Post-development

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In 1996, the U.S. Geological Survey (USGS) initiated the Front Range Infrastructure Resources Project (FRIRP) designed to provide information to land-use planners, decision makers, and the public regarding the location and characteristics of water, aggregate, and energy resources along the Front Range corridor extending from Cheyenne, Wyoming, to Pueblo, Colorado. Within the broader framework of this project, a more restricted demonstration area (fig. 1) encompassing forty-five 1:24,000-scale quadrangles was established as a first step in the implementation of overall project goals. Energy resource issues within the demonstration area relate primarily to (1) the continued exploration and production of oil and gas resources in this heavily populated and growing part of Colorado, (2) the potential environmental impacts of past and present oil and gas production, and (3) the impacts of historic coal-mining, particularly in regard to the potential for subsidence over abandoned mines in recently developed areas or in areas currently being evaluated as residential, commercial, and/or industrial building sites.

In order to address aspects of the abandoned coal mine issue, the USGS and the Colorado Geological Survey (CGS) have jointly undertaken the development of digital map coverages based on previous studies pertaining to the location and distribution of abandoned underground coal mines in the Boulder-Weld coal field north and northwest of Denver. The coal field is located within Boulder and Weld counties, and extends for some 20 to 25 miles from Marshall in the southwestern part of the coal field to areas just north and east of the tri-cities area of Dacono, Frederick, and Firestone (fig. 1).

In order to address aspects of the abandoned coal mine issue, the USGS and the Colorado Geological Survey (CGS) have jointly undertaken the development of digital map coverages based on previous studies pertaining to the location and distribution of abandoned underground coal mines in the Boulder-Weld coal field north and northwest of Denver. The coal field is located within Boulder and Weld counties, and extends for some 20 to 25 miles from Marshall in the southwestern part of the coal field to areas just north and east of the tri-cities area of Dacono, Frederick, and Firestone (fig. 1).

Mining began in the coal field during the early 1860’s near Marshall (Marvine, 1874; Amuedo and Ivey, 1975), and continued into the 1970’s with the last mine closing in 1979 because of fire (Kirkham and Ladwig, 1980). Most of the coal (about 107 million tons) was produced from underground mines, although limited coal was produced from surface (strip) mines during the 1940’s and early 1950’s.

Digital coverages, based on maps included in a previous coal mine subsidence and land-use study (Amuedo and Ivey, 1975, after Lowrie, 1966; Colton and Lowrie, 1973) are being developed by the USGS and CGS that delineate the location and identification of coal mine shafts and adits, the extent of abandoned underground and surface coal mines, the estimated depth of ground cover (overburden) overlying the abandoned underground mines, and the location and orientation of bedrock faults that are present in the Boulder-Weld coal field. To create these digital coverages, base stable (mylar) originals of Amuedo and Ivey (1975) maps showing (1) the extent of mining, and (2) the depth of cover (overburden) above underground mines were used; both of these maps also show the location of mine shafts and adits, as well as the distribution of bedrock faults. Fault locations are based on Colton and Lowrie (1973), and are identified primarily from subsurface records including published coal mine maps, field mapping in abandoned mines, and coal exploration drilling programs. In most areas of the coal field, bedrock faults are not expressed on the ground surface because of the extensive Quaternary deposits that cover much of the area.

Coal mine data from the original maps (for example, extent, depth, etc.) for each 7.5’ quadrangle within the coal field was then photographically reproduced (on base stable mylar), and each quadrangle map was electronically scanned and converted to a Tagged Image File Format (TIFF) image that could be imported into Environmental Systems Research Institute (ESRI) ARC/INFO software for coverage development. Point, line, and polygon coverages were subsequently developed from the "on-screen" digitization of relevant features (for example mine shafts, mine extent, etc.) in the TIFF images for each quadrangle. Through this process, the following 5 composite coverages for all quadrangles within the coal field were created: (1) the extent of abandoned coal mines (polygon coverage), (2) the depth of cover (overburden) above abandoned underground coal mines (polygon coverage), (3) bedrock faults (line coverage), (4) mine shaft (hoisting shaft) locations (point coverage), and (5) rock slope (adit) locations (point coverage).

The coverages developed through this study are intended to provide the basic materials necessary for an initial assessment of lands that are underlain by historic coal mines in rapidly developing urban and commercial areas within Boulder and Weld counties. The availability of these coverages in digital format will provide an opportunity for planners and developers to incorporate these data with other relevant information within computer-based geograhic information systems (GIS) as a first step in determining those lands that may require special consideration with regard to development because of the potential for surface subsidence.

REFERENCES CITED

Amuedo and Ivey (consultants): Myers, A.R., Hansen, J.B., Lindvall, R.A., Ivey, J.B., and Hynes, J.L., 1975, Coal mine subsidence and land use in the Boulder-Weld coalfield, Boulder and Weld counties, Colorado: Colorado Geological Survey, Environmental Geology Series EG-9, 88 p.

Colton, R.B., and Lowrie, R.L., 1973, Map showing mined areas of the Boulder-Weld coal field, Colorado: U.S. Geological Survey Miscellaneous Field Studies Map MF-513.

Kirkham, R.M., and Ladwig, L.R., 1980, Energy resources of the Denver and Cheyenne Basins, Colorado--Resource characteristics, development potential, and environmental problems: Colorado Geological Survey Environmental Series EG-12, 258 p.

Lowrie, R.L., 1966, Analysis of the coal industry in the Boulder-Weld coal field, Colorado: U.S. Bureau of Mines Report of Investigations 6726, 79 p.

Marvine, A.R., 1874, The sedimentary rocks east of the Front Range: U.S. Geological and Geographic Survey Territorial 7th Annual Report, pp. 93-136.