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Reclamation of Petroleum Contaminated Sites
Submitted to Olga Petrov Instructor Pollution Control
Submitted by Rodney Michel Second Year Student Petroleum British Columbia Institute of Technology In partial fulfillment of the requirements of CHSC 3351 October 30, 2000
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SUMMARY Abandonment of petroleum wells can pose health and safety hazards to people whom live near by it or cause pollution if a reclamation plan is not implemented. A Corrective Action Plan (CAP) outlines the condition of a contaminated site based upon a series of analytical steps, then proposes the best possible solution to comply with local and federal regulations. The phase of the hydrocarbons, soil type, geology, hydrogeology, subsurface flow regime, disposal options available for wastes and costs of the site to be reclaimed are necessary to know in developing the CAP. Methods to clean a petroleum contaminated site include: excavation and disposal, drainage trenches and galleries, wells, soil venting, incineration, bioremediation, the OUUU process, vacuum extraction, and Vitrification. It is recommended that engineering technologists consult local, regional, and federal laws and regulations to ensure that their CAP is within compliance.
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INTRODUCTION Industry and individual pollution of the environment and chemicals has occurred for over a century. This report explains the process of reclamation through the use of key steps in assessing the extent of reclamation needed with various options available to complete the primary reclamation tasks.
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Sources of petroleum pollution Industry and individual pollution of the environment with petroleum and chemicals has occurred for over a century. Chemical plants, refineries, oil drillers, wells, fuel depots, service stations and pipelines. An erroneous thinking was that the soil would absorb the petroleum and ‘wash it away’. This has lead to an enormous pollution problem and created a need for methods to remove petroleum from soil and water to prevent ingestion by people and higher organisms in the food chain. Numerous studies of the effects of contact with petroleum free radicals with humans have linked exposure with cancers and other serious illnesses. This gives rise for a need for the petroleum engineer, geologist and technologist to plan well development programs that prevent contamination in the first place and evaluate the costs of properties that already have contamination with allocation for well site remediation or emergency clean-up contingencies for their employment entity. Abandoned and unplugged wellsites pose health and safety hazards to people whom live near by it or cause pollution. Rusted out casings may cause natural gas pooling and leaks into basements or water wells or provide conduits for salt brine from deeper formations to pollute fresh groundwater. Sometimes the well itself leaks petroleum. Generally the well must be plugged with a non-porous medium such as cement to seal off zones from contacting each other. In Pennsylvania, the Oil and Gas Act of 1984 allowed that wells abandoned before 1985 to be classified as orphan wells where the Pennsylvania Department of Environmental Protection could plug the well using funds charged to operators via surcharges on permit application fees for new oil and gas wells. Overview of reclamation to oil and natural gas operators
*Appendix I of this report contains a policy overview from the Government of British Columbia in respect to exploration, development, and production of petroleum, natural gas, and geothermal resources with respect to aboriginal rights issues. "The Engineering and Operations Branch primary functions include approving new wells, pipelines and facilities and conducting drilling, construction and operations inspections." **Appendix II of this report contains references to the Alberta Environment, Land Administration Division and the Public Lands Act. Reclamation is the responsibility of the oil and gas operator and land must be returned to "equivalent land capacity". The Environmental Handbook from the Utah Division of Oil, Gas & Mining gives a well thought out approach to the reclamation process. This 40-page handbook can be downloaded for free at their website at: http://dogm.nr.state.ut.us/oilgas/PUBLICATIONS/ENVBOOK.HTM Soil and water contamination policy considerations
US EPA Methods form the basis of most analysis methods for determining total petroleum hydrocarbon measurements. The method chosen depends upon the target site being a well, storage, or transportation facility. Some risk assessment factor include:
Corrective action plan (CAP)
A report outlining the condition of a contaminated site may be required by state/provincial or federal authorities like the EPA outlined below in Table 1.
Table 1: Correction Action Plan Petroleum compound concentrations in soil or water that are accessed include benzene, toluene, ethyl-benzene and xylenes (BTEX). The identification of the lighter molecular weight HC is difficult.
