Groundwater Quality Sampling Schedule

Groundwater Quality Sampling Schedule

Friday, October 29, 2021
The Upper Big Blue NRD is divided into twelve groundwater quality Management Zones (map below). The median nitrate value for that zone determines the phase of management and therefore, rules and regulations. 

Taking a step back, the median nitrate value for a zone is the product of water samples collected from a specific network of wells. These wells are selected based on construction and geology.  A well that provides accurate results is screened in one portion of the aquifer only, and does not have multiple screens. The screen also does not transect geological confining units such as clay layers, which could mix shallow and deep water. 

Currently, there are 287 wells in the water quality network. Most of the wells are irrigation, with some monitoring, domestic and public wells. To annually collect a water sample at each of these wells would be incredibly difficult given the sheer size of the District - over 1.2 million irrigated acres! Therefore, a rotation of zones below the Phase II trigger of 7.0 ppm was created. This means that if the median nitrate value of a Zone is below 7.0 ppm, it will be sampled once every three years. If the median nitrate value is above 7.0 ppm, that Zone will be sampled annually.

In 2021, district staff sampled wells in Zones 1, 2, 3, 5, 6, 7, 8, and 11. In 2022, District staff will sample wells in Zones 1, 2, 3, 5, 6, 9, 10, 11, and 12. 

Thank you to all irrigation, domestic, and monitoring well owners for your continued cooperation. Protecting groundwater quality is an important task and your support is valuable.