Well‐Water Quality Changes Correlated with Well Pumping Time and Aquifer Parameters—Fresno, Californiaa

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Abstract
Ground‐water chemical quality in alluvial valleys can be stratified, which can cause well‐water quality to vary with pumping time, especially after a pump shutdown of several hours. These changes in chemical quality could have public health implications for automatically controlled high‐capacity municipal water wells that pump directly into the distribution mains.For a large number of municipal wells, the shapes of the curves for the change‐in‐specific electrical conductivity and the NO3‐N content of well water during the first 96 minutes of constant rate pumping are reported after a 24‐hour shutdown as compared with “steady‐state” quality. The variables recovery‐transmissivity, well specific capacity, type of well construction, and equivalent specific yield of aquifer computed from driller's logs of the bore holes were considered in the analysis.The results showed that well‐water quality vs. time curves vary in shape and are related mainly to the well depth and the depth to the perforations. The “steady‐state” specific electrical conductivity and NO3‐N values were significantly correlated to each other and inversely to recovery‐transmissivity and equivalent specific yield. The specific capacity of wells was related to the recovery‐transmissivity and to type of well construction.