Cleaning Cleveland’s water from orange to clear: Remediation of contaminated water at Saltburn, Cleveland as a result of historical ironstone mining

Background

East Cleveland is situated in North East England and has undergone large-scale deep ironstone mining since the mid-19th Century. When mining operations ceased in

the 1960s, the dewatering pumps were removed, resulting in the re-bound of iron-rich mine water. On 18th May 1999, the mine water breached the surface in the steep-

sided, narrow, wooded valley of the Saltburn Gill. The mine water quickly turned this high-quality watercourse bright orange, smothering the stream bed with ochre,

reducing the penetration of sunlight in the water and depleting oxygen levels; as a result, the ecology of the water body was adversely affected. Mine water from the

discharge continued to enter the Saltburn Gill impacting several other water bodies, including a groundwater body and the Skelton Beck, before discharging to the North

Sea, occasionally forming a large ochre plume.

Local residents, concerned about the pollution in the Saltburn Gill, formed the Saltburn Gill Action Group (SGAG) in 2005. The SGAG is a community-based organisation

comprising local residents and representatives from the local Parish and District Councils, Tees Valley Wildlife Trust and Groundwork in addition to local officers from the

Environment Agency and geoscientists from Teesside University. Funding was raised by the group, from a variety of sources, to employ environmental consultants Entec

UK Ltd in 2007, to conduct a study assessing the impact of the mine water discharge. Collaboration between SGAG and the Environment Agency resulted in the Coal

Authority being approached to offer advice on this study.

Saltburn Gill was ranked as being the 3rd worst metal mine water discharge in England by the Environment Agency.

Following the Energy Act 2011 and funding from the Department of Environment, Food and Rural Affairs (Defra), the Coal Authority constructed a mine water treatment

scheme in the area, employing J N Bentleys as the main contractor. The scheme intercepts the mine water and removes the iron prior to discharging clean water to the

Saltburn Gill. The construction of the treatment scheme will enable two surface water bodies to obtain WFD ‘good status’ for Saltburn Gill and possibly the affected

groundwater body in the next River Basin Cycle.

The Coal Authority

The Coal Authority is a Non-Departmental Public Body, established in 1994. The Coal Authority’s statutory duties are set out in the Coal Industry Act 1994.

The Coal Authority has no statutory obligation to remediate mine water, but strives to ensure that as far as reasonably practicable, water bodies comply with the

European Union Water Framework Directive (WFD). Working to a priority discharge list compiled by the Environment Agency, the Coal Authority currently manages over

60 discharges from coal mines abandoned prior to 1999. In contrast to coal mines, no similar body is in place to tackle pollution from abandoned metal mines (e.g.

former lead, zinc, and ironstone mines). Many of these mines ceased operating in the early 20th Century and it is no longer possible to trace the owners of these

disused sites. Following the introduction of the Energy Act 2011, the Coal Authority has been permitted to undertake work on disused metal mine water discharges, such

as Saltburn Gill.

Mine water treatment scheme function and layout

The mine water treatment scheme at Saltburn Gill has been implemented in two phases:

Phase 1 was completed in July 2013. Construction of two settlement lagoons with aeration cascades and a drying

bed for ochre sludge. Monitoring data indicated that Phase 1 infrastructures reduced the iron concentration in the

raw mine water by approximately 94%. The results obtained from Phase 1 have provided information for the

additional infrastructure required for Phase 2.

Phase 2 is due for completion in 2015. Construction of two further settlement lagoons and a polishing reed bed.

Once this improved design criteria is complete, the mine water will pass from the settlement lagoons to the reed

bed, which acts as a filter removing more iron from the mine water prior to discharge into the Saltburn Gill.

The treatment scheme at Saltburn has a design life of 25 years; although most elements of the scheme are

designed to last longer. It is envisaged that the scheme will only require refurbishment works after the first 25 years.

Regular maintenance will be required however, including the de-sludging of the lagoons into the sludge drying bed,

reed cutting, maintenance to the pumping infrastructure and general upkeep of the scheme as a whole.

Stages of mine water treatment at Saltburn Gill

Wetland (Phase 2)

Once completed, the mine water will pass from

the settlement lagoons through to a reed bed

system. The reeds will filter more iron out of the

water to an even lower level, before discharginginto Saltburn Gill.

