CHAPTER IV:GROUNDWATER BAUTISTA, GLADYS JOY B. CE-5B
GROUNDWATERGround water is that part of precipitation that infiltrates through the soil tothe water table. An important component of water resource systems
SOURCES OF GROUNDWATERPrecipitationInterceptionSubsurface flowSoil moisture
ZONES OF UNDERGROUND WATER Zone of aeration/ vadose zone - a zone that contains both water and air Saturated zone - where all the interconnected openings between rock particles are filled with water
Soil moisture- water in the upper layers of zone of aeration Groundwater- called the water in the zone of saturation Perched water table - when a small water body is separated from the main groundwater body by a relatively small impermeable stratum. Capillary fringe/ tension-saturated zone - the place above the water table. In this region the pore space is completely filled with water. Groundwater may be recharged or discharged
How ground water occur in rocks?
Two characteristics of all rocks thataffect the presence and movement ofground water :Porosity - size and amount of void spacesPermeability -the relative ease with which water can move through spaces in the rock.
Water table It is a surface of a water body that is constantly adjusting itself toward an equilibrium condition. If there were no recharge to or outflow from the ground-water basin, the water table would eventually become horizontal.
A 10-year well hydrograph showing climaticeffects on ground-water level.
Aquifer is an underground layer of water-bearing permeable rock or unconsolidated materials (gravel, sand, or silt) from which groundwater can be extracted using a water well.
2 types of aquifer: Unconfined aquifers - are those into which water seeps from the ground surface directly above the aquifer.
Confined aquifer/artesian aquifer – are separated from the ground surface by an impermeable layer and are generally at greater depths than unconfined aquifers.
DISCHARGE OF GROUNDWATER DISCHARGED BY: TRANSPIRATION AND EVAPORATION SPRINGS SUBSURFACE FLOW WELLS
Groundwater movement Groundwater flows underground in response to elevation differences (downwards) and pressure differences (from areas of high pressure to areas of low pressure).Darcys law relates the rate of the groundwater movement (Q) to the hydraulic conductivity (K), the cross-sectional area (A) and to the hydraulic gradient or slope of the water table (h/l) : The hydraulic conductivity depends on the permeability of the rock and on the properties of the water. Water generally flows in the direction of the hydraulic gradient and slope of the water table. Q= Kah/l
DETERMINATION OF PERMEABILITY PERMEABILITYThe ability of a substance to allowanother substance to pass throughit, especially the ability Of a porousrock, sediment, or soil to transmitfluid through pores and cracks. PERMEAMETERSDevice use to determinepermeability
Wells and Pump Well is an excavated hole, usually a vertical shaft, in the earth allowing access to groundwater Pumping a well lowers the water level around the well to form a cone of depression in the water table. If the cone of depression extends to other nearby wells, the water level in those wells will be lowered.
HYDRAULICS OF WELLS Static Water Level [SWL] (ho) is the equilibrium water level before pumping Commences • Pumping Water Level [PWL] (h) is the water level during pumping • Drawdown (s = ho - h) is the difference between SWL and PWL • Well Yield (Q) is the volume of water pumped per unit Time • Specific Capacity (Q/s) is the yield per unit drawdown
THIEM EQUATIONUnconfined RadialFlow
Radial Confined Flow
OTHER WELL TESTS:RECOVERY TESTSSLUG TESTSLEAKY AQUIFER TESTSSTEP DRAWDOWN TESTS
Types of Wells
SCHEMATIC DIAGRAM OF AUGER FLIGHT AUGER FLIGHT FLIGHT – each section of the auger
Sources of contamination ingroundwaterSalt contaminationLeakage and spillsPesticides and fertilizersWaste disposals
Advection- describes movement of contaminant with and at the speed of the moving water Dispersion- it leads to a spreading of concentration fronts as they evolve over time and enhanced mixing of contaminated water with surrounding uncontaminated water. Molecular diffusion- spreading of contaminants from the pore space from regions of high concentration to low cow concentration in response to concentration gradients Radioactive decay- results in the transformation of a radioisotopes into one or more daughter products. Volatilization- phase transfer into soil gas in the unsaturated zone. Sorption-absorption- transfer into soil and rock particles
MITIGATION Cleanup of contaminated groundwater tends to be very costly. Effective remediation of groundwater is generally very difficult. . Most of these treatment methods involve the filtration of the contaminants of concern, and additional protection may be garnered by installing well-casing screens only at depths where contamination is not present. Well water for personal use is often filtered with reverse osmosis water processors; this process can remove very small particles. A simple, effective way of killing microorganisms is to bring the water to a full boil for one to three minutes, depending on location.
SHOCK CHLORINATIONShock chlorination/well sanitation issimply the process of adding a sanitizer tothe well in high concentrations to destroyany bacterial growth. Shock chlorination iseffective in reducing an iron bacteria,hydrogen sulfur, or coliform bacteriaproblem