A Comparison of 1988-1990 Flavor Profile Analysis Results with Water Conditions in Two Northern California Reservoirs

Abstract

Flavor Profile Analysis (FPA) results were compared with water quality data for two storage reservoirs of the East Bay Municipal Utility District in Oakland, California to determine what conditions exist at the time of an earthy or musty taste and odor episode. Strong musty and earthy aromas coincided most frequently with fall Anabaena sp. blooms and summer Anacystis sp. blooms. Occasional Aphanizomenon sp. blooms were concurrent with Anabaena sp. blooms, so odor problems associated with Aphanizomenon sp. could not be distinguished. Geosmin concentrations of 30-140 ng/L were found in water containing 100,000-300,000 Anabaena sp. cells/100 mL, but 2-methylisoborneol concentrations never exceeded 25 ng/L. Both reservoirs experienced relatively odorless large spring diatom blooms resulting in high chlorophyll a concentrations, so chlorophyll a alone did not serve as a helpful indicator of imminent odor problems. Fall cyanobacteria blooms closely followed the onset of reservoir destratification, so weekly temperature and dissolved oxygen depth profiles successfully predicted the start of a cyanobacteria bloom. Musty and earthy odors in the filter plant effluent were lower than those in the influent, but effluent FPA numbers reached 4 during two large taste and odor episodes, suggesting that granular activated carbon installed 1-2 years earlier may not remove all odor-causing compounds of a large taste and odor episode.