Natural And Artificial Tracers In Ground Water

Introduction

•The fundamental idea of the tracer technique is simple and clear.

•water is “marked” with the aid of a tracer and its propagation is followed.

•it has useful means in almost all fields of applied hydrology and hydrogeology.(groundwater, rivers, lakes, glaciers, etc.)

Groundwater tracing

Groundwater tracers include any substance that can become dissolved or suspended in water, or attached to the water molecule, and recovered or measured from a water sample that can be used to trace the source of groundwater in terms of its specific or relative location and time of recharge. Groundwater tracers can include both artificially introduced and naturally occurring substances

Why is tracing important?

•Tracing techniques can be used in all types of hydrological and hydro geological environments to obtain information about water movement and contaminant transport.

•water tracing was initially developed for the investigation of karst aquifers.

Type of Tracers

1.Natural Tracers

it involves the use of naturally occurring components of a water sample to determine information about the source and age of the sample.

Used in case of age-dating.

Environmental isotopes are now used to trace not only groundwater provenance, but also recharge processes, subsurface processes, geochemical reactions and reaction rates.

The most commonly used natural tracers are isotopes. Some are:-

–Oxygen Isotopes.

–Isotopes of Hydrogen

–Nitrogen

–Carbonate, organic carbon and hydrocarbon

2. Artificial Tracers

they can be used to evaluate the extent to which aquifers interact with surface water features, providing information on groundwater flow paths, travel times, velocities, dispersion, flow rates and the degree of hydraulic connection.

they should have low toxicological impact.

This differs from natural tracers methods which rely on the measurement and interpretation of background concentrations of the chemical constituents of water, such as major ions, stable or radioactive isotopes.

Fluorescent Dyes

Carbonate, organic carbon and hydrocarbon
Sulphur
Nitrogen
Chlorine
Bromine, lithium and boron
Strontium

Tracer tests

There are two basic types of dye tracer tests:-

1.Qualitative Tracer Tests.

2. Quantitative Tracer Tests.

Applications

Possible applications of the tracer technique in different aquifer types

Karstic aquifers

•Regional surveys of groundwater flow

•Establishment of conceptual models of karst systems

•Detection of karstic networks

Alluvial aquifers

•Regional investigations of groundwater flow

•Delimitation of catchments (containment areas)

•Delimitation of contaminant leakage zones

Hillslope groundwater and fractured aquifers

•Detection of flow paths in hard rocks

•Investigation of water bearing structures (e.g. joints, fractures and layering)

Main focuses of tracer investigations in hydrogeology

•Catch works (wells, springs)

•Groundwater protection zones

•Recharge area

•Risk assessments, simulation of hazards

•Ancient waste deposits, contaminated sites

•Interaction between ground and surface water

•Evidence of “foreign water”

•Determination of aquifer parameters/ groundwater modelling

•Expertise in case of damage

•Boreholes, groundwater observation network

Advantages and Disadvantages

Conclusion

•Groundwater, in its natural state, contains environmental isotopes and conclusions may be drawn from the distribution variations.

•The distribution of the stable isotopes, deuterium and oxygen-18, of groundwater correlated with average isotopic data of precipitation define the origin and movement of subsurface waters.

•Radioisotopes, such as tritium, provide valuable information on recent recharge whereas carbon-14 data show slow-moving groundwater.

•The use of isotope techniques which complement hydrochemical and hydrogeological studies should be encouraged in both surface water and groundwater resource development.