It is National Groundwater Awareness Week March 11-17, 2012, and apparently Awareness Week is in its second decade of existence. Who knew, and that’s the problem, most people are unaware of groundwater despite its importance and impact on our lives. Recently, the US Geological Survey, USGS, reported that in 2007 105 million people, about a third of the population receive their drinking water from one of the 140,000 public water systems across the United States that use groundwater as their source. In addition, 15% of the population obtains their water directly from groundwater using private drinking water wells. Groundwater is also used for irrigation. Groundwater is an important natural resource, especially in those parts of the country that don't have ample surface-water sources, such as the arid West. Groundwater is a renewable resource, but not unlimited. Groundwater recharges at various rates from precipitation and other sources of infiltration.
Unlike other natural resources or raw materials, groundwater is present throughout the world varying from place to place, depending on rainfall conditions and the distribution of aquifers (rock and sand layers in whose pore spaces the groundwater sits). Precipitation and soil type determines how much the shallower groundwater is recharged annually. However the volume of water that can be stored is controlled by the reservoir characteristics of the subsurface rocks. Generally, groundwater is renewed only during a part of each year through precipitation, but can be abstracted year-round providing a reliable and clean source of drinking water to much of the population provided there is adequate replenishment, and it is protected from pollution. We need to be aware of the source of our groundwater it’s natural recharge rate and protect our aquifers from over use and contamination.
Groundwater is usually cleaner than surface water and as source water for drinking water supplies it is often superior to surface water. Groundwater is typically protected against contamination from the surface by the soils and rock layers covering the aquifer. This water is the only available clean drinking water in many areas. However, rising population, changes in land use, agriculture and industrialization increasingly place groundwater in jeopardy of contamination. Once contaminated, groundwater is very difficult to clean and often after removal of contaminated plumes only long term abandonment of use to allow for natural attenuation is the only possible course of action. Precious groundwater resources increasingly need to be protected from contamination and well managed to allow for sustainable long-term use.
Though the water quality of the public water supply systems is regulated by the US EPA under the Safe Drinking Water Act (SDWA), drinking water supplies are only tested for slightly over 90 contaminants (many of them natural impurities) when there are over 80,000 chemicals known in the United States. In addition, the US EPA only regulates the finished water delivered to consumer through public water supply systems. The underlying groundwater quality often has not been tracked by the US EPA. In their study of the quality of groundwater sources in the United States, the USGS found trace levels of pesticide compounds (not regulated under the SCWA) or VOCs in 64% of the groundwater samples taken from public water supply wells. Three-quarters of the organic-contaminants contained an herbicide (atrazine or simazine) or an herbicide degradate (deethylatrazine), and about 40% contained the solvents perchlorethene or trichloroethene. Pesticides and VOCs were detected in a significantly greater proportion of samples from unconfined aquifers than in samples from confined aquifers. The groundwater with the greatest number of contaminants was consistently from shallower unconfined aquifers demonstrating the natural protection provided by a confining geological layer.
Groundwater typically contains geological trace elements such as arsenic, manganese, strontium, iron, and boron and radionuclides (radon, radium, and gross alpha-particle radioactivity). These contaminants originate from the rocks and sediments that contain the aquifers and are entirely natural, but there are health related maximum contaminant level standards for these elements within the SDWA. For groundwater supplies, the concentration of these geological contaminants does not change quickly over time and remains rather constant in any given region. What is changing is the appearance of modern pesticides and herbicides, substances atrazine or simazine and their breakdown products in groundwater. These chemicals slowly percolate into groundwater from land application of pesticides and herbicides used for greener lawns and gardens or for agriculture. They appear in shallower groundwater supplies. Another source of contamination of groundwater is our septic systems. It is estimated by various sources that 25-35% of all US homes use septic systems.
