Geosmin and 2-methylisoborneol monitoring versus a combination of sensory and chemical analyses in drinking water odor evaluation

ABSTRACT Odor occurrences in Summit Water Treatment Plant (SWTP) drinking water were evaluated by two methods. One method was the common practice of monitoring geosmin (GEO) and 2-methylisborneol (2-MIB) only. It led to the conclusion that the odor events primarily originated from Silverwood Lake (a water source for SWTP) and took place during late summer and mid-fall to early winter. The other method combined flavor profile analysis (FPA), gas chromatography/mass spectrometry (GC/MS) and Sensory GC. FPA captured a recurring moldy odor, unlike the earthy/musty odor expected from GEO and 2-MIB. 2-isopropyl-3-methoxypyrazine (IPMP) was identified as its cause by GC/MS and Sensory GC. More importantly, IPMP and its moldy odor were mainly produced in Lytle Creek (the second water source for SWTP) from late fall to mid-winter. Thus, monitoring only GEO and 2-MIB led to incomplete understanding of the chemical causes as well as the spatial and temporal patterns of SWTP's odor events. The case study serves as a precaution against equating the presence of GEO and 2-MIB with the overall drinking water odor occurrences despite the popularity of the approach. Instead, a combination of FPA and, as needed, subsequent GC/MS and Sensory GC is necessary for complete drinking water odor evaluations.