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Bacteria Beach: “A day at the beach should never make you sick!”

Our Environmental Science Senior Practicum Project re-evaluates the effectiveness of the “3-Day Rule”, a current warning to avoid beach water contact for 3 days following a rainstorm. A rainstorm carries upper watershed pollutants and bacteria down to the beach, creating a danger for surfers, swimmers, and other beachgoers. Beach water quality is tested by looking at levels of fecal indicator bacteria (FIB) present in ocean water samples. These bacteria do not actually cause human health problems, but indicate the presence of pathogens that may harm humans by causing sickness. We looked at the densities of FIB during a rain event and for the 10 days following the storm in order to determine when it is safe to swim. We have found some very interesting results!

Our data analysis has been a long but rewarding journey. Our client, Heal the Bay, provided us with a huge dataset consisting of over 86,000 data points! We chose to focus on years 2005-2012. We examined 32 beaches in Los Angeles County and Orange County and divided them into three beach types: Enclosed, Open, and Storm Drain Impacted; each type was analyzed separately. One of our most significant findings is that enclosed beaches continue to exceed permissible bacteria levels for 10 days after a rain event! We also categorized rainfall into four categories – light, moderate, heavy, and very heavy – to see the effect of rain intensity on FIB levels.

We’ve been very fortunate to have great advice and teamwork throughout this project. Our advisor, Dr. Mark Gold, is an expert in this field and has taught us much about the inner workings of water policy in Los Angeles and the entire United States. He also insisted that we develop a strong relationship with our client, Heal the Bay. Without this relationship, and especially without the help of Amanda Griesbach and Mike Grimmer, we would not have gotten as far with data analysis. Through our meetings and constant communication with them, we’ve learned a lot about FIB standards in California and also how to use the data set. We also found a friend in the UCLA Statistical Consulting Department. Phil Ender met with us each week to aid in our analysis and run appropriate tests in Stata. One of the biggest successes of our project was meeting these wonderful people, and their support has definitely played a huge role in our research. We are looking forward to these next few weeks, as we compile our results into meaningful analyses that will impact California beach water policy and beachgoer safety. Stay tuned for safer swimming!

We would like to add that we would have never gotten through all these data without our late ice-cream apple crisp nights.

— The Heal the Bay Beach Water Team

The Heal the Bay Beach Water Team is made up of the following UCLA students: Serena Lominico, Joel Slater, Mitchell Anderson, Marlene Alvarado, Kymberly Alvarez, Alexis Arnold, and Lily Tsukayama.