Why people ask for exisiting formation?

Depending on Existing Information Sources to choose a suitable site for borehole drilling!

It is essential to ask for the formation of certain geological areas before deciding to drill a borehole. Most contractors have successfully constructed boreholes in places they have never been to by just asking for existing ground formation from experts and other contractors. The following are some sources for ground information that you can depend on in choosing a site.

Maps:
Topographic maps provide the most basic information for undertaking a well-siting program. While community names and locations may not always be correct, the terrain and the rivers are likely to be accurate and provide general indications of the situation of the land and accessibility. Geological and hydrogeological maps present and summarize a great deal of complex information in a succinct visual form. Hydrogeological maps at similar scales are much more rarely found. The map legend is as important as the map itself, as it contains much descriptive information which is necessary to get the most from the map itself. More recently there have been useful approaches to the production of maps of groundwater development potential, often at a more local scale. On these, existing hydrogeological information and borehole data are depicted and interpreted to indicate where there is good potential for using groundwater and where there are likely to be significant constraints in terms of both quantity and quality to the provision of water supplies.

Documents:
A wide variety of documents, including project reports, master plans, geological surveys, consultants’ and drillers’ reports, NGO project documents and academic studies and meteorological data (i.e. rainfall), can provide useful information about the areas where groundwater development is proposed.

Field visits and interviews can provide considerable information from the community on groundwater resources, including seasonal fluctuations. In addition, relevant information on source preferences, water uses, gender issues and economic interests can be collected. These will all influence the selection of a suitable location for the well.

Drilling records, databases and data exchange:
Often, the most reliable information on local geology and hydrogeology comes from the field experience of previous drilling and well-digging activities. Ideally, such experience is encapsulated in drilling logs and geologists’ logs which are held in national databases. In reality, however, such records are often not kept (especially if the well is unsuccessful), not submitted (especially in the case of NGOs and individuals), or not collated (especially when Government resources are limited, and a higher priority is placed on new construction than on record keeping). In the best cases, such logs, records and databases can be extremely useful sources of information.

The extra cost in a Borehole construction program of collecting such data is relatively small, and the incremental benefits for siting from the cumulative knowledge, improved interpretation and enhanced conceptual model of local groundwater occurrence are very large. It would be even more beneficial if drilling results were subsequently compared to the specific well-siting techniques used in a systematic, site-by-site and overall project evaluation.

Such an assessment of siting “success” of course reflects on the operator as well as the technique, and this is very rarely done and almost never published. It is also made difficult because siting and construction are often undertaken by different organizations. If these are private contractors or consultants, they may treat the siting data as commercially confidential information which they are unwilling to share.