Report for Council Liaison Meeting 13th June 2001

See also Report 2 and Site History

Introduction:

The community of Bletchley record that the WDA201 license site still smells.

The cap to C2N is breaking up3 with the potential to:

  1. Cause air to enter the waste which will reduce system efficiency and increase risk of combustion within waste mass.
  2. Allow uncontrolled emissions of landfill gas to continue over a large surface area
  3. Allow increased leachate generation (another source of dour)
There is a problem with hydrogen sulphide levels in gas wells (2000ppm) which are known to leak at the well heads. This would suggest that the seal is damaged and that the well is under insufficient suction to enable full gas control. The latter suggests that some rebalancing is necessary or that the suction imparted by the flare system is insufficient to effect gas control on area C2N.

The presence of high leachate levels in vertical gas wells and insufficient sub-surface drainage continues to be a problem3 and this reduces the effectiveness of the gas wells and the lateral influence of the vertical wells. This, combined with the limited seal and poor capping will result in excessive air ingress levels as soon as any suction is applied. Leachate is recorded is still escaping.

Leakages have been noted on numerous occasions3,4,5,6 (EA reports, community gas monitoring). EA reports leaks around well heads resulting in odour events. The use of ‘gaffa tape’ to seal well heads as noted by the EA5 is not a ‘best practice’ engineering approach by any stretch of the imagination.

Letter received from Ms Vikki Fox (SWS) dated 6th June 2001 reads:

‘It is important to note that the initial findings of the EHO is that ‘…it is generally agreed that there are no long term health effects of H2S less than 10 parts per million – some 300 times our highest reading so far of 35 parts per billion….’’ We record that it is a matter of record that levels of up to 71ppb have been recorded in the community by the Environment Agency. We would also record that according to HSE guidance literature7 exposures to levels as low as 10-15ppm for several hours have resulted in reversible eye damage, characterized by irritation and inflammation of the cornea and conjunctivae. We do not think that this represents ‘no long term health effects’.

From the literature1, The Health and Safety Occupational Exposure limits for H2S are:

Long term exposure limit (8hr TWA) LTEL: 14 mg/m3 (9800ppb)

LTEL/40: 0.35 mg/m3 (245ppb) Short term exposure limit (15 minute) STEL: 21 mg/m3 (15000ppb) STEL/40: 0.531 mg/m3 (375ppb) The LTEL/40 limit is actually 3.45 times the maximum recorded measurement of 71ppb (29% of LTEL/40). The LTEL/40 figure is recommended by the HSE for use in situations where atmospheres containing MIXED toxicants are encountered. It must be remembered that this landfill site is emitting mixed toxicants and not simply H2S.

Air quality guidelines2 issued by the World Health Organisation (WHO) have been developed to provide a basis for protecting human health from the adverse effects of air pollution.

WHO exposure limits are:

Sensory annoyance guideline for H2S (30min TWA) EL: 0.007 mg/m3 (5ppb)

Long term exposure limit (24 hr TWA – Health) WHO LTEL: 0.15 mg/m3 (106ppb)

The measured values have been in excess of 14 times the WHO sensory annoyance levels. Far higher than the Nant-y-Gwyddon site in S. Wales where the WHO level was exceeded by a factor of 3.

In conclusion, since gas monitoring of other gases is not been carried out or quantified, the harmful effects on health are not known. In any case, the recorded levels have been close to the WHO health effect levels and have regularly exceed the annoyance guidelines.

Community Gas Monitoring:

Whilst we applaud the monitoring now taking place, it would appear from the literature1, that meteorological monitoring of ambient wind speed, direction, relative humidity and temperature. Community meteorological monitoring must take place in tandem with the gas monitoring if any value is to be attributed to the study. SWS have been aware of this since their discovery of the Entec report which spells out the guidance.

