How we monitor
We monitor pesticides in groundwater in two networks:
- Community supplies: 40 school sites. These monitoring wells were selected without any consideration of pesticide use.
- Regional network: 40 regional sites. Chemical use was considered when selecting some of these monitoring wells, so pesticides are more likely to be detected in groundwater from these sites.
The sites are monitored every four years. The regional network sites were initially sampled in 2003-2004 and the community supply sites in 2004-2005. The indicator will next be updated in 2017.
Data was collected in 2012/13.
Previous to this an investigation was undertaken of pesticide contamination of groundwater supplies looking at a likely worst case selection of sites where agrichemicals were known to have been used. This study is reported in an Waikato Regional Council technical report by JC Hadfield and D Smith.
We collect groundwater samples from each of the monitoring wells, using the groundwater sampling protocol developed by the Institute of Geological and Nuclear Sciences. The samples are analysed in the laboratory for trace levels of organonitrates, organophosphates and organochlorines (OCNPT).
We also check for pH, conductivity, total dissolved solids, alkalinity, CO2, calcium, magnesium, nitrate, hardness, sodium, potassium, chloride, sulphate, boron, total iron, manganese copper and zinc.
The data is stored in Waikato Regional Council’s Hydrol database.
The indicator has four categories for pesticides in groundwater. This indicator shows the proportion of monitoring wells in each category. The categories for pesticides in groundwater are:
|Excessive||> MAV||Occurrence of pesticides exceeds the maximum acceptable value (MAV) for drinking water|
|High||50-100 % MAV||Safe for drinking when sampled, but pesticides detected at over half the MAV|
|Low||< 50% MAV||Pesticides detected, but at less than half the MAV|
|Non-detect||< detection limit||No pesticides were found at the time of sampling|
The Ministry of Health specifies the maximum acceptable values for pesticides in drinking water.
This indicator's data file provides pesticide analysis parameters and detection limits.
This indicator is limited by the extent to which the selected sites represent the Waikato region’s very large and highly variable groundwater resource.
Care is taken to base this indicator on information from sites which are well documented (with log, construction and location information), distributed widely throughout the region and represent all major aquifer areas. The monitoring networks have been selected primarily on their hydrogeological setting rather than high chemical use.