Reports
The water resources of Carroll and Frederick Counties
1958, Meyer, G. and Beall, R.M.
Bulletin 22
Abstract
Carroll and Frederick Counties are in central Maryland and include parts of the Piedmont and Blue Ridge physiographic provinces. The Piedmont, which includes most of the area of these counties, is underlain by metamorphic rocks of Precambrian or Cambrian age, chiefly schist and phyllite and associated marble and limestone. At its west edge, along the east foot of Catoctin Mountain, the Piedmont is underlain by Cambrian and Ordovician limestone and Triassic shale and sandstone. The Blue Ridge includes the mountainous western part of Frederick County and is formed chiefly by metabasalt and quartzite and smaller bodies of shale, conglomerate, slate, and phyllite.
The average daily use of ground water in Carroll and Frederick Counties in 1956 and 1957 was about 6.6 million gallons, of which about 16 percent was for institutional and public supplies, 15 percent for industrial and commercial supplies, and 69 percent for rural domestic and farm supplies. Ground water in small to moderate amounts is available nearly everywhere. Under especially favorable conditions of geology and hydrology, moderately large supplies are obtainable, but prospecting is required to outline the favorable areas. Application of available knowledge of the occurrence of ground water in the rocks of these counties may aid substantially in the location and development of groundwater supplies in untried areas. Optimum development requires that well construction, well-field patterns, and pumping regimens be adapted to the local geohydrologic conditions.
In most of the rocks ground water occurs chiefly in pores and fractures in the mantle of semidecomposed rock that underlies the surface and in fractures in the fresh bedrock below. Solution by moving water has enlarged the openings in the carbonate rocks to a much greater degree (some of the openings being of cavernous dimensions) than in the siliceous rocks, and the wells of largest yield generally penetrate the carbonate rocks. Statistical analysis of well records shows a general relation among the yield of a well, ground-water levels in the vicinity, the geology, and the topography. Most wells yield 5 to 20 gpm, but those favorably situated geohydrologically may yield as much as several hundred gallons per minute. Owing to small storage capacity of the rocks resulting from their low porosity and to low permeability, continuous pumping may result in a substantial decrease in well yield. Pumping tests long enough to enable predicting the effect of long-term pumping should be made before it is concluded that a satisfactory yield is obtainable from a well. Test drilling, detailed geologic mapping, and aquifer and well-performance tests, should precede development of major ground-water supplies.
Geophysical methods used in the ground-water study of Carroll and Frederick Counties include electric and temperature logging and current-meter surveys. Drilling-time logs also were made. Aquifer tests and well-performance tests, particularly specific-capacity step tests, were made to determine the performance characteristics of wells and the water-bearing ability of aquifers.
Periodic measurements of water levels in wells show that ground-water levels fluctuate in a more or less uniform pattern from year to year, the levels being highest in the late winter and early spring and lowest in the late summer and early fall. The yields of wells vary with the amount of ground water in storage. When droughts occur during periods when ground-water replenishment normally begins, well yields may be seriously reduced. The water-level observations show no overall long-term upward or downward trend. In a few localities heavy pumping has lowered ground-water levels appreciably, reducing well yields.
Chemical analyses of well and spring water show that few problems of chemical quality of ground water exist in Carroll and Frederick Counties. The siliceous rocks yield water generally low in mineral content, with the exception of the Triassic sediments which yield hard water. The carbonate rocks yield hard water. Locally, high iron concentration may be an objectionable feature. Ground-water temperatures fluctuate seasonally, but generally not more than a degree or two. The average ground-water temperature is 53° F.
