Dear John
Re: Preliminary Contamination Investigation
Lots 2 and 3, Henry Lawson Drive, Milperra, NSW
Attached is the Executive Summary of our report (Ref: 99623151-07, dated October 1999)
We would request that any material used from this document for any purpose is appropriately referenced as being obtained from the report and that the full report should be made available if further information or clarifications are required.
Yours faithfully
GOLDER ASSOCIATES PTY LTD, Dr Chris Farias, MRACI C Chem Project Manager
This report presents the results of a preliminary contamination investigation carried out by Colder Associates on a site located at Lots 2 and 3 (DP 576251), Henry Lawson Drive, Milperra NSW, Lot 2 has an area of about 2.9 hectares and Lot 3 an area of about 0.97 hectares.
The purpose of this investigation was to provide Co-Bolt Constructions Pty Ltd with a broad-based indication of the presence of ground contamination in the context of the proposed use of the site for residential purposes. The issues identified are aimed at providing a basis for further discussion with Council and to assist with evaluating the feasibility of developing the site for its proposed use.
The work Consisted of a review of site information, a soil vapour survey, a limited sampling and analysis program and an assessment of the results. The results of laboratory analysis were interpreted by comparison with investigation levels recommended by the NSW EPA.
The results indicate that the site was filled in the early 1970s. The fill was placed over an area of about 3 hectares and appears to have been uncontrolled . Other subsequent activities on the site include a nursery and a workshop for repair of semi-trailers.
The results of a soil vapour survey indicated elevated concentrations of methane up to 42 % by volume in the subsurface. This concentration is above the explosive limit of 5% volume. The methane concentrations in conjunction with other data indicate the presence of decomposing putrescible waste over a majority of the site.
Based on the testpits excavated, the sub-surface conditions on the site generally consisted of:
Capping material with an average depth of about 1 m;
A Soil / Waste mixture with an average depth of about 0.5 m:
A Waste Layer with an average depth of about 3 m. The layer contained putrescible waste and other material including timber, paper. metal, plastic and glass;
A soil layer with an average depth of about 0.2 m immediately underlying the Waste Layer. This layer was discoloured and had an odour. Below this layer there was residual soil without any odour or discolouration.
Sampling was carried out in all layers except the Waste Layer as the majority of the waste in this layer was putrescible with little to no soil observed. Also. based on discussion with the NSW EPA and Landfill operators, acceptance of this waste at a landfill would normally be characterised by visual and odour observations, not chemical analysis. In addition, sampling of the Soil beneath the Waste Layer was expected to provide information on contamination which could have potentially migrated downwards from The Waste Layer.
The result Of laboratory analysis indicated that the concentrations of contaminants in some samples exceeded the NSW EPA recommended health and environmental investigation levels for residential use of the site. In addition the environmental investigation levels (ANZECC B) were also exceeded at further locations. Contamination was identified both in the fill above the waste layer and in the immediately underlying soil layer. There are indications that parts of The Waste Layer may be also be chemically contaminated based on:
The contamination identified in the soil / waste mixture above the Waste Layer and that in the soil below the Waste Layer;
The heterogeneous nature of the waste encountered; and
Information which suggests that the type of fill placed was uncontrolled;
An earlier investigation report by others which was reviewed as part of the present work indicated that the leachate from the waste was impacting on the surface water and groundwater. Depending upon the strategy for development of the site further investigation of these issues will be required
In the context of the proposed development of the site, the two remediation options that can be considered are:
Excavation and off-site disposal of contaminated soil;
On-site containment and management;
Excavation and off-Site disposal of the fill will involve excavation of the discrete layers of the fill followed by and assessment of the soils that can be retained on the site and materials required to be disposed off- site to a landfill. This option for remediation is considered likely to be the most expensive with the major cost being for the excavation and disposal of the existing fill, import of clean fill, project management of the remediation and implementation of the measures to control other environmental impacts.
Since the sources of contamination will he removed, this approach will minimise risks related to environmental issues such as landfill gases and leachate formation. However, there will still be the issue of groundwater contamination to be resolved and will require further investigation.
The implementation of this option will require:
A detailed investigation of the excavated material in terms of the types, quantities and disposal requirements for the materials identified.
Assessment of disposal options for the wastes. The issue of disposal of industrial or hazardous wastes, if present, can he particularly complicated as there are currently no landfills approved by the NSW EPA to accept industrial or hazardous wastes. Hence the waste may need to be immobilised prior to obtaining approval for disposal. Further some chemical wastes governed by chemical control orders such as PCBs may have particularly stringent requirement for handling, storage and disposal;
Validation of fill imported on to the site to ensure that it meets with the criteria with respect to concentrations of contaminants;
Consideration of environmental management issues;
Approximate volumes of fill are as follows:
Capping Layer: 30,000 m3
Soil / Waste mixture: 15,000 m3
Waste Layer: 90,000 m3
Soil Layer (discoloured) 6,000 m3
However, it must be stressed that the volumes presented above are only indicative estimates based on the limited investigation Carried out. Significant variations may be encountered due to unexpected conditions related to the type and volume of wastes. The likelihood of these significant variations should be considered before the implementation of any remediation strategy for the site.
According to verbal information front the NSW EPA and landfill operators, we understand the waste could be classified as putrescible waste mixed with inert or solid waste and can potentially be disposed of to a landfill licensed to accept Class 1Solid Waste. The ability and cost to dispose of the waste off-site is a significant issue. Confirmation that this approach is acceptable and that the waste can be disposed off-site should be obtained prior to finalisation of any remediation strategy. Further, there may be areas of potential or obvious contamination with chemical or other wastes including in areas where the overlying' soil / waste mixture was identified as being contaminated. When encountered this material should be managed in accordance with NSW EPA requirements.
An alternative remediation strategy of containment of the contamination could be considered. In this case, in addition to approval by NSW EPA, Council and other authorities, the following major issues will need to be considered;
Construction of a very low permeability barrier such as a concrete slab or a clay capping over the majority of the site;
Extensive landfill gas control and on-going monitoring
A cut-off trench around the perimeter of the site to prevent groundwater from entering and leaving the site with on-going monitoring of surface water and groundwater;
Preparation and review of an on-going management plan for any subsurface work carried out on the site.
Either of the above options for remediation will require an environmental management plan to be implemented during the remediation. This will include but not be limited to:
Community consultation;
Control of air emissions, including methane;
Groundwater control, treatment and disposal during excavation;
Control of surface water run-off;
Dust and odour control;
Subject to NSW EPA and Council approval, the development of the site for low-density residential use would most likely require the excavation and disposal option. The containment and management option of remediation may be able to be considered for development of the site' for medium to high density residential or industrial. However all the issues related to minimising the risk to human health and the environment discussed will need to be considered and approved by NSW EPA and Council prior to implementation.
For any proposed development the Council may require a NSW EPA Auditor for contaminated land to be involved in the selection of a remediation strategy and to eventually sign-off on the site.
Golder Associates