Geology of Northeast Texas

Geology of Northeast Texas

Water wells across Northeast Texas draw their water from beds of sand. The beds of sand are saturated with water, usually under artesian pressure, and the water travels through the pours of the sand bed. These beds of sand are found in a number of clearly defined formations and vary in color, coarseness, thickness, cohesion and purity. Water quality can also vary hugely from one formation to another, and even in the same formation from one location to another. A given formation has many individual layers of sand that interconnect with one another. The individual layers or "lenses" of sand begin, taper thicker and then thinner somewhat in the shape of a magnifying glass laid horizontally in the ground. This is why in one location a person may complete a well at a certain depth, and just a mile away a well into the same aquifer may be at an entirely different depth. Most wells drilled in Northeast Texas are drilled into the formations described below. Hardness is not mentioned much as it is very seldom a problem in any of the formations discussed. On the extreme edges of Northeast Texas there are some other aquifers which are not detailed here. All of these formations outcrop (rise to the surface) in various areas of the Northeast Texas area and taper away. If you live in an area where these aquifers are not present, call us and we can inform you of what aquifers may exist in your location.

Starting at the top of the ground, the formations typically encountered are as follows:

Sparta Formation

The Sparta Formation is not present across all of Northeast Texas, but rather is found typically at the relatively higher elevations of given areas as a cap over other formations. Through time the terrain eroded away from these high points, and the formation tapered thinner and thinner toward valleys and creek beds until it reached the harder more consolidated underlying Weches or Queen City Formations. The Sparta consist primarily of loose unconsolidated fine to coarse, light colored sand lenses intermingled with light colored clays (white, yellow, salmon, red). In places where the formation has enough depth, good to fair quality water can be found in useful quantities. The Sparta varies in thickness up to 280' thick where present, but is seldom deeper than 120'. Usually water from the Sparta Formation is low in iron, although there are exceptions, and the pH is typically 4.5 to 5.5 - quite acidic. Commonly the iron levels are low enough for residential use without the necessity of an iron filter, but the pH is a problem wherever copper or galvanized plumbing is used. An acid neutralizer filter can be used to correct the pH problem, but a by product of the acid neutralizer is added hardness to the water. Plastic plumbing handles this water nicely without filtration. Sparta water is also suitable for irrigation and pond maintenance. Contact C. Miller Drilling to find out whether the Sparta Formation may be present at your proposed drilling site. When drilling through the Sparta in search of deeper formations, sometimes surface casing is necessary to case off the sands and prevent hole collapse.

Weches Greensand Formation

The Weches Formation, the next formation under the Sparta, is usually about 60' thick and consist principally of interbedded glauconite, glauconitic clay, and sand. The Weches Formation typically is not considered a viable source of water for water wells, and is significant only in that it acts as an impermeable base the Sparta Formation. Like the Sparta formation, the Weches is often not present at all.

Queen City Formation

The Queen City Formation, under the Weches (if present), consist mostly of thick bedded to massive crossbedded very fine to fine quartz sand that is interbedded with silt and clay. Stringers of lignite and clay are present in the upper portions of the formation and layers of shale are found deeper in the formation. The maximum thickness of the formation is about 400' thick, but it is typically 200' to 300' thick. Small to moderate amounts of water are available to wells in the formation, but high iron content is the rule in the Queen City, as well as acidic pH. As always there are occasional exceptions to the rule. The sands, clays and shales in the formation vary from light grays to medium and dark clays. Typically the darker the sands, the higher the iron content. Iron filtration is an option, but when the cost of a good iron filter is added to the cost of the well, it is commonly as expensive or nearly as expensive as the cost of a well drilled deeper into the Carrizo or Wilcox Formations which might not require filtration. There is of course a value to be attached to not having to keep an iron filter operational. Water in this formation is useful for irrigation and pond maintenance where no filtration is involved.

Reklaw Formation

The Reklaw Formation, under the Queen City, consist of a layer of dark silty shale typically 30' to 40' thick over a layer of dark gray to green, very fine glauconitic silty sand typically 20' to 30' thick for a total formation thickness of 50' to 70', but is up to 130' thick in certain areas. The shale layer is important in that it provides an impermeable separation between the Queen City Formation and the Carrizo Formation. The Formation is not considered a source of water to water wells.

Carrizo Formation

The Carrizo Formation, under the Reklaw, consist largely of white to light gray, fine to medium quartz sand. However, small amounts of silt and clay are present in the upper part of the formation. The Carrizo yields small to moderate quantities of water to wells. In certain areas, Carrizo water has an acidic pH, and where the acidic pH is found, usually iron content problems are found. In other areas the Carrizo waters are alkaline in pH and have very low iron contents. Hardness is very seldom a problem. C. Miller Drilling's experience can help you determine where it is a good bet to complete a well into the Carrizo, and where it would be a better bet to continue deeper into the Wilcox Aquifer. Typical thickness of the Carrizo is 50' to 100', but is up to 150' thick in some places and in other places is mostly shale so as to not be detectable. Water found in the Carrizo is typically hundreds of years old, having entered the ground before there were any man made chemicals around to pollute.

Wilcox Formation

The Wilcox Formation, under the Carrizo, is the principle source of good quality ground water across Northeast Texas. The Wilcox varies in thickness from 0' in the extreme outcrop area (where it is at ground level), but typically 400' to 960' thick where it is not outcropped. The formation consists of cross-bedded layers of shale, lignite and sand with intermingled combinations of these layers. Medium to very fine quartz sands constitute about half of the Wilcox. Individual layers of sand are generally not thick, but some beds are as much as 70' thick or more. Since the Wilcox is comprised of several layers of sand and shale, wells are not usually drilled to the bottom of the formation, but rather they are drilled to the bottom of one or more of the sand layers in the formation. Sands and shales in the Wilcox are typically light gray in color. Like the Carrizo, the water in the Wilcox is typically hundreds or thousands of years old, having entered the ground at a time when there were no man-made chemicals to pollute. Water in the Wilcox is usually very low in iron and hardness and has an alkaline pH. The Wilcox Aquifer is generally accepted as the best choice for installation of water wells where the most palatable water available is the goal of the project. Quantities of water are usually sufficient to meet typical project needs.

Midway Formation

The Midway Formation begins at he bottom of the Wilcox, and consists mainly of calcareous clay and is impermeable in nature. The formation is not considered a source of water for water wells. The formation is significant as it is typically considered the bottom of available fresh water zones throughout most of Norteast Texas.

While the Wilcox is generally accepted to be the best choice for installing a well where the most palatable water possible is the goal of the project, there are certain areas where the deeper portions of the Wilcox contains water that is high in Sulfides, Chlorides and/or sodium. There are also areas where the Wilcox contains iron at problematic levels and acidic pH. Chances are we have drilled wells near your location and have experience about the water quality in the Wilcox near you. If you want more information about the probable water quality of the Wilcox in your location, give us a call and we'll be glad to help.