During the environmental evaluation process, we met with drilling engineers working on the wells. They explained the drilling process and the in-field problems they were having. As part of these exchanges we suggested the design of a specialized muffler consisting of a pit or concrete enclosure filled with rocks. The steam would enter the bottom of the enclosure, flow through the rocks and out the open top. The rocks would slow the flow and cause the steam to spread out and fill the whole enclosure. Since the exit area would be much larger than the inlet area of the pipe, the flow velocity would be reduced. The rocks had to be resistant to impact from the rocks brought up with the steam. A large mock-up was constructed on a flatbed truck that demonstrated the efficacy of the principle. After launching a torrent of rocks into the sky, the proper weight was determined and the noise was significantly reduced. Noise from venting has been reduced from 130 dBA at 50 feet from a free-venting well to 72 dBA at 50 feet from a power plant venting through a rock muffler. Rock mufflers are now in use at geothermal plants throughout the world.

In 1979, MLA was selected by the Department of Energy in a national competition to perform long term monitoring and analysis of noise due to geothermal development activities. The final report was submitted to the Department of Energy in 1982 under Contract DEAC-0179-EV06200.