Abstract: Impact of Groundwater Withdrawal on a San Francisco Bay Wetlands

Christina M. Scott, Russell Fitzpatrick

This study investigated water quality conditions and water levels in a wetland area adjacent to San Francisco Bay in Sunnyvale, California. The objective was to detect changes in these data and in the wetlands vegetation after the start-up of a nearby groundwater remediation system. Samples from 4 shallow well points and several surface water bodies were collected monthly between December 1990 and December 1991 to establish a baseline. The samples were analyzed for general minerals, pH and hardness. Quarterly photographic documentation monitored changes in seasonal surface water bodies and vegetation.

These data were then compared to data collected after groundwater extraction began upgradient of the wetlands. After eighteen months of pumping, several conclusions about the impact of the groundwater withdrawal can be made. Seasonal fluctuations in water quality and water levels are still observed. An artificial reverse groundwater gradient was detected in an area of the wetlands. Water quality conditions in this area have become more saline. Water levels in the wetlands area, although slightly lower, are primarily effected by rainfall events. The aerial extent of the wetland vegetation does not appear to have visibly changed.

AAPG Search and Discovery Article #90958©1995 AAPG Pacific Section Meeting, San Francisco, California