Publication Summary

Saltwater intrudes into Salmon Bay as a result of operation of the Hiram Chittenden Locks, which connect the Lake Washington Ship Canal with Puget Sound. Depending on the levels of salinity present, sediments in certain areas may be classified as marine, low-salinity, or freshwater. These classifications can affect sediment cleanup decisions.

To evaluate the appropriate classification, sediment pore water salinity levels in Salmon Bay and Lake Union were determined using conductivity and temperature measurements.

Saltwater intrudes into Salmon Bay as a result of operation of the Hiram Chittenden Locks, which connect the Lake Washington Ship Canal with Puget Sound. Depending on the levels of salinity present, sediments in certain areas may be classified as marine, low-salinity, or freshwater. These classifications can affect sediment cleanup decisions.

To evaluate the appropriate classification, sediment pore water salinity levels in Salmon Bay and Lake Union were determined using conductivity and temperature measurements. The results were then compared to sediment pore water definitions in the Washington State Sediment Management Standards (WAC 173-204-200). Pore water salinity results were also compared to the U.S. Army Corps of Engineers (USACOE) real-time water column monitoring data, to see if these data sets could be correlated for predicting pore water salinity levels.

Pore water salinity values ranged from 0.16 o/oo (parts per thousand) to 13 o/oo. A little over 50% of the sediment samples collected had salinity values that would classify them as low salinity sediment (>0.5 to <25 o/oo). Under conditions present at the time of sampling, there was a trend towards lower salinity levels moving east from the locks.

Sediment pore water conductivity data were correlated with USACOE data for two of the transects, using multiple correlation equations. The models describe conditions at the time of the study. Small sample sizes and highly variable conductivity values result in models that may not be very reliable in predicting pore water salinity levels. Despite the limitations, the models do provide an approximation of sediment conductivity levels.