Ground Water: Where Does It Come From?
Water under the earth's surface is called ground water. It is stored in, and moves slowly through, rock strata called aquifers. It represents, in terms of storage at any one time, the largest single source of fresh water available to and commonly used by man. The aquifer literally carries water underground. The aquifer may be a layer of gravel or sand, a layer of sandstone or cavernous limestone, a rubbly zone between lava flow, or even a large body of massive rock, such as fractured granite.
The quantity of water that a given rock can contain depends on the rock's porosity - the total measure of the spaces among the grains or in cracks that can fill with water. If water is to move through rock, the pores must be connected to one another. If the rock has many connected pore spaces big enough that water can move freely through them, the rock is said to be permeable.
As ground water moves through permeable rocks, it moves around and between neighboring impermeable ones; thus, like surface water, it takes the paths of least resistance. Although it moves slowly, it may travel for miles before it emerges as a spring, seeps unseen into a stream, or is tapped by a well.
Ground water is simply water that fills pores or cracks in subsurface rocks. It is ultimately replenished by precipitation, according to the local climate and geology, and is unevenly distributed in both quantity and quality. When rain falls or snow melts, plants and soils take up water. Some water is evaporated to the atmosphere from plant leaves, most runs off to streams, and some percolates down into the pores or cracks in rocks.
When rain falls, the first water that enters the soil replaces water that has been evaporated or used by plants during a preceding dry spell.
After the thirsty plants and soil have had enough water and if rain continues to fall, the excess water will drain to the water table, the top of the zone in which openings in rocks are saturated. Below the water table, all the openings, crevices, and pores are full of water. The raindrops have, at last, become ground water, and thus are free to move from the saturated rocks to a nearby stream or into a well being pumped.
Back to Top
How much water will my well provide?
Water used for families has, over the years, been determined to average 75 gallons per person per day. Thus, the average family uses 300 gallons per day. Most usage occurs during two peak times -- first thing in the morning and immediately before people go to bed. Through its regulations, the State of Maryland has established minimum standards for water well yields. These standards require that a well be capable of producing at least one gallon of water each minute and that this water plus water standing in the well equal or exceed 500 gallons in two hours. This ensures that the well can supply both overall daily use and peak demand.
Back to Top
How was my well constructed?
There are basically three ways in which a well is constructed: hand dug, driven or drilled. Before modern technology was available, wells were dug by hand. Most of these wells are shallow, (10-40 feet deep) and wide. The shallow depth and poor sealing make this type of well more open to contamination, especially from surface runoff, and sometimes results in failure to supply water during dry weather periods. Some of these wells are still in use.
Most of the well construction today in Carroll County is done by drilling. Narrow holes are drilled 100 feet or more below the surface. Some wells reach depths exceeding 500 feet. Casing must extend through the weathered zone and be seated at least 2 feet into the bedrock and be sealed in place using cement or other approved material. A minimum of 8 inches must extend above ground level. Casings reduce the occurrences of contamination of well water from surface sources and make the water supply more reliable.
Back to Top
How can I protect my water supply?
Practicing water conservation is one way to develop habits which will be especially beneficial during periods of dry weather when water supplies are low. Water conservation can also prolong the life of a septic system, reduce the cost of municipal sewage treatment, and save energy.
There are several ways that water usage can be reduced, either through mechanical methods or by adjustments in daily routine. The mechanical methods of conservation include low-flush toilets, low-flow shower heads, and faucet aerators.
The other methods of saving water cost very little and involve a little though before turning on the faucet. Here is a list of some of the many activities which will save the most water.
- Use the trash can instead of the toilet for disposing of cigarette butts, tissues, spiders, etc. Some toilets use 7 gallons of water every time they are flushed.
- Take short showers instead of baths. Showering, especially when the shower head is equipped with a flow restrictor, uses much less water than filling the bath tub. Of course, self-restraint must be exercised in the amount of time spent in the shower.
- Turn the faucet on only when needed. Don't leave the water running when brushing your teeth, washing dishes, or while hand laundering.
- Wash only full loads when using the dishwasher, or the washing machine. This also saves energy.
- Fix all leaky faucets as soon as possible. You can waste between 15 and 400 gallons of water a day through leaks. Hot water leaks also cost a great deal of energy.
