H₂S SCREENING MODEL · TECHNICAL NOTE
Hydrogen Sulphide Emissions and Receptor Concentrations During Landfill Excavation
Source-term formulation, receptor screening and control-performance requirements.
Marcus Holden MCIWM CRWM · Holden Environmental
Download the complete technical note (PDF, 9 pages).
From source evidence to receptor screening
A gas concentration is not an emission rate.
The screening model bridges the gap between H₂S measured in landfill gas and the concentration that could reach a worker, an on-site location or an off-site receptor.
It converts each release mechanism into a transparent mass source, applies event duration and demonstrated containment, and then screens receptor concentrations using a simplified dispersion relationship.
Three release pathways
The model keeps fundamentally different sources separate so that a modest routine emission does not conceal a much larger short-duration event.
Diffuse face
H₂S mass flux released across an exposed waste surface. The source term depends on measured or published flux and the area open at one time.
Disturbed waste
Gas liberated as waste is excavated, loaded or placed. The source depends on waste throughput and the gas volume released per unit of waste.
Localised event
A short release from a gas pocket, connected void or damaged collector. Flow, duration and source dimensions control the acute screening result.
What the model calculates
Each stage remains visible, allowing assumptions to be challenged, replaced by measurements and tested for sensitivity.
1 · Source term
Converts ppmv, surface flux, gas flow and waste disturbance into H₂S mass release in g/s or kg/h.
2 · Receptor screen
Calculates concentration–distance profiles and screening concentrations at defined receptors for selected wind and event assumptions.
3 · Control duty
Quantifies the direct source reduction required to meet a selected comparison level and exposes when a proposal depends on exceptional containment.
Synthetic worked example
The paper uses a deliberately generic example at 5,000 ppmv H₂S and 1 m/s wind. It demonstrates the calculation sequence; it does not represent a particular landfill or proposed operation.
Routine disturbance
0.044 kg/h
6.3 µg/m³ at 250 m over 30 minutes.
Localised release
2.125 kg/h
52.0 µg/m³ at 250 m over 30 minutes.
Major localised release
10.626 kg/h
519.8 µg/m³ at 250 m over 30 minutes.
The engineering point: a plausible short-duration release from connected gas volume can outweigh diffuse face emissions by orders of magnitude. Controls aimed only at the exposed face may therefore leave the controlling hazard unchanged.
A screening model — not a regulatory prediction
Useful for
- testing routine and credible localised releases;
- screening worker and public receptors;
- setting monitoring and weather limits;
- testing face size, throughput and containment;
- identifying when detailed assessment is required.
It does not replace
- site-specific atmospheric dispersion modelling;
- occupational-hygiene assessment;
- field monitoring and validation;
- a task-specific safe system of work;
- demonstration of regulatory compliance.
Planning excavation where H₂S may be present?
Holden Environmental can develop the source terms, receptor screening, monitoring requirements and control-performance criteria needed to support an engineering decision.