Wells – Processes – Distinct – separate injection and producing wells
Reexamination Certificate
2001-05-10
2002-10-15
Shackelford, Heather (Department: 3673)
Wells
Processes
Distinct, separate injection and producing wells
C405S128150, C405S128200, C405S128250, C405S128300, C405S128450
Reexamination Certificate
active
06464005
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field
The invention is in the field of remediation of earth and groundwater contamination, particularly petroleum contamination.
2. State of the Art
An evolution of processes has occurred in the remediation industry over the years. Early in the history of hazardous waste and petroleum waste clean ups, methods were primitive, involving mostly what is referred to as “dig and haul” technology. This method involves digging contaminated soil vertically and laterally until the contamination that can be detected has been removed. This method is limited in its effectiveness due to the extreme amount of site disturbance, high cost, drastic impact on the use of the property at the site, severe safety problems, and a tendency to miss contaminated pockets.
Later developments of remediation technologies include mechanical treatment methods and biological methods. Mechanical methods include soil washing, high volume sparging (air injection), vapor extraction, pump and treat, and surfactant treatment. These methods rely upon manipulation of physical properties to force contamination out of the soil or groundwater. These methods have a wide range of effectiveness; some are expensive and some take a long period of time to reach an asymptotic treatment level. At least one method, surfactant treatment, may result in masking the contamination rather than removing it.
Biological methods come and go, partly because the processes of biological treatments are incompletely followed and partly because biological processes are frequently patchy in their effectiveness. Cultivated bacteria injections, bioventing, nutrient injection, and biosparging are intended to use natural biological processes with either cultivated biota or naturally occurring microbes to degrade contaminants through metabolism. spreading in the contaminated media. The biofilm tends to reduce groundwater and gas movement, effectively reducing remedial action. Further, there are generally limits established by states for the concentration of nitrate in groundwaters, requiring in many states that the concentration of nitrate in groundwater be less than 10 mg/L. However, nitrates have been shown to degrade petroleum from 3 mg/L to nondetectable concentrations in as short a time as one month (Mihelcic, James R. and Richard G. Luthy,
Microbial Degradation of Acenaphthene and Naphthalene Under Denitrification Conditions in Soil
-
Water Systems, Applied and Environmental Microbiology
, May 1988, pp. 1188-1198).
The movement of any injected air through water is referred to as sparging. Biosparging is the process of injecting air, under pressure into a subsurface aquifer for the purpose of oxygenating the groundwater.
Biosparging accelerates metabolism of petroleum in groundwater and soil. Aerobic metabolism is a more rapid process of petroleum degradation than is anaerobic metabolism. Biosparging infuses oxygen rapidly into the groundwater, at a rate of about 8 pounds of oxygen dissolved into the groundwater each hour. To metabolize one mole of hexane, for example, requires 9.5 moles of oxygen. Research has found that one-fourth of the available carbon is used to produce microbial mass (Wetzel, Robert G.,
Limnology
, page 640, W. B. Saunders Company, West Washington Square, Philadelphia, Pa. 19105). The other three-fourths of the available carbon is excreted as carbon dioxide. Biological systems must avoid the buildup of CO
2
or aerobic metabolism is overwhelmed and shuts down. Metabolism of hydrocarbons in the presence of oxygen takes place in the soil, just as in the groundwater.
While the various processes described are effective under certain circumstances and conditions, they all leave something to be desired in terms of results and none are universally applicable to varying conditions of petroleum soil and groundwater contamination.
Nutrients are essential ingredients for all biological systems. If the biological system is being cultivated to consume hyrdocarbons, nutrient levels must be maintained for the microflora to thrive. Nutrient injection has increased in popularity, accelerated by the research work performed by Albert Venosa, et al. at Delaware Bay, reported at
Bioremediation of an Experimental Oil Spill on the Shoreline of Delaware Bay, Environmental Science and Technology
, Cincinnati, Ohio; Vol. 30, No. 5, pp. 1764-1775, 1996. Venosa's work was in open water and did not actually inject nutrients, but his methods and conclusions showed that nitrate aggressively degrades hydrocarbons. When oxygen is depleted, there are other electron acceptors that will degrade hydrocarbons, including nitrate, sulfate, manganese and iron. Mihelcic and Luthy reported at
Microbial Degradation of Acenaphthene and Naphthalene under Denitrification Conditions in Soil
-
Water Systems, Applied and Environmental Microbiology
, May 1988, pp. 1188-1198, that 0.8 moles of nitrate were required for each mole of carbon dioxide produced when petroleum is metabolized. Nitrate and other forms of lithogenic nitrogen are found in low concentrations in natural water. Nitrate in natural groundwater which is not affected by human activities is usually less than 1 mg/L. Ideal ratios for carbon:nitrate:phosphate concentrations are documented for aquatic macroflora. Nutrient ratios for aquatic macrophytes and algae are reported to be 40:7:1 (Wetzel, Robert G.,
Limnology
, page 640, W. B. Saunders Company, West Washington Square, Philadelphia, Pa. 19105). One of the inventors has been told by USGS, Denver office personnel, that the ideal carbon:nitrate:phosphate ratio in soil is 160:1:0.08.
Nutrient injection is subject to at least two major drawbacks. First, injected nutrients do not spread well without a dispersal agent and nutrient injection methods require a consistent distribution system. The second drawback is that nutrients do not survive long in the environment, being readily attacked by a host of biological systems in the environment. Nitrates dosed into a contaminant zone in high concentrations tend to develop biofilms in the soil that can trap the nutrients and prevent them from
To try to overcome problems with particular methods, various combinations of methods have been suggested.
U.S. Pat. No. 5,575,589 discloses a remediation system for groundwater wherein a trench is dug across the natural flow stream of the contaminated groundwater. A perforated injection pipe is laid in the trench with porous material filling the trench above the injection pipe to a location just above the top level of the water table. A perforated extraction pipe is laid in the trench above the top of the water table above the injection pipe and the trench is back filled. The top of the trench is sealed with air impervious material such as clay or concrete.
Air is injected through the injection pipe into the water flowing through the porous material. The air bubbles through the water, apparently remaining substantially in the porous material of the trench and is collected by the extraction pipe which is maintained under vacuum. The patent also teaches that ammonium orthophosphate may be trickled into the trench to biodegrade the biodegradable contaminants.
U.S. Pat. No. 5,221,159 discloses a remediation system with bore holes extending down into the groundwater aquifer through which oxygen-containing gas is injected into the water to stimulate microorganism activity. Extraction wells extend into the vadose zone above the water aquifer. Vacuum in the extraction wells draw injected gas and volatile contaminants out of the vadose zone.
U.S. Pat. No. 3,846,290 discloses an injection well for injecting nutrients and air into contaminated groundwater and an extraction well to extract treated water from the groundwater. The water extracted causes flow of the air and nutrients between the injection well and the extraction well.
U.S. Pat. No. 5,398,757 discloses a remediation system wherein a fluid (liquid or gas) is injected into the bottom of a bore hole from where it flows into and through the contaminated material, picking up contaminants, and t
Mallinckrodt Robert R.
Mallinckrodt & Mallinckrodt
Mitchell Katherine W
Shackelford Heather
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