Usgs groundwater age dating
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(2) Relate the groundwater ages to the observed changes in herbicide concentrations measured in the wells by DPR during the last decade.
Science Plan: About 30 wells will be selected for sampling in consultation with DPR.
It is important that water NOT enter the area behind the cone seal in the cap.
The study area is a high priority setting to better understand the relation between groundwater-age distribution and trends in pesticide concentrations.
The objective of this study is (1) Estimate the recharge age of water sampled from a subset of domestic wells (~30) in the DPR monitoring network in Fresno and Tulare Counties.
When the unsaturated zone is relatively thin, the unsaturated-zone air composition tracks that of the troposphere (Oster et al., 1996).
It is reasonable to assume unsaturated-zone SF concentrations closely track tropospheric concentrations to unsaturated zone depths of less than 10 m (Weeks et al., 1982; Busenberg et al., 1993), in deeper unsaturated zones, there is a lag time for diffusive transport of SF through the unsaturated zone.