Case Study No 3 Belle Glade FL 20731 Injection Facility Overview

The Belle Glade site, located southeast of Lake Okeechobee in south-central Florida, illustrates some of the problems that can develop with acidic-waste injection when carbonate rock is the confining layer. Contributing factors to the contamination of the aquifer above the confining zone were the dissolution of the carbonate rock and the difference in density between the injected wastes and the formation fluids. The injected waste was less dense than the groundwater because of its lower salinity and higher temperature.172

The injected fluids include the effluent from a sugar mill and the waste from the production of furfural, an aldehyde processed from the residues of processed sugar cane. The waste is hot (about 75°C to 93°C), acidic (pH 2.6 to 4.5), and has high concentrations of organics, nitrogen, and phosphorus.173 The waste is not classified as hazardous under 40 CFR 261, and the well is currently regulated by the State of Florida as a nonhazardous injection well. The organic carbon concentration exceeds 5000 mg/L.

The well was originally cased to a depth of 456 m (1495 ft), and the zone was left as an open hole to a depth of 591 m (1939 ft). The depth of the zone has been increased twice. Seasonal injection (fall, winter, and spring) began in late 1966; the system was inactive during late summer.

Injection rates ranged from 25 to 50 L/h (400 to 800 gal/min), and wellhead injection pressures ranged from 2.1 to 4.2 kg/cm2 (30 to 60 psi). By 1973, injection had become more or less continuous. From 1966 to 1973, more than 4.16 billion liters (1.1 billion gal) of waste had been injected.172

At the time injection began, a shallow monitoring well was placed 23 m (75 ft) south of the injection well in the upper part of the Floridan aquifer above the confining layer. A downgradient, deep monitoring well was placed in the injection zone 300 m (1000 ft) southeast of the injection well. Another shallow well, located 3.2 km (2 miles) southeast of the injection site at the University of Florida's Everglades Experiment Station, has also been monitored for near-surface effects.

Acetate ions from the injected waste were detected in the deep monitoring well 300 m (1000 ft) southeast of the injection well in early 1967, a matter of months after injection began.174 In 1971, about 27 months after injection began; evidence of waste migration was detected at a shallow monitoring well in the upper part of the Floridan aquifer. Dissolution of the carbonate confining layer by the acidic waste was the main reason for the upward migration. However, the lower density of the injected wastes compared with that of the formation waters (0.98 g/mL vs. 1.003 g/mL) served to accelerate the rate of upward migration.174 In an attempt to prevent further upward migration, the injection well was deepened to 684 m (2242 ft), and the inner casing was extended and cemented to 591 m (1938 ft). When waste injection was resumed, evidence of upward migration to the shallow aquifer was observed only 15 months later. By late 1973, 7 years after injection began, the waste front was estimated to have migrated 1 to 1.6 km (0.6 to 1 mile) from the injection well.173

The injection well was deepened a third time, to a depth of 900 m (3000 ft).175 A new, thicker confining zone of dense carbonate rock separates the current injection zone from the previous zone. As of early 1989, the wastes were still contained in the deepest injection zone. For details on acid injection into carbonate rock refer to Clark.176

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