Minimum design requirements for the protection of waters
Section 4, Issue 5 of these guidelines contains design requirements for protection of waters. The design requirements described in this section are the minimum requirements that must be met when occupiers are developing and selecting cost-effective techniques suitable and appropriate to satisfy the environmental objective for the protection of waters. They are not 'one size fits all' requirements. Because of the nature of the facility or its location, the proponent may identify the need for a more rigorous design, or the EPA or the local planning authority may determine that more stringent requirements need to be imposed.
Working surfaces
Goal
To ensure storage areas, active composting surfaces, and associated access roads are constructed to prevent the pollution by leachate of subsoil, groundwater and surface water bodies and to allow all-weather vehicular access to any part of the processing site that needs to be reached by vehicles
Minimum design requirement
The working surfaces, including the incoming organics, final product, process residuals and contaminated material storage areas, the active composting pad (for windrow composting) and access roads, must:
- be bunded and graded sufficiently to prevent both run-on and run-off of surface water
- be designed and constructed from an inert low-permeability material such as compacted clay, modified soil, asphalt or concrete over a compacted base able to support, without sustained damage, the load of material on it and the load of any machinery used in the composting facility
- be able to support all structures, machinery and vehicles as applicable and allow access to any utilised part of the processing site, irrespective of the weather conditions; vehicles may include:
- transport vehicles used for the delivery of organics and the transport of finished products
- mobile equipment used in all phases of all the processes operated on the site
- fire-fighting vehicles and equipment.
Leachate barrier system
Goal
To prevent the pollution by leachate of subsoil, groundwater and surface water bodies over the period of time that raw organics or products remain on the premises, beyond the closure of the facility, and until the premises has ceased to pose potential environmental threats
Minimum design requirement
The material processing or storage areas of the facility must have a leachate barrier system that forms a secure barrier between the groundwater, soil and substrata and the composting or stored organics. Acceptable leachate barriers include:
- a clay or modified soil liner consisting of at least 600 mm of recompacted clay with an in-situ permeability (K) of less than 10-7 ms-1. Such liners should be placed in successive layers up to 300 mm uncompacted thickness. Each underlying layer should be scoured to prevent excessive permeability due to the lamination.
- a natural geological barrier that is proven by competent geotechnical investigations to provide a secure barrier between the groundwater, soil and substrata and the composting organics, equivalent to the 600-mm recompacted clay above
- a concrete or asphalt cement pad of a thickness of at least 100 mm, designed to withstand the loads from all machines, vehicles and equipment that are required to operate the facility.
The basis of the design adopted for the leachate barrier system must be documented in the water management plan.
Leachate collection system
Goal
To ensure that leachate is collected efficiently at the composting and related processing facility for further management, thereby avoiding water pollution and/or odour problems
Minimum design requirement
The leachate collection system must include:
- conduction of all feedstock storage, active composting and mature compost storage on a specially prepared low-permeability pad (see 'Working surfaces' and 'Leachate barrier system' in this section)
- installation of a drainage layer underneath the processing area to provide adequate leachate drainage from composting organics. This may consist of a bed of coarse material such as wood chips, or alternatively the processing platform may permanently incorporate a drainage layer designed to withstand the loading, working and removal of compost.
- for small-scale facilities or facilities in drier areas, incorporation of an absorbent material in compost and at the base of the pile
- design and maintenance of the slope and orientation of windrows and/or leachate drains such that free drainage of leachate to a collection drain is permitted and ponding of leachate is avoided
- shaping of the piles and windrows to maximise run-off and hence reduce infiltration
- enclosing of leachate drains to reduce the emission of odours.
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Leachate storage system
Goal
To ensure that leachate is stored efficiently at the composting and related processing facility for further management, thereby avoiding water pollution and/or odour problems
Minimum design requirement
The design of the leachate storage system must at least comply with the following requirements:
- Leachate must be collected and stored in either a dam that is lined (see below for acceptable characteristics) or in above-ground storage tanks.
- Above-ground storage tanks must be surrounded by a bund with a capacity of 110% or greater than that of the tanks within the bund. (Note: Above-ground tanks are the preferred option for leachate storage.)
- Leachate dams or tanks must have monitoring equipment installed (such as high-level alarms that are interlocked to the discharge pump or line), or the occupier must implement management practices to ensure that they cannot be overfilled
- If the leachate dam or tanks are open at the top, they must be capable of at least accepting the run-off or leachate generated by any 1-in-10-year, 24-hour-period storm event without overflowing.
Acceptable characteristics of a suitable leachate-dam liner include:
- There should be a clay or modified soil liner consisting of at least 900 mm of recompacted clay with an in-situ permeability (K) of less than 10-9 ms-1. Successive layers should be of compatible material, and each underlying layer should be scoured to prevent excessive permeability due to the lamination. The sides should generally have a slope not exceeding a gradient of one vertical to three horizontal, in order to allow suitable compaction of the barrier and to facilitate subsequent testing.
