must not result in an increase the depth of the river when compared to its lowest depth at anytime in the last 10 years. This means that the material which is removed by maintenance dredging is either material that has washed into the River Tess from the sea or suspended material carried down the river from upstream which has deposited on the riverbed.

Any dredging which increase the depth of the river is classified as capital dredging and once again is permitted only by marine licenses issued by the Marine Management Organisation.

PD Ports only carries out maintenance dredging using either its own dredgers (Heortnese / Cleveland County retired 2021 / Emerald Duchess due 2024) or occasionally using contracted vessels (i.e. UKD Orca). The dredgers used are trailing hopper suction dredgers, as such they do not cut into the riverbed and will only remove relatively loose material. PD Ports also use an adapted tug (Tees Guardian) fitted with an underwater bulldozer blade to level out the riverbed after dredging.

Marine Licences

PD Ports is required to apply for licences which define what can be disposed of at sea and any requirements for mid-term sampling of materials. PD Ports obtained a three year dredging license (MLA/2012/00141) in 2012, which was extended to the end of 2015 due to delays in processing of the information for the subsequent license. The subsequent and latest marine license (MLA/2015/00088/6) for disposal at sea was issued in 2015 for 10 years, which defines what can be disposed of at sea and requirements for mid-term sampling of materials.

Maintenance Dredging - Clean or Dirty?

The dredging industry portrays maintenance dredging as a clean operation as they explain it is mainly taking material that has washed into a river from the sea back to sea, when compared to capital dredged where historic contaminated sediments could be a major part of what is dumped at sea. In reality maintenance dredging is only clean if the material it removes has not been contaminated, so any ongoing pollution or one of incidents will results in contaminated material being disposed of at sea.

The River Tees has historically been a highly polluted river due to the over 140 year history of heavy industry along its banks which used the river as a disposal route for unwanted materials (waste/toxic chemicals). It is accepted that the sediments laid down in previous decades were widely contaminated with toxic chemicals and as such capital dredging which digs into these sediments requires extensive sampling to be undertaken to determine whether the material is suitable for disposal at sea - see Teesworks - Capital Dredging the Tees to find out more about recent capital dredging of the River Tees Estuary.

Maintenance dredging as described above in an unpolluted river could be a chemically clean operation, however in order to obtain a license for disposal at sea samples have to be taken to in order to determine whether the material is compliant with the international OSPAR convention.

OSPAR Convention

The OSPAR Convention defines the process that countries have to undertake to ensure that only compliant materials are disposed of at sea. In the UK CEFAS have determined a set of Action Levels for the ranges of chemicals which are specified in the convention and which are used to assess whether material should be disposed of at sea. Most chemicals have 2 action levels, above level 2 material cannot be disposed of at sea and below this level but above action level 1 disposal at sea should only be undertaken if this is safe.

The River Tees could be expected to be highly contaminated with a range of hydrocarbons due to the long use of the river banks for the production of coke and its byproduct coal tar, chemical works and oil processing. Some of the most toxic hydrocarbons are polycyclic aromatic hydrocarbons (PAHs) and these are the hydrocarbons which are specifically regulated under OSPAR. However, there is only an Action Level 1 for PAHs, 0.1mg/kg, but no Action Level 2.

PAHs

The River Tees samples taken to allow maintenance dredging always contain 100s / 1000s of times the CEFAS PAHs Action Level 1 concentration and so a decision has be made about whether dredged material should be disposed of at sea. It appears that the logic that is followed is that this high level is not suitable for disposal at sea, however as it has always been at this level and disposal at sea has been allowed, it is acceptable for new materials to disposed of at sea.

In the absence of an Action Level 2 for PAHs has meant that CEFAS adopting the Gorham-Test to understand whether PAHs present a hazard or not. The Gorham-Test is not a single level but instead works by splitting PAHs into low and high molecular weight PAHs which are assessed separately. The Gorham-Test has 2 levels equivalent to Action Levels 1 and 2, the effect-range low (ERL) and effect-range median (ERM).

