W6 AM Evaluation of Groundwater Communication with Surface Water and Contributions to Sediment Toxicity
Wednesday, 16 November 2005: 8:00 AM - 11:40 AM in 324-326

(CHA-1117-671728) Integrated tools for identification and verification of contaminated groundwater discharge zones in coastal environments.

Chadwick, B¹, Paulsen, R², Smith, C², Groves, J², Guerrero, J¹, Hawkins, A³, ¹ US Navy - SPAWAR Systems Center San Diego, San Diego, CA, USA² Coastal Monitoring Associates, San Diego, CA, USA³ Naval Facilities Engineering Service Center, Port Hueneme, CA, USA

ABSTRACT- Contaminant exposure and mass loading associated with groundwater discharge to surface water is a significant issue at coastal landfills and hazardous waste sites. Assessment of these sites is often difficult due to complex hydrogeolgical and geochemical processes including complex lithology, tidal forcing, freshwater-saltwater interaction, and redox gradients. Traditional approaches have relied primarily on upland and shoreline monitoring wells, coupled with groundwater modeling. While there are powerful tools, the findings from such assessments have often been met with skepticism due to the difficulty in verifying the predicted discharge locations and concentrations. We have developed a methodology for verification and quantification of exposure and mass loading, and optimization of remedial action at these sites based on two coupled technologies, the Trident and UltraSeep. The Trident is a multi-sensor probe that allows rapid screening of the offshore area to identify potential discharge zones based on conductivity and temperature contrast, and/or site-specific chemical tracers. The probe can also be used to collect sub-surface samples for chemical analysis. The UltraSeep is a continuously-logging seepage meter with flow proportional water sampling capability. Based on discharge zones identified with the Trident, the UltraSeep is used to quantify discharge rates and associated chemical loading. This protocol and the Trident and UltraSeep technologies will be described, and case studies will be used to illustrate the application and limitations of the approach for identification and verification of groundwater discharge zones.

Key words: groundwater discharge, surface water, coastal