Hydraulic and earth engineering – Soil remediation – In situ contaminant removal or stabilization
Reexamination Certificate
1999-12-02
2002-03-05
Suchfield, George (Department: 3672)
Hydraulic and earth engineering
Soil remediation
In situ contaminant removal or stabilization
C166S306000, C166S370000, C166S371000, C166S372000, C166S090100, C210S170050, C210S747300, C210S759000, C210S760000, C405S128450, C405S128500
Reexamination Certificate
active
06352387
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, in general, to the remediation of contaminated soil and groundwater. It relates to an in situ method and apparatus to deliver chemical reagents that serve to degrade and/or enhance recovery of organic contamination in soil and groundwater.
2. History of the Related Art
Contamination of subsurface soil and groundwater from the release of hazardous substances has become a significant problem in populated and industrialized areas of the world. The contamination stems from intentional or unintentional releases of hazardous substances from above- and below-ground storage vessels such as tanks and conveyance piping, materials handling practices such as degreasing and other cleaning operations, and other product transfer operations. The released products that are in themselves hazardous or contain hazardous constituents include: petroleum products such as gasoline, diesel fuel, heating oil, jet fuel, and a variety of lubricants; halogenated solvents such as perchloroethylene, trichloroethylene, and freons; and non-halogenated solvents such as hexane, benzene, and ether.
The releases of these substances to the ground surface or into the subsurface presents a risk of human exposure that is unacceptable for human health and ecological factors. Many of the contaminants are known carcinogens and excessive exposure to them has been shown to increase the probability of contracting certain diseases including various forms of cancer. Potential human exposure routes include: inhalation of the volatile contaminant species which can occur as the contaminants in soil and groundwater evaporate into breathing zones; incidental ingestion of contaminated soil; and ingestion of or dermal contact with contaminated groundwater from a potable drinking water well. In response to these concerns, federal, state, and local governments have enacted environmental legislation requiring property owners to investigate and remediate their properties that contain contaminated soil and/or groundwater.
Many techniques have been developed and used over the past two decades to remove or destroy contaminants in soils and groundwater. Early forms of remediation included excavation of contaminated soil for landfill disposal and extraction of contaminated groundwater from wells, above ground treatment followed by discharge to a sewer system or reapplication at the subsurface. Because these methods generally involved substantial financial expenditure and were mostly ineffective, more advanced, in situ methods and techniques of treatment have been developed. These in situ methods include bioremediation, surfactant flushing, and chemical oxidation.
Bioremediation techniques rely on the stimulation of naturally-occurring subsurface bacteria or augmentation with foreign bacteria that, in turn, metabolize the subsurface organic contamination thereby reducing the concentration of the contaminant in soils and groundwater. The effectiveness of in situ bioremediation techniques relies on the uniform and comprehensive delivery of reagents such as inorganic nutrients, oxygen, and bacteria to the region of the subsurface targeted for treatment. Typically, reagent delivery has been accomplished through wells, irrigation trenches, injection lances, or french drains, all of which are established by prior art. Through numerous applications of bioremediation techniques at contaminated sites, it has been shown that these means to deliver reagents do not provide an effective system to supply the necessary reagent flow. Further, each well can reach only a limited volume of soil and groundwater, and, therefore, a large number of the wells, trenches, etc., must be emplaced at a site in order to address an entire contaminated soil or groundwater volume.
Surfactant flushing techniques rely on the delivery of a reagent to the subsurface that serves to reduce the surface tension of organic contaminants which are adhered to soil particle surfaces (commonly referred to as “adsorbed contamination”) or trapped in the interstitial spaces between soil particles (commonly referred to as “absorbed contamination”). When the delivered chemical reagent (surfactant) contacts the absorbed or adsorbed contaminants (collectively referred to as “sorbed contaminants”) the sorption forces are reduced, thereby increasing the mobility of the contaminant which, in turn, increases its ability to be collected and extracted by groundwater extraction (pumping) techniques. Once again, effective application of this technique relies heavily on the delivery device since the surfactant reagent must contact all portions of the soil and groundwater volume that contains the organic contaminant. As with other in situ techniques, surfactant flushing relies on conventional chemical reagent delivery devices such as wells, trenches, injection lances, and french drains to effect emplacement of the surfactant solution. Experience with these devices has again demonstrated that their ability to effect reagent delivery to any significant volume of soil or groundwater surrounding the device is limited since they rely solely on gravitational forces, which may be enhanced by pressurizing the reagent fluid. These apparatus do not promote mixing and turbulence needed to adequately disperse the reagent fluid.
Similarly, chemical oxidation techniques using hydrogen peroxide, Fenton's Reagent (a combination of hydrogen peroxide, acid, and metal salts) as discussed in Hawley's Condensed Chemical Dictionary, 11
th
Edition, Van Nostrand Reinhold, Publishers, 1987, potassium permanganate, sodium permanganate, and ozone rely on the delivery of reagents to the subsurface using wells, trenches, injection lances, or french drains. In addition to their limited effectiveness in comprehensively and economically delivering the required reagents, the use of these conventional delivery techniques can result in dangerous pressure buildup within these devices because of the pressure and heat generated by the reactions that result from chemical oxidation of the contaminants by the supplied oxidation reagents. Generally, a substantial quantity of the oxidizing fluid, in relatively high concentrations (15% to 50% by weight in aqueous form) is needed to effect the desired decomposition of the organic contaminants. Experience with the application of these quantities and concentrations of oxidizing fluids has shown that undesired consequences occur. For example, without adequate dispersement of the reagents from the application apparatus into the surrounding soil and groundwater matrix, the oxidizing fluid can: (1) react with itself, producing large quantities of oxygen gas, which, in combination with the vaporized organic constituent, produce dangerous, explosive conditions; (2) lead to inefficient use of the oxidizing solution; and (3) can cause runaway overpressurization of the apparatus leading to sudden blowout of the apparatus, its components, and/or soil and groundwater surrounding the apparatus.
SUMMARY OF THE INVENTION
The present invention relates to an apparatus to effectively deliver chemical reagents to the subterranean environment in a uniform, comprehensive manner, to enhance mixing and lateral and vertical dispersion of the reagents to the soil and groundwater surrounding the apparatus. The chemical reagents delivered by the apparatus include those capable of oxidizing, degrading, or enhancing solubility and mobility organic contaminants sorbed to soils or dissolved in groundwater. The method and apparatus which comprises the present invention accomplishes remediation of soil and groundwater contaminated with undesirable organic compounds by overcoming deficiencies in the art with respect to the delivery of the reagents needed to bring about oxidation, degradation, or solubility and mobility enhancement.
The invention method includes the installation of a plurality of recirculating reagent delivery devices or wells into the subsurface, injection of select chemical reagents into each of the recirculating wells,
Briggs Robert A.
Steele, II S. Robert
Dowell & Dowell , P.C.
Suchfield George
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