MANAGING OUR PAST - GARTH TONMAWR 'LAGOONS' EarthCache

You can walk, cycle or drive to the site along a single track road.

YOU CAN SEE THE LAGOONS THROUGH THE FENCE. YOU DO NOT NEED TO ENTER THE SITE

FOLLOW THE SAFETY GUIDELINES POSTED ON THE FENCE

Discharges of polluted water from underground coal mines have long been a problem in the traditional coal mining areas of Wales.  The mine water at Pelenna is acidic from both drift and deep mines. The stream here is a tributary of the river Afan which enters the sea at Port Talbot

This is a picture of the site when it was an active colliery

The area has been affected by mine water discharges for over 25 years leading to severe discolouration of approximately a 7km length of the river.

It is only in recent decades with the cessation of active mining in parts of the coalfields that mine water discharges have begun to emerge as the water table recovers from artificial control during mining operations. Work began on these settlement lagoons in 1994 and took 5 years to complete

How  is  coal mine water treated at this site?

The mine water is captured  emerging by gravity from the mines. Mine water is brought to the top of a cascade structure. Water flows down these steps, which mixes in air.

The air encourages the dissolved iron in the water to become solid, and raise the pH of the water, (that is reducing the acidity).

The water then flows into lagoons where the iron has time to settle at the bottom for removal. These are constructed with honeycomb mat stabilised local colliery waste for the bunds and red brick walls between cells.

The  Coal Authority uses this natural or “passive” method, ie  settlement lagoons and reed beds, to remove iron from mine water that was polluting the Nant Pelenna and downstream the River Afan.

Finally the treated water is discharged back to Nant Blaenpelenna.

Pollution Remediation

The raw mine water has an average iron concentration of ~32mg/l.

Although not toxic in itself, iron within the mine water oxidises and precipitates out of solution within the water course and can result in the smothering of river beds.

When the Garth Tonmawr MWTS was originally constructed it consisted of five cells in series with a total treatment area of 6370m². The cells consisted of:

• Cell 1 Aerobic settlement lagoon (2480m²).

• Cell 2 Reducing and Alkalinity Producing System (RAPS). This is an anaerobic downward flow

  wetland, formed from organic compost overlying a non-dolomitic limestone base (970m²).

• Cell 3 Aerobic wetland (980m²).

• Cell 4 Reducing and Alkalinity Producing System (RAPS). This is an anaerobic downward flow

  wetland, formed from organic compost overlying a non-dolomitic limestone base (980m²).

• Cell 5 Aerobic wetland (960m²).

  

• A schematic diagram of the original design for Garth Tomawr (Wiseman, 2002).

Why does  coal mine water need to be treated?

When a coal mine closes, the pumps that were used to keep the water out of the mine while the mineral was extracted are switched off and removed.

Over time the water level recovers within the mine and picks up naturally occurring minerals from the rocks, such as iron. This can coat river beds, stopping plant growth, causing wildlife to move on as they no longer have food.

YOU WILL NEED TO WALK UP THE UNPAVED ROAD AT THE SIDE OF THE LAGOONS TO ANSWER THE LOGGING REQUIREMENTS

1. You must visit the site
2. How many settlement lagoons can you still see?
3. What colour is the sludge? What mineral does this suggest to you?
4. What difference can you see  between the uppermost and lowest lagoon?
5. Describe some of the aspects of the environment likely to be significantly affected by the development including, people, fauna, flora, soil, water, air, climate, architectural and archaeological heritage, landscape and the inter- relationship between the above factors.
6. YOU MUST include a photo of you, or a personal item somewhere identifiable near the front gate.

~ From the guidelines: You do not need to wait for permission to log. Requiring someone to wait is not supported by the EarthCache guidelines.

You should send  your logging task  answers through the message centre or by email

Then log the EarthCache. When I review your logging task answers, I will contact you.

Don’t include the answers in your log even in an encrypted form.

You should carry out these educational tasks as required by the EarthCaching organization, as a condition of logging the cache. Logs that do not adhere to these guidelines will be deleted without notification.

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BUT PLEASE DO NOT POST PHOTOS OF THAT GIVE THE GAME AWAY!

☆☆☆ Congratulations on FTF to melin boy ☆☆☆