Contaminated agricultural land

Aim of this document

This document discusses how contaminated agricultural land (CAL) can be identified, assessed and managed.

Introduction

We have a problem. Our modern farming techniques have left residues in the soil from a variety of pesticides and chemicals. These chemicals threaten public health increasingly as urban growth overtakes former agricultural lands.

In New South Wales today there are probably thousands of hectares of land that have been adversely affected by agricultural practices. Take, for example, the potentially hazardous pesticide residues found in former and current banana plantations on the North Coast. Other intensive agricultural industries that might leave contamination include cotton, sugar cane, vegetable gardens, fruit orchards, potatoes, and corn. Although contamination problems are usually most prevalent in rural areas, problems are also expected around urban fringes where there is intensive small cropping.

This document grew from the experiences of officers in the EPA's North Coast Office in managing contaminated former bananalands around Coffs Harbour. Much of the material was taken from the draft Contaminated Agricultural Lands Management Advisory Committee (CALMAC) report.

Identifying CAL

Useful publications

The main document that gives a framework for investigating any contaminated land in this State, including contaminated agricultural land, is the Australian and New Zealand Guidelines for the Assessment and Management of Contaminated Sites, prepared by the Australian and New Zealand Environment and Conservation Council (ANZECC) in 1992.

The Contaminated Sites Section of the EPA has also prepared guidelines for specific issues, such as assessing cattle tick dips and former banana plantations. (The latter is hereafter referred to as the bananalands guidelines.)

The bananalands guidelines give specific advice on assessing former banana plantations to see if they are suitable for urban redevelopment. The bananalands guidelines follow the framework of the ANZECC guidelines, but provide more industry-specific detail on contaminants and sampling densities. The EPA intends eventually to prepare similar guidelines for other contaminating industries.

Principal contaminants

The first step in investigating whether land is likely to be contaminated is to find out what chemicals have been used on the land. This information will usually come from NSW Agriculture and/or local councils. These authorities will know the principal industries and types of agriculture that have operated in the region, what chemicals may have been used, and (in some cases) where the industries and contaminants may be found. Current and past land users should also be interviewed for this information.

Although it is vital to get local information about contaminants, we can make generalisations about some contaminants because we know they persist in the environment and were widely used in this State. These generalisations are discussed below.

Types and applications of pesticides

Two broad divisions of pesticides have been used in agriculture:

inorganic pesticides,for example, arsenical and mercurial compounds
organic pesticides,for example, organochlorines or OCPs (more correctly termed chlorinated hydrocarbons), organophosphates or OPs (more correctly termed phosphate hydrocarbons), carbamates, synthetic pyrethroids, and growth regulators.

As an indication of the variety of chemicals that might be found, there are currently:

93 products registered for use on sugarcane
96 products registered for use on bananalands
157 products registered for use on cotton
223 products registered for use on cereals
40 products registered to control ectoparasites on cattle.

Carbamates, synthetic pyrethroids and growth regulators have little or no residual activity (that is, they are highly biodegradable) and their use in agriculture has been limited in the past largely because of this. While a number of organophosphates have been identified as causing acute but relatively short-lived toxic residue problems, much more extensive problems have been encountered in New South Wales with OCPs and arsenical pesticides; these are discussed below.

Arsenic. Arsenic has unusual and complex environmental chemistry. Oxidation-reduction, ligand exchange, precipitation and adsorption all occur together, so that there are many different arsenical forms.

In New South Wales arsenical compounds have been used at different times as weedicides, termiticides, and general pesticides. In banana plantations, for example, weeds were commonly controlled by first treating with lead arsenate and then with arsenic pentoxide.

Arsenic was mostly replaced by the OCPs in the 1950s and 1960s, but is still in limited use today.

Organochlorine pesticides (OCPs). An enormous range of organochlorine pesticides has been and still is used around the world. Four organochlorine pesticides have been commonly used for agriculture in Australia:

DDT (as total DDT inclusive of its metabolites DDD and DDE)
dieldrin (as dieldrin and as the metabolite of aldrin)
heptachlor (the epoxide metabolite)
endosulfan.

