Gross Pollutant Trap Cleaning Safe Work Method Statement

Confined space entry requirements depend on the specific GPT design and whether worker entry is required for cleaning or maintenance, not the GPT type alone. Determine confined space classification by assessing three criteria: (1) Does the space have restricted means of entry or exit that would make evacuation difficult? (2) Is the space designed or intended primarily for continuous human occupancy? (3) Does the space present risk of atmospheric contamination, engulfment, or configuration hazard? Many simple basket-style GPTs installed in standard stormwater pits can be serviced from surface level without entry - workers remove pit cover, lift out basket using hook or grab, empty basket, and replace it without entering the pit structure. These operations don't require confined space entry procedures if workers remain at surface level throughout. However, even shallow pits require atmospheric testing before removal of covers due to potential gas release when opening. Large underground vault GPTs, treatment chambers, constructed wetlands with sumps, and proprietary devices with internal maintenance requirements often require worker entry for thorough cleaning, component inspection, or repair work - these spaces typically meet confined space criteria requiring full entry permits, atmospheric testing, standby persons, and emergency procedures. Some medium-sized GPTs fall into grey areas where entry may be optional - cleaning can be accomplished from surface using extension tools and vacuum equipment, or workers can enter for more thorough cleaning. Best practice applies confined space protocols whenever any doubt exists about space classification or if workers will place any body parts into structures even without full entry. The key distinction is whether workers will enter the space (head and shoulders into structure) versus service from outside. Review each GPT design individually, conduct risk assessment considering atmospheric hazards from decomposing organics, configuration hazards from restricted access, and engulfment hazards from sediments or sudden water inflow, then document confined space determination. For GPTs regularly serviced, maintain site-specific confined space register identifying which structures require entry procedures and which can be serviced from surface level, providing clear guidance for maintenance crews and ensuring consistent safety approach across GPT cleaning program.

Gross pollutant traps present multiple atmospheric hazards from decomposition of trapped organic materials in oxygen-deficient environments. Hydrogen sulphide (H2S) is the most significant toxic gas hazard, generated by anaerobic bacterial decomposition of organic matter trapped in GPTs including vegetation, food waste, and animal carcasses. H2S concentrations can reach immediately dangerous levels (100+ ppm) in poorly ventilated GPTs, causing rapid unconsciousness and death at high concentrations. H2S has characteristic 'rotten egg' odour at low concentrations but causes olfactory fatigue at higher levels preventing workers from detecting increasing concentrations - never rely on odour for H2S detection. Methane (CH4) generates from anaerobic decomposition creating both asphyxiation hazard through oxygen displacement and explosion hazard when mixed with air at 5-15% concentration. Carbon monoxide (CO) may be present from combustion products in stormwater runoff or decomposition processes. Oxygen deficiency occurs as decomposition processes consume oxygen in confined GPT atmospheres, with levels dropping below 19.5% safe minimum causing impaired judgment and eventually unconsciousness. Some GPTs in industrial catchments may contain additional toxic gases from chemical contamination requiring assessment beyond standard 4-gas monitoring. Required gas detection equipment is a calibrated 4-gas detector measuring oxygen (safe range 19.5-23.5%), combustible gases/methane (must be below 5% LEL or Lower Explosive Limit), hydrogen sulphide (must be below 10 ppm for safe work), and carbon monoxide (must be below 30 ppm). Detectors must have current calibration (typically 6-month maximum interval) and be bump tested before each use to verify sensor response to test gas. Conduct atmospheric testing before removing GPT covers, immediately after opening (allowing initial venting period), before any worker entry, and continuously during entry if confined space work required. Test atmosphere at multiple depths as gases stratify with heavier gases (CO2, H2S) settling at lower levels and lighter gases (methane) rising to upper areas. If any parameter fails safe limits, implement forced ventilation using portable blowers and retest after ventilation period - never attempt entry to unsafe atmospheres without supplied air respiratory protection. Even for surface-level GPT servicing without entry, atmospheric testing before opening is essential as gas release when covers removed can expose workers to dangerous concentrations. Environmental conditions affect gas generation and accumulation - hot weather increases decomposition rates and gas generation, stagnant periods without stormwater flows allow gas accumulation, and recent storm events may flush some gases but introduce new contaminated materials beginning fresh decomposition cycles. Regular cleaning programs that prevent excessive organic material accumulation reduce atmospheric hazard severity compared to infrequent cleaning of heavily loaded GPTs containing months of decomposing material.

