The Chemical History of Some Spring Waters in Carbonate Rocksa

Abstract

ABSTRACTInsights into the chemical and Hydrogeologie history of spring waters in carbonate rocks can be gained from a study of the chemical quality of such waters and of the waters which feed springs. The median Ca2+/Mg2+ ratio was 3.4 in 29 spring waters from folded and faulted carbonate rocks near State College, Pennsylvania, indicating ground‐water flow predominantly in limestone. The mean dissolved oxygen content was 7.7 mg/1 or 71% of saturation consistent with subsurface flow chiefly under water table conditions. Most of the dissolved solids (as specific conductance) including pollutants such as Cl and NO3 were added to spring waters during ground‐water flow. Specific conductances ranged from 180 to 476 micromhos, with a mean of 347 micromhos. CO2 pressures were from 10−1.9 to 10−2.6 atm with a mean of 10−2.2. atm. The CO2, which is chiefly introduced as gas by downward diffusion from the soil zone, gives spring waters the capacity to hold about 3 times more hardness and alkalinity than streams in equilibrium with the atmosphere. However, all spring waters were undersaturated with respect to calcite and dolomite because of their short residence times as ground water. Dye tracing of ground‐water feeding springs in two drainage basins gave residence times of 2–6 days for subsurface flows of about 4,000 feet. The specific conductance and carbonate saturation data indicate that ground‐water residence times of the 29 spring waters average somewhat longer than 2–6 days.