There are many different types of septic system designs. The most common type used for single family homes consists of a septic tank and leach field. A septic tank can be an anaerobic (without air) tank or an aerobic tank (with air). The anaerobic system is a single chamber tank that receives the toilet and drain waste from the house and allows the solids to settle down to the bottom of the tank where the anaerobic bacteria that live in the tank digest the organic materials while the effluent (water around all that stuff) flows out to the leach field to be purified by passing through soil until it reaches the groundwater. The final finishing for septic waste is the leach field or other soil absorption system, where it percolates into the soil, which provides final treatment by removing harmful bacteria, viruses, and nutrients. This is a natural process requiring suitable soil for successful waste water treatment, but even with the most suitable soil septic systems cannot remove chemicals from the water. Household cleaners, fertilizers, pesticides, pharmaceuticals and personal care products will just pass through the system and begin to appear in the recharge to the groundwater.
As our homes are filled with ever more powerful and chemical laden cleaners, antibacterial soaps, pesticides, herbicides, paints, petroleum products, insecticides and drugs-all the wonders of modern life, these things find their way into our waters. Through stormwater runoff and waste water treatment plants these things easily find their way to our surface waters. Waste water treatment plants are no more equipped to treat waste water for these chemicals than a septic system is and quite frankly none of these public supplies of water are routinely tested for these substances. Waste water treatment plants do not have chemical removal processes. Through our septic systems, and gardens and yards these contaminants are appearing in our groundwater. Although each septic system and yard can make an insignificant contribution to ground water contamination, the sheer number of such systems and their wide spread use of pesticides and herbicides in every area make them serious contamination sources. What goes down the drain or is sprayed and spread in the garden goes into the groundwater. To make a difference we all need to protect our groundwater.
The following actions to protect groundwater from contamination and are based on recommendations from the National Groundwater Association:
1. Properly store hazardous household substances like paints, paint thinners, petroleum products, fertilizers, herbicides, insecticides, and cleaning products in secure containers
2. Mix hazardous household substances over concrete or asphalt where they can be cleaned up or absorbed onto disposable media like paper towels and then properly disposed of with hazardous material waste.
3. Dispose of hazardous household wastes at an appropriate waste disposal facility or drop-off. Most landfills and city trash programs have these drop-offs.
4. Do not put hazardous household wastes down the drain or in the toilet ever,
5. Do not put any wastes down a dry or abandoned well or use sinkholes as waste disposal holes.
6. Service your septic system regularly at a minimum service it according to local health department recommendations
7. Check your private drinking water well annually to make sure the sanitary seals are intact.
8. Decommission abandoned wells on your property using a qualified water well contractor
9. Fix or replace any leaking aboveground or underground tanks storing hazardous substances. All underground storage tanks should have secondary containment to prevent contamination of the subsurface. All tanks will eventually fail.
Showing posts with label George Harlow USGS. Show all posts
Showing posts with label George Harlow USGS. Show all posts
Monday, March 12, 2012
Thursday, November 4, 2010
Groundwater in Virginia
According to George Harlow at the US Geological Survey (USGS) in Richmond, VA about 34% of all drinking water in Virginia is supplied by groundwater and there are 1.7 million Virginians whose drinking water is sourced from groundwater and supplied by their own private wells. The information below is from a talk Mr. Harlow gave and the Private Water Supply Handbook.
The geology-the underlying types of soil and rocks of an area determines the characteristic and availability of groundwater. To survive over time, a population must live within the carrying capacity of its ecosystem, the most important element of the ecosystem is potable water. Without water there can be no life. Water is needed for drinking, bathing, to support irrigated agriculture and industry. In Virginia, our rainfall is usually adequate and there is limited need to irrigate. Precipitation and soil type determines how much the shallower groundwater is recharged annually. However the volume of water that can be stored is controlled by the reservoir characteristics of the subsurface rocks. Groundwater may be present today that was precipitation months, years or eons ago. Using more groundwater than is recharged through precipitation is unsustainable over the long run.
