At the January 13, 2026 Board of Mayor and Aldermen meeting, Alderman Whitmer asked the question that explains most of Thompson's Station's growth. Two more developments were about to buy into the next expansion of the town's wastewater plant. After those approvals, how many gallons were left?
According to the meeting minutes, Assistant Administrator Banks answered that "approximately 260,000 gallons would be remaining currently."
Thompson's Station's growth is measured in gallons per day. The town owns and operates the sewer capacity that new subdivisions and storefronts need, and it sells that capacity ahead of time, in reserved blocks. In 2026 it also put a fixed share aside for businesses that generate sales tax. If you are comparing towns south of Franklin, this gallon ledger explains more about when and where new homes appear than any acreage map.
Two small plants and a partial map
The town runs two systems. The Heritage plant sits at the end of Thompson's Ridge Road and serves the commercial area near the Heritage schools and Town Center. The Regional system sits near the Nutro Dog Park off Highway 31. The developers of Tollgate Village, Bridgemore Village and Fields of Canterbury built it in 2006, and the town later took over its management. The Regional plant is at 4549 Columbia Pike, went into service in 2005 and handles most of the town's flow.
The town's wastewater department says it serves only part of the town. The areas it lists are Allenwood, Avenue Downs, Bridgemore Village, Fields of Canterbury, the Heritage Commons Commercial District, Tollgate Village and Whistle Stop.
Two parcels with the same zip code, the same county and similar views can face completely different paths to development, depending on which side of the service-area line they sit.
How a gallon gets sold
Capacity is reserved through a written agreement, and since 2026 the deals have been large enough to show up in public records. At the January 13 meeting, the board approved memoranda of understanding that let two projects pay their full wastewater impact fees upfront, instead of a deposit, to lock in space in the Phase I plant expansion.
| Reservation, approved January 13, 2026 | Gallons per day | Wastewater impact fee |
|---|---|---|
| 1735 Old Thompson's Station Road, DYTMD, LLC | 31,250 | $1,404,835 |
| 2762 Critz Lane | 10,500 | $472,024.56 |
The DYTMD fee was due by July 13, 2026, or earlier if plans were approved. Whitmer noted that these were the third and fourth projects to buy into the next expansion, after St. John and GBT. At the same meeting the board passed Ordinance 2025-017, which raised wastewater impact fees and effluent disposal fees by 5.01% under a review the town holds every odd year.
Gallons are a cost a developer pays before a single foundation is poured. For a subdivision, that fee becomes part of the land basis, and it shows up later in what the finished home costs.
Why commerce gets a reserved share
Mayor Brian Stover said it plainly to WKRN in January 2025, while discussing the retail project that became Sagefield: "Sales tax revenue is what we live off of in this town."
The town's own audit backs him up. In fiscal year 2024–25 the town recorded $2,913,045 in local option sales tax and $535,594 in property tax revenue. It also collected $1,423,272 in governmental building permit and impact fees, plus $1,257,208 in wastewater impact fees. In a town funded mostly by sales tax, sewer capacity is how it builds its tax base.
The 2026 rules reflect that. At the January meeting, Administrator Wood said the town needs to protect its "economic development interests and ability to expand our tax base" given what it has invested in the wastewater system. Then on March 10, 2026, the board passed Resolution 2026-004. It replaced the old fixed reserve of 150,000 gallons per day for economic development, which had been used up, with a percentage of active capacity:
- 15% of active capacity reserved for nonresidential and economic development uses
- 2.5% reserved for emergencies and contingencies
Because the reserve is a percentage, it grows each time the plant grows. Every future expansion puts roughly one gallon in six beyond the reach of a residential subdivision before anyone files an application.
Sagefield shows the same priority from the other side. Its June 23, 2026 staff report describes a 496,366-square-foot, 16-building commercial project at 1733 Lewisburg Pike. Staff recommended approval on the condition that the developer pay $2,360,025 as a drip-field-in-lieu fee and $7,338,482 in wastewater impact fees, and that it build sewer improvements on Critz Lane. Those figures were recommended conditions, not recorded payments. In its July 23, 2026 coverage of the State of the Town address, WKRN reported that Sagefield was set to begin construction this year.
