Groundwater in the Wellington region is used extensively for drinking water, stock supply, irrigation and industry. Groundwater also provides baseflow to rivers, streams and wetlands, or forms natural springs or seeps where it discharges at the ground’s surface. The protection of these surface water ecosystems requires careful management of the quality and quantity of the underlying groundwater.
To assist with the sustainable management of groundwater resources in the Wellington region, Greater Wellington conducts regular monitoring of groundwater quality at 83 sites across the region (comprising 82 wells and 1 spring), shown on the map below. Key indicators of groundwater contamination (typically arising from land use intensification and/or on-site wastewater disposal systems), along with general chemistry results, are presented in this report:
Nitrate-nitrogen - a key indicator of groundwater contamination typically arising from land use intensification and/or on-site wastewater disposal systems. Nitrate in groundwater can affect its quality for drinking-water supply. The Drinking Water Standards for New Zealand (DWSNZ) sets a Maximum Acceptable Value (MAV) for nitrate at 50 mg/L (equivalent to nitrate-nitrogen of 11.3 mg/L), based on a risk to bottle-fed babies (Water Services (Drinking Water Standards for New Zealand) Regulations 2022).
E. coli bacteria - a key indicator of groundwater contamination by microorganisms, some of which can cause diseases. Faecal bacteria from livestock, onsite wastewater discharges, stormwater and other sources can contaminate groundwater. Any detection of 1 cfu/100 ml exceeds the DWSNZ.
Saline intrusion - a key indicator for seawater contamination in coastal wells. The difference in conductivity between seawater and fresh groundwater is very marked, making it a useful indicator.
Dissolved reactive phosphorus - Dissolved reactive phosphorus is a nutrient that can affect surface water quality.
Dissolved metals - Dissolved metals can affect the quality of groundwater for drinking-water supply and can be indicators of groundwater contamination by anthropogenic activities.
Chemistry - major ion chemistry can provide information about the recharge sources of the groundwater, residence time in the aquifer and groundwater flow patterns.
Groundwater quality monitoring sites are spread across the region, with the total number of sites in each of the five Whaitua (main river) catchments listed below:
Scroll/zoom on the map to find areas of interest. Hover over a monitoring site for details and click on it to open popups with links to more information. See the results pages for details on the Nitrate-nitrogen and E. coli ratings in the map hover labels. See the methods page for monitoring network information and “Connectivity to surface water” category descriptions.
Note: circles marked with a star (⋆ ) above have two bores in the same location at different depths.
Full monitoring data is downloadable on the Resources page of this report and additional information for each nitrate-nitrogen, E. coli and dissolved reactive phosphorus site is available at Land and Water Aotearoa (LAWA). Click on sites in the monitoring network above for their links to LAWA. The video below explains LAWA groundwater information further.
This web report may be cited as: GW 2023. 2022/23 Groundwater quality monitoring report. Greater Wellington.
A static PDF version of this report can be viewed and downloaded here. Reports for previous years can be found here