The nature of the soils and rocks varies across Virginia by physiographic province. The geological regions of Virginia are (from east to west) the Coastal Plain, the Piedmont, the Blue Ridge, the Valley and Ridge and the (Cumberland) Plateau. There is also a limited areas of Mesozoic Lowlands within the Piedmont that is not a geographic region but is a physiographic province and is groundwater rich. I happen to live within the Mesozoic Lowlands. The natural occurrence and availability of groundwater depends on the geological conditions.
The Costal Plain of Virginia is composed mostly of unconsolidated geologic deposits and extends from the Atlantic coast to the “fall zone” a geological line that runs north-south through Fairfax, Fredericksburg, Richmond, and Petersburg. At its widest portion the Costal Plain is over 100 miles wide. Costal Plain deposits consist of alternating layers of unconsolidated sand, gravel, silt, shell strata and clay and slopes generally southeast. There are two groundwater systems, an unconfined aquifer and a lower artesian aquifer both flow in the general direction of the topography slope towards the ocean. In unconsolidated sediments well casings must reach to the water table and the well must be screened in the saturated zone, but just about anywhere you drill a well, you will find groundwater. Water tends to be of good quality for the most part, but there are areas where over pumping has resulted in salt water intrusion and areas where iron and hydrogen sulfide occur. It is very possible with little more population growth that during drought years Fairfax and the Norfolk-Virginia Beach area will have inadequate water.
The Piedmont is bordered by the “fall zone” on the east and the Blue Ridge Mountains on the west. The Piedmont is the largest geological region in Virginia and has a diverse geology largely dominated by igneous and metamorphic rocks, with some areas of sedimentary rocks. The area has limited overburden and the fractures and fault lines formed in the rocks store and transmit groundwater. The size and number of water bearing fractures decrease with depth so significant supplies of water are generally located in the first few hundred feet. There is a wide variation in groundwater quality and yield ranging from under 1 gallon to over 50 gallons a minute. The largest yields are obtained where fracture and fault system are extensive along the base of the Blue Ridge Mountains. In other areas of the Piedmont, disintegration of the granite bedrock forms a zone of granular material with slow recharge and relatively high and annoying amounts of iron and sulfur. To be productive a well must be located within a fracture. Water tends to be hard and in many areas contains high levels of iron, sulfur, and can be acidic.
The Mesozoic Lowlands are within the Piedmont region. These areas consists of an interbedded sequence of sedimentary and basaltic rocks. The rocks of the lowlands are highly fractured and overlain by a thin cover of overburden. The lack of overburden limits natural protection to the aquifer. The sedimentary rocks are productive aquifers. The soils are described by the USGS as Balls Bluff Siltstone with a gravel, sand and clay type bedding plane. In the siltstone bedding plane, the fractures within the rock run predominately north south. Thus while ground water flows generally speaking west to east, water or a contaminant that catches a fracture will carry the contaminant to depth in a north south pattern. Contaminants can enter the groundwater at these fractures spread easily. Groundwater is easy to locate and tends to be hard.
The Blue Ridge province lies to the west of the Piedmont and is a narrow zone (4-25 miles wide) of mountains that runs from North Carolina to Maryland with the highest elevations in Virginia. The bedrock is near the surface and relatively impervious and contains limited amounts of water in joints, fractures and fault zones. Igneous and metamorphic rocks are most common on the eastern slope (and into the Piedmont) and sedimentary rocks are common on the western slope. Water yields are low and limited and typically very high in iron. Water containing fractures can be few and far between and it is very possible not to find water on a home site or to have a well run dry regularly.
The Valley and Ridge region is to the west of the Blue Ridge Mountains and is underlain by consolidated sedimentary rocks of limestone, dolomite, shale and conglomerate. Limestone and dolomite occur beneath lowlands, such as the Shenandoah Valley (also within the lowlands between the Potomac and the Catoctin Mountains) these deposits consistently form productive aquifers. Karst features such as sinkholes, caves, and large springs are found in the Valley and Ridge province. The ridges in the upland area are typically underlain by sandstone and shale with limited groundwater yield. Limestone frequently contains underground channels that store and transmit groundwater. Rapid movement of water in the limestone area makes the pollution potential high. Aquifers are often recharged directly by streams crossing fault zones giving wells in these areas the highest yields. This direct surface water to groundwater recharge can create serious water quality problems. The groundwater in these zones bypasses any natural filtration the soil might have provided. The quality of the groundwater would reflect the quality of the seasonal streams and surface water and tends to be acidic.
