Temporal changes in the vertical distribution of flow and chloride in deep wells.
The combination of flowmeter and depth-dependent water-quality data was used to evaluate the quantity and source of high-chloride water yielded from different depths to eight production wells in the Pleasant Valley area of southern California. The wells were screened from 117 to 437 m below land surface, and in most cases, flow from the aquifer into the wells was not uniformly distributed throughout the well screen. Wells having as little as 6 m of screen in the overlying upper aquifer system yielded as much as 50% of their water from the upper system during drought periods, while the deeper parts of the well screens yielded 15% or less of the total yield of the wells. Mixing of water within wells during pumping degraded higher-quality water with poorer-quality water from deeper depths, and in some cases with poorer-quality water from the overlying upper aquifer system. Changes in the mixture of water within a well, resulting from changes in the distribution of flow into the well, changed the quality of water from the surface discharge of wells over time. The combination of flowmeter and depth-dependent water quality data yielded information about sources of high-chloride water to wells that was not available on the basis of samples collected from nearby observation wells. Changing well design to eliminate small quantities of poor-quality water from deeper parts of the well may improve the quality of water from some wells without greatly reducing well yield.
Izbicki
John A
JA
US Geological Survey, San Diego, CA 92123, USA. jaizbick@usgs.gov
Christensen
Allen H
AH
Newhouse
Mark W
MW
Smith
Gregory A
GA
Hanson
Randall T
RT
D002712:Chlorides / Q000032:analysis / Q000737:chemistry*; D005618:Fresh Water / Q000737:chemistry*; D014872:Water Movements
D002712:Chlorides