Types of Aquifers
Unfortunately, owing to increased labor costs and declines in profitability at most sites, many of these wells have fallen into a state of disrepair and have been either plugged, stuffed up, or overgrown with trees. Some of these wells have been contaminated by garbage dumped into them. In sinkhole injection, operations are simple. The canal attendant, who normally resides nearby, visits the site twice a day to read the Parshall flumes, collect water samples, and open or close sluice gates.
The earth canals need to be kept clear to ensure maximum delivery of water. The settling basin has to be cleaned of accumulated sediment and vegetative growths once every four to five months. Vandalism, resulting in damage to sluice gates, sinkholes, and monitor wells, is also a problem in the maintenance of the system. Level of Involvement In Argentina, most of the experimental use of this technology has been done by the government in both the provinces of San Juan and Mendoza. In Paraguay, the government, in conjunction with international organizations, has been conducting experiments to quantify the recharge provided by different recharge systems.
In general, the implementation and maintenance of these technologies in urban areas have been carried out by municipal governments, but in rural areas by he private sector. Both the private sector and the Government of Barbados have been involved in the successful implementation of artificial recharge schemes. The private sector, primarily represented by the sugar industry, has encouraged the development of this technology and provided land, manpower, and water.
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The government, represented by the Water Authority, has provided technical expertise and financing. In Jamaica, there is a cadre of well-diggers who can be contracted by the government, plantation owners, and other landowners to both dig and maintain drainage wells. An ongoing educational program informs landowners of the need to maintain wells on a regular basis, the potential for groundwater recharge from the wells, and the need to monitor contamination of the groundwater.
This cost is primarily related to the construction of the inflow settling basin and channels conveying the runoff water to the sinkholes. Water traps have been successfully used for more than 25 years in Argentina. They have been very useful in reducing sedimentation and risk of flooding. Cutwaters proved a significant source of water to communities during the droughts of and in the Paraguayan Chaco.
Even though groundwater recharge is not the principal intended use of drainage wells, it is a major indirect beneficiary. Infiltration rates in coral rock in Barbados have been estimated at between 6. In Jamaica, total recharge over 18 months amounted to 4 million m 3. Two groundwater mounds were detected downgradient of sinkholes. One mound indicated an increase of 4. Divergent radial flows developed from both of these mounds.
Once recharge ceased, the mounds gradually disappeared over a two-month period. In general, most wells influenced by artificial recharge have shown declines in salinity levels. Suitability In areas where groundwater is an important component of the water supply, and rainfall variability does not allow for a sufficient level of aquifer recharge by natural means, these technologies provide for the artificial enhancement of the natural recharge.
Aquifers and Groundwater
Storage of surface runoff in underground aquifers in arid and semi-arid areas has the advantage of minimizing evaporative losses. However, use of these technologies requires an appropriate geological structure. In areas underlain by igneous rock, the natural fracture lines can be expanded by injection of water under pressure and infusion of a sand slurry into the gaps thus created. Given the cost of this latter measure, however, use of natural limestone or sandstone formations, such as are common in the Caribbean islands, is preferred and most cost-effective.
In most cases, the surface water runoff is not pre-treated before injection. In karstic terrain, dye tracer studies can assist in acquiring this knowledge. Cultural Acceptability Artificial groundwater recharge is generally well accepted by communities in areas where it is used. Information Sources Contacts B.
Fax Basil P. Alberto I. Aquifers are natural filters that trap sediment and other particles like bacteria and provide natural purification of the ground water flowing through them.
Like a coffee filter, the pore spaces in an aquifer's rock or sediment purify ground water of particulate matter the 'coffee grounds' but not of dissolved substances the 'coffee'. Also, like any filter, if the pore sizes are too large, particles like bacteria can get through.
This can be a problem in aquifers in fractured rock like the Snake River Plain, or areas outside the sediment-filled valleys of southeast Idaho. Clay particles and other mineral surfaces in an aquifer also can trap dissolved substances or at least slow them down so they don't move as fast as water percolating through the aquifer.
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Natural filtration in soils is very important in recharge areas and in irrigated areas above unconfined aquifers, where water applied at the surface can percolate through the soil to the water table. For example, in the lower Portneuf River valley Figure 1 , a protective layer of silt in the southern valley provides natural protection to the aquifer from septic systems, pesticide application, and accidental chemical spills.
Despite natural purification, concentrations of some elements in ground water can be high in instances where the rocks and minerals of an aquifer contribute high concentrations of certain elements. In some cases, such as iron staining, health impacts due to high concentrations of dissolved iron are not a problem as much as the aesthetic quality of the drinking water supply. In other cases, where elements such as fluoride, uranium, or arsenic occur naturally in high concentrations, human health may be affected. How is an Aquifer Contaminated? As shown in Figure 3 , an aquifer can be contaminated by many things we do at and near the surface of the earth.
Contaminants reach the water table by any natural or manmade pathway along which water can flow from the surface to the aquifer. Deliberate disposal of waste at point sources such as landfills, septic tanks, injection wells and storm drain wells can have an impact on the quality of ground water in an aquifer. In general, any activity which creates a pathway that speeds the rate at which water can move from the surface to the water table has an impact.
In Figure 3 , waste water leaking down the casing of a poorly constructed well bypasses the natural purification afforded by soil.
Aquifers and Groundwater
Excessive addition of fertilizer, agrichemicals, and road de-icing chemicals over broad areas, coupled with the enhanced recharge from crops, golf courses and other irrigated land and along road ditches, are common reasons for contamination arising from non-point sources. An underground layer of permeable rock, sediment usually sand or gravel , or soil that yields water.
The pore spaces in aquifers are filled with water and are interconnected, so that water flows through them. Sandstones, unconsolidated gravels, and porous limestones make the best aquifers. They can range from a few square kilometers to thousands of square kilometers in size. All rights reserved.