Organochlorines were first introduced as insecticides in horticulture and agriculture during World War II. In the years that followed their use increased rapidly. In New South Wales they have been used extensively in orchards, cottonfields, potatoes, tomatoes and small-cropping, banana and sugar plantations, and livestock dipping baths.

There has been a gradual decrease in the agricultural use of these pesticides since the 1970s. Agricultural use of DDT was banned in 1986 and agricultural use of the cyclodienes (aldrin, dieldrin, heptachlor and chlordane) was restricted in 1987.

Other pesticides. A number of other pesticides (including OPs, carbamates and synthetic pyrethroids) pose significant potential adverse environmental and public health risks. Organophosphates are generally acutely toxic, but only a few - methyl parathion, dimethoate, guthion, chlorpyrifos, diazinon and fenitrothion - have caused concern because of their persistence in the environment. Carbamates, synthetic pyrethroids and growth regulators have little or no residual activity and therefore pose few problems with respect to soil contamination.

Extent of contamination

In New South Wales broad-acre contamination is mainly associated with areas of intensive agriculture and horticulture, such as the North Coast banana plantations, the Namoi/Gwydir cotton growing areas and the Murrumbidgee Irrigation Areas (MIA). The number of cattle dip sites is believed to be about 1700, and sheep dip sites are thought to number more than 60,000. The area of lands used for banana, cotton or other intensive industries that might be contaminated has not been calculated.

It is important to note, though, that small-cropping, local orchards and market gardens are all significant consumers of pesticides and farm chemicals. There are generally fringes of small plantations, orchards and market gardens around all towns and cities. These areas are eventually overtaken by urban growth. Their potential for adverse health and environmental effects should not be ignored.

The EPA has released a discussion paper on orchards and market gardens. The discussion paper recommends a sampling regime to verify that orchards and market garden sites proposed for sensitive land use are not contaminated.

Historical information

After the likely contaminants associated with certain industries have been identified, the next step is to consider whether those industries have operated in the subject area. This can be answered by reviewing the historical information.

Historical information may be gleaned from a variety of sources, including:

air and ground photos, available from local councils, the Department of Land and Water Conservation (DLWC), or historical societies
local and State-produced maps
local and State government agency files
local knowledge (preferably presented in the form of statutory declarations)
trade journals and yearbooks
local literature and historical society information
information from support industries, such as fertiliser and pesticide suppliers.

Making as much use as possible of the historical information is very important to the overall efficiency of the investigation. Provided the information is reliable, it can be used to limit the field testing to areas that were used for the industry type in question. Remember, however, that if there is any doubt about whether the land was or was not used for a potentially contaminating land-use, field testing will be needed for verification.

In most agricultural industries there will be places where soil contamination is particularly likely to have occurred, such as pesticide storage and mixing sites. Another example, in cotton lands, is the area used to load and clean out the cropdusters. Investigators must make every effort to find out whether such sites are present on a site, as they need to be given special attention in the field sampling phase.

Sampling guidelines

If historical evidence shows that there is a significant risk that land was previously used for intensive agricultural or other industry types, and the land is now needed for more sensitive uses, field sampling will be necessary.

Sampling requirements

Preparing a sampling plan that will locate all significant contamination on a site with a reasonable level of confidence is a difficult task. It should be done only by trained professionals. Sampling plans must take into account a number of factors, including the type of chemicals and way they were originally applied, their expected concentration and distribution, the proposed land use and potential receptors, and the predicted environmental fate of the contaminants.

One of the critical decisions will be whether using composite samples will be an acceptable or desirable method of investigation. Composite samples are those that contain a number of sub-samples from several soil locations. For example, an investigator might decide that an old growing area may be adequately assessed by taking four samples within that area, then mixing them all up together to form one sample for analysis. The advantage of this technique is its lower analysis cost. The disadvantage is the loss of sensitivity in the sample results. Hot spots may be overlooked in this way because the one high level might be averaged out by the surrounding low values. The critical factor is therefore the evenness of distribution of the contaminants that persist in the ground; expert judgement is needed.

