Construction sites, including urban subdivisions, that do not incorporate appropriate erosion and sediment controls can yield high pollutant loads during rainfall events. These loads include both coarse sediment and fine sediment, manifested as elevated levels of turbidity in stormwater runoff. The resulting stormwater runoff can have a significant negative impact on receiving waters. Consequently, it is important that appropriate management practices be implemented on construction sites to minimise adverse impacts on waterways.
This paper outlines the EPA's approach to managing stormwater quality at construction sites under both the existing environmental legislation and the new Protection of the Environment Operations Act 1997. (See also About the POEO Act) It also provides guidance to local councils on appropriate elements of a council's erosion and sediment control policy.
The Protection of the Environment Operations Act (POEO Act) updates and consolidates the key pollution statutes under a single Act. The statutes it replaces include the Clean Waters Act and the Pollution Control Act.
The POEO Act provides a single licensing arrangement to replace the different licences and approvals under existing separate Acts relating to air pollution, water pollution, noise pollution and waste management. The Act aims to more clearly define those activities to be regulated by the EPA and by local councils.
Under the new Act, the EPA will be the environmental regulatory authority (known as the "appropriate regulatory authority" (ARA)) for the activities and industries specified in Schedule 1 of the POEO Act ("scheduled activities"), which must hold an environment protection licence. Separate Pollution Control Approvals will no longer exist.
Local councils will continue to regulate non-scheduled activities, except those undertaken by a public authority which the EPA will regulate, and those activities will include holding a water licence from the EPA. The EPA can issue a licence to regulate water pollution from a non-scheduled activity. If it does, the EPA becomes the regulator for the air, noise, waste and water impacts from the activity instead of the local council.
Factors to be considered by the EPA when deciding if a licence is to be granted include:
- any Protection of the Environment Policies;
- the objectives of the EPA, as specified in the Protection of the Environment Administration Act 1991, including the ecologically sustainable development principles which have been redefined;
- the impact on the environment of any pollution likely to be caused by the activity; and
- any public submission on the proposed activity received under the Environmental Planning and Assessment Act 1979.
Licences can be issued with conditions. Examples of requirements that may be attached to a licence are provided in the POEO Act. These include requirements to monitor, to provide certification of compliance with a licence, to undertake and comply with a mandatory environmental audit program and pollution studies, reduction programs and financial assurances.
Licences are no longer fixed-term annual licences but remain in force until suspended, revoked or surrendered. The EPA must review the licence at least once every three years, and give public notice of its intention to do so.
Background
One of the primary objectives of the EPA (specified in the Protection of the Environment Administration Act 1991) is "to protect, restore and enhance the quality of the environment in NSW, having regard to the need to maintain ecologically sustainable development". The EPA therefore has a strong focus on achieving environmental outcomes within a cost-effective framework.
From the perspective of stormwater quality management from construction sites, the EPA's primary focus is achieving an appropriate environmental outcome for the receiving waters. This focus is not primarily on how the outcome is achieved, but proponents are typically required to satisfy consent authorities that proposed activities will not impair the quality of the receiving waters.
The management of stormwater quality from construction sites is complicated by a number of factors, including:
- the inherent uncertainty in quantifying and predicting the anticipated degree of erosion, which is determined by both site characteristics and management activities;
- the difficulty in quantifying the likely effectiveness of soil stabilisation and sediment control measures in controlling pollution. A performance-based approach to design can generally only be adopted in relation to sediment basins, which are typically the final treatment measure prior to discharge from medium to large construction sites. It is not possible to confidently state the exact performance of "source controls" (eg silt fences) which may be employed at construction sites;
- the fact that erosion and sediment controls, such as sediment basins, can be expected to perform efficiently only up to a particular "design" storm event;
- the dynamic nature of construction sites, which constantly change throughout the development phase of a project. The associated pollution control measures must clearly be altered in response to such progressive changes; and
- erosion and sediment control plans (or soil and water management plans) are commonly prepared by the developer prior to a construction contract being awarded. Therefore the plan may not represent the construction program adopted by the subsequent contractor.
It also needs to be recognised that sediment pollution can also occur from sources other than soil erosion, including:
- concrete waste;
- dewatering of trenches, etc;
- stockpiles of imported materials (eg sand); and
- cutting of bricks, pavers and concrete.
In addition, it is also important that stormwater quality management from construction sites considers pollutants other than sediment (or suspended solids). These pollutants can include:
- nutrients, from fertilisers;
- herbicides and pesticides used in landscaping;
- acids from washing;
- building wastes and litter;
- paint and paint wastes; and
- oils, grease and fuel, from equipment operation and maintenance.
Management practices need to be implemented to address all sources of pollution on a construction site.
These issues have been considered by the EPA in the development of its approach, discussed below.
