Disposal of Overburden from Development Sites as Cleanfill Peter Nelson and Steven Brattle GHD Ltd., PO Box 6543, Wellesley St, Auckland Email: [email protected], DDI (09) 368 6248

Abstract The Auckland region is seeing increasing redevelopment of both urban and rural land. These projects often produce overburden (surplus soils) with low contaminant concentrations. Disposal of these soils has posed some issues. The Permitted Activity rules of the Auckland Regional Plan allow soils with low level contamination to remain on site but do not allow their use as cleanfill, thus adding significant cost to disposal. The applicable rules in the neighbouring Waikato region differ, and can allow soils designated as unacceptable in the Auckland region to be used as cleanfill. This presentation gives an analysis of key issues relating to the disposal/reuse, of overburden from two relatively modest projects in the Auckland region. The first project was the redevelopment of 4 hectares of market garden land for residential purposes. This resulted in the disposal of 2000 m3 of surplus topsoil that met the council’s residential land criteria but failed cleanfill criteria. The cost of landfill disposal was $130,000. The second project was the redevelopment of industrial/commercial land as a car park. 2000 m3 of soil was imported onto the site from another development site for use as fill. Although meeting the commercial/industrial soil criteria, the fill did not meet the Permitted Activity Criteria of the PARP:ALW for cleanfill. The contractor was required to obtain authorisation for any discharge of contaminants (other than sediment) under section 15 of the Resource Management Act 1991, or remove noncleanfill material from the site.

1.

Introduction

Over the next 50 years the Auckland region’s population is expected to almost double. As an example, the population of the southern sector of the Auckland region is expected to grow by more than 275,000 (an average of 5,500 people per year). Urban and rural capacity is being increased by intensified land development within the existing urban area and new development within greenfield sites. Regional councils use soil contaminant concentrations (environmental guideline values or soil acceptance criteria) specified in regional rules to establish the level of management required in land redevelopment. Past land use, including horticultural land use, has required developers to develop management protocols acceptable under these rules.

1

Where residual levels of contaminants fail to meet land use criteria defined in these rules, remediation may be required. The lowest cost to achieve a site condition that is protective of human health and the environment has usually been achieved by disposing contaminated material offsite. Where low level contamination occurs, it is possible that the land use criteria of the regional rules are not exceeded. For example, soils containing 0.7 mg/kg total DDT are acceptable for residential land use and 12 mg/kg total DDT are acceptable for industrial/commercial land use in the Auckland region. Where these land use contaminant levels are above the natural soil background levels soils surplus soils must be disposed of at a consented landfill consented. They cannot be used as topsoil at sites requiring topsoils or disposed of as cleanfill. This situation can add significant costs to land development.

2.

Contaminated Soil

2.1

Definitions

The Ministry for the Environment Cleanfill Guideline1 defines contaminated soils as: ... all soils with contaminant concentrations greater than natural background levels at the cleanfill site. These guideline also states that the detection of TPH, SVOCs, VOCs and PAHs would preclude the material from disposal at a cleanfill. The RMA Amendment Act 2005 defines contaminated land as follows: ``contaminated land'' means land of 1 of the following kinds: (a) if there is an applicable national environmental standard on contaminants in soil, the land is more contaminated than the standard allows; or (b) if there is no applicable national environmental standard on contaminants in soil, the land has a hazardous substance in or on it that— (i) has significant adverse effects on the environment; or (ii) is reasonably likely to have significant adverse effects on the environment The Cleanfill Guideline definition is prescriptive and the RMA definition allows assessment. 2.2 Regional Rules The proposed Auckland Regional Plan was notified in 2001 and became operative, subject to appeals, in June 20052. It pre-dates the definition of contaminated land in the RMA Amendment Act 2005. This plan prescribes soil acceptance criteria for contaminated land. These are based on the greater of 1. local background levels; 2. acceptance criteria specified in Guidelines for Assessing and Managing Petroleum Hydrocarbon Contaminated Sites in New Zealand’, MfE 1999;

2

3. acceptance criteria specified in the ‘Health and Environmental Guidelines for Selected Timber Treatment Chemicals’ (MfE, June 1997); or 4. soil quality guidelines specified in the ‘Canadian Environmental Quality Guidelines’, (Canadian Council of Ministers of the Environment, CCME 1999, including updates 2001 and 2002) The soil acceptance criteria for total DDT (ΣDDT) and polycyclic aromatic hydrocarbons, expressed as benzo[a]pyrene (BaP) equivalents, for residential and industrial land uses are given in Table 1. Table 1

