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MF970 Private Wells: Safe Location and Construction

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MF970 Private Wells: Safe Location and Construction Private Wells — Safe Location and Construction Water for residences beyond the reach of public wells when nitrogen sources are more than 400 feet from systems, either city or rural water district, usually is the well. supplied by a well. Surveys of private well water qual- The best time to help assure that a well produces safe ity show that on average only 40 percent meet the safe water is when a new well is being sited and drilled. This drinking water standards used for public systems. A publication addresses principles of safe well location and Kansas well survey showed 51 percent contain coliform construction. Wells also need annual maintenance and bacteria, which indicates recent exposure to the surface protection of the water supply, explained in a companion environment. Coliform bacteria do not thrive, or even K-State Research and Extension publication Private survive, for extended periods in an aquifer. Well Maintenance and Protection, MF-2396. Publication Eighteen percent of private wells contain E. coli MF-2409, Private Water Well Owner/Operator Manual, bacteria, an indicator of contamination by fecal material outlines important well information needs and can serve from sewage or animals. E. coli indicates a high risk of as a record book to store your well information. disease pathogens. One of four private wells contains nitrate above the maximum contaminant level (MCL) for Groundwater and Geology public water supplies. These contaminants usually can be Groundwater occurs everywhere below the ground traced to problems with well location or well construction. surface. It fills the spaces in sand, gravel, soil, and rock Construction and location are the most important formations. When a formation contains enough water that factors in protecting private well water. Private well can be removed at useful rates by a pump, it is called an surveys indicate about 80 percent of wells are deficient in aquifer. Aquifers are fractured rock, porous rock, sand, construction or location. The location is the separation dis- gravel, or a mixture of these. It may be a single mass, a tance and direction from potential contamination sources. layer, or a series of layers. Water flows through aquifers as a result of the driving force (head) and permeability. Well Regulations The well owner or water user is responsible for the Aquifers and Water Quality quality of water from a private well. No state or federal An aquifer that receives recharge directly from the regulations apply to the quality of the water supplied from surface is called an unconfined aquifer. Because an these wells. However, Kansas has regulated new well unconfined aquifer is recharged locally, activities near a construction and well repairs since 1975. Anyone who well pose a high risk to cause contamination. Most wells constructs (drills), reconstructs (repairs), or treats wells in western and south central Kansas and major stream must be licensed to perform these services. However, valleys are in unconfined aquifers. the owners can do the work on their own well without a Confined aquifers are beneath a zone of low per- license. They are required to file reports with the Kansas meability that minimizes direct recharge from the Department of Health and Environment (KDHE). surface. Confined aquifers are normally recharged at Well-drilling regulations and county sanitary codes much greater distances from the well. Activities near a specify a minimum 50-foot separation of the well from properly constructed well in a confined aquifer are much any source of possible contamination (some counties less likely to contaminate the well. Many wells in north use 100 feet or more). This separation distance is based central and eastern Kansas are in confined aquifers. on the soil’s filtering capacity for bacteria and other Other factors affecting potential contamination are microbes. Many contaminants, including nitrate, volatile depth to the water table, soil and geologic materials, per- organic chemicals (VOCs), fuel, petrochemicals, and meability in the recharge zone, and to a lesser extent, type some pesticides, are not filtered by the soil. Substantially and condition of vegetation. Recharge passes through an greater separation distances are needed to protect from unsaturated layer called the vadose zone or zone of aera- contaminants not filtered by soil. Research in Kansas tion above the water table. The top portion of the vadose shows there is a low incidence of high nitrate present in zone contains roots and most of the microbial activity. Kansas State University Agricultural Experiment Station and Cooperative Extension Service 1 Soil organisms break down many of the dissolved Sand and Gravel Aquifers with similar deposits compounds in water, and plant roots remove nutrients, that extend to the surface are particularly difficult to trace elements, and some other compounds. As water protect from contamination. In many cases, the mate- passes