11. Groundwater Resources

RPS objective

· Maintain groundwater quantity and quality to the extent that the use of the groundwater resources is sustainable.

Pressures

· There are currently 3,747 bores registered with the council and 279 resource consents to take groundwater in Northland, which equates to a volume of 49,602 m³ of groundwater per day. This places a large demand on Northland's groundwater resources.

· Poorly constructed and maintained bores can result in groundwater contamination.

· Changes in land use can not only result in an increase in the quantity of water taken from an aquifer but can also influence the amount of rainfall infiltrating into the aquifer (recharge) and groundwater quality.

· The change in rainfall trends and temperature as a result of climate change is likely to result in decreased recharge to groundwater resources, and increased potential for saltwater intrusion in coastal aquifers.

State

· Due to the varying geology in Northland, there are a large number of aquifers scattered throughout the region. These aquifers include large sand and shell bed systems such as the Aupouri Peninsula to small alluvial aquifers such as Russell.

· Groundwater quality at the majority of monitored sites meets the Drinking Water Standards for New Zealand 2005 (MoH 2005). The highest percentage of non-compliance with the drinking water standards for bacteria occurs in many of the coastal areas and in three of the volcanic aquifers: Ruatangata, Maunu and Maungakaramea.

· The majority of sites that exceed the guidelines for manganese and iron are fed from sand and gravel aquifers, while all sites monitored meet the guideline for nitrate.

· The majority of coastal bores monitored have higher electrical conductivity, and chloride and sodium levels than inland basalt aquifers, due to leaching from marine sediments.

· The mean age of groundwater in the following aquifers is likely to be greater than 45 years: Maungakaramea, Whatitiri, Three Mile Bush and Matapouri, which means that current groundwater quality may reflect the influence of historic land use activities in these areas.

· All results were below detection limit for pesticides at selected aquifers in Northland in 2002 and 2006, even though a site study in 2005 found pesticides to be mobile in Northland's Kiripaka soils.

· Of 45 Northland sites groundwater quality is improving at eight, deteriorating at seven and 15 sites showed slow changes in groundwater quality that probably indicates natural water-rock interaction. A further seven sites were identified as pristine.

Doing well

· Resource consent monitoring of bore construction and groundwater takes.

· State of the environment monitoring of groundwater quality and quantity as well as specific aquifer investigations.

Areas for improvement

· The number of people registering their ‘permitted takes' and location of bores with the Council to enable greater understanding of the ‘actual' amount of water taken from aquifers.

· Prioritise and implement recommendations in the preliminary hydrogeological reports based on current and potential future demands.

· Management of water allocation limits for aquifers in Northland to provide water use securities for uses and sustainable allocation of water resources.