Mass. Gen. Laws ch. 21 § 40
The director, his authorized representative, or personnel of the division of watershed management in the metropolitan district commission or of the Massachusetts Water Resources Authority may enter at reasonable times any property, public or private, for the purpose of investigating or inspecting any condition relating to the discharge or possible discharge of pollutants and may make such tests as may be necessary to determine the existence and nature of such discharge; provided, however, that personnel of said division may investigate or inspect only such conditions as affect the watershed system under the care and control of said division, and provided, further, that personnel of the Massachusetts Water Resources Authority may investigate or inspect only such conditions as affect the sewer and waterworks systems under the care and control of said Authority. He may inspect any monitoring equipment or procedure required by the terms of a permit issued under section forty-three. The director or his authorized representative may examine any records pertaining to operation of treatment works, and any records required to be kept by the terms of a permit issued under said section forty-three.
Mass. Gen. Laws ch. 21, § 40