Closed Tyre Tip, Mid Wales
In
1997, Ward Jackson Associates
were asked by the owner, with the support of the Welsh
Development Agency, Land Reclamation Department, to carry out a hydrological
study and report on options for reducing pollution in the watercourse
downstream of an old waste tyre tip, located in rural Mid Wales in the
upper reaches of the Teme River catchment and surrounded by farmland.
The tip was made up of about 3 million disused tyres, buried in a steep-sided
side valley and covered with a thin capping of invert soil.
In 1989, the tip caught fire, probably
as a result of arson and although the initial fire had been brought under
control, the tyres had
continued to burn progressively beneath the soil cover. Various proposals
had already been put forward to extinguish the fire, but were either too
expense or impractical in the circumstances, or both. The culvert beneath
the tip had been damaged by the fire and was allowing residual tars and
oils from melting tyres to leak into the culvert and then into the downstream
watercourse. Added to these hydrocarbons were high levels of zinc and
iron oxides from the reinforcement used in the manufacture of the tyres.
The effect of storm flows through the culvert was particularly detrimental,
as this would flush very high concentrations of phenols, polynuclear aromatic
hydrocarbons (PAH's) and metal oxides into the watercourse. Even the system
of settlement ponds below the tip was ineffective during high flows, as
trapped contaminants collected and retained during dry-weather flows were
simply flushed through during a storm.
WJA's
solution, accepted by the Client and the funding authority, was to construct
a new 675mm diameter, 500 metre long culvert within farmland just outside
the site. This would intercept the two main streams entering the tip and
collect the surface water from the tip capping and adjacent farmland.
The culvert would discharged downstream of the site, leaving only groundwater
seepage flows to enter the old culver system. This would allow the existing
settlement ponds to be more effective. The proposals included the construction
of a lined lagoon to provide water storage for fire fighting.
The design and supervision of the
major drainage improvements, were successfully carried out by WJA.
Earthworks designed to help isolate underground fire and locally improve
the tip capping, were effective, resulting in markedly reduced temperatures
within the zone of combustion. WJA
also designed and supervised the installation of temperature monitoring
boreholes, installed across the width of the tip, to detect any breaching
across a grouted firebreak into parts of the tip previously unaffected
by burning. This required innovative drilling techniques to penetrate
the many layers of rubber tyres and their steel reinforcing wires.
WJA continued to sample leachate from the tip on completion and currently have a brief from the Environment Agency for ad hoc measurement and reporting on tip temperatures. These have continued to fall to near normal levels over the past two years.
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