For the purpose of more properly conserving the natural resources of any geothermal reservoir, field, or like area, or any part thereof (whether or not any part of the geothermal reservoir, field, or like area, is subject to any cooperative plan of development or operation (referred to in this section as a “unit agreement”)), lessees thereof and their representatives may unite with each other, or jointly or separately with others, in collectively adopting and operating under a unit agreement for the reservoir, field, or like area, or any part thereof, including direct use resources, if determined and certified by the Secretary to be necessary or advisable in the public interest.