When it comes to water, there is no place like Wisconsin
Groundwater
Water is the lifeblood of every living creature on earth. Approximately 70 percent of the earth's surface is covered with water. Through the wonders of nature, water can take on many different forms, from the water we drink, to the ice we use to chill a glass of lemonade, to the water vapor used to steam clean equipment. It is easy to understand the significance water plays in our lives. It may be much more difficult to understand the groundwater that exists below the Earth's surface.
When it comes to water, there is no place like Wisconsin. We are water rich. Between the mighty Mississippi River and the Great Lakes of Michigan and Superior, there are more than 15,000 lakes, 7,000 streams and five million acres of wetland. And that just scratches the surface. Below our feet Wisconsin has a buried treasure – 1.2 quadrillion gallons of ground-water. It is hard to grasp just how much water is stored underground unless you look at how much we use every day.
Each year about 29 trillion gallons of water fall as rain or snow on Wisconsin’s 36 million acres. Plants and animals consume some, some is returned to the atmosphere by evaporation, liquid changing into gas on the surface, or by transpiration, moisture given off from plants to the atmosphere. Some water becomes runoff, flowing into rivers, lakes and streams. The rest becomes groundwater by infiltrating or percolating, soaking into and through the soil, into groundwater aquifers. Aquifers are large areas of sand, gravel and rock that store water for later use.
If you could somehow pour all the water below ground on top, you'd need to trade in your ranch house for a houseboat: Wisconsin's groundwater could cover the whole state to a depth of 100 feet. Despite this abundance of groundwater, there is a growing concern in certain areas of the state about the quantity of good quality groundwater available for municipal (city, village, town), industrial, agricultural and domestic use. There is also concern about adequate base flow; the groundwater that sustains our lakes, streams and wetlands.
Getting a clean glass of water isn’t as easy as turning on the tap!
In Wisconsin, the quality and quantity of groundwater varies from place to place. The difference is caused by a combination of geology, varying precipitation and use. Cities and towns in the North Central and Northeastern third of Wisconsin receive the most precipitation in the state, but they are underlain by crystalline bedrock; a type of rock formation notorious for yielding only small quantities of water. Even though there may be plenty of rain, finding enough groundwater to supply municipalities in these regions can be difficult. Groundwater levels have been going down by hundreds of feet around some of Wisconsin’s growing metropolitan areas.
At last estimate, there were more than 850,000 private wells in Wisconsin. In areas where water moves through aquifers very slowly, private wells can still yield enough water for residential use. You can drill a hole just about anywhere in Wisconsin and find water. But is this water drinkable? Not necessarily. Ground-water can be contaminated in many ways. Clean groundwater is Wisconsin’s buried treasure that needs to be cared for and protected.
Hydrologic Cycle
Water might be called our most recycled resource. The water you showered in this morning may have contained the same water molecules that gave a dinosaur a cool drink during prehistoric times or carried the early explorers across our country. The distribution of the Earth's total supply of water changes but the quantity has remained constant. Remember, the water we use today is the water we will need in the future too.
Surface water and groundwater are part of the hydrologic cycle. The hydrologic cycle is the constant movement of water above, on and below the Earth’s surface. The cycle has no beginning and no end. You can understand it best by tracing it from precipitation.
Precipitation occurs in several forms, including: rain, snow, sleet, dew, fog and hail. Wisconsin receives an average 30 to 32 inches of precipitation per year. Rain can do three things once it reaches the Earth’s surface. It can filter into the ground, runoff into water bodies or evaporate. Rain, for example, wets the ground surface. As more rain falls, water begins to filter into the ground (infiltration). Approximately 70 to 90 percent of the water that falls to the earth's surface enters the soil. This water can become groundwater but most of it evaporates from the soil surface or is used by vegetation. How fast water soaks into, or infiltrates the soil depends on soil type, land use, slope of the land and the intensity and length of the storm. Water infiltrates faster into soils that are mostly sand rather than those made mostly of clay or silt. Almost no water filters into paved areas. Rain that cannot be absorbed into the ground flows across the surface forming runoff streams.
When the soil is completely saturated additional water moves slowly down through the unsaturated zone (drier, upper soil layers) to the saturated zone (wet lower layers or aquifer) replenishing or recharging the groundwater. The distance water has to travel to reach groundwater can range from a few feet to hundreds of feet. Water movement toward groundwater may take hours or years depending on the depth to the aquifer and the characteristics of the unsaturated zone. Water then moves through the saturated zone to groundwater discharge areas such as springs or artesian wells.
