Types of Water Wells- Bored Wells

From Royal Pump and Well VA

There are two main types of modern wells, they can  often be distinguished by the diameter of the bore hole. The two types are bored wells and drilled wells. There has been a shift towards well regulations and drilled wells in the past couple of decades, but in areas of the Appalachian Plateau and other locations where clean low yielding groundwater sources are found relatively close to the surface- usually under 100 feet below grade.

Bored wells get their name from the way they are constructed. Bored wells are constructed using a rotary bucket auger. They are usually completed by installing a perforated casing (also called cribbing) or using a sand screen with continuous slot. One advantage of bored wells is the large diameter of the casing, from 18-36 inched. It provides a water storage reservoir for use during peak demand periods. A disadvantage of utilizing a shallow groundwater aquifer is that it generally relies on annual precipitation for recharge. So these systems are often installed with an additional cistern to ride out water shortages may occur following long dry periods in summer and extended freeze up during winter months. It can also be more susceptible to contamination from surface land-use activities.

As opposed to the 6 inch diameter drilled wells, bored wells are generally used where the groundwater aquifers are both shallow and low-yielding. Typically, I see bored wells with between 0.5-1.0 gallon per minute yield. Though, I have heard of bored wells in Goochland with up to 5 gallons a minute. A well that yields only 0.5 gallon per minute will provide 720 gallons per day which is more than enough for a household. Bored wells range in depth from 30 feet to 100 feet. To compensate for the low-yield of the aquifer, large diameter bored wells serve as storage reservoirs to provide water during periods of high demand. A bored well with a diameter of 3 feet provides 53 gallons of water storage per foot of depth.

Because they are shallow, bored wells are susceptible to both contamination and drought. This is why they are falling out of favor. A large protected land area and proper location of the well reduces the possibility of contamination. A well should be higher than the surrounding ground surface for good drainage. All possible sources of contamination should be at a lower elevation than the well, and the distances to those contamination sources must comply with local Water Well Construction Codes but should be 100 feet from septic tanks and leach fields to be safe. Tests performed in the past have shown that bacterial contamination is usually eliminated after water has filtered through 10 feet of normal soil. Therefore, the well must be constructed to ensure that at least the top 10 feet of casing is watertight.

There is more than one approach to boring a well and several design variations. Bored wells can be completed with either jet or submersible pumps. They can also be completed with a technique called buried slab. With this method, there is a smaller upper well casing that is 4-8 inches in diameter and may or may not be exposed. This smaller well casing extends 10 feet or more feet below the ground surface and is embedded in a hole that is formed when the reinforced concrete buried slab is manufactured, or connected to a pipe cast in the concrete slab. This type of well can be confused with a drilled well. In other designs the concrete casing that ranges in diameter from 18 inches to 3 feet extends to the surface and the lining is sealed with grouting to at least 10 feet below grade and the pitless adapter is below that as seen above.