EXHIBIT 21 CLEAN HARBORS, INC. AND SUBSIDIARIES SUBSIDIARIES Principal State of Place of Incorporation Business ------------- ------------------------ Clean Harbors Environmental MA 1501 Washington Street Services, Inc. Braintree, MA 02185-0327 Clean Harbors of Natick, Inc. MA 1501 Washington Street Braintree, MA 02185-0327 Clean Harbors of Braintree, Inc. MA 1501 Washington Street Braintree, MA 02185-0327 Clean Harbors Services, Inc. MA 1501 Washington Street Braintree, MA 02185-0327 Clean Harbors of Baltimore, Inc. PA 1501 Washington Street Braintree, MA 02185-0327 Clean Harbors of Connecticut, Inc. CT 1501 Washington Street Braintree, MA 02185-0327 Clean Harbors of Kingston MA 1501 Washington Street Facility Corporation Braintree, MA 02185-0327 Murphy's Waste Oil Service, Inc. MA 1501 Washington Street Braintree, MA 02185-0327 Mr. Frank, Inc. IL 1501 Washington Street Braintree, MA 02185-0327 Northeast Casualty Risk VT 1501 Washington Street Retention Group, Inc. Braintree, MA 02185-0327 Spring Grove Resources DE 4879 Spring Grove Avenue Recovery, Inc. Cincinnati, OH 45232