The heavier molecular weight HC’s like tars and acid sludges from refining operations or old well sites have commonly occurred in lagoons as illustrated below in Figure 2. In this scenario decades of HC and chemical wastes were dumped creating sludge, asphalts and oil-saturated clay mounds near a stream. Since the groundwater table and bedrock is shallow, the concentration of pollutants and the proximity to a stream this site qualifies for careful remediation to control and isolate the contaminated site by landfill liners and adjust the acidic pH of the soil with lime. Then Portland cement is used to improve inter-particle binding culminating with drainage of excess liquids and leachate or drainage control.
Figure 2: Sludge or heavy oil pit occurrence with treatment components Note: Raoult’s Law considers equilibrium vapor phase concentrations as show by the equation:
Unified Soil Classification System (USCS) The initial exploration of the site geology, hydrogeology and chemistry are necessary components to a remedial program with the geology being the foundation. This program is usually costly during the sampling stage. It is important to know and understand and classify the soil using the Soil Conservation Service chart as shown below in Figure 3.
Figure 3: Soil Classification System Groundwater flow system vs. time An understanding of the effects of scale vs. time shown in Figure 4 must be understood in planning a remedial program.
Figure 4: Hydrogeological flow systems vs. time diagram CONTAINMENT OF CONTAMINATED SITES The capillary drainage is a slow draining process influenced by gravitational and buoyancy forces near landfill cap. Dissolution/percolation occurs when rainfall penetrates the landfill cap and causes convection or mixing of the contaminants before gravity causes downward migration. Consolidation/expulsion occurs within a zone of stabilized mass of the landfill forming a hydraulic barrier with low permeability of <10^-8 cc/seconds. The water table normally fluctuates seasonally and may rise and flow through the contaminated zone by groundwater infiltration to cause the displacement of pollutants by solute convection. And molecular diffusion rely upon gravity and effective porosity or interconnected pore channels within the landfill to cause downward migration into the groundwater. All of these factors add up to a total flow, which must be prevented to achieve landfill control. Various geological and meteorological mechanisms are shown in the following Figure 5.
Figure 5: Subsurface flow regime components with liner and cap Materials used as hydraulic barriers or liners Lining material application must be engineered to the contaminated site characteristics. It is important to realize that hydraulic conductivity measurements are used in choosing a liner. Normally conductivities <10^-9 m/s for laboratory conditions and 10-10,000 times greater for field conditions are factored into the engineering plan. An overview of materials, their uses and some conductivity values are shown in Table 2.
Table 2: Materials used as barriers and liners with properties Construction of cutoff walls The slurry wall method is commonly used and creates a vertical barrier by excavating a 0.6-1.5 wide up to 120m deep. Backhoes work well for up to 15m, draglines to 25m and clamshells for deep excavations which are then filled with a bentonite-water or lining medium. Vibrating beam method inserts an injection beam into the ground by vibration, usually 25m deep, and then slurry, grout or emulsion is injected into the soil to form the barrier. Control of the intersections of the underground walls, alignments and verticality are difficult with this method. Injection and jet grouting uses cement, bentonite or chemical grouts in deep soil barrier applications especially those involving large boulders or gravels via parallel, offset rows of holes. Difficulty with defects in the grout, control of injection profile and aging of the grout pose problems. Methods to clean up petroleum contaminated sites The treatment method may either be onsite or in situ. Table 3 below highlights the process with some advantages and disadvantages of each method. It should be realized that biological methods are slow, results are unpredictable and the use of additional chemicals may create more pollution than the petroleum!
Table 3: Onsite vs. In situ method of recovery Excavation and disposal This system is used when contamination is less than 6m and a one-time removal will suffice. Disposal and transportation costs are high, along with the fact that landfill sites may not be available and that the polluted medium is not treated, just merely relocated, nor does this method treat contaminated groundwater. Permitting, land farming and aeration of the contaminated soil before disposal may be required. The backfilling after excavation is based upon the compaction level of around 95%. Drainage trenches and galleries Used in depths of 7m or more to remove soil and groundwater to provide infiltration control. The collected liquids must be sent to a treatment system and the trenches may require bracing below 2m to meet OSHA or WCB requirements. The issues of dust, noise and truck traffic logistics must be considered along with some public consultation or relations plan set up. The use of perforated PE pipe, multi-directional drains or aqualude barriers have replaced trenching. A conventional vs. one-sided drain system utilizing the hydraulic gradient and velocity of the water flow in the subsurface to remove contaminants is shown below in Figure 6.
