Hydrogeological studies include a complex of activities related to the clarification of the hydrogeological situation. They usually precede the construction of new boreholes and shaft wells, indicate the exact and effective location of drainage facilities, and determine groundwater quantity and quality indicators.

The effectiveness and cost of hydrogeological investigations depend directly on the prior planning and evaluation of the required activities. Several phases of exploration activities can be distinguished:

First stage

• When carrying out a hydrogeological study, the following approach is usually used:
• Locating existing workings – boreholes, groundwater and surface water monitoring stations;
• The boundaries and location of surface water bodies, including springs, wetlands, lakes, marshes, rivers and streams are clarified;
• Infrastructure available in or near populated areas – drainage channels, ditches, drainage points, manholes, and collector systems shall be noted;
• Familiarity with existing geological and tectonic information;
• Check for existing anthropogenic impacts that affect the surface water and groundwater regime (including outcrops, quarries, etc.);

Fieldwork is preceded by preparation related to the collection of map material (topographic maps at different scales, geological and tectonic maps, and material from previous studies with hydrodynamic and hydrochemical maps).

Geological and hydrogeological profiles are constructed to enter and establish the extent of the site. These are based on geological, geophysical and hydrogeological reports as well as previous water level measurements. The profiles contain soil and stratigraphic information, major geological structures and lithology, geological boundaries at depth, water levels (for different periods if data are available), and existing engineering structures.

Hydrogeological studies also cover groundwater recharge, for which information on rainfall, river levels and quantities is needed.

Hydrogeological studies also cover groundwater recharge, for which information on rainfall, levels and quantities in rivers is needed.

The information gathered is analysed and summarised, and this includes a discussion of regional and local hydrogeology, an assessment of the sufficiency of existing information, and the identification of areas where further studies should be carried out.

Second stage

• A work plan is developed to characterise the study site. Specify:
• Study objectives;
• A proposal for the study is made – with the number of locations and depths of workings to be constructed, method of soil sampling and classification;
• Specify the testing intervals, type and number of laboratory tests;
• Determine the construction of the borings;
• Plan the number and type of experimental filtration field tests;
• Determine the frequency of water level measurements;
• Specify the number of water samples to be submitted for chemical, radiological and microbiological analysis;
• A schedule plan by period is required to complete the studies.

Field activities

The field activities for the hydrogeological investigations shall follow the work programme established in the previous stage. These include water abstractions, hydrogeological surveys in the local area, and the use of portable field laboratories to determine specific groundwater parameters, with prior mapping of the location of the study sites. In modern hydrogeology, the use of geophysical surveys in the search and discovery of groundwater is required. Exploration for water is carried out by various electrical methods in geoscience, the most common being the use of vertical electrical drilling, the method of own potential (SP method). The latter is carried out with specialised equipment/instrumentation (popularly known as GPR), which allows the preparation of profiles and the evaluation of aquifer intervals according to established statistical procedures.

Hydrogeological surveys need to be coordinated with the authorities of the Ministry of Water Resources or the Basin Directorates when the construction of exploratory or operational boreholes and workings is required.

The results of the surveys shall be duly documented by keeping logs, drawing up water abstraction maps and using geographical information systems to present the data obtained. A hydrogeological report shall be prepared, including hydrodynamic, hydrochemical, seepage coefficient and conductivity maps.