Aesthetic Groundwater Quality Impacts from a Continuous Pilot‐Scale Release of an Ethanol Blend
A pilot‐scale aquifer system (8 m3 continuous‐flow tank packed with fine grain sand) was used to evaluate groundwater quality impacts from a continuous release of 10% v:v ethanol solution in water mixed with benzene and toluene (50 mg/L each). The geochemical footprint (methane [CH4], volatile fatty acids [VFAs], pH, oxidation reduction potential [ORP], dissolved oxygen [DO], and temperature) was monitored more than 11 months. A rapid depletion of DO (from 5.3 to less than 0.1 mg/L) and a decrease of ORP (from 110 to –310 mV) were observed within 25 d of the release. The high‐biochemical oxygen demand exerted by ethanol resulted in strongly anaerobic conditions, indicated by the accumulation of CH4 (up to 17.9 mg/L) and VFAs (up to 226 mg/L acetic acid and 280 mg/L n‐butyric acid). Measurements at the sand surface (40 cm from the water table) using a portable combustible gas detector did not detect CH4. However, accumulation of VFAs (particularly n‐butyric acid) during the summer exceeded the secondary maximum contaminant level value for odor (odor levels extrapolated from aqueous concentrations), which represents a previously unreported aesthetic impact. Temperature variations (3.9 to 30.0 °C) significantly affected microbial activities, and a strong correlation was observed between groundwater temperature and CH4/VFAs generation (p less than 0.05). Overall, these results suggest that seasonal variation of odor generation and CH4 concentration should be considered at sites contaminated with fuel ethanol blends.
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Document Type: Research Article
Publication date: August 1, 2011