Cumulative Actions

OSPAR regulations do not exactly specify the amount of sediment that can be disposed of at sea, but leave this as a decision for each countries regulators. In the UK the regulator is the Marine Management Organisation, who issue the licence for disposal, and use the Government CEFAS laboratory to obtain the necessary scientific guidance.

The CEFAS opinions for the maintenance dredge disposal at sea make direct reference to the levels of PAHs as being above the normally acceptable level (2020 sampling and 2021 sampling), but make no mention of the amount of material which is being disposed of in the explanation of why dredging material disposal at sea is safe. However, the letter does state the annual quantity of material to be dumped at sea as only 250,000 wet tonnes. The letter was written prior to the application for variation 6 of MLA/2015/00088, which corrected the annual disposal from 250,000 wet tonnes to 2,500,000 wet tonnes, a factor of 10 increase.

Rate of disposal

Going back to fundamentals the exact concentrations in the sediment or the total amounts being disposed of at sea are only part of the picture. Damage is done to humans, animals, plants and any other living things, by the amount of material they are exposed to at any one time or cumulatively over a period of time, depending on the specific way in which a chemical is toxic. The exposure amount will be increased by higher levels of chemicals in the sediment, by larger amounts of sediment being disposed of at sea but also by the rate of disposal of the sediment.

The faster the rate of disposal the higher the concentration of chemical will be and so the more poisonous the sediment will be to the aquatic environment. Faster rate of disposal will also mean the concentration of a chemical will remain above the concentration at which it is toxic for longer. Very high concentrations may also slow down the rate of breakdown of the chemical, as the concentration of oxygen for oxidation is reduced by previous breakdowns and any microbial breakdown is swamped or even poisoned due to the high concentration.

UKD Orca

The UKD Orca was contracted to dredge the channel in Tees Bay from 25th September 2021 to 4th October 2021. This corresponded exactly when the first die off of marine life occurred and as the UKD Orca had been seen by users of the river. Many people immediately assumed that the UKD Orca must have been responsible for the marine die off.

This assumption was reinforced by errors made by PD Ports in the original Application Form for MLA/2015/00088 where the total dredge for the River Tees was stated as only 1,507,770 wet tonnes for sand and 930,065 wet tonnes of slit to be removed over the ten year period between 1st January 2016 to 31st December 2025, where these were in fact the amount that PD Ports expected to dredge every year. Similar errors were made for the Hartlepool dredge amount, i.e. 322,800 wet tonnes of sand and 128,480 wet tonnes of silt over ten years and not each year. These errors had not been corrected, so that when it was known that the UKD Orca had disposed of almost 150,000 wet tonnes at sea, this appeared to be 60% of the annual allowance of the incorrectly stated 245,000 wet tonnes, as per MLA/2015/00088 before variation 6 (June 2022).

The Application Form for variation 6 merely states “The licence currently has an admin error on the quantities so they do not align with the correct volume on the licence conditions.” The previous license MLA/2012/00141 did give annual breakdown of amounts to be dredged, so to someone in the know this is just an administrative error in MLA/2015/00088, but this was not the case for consultees who explicitly stated their opinions were based on the incorrect annual amounts i.e. CEFAS recommendations based on 2020 sampling and 2021 sampling.

It is now known that the UKD Orca removed 148,930 wet tonnes, 5% of the annual total amount allowed to be disposed of at the inshore Tees Bay A, 2,889,700 wet tonnes, which is normally 80% from the Tees channel and 20% from the Hartlepool channel. The UKD Orca was dredging 24 hours a day for 10 days, whereas, according to the mainentance dredging method statement, PD Teesport's own dredgers normally only dredge 8-10 hours a day for 6 day week. So in 10 days (2.8% of a year) UKD Orca had removed more material that the normal operation would in 18 days.

The UKD Orca dredge was about twice as fast as PD Teesport's normal dredging. So the dredging operation was definitely faster than normal, could this have been sufficient to cause the marine die off?