Current practice
The approach adopted to date of preparing and implementing an erosion and sediment control plan (or soil and water management plan) has generally not been based on achieving a specific environmental outcome, but on promoting a "good practice" approach. As noted previously, the direct linkage between specific management practices and specific environmental outcomes is often difficult to predict. The responsibility for achieving a satisfactory environmental outcome has therefore often been implicitly accepted by the consent authority.
Policy developments
A more "performance-based" approach
Many of the complexities and issues previously noted in relation to the management of stormwater quality from construction sites would clearly be more effectively managed if a more "performance-based" approach was adopted. Such an approach would enable the managers of construction sites to define and implement the most appropriate and cost effective mix of strategies to meet a specified performance outcome, thereby allowing flexibility and encouraging innovation.
Such a performance-based approach would require that the EPA or consent authority nominate the required performance, and allow the contractor/developer to adopt and refine management activities in order to satisfy that requirement. The stated outcome would typically constitute a maximum pollutant concentration (eg, 50 mg/L non-filtrable residues) in a specified rainfall event.
A practicable stormwater quality outcome in relation to construction sites could, in reality, only apply in rainfall conditions up to and including a "design" storm event. In larger storms, elevated pollutant levels would be recognised, although the contractor/developer would still be required to implement all practical measures to minimise stormwater pollution. Given this approach, the enforcement of a performance-based approach would rely on the demonstration, by either the developer or the consent authority, that the design rainfall event had been exceeded.
The risk of prescribed works failing to meet the required outcome would lie with developers, who may revise management actions in light of both such a "system failure" and the changing circumstances typical of construction sites. The onus should clearly lie with the developer to demonstrate either the achievement of the required outcome, or the extenuating circumstances (eg, rainfall data) justifying a failure to meet the outcome.
As identified previously, a performance-based approach can really only be adopted with any confidence in relation to the design and operation of sediment basins, which can only be practicably incorporated into medium and large scale development sites. A further complexity is the different design criteria to be adopted for sediment basins on different soil types (e.g coarse grained soils vs dispersive clay soils).
The new design criteria for sediment basins specified in Managing Urban Stormwater: Soils & Construction have been formulated to provide for a more performance-based approach to stormwater management at construction sites. Different criteria have been developed depending on the catchment's soil characteristics, and are described in Table 1.
Table 1 – Sediment basin design criteria Type C (coarse grained soils) |
Treatment process | Rapid settling |
Design principle | Settling of a design particle in the peak flow expected from a design storm |
Recommended design criterion | Settling a 0.02 mm particle in 25% of the peak flow from the 1 year ARI, time of concentration storm event |
Type F (fine grained soils) |
Treatment process | Slow settling |
Design principle | Containment of all runoff expected from a 5-day rainfall event with specified probability of exceedance |
Recommended design criterion | Containment of all runoff from the 75th percentile, 5-day rainfall event |
Type D (fine grained, dispersible soils) |
Treatment process | Flocculation and slow settling |
Design principle | Containment of all runoff expected from a 5-day rainfall event with specified probability of exceedance |
Recommended design criterion | Containment of all runoff from the 75th percentile, 5-day rainfall event |
These criteria specify the settling zone capacity considered necessary to achieve a maximum suspended solids discharge concentration of 50 mg/L for events with a magnitude smaller than the nominated design storm. A sediment storage zone capacity should also be provided, as described in the Soils & Construction document.
Each of the new sediment basin design criteria allows for the adoption of more stringent or lenient requirements in response to local conditions.
These criteria can be adopted as the sediment management performance objective for an erosion and sediment control plan (or soil and water management plan). It is, however, important that other objectives be established for pollutants other than sediment. A qualitative objective such as minimising the export of these pollutants to the maximum extent practicable could be adopted.
The 5-day storm duration for the "Type F" and "Type D" basins (See Table 1) is based on the time generally taken for runoff from a shorter duration storm to be collected in a sediment basin and flocculated to reduce suspended solids concentrations. These rainfall depths are provided for sites throughout the NSW in the Soils & Construction document
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"Good practice"
The EPA therefore considers that two approaches to stormwater quality management from construction sites are appropriate:
- continuation of the "good practice" approach; and
- a performance based approach.
A decision on which approach to adopt can be made by the consent authority, in consultation with the contractor/developer. Generally for smaller sites, it is expected that the good practice approach will be adopted. On larger sites where accurate and reliable rainfall data can be collected, a performance-based approach may be adopted.
The "good practice" approach is based predominantly on the implementation of management practices specified in an erosion and sediment control plan (or soil and water management plan). Any enforcement activities would continue to be based largely on the implementation and maintenance of the approved management practices.
Within this context, a definition of "good practice" is noted below.
