ENGINEERING [WASTES DISPOSAL]

UNDERGROUND WASTE DISPOSAL

The underground disposal of wastes geological formation is a universally accepted practice.

Human beings through time have always disposed of dead, demotic waste excrement in this manner.The soil and geological formations that are the waste receptors have naturally been assumed to posses the capacity to treat and convert these wastes into harmless states and sometimes more useful forms.

      Industrialization with attendant production process also continuously and inexorably generates large amount of wastes that are disposed of on the land surface as well as directly and indirectly underground.

Many of these wastes that are disposed or their geochemical derivatives are harmful to humans as well as to take the general ecosystem,this is one of the reasons some countries like Nigeria are committed to national policy that will ensure sustainable development based on proper management of the environment which demands positive and realistic planning that balances human needs against the carrying capacity of the environment.(Albert Tobi,1999).

In the United States, Wastes injection practice dates back to the early 1930's and UGEPA(2010) reports that more than nine billion gallons of wastes are injected into geological formations in the continental United States annually.

    This is exclusive of further and additional daily injection of more than two billion gallons of brine from oil and gas production operations.

     Existing organizations in Nigeria recognizes and recommends the use of approved land application and underground waste disposal.

While underground waste injection is more prevalent not in the petroleum industry,this is because wastes management in Nigeria is a major problem for both Government and Industries and there indicates that waste injection is already being considered a viable option for disposing wastes.

     Areas which generates up to ½ billion gallons of wastes water daily is presently seeking partnership with the private sector fir the management of water water(Also,2011).

INJECTION WELLS

EPA's general Underground Injection Control (UIC) regulations, established by SDWA in 1974, Satisfies the criteria to evaluate injection control propane.

* CATEGORIES OF WELLS

      

     Injection wells are separated into distinct categories. This categorization is necessary to practice and it is considered information on existing wells,well construction technology and on variety of fluids injected into wells

*CLASSES OF INJECTION WELLS

     Well Classification:- The UIC regulations classify all injection wells into five basic categories or classes with both general and specific requirements for each class well.

CLASS I INJECTION WELLS

   Class one(1) injection wells are used to dispose off wastes classified as large hazardous below the lowermost earth formation containing an underground source of drinking water located within one-quarter mile of the well box. Class 1 injection wells are commonly used to dispose wastes that are not necessarily classified as hazardous wastes or operators of hazardous wastes management facilities to inject hazardous wastes.

Other than class I wells, other industrial and municipal disposal wells which injects fluids beneath the lowermost formation.

  Class I wells are subdivided by the type of wastes injected, Hazardous, Non-hazardous and Municipal wastes.

CLASS I WELLS [NON-HAZARDOUS]

    Non hazardous wastes are any other industrial wastes that do not meet the legal definition of hazardous wastes and can include a wide variety of fluids, such as those from food processing, Texas and Kansas have the greatest number of wells in this category because those states have industries that generates large quantities of non-hazardous wastes.

Non-hazardous industrial class I wells are located in 19 states.

CLASS I WELLS [NON-HAZARDOUS]

   

    Hazardous wastes are those industrial wastes that are specially defined as hazardous in the federal law and rules.

    Many of these wells are located along the Texas Louisiana Gulf Coast. This area has a large number of waste generators such as refineries and chemical plants as well as top geologic formations that are used for the injection of wastes.

CLASS I WELLS [MUNICIPAL]

   Municipal wastes which are not specifically defined in federal regulations are wastes associated with sewage effluent that has recieved treatment.

  Disposal of municipal wastes through injection wells is currently practical only in Florida.

   In Florida, This wastes disposal practice is often chosen due to a shortage of available land, strict surface water discharge limitations, extremely permeable injection zones and cost effectiveness.

 

CLASS II INJECTION WELLS

  

   These are wells which injects fluids which are brought to the surface in connection with conventional oil or natural gas production. They are used for enhanced recovery of oil or natural gas and for the purpose of storing hydrocarbons that are liquid at standard temperature and pressure. The number of class II wells varies from year to year based on fluctuations in oil and gas demands and production.