Soil acceptance criteria of ΣDDT and BaP equivalents in soil (mg/kg dry weight), ARC PARP:ALW Rules 5.5.40 and 5.5.41 ΣDDT

BaP eq

Background - range3 Tier 1 soil acceptance criteria Commercial/industrial use All pathways4

11

Canadian Environmental Quality Guidelines (CCME, 2002) - Residential5

0.7

Canadian Environmental Quality Guidelines (CCME, 2002) - Industrial

12

The Auckland Regional Council (ARC) specify the Cleanfill Guideline definition of contaminated soil and does not allow soils with detectable TPH, SVOCs, VOCs and PAHs to be classified as cleanfill, thus soils that meet the land use soil criteria given in Table 1 may not be acceptable as cleanfill.. The Proposed Waikato Regional Plan as amended by decisions and the Environment Court was updated to August 20056. This plan does not prescribe soil acceptance criteria for contaminated land, but rules reserve the council’s control over the methods of assessment, specifically in terms of: water quality protection guidelines; background soil concentrations; soil acceptance criteria; guidelines recognised by Environment Waikato; acceptable international standards; and leachability tests to demonstrate the mobility of contaminants present. The Environment Waikato (EW) rules allow more flexibility than those applied by the ARC. In the Waikato region, DDT commonly occurs in pastoral soils. EW has estimated (in-house) the average and median concentrations of ΣDDT in 221 Waikato soil samples analysed in 2002 as 0.68 mg/kg and 0.32 mg/kg. From these results, EW concluded DDT is a common broad-scale

3

contaminant similar to lead. The lowest applicable guideline normally applied by EW for ΣDDT in urban residential soils is the Canadian CCME 0.7 mg/kg and the next guideline currently applied to ΣDDT (for protection of human health) is 7.9 mg/kg. On this basis, and with respect to the RMA Amendment Act (2005) definition of contaminated land, EW do not regard soils with less than 0.7 mg/kg total ΣDDT as being contaminated with DDT in relation to their regional plan definition of cleanfill. In other words, soils with less than 0.7 mg/kg ΣDDT would meet the EW definition of cleanfill7. 2.3

Organochlorine Programme

The Organochlorine Programme, undertaken by the Ministry for the Environment, reported ambient concentrations of DDT in non agricultural soils8. The DDT concentrations reported by the MfE for are summarised in Table 2. Table 2

Range of Ambient Concentrations of DDT (mg/kg) in New Zealand Soils

Forests

0.0001-0.006

Indigenous grassland

0.0006-0.004

Provincial centres

0.001-0.24

Auckland

0.002-0.07

Christchurch

0.21-0.86

2.4 Disposal Costs Excavation of contaminated material and disposal off site has been widely adopted as offering the lowest cost method of remediation. However, the costs for disposal have increased and are continuing to increase. Factors in this are: Stricter standards for landfill acceptance have increased costs in the design and operation of landfills, Available landfill space is restricted Landfills are now remote from the major urban centres, resulting in higher transportation costs. Full cost recovery means high costs for landfilling low level contaminated topsoils from development sites. Proposed levies on waste acceptance will impact on contaminated land remediation. An associated non-financial consideration is the management of impacts associated with large scale offsite transport of contaminated soil, where truck movements must take place through surrounding residential areas.

4

3.

Case Study: Horticultural Soils and DDT

This project involved the development of a 4 hectare plot of former market garden land for residential purposes in Pukekohe. The land had an 80 year history of market garden use that triggered the need for a contaminated site investigation to support consent applications for the proposed site development. In two sampling events, low level DDT contamination in topsoils was found across the site. The first sampling collected 3 representative samples, each consisting of 10 core samples to depth of 200 mm. These core samples were composited for analysis. The second sampling event collected a single sample at the centre of the initial representative sampling areas at 300 mm and 600 mm to obtain a depth profile of the contaminant concentration. The results obtained are summarised in Table 3. Table 3

ΣDDT concentration (mg/kg) in soil before earthworks

Event

Depth (mm)

A

B

C

1

0-200

1.41

1.26

1.01

300

1.7

1.37

0.09

600

0.04