through the vadose zone, suspended particles and rial in the unsaturated zone is the same as the aquifer most organisms are filtered out. Compounds dissolved and permeability can be high. Excess nitrate and other in the water may be adsorbed on soil particles, precipi- soluble compounds in the surface soil are easily trans- tated, or chemically combined to form new compounds. mitted to the groundwater. Plant growth is often limited Healthy perennial vegetation with a deep root zone and by low water-holding capacity or droughty nature of thick vadose zone of moderate permeability are ideal to sandy soil. Adsorption capacities and microbial activity assure high quality groundwater recharge. is less in other soils with low organic levels common in Water quality is greatly affected by the rate of sandy soils. recharge, the volume of storage, and the rate of flow Limestone Aquifers require special attention in two through the aquifer. Slow rates of recharge allow greater situations. The first is where sink holes are common, root uptake and more time for soil organisms to break called Karst topography. The second is where the rock down dissolved and suspended materials in the water. is exposed or covered only by a shallow layer of soil. Slow recharge also allows more time for other reactions Sinkholes and exposed bedrock provide direct connec- between contaminants, soil, and rock. Minerals in the tions for contaminants to easily enter the groundwater soil and rock may be dissolved into water. Large stor- and contaminate wells. Shallow soil layers provide only age volumes in an aquifer help dilute contaminants and slight protection. These situations pose a serious risk for enable a well to produce during long, dry periods. Rapid groundwater contamination. flow through the aquifer makes it self-cleaning and also Water in limestone aquifers is primarily in cracks, subjects it to water shortage during dry periods. joints, and solution channels. These spaces tend to be The water quality of an aquifer is normally variable. large compared with pore spaces in other types of aqui- Deep aquifers tend to vary less in a region because of fers. As a consequence, the flow in limestone aquifers the factors previously mentioned. However, groundwater may be rapid and the filtering action poor. However, quality is not uniformly good or poor, even over rela- rapid flow through the aquifer tends to make contami- tively short distances. nation events of short duration. Two aquifer types, discussed in the following paragraphs, deserve special attention when considering a Protect Well Water by Good Location private well. These conditions exist in Kansas. Therefore, Locating a domestic well to safeguard water qual- hiring a knowledgeable, experienced, and licensed well ity requires consideration of geology, topography, and driller is extremely important. It is a driller’s business to potential contamination sources within at least 400 feet understand and plan for these special situations. of the site. Historically, wells were located near the point Figure 1. Groundwater contamination occurs from many sources and usually moves in concentrated plumes. Figure 1 2 of maximum use. Because livestock required the most Groundwater Flow water at a farmstead, the well was often located in, or There is a natural movement or flow of water in very near, livestock lots. This placed the well near a the aquifer that likely follows the general slope of the major contamination source. The house and shop were surface. However, nonuniform properties in the aquifer almost always upslope from the livestock. This meant the and sloping formations can cause differences. Pumping well was very likely downslope from other potential pol- from wells also influences groundwater flow direction lution sources. A location near and especially downslope and rate. As water is removed from the well, water in the from contamination sources increases the potential for aquifer surrounding the well flows toward the well creat- well pollution. ing a “cone of depression.” The first rule for protecting well water quality is to More of the water entering the well flows from the keep the well upslope from potential sources of con- uphill side and the cone of depression becomes oval in tamination. Current contamination sources are easy to shape. The size of the cone depends on the permeability identify. However, past activities may not always be obvi- and storage in the aquifer and the rate and duration of ous and many contaminants have a long life. An attempt pumping. Household wells are usually pumped for a few should be made to determine if potentially hazardous minutes to a few hours at a time. In coarse gravel aqui- activities occurred at or near the site. Many contaminated fers, both large storage and high permeability result in wells were constructed in or near old feedlots, storage a small cone of depression. By contrast, an aquifer with facilities, disposal sites, landfills, privies, or septic sys- lower permeability and storage values will have a larger tems. See relationships of sources and well in Figure 1.
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