1. n. [Drilling Fluids]
Abbreviation for equivalents-per-million. This unit of concentration is determined by dividing the number of equivalents of a substance by the weight of the solution that contains the substance, expressing the result as parts per million, and then dividing by the valency. For example, a solution containing one milligram of calcium in one kilogram of solution contains 1 ppm calcium. By dividing the ppm by the valency of calcium, which is 2 in this case, the result is the epm of calcium, 0.5 epm.