Groundwater Conditions in the Special Quantity Subareas
In January, two “Special Quanity Subareas” (SQSs) were designated in parts of Butler/Saunders and Platte/Colfax counties due to concerns about the long-term viability of their groundwater supplies (see story above). So what makes these areas different than other parts of the district?
In a word: geology. The aquifers underlying the SQS regions are largely “confined” (also known as artesian aquifers) and are sealed off by layers of clay or other impermeable material. Water levels in these types of aquifer can be highly variable during the year because they depend on pressure in addition to the amount of water in the aquifer. During the summer, especially if many high capacity wells are running at the same time, this can cause large pressure drops in the aquifer and corresponding declines in the static water level. On a positive note, at the end of the irrigation season the pressure in the aquifers starts to return to normalxx and usually by November wells are able to operate as they did before.
However, both SQS regions were hit hard by drought conditions in 2012 and 2013. In a typical year, the district might receive 1 or 2 complaints about domestic wells going dry (if any); in 2012, we received more than 3 dozen, with the majority coming from land now located in one of the SQSs.
The district’s dedicated monitoring wells take water level readings every few hours. Looking at the data for the SQS areas for 2012-2013, a concerning trend became clear. During mid-summer water levels were dropping much lower than normal, even for confined aquifers like the ones in the SQS areas.
Based on this data, the NRD made the decision to create the Special Quantity Subareas to help prevent large mid-summer declines and the resulting water shortages to area wells. Within the SQSs, no new or expanded irrigated acres are allowed, flow meters will be required on irrigation wells beginning in 2015, and acre-inch allocations will be put in place for irrigation (allocation amounts are yet to be determined).