The smallest geological region of Virginia is the Cumberland Plateau also called the Appalachian Plateau which includes the southwester tip of Virginia. This region is underlain by sedimentary rocks, primarily sandstone, shale and the coal. It is the presence of coal that has most determined the fate of this region. The groundwater travels in the coal veins. The gentle folding of these formations has created domes and basins and faulting has occurred. Groundwater quality is generally best in the bedrock above the stream level. The groundwater in the stream level contains high concentrations of sulfate, sulfite, nitrate, iron and carbon dioxide. The water improves at 150-300 feet below this area. Groundwater is generally used for small domestic purposes and processing coal. The shallow nature of the groundwater allows for relatively easy contamination.
The quality and minerals in the groundwater are determined to a large extent by the local geology. Virginia is rich in water our actions will determine if we remain so. The process by which water from rainfall, snowmelt, streams and rivers flows into water bearing geologic formation is the groundwater recharge process. The climate change models (as limited and faulty as they may be) predict that Virginia will become a bit wetter and warmer (think North Carolina). A failure of the water supply in Virginia will be due to our own actions and decision. The land surface through which groundwater is recharged must remain open and uncontaminated to maintain the quality and quantity of groundwater of the Commonwealth of Virginia.
The geology-the underlying types of soil and rocks of an area determines the characteristic and availability of groundwater. To survive over time, a population must live within the carrying capacity of its ecosystem, the most important element of the ecosystem is potable water. Without water there can be no life. Water is needed for drinking, bathing, to support irrigated agriculture and industry. In Virginia, our rainfall is usually adequate and there is limited need to irrigate. Precipitation and soil type determines how much the shallower groundwater is recharged annually. However the volume of water that can be stored is controlled by the reservoir characteristics of the subsurface rocks. Groundwater may be present today that was precipitation months, years or eons ago. Using more groundwater than is recharged through precipitation is unsustainable over the long run.
The nature of the soils and rocks varies across Virginia by physiographic province. The geological regions of Virginia are (from east to west) the Coastal Plain, the Piedmont, the Blue Ridge, the Valley and Ridge and the (Cumberland) Plateau. There is also a limited areas of Mesozoic Lowlands within the Piedmont that is not a geographic region but is a physiographic province and is groundwater rich. I happen to live within the Mesozoic Lowlands. The natural occurrence and availability of groundwater depends on the geological conditions.
The Costal Plain of Virginia is composed mostly of unconsolidated geologic deposits and extends from the Atlantic coast to the “fall zone” a geological line that runs north-south through Fairfax, Fredericksburg, Richmond, and Petersburg. At its widest portion the Costal Plain is over 100 miles wide. Costal Plain deposits consist of alternating layers of unconsolidated sand, gravel, silt, shell strata and clay and slopes generally southeast. There are two groundwater systems, an unconfined aquifer and a lower artesian aquifer both flow in the general direction of the topography slope towards the ocean. In unconsolidated sediments well casings must reach to the water table and the well must be screened in the saturated zone, but just about anywhere you drill a well, you will find groundwater. Water tends to be of good quality for the most part, but there are areas where over pumping has resulted in salt water intrusion and areas where iron and hydrogen sulfide occur. It is very possible with little more population growth that during drought years Fairfax and the Norfolk-Virginia Beach area will have inadequate water.
