TIROHIA LANDFILL RISK ASSESSMENT

Transcription

1 TIROHIA LANDFILL RISK ASSESSMENT Miljenko Pavlinic, Waste Services Manager, Eric Souchon, General Manager HG Leach & Company Ltd. Ph , Fax , 1 Introduction H G Leach & Company Ltd is a family business specialising in quarrying, civil engineering contracting and waste disposal. The Tirohia Quarry is owned an operated by H G Leach & Company Ltd who has run the operation continuously for about 49 years, since Prior to that the quarry was operated continuously and owned by the Sumner family since the early 1930 s. As a part of the quarry rehabilitation plan, the Company is developing a modern landfill within the exhausted portion of the quarry. The Company lodged its resource consents applications in March 1998, and the consents were granted later that year. The grant of consent was appealed, but in late January 2001 the Environment Court upheld the grant of consent, with the final consent conditions being released by the Court on 28 th April Immediately following the Court decision, the Company commenced the landfill construction. The target opening date is the 1 October The objective of the paper is to illustrate the risk assessment process that was formally undertaken by H G Leach & Company Ltd, prior to the commencement of landfill construction. 2 Site The following short description of the site is aimed at enabling the reader to understand the rationale of the various assumptions that formed the basis of the risk assessment. The quarry is situated in the head of a valley in the foothills of the Kaimai Ranges, 7 km south of Paeroa. Andesite rock is quarried to generate a wide range of grades of aggregate for commercial use. Quarrying over the past 50 years resulted in the formation of the narrow valley, opening to the north. The remnant ridge forms the barrier between the quarry and the terrace flats and Hauraki Plains to the west. The geology of the area comprises Late Miocene and Pliocene volcanic deposits. The Hauraki Plains to the west are underlain by Quaternary age; volcanic- derived fluvial sediments, peat and primary volcanic deposits (pyroclaastic flows and air fall ash). The floor of the quarry is underlain by breccia dome (1). There are no known faults located in or adjacent to the quarry. The surface drainage of the wider area is via entrenched, steep-sided, ephemeral streams that flow to the north and south around the Tirohia Quarry. The streams have steep

2 gradients and include waterfalls. Owhakatina Stream with its tributaries drains the areas to the western, northern and eastern sides of the Tirohia Quarry. The Owhakatina Stream is a tributary of the Waihou River, which discharges to the Hauraki Gulf, close to Thames. Regional groundwater flow is from the Coromandel Kaimai range westward to the Hauraki Plains, the latter being a major groundwater discharge zone characterised by swamps and peat growth. The principal groundwater system underplays the quarry at depth (approximately 60 m underlying the quarry floor), and flows in a north/northwesterly direction. (1) The hydraulic conductivity measured with falling head field tests is as follows: breccia 1*10-6 m/s to 8*10-10 m/s average being 1*10-7 m/s, andesite 2*10-8 m/s to 8*10-10 m/s Arguably with 60 m above the groundwater and the estimated average conductivity 1*10-7 m/s it would be reasonable to develop the landfill without any engineered liner but only with well designed leachate drainage and collection system. However because of the trend driven by consultants, regulatory authorities, various professional submitters to the resource consents applications, the Company was granted the resource consents specifying an engineered composite liner (being 600 mm of clay k<1*10-9 m/s and 1.5 mm HDPE liner) and a quite substantial groundwater monitoring programme. More detailed description of the Tirohia Landfill concept design can be found in the paper presented by D. Kimpton & E. Souchon. 3 Risk Assessment 3.1 Methodology The Company decided to undertake a risk assessment of the landfill development, operation and post closure prior to the construction commencement. The assessment did not include assessments of commercial risks, loss of control of the waste stream or possible future legislation that may jeopardise the viability of the investment. Those risks had been previously assessed, and formed part of the commercial decision to apply for consent in the first instance. The landfill development, operations and post closure care comprise of many activities and events that may eventually go wrong and pose a financial, environmental and health and safety risk. Risk is defined as follows (2,3): RISK = PROBABILITY * CONSEQUENCES The process of risk assessment followed the steps below: Event identification Assessment or calculation of the probability of the event Evaluation of the consequence of the event Establishment of a risk hierarchy The main challenge was to establish a process that would result in consistent and comparable values so that a risk hierarchy could be developed. Widely adopted practice in risk assessment is to mark the probability and consequences in relative marks such as high, low, etc. Such an approach may result in useful conclusions if a range of events is