  Class II wells falls into three categories.

*DISPOSAL WELLS

*ENHANCED RECOVERY WELLS

*HYDROCARBON STORAGE WELLS

DISPOSAL WELLS

  During oil and gas extraction, brines are also brought to the surface,brines are separated from hydrocarbons at the surface and re-injected into the same or similar underground formations for disposal. Waste water from hydraulic fracturing activities can also be injected into class II wells.

ENHANCED RECOVERY WELLS

   Fluid consisting of brine, freshwater, steam polymers or carbon dioxide are injected into the oil bearing formation to recover residual oil in limited application, natural gas, the injected fluid thins(decrease the viscosity) or displace small amounts of extractable oil and gas, oil and gas is the available for recovery.

     Enhanced recovery wells are the most numerous types of class II wells. They represent much as 80 percent of the total amount of the "pump and treat" process as follows:-

- Contaminated waster is brought to the surface.

- The water is treated to remove as much of the contaminant as possible.

- The treated water is injected through a well back into the same formation

- This process is repeated until contaminant concentrations are reduced and additional removal is not possible.

HYDROCARBON STORAGE WELLS

   Liquid hydrocarbons are injected into the underground formations such as (salt carvens) where they are stored generally.

    Class II injection wells have been used in oil field related activities since 1930's. Today, there are approximately 170,000 class II injection wells in 31 states. All class II injection wells are regulated either by a state agency which has been granted regulatory authority over the program or by USEPA.

    Class II wells are subjected to a regulatory process which requires a technical review to assure adequate protection of drinking water and administrative review defining operational guidelines.

 

 CLASS III INJECTION WELLS

 

    These are wells which injects for extraction of minerals or energy, including mining of sulphur by the Frasch process, solution minning of minerals into combustion of fossil fuels and recovery of geothermal energy.

   Class III injection wells are used to mine:-

* URANIUM

* SALT

* COPPER

* SULPHUR

Class III injection wells are found in 18 states. Every class III injection wells, whether located in a primary or direct implementation states must be permitted through ten authorized regulatory agencies.

The operating permit requires that a well meets regulations the state has adopted to ensure the protection of USDW. This permits may include specific requirements for well construction, monitoring,mechanical integrity testing, maximum allowable injections, pressure and reporting proper closure or plugging of all class III injection wells must be conducted in a manner to protect USDWs from potential contamination.

    THE TECHNIQUES USED FOR MINERAL EXTRACTION ARE DIVIDED INTO TWO BASIC CATEGORIES.

Which are;

* SOLUTION MINNING

* IN SITU LEACHING

SOLUTION MINNING

   

     Solution minning techniques are used primarily for the extraction of salts and sulphur. For common salty, the solution minning process involves injection of relatively fresh water, which then dissolves the underground salt formation. The resulting brine solution is pumped to the surface, either through the space between tubing and the casing in the injection well or through seperate production wells.

CLASS IV INJECTION WELLS

    Class IV wells are shallow wells used to dispose hazardous or radioactive wastes into or above a geologic formation that contains an underground source of drinking water.

   In 1984, the (USDW) EPA banned the use of class IV injection wells, these injection wells may only operate as part of EPA or state authorized ground water cleanup action.

    The only allowable class IV wells are used to clean up ground water contaminated by hazardous chemicals.

CLASS V INJECTION WELLS

     The class V wells are used to inject non-hazardous fluids underground. Most class V wells are used to dispose off wastes into or above underground sources of drinking water. The disposal purpose can pose a threat to ground water quality if not managed properly.

   

    The different types of class V wells pose various threats. Most class V wells are shallow disposal systems that depends on gravity to drain fluids directly into the ground. Over 20 wells subtypes fall into the class V category.

    The EPA's regulations defines class V wells as injection wells not included in other well classes. As a result in addition to shallow wells, the class V wells category included deep complex wells used at commercial and Industrial facilities.

    Complex class V wells may include:-

* AQUIFER STORAGE AND RECOVERY WELLS

* GEOTHERMAL ELECTRIC POWER WELLS