Disused sheep-dip sitescan be identified in a number of ways. For example, the landowner may locate the sheep-dip site in an effort to protect his or her family and livestock from harmful effects. Once the landowner has identified the sheep dip, the location should be recorded for future reference. Preferably the council should be made aware of the sheep dip's location, so it can be properly managed and added to its register.
In the course of a subdivision application, territorial authorities will check contamination issues. If the site history indicates a sheep farm, then any evidence of its existence needs to be followed up. The regional council may also detect adverse environmental effects in the groundwater or nearby surface water that can be traced back to an old dip site. Councils may also decide on a proactive programme to identify old sheep-sip sites on their property or in rural areas where land-use changes are occurring.
Appendix 1 provides a practical checklist that councils can hand to current landowners to help them identify and characterise former sheep-dip sites and the activities that occurred at the site. It lists relevant questions to address in that context and provides some management options.
4.1 Structural evidence
When determining if a sheep-dip site was previously located on a property there are a number of potential indicators to consider. Dip sites are often located near sheep yards, woolsheds or bore-water supplies, but their exact location may not be obvious. When investigating the location of a former sheep-dip site, consider where dip chemicals were stored and disposed of. Structures associated with disused sites include old plunge dips, which were often concrete structures, or shower booths. However, these structures may be covered over or may have even been removed, sometimes leaving suspicious ground depressions.
4.2 Anecdotal evidence
The most common and successful method for identifying previous sheep dips is through anecdotal information from current or previous landowners, especially when they used the land for agricultural purposes. Anecdotal information is particularly useful when the sheep-dip structures have been removed from the site and there is no visual evidence of the dip. For example, in a trial survey comparing anecdotal site identification versus aerial survey maps in the North Raglan area in 2003, it was found that two-thirds of old dip sites were no longer accompanied by obvious above-ground structures, with many having been buried or removed. This means that anecdotal information from people living at the time a dip was in use may be the only means of identifying the general area of a former sheep-dip site, short of extensive soil sampling.
Apart from landowners, sometimes stock sales agents and veterinarians in the area know a great deal about former sheep farms and may have records. Another option is to ask old-time shearers to locate the former shearing sheds in the area. The use of local historians or other researchers may prove valuable when assessing building permits or valuation records to help identify sheep yards, associated farm buildings and dip-like structures.
Although gathering anecdotal information is the best way to identify former sheep-dip sites, it relies on goodwill. Due to the liability associated with contaminated sites, information is often provided unofficially and landowners may be concerned about passing on information that may decrease the value of their property. However, the experience in survey work has been that landowner responses have generally been very supportive. It is important to keep in mind, though, that anecdotal information may be incorrect, either through mistake (especially after a long passage of time or via second-hand account) or deliberate intent.
Local knowledge is progressively being lost as generations pass and farms change hands. It is probable that this information resource will largely disappear as a means of identifying old dip structures within the next decade. Even now, it is often necessary to locate members of the most long-established surviving farming families in a district to gain the best insight into the number and location of old sheep dips in a given area. This means that if useful information on the location of dips is to be recorded for future reference, some urgency is required on the part of the current owner.
4.3 Old aerial photographs and public records
Old aerial photographs can be used to identify structures often associated with sheep-dip sites, including woolsheds and yards. However, the scale of historical aerial photographs across most of New Zealand usually only allows stockyard areas to be identified and not sheep-dip structures themselves. However, from survey work in North Raglan it would appear that only about half of identified stockyard areas had associated dips, with the other half being some distance from the stockyard.
When making use of aerial photographs in this way it is important to remember that dip structures and stockyards come and go, depending on the favoured parasite control method at the time. In some cases, the photograph may have been taken before a dip was constructed. As a result, aerial photographs are recommended only as a useful initial method to identify potential sites, if the photo quality allows.
Regional and city/district councils and public libraries may also hold some historical information or maps about the site in their archives, which could help to localise sheep dips and associated buildings. Also, reports from previous investigations into contamination issues that could be relevant may have been stored on council records. For councils, a review of existing information on their databases is probably a good starting point. Landowners, or consultants acting on their behalf, could enquire about publicly held information from councils via an official information request.
4.4 Soil and water sampling
Water and soil sampling is another method for identifying contaminated sheep-dip sites (see section 5 for further information). Limited soil assessments are sometimes undertaken as part of a due diligence investigation, and may identify chemicals previously used in sheep dipping. Routine surface-water and groundwater monitoring may also be undertaken as part of regional council water-quality monitoring programmes and may lead to identifying the source of a contaminant discharge. Extensive sampling, however, is usually not done for the original identification, but serves as a confirmation in combination with other evidence that a sheep dip may have existed at the site.
4.5 Screening food products
Food products are being screened in Australia to identify chemical residues that indicate historical sheep-dip sites. This method identifies farms that produce contaminated meat, milk or crops. For this concept to be applied in New Zealand, additional monitoring of primary agricultural products would be required. Surveys of this type are provided for when evidence for the need is demonstrated. When a non-compliant level of a contaminant is found in an animal product, measures are applied to the livestock or the farm (or both) under the Animal Products Act Regulated Control Scheme 2004 to achieve compliance. The legislative power for sampling primary products more or less directly from farms currently lies with central government, however, and so this method of residue screening is not easily available to local government. Similarly most − although not all − testing and interpretation are done by central government (see under New Zealand Food Safety Authority at www.nzfsa.govt.nz).
4.6 Sniffer dogs
In Australia, sniffer dogs are used effectively to identify a range of organochlorine-contaminated sites. However, using these dogs in a trial conducted in New Zealand in 2004 did not deliver satisfactory results on all occasions. Therefore, this method is currently not considered viable in New Zealand, although it might become feasible in the future if the dogs are trained under New Zealand conditions and deliver reliable results similar to those in Australia. This method would likely be more acceptable to landowners, as it is a non-threatening approach. (See Appendix 8 for more information on this as a sampling strategy.)