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Conducting of Hydrogeological Investigations
A hydrogeological survey is an investigation of the hydrologic and geologic parameters at the subsurface level in a particular area. Hydrogeological maps may be formulated with the data gathered during such a study. It involves the detailed evaluation of the water-bearing levels of rocks and their capability for filtration. Moreover, the intrinsic ability of these rocks to either store or resist water is also assessed. The pressure, type and quality of the underground water is noted, delving into the intensity of the water flow through pores or fractures.
The Importance of Hydrogeological Surveying:
A hydrogeological survey is done to determine the underground water level. Hydrogeological surveying is conducted prior to drilling a borewell in order to ascertain the and quantity of water available at a particular location. It has been well established that underground water is a better source of drinking water than surface water. This is due to the following reasons:
Lower chances of pollution, especially if it is at least twenty meters away from the sanitary work.
Water becomes naturally purified as it flows through sand and stone.
Borewells remain shut and therefore have a reduced chance of contamination.
Greater chances of water availability in summer as the water sources are situated at a deeper level.
Methodology of Conducting A Hydrogeological Survey:
METHODOLOGY 1: Vertical Electrical Sounding (VES)
The hydrogeological survey is conducted using an ABEM SAS 1000 geophysical resistivity survey equipment (Terameter) which is a Sweden made equipment widely known for the accuracy of the deep earth measurements. A methodology known as Schlumberger array is generally used for data collection and the surveys are conducted for a range between 15 m to 200 meter depending on the availability of space and the required depth for penetration. The field data (apparent resistivity) are first collected and plotted in a logarithmic graph on the site to evaluate the survey for the resistivity values, resistivity breaks and possible groundwater occurrences to make decisions. The survey is continued until the best data plot is obtained and then studying the data in detail considering the layer modules and resistivity. A number of attempts are made for the best data matches and the important plots are included in the geological survey report to share views and decision making.
Further information is gathered from historical data done around the survey area with the aid of Google Map and the study in relation with major structural features that can noted. Also, the team make visits to the existing water sources of in the land and the surrounding to gather hydrogeological information. A GPS is used to obtain the coordinates of the locations with an error margin of 1-10 meters.
METHODOLOGY 2: Self Potential (SP)
Under single, three and 33 frequency levels, the equipment captures the natural deep underground electromagnetic signal emissions of various depths. In the field two electrodes are used to gather deep ground information for a depth of 150 meters in number of localities in a chosen profile line by the geologist.
In the equipment, this data is arranged systematically in reference to line number to obtain when necessary as vertical columns of self-potential data in millivolts enabling us to make graphs and profiles. Also, the equipment captures the measurements in 3 frequencies which can use to select a line for an EM profile or location for a VES survey.
Some information are gathered from the available Google Map and studied in relation with major structural features that can be marked over the map. Also make visits to the well in the land and the surrounding to gather hydrogeological information. A GPS is used to obtain the coordinates of the locations with an error margin of 1-10 meters.