Abandoning Monitoring Wells: Safety Issues
Monitoring wells are typically constructed to gauge the extent of contamination, assess water quality and conduct other hydrogeologic studies. Depending on its objective, the monitoring well may remain in use or may be abandoned permanently. When declared inactive, the well is many a times left as it is. Open unused wells are hazardous to life and environment:
• Contamination may spread from one location to another.
• Groundwater may move upwards and leak.
• Others may get tempted to unlawfully dispose off waste in abandoned wells.
• Humans and animals may fall in inactive wells and get trapped or hurt. The risks of inadequately abandoned monitoring wells show that properly plugging the well is important for safe sustenance of life. Correct closure of monitoring wells is key to environmental construction and follows the principles of loss prevention system (LPS). Following measures should be taken when abandoning a monitoring well
• Plan for proper plugging of the well. Avoid making hasty decisions which may eventually lead to loss or near loss incidents. • Consider the well design and construction to determine the most suitable plugging materials and procedures. • Ensure that the personnel working on the project are well trained and follow LPS.
• If possible, remove well fixtures including casing, annular seal, filter pack and sampling mechanism before closing the well. Hollow stem auger is usually appropriate for this purpose.
• Grout the well borehole with cement, bentonite or a mixture of cement and bentonite. If using bentonite/cement mixture, be sure about the proportion in which individual components are mixed.
• Try to finish closing the well the same day. If this is not possible, cover the well opening with a secure cover that is too heavy to be lifted manually. This prevents easy displacement of the cover so unsuspecting passers by and animals do not get trapped.
• After the well has been plugged, lock its cover securely.
• Keep surroundings of the abandoned well clean.
• Label the well clearly so when needed, it can be easily identified.
• Document the well closing procedure in detail. Record information such as names and contact information of people responsible for plugging the well, worksite details, date of closure, sealing materials used, amount of sealants used, exact procedure followed, type of cover, its locking mechanism, formulae used if any, schedule, flowcharts and any other special information necessary. Save the file properly for easy and quick retrieval.