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What Aquifers Supply Water Wells in North Texas?

Quick Answer

North Texas private wells draw from the Trinity aquifer (central/western) or the Woodbine aquifer (eastern counties). Depth, yield, and water quality differ.

Knowing which aquifer sits under your property is the fastest way to set expectations for how deep you’ll drill, what your water will be like, and what it will cost. Across the 19-county DFW service area, two aquifer systems supply almost all private wells — and they differ in where they’re found, how deep they run, and how they behave.

The Two Primary Aquifers

Trinity Aquifer System

The Trinity aquifer is a system of stacked Cretaceous-age sand and limestone formations that supplies wells across central and western North Texas. It is divided into three main productive units:

Trinity ZoneFormationTypical Depth in North TXWhat it means for your well
Upper TrinityPaluxy150–350 ftSandy limestone; drills faster
Middle TrinityGlen Rose250–500 ftDense limestone; drills slower
Lower TrinityTwin Mountains400–700+ ftCoarse sand and gravel; high-yield where reached

Water moves through the Trinity via pore spaces in the sand units and natural fractures in the limestone, so production is hit-or-miss by location: a fractured zone at 350 ft might give 10 GPM, while a tight zone at the same depth a county over gives under 1 GPM. An experienced driller watches the rock coming up as the hole deepens and can usually pick out the water-bearing intervals.

Counties primarily served by the Trinity aquifer: Wise, Cooke, Parker, Hood, Erath, Somervell, Denton (western), Tarrant, Johnson, Ellis, Grayson (western)

Typical Trinity water quality characteristics:

  • Hardness: High (200–400+ mg/L as CaCO₃) — limestone dissolves into the water
  • Iron: Usually low
  • Total dissolved solids: Moderate (300–700 mg/L)
  • Bacteria: Very low in properly constructed wells
  • Sulfur: Occasionally present, particularly in deeper zones

Woodbine Aquifer

The Woodbine aquifer is a Cretaceous-age sandstone formation beneath the eastern portion of North Texas. It sits apart from the Trinity and is generally shallower, and it behaves differently — water seeps through the tiny spaces between sand grains rather than through fractures in rock.

Counties primarily served by the Woodbine aquifer: Collin (eastern), Grayson (eastern), Fannin

Woodbine aquifer characteristics:

  • Depth: Typically 100–300 ft
  • Yield: 5–20 GPM in productive zones
  • Drilling cost: Lower — sandy formation drills faster and requires less bit wear
  • Screen required: Yes — sand wells require a well screen to let water in while keeping formation sand out
  • Hardness: Moderate
  • Iron and manganese: Often elevated — the most common water quality treatment issue

Nacatoch Aquifer

The Nacatoch Sand is a Cretaceous-age formation along the eastern edge of the service area. It is the primary local aquifer in Hunt and Navarro counties, where the Trinity lies too deep and the Woodbine is thin or saline. The Nacatoch is a TWDB-designated minor aquifer of alternating sand and clay. Yields are modest and water can be moderately mineralized. In far southeastern Navarro County, a small portion of the Carrizo-Wilcox aquifer enters the picture.

CharacteristicTrinityWoodbine
Typical depth (North TX)200–700 ft100–300 ft
Drilling cost per footHigherLower
Typical yield3–15 GPM5–20 GPM
Water hardnessHighModerate
Iron contentLowModerate to high
Well screen neededUsually notYes
Drought vulnerabilityModerateLower (large storage volume)

How Aquifer Geology Shapes the Well

Trinity wells bore through hard limestone that may stay dry until the bit reaches a fracture. A driller can go hundreds of feet with no water, then hit a crack that fills the casing quickly. Some Trinity wells are finished open-hole — left uncased at the bottom — because the limestone is solid enough to hold the borehole open without a screen.

Woodbine wells drill through sand that starts giving water near the top of the productive zone. A stainless steel wire-wound screen goes in at the base of the casing to let water flow while keeping sand out, and its slot size is matched to how fine the Woodbine sand is at that depth.

GCD Management by Region

Aquifer protection in North Texas is handled by Groundwater Conservation Districts (GCDs) organized by county, not by aquifer:

GCDCountiesAquifer(s) Managed
North Texas GCDCollin, Denton, CookeTrinity and Woodbine
Upper Trinity GCDWise, Parker, HoodTrinity
Prairielands GCDJohnson, Ellis, SomervellTrinity
Northern Trinity GCDTarrantTrinity
No GCDHunt, Kaufman, Navarro, Rockwall, Palo Pinto, othersNacatoch, Woodbine, Trinity (varies); TDLR-only

In counties without a GCD, a licensed TDLR driller is required but no pre-drill permit is needed.

