CHAPTER IV:

GROUNDWATER

BAUTISTA, GLADYS JOY B.CE-5B

GROUNDWATER

Ground water is that part of precipitation that infiltrates through the soil to the water table. An important component of water resource systems

SOURCES OF GROUNDWATER

PrecipitationInterceptionSubsurface 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 that affect the presence and movement of ground water :

Porosity - size and amount of void spaces

Permeability -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 climatic effects 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 EVAPORATIONSPRINGSSUBSURFACE FLOWWELLS

Groundwater movement

Groundwater flows underground in response to elevation differences (downwards) and pressure differences (from areas of high pressure to areas of low pressure).

Darcy's 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 allow another substance to pass through it, especially the ability Of a porous rock, sediment, or soil to transmit fluid through pores and cracks. PERMEAMETERS Device use to determine permeability

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 WELLSStatic 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 EQUATION Unconfined Radial Flow

Radial Confined Flow

OTHER WELL TESTS:

RECOVERY TESTS

SLUG TESTS

LEAKY AQUIFER TESTS

STEP DRAWDOWN TESTS

Types of Wells

FLIGHT – each section of the auger

SCHEMATIC DIAGRAM OF AUGER FLIGHT AUGER FLIGHT

Sources of contamination in groundwater

Salt 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 CHLORINATION

Shock chlorination/well sanitation is simply the process of adding a sanitizer to the well in high concentrations to destroy any bacterial growth. Shock chlorination is effective in reducing an iron bacteria, hydrogen sulfur, or coliform bacteria problem