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Spring Hill, TN · French Drain Specialists

Local Guide · Williamson County TN

Maury Silt Loam Drainage in Williamson County

Why the fragipan layer beneath every Spring Hill and Thompson's Station yard creates chronic drainage problems, and what an actual fix looks like.

If you live in Spring Hill, Thompson's Station, Columbia, or the rural areas of southern Williamson and northern Maury County, the dominant soil under your home is almost certainly one of three closely related silt loam series: Maury, Mountview, or Dickson. All three look essentially the same at the surface. All three behave the same way after rain. And all three are the reason yards here stay soggy long after the storm has passed.

The common factor is a layer called a fragipan. This guide explains what the fragipan is, why it matters, how to confirm it is on your property, and what kind of drainage system actually works on top of it.

What the Fragipan Is

A fragipan is a dense, slowly permeable subsurface soil horizon. In Maury silt loam it typically appears between 18 and 30 inches below the surface. The topsoil and the upper subsoil drain at a normal rate (1 to 2 inches per hour of vertical infiltration). The fragipan drains at 0.06 to 0.20 inches per hour, roughly an order of magnitude slower. Once water reaches the fragipan, it effectively stops moving downward and starts moving sideways.

The fragipan formed naturally over thousands of years as fine silt and clay particles migrated downward through the soil profile and accumulated in a thin band. The accumulation cemented the soil grains together, creating the dense layer. It is not compacted by anything humans did. It is part of the natural soil profile of the Outer Central Basin and the Western Highland Rim transition zone where Spring Hill sits.

You can verify the fragipan in your soil with the USDA's public soil survey tool: USDA Web Soil Survey. Enter your address, draw a small Area of Interest around your house, and pull up the Soil Properties report. Look for the Fragipan field in the Restrictions section. For most Spring Hill addresses, it shows a depth between 18 and 30 inches.

Why It Causes Drainage Problems

When a 2 inch rain hits a Maury silt loam yard, the topsoil absorbs the water at a normal rate for the first 30 minutes or so. The water moves downward until it reaches the fragipan. There it stops. The topsoil above the fragipan starts to fill with water from the bottom up. The yard turns to mud.

The water then begins to move sideways through the saturated topsoil layer, following any slope that exists at the surface. It heads toward the lowest point on the property, often a yard corner, a swale between two houses, or a foundation wall on the downhill side of the structure. If the foundation is on the downhill side, the water pools against the wall and starts to exert hydrostatic pressure.

Three things happen next. First, the yard stays muddy for several days as the trapped water slowly evaporates and slowly seeps through the fragipan. Second, foundation walls and crawlspace floors see persistent moisture against them, which over time degrades any waterproofing and accelerates cracking. Third, the wet-dry cycling around the foundation contributes to differential soil movement that can crack walls, stick doors, and ultimately require structural repair.

Why a Surface-Only Fix Does Not Work

Many homeowners try surface re-grading, downspout extensions, or shallow swales as a first attempt. These work when the only drainage problem is surface water from inadequate grading or downspouts that discharge against the foundation. They do not address the trapped subsurface water above the fragipan because they do not reach it.

A French drain at 12 inches deep (which is the depth a casual contractor might quote) does almost nothing on Maury silt loam. The trench sits entirely within the topsoil, well above the fragipan. The water trapped beneath the topsoil cannot reach the pipe because it has no path through the dense layer.

What Actually Works

The trench needs to reach to or below the fragipan. For typical Spring Hill yards that means 24 to 36 inches deep. The perforated pipe sits in the gravel envelope at that depth, where the trapped water can flow into it. The pipe routes to a daylight outlet that bypasses the fragipan entirely, often on a downhill property edge where the elevation difference allows gravity flow.

Where a daylight outlet is not possible, the pipe terminates in a sump pit with a primary pump and a battery backup. The pump moves the water to a discharge point on the surface, well clear of the foundation. The total system handles both the trapped subsurface water and the surface ponding it caused.

See our French drain installation page for the full process, or the cost guide for typical project pricing.

Related Local Soil Notes

The University of Tennessee Extension provides agronomic information on fragipan soils and drainage management at UT Extension drainage publications. The publication is focused on agricultural settings but the soil mechanics are the same for residential drainage.

For neighborhood-specific context, see our service pages for Thompson's Station and Columbia, both of which share the same soil profile as Spring Hill.

FAQ

What is a fragipan?
A fragipan is a dense, compacted subsoil horizon that occurs naturally in many middle Tennessee soils. It looks like normal subsoil but it behaves almost like a clay cap: water moves through it at a small fraction of the rate it moves through the topsoil above. In USDA Web Soil Survey terms, the fragipan in Maury, Mountview, and Dickson silt loam soils is described as having very slow permeability, typically 0.06 to 0.20 inches per hour.
Which Williamson County soils have a fragipan?
The major Outer Central Basin soils all have one. Maury silt loam, Mountview silt loam, and Dickson silt loam are the most common in the Spring Hill and Thompson's Station area. All three develop a fragipan at depths typically between 18 and 30 inches. Some areas of Hampshire silt loam, common further south into Maury County, also show fragipan characteristics.
How do I know if my Spring Hill yard sits on fragipan soil?
Two ways. First, look up your parcel on the USDA Web Soil Survey. It returns the soil series for any address in the country. If your soil is Maury, Mountview, Dickson, or Hampshire silt loam, you have fragipan. Second, the symptoms are diagnostic. If your yard stays soggy for 24 to 72 hours after a 2 inch rain, has chronic wet patches that re-appear every spring, or shows water at the foundation after storms, fragipan-driven drainage is almost always the cause.
Can drainage problems be fixed without dealing with the fragipan?
Mild surface ponding problems can sometimes be fixed by re-grading and adding catch basins, without touching the fragipan layer. Subsurface saturation problems require cutting through or below the fragipan to give the trapped water a path out. There is no surface-only fix for fragipan-driven saturation. The trench needs to physically reach to or below the impermeable layer.
Why don't drainage contractors elsewhere talk about fragipan?
Fragipan layers are not universal. Dallas-Fort Worth has Blackland Prairie clay. Houston has expansive Beaumont clay. The Atlanta and Charlotte areas have Cecil red clay. Each of those creates its own drainage challenges but the mechanism is different from a fragipan. A national drainage contractor may not know the specific fragipan technique unless they have worked in the Outer Central Basin or similar geographies (parts of southern Indiana, central Kentucky). Local Spring Hill contractors who have worked here for years usually know it instinctively.
Does the fragipan affect new construction differently than older homes?
Yes. New construction in former pasture often skips a drainage plan entirely because the developer is not building on the lot and the builder follows minimum grading codes. The fragipan does not care about lot lines: the moment the topsoil is disturbed and re-graded, water paths change. Many new Spring Hill subdivisions develop drainage problems in the first or second rainy season after move-in. Older homes have already encountered any problems and either have a fix in place or have shown what the symptoms look like.
Think your yard sits on fragipan soil?

We'll come walk the property, look at the soil profile, and tell you straight whether a French drain at fragipan depth is the right fix. Free, no obligation.

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