The EPA does not encourage the use of composite sampling in areas where there may be hot spots. If it is not possible to prove that the contaminants are evenly distributed, but cost is an important consideration, composite sampling may be used, but the results must be compared with an 'adjusted' threshold level. See Threshold levels for more details.

In the bananalands guidelines a number of factors were considered in determining the sampling densities recommended. The two major known contaminants in former bananalands are arsenic and dieldrin. Both were extensively applied by hand until the 1970s. Dieldrin is slowly biodegradable, but arsenic does not decompose. Both contaminants are expected to bond strongly to soil particles; this is likely to restrict most contamination to the upper surface soil levels. Contaminants are more likely to be redistributed by transport of soil rather than by chemical leaching. Based on the known application methods, contaminants might be expected to be relatively evenly distributed in the growing areas, but hot spots are expected around chemical mixing and pumping sites, and possibly also around the old banana sheds where pesticides were stored.

Given the foregoing information and assumptions, a recommended sampling protocol was formulated in the bananalands guidelines. It initially comprises four four-part composites to each hectare of land thought to have been previously used as a banana growing area. Closer point sampling is required if the composite 'screen' sample returns anomalous results.

Further testing is required for soil 150 mm below the surface if the surface soil is confirmed to be contaminated. Closer sampling is automatically required around any known or suspected chemical mixing or storage sites.

In reality protocols for the sampling vary somewhat depending on the type of contaminants under investigation, the quality of the results required, and the professionalism of the investigator. However, a number of minimum standards are routinely required. They include keeping organic samples below 40C, using instrument decontamination procedures between samples, using chain-of-custody procedures, and following quality control and assurance practices.

Analysis requirements

Following the historical review, the investigator should have a reasonable feel for which contaminants might be present at the subject site. All available historical information on pesticide and chemical use must be reported to make sure all the likely contaminants are identified. For example, historical researching into banana pesticide practices showed that arsenic was commonly applied as an oxide, but was sometimes applied as lead arsenate; this meant that lead had to be included in the routine testing requirements.

The EPA requires that all results provided to it for assessing whether a site is acceptable for a particular land use be analysed by a laboratory registered by the National Association of Testing Authorities (NATA). Initial testing may be performed by other laboratories or in the field, but all final analyses and validation sampling should be done by a NATA-registered laboratory. Note that there are different classifications of NATA registration; the appropriate classification for contaminated lands is usually 'registered to test for constituents of the environment'.

Interpreting the results

Once the analysis results are available the next step is to interpret what they tell us about the likelihood of chemical residues in the study area. This again requires professional judgement, and you should initially ask the Contaminated Sites Section of the EPA for advice. However, once you have investigated a number of cases in an area interpreting the results will become fairly routine.

The local council will generally be the authority that needs the testing, as part of the development approval process. The council will therefore generally be the 'first line of assessment'. Initially, the council would probably seek advice from State authorities, particularly the EPA and NSW Health,to help it interpret the testing results it has received. Experience on the North Coast has shown that council officers become familiar with the common local scenarios of contaminated agricultural land quite quickly. The council can then usually discern which cases can be approved routinely, and which ones should be referred to State authorities for specialist advice.

Threshold levels

In their 1992 guidelines ANZECC set out the regulatory basis for using investigation threshold levels (ITLs). These levels are set separately by ANZECC or the National Health and Medical Research Council (NHMRC) on health or environmental criteria. The decision as to whether to use health or environmental ITLs should be based on which is the most exposed or sensitive group at the site.

If hot spots are not anticipated, it is acceptable to compare the average concentration of the contaminants with the ITLs to determine whether a site or an area is contaminated. Any sample measurement that has contaminant concentration 25 per cent or more higher than the ITL should be considered as a potential hot spot that warrants further investigation. This normally involves taking a number of samples in the area surrounding the sampling location in question.

