Petroleum refining and petrochemical products
Miscellaneous chemical products
Agricultural chemical products
Inorganic chemical products
Metals and minerals
Aerospace and related industry
5868 2888 687 525 254 475 672 169
Percent of Total
51 25 6
year. The remaining 24% was divided among six other industrial categories: miscellaneous chemical products, agricultural chemical products, inorganic chemical products, commercial disposal, metals and minerals, and aerospace and related industry.
Although the general composition of each shipment of wastes to an injection well may be known, a number of factors makes it difficult to characterize fully the overall composition of industrial wastewaters at any one well. These factors include the following15:
1. Variations in flow, in concentrations, and in the nature of organic constituents over time
2. Biological activity that may transform constituents over time
3. Physical inhomogeneity (soluble and insoluble compounds)
4. Chemical complexity; an example of the complexity of organic wastes is illustrated in the work of Roy and colleagues,16 which presents an analysis of an alkaline pesticide-manufacturing waste—this waste contained more than 50 organic compounds, two-fifths of which could not be precisely identified
Although no systematic database exists on the exact composition of deep-well-injected wastes, in a survey of 209 operating waste-injection wells, Reeder17 found that 53% injected one or more chemicals identified in that study as hazardous. The U.S. EPA gathered data for 108 wells (55% of total active wells) that were under operation.3 A little more than half of the undiluted waste volume was composed of nonhazardous inorganics (52%). Acids were the most important constituent by volume (20%), followed by organics (17%). Heavy metals and other hazardous inorganics made up less than 1% of the total volume in the 108 wells. About a third of the wells injected acidic wastes and about two-thirds injected organic wastes. Although the percentage of heavy metals by volume was low, almost one-fifth of the wells injected wastes containing heavy metals. An injected wastestream is composed of the waste material and a large volume of water. It is reported that typical ratios in the total volume of injected fluids are 96% water and 4% waste.
The U.S. EPA gathered data also showed that the average concentration of all the acidic wastes exceeded 40,000 mg/L. Concentrations of metals ranged from 1.4 mg/L (chromium) to 5500 mg/L (unspecified metals, probably containing multiple species). Five of the 18 organic constituents exceeded 10,000 mg/L (total organic carbon, organic acids, formaldehyde, chlorinated organics, and formic acid); four others exceeded 1000 mg/L (oil, isopropyl alcohol, urea nitrogen, and organic peroxides).
20.2.3 Geographic Distribution of Hazardous Waste Injection Wells
The use of wells for disposal of industrial wastes dates back to the 1930s, but this method was not used extensively until the 1960s, when it was implemented primarily in response to more stringent water pollution control regulations.
The number of industrial-waste injection wells more than doubled between 1967 and 1986.3 In 1986, Class I injection wells were concentrated in two states, Texas (112 wells) and Louisiana (70 wells), which between them had a total of 69% of all wells (263 wells). Growth from 1984 to 1986 was concentrated in Texas, with a 38% increase from 81 to 112 wells. The only other states to show a significant increase from 1984 to 1986 were Indiana (13 proposed wells) and California (7 proposed wells). Nine states had had industrial-waste injection wells in the past but did not have any permitted Class I wells in 1986 (Alabama, Colorado, Iowa, Mississippi, Nevada, North Carolina, Pennsylvania, Tennessee, and Wyoming). One state (Washington) had a Class I well in 1986, but no record of industrial wastewater injection before that year. The total number of industrial-waste injection wells increased to 300 at the end of the 1990s and beginning of this century, approximately 100 Class I hazardous waste injection wells and about 200 Class I wells that hold nonhazardous waste.1,18
Figure 20.1 shows the number of Class I wells in the 1986 survey by state, divided into U.S. EPA regions, and also indicates the regulatory status of such wells in each state as of 1989. The map shows the heavy concentration of hazardous waste injection wells in three geologic basins: Gulf Coast, Illinois Basin, and the Michigan Basin.3
20.2.4 Design and Construction of Deep-Injection Wells
The following subsections give a description of the design and construction of deep-injection wells.19-23
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