Figure 6: Conventional vs. one-sided drain system Wells Wells are the most commonly used system to collect water and the pollutants from great depths. The equipment used is inexpensive and relatively available, but the design requires air or electric lines to each well; plus the monitoring controls as shown in Figure 7 and seasonal adjustments are fairly expensive. Multi phase HC system collection is difficult. Many well system designs exist based upon the following factors:
Figure 7: Monitoring well types Soil venting This soil venting system as illustrated below in Figure 8 is quick and excellent in removing VOC’s from soil and is inexpensive to install and operate. Porosity, permeability, moisture content and particle size affect the effective radius of pollutant removal. The disadvantages are that it will remove only 50% of the HC vapors are not a stand-alone technology and the vapors may require incineration and explosion-proof equipment.
Figure 8: Soil venting system Incineration The incineration method completely cleans up the soil and produces sterile ash for backfilling. Permits are required with implementation and completion of the program occurring quickly. A major disadvantage is that air pollution is generated and tightening regulatory controls and political acceptance make this a more expensive option. Bioremediation of contaminated soils Bioremediation relies upon using microorganisms to decontaminate a petroleum-polluted system. The only biological species known to metabolize oil are bacteria, fungi and yeasts. Oxygen levels are very important in the effectiveness and success of this technology; therefore aeration and agitation or mixing systems are employed to insure adequate digestion of the petroleum. Then the issue of using various agricultural fertilizers to C:N ratios of 60:1 and C:P ratio of 800:1 may pose groundwater and cost issues. It has been determined that nitrogen levels of >5ppm and phosphorus of >1ppm be used to ensure that microbial activity is not lost. The temperature and pH of the soil affects microbial metabolism with 30ºC and pH 7.0-7.5 as optimal respectively.
A field/laboratory case study was completed in the Norman Wells are of the North West Territory and Swan Hills in Alberta to determine the effectiveness and presence of oil-utilizing bacteria under varying conditions of 4º and 30ºC under varying conditions of phosphorus/nitrogen enrichment. It was found that bacterial populations developed on high quality crude oils have only minor ability to digest low quality crudes. Whereas bacteria raised on low quality crudes were able to easily digest the high quality crudes. The OUUU Process This process uses ozone, UV light, ultrasonics, and ultrapure water to destroy contaminants. Ultrapure water acts as a solvent that flushes the contaminants out of the soil for conversion to CO2, water and salts. This is a clean method, but creates a situation where the contaminants are in liquid suspension and require centrifuging and ozone treatment which breaks down the HC=HC double bonds (alkenes), some PCB’s, PCP’s, TCP’s, benzene and cyanide. Ozone (O3) is active oxygen with the following constraints: it is unstable and oxidizes easily, must be generated on site, cannot be bottled or stored and needs a special reactor with catalysts for max efficiency. The reactor contains the UV and ultrasonic source; which works in conjunction with the ozone thus increasing effectiveness by 300% vs. ozone-only treatment. Basically the ultrasonic creates a thin liquid film that increases surface area for greater gas transfer and reduced bubble coalescence. And the UV keeps the crystals clean for maximum film penetration and preparation for final rinsing. This system has the advantage of no by-products and the operating costs are low and the EPA is very supportive of this method. Vacuum extraction This process uses vacuum extraction systems to clean up contaminated soils and ground waters in situ. Also a dual extraction system may be used to remove both HC’s in liquid and vapor phase in a wide variety of geological settings. Normally the VOC’s are removed first in complex contaminated sites. The costs of this method are low. Vitrification Considered an expensive ‘fringe’ technology this method converts a soil mass to a glass block. The cost limitations, lack of long term data, heavy power demands, pollution control permits and depth limitations of 6m must be considered before implementing this process.
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CONCLUSIONS It has been concluded that a proper assessment of the overall conditions of a site must be completed before a Corrective Action Plan can be developed. Also the parties involved in the reclamation process, include: the company responsible for the lease or surface owners, adjacent people whom live near the site and use soil or water resources; local, regional, and federal levels of government; along with various engineering or contracting firms that specialize in the reclamation process.
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RECOMMENDATIONS It is recommended that engineering technologists consult local, regional, and federal laws or regulations to ensure that the Corrective Action Plan is within compliance.
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REFERENCES Books
Internet Sources
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