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Heating with geothermal systems 189

Fig. 5.11 Geological map of Boise, Idaho showing the Foothills Fault and related linears,
after [11].

Fig. 5.12 Cross-section looking NW through the well BHW-1 in Fig. 5.11, modified from [12].

5.3.2.1 Boise Warm Springs Water District (BWSWD)
The original Boise Warm Springs geothermal district heating system began in 1892
and was the first such company in the United States. The current Boise Warm Springs
Water District was established in 1987 as a private company in the state of Idaho. This
company serves about 300 users, nearly all private residences, with hot water from its
two production wells in the eastern part of the city; see Fig. 5.13. The wells are located
just south of the Foothills Fault, penetrate the hanging wall, and intercept the fault at a

shallow depth. The water is at a temperature of about 79 C, a value that has stayed
remarkably constant over more than a century of exploitation. Usually only one of
the two wells is needed to meet the demand.
An interesting feature of the BWSWD is that it is an open system. The hot
geothermal fluid is sent out via a single-pipe distribution line with users tapping