Application of impeller flowmeter and discrete water sampling techniques for improved groundwater well construction

Groundwater production wells are commonly designed to maximize well yield and, therefore, may be screened over several water-bearing zones. These water-bearing zones are usually identified from indirect information, such as geologic and geophysical logs. These indirect data are used to infer the hydraulic properties and water quality of the water-bearing zones. However, the reliance on indirect data can result in production wells that may be drilled deeper than necessary and screened through zones having low permeability and poor-quality groundwater. Direct data are provided by wellbore-flowmeter logs and downhole water-quality samples collected under pumping conditions, in an existing production well. The data obtained from one well can be applied to other proposed wells in the same hydrologic basin. In this study, flowmeter logs and downhole water-quality data were collected from three long-screened production wells within a multi-layered coastal aquifer system in the Santa Clara-Calleguas Basin, Ventura County, California. Results show that these wells yield most of their water from thin intervals. The importance of these intervals to well yield was not obvious based on indirect geologic or geophysical data. The flowmeter logs and downhole water-quality data also show that small quantities of water could degrade the total quality of water from the well. The application of flowmeter and downhole water-quality data to well design can reduce installation costs and improve the quantity and quality of water yielded by wells in complex multiple-aquifer systems.