If composite sampling is used in areas where hot spots may exist, each individual composite sample measurement (rather than the average of the measurements) must be compared with an 'adjusted' ITL. The most conservative adjustment is to divide the number of sub-samples that make up the composite sample. If the adjusted ITL is exceeded, individual subsamples must be tested and compared with the non-adjusted ITL.

Validation sampling

Validation sampling is the sampling required to establish that a site is acceptable for a particular land use, generally after it has been rehabilitated. The requirements for this phase of sampling will vary from situation to situation, but will generally be on a scale similar to that of the investigation sampling done before the site was rehabilitated. Validation samples should always be analysed at a NATA registered lab.

Consultants

One of the primary requirements of any investigation is that it must be done by an independent assessor. As neither the EPA nor the local council will have the resources to do such work, it is generally left up to the developer to hire a consultant.

In this State there is currently no system for accrediting environmental consultants. Minimum qualifications for consultants are provided in the 1992 ANZECC guidelines. For industrial contamination issues the EPA generally requires consultants to be able to comply with these requirements. However, an inherent problem related to contaminated agricultural land is that because developers or home owners must pay for the investigation the cost is a major consideration. Almost all the environmental consultants are based in the major cities; this raises the cost of investigations of contaminated agricultural land in rural areas.

Experience in dealing with former bananalands has shown that consultants with other skills who live in rural areas (for example, those specialising in geotechnical or soil science) can learn how to carry out contaminated land investigations. However, this is likely to be true only if the EPA or the local council has the resources to give the consultant very close guidance while he or she is learning.

In the bananalands situation, consultants are expected to show that they have:

tertiary qualifications in a relevant discipline, such as environmental engineering
a thorough understanding of the issues involved in contamination testing and the relevant EPA and ANZECC guidelines
a certificate from a recognised insurance company stating that they have professional indemnity insurance for at least $2,000,000, and that the insurance company understands that the consultant is engaging in contaminated land investigations.

As contaminated agricultural land is generally a broad-acre issue, the community will usually become familiar with the problems and possible solutions quite rapidly after the first few cases are identified. In some cases, this might lead to cases of 'midnight dumping' as people seek an easy way out of their often expensive problems. One way authorities can try to prevent this is to encourage the consultants to feel responsible for their clients' actions. It is therefore vital that the EPA encourages consultants to be ethical at all times.

The NSW EPA has endorsed a consultant accreditation system established by the Victorian EPA under Victorian legislation. A list of accredited auditors has been circulated to all councils in New South Wales. These auditors are technically competent professionals who can review the work done by other consultants. They provide a pool of technical expertise that councils can call upon for an independent review of contaminated sites reports.

Reporting requirements

The 1992 ANZECC guidelines provide a comprehensive guide to general reporting requirements for contaminated site assessment reports in its Appendix 1. The EPA has also issued draft guidelines for consultants reporting on contaminated sites.

It is hoped that eventually all contaminated agricultural land investigation reports can be standardised so they can be easily put into a database held by each council. This data may then be periodically downloaded on to an EPA regional or Statewide database for collation. The information will then be used to interpret contamination trends, which will in turn allow investigation guidelines to be progressively refined.

The EPA recognises that to manage the large amounts of information generated in CAL investigations there needs to be a standardised set of requirements for reports. The following list covers most of the fields that should be included in the standard reporting requirements for CALs. Refer to the EPA's draft guidelines for more information.

Site identification

street address, postcode
Lot, DP Number, parish, county
Local Government Area (LGA), electorate
external (for example, consultant's) reference number
easting and northing and Australian Map Grid sheet and zone
map showing major features, scale, north point

Ownership details

owner name and address
occupier name and address

Consultant

name and address

Land use

current land use and zoning status
proposed future land use

Site history

potentially polluting activities carried out on site
period in which activities were believed to have been carried out
any information regarding the location of likely hot spots
information sources consulted

Site details

topography
relevant geographical or cultural factors
aspect and degree of dominant slope

Site sensitivity

human access to the site
ecosensitivity (for example, the proximity to wetlands)
sensitive adjacent land uses
potential for off-site contaminant migration

Testing results

sample identifier
analyses tested
medium sampled (for example, soil or groundwater)
type of sample: point or composite?
analyses, results and the units of measure

Laboratory

name and address
NATA registration?
analysis methods used
preparation procedures
detection limits
results provided on dry weight basis?
laboratory QA/QC procedures used
date of analyses

Rehabilitation status

notice issued?
any rehabilitation works completed or underway?

