Ground Water

Water

Most of the drinking water in the country starts as groundwater.  Rural areas use both dug wells and drilled wells to extract water from the ground.  Towns and cities with centralized water distribution use water systems with drilled wells to serve their residents.

Groundwater is simply water that is beneath the surface of the earth. It enters the ground through precipitation, and is stored in aquifers.  The water cycle describes the contiguous cycle of water on the planet, and how it enters the ground.

Dug Wells

Old fashioned dug wells tap the water by simply digging a hole deep enough to reach the water table. The hole is then lined with rock to prevent it from caving in. While cheap compared to drilled wells, there are some serious drawbacks.  The average depth of a dug well is less than 25 feet. This depth causes the wells to be highly dependent upon seasonal precipitation and the aquifer level to maintain an adequate supply of water.  Simply put, if it doesn’t rain, the water table falls, and the well runs dry.  If too many wells tap the local aquifer, the water table falls, and the well runs dry.

Obviously these types of wells do not work in areas where there is no aquifer within 25 feet (mountains), or in areas where there is simply no earth to dig into (solid bedrock).  There are also water quality considerations to consider with a dug well. The ground does an admirable job of filtering the water, but there just isn’t enough filtering taking place with wells the depth of a dug well thus allowing surface contaminants  to be present in the water. Road salt contamination is a particular danger in the Northeast.

Drilled Wells

Modern drilled wells are constructed by using a hydraulic rotary drilling rig.  The average depth of a drilled well in New Hampshire is approximately 360 feet.  The average length of casing required is 60 feet. A new well drilling rig today costs over $500,000  and it can take a crew of three individuals two to three days or more to complete the drilling of  a new well.  Our well drilling crew consists of two licensed, experienced drillers and one driller’s helper.  Three vehicles generally arrive on a drill site: the well drilling rig, the water service truck, and a one-ton vehicle that carries a small back-hoe to dig the mud pit, plus various tools and of course, lunch!

Once the well rig is set up over the specified site, a six inch hole is drilled into the ground until competent bedrock is reached.  Generally, the well driller will bore into this bedrock an additional 10 to 25 feet or more, depending on the hardness of the rock, before steel casing is set.  A drive shoe on the end of this casing has a hardened edge which protects the end of the casing, allowing it to be sealed properly into the drilled borehole. This process seals off the surface water that a dug well normally taps.  A smaller bit is then used to drill further into the bedrock.  Water in the bedrock is under static pressure that will seek its static level once the fractures in the rock are encountered. The flow of the well is determined by how many water bearing cracks and fissures are encountered. If enough water cannot be achieved with the drilling process, a technique called hydrofracturing is used to increase the yield.