An acre-foot is the amount of water it takes to cover one acre, about the size of a football field, one foot deep. That’s 325,851 gallons.
Water planners in the West use acre-feet because they measure in bulk: reservoirs, irrigation rights, a city’s yearly supply. The number shows up in the Site Layer 4 records too. The developer has described its water use two very different ways, less than 15 acre-feet a year and no more than 800. This post puts those numbers in terms you can picture.
One acre-foot in everyday terms
| Measure | One acre-foot equals |
|---|---|
| Gallons | 325,851 |
| Gallons per day, spread over a year | about 890 |
| Olympic swimming pools (about 660,000 gallons each) | about half of one |
| People’s indoor home use for a year | 9 to 11 people |
The last row uses the USGS estimate that each person uses 80 to 100 gallons a day indoors at home. Indoor use doesn’t count lawns and gardens, which can add a lot in summer.
The two Site Layer 4 numbers
The larger figure is about 53 times the smaller one. At 800 acre-feet a year, the project would use about as much water as everyone in Platte County uses indoors at home.
| Less than 15 acre-feet a year | No more than 800 acre-feet a year | |
|---|---|---|
| Where it appears | Applicant’s June 2026 county application | February 2026 correspondence with Wyoming DEQ, from an earlier cooling assumption |
| Gallons a year | under 4.9 million | up to 260.7 million |
| Gallons a day | under 13,400 | up to 714,000 |
| Olympic pools a year | about 7 | about 395 |
| Same as indoor home use for | 134 to 167 people | 7,100 to 8,900 people |
For scale, Wheatland had 3,588 residents at the 2020 census, and all of Platte County had 8,605.
Evidence label: APPLICANT STATEMENT. Both figures come from the developer and its consultant, not from an independent measurement. The records don’t say whether they cover the same facilities, phases or water uses, so they aren’t a low and high estimate of one thing. (Water)
Why 800 matters in Wyoming law
In Wyoming, 800 acre-feet a year is the point where the State Engineer has to weigh in. Under W.S. 35-12-108, an industrial siting applicant whose facility needs at least 800 acre-feet of Wyoming water a year gets a review from the State Engineer, the official who oversees the state’s water rights. The public can submit written comments in that review. A separate hearing is up to the agency.
That review only applies through the Industrial Siting process. If a project’s water use is exempted from Industrial Siting jurisdiction, the 800-acre-foot review may not happen. Other water-right and well-permit rules can still apply. (State oversight)
So the gap between 15 and 800 isn’t only about scale. One number falls far under the line, and the other sits right at it.
What we still don’t know
The records reviewed so far don’t answer any of these:
- Which figure reflects the current design, or whether both are still in play
- Where the water would come from: wells, a municipal supply, or purchased rights
- Whether there’s a cap on water use for the whole campus
- Which state permitting route the project will take, which decides whether the 800-acre-foot review applies
I’m tracking these in the DEQ records diary and on the Water page.
Sources
- Water Education Foundation: Acre-foot. 325,851 gallons; an acre is about the size of a football field.
- USGS: How much water do I use at home each day?. 80 to 100 gallons per person per day, indoors.
- Wheatland, Wyoming and Platte County, Wyoming, 2020 census populations.
- Wyoming Statutes Title 35, W.S. 35-12-108 and 35-12-119.
- State 44: Water and State oversight.
Olympic pool figure: about 660,000 gallons, a 50 m by 25 m pool at its 2 m minimum depth. The per-day and per-person figures are my own math from the numbers above.