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Development Applications involving Dewatering
Applications for development that incorporates disposal of dewatering discharge.
OBJECTIVES:
Where a development is located on land under the City’s jurisdiction and dewatering is required as part of development, then an application for dewatering operations shall be submitted to the City.
The Swan River Trust has advised of the following water quality criteria for dewatering:-
Dewatering can significantly affect the water quality of the river especially when the discharge is from polluted groundwater. The Swan River Trust receives numerous complaints associated with dewatering operations which can cause discolouration and turbidity in the river. Nutrients and toxic chemicals can also enter the waterway in this way. All construction sites requiring dewatering where the discharge enters the river either directly or indirectly require approval from the Swan River Trust prior to discharge commencing. Comprehensive guidelines for dewatering are available from the Swan River Trust.
Discharged waste water shall meet the water quality criteria as set out below. Variance from the water quality criteria must be approved by the Swan River Trust in writing prior to the commencement of dewatering. It is the responsibility of the proponent to ensure that the discharge waters meet the water quality criteria and to take measures to prevent pollution or degradation of the receiving water.
Acceptable Water Quality Criteria Table (taken from SRT/Assessment Support Section/Policy SRT/DE6 – Dewatering)
| Water Quality Indicator | Disposal Criteria for Dewatering Wastewater
|
|
Dissolved Oxygen |
Disposal to water bodies or drains emptying in to the Swan estuary are not to alter the background levels by more than 10% in the receiving environment. |
|
PH |
Not to alter from the background level in the receiving environment by more than 0.5 units, nor fall outside the range of 5-9. |
|
Temperature |
Not to vary more than 20C from background levels of the receiving environment. |
|
Nutrients |
Disposal water is not to exceed Total Phosphorous concentration of 0.1mg/L and Total Nitrogen concentration of 1.0 mg/L, or to cause an algal bloom. |
|
Turbidity |
Disposal to water bodies or drains emptying in to Swan estuary, are not to alter the background levels by more than 105, or cause a visible reduction in colour or light penetration of the receiving environment. |
|
Odours and Colours |
Disposal shall not cause objectionable odours or visible colour changes in the receiving water. |
|
Floatable Matter |
No visible floating oil, grease, scum, litter or other objectionable material shall enter the receiving environment. |
|
Settleable Matter |
The level of settleable matter shall not result in deposits which adversely affect the recreation and ecosystem values of the receiving waters. |
|
Salinity (TDS) |
The level of salinity shall not result in a variance greater than 10% of the background level, in the receiving environment. |
|
Toxins |
The level of toxins shall not change the background levels by more than 10% in the receiving environment, or exceed levels for which there is evidence of lethal or sub-lethal toxic effects or undesirable physiological responses in humans, plants, birds, animals, fish or other aquatic life. |
If groundwater investigations indicate the existing groundwater do not conform to the Australian and New Zealand Guidelines for Fresh and Marine Water Quality [ANZECC and ARMCANZ 2000] water quality criteria, then any extracted ground water must be contained and treated before release into the City’s storm water system.
The City will direct any discharge to cease if any part of the policy is breached.
Please note:
Temporary and permanent ground water discharge
1) If exceptional circumstances exist where ground water discharge can not be contained on site and/or discharged into sewer or installed a re charging bore on site , then direct disposal of ground water to the City’s drainage system may be considered.
2) As part of all dewatering applications a copy of the Construction Management Plan and copies of the SRT and Water & Rivers Commission approval letters will need to be attached.
PROCEDURE DETAILS:
Applications for dewatering must follow the guidelines and fee structure as per the City of Perth Dewatering Applications (which enclose the following SRT guidelines).
Applicant’s responsibility
It is the responsibility of the applicant to ensure that the dewatering discharge does not pollute or degrade the receiving waters.
The City will direct any dewatering discharge to cease if any part of the policy is breached.
Referrals
As part of its consideration of any application, the City may seek advice from any agency or organisation. It is expected that the following authorities / organisations would be consulted:
Department of Water
Department of Environment and Conservation
Local governments abutting the Swan and Canning rivers
Health Department of WA
Water Corporation
Main Roads WA
Related Policies
SRT/EA1 – Conservation, environmental and landscape protection
SRT/EA3 – Floodprone land.
Water and Rivers Commission’s (draft) Water Quality Protection Guidelines No. 17 – Planning and management of project site dewatering (applies to water discharges to surface and groundwaters).
Further Advice
A groundwater extraction licence from the Waters and Rivers Commission may be required for dewatering projects.
Proposals involving the disposal of the dewatering wastewater in a wetland listed under System Six or the Swan Coastal Plains Lakes Environmental Protection Policy 1992, require approval from the Department of Environment and Conservation (DEC).
Proposals involving the disposal of the dewatering wastewater into a stormwater drain, compensation basin or on land owned by other parties require consent from the landowner or relevant authority.
If the dewatering wastewater is found to be contaminated with toxins, then approval from the DEC and Health Department of Western Australia must be sought.
Terminology
Salinity: Dissolved salt concentration
Settleable Solids: Suspended Solids – a measure of (solid) contaminants in the discharge water which are removed by a settling phase in the treatment process.
Suspended Solids: Suspended solids – a measure of (solid) contaminants in discharge water which include settleable solids, and those which are not so easily removed and may cause impacts such as increased colour or reduce visibility in the receiving waters.
Toxins: Include any substances which may be harmful to aquatic flora or fauna, or ecosystems closely associated with the river.
Flocculation: The aggregation of solid particles in a liquid.
Background Level: A level of water quality (measured in a manner and a location specified by the Swan River Trust) in the surface water outside the influence of the dewatering discharge (receiving environment).
Receiving Environment: An area covering 50 metres radius from the point of discharge being the area within the influence of the dewatering discharge.