Dye Study in Groundwater at Cowell Beach

May 2013

Note that dye has been observed (red to pink) in the canal connecting the pipe to Neary Lagoon. Click here to see a picture of the dye in the canal.

The Civil and Environmental Engineering Department of Stanford University in collaboration with the City of Santa Cruz is conducting a dye tracer study in the groundwater of Cowell Beach. The goal is to determine if water in the storm drain connecting Neary Lagoon to the beach, which is buried in the sand at the beach in the summer, can be transported to the surf zone of Cowell Beach. Ultimately, the information obtained from the study will help identify sources of pollution to the beach in the summer. The results of the study can also inform the extent to which contaminated groundwater may serve as a source of pollution to other beaches along the California coast.

Cowell Beach is a popular and important beach to residents and visitors in Santa Cruz. It has historically had poor water quality and has been called the most polluted beach in California. Recent research conducted by Stanford University in collaboration with the city and county of Santa Cruz identified that the storm drain leading from Neary Lagoon to the beach could be a source of contamination. Cowell Beach has elevated levels of fecal indicator bacteria (e.g., Enterococcus, and E. coli) based on routine monitoring conducted by the County of Santa Cruz Health Department. Fecal indicator bacteria do not typically cause illness, but their concentrations indicate the presence of pathogenic organisms that are found in warm-blooded animal (e.g. human) waste. Swimming in water with high concentrations of fecal bacteria from sewage or runoff correlates to increased odds of becoming ill based on results of epidemiology studies of swimmer health conducted around the world.

The dye we are using is called rhodamine WT and is used in many environmental applications. We will be placing it in the storm drain that runs from Neary Lagoon to Cowell Beach on May 13, 2013. From here it will potentially be transported towards the beach in the pipe and through the beach sands to the ocean. The process may occur within a week, but may also take months. Alternatively, the dye may never show up in the ocean at all. If the dye is transported to the ocean, it may be visible to the naked eye, but it also may not be visible if the concentration is sufficiently low. The dye will not harm swimmers or surfers if they come into contact with it. Below is a link to the material safety data sheet and answers to frequently asked questions about the dye study.

The Principal Investigator of this project is Professor Alexandria Boehm at Stanford University. Her work focuses on understanding environmental and anthropogenic variables that influence the presence of pathogens and fecal indicator bacteria in bathing waters.

More information related to this project can be found in the following: