High Plains States Groundwater Demonstration ProgramParts1&2

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Large -Scale Recharge Operations There is an implicit difference between the connotations of "groundwater recharge" and "aquifer recharge." Groundwater recharge is often interpreted narrowly as the mitigation of local or transient groundwater drawdown conditions. Aquifer recharge implies overall replenishment of groundwater throughout an aquifer formation. Consequently, aquifer recharge implies substantially greater scope that may entail more comprehensive planning, large -scale water transfers, or the integration of different recharge strategies. There are few large aquifer formations in the United Sates. Notable examples include the High Plains and Ogallala Aquifer system in the Great Plains area, the Dakota sandstone in the northern plains, and the Edwards Aquifer in central Texas. Other extensive aquifers, such as the Dakota sandstone and the St. Peter sandstone, convey water over great distances, but as a rule most aquifers are only of local extent (Leopold, 1974). The High Plains Aquifer overlaps the Ogallala geologic formation which explains why the names are often used interchangeably. The High Plains Aquifer is a tremendous resource, and the associated water management problems are impressive. Concerns for the aquifer and future water use is common in scientific literature and the news media: In the United States, one -fifth of all irrigated land gets water from a vast underground reserve know as the Ogallala Aquifer. It is one of the planet's greatest aquifers, spanning portions of eight states, from South Dakota in the north to Texas in the south. In its southern reaches, the Ogallala gets very little replenishment from rainfall and decades of heavy pumping have taken atoll. The volume of water depleted to date is equal to the annual flow of eighteen Colorado Rivers" (US Water News, 1999). Groundwater depletion can provide incentives to find alternative water sources or apply conservation measures. In northern New Mexico, the quality of groundwater available from the High Plains Aquifer has deteriorated to the point where alternative surface water supplies are being explored. San Antonio, Texas, has implemented an extensive reclaimed water reuse program to conserve superior quality water from the Edwards Aquifer. In recent years, some major water transfers and conjunctive use plans have been pursued to utilize recharge as a storage alternative. Examples include the existing water banking operations involving the Central Valley Project and State Water Project in California, the seasonal storage and recovery operations to supply peak demands in Las Vegas, Nevada, and other conjunctive water exchange programs that involve, or are proposing, additional use of water allocations from existing large -scale surface water projects. As groundwater resources are constrained, economics may favor other similar large -scale conjunctive use plans and multi -State coordinated efforts to conserve and replenish aquifer resources. Appropriate mechanisms to administer and support these activities are essential to anticipate the ultimate limitations of groundwater resources. Program Summary Report Part 1— Overview, Results, and Findings Z. I i