Good Practice The management of an activity to achieve an ongoing minimisation of the activity's environmental harm through cost-effective measures assessed against the measures currently used nationally and internationally for the activity. These measures include an appropriate mix of management practices, programs, processes, siting criteria, operating methods, measures or devices that are compatible with the characteristics of the site and the activity. |
The document Managing Urban Stormwater: Soils & Construction contains a range of management measures or practices (termed "Best Management Practices" or BMPs) which, when appropriately selected, designed and implemented, are compatible with this "good practice" approach. Conversely, an inappropriately selected BMP does not constitute "good practice", even if designed, installed and maintained in accordance with this document. Clearly, development activities must be responsibly managed and practices competently chosen in response to site opportunities and constraints.
"Good practice" also involves managing stormwater quality as close to the source as practical, rather than relying solely on a downstream control such as a sediment basin. These source controls include minimising disturbed areas, prompt stabilisation / revegetation and the employment of sediment filters (eg, sediment fences) close to disturbed areas. This "treatment train" approach is described in more detail in the Soils and Construction document.
This is consistent with the concept of "cleaner production", which aims at the design of processes from the outset to minimise pollution and the creation of waste, rather than relying on "end-of-pipe" measures to reduce the problem.
It is important to note that "good practice" extends beyond the preparation of an erosion and sediment control plan (or soil and water management plan). It is equally important that the plan be appropriately implemented and monitored, and the monitoring results be used to improve implementation or revise the plan if required. This cycle of continuous improvement (effectively an environmental management system) is illustrated in Figure 1.
Effective implementation of a plan can be heavily dependent on the skills of staff on a construction site. It is therefore important that appropriate staff training is undertaken.
Figure 1 – Continuous improvement in stormwater quality management 
Enforcement
The EPA's Prosecution Guidelines recognise that the EPA has considerable discretion in the way in which it deals with breaches of environmental laws, including the offence of pollution of waters. Each case will be assessed on its merits, to ensure that the best strategy to achieve the desired environmental outcome is selected. In some cases this may be prosecution, in other cases it may be different strategies such as issuing notices, requiring cleanup etc.
The Prosecution Guidelines specify factors which are to be taken into account in deciding whether to bring a prosecution, including:
- the seriousness or, conversely, the triviality of the alleged offence or that it is of a "technical" nature only;
- the harm or potential harm to the environment caused by the offence;
- any mitigating or aggravating circumstances;
- the degree of culpability of the alleged offender in relation to the offence;
- the availability and efficacy of any alternatives to prosecution; and
- whether the breach is a continuing or second offence.
In determining its course of action, the EPA will take into account, along with other matters, the nature of any compliance programs in existence. This is not to say that the EPA will not prosecute where compliance programs are in place: simply that this is a factor which will be considered along with others.
The EPA encourages local councils to adopt these factors in relation to activities over which they exercise prosecution powers, including non-scheduled activities under the POEO Act.
The EPA recognises that a viable enforcement policy is necessary. The EPA also is committed to encouraging preventative policies.
Stormwater management will be addressed by councils through planning approvals and the notice powers and enforcement provisions of the POEO Act. For those activities caught up by the Integrated Development Approvals process where the EPA may be issuing an environment protection licence, the EPA will be required to prescribe its requirements in relation to erosion and sediment control earlier in the determination process.
The most effective way to control stormwater pollution really comes through the planning and approval processes. The EPA therefore encourages councils to enhance their role in managing stormwater quality from construction sites. Councils are encouraged to develop and erosion and sediment control policy for their local government area, or a joint policy could be developed on a regional basis. The policy can include:
- policy objectives;
- commitment by council to ensure that erosion and sediment controls are developed and implemented on all construction sites, based on approved erosion and sediment control plans (or soil and water management plans); and
- council commitment to monitor and enforce the implementation of these controls.
The development, implementation and periodic review of such a policy may constitute an element of Council's Implementation Strategy of the stormwater management plans, prepared in accordance with Direction issued by the EPA under Section 12 of the Protection of the Environment Administration Act 1991. These stormwater management plans are required to establish objectives for stormwater quality management of new developments.
Further guidance on the preparation of an appropriate policy for stormwater quality management from construction sites can be obtained from the Department of Land and Water Conservation and the EPA.
The EPA recognises that appropriate stormwater quality management from construction activities is an important component of improving the health of our waterways. The EPA is committed to working with local councils, the development and construction industries to ensure that appropriate management practices are implemented on construction sites.
Managing Urban Stormwater: Soils & Construction is a whole-of-Government document that contains a suite of techniques which will, when appropriately selected, designed and implemented, provide an appropriate basis for effectively managing stormwater quality from construction sites.
1 Based on a paper presented at the Stormwater Industry Association's "Managing Urban Stormwater: Soils and Construction Workshop", Concord, 27 August 1998.
