Reading a well, reading an aquifer

Trap one: the datum

“Depth to water: 41 feet” is measured from a reference point — and reference points get re-surveyed. Mix two datums in one series and you manufacture a cliff that never happened; we once found spurious ±2,700-foot “head changes” in exactly this way, and now keep every well’s series datum-consistent and never pool raw depths across wells — corridor trends pool per-well anomalies instead.

Trap two: one well is a point, not an aquifer. A single declining well can be local drawdown from a neighbor’s pump; an aquifer story takes many wells moving together — which is what the corridor trends test.

Trap three: which law your aquifer obeys

Alluvial wells along a stream are usually tributary — the river on a delay, administered in priority (lesson D1). But the Denver Basin bedrock aquifers — Dawson, Denver, Arapahoe, Laramie–Fox Hills, stacked like plates under the metro area — are governed differently: that water is allocated to the overlying landowner on an aquifer-life basis, largely outside the call system, and designated basins on the eastern plains are administered by the Ground Water Commission rather than the water courts. Same drill rig, different constitution.

You can see the distinction drawn: the 3D aquifer x-ray renders each Denver Basin unit as its own head surface inside surveyed formation geometry — the surfaces you are looking at answer to a different body of law than the river above them.

What this does not let you conclude

Aquifer assignments come from DWR’s decoded picks and can be wrong for individual wells; whether a specific well is tributary, not-nontributary or nontributary is a legal and engineering determination with real money riding on it — made in applications and hearings, not from a chart. Advisory reading aid on public data — never an administrative or legal conclusion, and never a substitute for DWR administration or an engineer’s analysis. Our methodology has not yet had outside expert review: how this is built.