Groundwater flows towards the well into the cone of depression which can change the natural direction of groundwater flow within the area of influence around the well. If the cones of depression for two or more wells overlap, there is said to be well interference. This interference reduces the water available to each of the wells. The cone of depression from a well might extend to a nearby stream or lake.
This lowers the water table below the stream or lake level. As a result, the stream or lake begins to lose water to the groundwater aquifer near the well. This is know as induced recharge. Streams and wetlands can be completely dried up by induced recharge from well pumping. The Oregon Water Resources Department considers wells within 0.
Its trace perimeter on the land surface defines the zone of influence of a well. Also called cone of drawdown. Confined aquifer : Aquifers that are wedged between layers of relatively impermeable materials and are consequently under pressure. Also know as an artesian aquifer. Confining Layer : geological material through which significant quantities of water can not move; located below unconfined aquifers, above and below confined aquifers.
Also known as a confining bed. Contaminant : An undesirable substance physical, chemical, biological, or radiological not normally present, or an unusually high concentration of a naturally occurring substance, in water, soil, or other environmental medium.
Drawdown: The vertical distance groundwater elevation is lowered, due to the removal of groundwater. The distance between the static water level and the surface of the cone of depression. Flowing Artesian Well : When the top of a well in a confined aquifer is below the potentiometric surface, water will flow out of the well under pressure.
Groundwater: Water occurring in the zone of saturation in an aquifer or soil. Water beneath the surface of the earth which saturates the pores and fractures of sand, gravel, and rock formations. Groundwater barrier : Rock or artificial material with a relatively low permeability that occurs or is placed below ground surface, where it impedes the movement of groundwater and thus may cause a pronounced difference in the heads on opposite sides of the barrier.
Also called a confining layer. Head : Height of the column of water at a given point in a groundwater system above a datum plane such as mean sea level. It is also a measure of pressure as in a confined aquifer where the elevation of the groundwater does not equal its head because it is under pressure. Hydraulic Conductivity K : A coefficient of proportionality describing the rate at which water can move through a permeable medium. It is a function of the porous medium and the fluid.
See permeability. Hydraulic Cycle : The continuous circulation of water between the earth and the atmosphere, through condensation, precipitation, runoff, percolation, evaporation, transpiration, groundwater storage and seepage, and re-evaporation into the atmosphere.
Hydraulic Gradient i : Slope of a water table or potentiometric surface. Groundwater flows from points of high elevation and pressure to points of low elevation and pressure. The difference in hydraulic head divided by the distance along the flowpath.
Impermeable : Characteristic of geologic materials that limit their ability to transmit significant quantities of water under the head differences normally found in the subsurface environment. Leaking Underground Storage Tank LUST : An underground tank which has a structural rupture and its contents are leaving their containment and entering the surrounding environment.
Nonpoint source: Pollution of the water from numerous widespread locations that are hard to identify and pin-point. Perched Aquifer: An aquifer containing unconfined unpressurized groundwater held above a lower body of groundwater by an unsaturated zone; often a result of clay lenses in the soil strata. Point source : Pollution of water from one place in a concentrated manner that is easy to identify.
Pollution Plume : an area of a stream or aquifer containing degraded water resulting from migration of a pollutant. It extends from the source of contamination to another point in the direction of the water flow.
Porosity : The capacity of soil or rock to hold water. The ratio of the volume of void spaces in a rock or sediment to the total volume of the rock or sediment. Potentiometric Surface : An imaginary surface formed by measuring the level to which water will rise in wells of a particular aquifer. For an unconfined aquifer the potentiometric surface is the water table; for a confined aquifer it is the static level of water in the wells. Also known as the piezometric surface. Public Water System PWS EPA : Any water system providing water for human consumption for an average of at least 25 persons per day or 15 or more service connections and in use for at least 60 days each year.
Further defined as follows:. Recharge area : Area of land allowing water to pass through it into an aquifer by surface infiltration. This process occurs naturally when rainfall filters down through the soil or rock into an aquifer, usually in the higher gradient section overlying the aquifer. Static Water Level: The level of water in a well that is not being pumped.
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