Rutherford County Septic Systems: The Soil and Growth Numbers

Last reviewed 2026-07-25. Journalists, researchers, and community groups are welcome to cite any figure on this page with attribution and a link.

Rutherford County is one of the fastest-growing counties in Tennessee, and it sits on karst limestone where soil runs shallow to rock. This page collects the verified figures behind both of those statements: population and growth from the Census Bureau, soil depths from USDA, and the thresholds written into the state's own soils handbook.

We maintain this page as a public reference and welcome citation. Every number below is attributed in the sentence that uses it and linked to its primary source at the bottom.

Growth: a county adding people faster than the state

The Census Bureau's QuickFacts page for Rutherford County puts the population at 386,352 as of the July 1, 2025 estimate, 13.1 percent higher than the 2020 count. Tennessee as a whole grew 5.8 percent over that same stretch. Murfreesboro accounts for a large share of it: the city stands at 171,178, an increase of 18,353 residents since 2020. Rutherford is the fifth-largest county in Tennessee by population.

The Tennessee State Data Center at the University of Tennessee's Boyd Center reports that Rutherford County added 6,266 residents in 2025, the second-largest numeric gain of any county in the state. Growth like that means new houses, and outside the sewered areas a new house means a new subsurface system. One thing we want to be clear about: there is no published count of septic households in Rutherford County, so this page does not offer one and does not estimate a share from the population figures above.

The 36-inch line in TDEC's soils handbook

The Tennessee Department of Environment and Conservation, Division of Water Resources, publishes the Soils Handbook of Tennessee for subsurface sewage disposal. Among the conditions it lists that disqualify soil from percolation testing are soils with insufficient depth to rock, given as less than 36 inches in karst and less than 30 inches in non-karst areas, along with areas occupying the bottoms of sinkholes. Rutherford County is karst. That 36-inch figure is not a guideline about performance. It is the point at which soil is disqualified from the test that decides whether a conventional field goes in at all.

Now put that next to the soil. The USDA Natural Resources Conservation Service publishes Official Soil Series Descriptions, and two of them were type located in Rutherford County, Tennessee. The Barfield series runs 8 to 20 inches to limestone bedrock. The Talbott series runs 20 to 40 inches. Barfield sits entirely below TDEC's karst threshold and Talbott straddles it, with its shallow end below the line. Two soil series named from and defined by this county describe ground the state's own handbook treats as marginal or disqualifying. The comparison in the table is ours; the depths and thresholds are theirs.

Depth ranges come from the USDA NRCS Official Soil Series Descriptions. Thresholds come from TDEC's Soils Handbook of Tennessee. The comparison between them is ours.

What USGS has measured in this ground

The US Geological Survey described the underlying condition plainly in Water-Resources Investigations Report 97-4097: the thin soils of the Central Basin offer little or no resistance to infiltration of contaminants above the bedrock surface. Rutherford County sits in the Central Basin. For a drain field, soil depth is not a detail. Soil is the treatment medium, and the shallower it runs, the less of it there is to do the work between the drain lines and the rock underneath. A conventional field is not a pipe to somewhere else. It is a slow handoff to the ground, and the ground has to be deep enough to accept it.

A second USGS study, Scientific Investigations Report 2005-5281, mapped sinkhole flooding in the Murfreesboro area and covered 78 sinkholes across approximately 144 square miles. Two things to be precise about. That study counted sinkholes and examined flooding; it did not count septic systems and makes no claim about them. And TDEC's disqualification for areas occupying the bottoms of sinkholes is a siting rule about where a field may go, not a statement that sinkholes damage existing fields. Both facts are useful. Neither one supports the dramatic version you sometimes see repeated.

Pumping intervals: recommendations, not requirements

There is no pumping interval in Tennessee's subsurface sewage disposal rule, 0400-48-01-.13. Anyone telling you the state requires a pump-out every so many years is repeating something that is not in the rule. What does exist is guidance. The Tennessee Department of Health recommends pumping a septic tank every four years. The US Environmental Protection Agency recommends every three to five years for a typical household system. Both are recommendations, and neither carries the force of a state pumping mandate.

Neither recommendation is adjusted for local geology, because both are written for a general audience. Our own reading, offered as judgment and not as a source, is that ground described by an 8 to 20 inch soil series and a 36-inch disqualification threshold argues for the shorter end of the EPA range rather than the longer. A tank pumped on schedule protects the drain field, and on shallow soil over limestone the drain field is the part with the least margin to spare.

What this page does not claim

A citable page is only as good as the things it refuses to say. Several numbers that circulate in this industry could not be verified for Rutherford County, so they are absent here on purpose:

• No count or percentage of county households on septic, because no published figure exists and estimating one from population would be invention.
• No septic failure rate, and no count of failing or failed systems anywhere in the county.
• No count of permits issued for new subsurface sewage disposal systems.
• No groundwater contamination incident count, and no claim tying a specific contamination event to septic systems here.
• No claim that sinkholes swallow drain fields, and no count of systems affected by them, because the USGS study counted sinkholes and studied flooding.

Sources & Methodology

Every figure above was taken from the primary sources below (accessed 2026-07-25). Where a number is derived (arithmetic on published figures) or covers a broader period or area, the text says so.

1. US Census Bureau QuickFacts, Rutherford County, Tennessee — population 386,352, 13.1 percent growth since 2020, Murfreesboro 171,178
2. Tennessee State Data Center, UT Boyd Center for Business and Economic Research — 6,266 residents added in 2025, second-largest numeric gain in the state
3. TDEC Division of Water Resources, subsurface sewage disposal systems and the Soils Handbook of Tennessee — karst and non-karst depth-to-rock disqualifications, sinkhole bottoms
4. USDA NRCS Official Soil Series Descriptions, Barfield series — 8 to 20 inches to limestone bedrock, type located in Rutherford County
5. USDA NRCS Official Soil Series Descriptions, Talbott series — 20 to 40 inches to limestone bedrock, type located in Rutherford County
6. USGS Scientific Investigations Report 2005-5281, sinkhole flooding in the Murfreesboro area — 78 sinkholes across approximately 144 square miles
7. USGS Water-Resources Investigations Report 97-4097 — thin soils of the Central Basin and infiltration above the bedrock surface
8. US EPA, How to Care for Your Septic System — three to five year pumping recommendation