Deep-well injection, 29 into

Deep-Well Injection Deep-well injection for the disposal of liquid wastes involves injecting the wastes deep in the ground into permeable rock formation (typically limestone or dolomite) or underground caverns. 

After further polishing, such as clarifying and filtering, if necessary, the biologically treated groundwater may be reinjected into the aquifer in an operation similar to deep well injection.66... 

The technology of deep-well injection has been around for more than 70 years. Most Americans would be surprised to know that there is a waste management system already in operation in the U.S. that has no emissions into the air, no discharges to surface water, and no off-site transfers, and exposes people and the environment to virtually no hazards. 1 The U.S. Environmental Protection Agency (U.S. EPA) has stated that Class 1 wells are safer than virtually all other waste disposal practices for many chemical industry wastes. 

A substance may exist in one of three phases—solid, liquid, or gas. The mobility of a substance in the subsurface is influenced by which of several forms or species it may take. Species in deep-well-injection formations fall into six main categories3 ... 

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. 

Metals are divided into light (also called alkali-earth metals) and heavy. All toxic metals are heavy metals except for beryllium and barium. Additionally, other categories of elements that are or may be significant chemically as dissolved species in deep-well-injection zones include the following ... 

Acid-base equilibrium is very important to inorganic chemical reactions. Adsorption-desorption and precipitation-dissolution reactions are also of major importance in assessing the geochemical fate of deep-well-injected inorganics. Interactions between and among metals in solution and solids in the deep-well environment can be grouped into four types1 2 3 4 ... 

FIGURE 20.10 Proposed geochemical model of waste after injection into the subsurface. (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.)... 

Abstract Deep well injection is the disposal of concentrate into the voids and pores of rocks deep underground. Concentrate is injected down a well that consists of several layers of casing and grouting. Porous rocks are then used to contain the concentrate, while shale, clay and other impermeable rock formations are used to prevent the water contaminating aquifers. The conditions required for deep well injection are quite specific, and as such this disposal option is not widely employed. 

In the chloride process, wastewater problems can arise, especially if the raw material contains <90% Ti02. The metal chloride by-products are sometimes disposed of in solution by the deep-well injection method (e.g., at Du Pont). The metal chloride solutions are pumped via deep boreholes into porous geological strata. Special geological formations are necessary to avoid contamination of the groundwater by impurities. 

For the selection of a deep-well injection process many factors are taken into account. The depth of the well is selected to avoid the contamination of fresh water and takes into consideration the nature of the underlying rock. The rock should be stronger but permeable enough to adsorb the liquid wastes. The site must be tested on a pilot scale before it is actually used. 

The four ultimate disposal methods defined by the EPA are landfarming, deep-well injection, landfilling, and ocean dumping. Landfarming, used for organic wastes, relies on nutrients in the soil to convert wastes into nonhazardous materials that may enrich the soil. The latter three methods concentrate on containing, not converting, wastes and may be used on various waste types. Briefly describe each of these four disposal methods. 

As described in an earlier problem, deep-well injection is an ultimate disposal method that transfers liquid wastes far underground and away ifom freshwater sources. Like landfarming, this disposal process has been used for many years by the petroleum industry. It is also used to dispose of saltwater in oil fields. When the method first came into use, the injected brine would often eventually contaminate groundwater and freshwater sands because the site was poorly chosen. The process has since been improved, and laws such as the Safe Drinking Water Act of 1974 ensure that sites for potential wells are better surveyed. 

Deep well injection, done by pumping liquid wastes into a permeable stratum sandwiched between impermeable strata, at depths of one to three miles, was ruled out because of probable migration of wastes through the permeable stratum to distant acquirers. The method is used, however, with some non-radioactive wastes. 

Figure 1.8. An example of a deep-well injection facility. Monsanto s facility near Pensacola, Florida, injects acidic waste streams more than 1000 ft deep into the Lower Limestone of the Floridian Aquifer. Observed reactions include dissolution of limestone, reactions among the wastes under higher pressure and temperature, and suppression of microbial activities (Boulding, 1990).

When desalting brackish water far inland, the discharge of the concentrated brine may pose a serious problem. For the case where neither deep-well-injection nor a discharge into a river or canal is possible, a hybrid plant consisting of a reverse osmosis process as a first stage and a special crystallization process as a second stage seems to be feasible (Figure 6.27). 

Deep-Well Injection Today, EPA regulations generally ban deep-well injection. In deep-well injection, pumps move liquid wastes through pipes deep into the earth into porous rock formations or natural underground domes. Normally, the well depth is below any useful imderground water sources. If there are suitable sites, deep-well injection can avoid transportation costs and processing costs. 

The U.S. Environmental Protection Agency (EPA) maintains the Toxic Chemical Release Inventory. This database summarizes estimated chemical releases from industrial sources to air, water, land, and the subsurface by deep-well injection in the United States. Not all industrial sources are required to provide release data to the EPA, and nine of the solvents discussed in this chapter are not included in the database. The information provided, however, indicated that about 99,364,390 kg of solvents were released into the environment in 2011, and that the major solvents were hexane, methanol, and toluene (Table 16.1.2). On a weight basis, methanol accounted for more than half of the releases. With the exeeption of nitrobenzene and pyridine, the major on-site releases were made to the atmosphere. For... 

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. 

The previous chapter examined the geochemical processes that can occur in the deep-well environment. The type and outcome of reactions that will actually occur when a waste is injected, however, depend on its chemical characteristics and on injection-zone conditions. This chapter examines six major environmental factors that must be taken into consideration. 

---