Strata Engineering Corporation performed a detailed state-of-the-practice review and established sealing criteria. A thorough evaluation of the materials and techniques used to seal geotechnical exploratory holes was performed, and a comprehensive set of sealing guidelines was developed and published as NCHRP Report 378, Recommended Guidelines for Sealing Geotechnical Exploratory Holes. The guideline document presents a great deal of information to aid in sealing an exploratory hole, but the decision to seal the hole is based on the abandonment practices established by the appropriate agency. The guideline document contains information on seal criteria, materials, and placement; a chapter on seal verification; and seal selection flow charts that can assist in the selection of an appropriate seal material.

Geotechnical exploratory holes often penetrate water-bearing formations and can become conduits for contamination of groundwater or for loss of groundwater. To protect the subsurface environment, water-resource agencies require the use of water-well drilling techniques and regulations for borehole sealing, which increase costs to transportation agencies and require modification of procedures and the purchase of new equipment.

Research was needed to develop suitable seals that would adequately protect the subsurface environment and be cost-effective for use by transportation agencies and their contractors. The objectives of the research were to develop (1) technical guidelines for materials and methods for placing seals that protect groundwater from contamination and loss, and (2) methods for verification of the effectiveness of these seals.

In addition to the published Guidelines, loan copies of the agency's final report detailing the development of the recommended guidelines are available from the NCHRP.