The Sediment Chemistry Index (SCI) combines data on the concentrations of selected chemicals for which state Sediment Quality Standards Chemical Criteria have been set into an overall index of chemical exposure. Sediment quality is a key indicator of a healthy ecosystem, and high-quality sediments support a diverse and important biological community.

• The Sediment Chemistry Index (SCI) can range from 0 to 100, with higher values indicating less exposure to chemicals and thus healthier sediments. Values greater than or equal to 93.3 reflect minimum exposure to harmful contaminants.
• Sediments in greater Puget Sound sampled between 1997 and 2022 were in good condition with regard to the measured set of chemicals. SCI measures were above the minimum exposure threshold value.
• Five of six urban bays sampled from 1998 through 2022 also show sediments in good condition or improving. SCI scores in Elliott Bay have improved from baseline sampling in 1998, but still do not reach the threshold level of minimum exposure.
• Sediment contamination typically changes very slowly over time unless contaminant inputs increase. SCI values generally held stable in subsequent rounds of sampling (did not make gains or lose ground relative to the baseline), therefore, progress for this indicator is assessed as No Trend.