The Hidden Jewel
Groundwater Resource Evaluation
Groundwater is the source of drinking water for more than fifty percent of North Carolina’s population and it provides water for nearly one hundred percent of homes in rural areas of the state. This important water resource can typically be utilized without treatment and represents one of our most vital natural resources. Because groundwater is found below ground, it is a hidden resource that is often poorly understood. Preservation and protection of the quality and quantity of groundwater resources forms a major segment of the professional services the geologists and hydrogeologists of Northwest Geoscience provide our clients. These services typically entail the identification and assessment of sources of groundwater pollution and the development of remedial programs to restore the quality of an impacted groundwater system. These services restore groundwater quality so that a safe and dependable water supply is preserved for the public. We also work with water suppliers, engineers and well contractors to find and develop groundwater resources for domestic, industrial and municipal users.
North Carolina’s groundwater typically occurs in two geologic environments that determine the suitability of the water based on the quantity and geochemical characteristics affecting its potability. The area east of the Fall Line is made up of unconsolidated sediments of the coastal plain. These materials form a series of gently dipping geological formations that lay vertically one on top of the other and are classified as aquifers or aquitards based on their geologic nature. Aquifers consist of coarser grained materials such as sand or shell beds which contain vast quantities of water, whereas aquitards consist of mud and clay that form units that confine aquifers on the top and bottom. The confining action forces the water in the aquifer to be pressurized so that it rises above the top of the geologic unit. Regional aquifer systems such as the Castle Hayne Formation can yield hundreds of gallons per minute (gpm). The chemical character of the water in the coastal plain tends to be slightly hard, and in some areas may contain objectionable concentrations of iron and sulfur that require treatment prior to use. Special measures to restrict extremely high quantities of water from being removed from some of the aquifers near the present day coastline are needed to prevent salt water from entering the aquifer from off-shore.
Groundwater in the piedmont and mountain regions occurs in the shallow regolith and weathered rock zone above bedrock. The bedrock is fractured to depths of approximately 500 feet. These two zones form what is known as the reservoir-pipeline aquifer system. In the shallow aquifer, water is contained within the pores between the individual soil grains; in the bedrock zone, the fractured rock acts as a system of pipelines that transmit the groundwater along zones of weakness. Groundwater yields in the piedmont and mountain region rarely exceed 100 gpm and most individual domestic wells typically yield only between 3 and 10 gpm. The quality of water in this region is typically soft and slightly aggressive. In some areas it may have elevated concentrations of iron, but these rarely require treatment. Industrial and municipal groundwater systems often provide excellent quality water supplies where quantities less than 100,000 gallons per well are sufficient. In small communities and towns, multiple wells can often provide upwards of a million gallons of water per day. Historically, areas where adequate surface water supplies are available have tended to overlook the reliability of groundwater due to the conceived higher reliability of a water source that can be seen.
Our staff has performed groundwater resource evaluations in all areas of the state and has assisted engineering firms in drilling test wells, performing pumping tests, evaluating geophysical logs and assessing water quality as the initial tasks in the design and construction of industrial and municipal well systems. We have worked directly with well contractors in supervision of well construction, assessing declining well yields and water quality problems. Major municipal well construction projects include development of a wellfield at Bald Head Island, a deep fractured rock well for the Town of Banner Elk, four individual municipal wells in the coastal plain at the South Mills Water Association, and bedrock wells for the Town of Liberty.