3 narrowed to one particular activity. In the case of a specific task the result would be too subjective and misleading. 3.2 Risk Identification The first step of the process was the identification of the events associated with the development, operation and closure of the Tirohia Landfill. The identified risks have been grouped as follows: Leachate Related Risks o Leachate pipe through the bund failure - surface water contamination o Leachate pond overflow - surface water contamination o Leachate pond liner failure - surface water contamination o Leachate spill in transport and pumping- surface water contamination o Leachate leak through the bund - surface water contamination o Leachate leak to the unconfined area within the landfill - surface water contamination o Leachate breakthrough the liner - surface water contamination o Leachate breakthrough the liner - groundwater contamination o Leachate collection system failure - clogging o Leachate collection system failure - drainage pipe collapse Landfill Gas Related Risks o Landfill gas explosion o Fire High wall stability Related Risks o Falling Debris - damage to plant o Falling Debris - staff injuries o Falling Debris fatality Resource Consent Related Risks o Prosecution under RMA o Abatement notice to stop landfilling and close the landfill Occupational Safety and Health Related Risks o Damage to plant during operation or construction o Injuries during operation or construction o Fatality during operation or construction Other Risks o Hazardous waste dumping o Sabotage

4 3.3 Probability The most challenging task was the evaluation of probability. Although a relative number expresses the probability, it is important to use consistent units as a base for the calculations. The probabilities adopted are shown in Table 1. For example, where an event might be caused by a storm event of say 1 in 100 year storm, the probability used was 0.01 because the system was designed to cope with 1:100 year event. Where the event could be caused by the earthquake, the return period of 2500 years for the MCE (Maximum Credible Earthquake) was used. For accidents and injuries, the probability was calculated using Company health and safety statistics. It still remains unavoidable to assign arbitrary figures were no data was available. The probability of the groundwater contamination caused by the earthquake was arbitrarily reduced to 0.01 as we considered that 60 meters of breccia or rock underneath the liner was unlikely to be so significantly affected by an earthquake, to allow direct flow of leachate to groundwater, without purification, as a result of passing through 60 meters of low permeability strata. For the RMA related risks, it was assumed that an abatement notice or prosecution may only be likely in the case of a major disaster, which is outside the Company s control. Table 1. The adopted probabilities for different events Event Cause Probability Leachate Related Risks leachate pipe through the bound earthquake leachate pond overflow storm event leachate pond liner failure surface water contamination earthquake leachate spill in transport and pumping accident on SH probability leachate leak through the bound earthquake leachate leak to the unconfined area within the landfill once in 5 years Liner failure groundwater contamination Earthquake probability * leachate collection system failure clogging leachate collection system failure pipe collapse Landfill Gas Related Risks Explosion Fire High wall stability risks Minor damage to plant

5 Major damage to plant earthquake injuries minor earthquake injuries permanent disability earthquake Fatality Resource Consent Related Risks prosecution under RMA abatement notice to stop landfilling OSH Related Risks Minor damage to plant- Company statistics Major damage to plant -Company statistics injuries minor- Company statistics injuries permanent disability fatality - every 600 injuries Hazardous waste dumping arbitrary Sabotage arbitrary Impact Table 2 shows the impact of an event that was expressed in monetary value for full recovery in each case. For some cases, such as leachate collection system failure, the operational cost of a new, alternative system was allowed as well. For injuries and fatalities, the Manual figures were used. Table 2. The costs of full recovery for different events Event Cost Description of the assumed cost Leachate Related Risks pipe replacement and disposal of leachate pipe through the bound $24,950 contaminated water leachate pond overflow $4,950 disposal of contaminated water liner repair and disposal of leachate pond liner failure $8,550 contaminated water leachate spill in transport and pumping $2,000 site cleanup and disposal bund repair and disposal of leachate leak through the bound $24,950 contaminated water leachate leak to the unconfined area within the landfill $4,950 disposal of contaminated water groundwater remediation and leak Liner failure $4,622,000 detection and repair leachate collection system failure $5,000 repair $230,480 alternative system and cost of pumping Landfill Gas Related Risks compactor replacement cost + cleanup Explosion $502,000 costs Fire $2,000

