Controls on the quality variations of some carbonate spring waters

Abstract

In carbonate-rock terranes in central Pennsylvania a spring's discharge characteristics and water chemistry can be predicted from its geographic and hydrogeologic setting. Springs located near non-carbonate ridges (conduit-type) receive much of their recharge as mountain runoff entering sinkholes, have waters low in solutes, and a large variability in water quality and discharge. Springs in mid-valley areas (diffuse-type) receive water chiefly by infiltration through soils, or from a deeper circulating ground water flow system, and discharge water with higher total dissolved solids (TDS) and less variation in solute amounts and discharge. A spring's flow is a much more important control on its water chemistry than is season, particularly for diffuse-type springs. In conduit spring waters TDS increase in the early part of the storm hydrograph, decrease during the middle of the storm peak because of recharge via sinkholes, and finally increase as the storm pulse dissipates. In diffuse spring waters TDS increase and decrease nearly simultaneously with discharge following a storm as infiltration through soils near the spring leaches salts to the ground-water table. Based on precipitation and discharge records it took 6 and 60 days respectively, for 50% of the ground water introduced following a storm to leave a conduit and a diffuse type spring system.