The Maine Water Well Commission understands that MAGFILL is a popular product to be used in providing a conductive grout in geothermal well drilling, and in grouting operations. It is the Commission’s opinion, however, that this product is not compatible with the Well Driller’s and Pump Installer’s Rules (CMR 10-144, CH. 232).
The use of MAGFILL to create a conductive annulus in geothermal well construction is incompatible with the Rules in the method of delivery of the product and the characteristics of the product. The Rules call for thermally enhanced grout to be placed by the tremie method, with the tremie first installed to the bottom of the borehole (from 602.2). This thermally enhanced grout is to have a maximum coefficient of permeability of 10-7 cm/sec. MAGFILL does not meet this coefficient of permeability. The use of crushed stone is called for when there is a significant loss of grout to large open bedrock fractures. Crushed stone is generally considered safe to interact with groundwater that has a potential to be consumed. MAGFILL has not been given this distinction as its composition includes up to 1% other, non-mineral, components that may include contaminants to drinking water.