Attenuation of pollution in

groundwater

From : Vishwanath Awati

USN : 2VX15CWM23

Most 'normal' contaminantsMicrobiologic pollutants

Inorganic or organic pollutants• Heavy metals and dissolved solids, B, Na, K, Mg, Ca, Cl, NO3 etc

FROM different source groundwater polluted, this affects on groundwater user, Like health problems.

To outcome above problem needs to remove or reduction of pollution before use of groundwater.

Attenuation of pollution Pollutants in groundwater tend to

be removed or reduced in concentration with time and with distance travelled

The rate of pollution attenuation depends on the type of pollutant and on the local hydro geologic situation

(from ref.1).

(from Coombs el at., 1999).

Factors affecting microbe survival and half-life

SIGNIFICANCE OF THE UNSATURATED ZONE

Attenuation is generally most effective and biological activity is greatest.First line of natural defense against groundwater pollution.

SIGNIFICANCE OF THE SATURATED ZONE

Generally at much lower rates because groundwater moves more rapidly.

Dispersion and dilution will play an important role in reducing contaminant concentration.

(from ref.2).

(from ref.2).

Mechanisms involved include:-

Filtration Sorption Chemical processes Microbiological decomposition Dilution

(from ref.1).

•Mechanical filtration is more effective for microbiological and chemical contaminant.

FiltrationPhysical filtration: suspended particulates

trapped by earth. •When flow from surface water to subsurface water.

Example. RBF method. Most effective method of attenuation mechanism

•Pharmaceutical compounds (medical drug traces from human use )may not always be sufficiently removed by bank filtration.

(from ref.1).

Mechanical filtration

(from ref.3).

•Sorption is the common term used for both absorption and adsorption.

SORPTION

•Sorptive materials are Clays, metallic oxides, hydroxides, organic matter.

• some extent chloride, nitrate, sulfate are removed.

•Chemical processes Chemical filtration(ion exchange) : aquifer soils react with soluble

chemicals in the water.

Precipitation reactions for Major constituents involve are Ca, Mg, bicarbonates and sulfate.

Precipitation potential include Arsenic, barium, Cadmium, copper, cyanide, fluoride, iron, lead, zinc.

Above water table oxidation of organic matter major mechanism.

Example generalized concept of aerobic organic decomposition

(from ref.1).

Example: Generalized aerobic organic matter decomposition

Complex organic matter

simple organic matter

Oxidation or

reduction

Microbiological decomposition1. Biological filtration : microorganisms

remove and digest by dissolved or suspended organic material and chemical nutrients.

2. Pathogen like bacteria , viruses are largely removed by passage through soil of clay and silt of 1m length .

Subsurface soil as filter

Dilution• Hydrodynamic dispersion occurs microscopic and macroscopic scales. • Volume groundwater increases than concentration decreases with distance travels.

• Dilution is major mechanism pollutants reach the water table.

Example:

Dilution

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