Evaporation occurs when water from such surfaces as oceans, rivers and ice is converted to water vapor. Evaporation, together with transpiration from plants, rises above the Earth’s surface, condenses, and forms clouds. Transpiration is the process by which plants release water to the atmosphere. Water from both runoff and from groundwater discharge moves toward streams and rivers and may eventually reach the ocean. Oceans are the largest surface water bodies that contribute to evaporation. It is estimated that 39 inches of water annually evaporates from each acre of ocean.
After water vapor is drawn into the atmosphere it can be transported over hundreds of miles by large air masses. When water vapor cools, it condenses to form clouds. As water condenses within clouds, water droplets increase in size until gravity pulls them to the Earth's surface as precipitation.
What is Groundwater?
Groundwater is fresh water (from rain or melting ice or snow) that soaks into the soil and is stored in the pores (tiny spaces) between rocks and particles of soil. Approximately 70% of Wisconsin’s residents and 97% of Wisconsin’s communities rely on groundwater to meet their water supply needs. Groundwater can stay underground for hundreds of thousands of years or it can come to the surface and help fill rivers, streams, lakes, ponds and wetlands. Groundwater can also come to the surface as a spring, artesian well or be pumped from a well.
How Does the Ground Store Water?
Groundwater is stored in the tiny open spaces between rock, sand, soil and gravel. How well loosely arranged rock (such as sand and gravel) holds water depends on the size of the rock particles. Layers of loosely arranged particles of uniform size (such as sand) tend to hold more water than layers of rock with materials of different sizes. This is because smaller rock materials settle in the spaces between larger rock materials, decreasing the amount of open space that can hold water. Porosity is how well rock material holds water. Porosity is dependent on the shape of the rock particles and the amount of pore space available. Round particles will pack more tightly than particles with sharp edges. Material with angular-shaped edges has more open space and can hold more water.
Groundwater is found in two zones. The unsaturated zone, also called the vadose zone, is immediately below the land surface. It contains water and air in the open spaces or pores. The saturated zone, a zone in which all the pores and rock fractures are filled with water, is below the unsaturated zone. The boundary between the unsaturated and saturated zones is called the water table. The water table is the top of the saturated zone and may vary in depth from place to place and year to year. It may be a few feet below the surface or hundreds of feet below the land surface. The water table may rise or fall depending on many factors. Heavy rains or melting snow may cause the water table to rise, or an extended period of dry weather may cause the water table to fall. Extensive pumping of water by high capacity wells can lower the water table.
How Groundwater Moves
What is an Aquifer?
An aquifer can form where groundwater moves rapidly, such as through gravel and sandy deposits. An aquifer has enough groundwater so that it can be pumped to the surface and used for drinking water, irrigation, industry or other uses. An aquifer is the area where groundwater is stored naturally before being used or discharged to the surface.
For water to move through underground rock, pores or fractures in the rock must be connected. If rocks have good connections between pores or fractures and water can move freely through them. These rocks are referred to as being permeable. Permeability refers to how well a material transmits water. If the pores or fractures are not connected, the rock material cannot produce water and is therefore not considered an aquifer. When water does not readily move through material, the material is considered impermeable. A layer of such material would be considered a confining layer. Confining layers are often made of clay or shale. The amount of water an aquifer can hold depends on the permeability and porosity of the underground materials present.
An aquifer may be a few feet to several thousand feet thick, less than a square mile or hundreds of thousands of square miles in area. For example, the High Plains Aquifer underlies about 280,000 square miles in 8 states including: Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming.
How Does Water Fill an Aquifer?
Aquifers get water from precipitation (rain, snow, etc…) that filters through the unsaturated zone. Aquifers can also receive water from surface waters such as lakes and rivers. This taking in of water is called recharge. Recharge areas are where aquifers take in water. When the aquifer is full, and the water table meets the surface of the ground, the water stored in the aquifer can appear at the surface as a spring or artesian well. These are known as discharge areas. Discharge areas are where groundwater flows to the land surface. Water moves from higher-elevation areas of recharge to lower-elevation areas of discharge through the saturated zone.
How do we get water from an Aquifer?
Wells are used to remove water from aquifers. Basically, a well is a hole drilled into an aquifer. A pipe and a pump are used to pull water out of the ground. A screen filters out unwanted particles that could clog the pipe. Wells come in different shapes and sizes. It depends on the type of material the well is drilled into and how much water is being pumped out. Cities often store this water for later use in water towers to provide water pressure.