The process got faster in April
The other March change is about procedure. Ordinance 2026-002 moved capacity reservations from mandatory board review to staff review, unless an applicant asks to change the standard agreement. It applies to applications submitted after April 1, 2026. The board also approved an updated standard reservation agreement, Resolution 2026-007.
The ordinance sets a $250 minimum application processing fee and splits capacity into two types. "Active Capacity" is paid for and usable. "Inactive Capacity" holds a place in a future expansion but does not support planning or permit approvals. For anyone looking at land, this matters. A parcel can have a capacity reservation and still be years away from a building permit.
Residents inside the Regional service area can request a capacity reservation through the Community Development Department.
Outside the map, the rules come from the state
If a parcel is outside town sewer service, its options come from Tennessee's septic rules or from a developer-built treatment system.
The Tennessee Department of Environment and Conservation sends Williamson County septic applicants to the county and requires a septic permit before construction. If land is divided into two or more lots that will use septic, TDEC requires a subdivision evaluation with a survey and soils map. The exception is a division where every tract is at least five acres. The state subsurface sewage rule requires each septic lot to have room for the original system and a duplicate replacement area. It also sets out soil evaluation requirements, and a high-intensity evaluation of the subdivision, or of at least 20,000 contiguous square feet per lot, is one of the paths it allows.
Some properties use a third option. In a memorandum of understanding, the town said Robson Property Group's land at 2601 Tom Anderson Road was outside the Regional service territory and had no town capacity or foreseeable service plan. The town authorized a developer-installed Bio-Clere system of at least 15,000 gallons per day, with space to expand to 100,000. Once the town accepts the system, it controls the capacity and the connections.
Being inside the map does not guarantee a connection either. A self-storage facility at 4445 Columbia Pike is inside the Regional service map and holds a 9,350-gallon reservation. It was still waiting to connect, and in the meantime had approval for pump-and-haul service capped at 100 gallons per day until the new membrane plant was running.
All of this is general information about public rules. It is not legal, engineering or financial advice. If you are looking at a specific parcel, confirm its sewer status and septic feasibility with the town, the county and your own professionals.
Where the capacity count stands
The public record does not settle on one number. The town's project pages still describe both systems as "at capacity" and say the lagoon-to-membrane conversion is being designed, with permitted capacity rising from 470,000 to 1,000,000 gallons per day. WKRN reported that at the July 23, 2026 State of the Town address, Mayor Stover described a new $39 million wastewater system as complete and said it would keep the town ahead of growth. The March 2026 minutes refer to a 1.5 million gallon-per-day plant and a three-phase expansion to 3.3 million. The figures conflict, so a buyer should get the current capacity status of any specific parcel directly from Community Development.
What the gallon ledger means for prices
Advertised new construction in Thompson's Station currently starts at very different prices. Beazer's Parson's Valley advertises townhomes and single-family homes from $469,990. Drees advertises The Townes at Whistle Stop from $699,900. Phillips Builders lists homes in Tollgate Village at $924,900 and $944,900. Celebration Homes advertises a new Thomas Downs phase as coming soon, starting at $1.2 million.
For county-level context, Greater Nashville REALTORS reported 1,163 residential closings in Williamson County in Q3 2026, at a median price of $1,075,000. That is a countywide figure, not one for Thompson's Station alone.
New-home supply here does not respond to demand the way it would in a town with abundant sewer. Each new phase depends on a reservation, a fee paid upfront and a plant expansion. After the 2026 rules, it also comes after a 17.5% set-aside for commerce and emergencies. Supply arrives in batches as the plant grows.
Questions buyers ask about Thompson's Station sewer
Is my subdivision on town sewer? The town lists Allenwood, Avenue Downs, Bridgemore Village, Fields of Canterbury, the Heritage Commons Commercial District, Tollgate Village and Whistle Stop. Confirm any specific address with the town.
Can a capacity reservation be bought for a single lot? Residents in the Regional service area can request one through Community Development at (615) 794-4333, ext. 12. Standard requests submitted after April 1, 2026 go through staff review.
Does a reservation mean a lot is buildable? No. Under Ordinance 2026-002, inactive capacity holds a place in a future expansion but does not support planning or permit approvals.
If you are weighing a lot, a farm parcel or a new-construction phase in Thompson's Station, CHORD Real Estate can help you find out where that address stands on the town's capacity ledger before you make an offer. Request your personal Real Estate Concierge.
