Geothermal energy in the United States Geothermal Data System (NGDS). Through the NGDS, many older paper archives and drill logs that are stored at state geological surveys are now being digitized and made available for free to the public. The underground hot water and steam used to generate geothermal power may contain chemicals that could pollute the air and water if released at the surface. Hydrogen sulfide, which is toxic in high concentrations, is sometimes found in geothermal systems. Newer methods of generating geothermal power separate the hot steam collected underground from the steam used to power turbines, and substantially reduce the risk of releasing air-polluting
Songs from the Underground 2.0". "Sold My Soul to Yo Mama" (a track made by Linkin Park turntablist and sampler Joe Hahn, which includes samples from songs "Points of Authority" and "Papercut"), was released exclusively for "LP Underground 4.0". "Announcement Service Public" and "QWERTY" are found in the "LP Underground 6.0". "Hunger Strike", a song by Temple of the Dog, was performed by its lead singer Chris Cornell (whom the band toured with), and features a surprise guest appearance by Linkin Park lead vocalist Chester Bennington. Inside the physical CD, a leaflet can be found, inside which includes a free trial for a membership