Removing water lowers the water level in the well. The difference between the initial water table depth or static water level (elevation of the water table above sea level) and the pumping water level causes water to move in the aquifer. Since the pumped well water level is lowest the water from the surrounding aquifer flows toward the well to replace the water being removed. Shallow wells may go dry if the water table falls below the bottom of the well. Some wells, called artesian wells, do not need a pump because of natural pressures from the slope of the aquifer and/or confining layers that force the water up and out of the ground naturally under pressure.
Rate of Groundwater vs. Surface Water Movement
Surface water generally flows in rivers or streams at velocities of 2-8 miles per hour. Rate of surface water flow is determined by slope of the land, amount and rate of precipitation, rate of infiltration and evaporation, amount and type of vegetation and land use.
Groundwater moves through the spaces (pores) between particles of a saturated material anywhere from 0.1 foot per day to 3 feet per day. That translates into movement of 35 to 1,100 feet per year for groundwater. Ground-water moves only if sufficient pressure is available to force water through the spaces between porous aquifer materials. Geology helps to controls the rate of groundwater movement. The size of the cracks in rocks, the size of the pores between soil and rock particles, and whether the pores are connected determine the rate at which water moves into, through and out of the aquifer. Water generally moves quickly in coarse sand, sometimes as much as several feet per day. Openings between the grains are large and interconnected, resulting in high permeability. Very fine-grained material like clay has many pores where water can be stored, but the pores are so small that moving water through or out is difficult. Clay formations are relatively impermeable -- water may move only a few inches a year. Permeability in limestone, on the other hand, primarily depends not on pore spaces, but on the size, frequency and distribution of fractures and cracks.
The slope of the aquifer also helps to determine the rate of groundwater movement. In other words, the slope of the water surface between two points in an aquifer and the aquifer material determines how rapidly groundwater moves from one location to another.
Wisconsin's Aquifers
An aquifer is a rock or soil formation that can store or transmit water. Wisconsin's groundwater reserves are held in four principal aquifers: the Sand and Gravel Aquifer, the Eastern Dolomite Aquifer, the Sandstone and Dolomite Aquifer, and the Crystalline Bedrock Aquifer.
Sand and Gravel Aquifer
The sand and gravel aquifer is the surface material covering most of the state except for parts of southwestern Wisconsin. It is made up mostly of sand and gravel deposited from glacial ice or in river floodplains. The glacial deposits are loose, so they are often referred to as soil -- but they include much more than just a few feet of topsoil. These deposits are more than 300 feet thick in some places in Wisconsin.
The sand and gravel aquifer was deposited within the past million years. The sand and gravel outwash plains now form some of the best aquifers in Wisconsin. Many of the irrigated agricultural lands in central, southern and northwestern Wisconsin use the glacial outwash aquifer. Because the top of the sand and gravel aquifer is also the land surface for most of Wisconsin, it is highly susceptible to human and naturally occurring pollutants.
Eastern Dolomite Aquifer
The eastern dolomite aquifer occurs in Eastern Wisconsin from Door County to the Wisconsin-Illinois border. It consists of Niagara dolomite underlain by Maquoketa shale.
These rock formations were deposited 400 to 425 million years ago. Dolomite is a rock similar to limestone; it holds groundwater in interconnected cracks and pores. The water yield from a well in this aquifer mostly depends on the number of fractures the well goes through. As a result, it's not unusual for nearby wells to vary greatly in the amount of water they can draw from this layer.
Where the fractured dolomite bedrock occurs at or near the land surface, the groundwater in shallow portions of the Eastern Dolomite Aquifer can easily become contaminated. In those areas (such as parts of Door, Kewaunee and Manitowoc counties), there is little soil to filter pollutants. Little or no filtration takes place once the water reaches large fractures in the dolomite. This has resulted in some groundwater quality problems, such as bacterial contamination from human and animal wastes. Special care is necessary to prevent pollution.
The Maquoketa shale layer beneath the dolomite was formed from clay that doesn't transmit water easily. Therefore, it is important as a barrier or shield between the Eastern Dolomite Aquifer and the Sandstone and Dolomite Aquifer.
