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<br />
<br />Artificial Recharge of Ground Water in Colorado
<br />A Statewide Assessment
<br />
<br />In most cases, Colorado coal was produced by the room-and-pillar method, the preferred mining
<br />method prior to World War II. This type of mining is more suitable for underground water
<br />storage as the remaining void space in the mine may provide a substantial volume for water
<br />storage, Longwall mining, the method of large underground mining today, results in a larger
<br />area being mined but causes subsidence immediately behind the extraction panel. With this
<br />method, the void space remaining is completely transferred into subsidence of the overburden
<br />rock called the 'gob' zone, which may not provide water storage opportunities, To adjust mine
<br />volumes for subsidence and the associated reduction in storage volume (wet or dry), the
<br />calculated storage volume based on production was reduced by 50 percent.
<br />
<br />Many abandoned mines are already full of water through natural recharge, In these cases, the
<br />existing mine water may be produced but there is no 'dry' volume available for incremental
<br />storage, Partially filled or dry mines provide greater opportunities for artificially storing water.
<br />For each of the storage sites listed in Table VII-2, an estimate of both the dry and wet storage
<br />volume was made, To achieve this, water-level data available from the Division of Water
<br />Resources were compared to overburden maps for mine areas such as Boulder/Weld coal field
<br />(Roberts and others, 200 I), If these data were not available, mining companies and consultants
<br />were contacted for additional information,
<br />
<br />In eastern Colorado, the primary storage sites are located along the eastern flank of the Rocky
<br />Mountains (Figure VIlA), Three storage sites were identifIed in the Denver Coal Region:
<br />Boulder/Weld, Leyden, and Colorado Springs, One storage site was assigned to the Canon City
<br />Coal Region, Two storage sites were identified in the Raton Mesa Coal Region: Walsenburg,
<br />and Trinidad, Approximately 435 million tons of coal production is reported for eastern
<br />Colorado mines now abandoned, This yields an estimated 123,000 acre-feet of equivalent water
<br />volume available for storage. About 85 percent (104,000 acre-feet) of this volume has already
<br />been flooded by natural recharge, leaving only 19,000 acre-feet available for new ground-water
<br />storage, Most of the abandoned underground mines east of the Rocky Mountains are flooded by
<br />natural recharge,
<br />
<br />In western Colorado the coal fields identified as possible storage candidates are the Somerset
<br />coal field, Durango coal field, Roadside/Cameo mines near Palisade, the Carbondale/Grand
<br />Hogback coal fields near Glenwood Springs, and the Yampa coal field (Figure VII-4),
<br />Approximately 230 million tons of coal production has been reported from western Colorado
<br />mines that are now abandoned, This yields an estimated 64,000 acre-feet of equivalent water
<br />volume available for storage, Unlike eastern Colorado where most abandoned mines are
<br />flooded, western Colorado mines are generally only partially flooded leaving approximately
<br />36,000 acre-feet available for new ground-water storage,
<br />
<br />In aggregate, abandoned coal mines in Colorado do not represent a significant storage volume
<br />compared to surface-water reservoirs, Locally, however, underground water storage does
<br />provide a viable, alternate water-management strategy to augment existing storage capacities,
<br />The success and difficulties encountered in Arvada's Leyden Coal Mine project will determine
<br />the extent of implementation of this storage concept.
<br />
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