The most recent groundwater quality survey was undertaken in October and November 2019. The reason for this work was to assess the state of the environment and identify any risks and compliance issues.
The report detailing the findings from the 2019 survey has been released. Download it here (pdf, 6.4 MB)
Potential public health risks identified
Due to its unconfined/semiconfined (leaky) nature, the aquifer underlying the Motueka/Riwaka Plains, does not meet the DWSNZ definition for secure groundwater. The 2019 survey identified various risks to the security of the groundwater quality in the Motueka/Riwaka Plains. These risks included:
The construction, take and use of bore water in the Tasman District area is governed by the Tasman Resource Management Plan (TRMP) in Chapter 16, Clause 16.12. Because they are historic, many of the private bores sampled in the 2019 survey did not meet with requirement in the TRMP regarding the prevention of surface water or other contamination entering the bore.
Borehead security was variable. For example, some had rubbish or chemicals stored near the bore. Some were located in low-lying areas or stormwater drains. Some bores were not appropriately sealed, potentially allowing access to birds and vermin, along with dust and dirt to enter into the bore. These poor practices were not intentional, but rather a lack of knowledge of the property owners.
Overall, the water quality in the Motueka/Riwaka Plains is good. The majority of the chemical parameters tested for were well within the Drinking Water Standards for New Zealand (DWSNZ) for both the health significant and aesthetic factors (Ministry of Health, 2018). Despite the widespread agricultural and horticultural activities on the plains, nitrate concentrations were low, with the majority of bores sampled under 50% of the maximum acceptable value in the DWSNZ.
Results show stable water quality with only sporadic and low level faecal contamination. Only 2% of samples were positive for E.coli (Escherichia coli, a faecal indicator bacteria) and 18% contained total coliforms. Protozoa was not sampled for in this survey. It is expected that the risk of protozoa contamination is low considering the lack of animal farming on the plains, but cannot be ignored.
River water, which is the main source of recharge for the Motueka / Riwaka Plains aquifer, was of good quality at the time of sampling. Spring water quality was also good at the time of sampling.
Groundwater quality in the Motueka / Riwaka Plains has remained of good quality throughout the years of sampling. Most of the water chemistry parameters have remained below the DWSNZ maximum acceptable value and guideline value (MAV and GV respectively).
The latest four yearly national groundwater investigation undertaken by the Institute of Environmental Science and Research (ESR) was in 2018. The 2018 ESR survey tested for pesticides, emerging organic contaminants (EOCs) and glyphosate. A selection of bores in the Tasman region was tested for EOCs and glyphosate for the first time in 2018, with two bores selected in the Motueka / Riwaka Plains.
Pesticides have been tested in the Tasman region by ESR since 1998. Pesticide residue detections throughout the years (including in 2018) were all well below the MAV in the DWSNZ.
Emerging Organic Contaminants
Emerging organic contaminants (EOCs) are components or active ingredients in products that are commonly used by humans. EOCs detected in the Tasman region include sunscreens, caffeine, pharmaceuticals and hormonal by-products. Because the effects of EOCs are largely unknown, they do not have MAVs from the DWSNZ. Both bores in the Motueka / Riwaka Plains had detections of EOCs, however the compounds detected were in nanogram concentration (0.000 000 001 grams or 1 part per billion). One bore had detections suspected to be caused from a potential sewerage leak. This bore is being followed up on accordingly by the Council utilities department.
Glyphosate is commonly known as RoundUp or Drexel. Glyphosate was not detected in any of the bores selected by ESR for testing in the Tasman region.
If you have your own bore that you use for domestic/drinking purposes, please refer to the Ministry of Health links below on how to protect your bore water supply
If you have any questions about the survey itself, please email email@example.com or phone 03 543 8680. Alternatively contact Joseph Thomas, Resource Scientist, on 03 543 8494.
If it is a health-related question, please contact the duty Council Environmental Health Officer or the Nelson Marlborough Public Health service.