Natural Attenuation of Aromatic Hydrocarbons in a Shallow Sand Aquifer

Abstract

Inadvertent release of petroleum products such as gasoline into the subsurface can initiate ground water contamination, particularly by the toxic, water‐soluble and mobile gasoline components: benzene, toluene and xylenes (BTX). This study was undertaken to examine the processes controlling the rate of movement and the persistence of dissolved BTX in ground water in a shallow, unconfined sand aquifer. Water containing about 7.6 mg/ L total BTX was introduced below the water table and the migration of contaminants through a sandy aquifer was monitored using a dense sampling network. BTX components migrated slightly slower than the ground water due to sorptive retardation. Essentially all the injected mass of BTX was lost within 434 days due to biodegradation. Rates of mass loss were similar for all monoaromatics; benzene was the only component to persist beyond 270 days. Laboratory biodegradation experiments produced similar rates, even when the initial BTX concentration varied. A dominant control over BTX biodegradation was the availability of dissolved oxygen. BTX persisted at the field site in layers low in dissolved oxygen. Decreasing mass loss rates over time observed in the field experiment are not likely due to first‐order deeradation rates, but rather to the persistence of small fractions of BTX mass in anoxic layers.

An Overview of the Persistent Organic Pollutants in the Freshwater System

“…Benzopyrenes, once get into the fresh water system, is either photo-degraded at the surface of waters or biodegraded gradually, however, their adsorption to particulates slows down the rate of natural assimilation. After entry, xylene may remain in fresh water for months or more but it gradually breaks down into relatively less harmful or harmless organics [58]. Trichloroethane and other halogenated hydrocarbons degrade naturally by photo-oxidation and biodegradation.…”

Implementing Monitored Natural Attenuation and Expediting Closure at Fuel-Release Sites

“…More than three decades of research has produced numerous laboratory and field studies have shown that microorganisms indigenous to the subsurface environment can degrade a variety of hydrocarbons, including components of gasoline, kerosene, diesel, and jet fuel (e.g., Jamison et al, 1975;Atlas, 1981Atlas, , 1984Atlas, , and 1988Young, 1984;Bartha, 1986;Wilson et al, 1986 andBarker et al, 1987;Baedecker et al, 1988;Lee, 1988;Chiang et al, 1989;Cozzarelli et al, 1990;Leahy and Colewell, 1990;Alvarez and Vogel, 1991;Evans et al, 1991a and1991b;Thierrin et al, 1992;Malone et al, 1993;Davis et al, 1994a and1994b;Lovley et al, 1995). In fact, almost all petroleum hydrocarbons are biodegradable.…”

Estudo da contaminação de poços rasos por combustíveis orgânicos e possíveis conseqüências para a saúde pública no Município de Itaguaí, Rio de Janeiro, Brasil

“…Este processo é causado pela sorção no solo, levando os compostos BTEX a se deslocarem a uma distância maior. Para Corseuil & Marins (1997) e Barker et al (1987), todos os álcoois primários podem ser biodegradados em preferência aos BTEX e consumir o oxigênio disponível, além de ser tóxico ou inibitório do crescimento dos microorganismos degradadores de BTEX.…”