Graphic by Lester McKee, Ph.D.

Jul 28, 2017

Guadalupe River is contaminated with mercury mining wastes from runoff associated with the historic New Almaden Mining District in the upper watershed that produced 40 million kilograms during its working life (1850-1975) and with PCB and other urban pollutants from a long history of urbanization and industrial land uses.

SFEI has been monitoring pollutant concentrations in the Guadalupe River during winter storms since October 2002. The result is one of the world’s most extensive data sets on mercury, PCBs, and other pollutant concentrations and loads in an urban river.  In a recent manuscript, SFEI staff used the dataset to answer three major questions:

  • How much did pollutant concentrations and loads vary among years? On average, flow-weighted mean concentrations of pollutants varied 4.4-fold between years, and annual pollutant loads varied by 7.1-fold.
  • How did the average load compare to the climatically adjusted mean load (deemed the best estimate of long-term mean)? Taking the average of measured annual loads resulted in an estimate that was 2.2 times lower than the climatically adjusted mean. Therefore, even when average loads are derived from long term data sets like this one, care must be taken to use a climatic adjustment technique to better determine a best estimate of the mean.
  • How did the observations in Guadalupe River compare with those from other parts of the world? Due to unique and local conditions, concentrations of mercury, phosphorus, DDTs, dieldrin, chromium, nickel, and possibly selenium in the Guadalupe River appear to be different from other watersheds. On the other hand, concentrations of PCBs, other trace metals, and the rest of the pollutants sampled appear to be similar to other urban systems.

Free access to the full manuscript is available until August 19, 2017 at the following link:

The study was made possible by funding provided by a number of agencies including the Clean Estuary Partnership (CEP), the Santa Clara Valley Water District (SCVWD), the US Army Corps of Engineers (USACE), the Bay Area Stormwater Management Agencies Association (BASMAA), and the Regional Monitoring Program for Water Quality in San Francisco Bay (RMP).

Programs and Focus Areas: 
Clean Water Program
Sources, Pathways, & Loadings