We recommend that MKBC obtain a copy of the ENTEC report so that they may carry out a proper assessment. To carry out the work effectively an independent firm of consulting engineers (e.g. Entec) should be appointed to carry out the monitoring

PALS recommend that further Landfill Gas Sampling and analysis is carried out and to ensure:

  1. Continuous monitoring on site of LFG emissions. This will allow detailed surface emission flux rates from the site to be determined.
  2. Continuous air monitoring using a number of devices positioned at various locations within the community surrounding the landfill.
  3. Collection of landfill gas and air samples for detailed compositional analysis by Gas Chromatography Mass Spectrometry (GCMS).
  4. Calls are made to the freephone 0800 telephone during an ‘odour event’ the measurement device and operative must travel as rapidly as possible to the site of the selected complaint. Measurements of air quality should then be made and air samples collected for detailed analysis. The complainant should be interviewed.
  5. Identify whether compounds in the air (not just Hydrogen Sulphide) are likely to produce an impact on human health or cause pollution of the environment.
Flare Stack Emissions:

The new flares at WDA201 should comprise the following features:

  1. A patented flare tip designed to maintain gas exit velocity over a range of flow rates
  2. High velocity operation creating high turbulence and gas/air mixing within shroud
  3. Air volume control damper to automatically vary the correct amount of oxygen to the flare
  4. A thermally insulated shroud designed to provide a flame retention time, reduce noise and maintain the internal temperature of the flare
  5. An automatic control system monitoring inlet gas composition, flow, temperature, flame state and exhaust gas emissions. Positive feedback to the flare from the controller based on monitoring data to provide peak combustion efficiency
  6. Safeguards against low oxygen and low flow conditions
  7. In line flame arrestor
  8. Slam shut valve to prevent release of unburnt gas to atmosphere in flame out situations
  9. Flow control valve
  10. Automatic re-ignition facilities (attempts to re-ignite 3 times, then shuts flare down)
  11. pre-mixing of fuel and air
  12. Provide run and standby flares/fans to allow LFG to be effectively flared during failures and scheduled downtime. This is at present not happening.
Atmospheric Dispersion Modelling of Landfill Emissions:

In order to assess the impact of the emissions form WDA201 it will be necessary to carry out an atmospheric dispersion modelling study of the landfill and flare emissions. The aim of the study will be to assess whether the atmospheric emissions from the site could result in the potential for a significant health or odour impact at nearby residences (apparently, the EA calls those affected ‘receptors’). The results of such an exercise will help to validate the air quality monitoring data collected in the community.

It would appear that the UK ADMS-2 modelling system is appropriate, but more modern software may now be available. Again, Entec could advise on this.

The modelling study will help SWS to assess exactly how their poor management of the site results in the release of plumes of LGF into the community and how the LFG is diluted and dispersed. In the light of this knowledge, future impact of SWS site activities can then be predicted and protocols can be imposed in the licence to protect the community. This is crucial.

Inputs required by the software are:

  1. Number of emission points and location of release points on site plan
  2. Pollutants released from each point
  3. Production schedules (when, how long, time of day?)
  4. Concentration of each pollutant requiring investigation
  5. Temperature of emissions at release point
  6. Release point height, diameter, orientation and volume flow/efflux velocities
  7. Any special information (e.g. release of water vapour)
  8. Details of local terrain
  9. Building dimensions of all on site buildings and off-site buildings in close proximity
  10. Meteorological data
  11. Flare stack emissions under normal operation
  12. Fugitive surface emissions
Conclusions:

The calcium sulphate filter based waste will continue to support hydrogen sulphide over the long term.

Follow all the recommendations of the ENTEC report1 (pp 165 – 174).

References:

  1. Investigation into Odour problems at Nant-y-Gwyddon landfill, south east Wales – Final Report; January 1998; For: Environment Agency, Welsh Region. Auth: Entec.
  2. Air Quality Guidelines for Europe; WHO Regional Publications, European Series No.23; 1987.
  3. EA site inspection report 0117958 15th May 2001.
  4. EA site inspection report 048535; 10th May 2001.
  5. EA site inspection report 048539; 22nd May 2001.
  6. EA site inspection report 048518; 11th May 2001.

    7. Toxicology of Substances in Relation to Major Hazards, Hydrogen Sulphide; HSE; HMSO 1990; ISBN 0 11 88 55 61 1

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