The Piedmont is bordered by the “fall zone” on the east and the Blue Ridge Mountains on the west. The Piedmont is the largest geological region in Virginia and has a diverse geology largely dominated by igneous and metamorphic rocks, with some areas of sedimentary rocks. The area has limited overburden and the fractures and fault lines formed in the rocks store and transmit groundwater. The size and number of water bearing fractures decrease with depth so significant supplies of water are generally located in the first few hundred feet. There is a wide variation in groundwater quality and yield ranging from under 1 gallon to over 50 gallons a minute. The largest yields are obtained where fracture and fault system are extensive along the base of the Blue Ridge Mountains. In other areas of the Piedmont, disintegration of the granite bedrock forms a zone of granular material with slow recharge and relatively high and annoying amounts of iron and sulfur. To be productive a well must be located within a fracture. Water tends to be hard and in many areas contains high levels of iron, sulfur, and can be acidic.
The Mesozoic Lowlands are within the Piedmont region. These areas consists of an interbedded sequence of sedimentary and basaltic rocks. The rocks of the lowlands are highly fractured and overlain by a thin cover of overburden. The lack of overburden limits natural protection to the aquifer. The sedimentary rocks are productive aquifers. The soils are described by the USGS as Balls Bluff Siltstone with a gravel, sand and clay type bedding plane. In the siltstone bedding plane, the fractures within the rock run predominately north south. Thus while ground water flows generally speaking west to east, water or a contaminant that catches a fracture will carry the contaminant to depth in a north south pattern. Contaminants can enter the groundwater at these fractures spread easily. Groundwater is easy to locate and tends to be hard.
The Blue Ridge province lies to the west of the Piedmont and is a narrow zone (4-25 miles wide) of mountains that runs from North Carolina to Maryland with the highest elevations in Virginia. The bedrock is near the surface and relatively impervious and contains limited amounts of water in joints, fractures and fault zones. Igneous and metamorphic rocks are most common on the eastern slope (and into the Piedmont) and sedimentary rocks are common on the western slope. Water yields are low and limited and typically very high in iron. Water containing fractures can be few and far between and it is very possible not to find water on a home site or to have a well run dry regularly.
The Valley and Ridge region is to the west of the Blue Ridge Mountains and is underlain by consolidated sedimentary rocks of limestone, dolomite, shale and conglomerate. Limestone and dolomite occur beneath lowlands, such as the Shenandoah Valley (also within the lowlands between the Potomac and the Catoctin Mountains) these deposits consistently form productive aquifers. Karst features such as sinkholes, caves, and large springs are found in the Valley and Ridge province. The ridges in the upland area are typically underlain by sandstone and shale with limited groundwater yield. Limestone frequently contains underground channels that store and transmit groundwater. Rapid movement of water in the limestone area makes the pollution potential high. Aquifers are often recharged directly by streams crossing fault zones giving wells in these areas the highest yields. This direct surface water to groundwater recharge can create serious water quality problems. The groundwater in these zones bypasses any natural filtration the soil might have provided. The quality of the groundwater would reflect the quality of the seasonal streams and surface water and tends to be acidic.
The smallest geological region of Virginia is the Cumberland Plateau also called the Appalachian Plateau which includes the southwester tip of Virginia. This region is underlain by sedimentary rocks, primarily sandstone, shale and the coal. It is the presence of coal that has most determined the fate of this region. The groundwater travels in the coal veins. The gentle folding of these formations has created domes and basins and faulting has occurred. Groundwater quality is generally best in the bedrock above the stream level. The groundwater in the stream level contains high concentrations of sulfate, sulfite, nitrate, iron and carbon dioxide. The water improves at 150-300 feet below this area. Groundwater is generally used for small domestic purposes and processing coal. The shallow nature of the groundwater allows for relatively easy contamination.
The quality and minerals in the groundwater are determined to a large extent by the local geology. Virginia is rich in water our actions will determine if we remain so. The process by which water from rainfall, snowmelt, streams and rivers flows into water bearing geologic formation is the groundwater recharge process. The climate change models (as limited and faulty as they may be) predict that Virginia will become a bit wetter and warmer (think North Carolina). A failure of the water supply in Virginia will be due to our own actions and decision. The land surface through which groundwater is recharged must remain open and uncontaminated to maintain the quality and quantity of groundwater of the Commonwealth of Virginia.
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