|
Water Facts
• Fluctuating Water Table
• Groundwater in Colorado
• Groundwater in La Plata County
• La Plata County Water Well Permits
Information in this section was found in "Ground Water Issues and Answers," published by the American Institute of Professional Geologists, Geological Survey Water Supply Paper 1576-J, "A Primer on Ground Water," a United States Department of the Interior, Geological Survey publication, (available at the Fort Lewis College Library), and The Groundwater Foundation.
Many people think of ground water as under ground lakes or streams. There are such things – in areas of cavernous limestone or volcanic lava flows – but mostly, ground water is simply water filling spaces between rock grains or in fractures and fissures in rocks. Such openings are most common near the land surface; at great depths, openings are closed by the great pressure of overlying materials. In our area almost all groundwater is found in tiny pore spaces within sandy rocks.
Groundwater supplies are replenished, or recharged, by rain and snowmelt. Plants consume much of the water that enters the soil, and a small amount is held on the soil grains by capillary forces, the same forces that hold enough water in a wet towel to make it feel damp after it has stopped dripping. Any surplus water percolates downward to the zone of saturation -- rock or soil in which every available space is filled with water. The top of the zone of saturation is called the water table.
When rain falls, the water table rises; in times of drought, the water table declines because of drainage to the natural outlets. Because of this fluctuation, a well that is not drilled very far below the current water table may intermittently "go dry" when the water table falls. In some areas of the world, people face serious water shortages because groundwater is used faster than it is naturally replenished.
The amount of water a rock can contain depends on the porosity of the rock – the spaces between the grains or the cracks that can fill with water. If water is to move through he rock, the pores must be connected. If the rock has a great many connected pore spaces, of which a large part are sizeable so that water can move freely through them, the rock is permeable. Large amounts of water are available to a well from saturated permeable rocks. But if the pores or cracks are small, poorly connected, or nearly lacking, the aquifer can yield only a small amount of water to a well.
The word aquifer comes from two Latin words: aqua, or water, and ferre, to bring. The aquifer literally brings water (underground, or course). The aquifer may be a layer of gravel or sand, a layer of sandstone or of cavernous limestone, or even a large body of nonlayered rock that has sizeable openings.
Ground water does not occur downward all the way to the core of the earth. Beneath water-bearing rocks everywhere, at some depth, the rocks are water-tight. This depth may be a few hundred feet, or more than likely tens of thousands of feet.
On average, permeability of rock grows less as depth increases. Most wells drilled deeper than 2,000 feet find little water. The pores and cracks in the rocks at great depths are closed up because of the weight of overlying rocks.
Groundwater is used for drinking water by more than 50% of the people in the United States, including almost everyone who lives in rural areas. The largest use for groundwater is to irrigate crops.
In La Plata County, the most productive aquifers are the Quaternary alluvium and terrace gravels (sands and gravels) and the Tertiary Animas, San Jose and Nacimiento Formations (sandstone and siltstone). Other rocks in our area are sometimes used as water sources. Quality and quantity vary greatly by formation. Water quality and quantity generally become poorer with increasing depth and age. The coal-bearing formations such as the Fruitland and Menefee are rarely used as aquifers because they contain gas, sulfur and iron, and are generally undesirable.
[back to top]
Information in this section was found at The Environmental Protection Agency > Colorado Drinking Water, the Water Information Program, and the "1999-2000 Report to the Water Quality Control Commission and Water Quality Control Division of the Colorado Department of Public Health and Environment by the Colorado Oil and Gas Conservation Commission – December 2000."
Additional information about Colorado water can be found at: The Colorado Division of Water Resources, the Colorado Department of Public Health and Environment, and Colorado Water Knowledge.
In Colorado, groundwater supplies eighteen percent (18%) of the water used in the state. Nineteen of 63 Colorado counties rely solely on ground water for drinking water and domestic uses. Colorado’s agricultural industry relies heavily upon ground water; approximately ninety-six percent (96%) of the found water produced is consumed by agriculture. As the population of the state continues to grow at an unprecedented rate, the number of people dependent on ground water is also increasing. Much of the growth is occurring in the mountainous areas where ground water supplies are limited and highly vulnerable to contamination.
Ground water protection is managed as two separate issues of quantity and quality in Colorado. Quantity issues are managed through the Colorado Division of Water Resources/Office of the State Engineer. The Colorado Water Quality Control Act, through a number of state agencies, protects quality. The Colorado Department of Public Health and Environment is the lead agency. The Colorado Water Quality Control Commission is responsible for promulgating groundwater classifications and standards.
Since 1990, the Colorado Oil and Gas Conservation Commission (COGCC) is an implementing agency for water quality standards and classifications adopted by the Water Quality Control Commission for ground water protection as it relates to oil and gas operations. The authority was provided by state legislation (SB89-181) and clarified by a Memorandum of Agreement between the agencies.
[back to top]
Information in this section was found at: The Environmental Protection Agency > Colorado Drinking Water, the Colorado Division of Water Resource, USGS Robson/Wright report "Groundwater resources of the Florida Mesa Area, La Plata County Colorado, 1995, and La Plata County Comprehensive Plan Working Document, 2000.
Many residents of La Plata County get drinking water from private domestic water wells or water systems. In fact, most residential developments in the unincorporated areas of the county rely on groundwater wells. In La Plata County, there are over 7,000 well permits with groundwater as their source. There are 46 community water systems, 63% of which have groundwater as the primary source; and 70 non-community water systems, 78% of which have groundwater as the primary source.
[back to top]
Source: Colorado Division of Water Resources – Durango, CO office
Rapid population growth in La Plata County has caused increased reliance on ground water as a source of supply for suburban and rural residents. In many developing areas, such as Florida Mesa, groundwater recharge is highly dependent on infiltration of irrigation water. As an example, Florida Mesa winter water levels in [domestic] wells generally are lower than summer water levels because of the lack of irrigation recharge during the fall and winter. As development occurs and agricultural land is taken out of production, there is a potential for groundwater to become depleted. Continued high rates of development in areas lacking central water systems increases the potential for dewatering aquifers and impact to existing wells.
Geologic studies show that beds of nearly impermeable shale separate sandstone beds and retard vertical water movement between deep and shallow aquifers.
[back to top]
|
