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Stream-aquifer interaction of alluvial and coal aquifers with the Piedra River in the northern San Juan Basin

PROJECTS

Stream-aquifer interaction of alluvial and coal aquifers with the Piedra River in the northern San Juan Basin, Archuleta County, Colorado, 2006-2007

Study Area: Piedra River, San Juan Basin, Colorado
Period of Project: 2006-2007
Project Number: CQ2
Project Chief: Ken Watts
Cooperator: U.S. Department of Agriculture Forest Service

BACKGROUND:

Coal beds in the Fruitland Formation have been extensively developed as a source of natural gas (methane) in parts of the San Juan Basin of southern Colorado and northern New Mexico. A substantial amount of additional coal-bed methane (CBM) development is proposed within the San Juan Basin of Colorado, including “infill” wells in previously developed areas and new wells in the relatively undeveloped eastern part of the basin in Archuleta County. Because fluid (water and gas) pressure in the coal has already been or will be reduced by as much as 1,500–2,000 feet during production, there is concern that depletion of streamflow of the Animas, Florida, Los Pinos (Pine), and Piedra Rivers has increased or will increase in the future.

Because, currently (2006), the Piedra River is in an area that is relatively unaffected by CBM production, it is an opportune location to evaluate pre-development stream-aquifer interaction of the Fruitland coal and alluvial aquifer along a major stream. Establishment of a ground-water monitoring network, prior to increased development of CBM nearby, is needed to define baseline conditions and allow measurement of the effects of future CBM development on heads in the coal aquifer near the Piedra River and to predict stream depletion that might result from CBM production. Assessment of ground-water flow direction and rates between the alluvium and the coals is needed before increased CBM production reduces reservoir pressure and affects stream-aquifer interaction. Aquifer tests also are needed to determine the hydraulic and storage properties of the coal aquifer near outcrop and to evaluate the effects of aquifer anisotropy on fluid flow. Resource managers of Federal lands in the San Juan Basin can use the proposed ground-water monitoring network to measure the effects of changes in CBM-reservoir pressure on ground-water levels near the Piedra River and the results from analyses of these data and from the aquifer test to predict and to evaluate previous predictions of stream depletion that result from CBM production.

OBJECTIVES:

The objective of the proposed study is to monitor current (2007) and future changes in ground-water/surface-water interaction and to determine the hydraulic and storage properties of the coal aquifer near the Piedra River in the San Juan Basin of Colorado.

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