Programme overview

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 Regional Council (Greater Wellington) conducts regular monitoring of groundwater quality at 78 sites across the region, shown on the map below. Three key indicators of groundwater contamination (typically arising from land use intensification and/or on-site wastewater disposal systems) 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 Standard 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 (MoH, 2018).

  • 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 (MoH, 2018).

  • 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.

Monitoring network

Groundwater quality monitoring wells are spread across the region, with the total number of wells in each of the five Whaitua (main river) catchments listed below:

  • Ruamāhanga - 47 (10 of which are not included in this report due to 3-yearly sampling).
  • Kāpiti Coast - 15.
  • Te Whanganui-a-Tara (Wellington and Hutt Valley) - 14.
  • Wairarapa Coast - 1.
  • Te Awarua-o-Porirua - 1.

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 methods page for more information on the monitoring network and each “Connectivity to surface water” category.