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

(LOC-1117-677572) Comparison of interstitial water sampling methods in near-surface sediments, lower Willamette River, Portland, OR.

Locke, William¹, Henderson, Cynthia¹, Martin, Todd¹, Hawley, Christine¹, ¹ Integral Consulting, Inc., Boulder, CO, USA

ABSTRACT- Understanding the contributions of chemicals in groundwater originating from upland sites is of increasing interest in sediment and surface water investigations in industrialized rivers and harbors. In particular, measurement of aqueous chemical concentrations in interstitial waters in near-surface sediments is important for identifying the relative contribution of chemicals migrating in groundwater to sediment and surface water contamination, sources of toxicity in sediments, and sources of bioaccumulative chemicals in the food web. A pilot study was conducted on the lower Willamette River in Portland, OR to evaluate a range of available methods for collecting sediment interstitial water samples for chemical analysis. Probable groundwater discharge areas were identified using existing hydrogeologic data, thermal infrared imagery, and temperature and conductivity measurements using the Trident System™, and UltraSeep™ seepage meters. Co-located samples of interstitial water were collected from near-surface sediments in areas of known or suspected groundwater plume discharge using the Trident System™, small- and large-volume peepers, vapor diffusion samplers, and bulk sediment centrifugation. Samples were analyzed for VOCs, SVOCs, pesticides, metals, and conventional parameters. Intra-method variability and bias among sample replicates were evaluated using intra-class correlation coefficients, Pearson's correlation coefficients, and percentage estimators of variation. Inter-method variability and bias among co-located samples were evaluated using a non-parametric Kruskal-Wallis test and graphical methods. Site-specific chemical partitioning coefficients were calculated using co-located bulk sediment and interstitial water chemistry. Major ions were evaluated to identify mixing ratios between groundwater and surface water in the sediment surface mixed layer. Spatial variability and the effects of sediment texture – which may be correlated with differential groundwater discharge rates – were also evaluated. Results are being used to select sampling methods and develop a sampling design for further investigations to characterize exposure-point concentrations of groundwater-related chemicals in sediment interstitial water on the lower Willamette River.

Key words: groundwater, sediment, sampling