Sandstone and Dolomite Aquifer
The Sandstone and Dolomite Aquifer consists of layers of sandstone and dolomite bedrock that vary greatly in their water-yielding abilities. In dolomite, groundwater mainly occurs in fractures. In sandstone, water occurs in pore spaces between loosely cemented sand grains. These formations can be found over the entire state, except in the North Central portion.
In Eastern Wisconsin, this aquifer lies below the Eastern Dolomite Aquifer and the Maquoketa shale layer. In other areas, it lies beneath the Sand and Gravel Aquifer. These rock types gently dip to the East, South and West, away from North Central Wisconsin, becoming much thicker and extending to greater depths below the land surface in the Southern part of the state.
The rock formations that make up the Sandstone and Dolomite Aquifer were deposited between 425 and 600 million years ago. The Sandstone and Dolomite Aquifer is the principal bedrock aquifer for the Southern and Western portions of the state. In Eastern Wisconsin, most users of substantial quantities of groundwater, such as cities and industries, tap this deep aquifer to obtain a sufficient amount of water.
Crystalline bedrock aquifer
The Crystalline Bedrock Aquifer is composed of various rock types formed during the Precambrian Era, which lasted from the time the Earth cooled more than 4 billion years ago, until about 600 million years ago, when the rocks in the Sandstone and Dolomite aquifer began to be formed. During this lengthy period, sediments, some of which were rich in iron and now form iron ores, were deposited in ancient oceans; volcanoes spewed forth ash and lava; mountains were built and destroyed, and molten rocks from the earth's core flowed up through cracks in the upper crust. The rocks that remain today have a granite-type crystalline structure. These are the “basement” rocks that underlie the entire state. In the north central region, they are the only rocks occurring beneath the Sand and Gravel Aquifer.
The cracks and fractures storing and transmitting water in these dense rocks are not spaced uniformly. Some areas contain numerous fractures while others contain very few. To obtain water, a well must pass through some of these cracks; the amount of water available to a well can vary within a single home site. The crystalline bedrock aquifer often cannot provide adequate quantities of water for larger municipalities, large farms or industries.
Many wells in the Crystalline Bedrock Aquifer have provided good water. However, most of these wells do not penetrate deeply into the rock. Water samples from deep mineral exploration holes near Crandon and deep iron mines near Hurley have yielded salty water.
Water Level Changes Associated with Groundwater Pumping
When pumping starts in an unconfined aquifer, most of the water is removed from very near the well. With continued pumping, water is removed further from the well lowering the water level at a greater distance from the well. This is referred to as draw down. Draw down decreases with the distance from the well until, at some distance, the water level remains relatively unaffected by pumping. Drawdown in the well continues to increase slightly with pumping. The resulting cone-like shape of the water surface is referred to as a cone of depression.
The size and shape of the cone of depression is determined by the aquifer materials and the amount of water being removed from the aquifer. Domestic wells typically have very little cones of depression. Irrigation and municipal wells typically have large cones of depression that may be up to 100 feet deep. These cones of depression can cause shallow neighboring wells to quit pumping water.
Factors Affecting Groundwater Declines
Under natural conditions, a balance existed between the volume of water entering an aquifer and the volume of water being discharged from an aquifer. With the development of water wells, the natural balance between recharge rates and discharge rates is disrupted. The overall groundwater supply has been depleted due to increased water usage or discharge.
Groundwater supplies also can be altered due to natural causes. Years of below-normal precipitation can alter the amount of water entering the aquifer. Likewise, seasonal and year-to-year differences in regional stream flow can cause fluctuation in localized groundwater levels.
The combination of intensive pumping and several years of below-normal precipitation can accelerate the downward trend in water levels. This is true because below normal precipitation often results in decreased groundwater recharge. More importantly, below normal precipitation generally results in increased groundwater pumping further reducing the water level.
There are areas in Wisconsin where streams are not running and springs are not flowing anymore because the groundwater feeding them is being pumped dry. In a growing number of places people are pumping groundwater faster than it can be replenished. Local scarcity of water sometimes pits communities against one another.
When a proposed water bottling plant in Adams County was opposed by citizen groups in 1999, the interest of policymakers and the public in water quantity issues bubbled to the surface. It became clear that state laws did not address the effect of high-capacity wells on nearby springs, wetlands or trout streams. The Big Springs case made people much more aware of the connection between groundwater, surface water and human activities.
How do you use groundwater?
