Exhibit 21 THERMO REMEDIATION INC. Subsidiaries of the Registrant As of May 29, 1998, Thermo Remediation Inc. owned the following companies: STATE OR JURISDISCTION OF PERCENT OF NAME INCORPORATION OWNERSHIP Benchmark Environmental Corporation New Mexico 100 Eberline Holdings Inc. Delaware 100 Eberline Analytical Corporation New Mexico 100 Thermo Hanford Inc. Delaware 100 TMA/NORCAL Inc. California 100 IEM Sealand Corporation Virginia 100 RPM Systems, Inc. Connecticut 100 Remediation Technologies, Inc. Delaware 100 GeoWest Golden Inc. Colorado 100 GeoWest TriTechnics of Ohio, LLC RETEC Thermal, Inc. Delaware 100 Thermo Fluids Inc. Delaware 100 TPS Technologies Inc. Florida 100 TPST Soil Recyclers of Calif. Inc. California 100 California Hydrocarbon, Inc. Nevada 100 TPST Soil Recyclers of Maryland Inc. Maryland 100 Todds Lane Limited Partnership (1% of which is owned directly by TPS Technologies Inc.) Maryland 100* TPST Soil Recyclers of New York Inc. New York 100 TPST Soil Recyclers of Oregon Inc. Oregon 100 TPST Soil Recyclers of S. Carolina Inc. Delaware 100 TPST Soil Recyclers of Virginia Inc. Delaware 100 TPST Soil Recyclers of Washington Inc. Washington 100 TRUtech L.L.C. Delaware 47.5* * Joint Venture/Partnership