Deep waste injection wells

TABLE 25-76 Important Design and Operation Considerations for Deep Wells Used for Waste Injection... 

Well-site selection Criteria for assessing the feasibility of a deep-weU-injection site include (1) uniformity, (2) large injection formation). Adjustment of pH and buffering of the waste maybe necessary. 

If yourfacility has a permit to inject a waste containing the toxic chemical into Class 1 deep wells, enter the 12-digit Underground Injection Well Code (UlC) identification number assigned by EPA or by the State under the authority of the Sate Drinking Water Act. If your facility does not hold such a p>ermit(s), enter not applicable, NA, in Section 3.1 la. You are only required to provide the UlC number for wells that receive the toxic chemical being reported. 

When calcium carbonate goes into solution, it releases basic carbonate ions (COf ), which react with hydrogen ions to form carbon dioxide (which will normally remain in solution at deep-well-injection pressures) and water. Removal of hydrogen ions raises the pH of the solution. However, aqueous carbon dioxide serves to buffer the solution (i.e., re-forms carbonic acid in reaction with water to add H+ ions to solution). Consequently, the buffering capacity of the solution must be exceeded before complete neutralization will take place. Nitric acid can react with certain alcohols and ketones under increased pressure to increase the pH of the solution, and this reaction was proposed by Goolsby41 to explain the lower-than-expected level of calcium ions in backflowed waste at the Monsanto waste injection facility in Florida. 

FIGURE 20.4 Site suitability for deep-well injection and locations of industrial waste disposal wells. (From U.S. EPA, Assessing the Geochemical Fate of Deep-Well-Injected Hazardous Waste A Reference Guide, EPA/625/6-89/025a, U.S. EPA, Cincinnati, OH, June 1990.)... 

The only means by which inorganic wastes can be rendered nonhazardous are dilution, isolation (as in deep-well injection), in some cases changes in oxidation state, and neutralization. Acidic wastes made up one-fifth of the injected waste volume and involved one-third of the injection wells in 1983. Most of the volume was from inorganic acids (hydrochloric, sulfuric, and nitric). Acid-base characteristics and neutralization were discussed in detail earlier, so the remainder of this section will focus on heavy metals and other hazardous inorganics (selenium and cyanide). 

Waste injection began in June 1975, and waste was first detected in the downgradient southwest deep monitoring well about 260 days later. To analyze the waste s physical and chemical properties after injection, the primary injection well was allowed to backflow into a holding pond for 5 days in November 1977. This waste was sampled periodically (and reinjected when the test was completed). About 4 years after injection began dilute waste arrived at the standby injection well 476 m (1560 ft) south of the primary well. 

From May 1968 to December 1972, the waste was injected at a rate of about 300,000 gal/d. The first injection well was completed to a depth of 259 to 313 m (850 to 1025 ft) (i.e., cased from the surface to 259 m with screens placed in the most permeable sections of the injection zone to a depth of 313 m). One shallow observation well was placed 15 m (50 ft) east of the injection site at a depth of 210 m (690 ft). Four deep monitoring wells were also placed in the injection zone, one at 15 m (50 ft) and three at 45 m (150 ft) from the injection well. 

Eight months after injection began in the second injection well, wastes had leaked upward into the adjacent shallow monitoring well. The leak apparently was caused by the dissolution of the cement grout around the casing. In June 1972,13 months after injection began in the second well, the waste front reached the deep monitoring well located 450 m (1500 ft) northwest of the injection well. Waste injection ended in December 1972. As of 1977, the wastes were treated in a surface facility.170... 

Pascale, C.A. and Martin, J.B., Hydrologic Monitoring of a Deep-Well Waste-Injection System near Pensacola, Florida, March 1970-March 1977, U.S. Geological Survey Water Resource Investigation 78-27, 1978. 

Kaufman, M.I. and McKenzie, D.J., Upward migration of deep-well waste injection fluids in Floridan aquifer, South Florida, J. Res. U. S. Geol. Surv., 3, 261-271, 1975. 

Fig. 16.8 Calcium concentration, deep monitoring well, 1963-1964, Waste Injection Projection, Florida. (From Goolsby, 1971.)...

Design and Operation Important design and operation considerations for deep-well injection are related to (1) well-site selection, (2) pretreatment, (3) installation of an injection well, and (4) monitoring. Important factors related to these design and operation considerations are reported in Table 25-76. As noted in the table, wastes are usually treated prior to injection to prevent clogging of the formation and damage to equipment. Particles greater than about 1 to 5 lm must be removed. Typically treated wastes must be filtered prior to... 

Other point sources of groundwater pollution include both deep injection wells and shallower dry wells used to inject chemical wastes (including radioactive waste) directly into the subsurface environment. While it is customary to make waste injections into deep aquifers that are salty or otherwise unusable for potable water, it is not unusual for injection wells to leak, or to force the flow of water from one layer of aquifer into another, resulting in contamination of an otherwise usable source of groundwater. 

Deep-well injection is used to transfer liquid wastes far beneath the ground. The injection wells must be placed as far away as possible from drinking water sources. The type of waste to be injected will affect the depth of the wells. 

Finally, the type of waste injected into the well is a determinant in how deep the injection will be made. The more toxic the waste, the farther down the disposal zone must usually be. Disposal zones have been classified into five different types ... 

K.P. Saripalli, M.M. Sharma, and S.L. Bryant, Modeling Injection Well Performance During Deep-well Injection of Liquid Wastes, J. Hydrology, 227(1-4), 41-55, Jan. 31 (2000). 

Mountain Arsenal Deep Injection Well was constructed in 1961, and was over 12,000 feet deep. Over a four-year period, 165 million gallons of waste were pumped into the well. Records indicate that pumping took longer than anticipated, because of the impermeability of the rock. (Thus, it may be assumed that pumping pressures were very high.) In 1966, use of the well was discontinued because of the possibility that the fluid injection was triggering earthquakes in the area . Details can be found in Reference [8]. 

Gardiner, M.A. and Myers, J., 1992. Geochemical modeling of the deep injection well disposal of acid wastes into a Permian aquifer/aquitard system in Texas, USA, in Yousif K. Kharaka and Ann S. Maest, eds, Proceedings - International Symposium on Water-Rock Interaction, vol. 7, pp. 385-388. 

Deep well disposal. Injection of tritium-containing liquid into isolated aquifers or depleted oil horizons is the most interesting option. This technique has been used increasingly for almost 20 years to dispose of industrial wastes. In the United States, for instance, some hundred injection wells have been drilled and are actually in operation at depths between 60 m and 3600 m. Although there are still licensing problems, this is a safe and economic way to dispose of tritiated water. 

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