What to Expect from Your Aquifer

If you’re planning a new well, your driller pulls the TWDB well-completion reports from nearby properties to see which aquifer zone produces best at your location and what depth to target. Knowing your aquifer up front sets realistic expectations for water chemistry and points to the right treatment system.

DFW Well Service drills into both the Trinity and Woodbine aquifer systems throughout the 19-county service area. Call (940) 536-8560 to discuss which aquifer underlies your property.

Frequently Asked Questions

What aquifers supply water wells in North Texas?
Two underground water layers supply almost every private well in North Texas, and which one sits under your property sets your likely depth, water quality, and cost. The first is the Trinity aquifer system — the water-bearing rock that wells tap — a stack of Cretaceous formations that includes the sandy Paluxy, the Glen Rose limestone, and the sandy Twin Mountains. The second is the Woodbine aquifer, a Cretaceous-age sandstone layer beneath eastern North Texas. The Trinity is the primary source in Wise, Cooke, Parker, Hood, Erath, Denton (western), Johnson, Ellis, and Somervell counties. The Woodbine is the primary source in Collin, Grayson, and Fannin counties. In Hunt and Navarro counties, the primary local aquifer is the Nacatoch Sand, not the Woodbine. In Kaufman the Trinity lies deep and groundwater is limited, and Rockwall has no aquifer rated for residential supply — its state groundwater planning value is effectively zero.
What is the Trinity aquifer?
The Trinity aquifer is the main groundwater source across central and western North Texas — a system of stacked Cretaceous-age formations. For your well, that usually means reaching a productive zone somewhere between 200 and 700 ft, with deeper wells in Hood and Erath counties. The system has three main zones: the Paluxy (shallowest and sandy), the Glen Rose (a harder limestone at moderate depth), and the Twin Mountains (the deep zone — coarse sand and gravel, and the highest-yield unit where it's reached). Water moves through pore spaces in the sand units and through fractures in the limestone, so yield depends on hitting a productive zone.
What is the Woodbine aquifer?
The Woodbine aquifer is a sandy, Cretaceous-age formation beneath the eastern portion of North Texas. It is the primary aquifer in Collin, Grayson, and Fannin counties. It also underlies Kaufman and Rockwall, but mainly at depth and with poorer water quality. In Hunt and Navarro, the shallower Nacatoch Sand — not the Woodbine — is the main local source. Because it is sand rather than limestone, the Woodbine drills faster and cheaper than the Trinity and usually produces 5–20 gallons per minute (GPM) from productive zones at 100–300 ft. The water is generally good, though it often carries elevated iron and manganese — the most common thing Woodbine well owners end up treating for.
Which aquifer has better water quality?
Neither one is better — they're just different, and your test results should drive treatment, not the aquifer name. Trinity limestone wells tend to have very hard water (high calcium and magnesium), slightly elevated total dissolved solids (TDS, a measure of how mineral-heavy the water is), and low iron. Woodbine sand wells usually show the reverse: lower hardness but elevated iron and manganese. Because the chemistry is specific to your well, treatment is matched to your actual test results, not to a general rule about the aquifer.
Are the Trinity and Woodbine aquifers regulated differently?
No — the rules follow geography, not which aquifer you drill into. Permitting is handled by Groundwater Conservation Districts (GCDs), the local districts that permit and oversee wells, and each district covers a set of counties regardless of aquifer type. The North Texas GCD, for example, manages both the Trinity and the Woodbine across Collin, Denton, and Cooke counties, while the districts in Hood and Erath counties oversee mostly Trinity production. So what sets your permit requirements is whether your county has a GCD, not whether you are tapping the Trinity or the Woodbine.
Are there other aquifers in North Texas besides the Trinity and Woodbine?
Yes, a few — they're just targeted less often. The biggest is the Nacatoch Sand, which is actually the primary aquifer in Hunt and Navarro counties on the eastern edge of the service area. Palo Pinto County draws from the Cross Timbers Aquifer (Pennsylvanian sandstone and limestone), typically at 100–450 ft. Shallow alluvial aquifers — water held in loose sand and gravel along the Trinity, Red, and Brazos river valleys — carry some water but sit too shallow and too exposed to surface pollution to serve as a reliable home supply. Farther west and northwest you reach the Seymour aquifer, and south of the service area the Edwards-Trinity Plateau aquifer extends into the Hill Country.

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