Liquefied Petroleum Gas (LPG), is a compressed by-product of petroleum
distillation. While Iowa is not a producer of petroleum or natural gas, it does
store large volumes of liquefied butane, propane, and ethane in excavated
"caverns" deep beneath the land surface. LPG products arrive in Iowa via
pipeline from Wyoming, Utah, and Canada and are injected into these underground
facilities, which provide safety, economy, and operating flexibility.
The storage caverns were excavated from shale or shaly limestone into rooms
about 20 ft wide and 20 ft high with 45 ft-wide pillars left for support. Two
LPG storage caverns are located in southeast Johnson County at depths of 490 ft
and 770 ft. They both began operation in the 1960's. In Polk County, three
storage caverns were excavated at depths of 375 ft, 595 ft, and 1,410 ft beneath
a single tract of land at the southeast edge of Des Moines. These became
operational between 1967 and 1970.