Ground-water aquifers and mineral commodities of Maryland
1969, Maryland State Planning Department, Maryland Geological Survey, and U.S. Geological Survey
Open File Report 69-02-1
The maps contained in this report show the statewide distribution of the significant mineral and ground-water resources of Maryland. The maps were compiled from either published or open-filed data and, therefore, do not represent new geologic data and information. Because the report was designed to provide a rapid, albeit generalized, overview of where the State’s natural resources are located, its chief utility is for geographic reference, rather than economic appraisal or engineering design. For example: although one of the maps shows the surface distribution of limestone formations in the State, it does not provide the detailed chemical or mineralogic information needed for commodity decisions. Similarly, the aquifer maps do not comment directly upon questions of water quality or yield at a specific site. Where data permit, the maps do, however, show which aquifers occur beneath an area by giving (in the case of the Coastal Plain) their approximate depth of occurrence. If more specific detail is required, the Maryland Geological Survey or its publications should be consulted.
There are ten aquifer maps. Maps I and II cover the Piedmont and Appalachian regions, occurring west of the Fall Line. The remaining eight maps show the known outcrop and subsurface distribution of the major Coastal Plain aquifers. The mineral commodities of the State are shown on Maps XI through XVI.
The geologically complex rocks of the Piedmont and Appalachian provinces are categorized into three hydrologic units, depending upon their productive capacities. For example, the geologic formations constituting Unit I have approximately a 20 percent change of yielding 50 gpm (gallons per minute) or more; on the other hand, this probability is reduced to 6 percent and 2 percent in Units II and III respectively. These are, of course, statistical inferences and provide only a very generalized representation of the water-yielding characteristics of the rocks. Local geologic anomalies can substantially alter these relationships.
The Coastal Plain aquifers occur as a series of irregularly shaped wedges that gently dip, generally less than 1°, to the south and east. The upper truncated edges of these formations outcrop as a series of concentric bands. There are, from west to east, the Patuxent Formation, Patapsco-Raritan (undivided) Formation, Magothy Formation, Aquia Greensand, Piney Point Formation, Manokin Aquifer and Pocomoke Aquifer. The latter two are everywhere buried beneath a surficial mantle of Plio-Pleistocene sands and gravels. Map X is a structure contour map showing the depth to the base of the Plio-Pleistocene sediments. Deep, linear areas on this map represent both recent (Susquehanna and Choptank) and ancestral (near Salisbury and Berlin) river channels; the thick, permeable nature of the latter is highly favorable for large capacity wells.
Except in their outcrop areas, all of the formations shown in Maps III to IX function as artesian aquifers. At the outcrop water-table conditions prevail. Under natural conditions the outcrop belts function as recharge areas in upland localities and discharge areas in lowland localities.
The Piney Point aquifer, which does not outcrop, is recharged by leakage through confining beds. Other major subsurface boundaries of this type are shown on the Aquia and Magothy maps.
The Patuxent and Patapsco-Raritan (undivided) Formations are multi-aquifer units. Although boundaries within these formations may be locally important, their complexity prevents a representation at the published map scale.
The six mineral-resource maps illustrate the general areas of occurrence of mineral commodities which are economically important to the State. Specific localities for mineral-producing operations within these generalized areas are determined by many factors including chemical quality and physical properties of the materials, the topography and ground-water conditions at the site, access to the site and its proximity to a ready market, and the value of the land relative to other uses.
Over 90 percent of the value of mineral production in Maryland is contributed by the production of sand and gravel, crushed stone and cement—materials of basic importance to the building and construction industries. Sand and gravel which is shown on Map XIII generally is limited to the Coastal Plain with the best deposits occurring along the western edge. On the other hand, Map XI shows that materials suitable for crushed stone are found in the Piedmont and Appalachian regions of central and western Maryland. Carbonate rocks as portrayed on Map XIII represent a special case of crushed stone in which the chemical quality is of more importance than the physical properties for such uses as cement and lime manufacture.
Clays and shales occur throughout the State, ranging from unconsolidated clays in the Coastal Plain to consolidated shales in the Piedmont and Appalachian regions. Map XIV depicts clays and shales.
The occurrence of the mineral fuels, coal and natural gas in Maryland is confined to the western part of the State. Geological tests in the Coastal Plain have not found any indications of petroleum or natural gas in that region. Mineral fuels information is shown on Map XV.
Miscellaneous mineral deposits as shown on Map XVI include talc and soapstone, high-silica sand, greensand, and diatomaceous earth. Present operations in these materials are small but there is future growth potential.