Water resources of Baltimore and Harford Counties
1956, Dingman, R.J., Ferguson, H.F., and Martin, R.O.R.
Baltimore and Harford Counties lie in two physiographic provinces, the Coastal Plain to the southeast and the Piedmont to the northwest. This report deals with the Piedmont province, where the rocks are largely hard Precambrian or lower Paleozoic schist, quartzite, granite, gabbro, marble, and phyllite. Ground water in the crystalline rocks generally occurs under water-table conditions, although artesian conditions exist locally. The source of all ground water in the area is precipitation. The precipitation averages about 43 inches per year and is generally rather evenly distributed throughout the year.
More than 70 percent of the drilled wells have yields of 10 gallons per minute or less, and only 2 percent have yields in excess of 50 gallons per minute. The Baltimore gneiss is an important aquifer in which the yields of 116 wells range from 0 to 110 gallons per minute and average a little better than 10 gallons per minute. A value for the coefficient of transmissibility obtained from a pumping test of a well in the gneiss was about 5,000 gallons per day per foot. The Wissahickon formation is divided into two rock types, an oligoclase-mica facies and an albite-chlorite facies. The yields of more than 230 wells in the oligoclase-mica facies average better than 11 gallons per minute. Generally, the best wells are in areas where the rocks are deeply weathered. The average yield of 76 wells ending in the albite-chlorite facies is 10 gallons per minute. The average depth of the wells in the Wissahickon is 92 feet. The Cockeysville marble is the best aquifer in the area. The marble weathers to a sand or sandy clay to depths locally in excess of 100 feet. The yields of 55 wells ending in the marble range from less than 1 to 80 gallons per minute and average about 19 gallons per minute. The average depth of wells in the marble is about 210 feet. The yields of wells are related to the topographic situation. The best wells are in the valleys and the poorest are on hilltops.
The total use of ground water in the area is about 4 million gallons per day, most of which is used for domestic or agricultural purposes. There are no public supplies (municipal) from a ground-water source in the Piedmont section of either county, although formerly several communities had public water supplies derived from wells.
The chemical character of the ground water is generally satisfactory for most uses, as shown by 61 chemical analyses of water from wells or springs. Dissolved solids in 51 samples average 105 parts per million. The hardness in 60 samples averages 59 parts per million. The hardest water is obtained from wells or springs in marble. The iron content is generally low, but it ranges from 0 to 3.5 parts per million.
Additional ground-water supplies are available for rural and domestic use, but supplies for industrial and irrigation use are limited to an estimated maximum of a few hundred thousand gallons a day.