Does evaporation help?
Evaporation and rainfall in this area are about equal when averaged over the year. Spring, when evaporation is low and rainfall high, is the critical time for system failure because the porous topsoil that overlay clay subsoils may already be saturated from snow melt and frost thaw. The annual potential evapotranspiration is about 44 inches, while average precipitation in Lancaster County is 30 inches.