Mellette County, SD Water Table Trend
Is the water table dropping in Mellette County, SD?
Over 47 years of USGS readings, the well tracking Mellette County's aquifer is rising, getting shallower over time: 1.5 ft per decade.
This is one representative well, not a county-wide survey, the same grain limit every page here discloses.
Mellette County's source well, in detail
Depth to water at the last reading was 7.9 ft below land surface. Readings span 1978-11-02 to 2025-06-17, 310 measurements from USGS well USGS-432554101065601 (40n32w21bbbb (Mt-78a)), part of the National Water Information System. The qualifying bar and the OLS fit behind this trend are documented in the methodology guide.
How Mellette County compares nationally
Mellette County sits at rank 168th of 1,449 ranked counties, ordered rising-to-declining, so a low number means a rising water table and a high one means fast decline. Mellette County, South Dakota is home to about 1,834 people. See the fastest-moving counties guide for how Mellette County stacks up against the most extreme cases nationally.
Depth and quality are separate questions
This page answers a depth question, not a quality one. A well in Mellette County can be stable in depth and still worth testing for quality, or declining and still test clean, the two are measured separately, and only a direct test settles the second one.