Monday, July 6, 2009

Private Drinking Well Components

Ground water is ubiquitous. About 15% of American households get their drinking water from private wells the majority of these wells are drilled wells that penetrate about 100-400 feet into the bedrock. To provide a reliable supply of water, a drilled well must intersect bedrock fractures containing ground water and recharge at a rate greater than the typical domestic demand of 5-10 gallons per minute. There are two types of pumps; a jet pump and a submersible pump. Most modern drilled wells are built with a submersible pump so that the ground water is not exposed to potential contaminants before it reaches your home. This is accomplished by utilizing a pitless adapter within the well. This adapter is designed to provide a sanitary seal at the point where the discharge water line leaves the well to enter your home. The device attaches directly to the casing below the frost line and provides a watertight subsurface connection, protecting the well from frost and contamination. In older pump installations, above ground jet pumps were often used, which potentially allowed the introduction of contaminants at the surface concrete well cap.

The essential components of a modern drilled well system are: a submersible pump, a check valve (and additional valve every 100 feet), a pitless adaptor, a well cap, electrical wiring including a control box, pressure switch, and interior water delivery system. There are additional fittings and cut-off switches for system protection, but the above are the basics. To keep the home supplied with water the system and well must remain operational. The components within the basement provide consistent water pressure at the fixtures. The pump moves water to the basement water pressure tank, inside the tank is an air bladder that becomes compressed as water is pumped in. The pressure tank moves the water through the house pipes so that the pump does not have to run every time you open a faucet. The pressure tank maintains the water pressure between 40-60 psi. After the pressure drops to 40 psi, the switch turns on the pump and the pressure in the tank increases. The 40 psi can feel a little anemic.

The submersible pump is a long cylindrical unit that fits within the 6 inch diameter well casing. The bottom portion consists of the sealed pump motor connected to a series of impellers separated by a diffuser that drives the water up the pipe to the plumbing system through the pitless adaptor and a pipe that runs from the well beneath the ground to the basement. Submersible pumps are more efficient than jet pumps and should last longer, but silt, sand, algae and excessive mineral content can impact their life. A submersible pump operating in low-sediment water may have a 15 year life while the same pump in high sediment water and without adequate sediment and check valve protection may fail in 5 or 6 years. The sediment and mineral content in groundwater acts as an abrasive that wears out the pump bearings and other moving parts and causes the pump to fail prematurely. The check valves will protect the water pump from loss of prime and having to work as hard each time the pump is activated.

For the plumbing system to function properly, the recharge rate in the well would have to equal at least the pump rate. The recharge rate or the well recovery rate is the rate that water actually flows into the well through the rock fissures. If the well can not recharge at the same rate at which water is being removed than the well, the system would suffer intermittent episodes of severe water pressure loss. The information on your wells performance can be obtained from the water well completion report on file with the department of health. The “stabilized yield” is the recharge rate. Since, water quality and water supply were primary selection criteria in my home search, my recharge rate is huge. I have a very strong well. However, the water pressure in the house is only adequate with either one shower running or the utility sink, tub and shower. A water pressure loss can result from a pump that is too small for demand, inadequate or a failing pressure tank, or a buildup of scale in the pipes. For example, if pressure was reduced when additional demand - turning on the dishwasher when someone was taking a shower that would be an indication that the water supply (either the pump or recharge rate) is inadequate for the household demand. Though, the pressure tank can smooth small flow demands, it cannot compensate for flow greater than the pump or well capacity. So a system that seems to have not quite strong enough pressure at all times, but continues to perform in that range while multiple faucets or plumbing draws are on-going could have a pressure tank problem.

If the system is working properly and there is adequate pressure in the pressure tank possible solutions to a water pressure problems are to install a constant pressure valve between the pump and the pressure tank. This is a relatively simple and cheap solution that may solve many problems, but not flow rate/demand problems. Adding an additional pressure tank capacity could smooth demand somewhat but only to the extent of the additional tank. The final solution is the most expensive; the pump could be replaced with a variable speed pump. The motor of this kind of pump can run up to twice as fast as a single speed pump. The speed of the pump is regulated by the water demand and adjusts the pump’s flow rate. If the well has enough supply a constant higher pressure could be delivered to the house. This is an expensive solution, one I think of as a luxury, but it can result in higher water pressure throughout the house.

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