HISTORY OF
Geology and Hydrology in the Springbrook Forest Area
by George DeBuchananne (1970)
Geology - Springbrook Forest is on the edge of the piedmont, lying just a short distance west of the fall line separating the coastal plain from the piedmont. The community is underlain by what geologists call the Oligoclase- mica facies of the Wissahickon formation. The Wissahickon formation, a specific type of rock, extends from the Philadelphia area across southeasterr Pennsylvania, northeastern Maryland and on into Virginia. The formation is pre-Cambrian in age (more than 560 million years old). As found in this area it is a banded or laminated quartz-muscovite schist, and phyllite of various compositions; locally it may be rich in the minerals chlorite, albite, or oligoclase.
In the eons since the sediments that now form the Wissahickon were first deposited, many chemical and physical changes have completely altered the original sediments into the schist found today. The original sands and clays were subjected to intense heat and pressures; twisted, folded and faulted; cut and intruded by hot igneous solutions or magma to form the metamorphic rock seen today. Erosional processes also have taken their toll of this formation by weathering of the solid rock into a red and grey, sticky soil that varies from 0 to 40 feet thick, and in the erosion of the hills and valleys to provide the topography so interesting today. The total range of topographic relief in the Forest area is more than 160 feet: from the creek valley to the top of the hill just south of the entrance.
Near where Stonington Road and Remington Drive come together at the foot of the hill the Wissahickon formation probably includes a quartz-mica pegmatite intrusive dike, since the mica (muscovite) that was mined near here before World War I occurs in pegmatite intrusives rather than in the schist. Sheets and small "books" of mica can still be picked up along the side of the road and near the Northwest Branch in this area.
The only gem stone found in this general area is golden beryl reported in the literature to have been found in the "Kensington mica mine" (See Chapter I). Small gamets, not of gem stone quality, can be picked out of the schist out- crops found along the Branch adjacent to the Forest.
Hydrology - The hydrology of the area can be divided into surface and subsurface hydrology; the former is the more spectacular because we can see it, but the latter has had a more important bearing on the development of the community since it permitted the development of individual water supplies.Records of the Geological Survey gaging station on the Northwest Branch about 400 feet upstream from Randolph Road indicate that during the last 45 years the highest instantaneous flow in the stream occurred 8 August 1953. On this day the rate of flow was 36,825 gallons of water per second. The lowest flow occurred in 1966 when, on August 30, 31, September 1, 3, 5 through 11, no water at all flowed past the gage. The average daily flow for a 35-year period of record was 22 cubic feet per second (or over 14, 000,000 gallons per day). For many years the Washington Suburban Water Supply District used this watershed as a source of raw water. More recently, however, this source has not been used.
Wells drilled in this area do not get their water directly from the soil zone or the weathered rock but rather from fractures encountered in the solid rock itself. This partially explains why your neighbor may have a better well than you do. His well intercepted more and/or bigger fractures than your well did. This occurrence of ground water also indicates that in general all of the water is chemically the same since it has a common origin and common history of occurrence. Exceptions do occur, but generally water from a Wissahickon well in Montgomery County will have a similar analysis to that of a well in Howard County.
Major differences in chemical quality of well water as used in your home usually are due to chemical action of the water on the metal pipes in the wells and the plumbing system used in the house. In isolated cases, due to a different mineralogical composition of the underlie rocks, differences in chemical composition of the water do occur. In such cases however, this difference in chemical quality is noticed when the well is first drilled and used, whereas in the former case, the water will be good when the well is first drilled but deteriorates as it is used over a period of years.