TCE and Flow Monitoring Methods Using an Existing Water Supply Well

Abstract

Several down-hole logging and sampling methods were used in a 335 m (1,100 ft) deep water supply well to monitor the distribution of trichloroethylene (TCE) and groundwater flow in a deep, multilayered aquifer system. The vertical distribution of TCE was assessed by collecting discrete-depth groundwater samples from the open well casing under non-pumping conditions and from 5 m (18 ft) intervals using a straddle-packer assembly under pumping conditions. The distribution of groundwater flow under pumping and non-pumping scenarios was assessed using spinner logs, temperature and fluid resistivity logs, and a FloVision survey. The combined data indicated that: (1) water containing TCE is confined to the uppermost water bearing zone in the screened interval; and (2) the well provides a conduit for downward migration of this water under non-pumping conditions. Subsequent long-term monitoring with pressure transducers has shown that vertical flow reversals occur in the well on a seasonal basis. The approach we developed can be used to monitor chemical and groundwater flow distribution in other areas where water supply wells already exist.