In Wisconsin, we us use nearly 205 million gallons of groundwater daily for drinking, doing dishes, making food and bathing. That's 55 gallons of groundwater per person per day. Fifty-five gallons of groundwater per person per day may not seem like much, but there are hidden costs for excessive water use. Your community may have to install new wells or water and sewer pipes to accommodate increasing demands. Pumping more water from private or public wells requires more energy, which costs more money. Treating used water, referred to as wastewater or effluent, to strict standards of purity requires money, resources and skilled workers.
Thirsty Cities
97% of Wisconsin's cities and villages count on groundwater to provide basic water-related services such as fighting fires, cleaning streets, filling the local pool, watering golf courses and parks, drenching shade trees, supplying commercial customers and satisfy the needs of thirsty residents at home. The average daily cost of supplying groundwater to a family of four in 2005 was between 26 and 35.2 cents – an increase of only a few cents since 1983.
A Fluid Economy
Water is vital to Wisconsin’s economic health. Its part of countless manufacturing processes, from metal fabrication to paper production to leather tanning. Some of our most important industries -- fruit and vegetable processing, cheese-making, dairy farming, meat processing and brewing -- need pure, clean groundwater to make the goods for which Wisconsin is famous.
Big operators aren't the only ones who need this valuable resource. Consider your local Laundromat, car wash, water bottlers, restaurants, health clubs, hairdressers…scores of services and products we use daily depend on groundwater.
Food processing soaks it up: processing one can of corn or beans requires nine gallons of water. Cars, fast or slow, also guzzle it up: six gallons of water are needed to produce one gallon of gasoline. And to manufacture that car and put four tires on it takes 39,090 gallons of water!
Wet and Wild
Thousands of tourists travel to Wisconsin each year to enjoy our fabulous water resources. They spent an estimated 11.8 billion dollars in 2005 alone. That’s a lot of fishing, boating, and swimming. What most people see is a favorite fishing hole, a secret pond with an expanse of cattails perfect for observing herons, or those wild rapids waiting to devour the raft or roll the kayak. What they don’t see is the groundwater flowing into those water bodies. After seeping through the soil and rock, groundwater discharges through springs and artesian wells, in low places where the water table meets the land surface, into streams, lakes and wetlands.
Agriculture
Wisconsin's farms use about 100 million gallons of groundwater a day to water livestock, maintain a high level of sanitation in the milk house and provide all-around cleanliness on the farm. A dairy cow producing 100 pounds of milk daily drinks 50 gallons of water each day. There are roughly 1,235,000 dairy cows in the state. This means they drink over 10.9 billion gallons of water per year.
Wisconsin also has an estimated 390,000 acres of irrigated farmland. Irrigation equipment uses about 182 million gallons of water per day during the growing season, almost all of it groundwater. On average, 80 percent of the water is consumed – it is used by plants and not returned immediately to the soil under the fields.
While irrigation has helped formerly marginal lands turn a profit, there is a cost. Excessive irrigation may leach nutrients, fertilizers and pesticides into groundwater and lower the water table.
Threats to groundwater
Unfortunately, groundwater is susceptible to pollutants. Groundwater is generally a safe source of drinking water. There are concerns that contamination may increase as toxins dumped on the ground in the past make their way into groundwater supplies. The soil cannot filter many manmade chemicals.
A well can be easily contaminated if it is not properly constructed or if toxic materials are released into the well or onto nearby soil. Toxic material spilled or dumped near a well can leach into (soak into) the aquifer and contaminate the groundwater drawn from that well. Leaching is the process where chemicals slowly pass through the soil and mix into the groundwater. Contaminated wells used for drinking water are especially dangerous. Wells should be tested to see what chemicals may be in the well and if they are present in dangerous quantities.
Pollutants can sink into the groundwater in areas where material above the aquifer is permeable. Groundwater can be polluted by landfills, septic tanks, leaky underground gas tanks and from overuse of fertilizers and pesticides. If groundwater becomes polluted, it will no longer be safe to drink. It is important for all of us to learn to protect our groundwater.
Sources of Contamination
Groundwater contamination occurs when man-made products such as gasoline, oil, road salts and chemicals get into the groundwater and cause it to become unsafe and unfit for human use. Some of the major sources of these products, called contaminants, are storage tanks, septic systems, hazardous waste sites, landfills and the widespread use of road salts and chemicals.
In rural areas, different threats to groundwater quality exist; animal waste, onsite sewage systems, fertilizers and pesticides are primary pollution sources. Farmers also must be careful about where and when they spread manure. Spring snowmelt or excessive rainfall can lead to fish kills and contamination of drinking water wells due to bacteria in manure that has run off from farm fields.