N

Sludge drying bed (Phase 1)

The ochre sludge is collected from the bottom

of the lagoons and placed into the drying bed,

where the ochre sludge is dried before

removal

Two cascades (Phase 1)

The mine water is pumped from an

abstraction borehole to the top of a

concrete aeration cascade. The

mine water is passed over the

concrete aeration cascade to

oxygenate the mine water.

Increasing the levels of oxygen

induces iron to precipitate out of the

solution.

Two lagoons (Phase 1)

From the cascade, the aerated mine water is

passed into two settlement ponds. Here,

over a period of 1-2 days, the majority of the

dissolved iron precipitates and settles to the

bottom for removal at a later date. The

treated mine water is discharged back intoSaltburn Gill.

Two cascades and two lagoons (Phase 2)

Two cascades and lagoons have recently

been constructed. When operational, they will

allow for a greater area of mine water to be

exposed to oxygen, resulting in the

precipitation of greater ochre quantities in the

new lagoons.

Expected Outcomes

Upon completion of Phase 2, it is anticipated that 99% of the iron will be removed from the mine water; the treatment scheme is expected to

remediate more than 3 km of water course.

The works at Saltburn are an excellent example of how close and open collaboration between members of the local community, public bodies and

construction contractors can result in a high quality, satisfactory output for all stakeholders. With the works so far delivered ahead of schedule and

under budget, the scheme has generated palpable benefits to members of the local community and the environment alike.

Benefits of treating the mine water

There are many benefits that the scheme has and will bring to the local environment and community. The scheme

has already significantly improved the local watercourse and reduced the amount of iron entering the North Sea.

The two primary sources of iron pollution have dried up, as a result of pumping the water from the mine workings

and lowering the ground water levels in the area.

• Much of the affected area lies within the Saltburn Gill Nature Reserve, a Site of Special Scientific Interest. It

contains ancient deciduous woodland that has been adversely affected by the mine water. Some trees have died

in the vicinity of the discharge, probably as a result of drowning. There has been an improvement to invertebrate

biodiversity and abundance in the water course, which will subsequently enhance the ability of the watercourse to

support other wildlife along the 2-3 km affected reach.

• There will be multiple benefits to local tourism. Saltburn Beach is a designated bathing water and is one of the

most popular surfing beaches on the east coast. The beach currently scores a ‘Pass’ under the Bathing Waters

Directive, but more stringent guidelines coming into force this year may result in a ‘Poor’ status. Remediating the

local water bodies would ensure that the beach retains the current ‘Good’ status and cleaning up the beach

should also attract more surfers to the area.

• Part of the affected coast is designated as a heritage site. Treating the mine water will enhance the appearance of

the area and will contribute to the strategy objectives for the heritage coast. There are also landscape benefits by

improving the general amenity of the area for both locals and tourists.

• WFD Status for three water bodies in the area will be improved: Saltburn Gill, Skelton Beck and a groundwater.

• A significant head of water existed behind the mine water discharge flowing into the Saltburn Gill. Prior to the

works undertaken by the Coal Authority, there was a significant risk that a sudden out-flow could have occurred if

the material impounding the water had failed; resulting in a severe pollution incident. Pumping of the water from

the mine workings has removed this risk.

Timeline of Events

In affiliation with:

Skelton Beck water body before the implementation of the treatment schemeSkelton Beck water body after the implementation of the treatment scheme

Conceptual model for mine water breakout in Saltburn Gill

Lumpsey

Longacres

2

1

7

4

66

5

9

8

1) Inflow of fresh groundwater from sand layers into shafts

2) Minor recharge to the workings through clay strata

3) Roof collapse enables groundwater inflow into workings

4) Roof collapse in workings restricts groundwater flow

5) Regional groundwater table provides driving pressure towards Saltburn Gill

6) Groundwater picks up iron load

7) Contaminated groundwater flow

8) Adit9) Adit collapse provides pathway for mine water

10) Mine water discharge 10

4

3

5

7Adapted from Entec Hydrogeological Study 2010

Ground levelKey

Abandoned workings

Water

Mineral leaching

Water table

Map of affected area and mine water treatment scheme

Key: - Location of mine water treatment scheme Easting: 467259 Northing: 519794

Pollution plume on the North Sea Heritage Coastline: impact of mine water from abandoned

ironstone workings of Cleveland, viewed from Saltburn sea front

TCA commence operation of Saltburn Gill mine

water treatment scheme

in conjunction with our construction partners J N Bentley

Neil McClure, Arabella Moorhouse, Helen Proffitt and Sinead Chamberlain