Proposed rehabilitation measures

Conclusions

Remediation options for CAL

Contamination from past agricultural practices may be broadly segregated into two groups: 'hot spot' and 'broad-acre' contamination. Hot spot contamination consists of limited volumes of relatively high levels of pollutants (compared with surrounding areas). Examples of this style of contamination are often quite different to those of broad-acre styles of contamination. Remedial options for hot spots tend to be quite case-specific, and will not be discussed at length here. If you have any questions on specific contamination hot spots see the Contaminated Sites Section of the EPA.

Broad-acre contamination is characterised by widely distributed, relatively low-level contamination. From our limited experience to date, broad-acre contamination is often restricted to shallow depths, unless the soil is unusually coarse or the surface has been heavily disturbed. The remediation options available for broad-acre contamination will vary depending on factors such as the type of pesticides used, the method of application and the redistribution of soil since application.

Notwithstanding these case-specific factors, there are a number of broad types of remedial options available. These are described below. The options are listed in approximate order of the EPA's preference.

On-site treatment technologies

One way of dealing with organic contaminants is to destroy or break down the contaminants while the soil remains in-situ or is excavated on-site. The most likely technology identified so far is bioremediation. However, bioremediation technology has had very limited success in dealing with inorganic contamination in soil.

Off-site treatment technologies

Overseas, the most accepted off-site destruction technology for organochlorinated wastes, including pesticides, is high-temperature incineration. In November 1992, the Independent Panel on Intractable Waste recommended against building a centralised high temperature incinerator facility in Australia. ANZECC has accepted this recommendation and also agreed to have management plans developed to set threshold concentrations for different categories of wastes.

Other off-site remediation technologies include soil washing (followed by disposal or storage of the contaminated solvents), thermal desorption (low-temperature incinerators with off-gas scrubbers), particle-size separation (with other disposal or treatment methods), chemical treatment (such as base-catalysed dechlorination (BCD) of scheduled organochlorine wastes), ball-mill pulverisation, and super-critical fluid extraction. The BCD process is presently being used successfully for destroying PCBs in contaminated soils. None of these technologies is commercially viable for treating contaminated soils in broad-area, low-level contamination at present. However, such technologies do exist in Australia and may be used in New South Wales in the future.

Off-site disposal

A number of organic wastes, including organochlorines, are controlled by Chemical Control Orders (CCOs) issued under the Environmentally Hazardous Chemicals Act (EHC Act) 1985. The Chemical Control Orders often prohibit off-site disposal of highly contaminated wastes, and the only option available may be to store the wastes in a secured storage area on-site or at a nominated off-site store, until a suitable alternative method of disposal becomes available.

For low-level contamination it may often be feasible to dispose of the material directly to a controlled landfill, if one is available. According to the legal definition (see, for example, the CCO on Organotin Wastes), a controlled landfill is one approved by the EPA and operated 'in accordance with a preconceived plan involving dumping, compacting and covering with soil in a way that minimises any adverse effect on the environment'. For most inorganic contaminants, the only other restriction recommended by the EPA is that the material passes a standard leach test (US EPA Toxicity Characteristics Leaching Procedure, TCLP).

Containment on-site

Isolating the contaminated soil by appropriate barriers may be an acceptable remediation method in many agricultural contamination situations where treatment or disposal options are not economically viable. The material should ideally be placed where it will not be susceptible to undue leaching or erosion. The area should be fenced to stop livestock getting in, but accessible if the material needs to be removed in the future. Putting the material in areas that will not be readily accessible in the future,such as under roads or house slabs,is not preferred but may be approved in some cases.