Air pollution can also lead to groundwater pollution. Particles clouding the air from car exhaust, smokestacks and dust from city streets or farm fields can contribute to groundwater contamination. These particles of hydrocarbons, pesticides and heavy metals settle on the ground, are washed into the soil by rain, and eventually trickle into aquifers. Although a rain shower may disperse the particles from the air, the rains can carry the pollutants down into the ground as the water hits land.
Accidents happen – over 1,000 spills of toxic or hazardous materials are reported each year in Wisconsin. Volatile organic compounds (VOCs) such as petroleum products account for many of the spills in the state. Topping the list is diesel fuel. Other substances, such as pesticides, paint, and ammonia, make up the rest. Most spills occur at industrial facilities or during transport of hazardous substances. Response efforts focus on containing and removing the hazardous material to a proper disposal facility. This protects groundwater and surface waters.
Storm water from roofs, driveways, parking lots and streets contains contaminants such as gasoline, metals, and bacteria it must be cleaned up or pretreated before it is put back in the ground using engineered storm water infiltration devices.
Thanks to recycling efforts since 1995, each year we have diverted about 40 percent of the Wisconsin generated solid waste from Wisconsin’s landfills. However, landfills may still be a major source of contamination. Modern landfills have protective bottom layers and leachate collection systems to prevent contaminants from getting into the water. Leachate is the polluted liquid that forms when water percolates through solid waste and mixes with chemicals in the waste. Many old landfills and dumps did not have protective liners or were natural attenuation designs. The natural attenuation designs hoped the soil would filter the buried chemicals and prevent them from leaching into the groundwater. If there was no layer or it is cracked, contaminants from the landfill (car battery acid, paint, household cleaners, etc.) can make their way down into the groundwater.
Dangers of Contaminated Groundwater
Drinking contaminated groundwater can have serious health effects. Diseases such as hepatitis and dysentery may be caused by contamination from septic tank waste. People are often poisoned by toxins that leach into their well water. The poisons may be from surface contamination or the result of natural sources. Some rocks contain heavy metals such as lead, arsenic, mercury and aluminum. These metals all have ill affects on human health and wildlife. It is important to remember that wildlife can also be harmed by contaminated groundwater.
Pollution Prevention
Many steps are being taken to keep pollutants from reaching groundwater supplies. Manufacturers are using fewer toxic raw materials. Consumers have switched to phosphate-free detergents and other less polluting household products. Pollution control measures such as the Clean Water Act have also been a big part of the protection of drinking water supplies.
Tips on Protecting and Conserving Groundwater
1. Dispose of chemicals properly.
2. Take used motor oil to a recycling center.
3. Limit the amount of fertilizer used on plants.
4. Take short showers.
5. Shut water off while brushing teeth.
6. Run full loads of dishes and laundry.
7. Check for leaky faucets and have them repaired.
8. Water plants only when necessary. It is best to water before 10 a.m. or after 7 p.m.
9. Keep a pitcher of drinking water in the refrigerator.
10. Get involved in water education.
Groundwater cleanup...Who Pays?
We all pay for contaminated groundwater. Groundwater contamination can be linked to land use. What goes on the ground can seep through the soil and turn up in drinking water, lakes, rivers, streams and wetlands. Tracking down and stopping sources of pollution is a lengthy and expensive process. It’s usually impossible to completely remove all traces of a pollutant. Conducting a partial cleanup of an aquifer to a usable condition can cost a substantial amount of money.
The owner or facility operator causing the pollution should pay the cost. But what happens when the owner is bankrupt, out of business or dead? Taxpayers must step in. Federal and state money is used for cleaning up sites and enforcing laws governing waste disposal and hazardous material spills.
When it comes to groundwater, prevention is the best strategy. This means looking at the many ways we pollute groundwater and finding methods to keep those pollutants from entering the groundwater. Landfills and wastewater lagoons need to be designed and operated to prevent infiltration to groundwater. Pesticides must be applied according to need and label instructions, and fertilizers and manure should be applied in carefully calibrated amounts to enhance crops without damaging the environment. With vigilance and care, we can protect our buried treasure.
Why is Cleaning Up Groundwater So Hard?
