Reports
Ground-water resources of Harford County, Maryland
1977, Nutter, L.J.
Bulletin 32
Abstract
Harford County straddles the Fall Line in northeastern Maryland and is about 80 percent in the Piedmont province and 20 percent in the Coastal Plain province. The Piedmont rocks consist of metamorphosed sedimentary and igneous rocks of Precambrian and early Paleozoic age. The Coastal Plain formations unconformably overlap the Piedmont rocks and consist of unconsolidated sand, gravel, and clay deposits of Cretaceous, Tertiary, and Quaternary age.
Wells in the Coastal Plain sand and gravel aquifers have the potential for yielding more than 500 gal/min in many areas because of the high transmissivity and storage capacity of those aquifers. The Piedmont aquifers have more limited water-yielding potential because water is stored in and transmitted through a highly varied system of fractures in the rock and in the saturated part of the saprolite. Well yields are extremely variable in the Piedmont aquifers, ranging from zero to more than 50 gal/min in most of the aquifers; the Cockeysville Marble probably has the potential for yielding more than 200 gal/min, but it has a small outcrop area. Small to moderate water supplies can be obtained in all sections of the county, although some areas have a fairly significant percentage of wells that are inadequate for household use.
Well yields in the Piedmont aquifers are governed by: geologic structure (joints, faults, cleavage, foliation); topographic position of the wells; lithology; thickness of the saprolite; and well depth. Wells yielding substantially more than the average (based on available well data) can be obtained by judiciously selecting well sites based on hydrogeologic knowledge and by drilling test wells in valleys or draws and along linear features, as mapped on aerial photographs. Data are presented documenting the substantially higher yield for wells drilled along linear features that apparently represent zones of fracture concentration in the rock and for wells drilled in valleys or draws.
The chemical quality of the water in both the Coastal Plain and Piedmont aquifers is generally good. The most common water-quality problems are high concentrations of iron and a low pH. In addition, manganese concentration is high in a few areas in the Coastal Plain, as is that of nitrate in a few areas in the Piedmont.
