A substantially sand-free, aqueous-based, bentonitic fluid comprising flaked graphite can help dissipate heat from operation of electrical lines buried underground. The fluid is used in drilling a borehole, such as in trenchless drilling, or in making a trench, for receiving and containing the lines. The fluid may also be applied directly to the outside and/or to the inside of pipe containing electrical lines. Thermal conductivities having values of about 1.6 to about 1.8 BTU/hr ft° F. or higher can be attained.