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Wastes from a wood preserving plant in Pensacola, Florida have contaminated the near‐surface sand‐and‐gravel aquifer with creosote‐derived compounds and pentachlorophenol. Contamination resulted from the discharge of plant waste waters to and subsequent seepage from unlined surface impoundments that were in direct hydraulic contact with the ground water. Two distinct phases resulted when the creosote and water mixed: a denser than water hydrocarbon phase that moved vertically downward, and an organic‐rich aqueous phase that moved laterally with the ground‐water flow. The aqueous phase is enriched in organic acids, phenolic compounds, single‐ and double‐ring nitrogen, sulfur, and oxygen containing compounds, and single‐ and double‐ring aromatic hydrocarbons. The ground water is devoid of dissolved O2, is 60–70% saturated with CH4 and contains H2S. Field analyses document a greater decrease in concentration of organic fatty acids, benzoic acid, phenol, 2‐, 3‐, 4‐methylphenol, quinoline, isoquinoline, l(2H)‐quinolinone, and 2(lH)‐isoquinolinone during downgradient movement in the aquifer than could be explained by dilution and/or dispersion. Laboratory microcosm studies have shown that within the study region, this effect can be attributed to rnicrobial degradation to CH4 and CO2. A small but active methanogenic population was found on sediment materials taken from highly contaminated parts of the aquifer.

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Coal‐tar derivatives from a coal‐tar distillation and wood‐treating plant that operated from 1918 to 1972 at St. Louis Park, Minnesota contaminated the near‐surface ground water. Solutions of phenolic compounds and a water‐immiscible mixture of polynuclear aromatic compounds accumulated in wetlands near the plant site and entered the aquifer. The concentration of phenolic compounds in the aqueous phase under the wetlands is about 30 mg/1 but decreases to less than 0.2 mg/1 at a distance of 430 m immediately downgradient from the source. Concentrations of naphthalene (the predominant polynuclear compound in the ground water) and sodium (selected as a conservative tracer) range from about 20 mg/1 and 430 mg/1 in the aqueous phase at the source to about 2 mg/1 and 120 mg/1 at 430 m downgradient, respectively. Phenolic compounds and naphthalene are disappearing faster than expected if only dilution were occurring. Sorption of phenolic compounds on aquifer sediments is negligible but naphthalene is slightly sorbed. Anaerobic biodegradation of phenolic compounds is primarily responsible for the observed attenuation. Methane was found only in water samples from the contaminated zone (2‐20 mg/1). Methane‐producing bacteria were found only in water from the contaminated zone. Methane was produced in laboratory cultures of contaminated water inoculated with bacteria from the contaminated zone. Evidence for anaerobic biodegradation of naphthalene under either field or laboratory conditions was not obtained.