564 



UNITED STATES MINERAL RESOURCES 



The method is generally used to measure texture; 

 thus, bedrock would normally have a high resistiv- 

 ity compared with overlying unconsolidated mate- 

 rials. By using diiTerent electrode spacings, it is 

 possible to "probe" to various depths and obtain a 

 general idea of depths and thickness of layered units 

 overlying bedrock. The method has been used suc- 

 cessfully in a wide range of geologic environments 

 and is a much cheaper way to obtain subsurface in- 

 formation than drilling (Bruce and Lundberg, 1964; 

 Peterson and others, 1968). 



Surface samples and bottom photographs provide 

 the best data for locating sand and gravel in off- 

 shore marine environments, although vibrocoring 

 or drilling supplemented by seismic-reflection pro- 

 files are needed for determination of thickness 

 (Emery, 1966). Seismic profiles across the con- 

 tinental shelf on the east coast show that a fairly 

 uniform covering of sand and some gravel a few 

 meters thick is present on the ocean floor (Schlee, 

 1968). 



PROBLEMS FOR RESEARCH 



The sand and gravel industry, like many of the 

 mineral industries, is currently beset with a wide 

 variety of source and utilization problems. The ma- 

 jor problem centers on land-use conflicts where land 

 containing potentially rich sand and gravel resources 

 is found to be more valuable for other uses and is 

 removed from mineral production. 



A great deal more sand and gravel is being cov- 

 ered by manmade structures than is being produced 

 for consumption (Cooper, 1970). A report on the 

 Denver, Colo., area disclosed that four times as 

 much aggregate has been lost through expansion 

 of the city and suburbs into areas containing po- 

 tential usable sand and gravel deposits than had 

 been consumed in construction (Sheridan, 1967). 

 The situation is probably similar in many other 

 metropolitan areas in the United States. The mil- 

 lions of cubic yards of sand and gravel lost annu- 

 ally could be made available with better planning. 

 Areas adjacent to large population centers should 

 receive high priority in locating and preserving 

 future sand and gravel resources. 



The heavily populated and urbanized Middle At- 

 lantic, New England, and Pacific Coast States pre- 

 sent the most immediate problems with respect to 

 sand and gravel resources because of (1) the rapid 

 depletion of currently operated deposits, (2) the 

 covering of potential resources by urban structures, 

 and (3) opposition to environmental disturbance 

 that might result from sand and gravel operations. 



If we are going to have sand and gravel for use, 



more efficient multiple use of the land will be re- 

 quired. Numerous examples of beneficial multiple 

 land use are demonstrated in the metropolitan Den- 

 ver, Colo., area (Sheridan, 1967). Initially, the sand- 

 and gravel-rich lands were used for agriculture. 

 Later, sand and gravel were extracted, and the 

 mined-out areas were subsequently used or are 

 now serving as critically needed sanitary land-fill 

 sites (garbage dumps). When the land is restored 

 to a usable profile and grade, it is reclaimed in one 

 of many ways, such as building sites for industrial 

 and commercial structures, shopping centers, or 

 churches, or as sites for recreational facilities, 

 streets, freeways, or parking lots. "The conversion 

 has been so complete and successful that, at many 

 locations, nothing remains to indicate that the rela- 

 tively temporary extractive operation existed" 

 (Sheridan, 1967). More of these successful multiple- 

 land-use projects are needed as vast acreages of 

 sand and gravel have been lost to production by 

 the rapid urban sprawl. Equally large deposits re- 

 main, however, in urban areas from which, with 

 thoughtful planning, the mineral potential can be 

 realized while still preserving the land for later 

 use. Several fairly detailed studies of site utiliza- 

 tion and rehabilitation practices for sand and gravel 

 operations have been made (Schellie and Rogier, 

 1963; Johnson, 1966; Bauer, 1965; Ahearn, 1964). 

 The widespread implementation of these practices 

 is needed. 



Environmental limitations are factors that must 

 be considered in the location and development of 

 sand and gravel deposits. The effects of traffic, 

 smoke, dust, noise, vibration, perils of excavation 

 or ponds, hazards of mining equipment, depression 

 of property values, unsightliness, water pollution, 

 and lowering water table must be determined prior 

 to the mining. 



The threat to animal and plant life, streambed 

 and runoff changes, and local flooding are problems 

 associated with the dredging of sand and gravel 

 that put limits on the location and type of deposits 

 which can be used. 



Large quantities of water are needed for process- 

 ing most sand and gravel deposits, and the avail- 

 ability of abundant, cheap water is becoming a fac- 

 tor in the location of plants. 



Local problems of the sand and gravel industry 

 vary in different geographic areas. In the Tucson, 

 Ariz., area, for example, problems are principally 

 those of (1) the thinness (8-10 ft) of the gravel 

 beds, (2) presence of caliche, which cements the 

 gravel and is a deleterious material, (3) inadequate 

 supplies of water, (4) thick overburden, and (5) 