In most cases the material will be contained below the finished ground level. The containment area should in these cases be covered by a brightly coloured membrane to alert future excavators of the presence of the material below.

In cases where sampling is done before subdivision it will often be possible to excavate and rebury contaminated surface soil during the road terraforming.

If contaminated soil remains on site, the EPA recommends that this information be noted on the s. 149 certificate issued under the Environmental Planning and Assessment Act for the site.

Alternative land use

In some cases the most realistic solution may be to change the proposed land use to a less sensitive one. For example, a moderately contaminated site would most probably not be suitable for residential developments. The costs, benefits and public health risks of the land for the various options will need to be assessed by the developer and local council to determine the most appropriate land use in each case.

Vertical mixing

The EPA publication Guidelines for the Vertical Mixing of Soil on Former Broad-Acre Agricultural Land addresses the problem of dealing with low-level contamination before sensitive development is approved. Vertical mixing involves the rotary tilling of a contaminated surface layer of soil to mix it with the uncontaminated underlying soil, providing an acceptable level of contamination at the surface. The circumstances in which vertical mixing is appropriate are very specific and may not be appropriate in all cases. The guidelines set out a checklist of requirements that should be met before vertical mixing can be approved. The Department of Land and Water Conservation is also producing a guideline to be used in conjunction with the EPA's on appropriate land management actions where vertical mixing is used.

More information on the vertical mixing guidelines is included in this Manual.

Other methods

EPA policy is to not be prescriptive in dealing with remediation technologies. It is important that each case is considered on its merits, and that innovative technologies are considered with an open mind.

The onus is therefore placed on the developer to propose what he or she considers to be a suitable means of dealing with the problem. In some cases, the developer may need to demonstrate the feasibility of the technology before it is used on a large scale. It may also be desirable to ask for community feedback on the proposal. The EPA will then consider the environmental and public health implications of the proposal, and make its recommendations accordingly.

Managing CAL

Successful management of CAL requires close liaison between the EPA and local council. In most cases CAL problems will come to light in the council's development approval process. If the council becomes aware that a development or building application is in an area known to have been used for intensive agriculture, it should be mindful of the contamination potential of that land. If it considers the risk of contamination to be significant it should ask for sampling.

If the contamination is then confirmed, the council should set up a system to note the details of the contamination, the nature of the remediation (if any), and any restrictions that need to be placed on activities on the site. Parts of the information in the system will need to be publicly accessible, particularly to potential purchasers and occupiers of the site. Other parts will need to be available only to the EPA and council, at the same time protecting the privacy of individuals.

Information relating to land contamination needs to be available to the appropriate people so that land use decisions can be made. Information about contamination may be noted on the s. 149 certificate (Environmental Planning and Assessment Act) relating to the property, or the property may be the subject of a notice issued by the EPA under the Environmentally Hazardous Chemicals (EHC) Act or the Unhealthy Building Land (UBL) Act. Councils are encouraged to adopt a policy in relation to chemical residues or land contamination that is noted in the s. 149(2) certificate. If information is available about previous land uses that may have been contaminating, or if the contamination is known, this information should also be noted on the certificate under s. 149(5). The Department of Urban Affairs and Planning has recently (September 1995) released guidelines (Contaminated Land) to help councils in decision making during the planning process.

During the conveyancing process notices issued under s. 35 of the EHC Act or s. 5 of the UBL Act can be acquired from the Central Register of Restrictions of the Land Titles Office or the EPA's Land Information Section.

Summary

The issue of contaminated agricultural land has been identified and must now be managed. The chemicals most likely to cause contamination problems today are arsenic and organochlorines, followed by organophosphates, and sometimes mercurial and lead pesticides.

To identify potentially contaminated agricultural land, start with a historical review, followed by soil testing if necessary. An expert consultant must be called in, at least initially.

Remediation options for CAL are severely limited.

Any information about land contamination can be noted on a property's s. 149 certificate (EP&A Act). Land use decisions should be made on the basis of this and supporting information.