Cleaning up contaminated groundwater often takes longer than expected because groundwater systems are complicated and the contaminants are invisible to the naked eye. This makes it more difficult to find contaminants and to design a treatment system that either destroys the contaminants in the ground or takes them to the surface for cleanup. Groundwater contamination is the reason for most of Superfund’s long-term cleanup actions. A Superfund site is a site that has sustained severe contamination. Most Superfund sites are old landfills or industrial areas.
Movement of Contaminated Groundwater
Contaminants that can dissolve in groundwater will move along with the water. These contaminants can potentially make it to wells used for drinking water. If there is a continuous source of contamination entering moving groundwater, an area of contaminated groundwater, called a plume, can form. A plume of contamination is an area of contaminated groundwater that moves together. A combination of moving groundwater and a continuous source of contamination can, therefore, pollute very large volumes and areas of groundwater. Some plumes at Superfund sites are several miles long. More than 88 percent of current Superfund sites have some groundwater contamination.
An Introduction to On-site Wastewater Treatment
In Wisconsin, more than 750,000 private septic systems use on-site wastewater treatment systems to meet their wastewater treatment and disposal needs. Residents in towns and cities are typically served by centralized drinking water systems and wastewater treatment facilities. Homeowners living in rural areas without access to municipal water treatment systems must rely on private wells to meet drinking water needs, and their own "mini treatment plant" to meet wastewater disposal needs.
The most common type of on-site wastewater treatment is the septic system. A septic system consists of four main components. The first component is a home’s indoor plumbing. This is simply the system of drains and pipes located inside a home that transports wastewater outside to the next major component, the septic tank. The septic tank is an underground, watertight container, made of concrete, fiberglass, or other durable material that resists corrosion.
The septic tank serves as the primary place of treatment for wastewater. Here, sludge (solids) settle to the bottom of the tank and partially decompose with help from bacteria. A layer of soaps, greases and scum float on top of the liquid wastewater. Over time, the floating scum and submerged solids accumulate and must be removed by a qualified septic contractor.
The liquid wastewater contained in the septic tank is called effluent. The effluent exits the septic tank and enters the next major component of a septic system, the drain field.
The drain field allows wastewater to percolate (infiltrate) into the surrounding soil through a series of underground, perforated pipes. The pipes are usually placed on top of a layer of gravel and sand. Above the pipes is a layer of clay or manmade impermeable barrier to prevent to effluent from floating to the surface. In areas where the water table is close to the surface or adequate filtration depth cannot be achieved, a mound system is used. A mound system is constructed on the surface and therefore creates a mound in the yard to process the effluent.
The soil is the final and most important component of a septic system. This is where the majority of wastewater treatment actually occurs. Through various physical and biological processes, most bacteria and viruses in wastewater, as well as some nutrients, are consumed as the wastewater effluent travels down through the soil layers.
Properly constructed and maintained septic systems pose little threat to the environment and human health. However, improperly functioning systems pose a contamination risk to groundwater and surface water supplies.
There are numerous ways for homeowners with septic systems to minimize the potential impacts that on-site wastewater treatment systems may have on the environment. These include:
Regular Inspection – One of the most important ways to care for your septic system is to have it inspected on a regular basis. This extends the life of a septic system and helps the homeowner avoid unnecessary and expensive repair and replacement costs. It is generally recommended to have a septic system inspected every 2-3 years.
Conserve Water – Hydraulic overload is a major cause of septic system failure. Low flow plumbing fixtures (faucets, toilets and showerheads) will minimize the amount of water entering a septic system.
Care of the Drain field – Trees and shrubs with deep penetrating roots should not be planted near the drain field because the roots can plug the perforated pipe structure. Heavy vehicles and equipment should not be driven or parked over the drain field because their weight can compact the soils and damage drain field components.
Household Waste Disposal – Limit the types and amounts of wastes poured down the drain. Garbage disposals can nearly double the amount of solids added to the septic tank and should be used sparingly, or not at all. Cooking oils and fats harden after disposal and block the septic tank inlet, or outlet, and even clog the soil pores surrounding the drain field reducing its effectiveness for filtrating wastewater. In addition, chemicals like paints, solvents, and pesticides should not be dumped down the drain. These items may kill microorganisms living in the septic tank and soil that help purify the wastewater. Without the bacteria, the untreated effluent can potentially enter the groundwater and contaminate drinking water supplies.
Homeowners who have a septic system that is properly designed and installed and correctly
operated and maintained should receive years of reliable service with minimum risks to human and environmental health.
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