Waste materials removed from GPTs require proper classification and disposal according to environmental protection regulations to prevent pollution from waste itself. GPT waste typically separates into distinct streams each with specific disposal requirements. Gross litter and debris (plastic bottles, cans, paper, general refuse) captured by screens and baskets usually classifies as general solid waste suitable for disposal at standard landfills, though some councils specify recycling of metal containers and plastics where practical. Organic vegetation matter including leaves, grass clippings, and branches can often be disposed to green waste facilities or composting operations if not heavily contaminated with other materials. Sediments and fine materials present more complex classification challenges. Sediments from GPTs in residential or low-contamination catchments may accept as general fill or soil-like waste. However, sediments from roadways, car parks, and industrial catchments often contain elevated concentrations of heavy metals (lead, zinc, copper from vehicle sources), petroleum hydrocarbons (oils, fuels, tire particles), and other contaminants. These contaminated sediments may classify as 'contaminated soil' or 'special waste' requiring disposal at facilities licensed to accept contaminated materials rather than general landfills. Waste classification requires chemical analysis testing representative sediment samples for contaminant concentrations and comparing results to classification thresholds specified in relevant state/territory environmental regulations - this testing may be required annually or more frequently for large-scale cleaning programs. Hazardous materials occasionally found in GPTs including paint containers, chemical drums, asbestos-containing materials, batteries, and electronic waste require segregation and specialist hazardous waste disposal. Animal carcasses found in GPTs (common in areas with fauna) require disposal in accordance with biosecurity and public health regulations, often requiring burial at specified depths or disposal at facilities accepting deceased animals. Liquid wastes including water pumped from GPTs during cleaning operations present additional considerations. Clean stormwater can often be discharged to stormwater systems or surface waters if not contaminated during cleaning operations. Contaminated water from pressure washing GPT components or from heavily polluted trap contents may require treatment or disposal as trade waste depending on contamination levels - discharge to sewerage systems typically requires trade waste agreements with water authorities. Some cleaning contractors use water recycling systems on vacuum trucks capturing and treating wash water for reuse rather than disposal. Maintain disposal records documenting waste quantities, classifications, disposal facilities used, and disposal dockets for each load. These records support environmental reporting requirements, demonstrate regulatory compliance, inform future waste management planning, and provide asset management data on GPT loading rates and cleaning frequencies. For large-scale municipal GPT programs, waste characterisation data supports catchment pollution load estimates contributing to water quality improvement planning. Incorrect waste disposal not only creates environmental risks but exposes operators to significant penalties under environmental protection legislation - recent prosecutions for improper disposal of contaminated waste have resulted in fines exceeding $100,000 demonstrating regulatory authorities' serious approach to waste management compliance.

Truck-mounted vacuum equipment creates significant hazards during GPT cleaning operations requiring specific controls beyond general equipment safety. The primary hazard is powerful suction created by vacuum pumps generating 50-70 kPa vacuum pressure (15-20 inches mercury) through 100-150mm diameter hoses. This suction force is capable of drawing in and retaining human hands, arms, or body parts creating serious injury including tissue damage, lacerations, and potential amputation if extremities drawn fully into hose. Suction hazard increases when vacuum hose inlet becomes partially blocked or restricted creating focused high-velocity flow. Workers must maintain minimum safe distance (3 metres) from hose inlet during operation and never place hands, arms, or any body parts over or near hose opening while vacuum operating. Use extension poles, hose positioning tools, or remote handling equipment to position and maneuver hoses in GPT structures rather than manual handling near inlet. Install inlet screens or guards on hose ends preventing large objects or debris from entering hose and creating blockages - however, these screens must not create false security leading workers to position near inlets. Vacuum hose blockages create additional hazards as blocked hoses under full vacuum pressure can fail catastrophically causing violent hose whip. Hose failures release enormous stored energy causing hose to flail violently potentially striking nearby workers. Monitor vacuum pressure throughout operation watching gauge for sudden pressure increases indicating blockages. If blockage detected, immediately reduce vacuum pressure to zero before investigating or attempting to clear blockage - never attempt to clear blockages while vacuum system operating. To clear blockages safely: shut down vacuum system, release all vacuum pressure, carefully inspect hose from safe distance to identify blockage location, clear blockage using tools from safe position, verify hose clear before resuming operation. Use hose restraints or positioning equipment preventing hose whip if connections fail under vacuum - while uncommon with proper equipment maintenance, connection failures have caused serious injuries from uncontrolled hose movement. Ensure vacuum operators trained in equipment operation including start-up procedures, vacuum pressure monitoring and adjustment, emergency shutdown procedures, blockage clearing procedures, and suction hazard awareness. Separate operator duties from field workers conducting physical cleaning - designate one person responsible for vacuum equipment operation who remains at truck controls throughout operation, separate from workers positioning hoses and conducting GPT cleaning. Establish communication protocols between field workers and vacuum operator using radios or hand signals allowing coordinated operation without workers approaching running equipment. Conduct pre-start equipment inspection checking hoses for damage, cracks, or wear that could lead to failure, verifying all connections secure and properly seated, testing vacuum relief valve function, confirming safety interlocks and shutoffs operational. Replace damaged or worn hoses immediately - hose failures typically occur at weak points from previous damage. Position vacuum trucks on stable level ground with parking brake applied ensuring vehicle stability during vacuum operation which creates significant vibration and mechanical loads. Establish exclusion zones around operating vacuum equipment preventing unauthorised access particularly by public or non-trained workers. Brief all workers on suction hazards before commencing GPT cleaning emphasising that vacuum equipment presents serious injury hazard distinct from other construction equipment they may be familiar with.