Deep well injection

For petroleum waste management a deep-well injection disposal process has long been used. This method transfers liquid wastes underground and away from fresh wastewater sources. It is also used to dispose of saltwater in oil fields. 

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 depth of the well is determined by the type and nature of the wastes. The more toxic the waste, the farther down the disposal zone must be. 

The wastewater to be disposed of should be low in volume, high in pollutant concentration, and must be difficult to treat with other methods. The wastewater should not react in the disposal zone and should also be biologically inactive. Nuclear wastes and petroleum wastes are often disposed of by this technique. 

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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. 

Applications Deep-well injection has been used principally for liquid wastes that are difficult to treat and dispose of by more conventional methods and for hazardous wastes. Chemical, petrochemical, and pharmaceutical wastes are those most commonly disposed of with this method. The waste may be liquid, gases, or solids. The gases and solids are either dissolved in the liquid or are carried along with the liquid. 

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 injec tion 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 injec tion to prevent clogging of the formation and damage to equipment. Particles greater than about 1 to 5 Im must be removed. Typically, treated wastes must be filtered prior to... 

Deep well injection Partial removal from Oil field brines low toxicity, Monitoring difficulty... 

Wastewater Deep Well Injection. This is an alternate wastewater disposal procedure and requires some treating prior to injection, such as filtration or pFI adjustment. Permits for this procedure require long lead times. Reference 4 gives prediction methods for refinery wastew ater, generation. 

Liquid waste disposal—evaporation, deep well injection (don t forget filtration and treating), mixing with river or ocean water (don t forget treating)... 

Disposal involves the use of postprocess activities that can handle waste, such as deep-well injection and off-site shipment of hazardous materials to waste-management facilities. 

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... 

Sources, Amounts, and Composition of Deep-Well-Injected Wastes. 785... 

Environmental Factors Affecting Deep-Well-Injection Geochemical Processes.806... 

Geochemical Characteristics of Deep-Well-Injection Zones. 810... 

Case Studies of Deep-Well Injection of Industrial Waste. 836... 

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. 

U.S. EPA regulations (53 Federal Register 28118-28157, July 26,1988) stipulate that deep-well injection of hazardous wastes is allowed only if either of the following two no-migration standards is met3 ... 

The sources, amounts, and composition of existing deep-well-injected hazardous wastes... 

Listed wastes also exhibit one or more of these characteristics. The significance of each of the characteristics listed above is discussed below and is summarized in Table 20.1.3 Deep-well-injected... 

Water-soluble volatile compounds may be involved, but vapor pressure and vapor density are not significant considerations in deep-well injection Greater than ambient temperatures. 

Source 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. 

A waste is toxic under 40 CFR Part 261 if the extract from a sample of the waste exceeds specified limits for any one of eight elements and five pesticides (arsenic, barium, cadmium, chromium, lead, mercury, selenium, silver, endrin, methoxychlor, toxaphene, 2,4-D and 2,4,5-TP Silvex using extraction procedure (EP) toxicity test methods. Note that this narrow definition of toxicity relates to whether a waste is defined as hazardous for regulatory purposes in the context of this chapter, toxicity has a broader meaning because most deep-well-injected wastes have properties that can be toxic to living organisms. 

As noted, deep-well-injected wastes are relatively dilute. Therefore, ignitability is not a significant consideration in deep-well injection, although in a concentrated form, individual compounds may exhibit this property. Ignitability has no further implications for the fate of deep-well-injected waste. 

The sources, amounts, and composition of injected hazardous wastes are a matter of record, because the Resource Conservation and Recovery Act (RCRA)5,14 requires hazardous waste to be manifested (i.e., a record noting the generator of the waste, its composition or characteristics, and its volume must follow the waste load from its source to its ultimate disposal site). The sources and amounts of injected hazardous waste can be determined, therefore, based on these records. Table 20.2 shows the estimated volume of deep-well-injected wastes by industrial category.3 More than 11 billion gallons of hazardous waste were injected in 1983. Organic chemicals (51%) and petroleum-refining and petrochemical products (25%) accounted for three-quarters of the volume of injected wastes that... 

Estimated Volume of Deep-Well Injected Wastes by Industrial Category... 

PROCESSES AFFECTING THE GEOCHEMICAL FATE OF DEEP-WELL-INJECTED WASTES... 

This section examines the major processes that affect the fate of deep-well-injected hazardous wastes. The focus is on processes that (1) are known to occur in the deep-well environment or (2) have not been directly observed but are theoretically possible. 

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 ... 

The term steady state is sometimes used to describe chemical systems where thermodynamically unstable species exist but the rate of conversion to stable species is so slow that a quasi-equilibrated state exists. Because deep-well-injected wastes may be very complex chemical systems, the attainment of true equilibrium is uncertain. 

The reversibility of reactions is another important characteristic in assessing the fate of deep-well-injected wastes. Depending on environmental conditions, reversible reactions readily proceed in either or both directions. Most acid-base reactions exemplify reversible processes. In aqueous solutions, relatively minor changes in such factors as pH or concentration can change the direction of these reactions. Irreversible reactions, typified by hydrolysis, have a strong tendency to go in one direction only. 

Immiscible-phase separation Transformation Processes No Fluids (such as gasoline) that are immiscible in water are a significant consideration in near-surface contamination. Deep-well injection is limited to wastestreams that are soluble in water. Well blowout from gaseous carbon dioxide formation is an example of this process that is distinct to the deep-well environment. 

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