Page 565 - Materials Chemistry, Second Edition

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536 Waste Management Practices: Municipal, Hazardous, and Industrial
disposed is through Class I wells (U.S. EPA, 2002a). Wells in this grouping are mainly used by
industries such as petroleum refining and metal, chemical, and pharmaceutical manufacture.
A total of 163 Class I hazardous waste injection wells are located at 51 facilities. Most are found
in Texas (78) and Louisiana (18). A small fraction of these facilities are commercial hazardous waste
injection facilities. These are the only facilities that can accept hazardous waste generated off-site for
injection. Ten are located in the Gulf Coast region while one is located in the Great Lakes region.
The HSWA made UIC regulations (1988) more stringent for Class I hazardous wells. This
resulted in strict no-migration standards and a petition approval process for the continued operation
of the wells. Of the 51 Class I hazardous waste facilities, 47 have approved no-migration petitions
that cover 123 wells. To receive a no-migration petition the facility must be capable of demonstrat-
ing that injected waste will not impact groundwater or surface water for 10,000 years. Such a
demonstration is often conducted using highly conservative mathematical and computer modeling
in addition to scientific and engineering data.
NonHazardous Waste Injection Wells
Non-hazardous deep injection wells inject industrial, low radiation, and municipal wastewater.
These wells must meet all the technical requirements of hazardous waste wells. Some states include
mining wells in this group and require that these wells meet all the requirements of other deep wells.
There are 366 Class I nonhazardous injection wells nationwide. These wells occur across 19
states, and most are found in Florida (112) and Texas (110). Florida is the only state with Class I
municipal waste disposal wells (104) (U.S. EPA, 2002a).
The EPA has submitted to Congress a study of Class I wells that describes the current Class I UIC
program, documents past compliance incidents involving Class I wells, and summarizes studies of
human health risks associated with Class I injection conducted for past regulatory efforts and policy
documentation. The program is described in Class I Underground Injection Control Program: Study
of the Risks Associated with Class I Underground Injection Wells (EPA 816-R-01-007 / March 2001).

17.4.3.2 Oil and Gas Injection Wells (Class II)

The oil and gas production industry accounts for a large proportion of the liquids injected via deep
wells. When oil and gas are extracted, large amounts of salt water (brine) are often brought to the
surface. About 38 L (10 gal) of brine are produced for each gallon of oil recovered. This brine is
often saltier than seawater and can contain toxic metals and radioactive substances. As a result, this
salt water cannot be discharged into surface water; rather, states have implemented rules that pre-
vent the disposal of brine to surface water bodies and soils, thereby making deep well injection of
this waste the prevalent form of disposal. The brine must be injected into formations similar to those
from which it was extracted. Over 2 billion gallons of brine are injected daily into injection wells
in the United States (U.S. EPA, 2002a).
The largest proportions of oil and gas field brines are injected into formations that contain trace
quantities of extractable oil and gas. Therefore, injection of brine can actually enhance the extrac-
tion of oil and gas from the formations. Class II wells exist where there is production of oil and gas.
There are approximately 167,000 oil and gas injection wells in the United States, most of which are
used for this so-called secondary recovery of oil. In this process water is pumped into the formation
that contains residual hydrocarbons. Some of the hydrocarbons are recovered along with the
injected water by extraction wells. In a common configuration, one injection well is surrounded by
four or more extraction wells. The recovered fluid is treated to remove most of the hydrocarbons in
an oil–water separator.
The second type of oil and gas injection well is a disposal well. In this system, excess fluids
from production and other activities directly related to the production process are injected solely for
the purpose of disposal.
Class II well facilities are required to adhere to strict construction standards except when his-
torical practices in the state and geology allow for different standards. A Class II well that follows