The depth to the water table varies from 5 to 12 metres. A network of six multi-level groundwater observation wells has been established at selected locations within the watershed. Monthly monitoring for water quality and hydraulic head began in May 1996. Hexazinone has been applied at various locations within the plain for the past 10 years. Results indicate that hexazinone is found throughout the watershed at concentrations of about 3 micrograms per litre or less near the surface of the water table.
Concentrations decrease rapidly with depth.
Nitrogen concentrations in groundwater throughout the site are negligible.