Between October and December 2021, a water quality survey was undertaken in the Waimea Plains. This is the sixth and most recent water quality survey undertaken in the plains.
Read the full Technical Report Waimea Groundwater Quality Survey 2021 (pdf 11 MB).
Of the 137 bores/wells sampled in the Waimea Plains, 56 sites (41%) had nitrate-N below 50% of the MAV (below 5.6 g/m3-N), 42 sites (31%) were between 50% of the MAV and the MAV (between 5.6 and 11.3 g/m3-N), and 39 sites (28%) were above the MAV (above 11.3 g/m3-N).
The highest nitrate-N concentrations in 2021 were found at the intersection of Bartlett Road/Ranzau Road West (31 g/m3-N) and along Blackbyre Road (30 g/m3-N). All bores/wells sampled between these two locations exceeded the MAV for nitrate-N. The area between Bartlett Road and State Highway 60 is where the UCA and the AGUA merges together and becomes hydraulically indistinguishable. Any discharge of nitrate-N from the UCA would be noticed here and would be contributing to the elevated nitrate-N concentrations at the Bartlett Road/Ranzau Road West intersection. Blackbyre Road is outside of the UCA reach, however water from Bartlett Road is likely to travel towards Blackbyre Road as the flow of groundwater progresses towards the coast.
Unconfined groundwater south of Brightwater shows most sites sampled being well below 50% of the MAV. North of Brightwater on both sides of the Waimea River, nitrate-N was near or above 50% of the MAV. East of the Waimea River and east of Burkes Bank, the majority of all four aquifers were near or above the MAV. West of the Waimea River, bores/wells in the AGUA along Cotterell Road/Moutere Highway/River Road/Waimea West Road were also near or above 50% of the MAV. It was anticipated that these areas would have higher concentrations of nitrate-N due to the overlying horticultural and agricultural activities.
The large number of samples where nitrate-N concentrations are near/above 50% of the MAV across the main horticultural and agricultural areas on the Plains shows that input from present-day activities are contributing to nitrate-N entering in the groundwater in all four aquifers.
You can learn more about nitrates in the Waimea Plains here.
To keep residents informed on groundwater nitrates in the Waimea Plains, we recently sent letters to property owners in a targeted area reminding them that elevated levels are still present.
Waimea Plains residents receive their household water from various sources. We are responsible for ensuring public reticulated water supplies are safe, secure and meet the national standards for drinking water – this means keeping nitrates below 11.3mg/L. All our Waimea Plains water supplies are below half this level.
However, owners of private water supplies are responsible for the safety of the drinking water they provide to their own or other properties.
Historical monitoring of water taken from bores across the Waimea Plains has long shown elevated levels of nitrate-nitrogen, especially in the Ranzau, Blackbyre and Bartlett Road areas.
Staff have just completed widescale testing of the aquifers which revealed nitrate levels remain elevated in some areas, particularly in the Eastern Waimea Plains.
Therefore, anyone using a private bore or well for drinking water needs to be aware of the situation so they can make informed decisions and if necessary consider having their water tested.
Taumata Arowai, the water services regulator for Aotearoa, provides information on how to get your drinking water tested for nitrates, ensuring your bore or well is secure, and information on water supply treatment options.
We have been carrying out our five-yearly synoptic testing, a general sampling survey to check groundwater nitrate levels. We will release the results of this study when they become available in the next few months. Residents who took part should have received a letter with a copy of their results.
If you have your own bore or well that you use for domestic/drinking purposes, please refer to the Ministry of Health links below on how to protect your water supply
If you have any questions about the survey itself, please email melanie.westley@tasman.govt.nz. Alternatively contact Joseph Thomas, Resource Scientist, on 03 543 8494.
If it is a health-related question, please contact the Nelson Marlborough Public Health Service on 03 546 1537 or via email at drinkingwater@nmdhb.govt.nz.
The Nelson – Marlborough Public Health website has more information on Drinking-water supply safety, including specific advice on how to ensure your bore or well is secure, as well as information on water supply treatment options.
If you have any questions about your drinking water bore or supply, you can contact Tasman District Council Environmental Health Officers on 03 543 8400.
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