6 High wall stability risks minor damage to plant $2,000 major damage to plant $500,000 compactor replacement cost injuries minor $17,000 Manual injuries - permanent disability $230,000 Manual fatality $2,500,000 Manual Resource Consent Related Risks prosecution under RMA $150,000 abatement notice to stop landfilling and close the landfill $1,500,000 bond OSH Related Risks minor damage to plant $2,000 major damage to plant $500,000 compactor replacement cost injuries minor $17,000 Manual injuries - permanent disability $230,000 Manual fatality $2,500,000 Manual hazardous waste dumping $48,400 cost of alternative disposal Sabotage $4,950 disposal of contaminated water 5 Risk Evaluation Results By multiplying the values of probability by the monetary values for the impacts of the events, the value for the risk was obtained. The Figure 1 shows the result of the risk assessment. The values obtained are useful to establish a risk hierarchy list. Although we have not been able to fully avoid subjectivity, it is considered that the process followed gives a good indication of the extent of the risks that are related to landfill construction. From the results it is clear that the highest risks are those associated with accidents and injuries, because of the nature of the operations. These risks are similar to quarry operations or risks in roading construction where heavy plant movement can cause accidents or injuries. The risks specific to the landfill operation (leachate leaks etc) are lower. The results of this assessment have been considered in the preparation of the Landfill Management Plan and the Health & Safety Plan for the landfill construction and operation.

7 Figure 1. Risk Evaluation Results leachate pipe through the bound leachate pond overflow leachate pond liner failure leachate spill in transport and pumping leachate leak through the bound leachate leak to the unconfined area within the landfill liner failure leachate collection system failure explosion fire minor damage to plant-rock falling major damage to plant-rock falling injuries minor-rock falling injuries permanent disability-rock falling fatality-rock falling prosecution under RMA abatement notice to stop landfilling and close the landfill minor damage to plant major damage to plant injuries minor injuries permanent disability fatality Hazardous waste dumping Sabotage Discussion and Conclusions The main conclusion of the risk assessment is that the Company is not exposed to additional risks that may be higher, when compared with the risks of its existing quarrying operations. The results of the exercise gave the Company a different perspective on the entire project. When the outcomes of this assessment are compared with the detailed design of the Tirohia Landfill to meet the requirements of the resource consent conditions, the question arises whether there is any merit to include a formal risk assessment of the site within the Resource Consent Application? It appears that most applicants, in order to accelerate the passage of a resource consent application for proposed sites, design the landfill on a prescriptive approach using a composite FML in conjunction with a 1*10-9 m/s clay liner, and extensive groundwater monitoring programme etc. This prescription is based on the CAE Landfill Guidelines or and the applicants do not fully examine the necessity for this level of control and the implications it has on capital costs, operating costs, control over conditions in the waste and long term environmental liabilities. By following such guidelines, designs fail to consider the significant contribution that natural geological formations can provide in safeguarding of the environment. As a result of the public process of notifying submissions, and hearings, these conditions usually become more prescriptive and add additional costs to the whole project. The beneficiary of the current practices is not necessarily the environment or public but importers of the lining materials, consultancies and laboratories

8 7 References 1. T Davies, J. Underhill, K Wood. Tirohia Landfill Report of Geology and Hydrogeology Worley consultants Limited Auckland March International Infrastructure Management Manual Wellington May The Project Management Institute, Inc. (PMI ), A Guide to the Project Management Body of Knowledge 1996 Edition 4. CAE Landfill Guidelines Christchurch April 2000