Modeling Volatilization of MTBE from Standing Surface Waters

Abstract

The discovery in California of methyl tertiary-butyl ether (MTBE) in surface waters used for recreational boating has raised concerns over the potential impact on drinking water quality. Concentrations of MTBE above the California secondary maximum contaminant level of 5 ppb have been reported. Here we present a model to predict the fate of MTBE in surface waters as a function of wind speed, water temperature, epilimnion depth, and lake surface area. The model was validated with MTBE concentration data from Lake Perris in southern California and Calero Reservoir in northern California. When applied to typical lake conditions in California [i.e., epilimnion depth <11 m (<35 ft) and water temperature >15ЊC], the maximum half-life for MTBE is <40 days for quiescent conditions, and as low as 6 days if the average wind speed is >4.5 m/s (10 mi/h). The model can be used for management of recreational boating based on a target MTBE concentration in the reservoir.

Seasonal and daily variations in concentrations of methyl-tertiary-butyl ether (MTBE) at Cranberry Lake, New Jersey

“…A similar half-life (10 days) was calculated by Stocking and Kavanaugh [9] for Lake Perris (9.1 km 2 or 2240 acre), also in California. Using a two-layer diffusion model, they fit monthly MTBE concentration decline after the boating season to a model in which a 4.5-m/s (10-mph) wind speed (close to the measured average) was assumed.…”

“…This rate is smaller than that observed on Donner Lake by Reuter et al [8], which was 8 kg/day, and is similar to that observed on Perris Lake [9], which was 1.6 kg/day. The surface areas of the lakes differ, however, and Perris Lake has the highest rate when its surface area is accounted for.…”

“…As part of the National Water Quality Assessment (NAWQA) program conducted by the US Geological Survey (USGS), Squillace et al [3] found that MTBE was the second most frequently detected volatile organic compound (VOC) in ground water in nine areas across the country. MTBE also has been found in urban storm runoff and streams [4], lakes [5][6][7][8][9], and improper disposal of used motor oil [10]. MTBE in the atmosphere over southern New Jersey was monitored from 1996 to 1998 [11,12].…”

“…MTBE occurrence has been documented in lakes in Nevada and California [6][7][8][9] and in northern New Jersey [5]. Concentrations of MTBE in Lake Tahoe, Nevada (500 km 2 or 123,000 acre), ranged from 0.18 to 4.2 mg/L, and the compound was found throughout the 30-m vertical profile [6].…”

Verification of Wind-Driven Volatilization Models

“…In this section, the considered equations are applied to test their predictive performance using the field data of methyl tertiary-butyl ether (MTBE) volatilization from Lake Perris, that is located in southern California, 20 km southeast of Riverside [23]. It is owned and managed by the California Department of Water Resources (DWR) as a drinking water reservoir [24].…”