- If the leachate dam is located in an area of poor hydrological conditions or otherwise poses a significant potential threat to surface or groundwaters, the clay or modified soil liner should be overlaid with a flexible membrane liner (FML) of permeability (K) for water of less than 10-14 ms-1. The FML should have material properties that ensure it can maintain this permeability for a period at least equivalent to the desired working life of the leachate dam. The FML should have a minimum thickness of 1.5 mm and should be laid according to the procedures outlined in an approved construction quality assurance program. All joins and repairs should be fully tested to ensure that the liner's integrity is not breached at these locations, and the FML should be protected against load-induced damage.
Surface water controls
Goal
To avoid the generation of excessive leachate and to prevent any sediment or pollutants from being carried off the premises
Minimum design requirement
The surface water controls must at least meet the following requirements:
- The facility must be designed to prevent surface water from mixing with the organics received and processed at the premises and the final products, process residuals and contaminated materials stored at the premises.
- All water that has entered processing and storage areas and water that has been contaminated by leachate must be handled and treated in the same manner as leachate.
- All surface water that has been collected from areas such as cleared or non-vegetated surfaces must be treated in accordance with Managing Urban Stormwater: Soils and Construction (Landcom, 2004). For large, exposed facilities the facility planner/site occupier should contact the EPA regarding the application of the Landcom guideline to their particular facility.
- Exposed areas at the composting and related organics processing facility site must be minimised. The occupier must not clear more than the minimum area needed.
- The facility should be designed to contain one or more catch basins capable of collecting all surface water generated from the design of a 1-in-10 year, 24-hour-period storm event without overflowing.
- It should be designed such that any surface water that has come in contact with the processing and/or storage area and/or that has been contaminated by leachate must be handled in the same manner as leachate.
Note: For sites where discharges of surface water to surface water bodies such as rivers, creeks and dams cannot be avoided, stringent quality and discharge conditions will be attached to the environment protection licence. Where such licensed discharges occur, discharge limits on the environment protection licence will be negotiated on a site-by-site basis. These negotiations will take into account the nature of the waste water, the available treatment options, and the available ambient water quality and flow objectives, such as the Water Quality and River Flow Interim Environmental Objectives for that catchment. (Copies of the Water Quality and River Flow Interim Environmental Objectives for each catchment can be obtained by calling the EPA's Environment Line on 131 555.)
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Groundwater and subsoil monitoring network
Goal
To provide an effective system for monitoring the characteristics of groundwater and/or subsoil at various parts of the premises and to rapidly detect any pollution of groundwater and/or subsoil
Minimum design requirement
The minimum requirements for establishing an effective groundwater and subsoil monitoring network are as follows:
- There should be one monitoring bore per aquifer, located down the hydraulic gradient from the processing area. Note: It is advisable, however, to also locate one monitoring bore per aquifer up the hydraulic gradient from the processing area so that you can establish whether any change in water quality detected down-gradient has been caused during the passage of the water under the processing area.
- When it is not possible to locate hydraulically up-gradient bores, a sufficient number of samples must be taken at compliance-point bores before composting and related organics processing activities start, in order to characterise the background characteristics of the groundwater.
- If only one thin (less than 5-m thick) aquifer is identified on site, then single, fully slotted bores are sufficiently reliable indicator bores for pollutants.
- If multiple aquifers are identified on site, or an aquifer of a thickness greater than 5 m is identified, the monitoring bores should be:
- a nest of bores, slotted over different intervals, or
- a multi-port bore, or
- an appropriate combination of both.
- When there is no evidence of groundwater, the groundwater monitoring and subsoil monitoring network must include the installation of suction lysimeters to extract pore water and monitor the vadose zone beneath the composting and related organics processing facility and at suitable locations surrounding the facility. This procedure will indicate the presence of leachate in the subsoil and allow its analysis.
- Monitoring wells should have a minimum internal diameter of 50 mm; have sampling ports of suitable strength, with slotted sections; and be gravel packed and have cement/bentonite seals between the sections. The occupier must ensure that the porous media surrounding the monitoring bores and the lysimeter cup are composed of material that does not affect the accuracy of the sample.
- The standpipe of the monitoring bores must be adequately sealed near ground level with cement-based grout and a security cover must cover the top of the standpipe; additionally, the standpipe must be constructed in such a way to prevent the ingress of surface water and to prevent extraneous material (such as insects) from getting into the well.
- For installation and bore maintenance, the following standard texts may be referenced:
- Handbook: Groundwater. Volume II: Methodology (USEPA 1991)
- Guidelines for Groundwater Monitoring at Municipal Landfill Sites (Hirschberg K-J 1993)
- Minimum Construction Requirements for Water Bores in Australia (ARMCANZ 1997).
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Page last updated: 12 July 2012
