Pensacola, Florida

Introduction

Contaminants and their levels
Two groups of chemicals were discharged at the site:

• Creosote (the most extensively used industrial wood preservative in the United States) a complex mixture of almost 200 organic componds:

• pentachlorophenol (PCP)
• diesel fuel was also released in lesser amounts

The contaminant plume separated into a dense, insoluble fraction and into a water soluble fraction. The water soluble fraction contained:

• 35% organic acids (max. total = 90 mg/l)
• 6% phenolic compounds (max. total = 8 mg/l)
• 4% single- and double-ring PAH (max. total = 13 mg/l)
• 25% NSO's (max. total = 37 mg/l)

American Creosote Works, Inc., was located within the city limits of Pensacola, FL and had been treating pine poles with wood preservatives nearly 80 years (1902-1981) prior to its closing in December 1981. The 18-acre plant site is situated approximately 600 yards north of Pensacola Bay near the entrance to Bayou Chico (Troutman et al., 1984).

Prior to 1950, creosote was used exclusively to treat poles at ACW. Subsequent to 1950, other wood preservatives such as pentachlorophenol (PCP) were also used. The plant utilized approximately 25,000 gallons of creosote per month and a smilar quantity of PCP prior to closing in 1981. It is estimated that approximately 3,500 gallons of "blowdown", or residual wastewater from the chambers were discharged to impoundments each week (Troutman et al., 1984).

Geology

The site is underlain to about 90 m by surficial deposits ranging in age from middle Miocene through. These deposits constitute the sand and gravel aquifer, which is the source of water supply for the city of Pensacola and the westernmost Florida Panhandle.

The sand and gravel aquifer consists of nonhomogeous fine-to-coarse grained, locally well sorted fluvial and deltaic sediments. The dominantly quartz sands and gravels are interbedded locally with discontinous silt and clay lenses. Abrupt changes in lithology are characteristic for this aquifer.

The top of the sand and gravel aquifer is coincident with the surface, with altitudes ranging from sea level near to coast to about 60 m above sea level in northern Escambia County. In the area of consideration, the base is defined by the top of the Pensacola Clay at an altitude of about 90 m below sea level.

Hydrology

Hydrologic facies (distribution of facies)
. The aquifer, the principal source of drinking water supply in the area, consists of deltaic, fine to coarse sand deposits, interrupted by discontinous silts and clays, which locally confine the aquifer. Near the site the aquifer is about 90 m in total thickness. Only the upper 20 m area affected by wood preserving waste.

Inorganic Chemistry

Inorganic constituents in the water show a strong response to the plume, indicative of extensive biodegradation that removes 0₂ and SO₄. Cross sections showing concentrations of various compounds:

Table 1. Inorganic Analysis of Water Samples from 6.1m Deep Wells (Godsy at al. (1992).
(Units are mg/l)

Organic Chemistry

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, 1(2H)-quinotinone, and 2(lHyisoquinolinone 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 microbial degradation to CH4 and C02. A small but active methanogenic population was found on sediment materials taken from highly contaminated parts of the aquifer.

Table 2. - Organic Analysis of Water Samples from 6.1 m Deep Well (Godsy et al. 1992)
All results in mg/l. ND=below detection limit, generally < 0.10 mg/l.

Table 3. - Chemical Analyses for Selected Organic Contaminants in Groud Water at a Depth of 18.3 m at sites 1 and 3 through 7 (Pereira and Rostad, 1986)
Concentrations in micrograms per liter; ND=not detected; -, not analyzed.

Disappearance of the plume

Microbiological data collected near the wood-treatment site suggest that an anaerobic methanogenic ecosystem contributes to a reduction in phenol concentrations in ground water. However, some of the compounds such as PCP may inhibit methanogenesis at concentrations exceeding 0.45 milligrams per liter (Troutman et al., 1984).

Remediation

References

• Beadecker, M.J., and Lindsay, S., 1986, Distribution of Unstable Constituents in Ground Water Near a Creosote Works, Pensacola, Florida, Chapter B. In Movement and Fate of Creosote Waste in Ground Water , Pensacola, Florida. U.S.G.S. Water Supply Paper 2285. p. 9-17.
• Franks, B. J., 1988, Hydrogeology and Flow of Water in a Sand and Gravel Aquifer contaminated by Wood-Preserving Compounds, Pensacola, Florida; U.S. Geological Survey, Water-Resources Investigation Report 87-4260.
• Godsy, E.M., Goerlitz, D.F., and Grbic-Galic, D., 1992, Methanogenic Biodegradation of Creosote Contaminants in Natural and Simulated Ground-Water Ecosystems; Ground Water, 30(2), p. 232-242.
• Pereira, W.E., and Rostad, C.E., 1986. Geochemical Investigations of Organic Contaminants in the Subsurface at a Creosote Works, Pensacola, Florida, Chapter E. In Movement and Fate of Creosote Waste in Ground Water , Pensacola, Florida. U.S.G.S. Water Supply Paper 2285. p. 33-40.
• Troutman, D.E., Goday, E.M., Goerlitz, D.F., and Ehrlich, G.G., 1984, Phenolic Contamination in the Sand-and-Gravel Aquifer from a Surface Impoundment of Wood Treatment Wastes, Pensacola, Florida; U.S. Geological Survey, Water-Resources Investigation Report 84-4230.