- Water your lawn and garden only when necessary. Mulching, cutting your grass less often in the heat of the summer, and watering in the coolest part of the day are all beneficial to the plants as well as for saving water.
- Wash your car only when necessary. Use a bucket of soapy water for washing and use the hose for rinsing only.
- Use a broom or rake instead of the hose for cleaning up leaf litter and grass clippings. Always keep in mind that you are the best mechanism for conserving water, our most precious resource. All it takes is a little thought and common sense.
Ground water is composed of a variety of chemical and biological constituents which occur in varying concentrations. Many of these constituents are part of the natural groundwater chemistry and are harmless or even beneficial, while others may be a result of ground water contamination and have a detrimental effect on the water. The concentrations of each of these constituents in ground water has an effect on its usability.
The pH of the water, which is a measure of the hydrogen ion concentration, should ordinarily test between 5.5 and 9 for domestic use. Water with a pH below 7.0, indicating acidity, may be corrosive and shorten the life of metal plumbing. Corrosion of the plumbing can introduce metals such as copper and lead into the water supply system. Visual indications of a low pH include green or blue-green stains from copper pipes, and red stains from galvanized fixtures. Water with a pH above 7 reacts as a base, and basic water can form scale. For drinking purposes, the Carroll County Health Department recommends that a treatment device be installed when the pH is below 6.0 to reduce corrosion to metal pipes. Use of plastic pipe eliminates the need for treatment.
Hardness of water is expressed in terms of the amount of calcium carbonate (CaCO3) contained in the water. Water is considered soft if it contains less than 60 parts per million (ppm) CaCO3; moderately hard with 60-120 ppm; hard with 120-180 ppm; and very hard with more than 180 ppm. Hardness in the range of 60-100 ppm is acceptable for most domestic water supplies. Hard water in excess of 100 ppm can result in scaling of pipes and water heaters, grayish laundry, and excess consumption of soaps and detergents.
Nitrogen occurs in various forms in water and each form has its own affect on usability. Nitrate, as nitrogen (NO3), in excess of 10 ppm may cause a condition in infants known as methemoglobinemia. This condition is a type of "blue baby" syndrome which is different from the more common oxygen deficient "blue baby" syndrome caused by a birth defect.
Concentrations of iron in excess of 0.1 ppm may result in rust stains on fixtures and laundry, red-brown colored water, metallic taste, blackish colored beverages (corrosion of pipes and pumps), and is associated with low pH. The recommended maximum iron concentration for drinking water is 0.3 ppm. This limit has been recommended primarily for reasons of taste and to avoid staining of plumbing fixtures and laundered clothes.
Lead is poisonous in low concentrations. Serious illness or death may result from prolonged exposure to relatively small quantities of lead. Treatment should be considered when levels are .015 ppm or higher.
Most natural ground water in all but very shallow aquifers is considered free from pathogenic bacteria; however, sometimes ground water in aquifers or distribution systems may become contaminated with polluted water or through poor construction.
The presence of coliform bacteria is an indication that the water may have been contaminated by fecal matter or surface washings. Fecal coliforms, as a group are not harmful, but certain strains can cause gastric disorders, and in young children, diarrhea and infection of the urinary tract. "The main significance of fecal coliforms, however, is that their presence could indicate the presence of fecal pathogenic bacteria."
In protecting the quality of your water supply, prevention from contamination is the key. There are several ways you can reduce the chances of your well being contaminated by surface sources. Some of these include:
- Don't tie your dog to the well casing. Fecal matter deposited by your pet close to the well could result in contamination. A large dog could also break or crack the casing, allowing pollutants to enter the well more readily.
- If you plant flowers around the casing, avoid heavy fertilization. Fertilizers, especially nitrogen and phosphorous, could find an easy route down the outside of the casing to the ground water.
- Avoid allowing drainage from streets, rooftops, driveways, feed lots, compost piles, etc. from running over or around the well casing. Storm water runoff from these sources carries substantial concentrations of pollutants.
Back to Top
Where can I get Help?
The Carroll County Health Department, Bureau of Environmental Health, has the responsibility of approving new well construction and will sample domestic wells under certain circumstances. If you suspect that you have a problem, you can call or come in to the County Health Department.
Back to Top