Welcome.
My name is Bob Borden and I will be the narrator for this presentation.
It has been developed to give you a general overview of a spreadsheet based tool for the design of emulsion injection systems.
Once distributed, these oils can be very effective in stimulating anaerobic bioremediation processes.
This design tool was developed jointly by North Carolina State University, Solutions-IES and CH2M Hill for the Environmental Technology Certification Program.
Before using this tool, you should have a good understanding of the emulsified oil process.
If you are not thoroughly familiar with this process, first consult the references listed at the end of this presentation.
First, I'd like to give you an overview of this presentation.
We will provide
a brief summary of the emulsified oil process,
describe a general procedure for designing these systems,
present some numerical modeling results used to estimate contact efficiency,
and then provide an overview of the design tool.
Finally, we will run through the design tool structure and direct you to other information sources.
In it's simplest form, the emulsified oil process consists of a few simple steps.
First, temporary or permanent injection points are installed.
Typically, a premixed emulsion is purchased from a vendor, diluted with water on site and injected.
Sufficient water must be mixed with the emulsion to distribute it throughout the target treatment zone.
Within a few days, the oil droplets stick to the soil particles, then slowly ferment to hydrogen and acetate which drive the anaerobic biodegradation process.
Before starting on an injection system design, you should complete a thorough evaluation to ensure that site conditions are appropriate.
Protocols are available from ESTCP and AFCEE to assist in this evaluation.
First, risks to critical receptors need to be controlled. The emulsified oil process is a relatively slow process. Depending on site conditions, it can take years before the beneficial effect of oil injection are apparent.
Secondary water quality issues also need to be considered.
When emulsified oils are injected, they generate anaerobic conditions which enhances biodegradation of the target pollutants.
However, anaerobic conditions also result in accumulation of dissolved iron, manganese and methane.
As groundwater migrates downgradient, these materials will gradually dissipate
However, the potential for downgradient migration needs to be considered.
Site conditions also need to be examined to ensure that the geochemistry is appropriate.
If inhibitory compounds are present or the pH is outside the desirable range, it may be difficult to stimulate biodegradation processes.
You also need to confirm that the target compounds are anaerobically biodegradable and that bacteria are present that can degrade the contaminants.
Finally, you need to be sure that you can inject sufficient water to distribute the emulsified oil.
This may sound trivial, but injecting enough water to distribute the emulsion can be a major challenge at some sites.
The injection process we are going to consider is for injection only.
Recirculation systems where groundwater is extracted and reinjected can be very useful in some cases.
However, construction and operating costs are often higher for recirculation systems.
More importantly for this tool, the design of these systems is more complicated and generally not amenable to the ‘standardized' approach incorporated into the design tool.
As a consequence, the design tool is only applicable to injection only systems.
In the design tool, you first select a general layout.
This can be either a grid approach or a barrier approach.
The treatment zone dimensions are determined.
A trial injection well spacing is selected.
Oil and water injection volumes per well are calculated to achieve a certain contact efficiency.
Based on the amount of oil injected and site conditions, a reinjection frequency is calculated.
Then the tool estimates capital and life-cycle costs.
This overall process is then repeated to evaluate the effect of well spacing on cost.
As I mentioned, there are two basic injection layouts, grids for area treatment and barriers.
Injection grids are typically used to distribute emulsions in source areas.
While most of the oil will be distributed in the higher permeability zones, this approach does bring the oil in closer contact with the contaminants, reducing treatment time.
In addition, the oils will ferment to hydrogen and acetate which can diffuse into lower permeability zones, stimulating biodegradation.
Obviously, the better the contact between the oil and the contaminant, the more effective the treatment.
Potential disadvantages of the grid approach include the larger number of injection points and greater amount of emulsion required.
Also, since you must inject water to distribute the oil, there is a greater potential for displacement of contaminants.
Barriers consist of rows of wells aligned perpendicular to groundwater flow to intercept a contaminant plume.
Barriers can be used to prevent contaminated groundwater from crossing a boundary or a series of barriers can be used to cleanup an entire plume.
Advantages of barriers include fewer wells, less substrate, and lower potential for contaminant displacement.
A disadvantage of barriers is that the contaminant must migrate to the barrier, which increases the cleanup time.
For area treatment, the important treatment dimensions are
the width, Y, perpendicular to groundwater flow,
the length, X, along the direction of groundwater flow, and
the vertical thickness, Z.
When wells are screened across more than one unit, use the thickness of the high K zones as the effective thickness.
For example, you might have a 10 ft thick zone contaminated with TCE.
6 ft of this zone is silty sand and 4 ft is very clean coarse sand
Essentially all the water is going zone going to go through the coarse sand, whether you like it or not.
In this case, you should design your system assuming you have an effective thickness of 4 ft.
Wells are assumed to be arranged in rows. The design tool allows the row spacing to be either 1 or 2 times the well spacing.
For barriers, the important dimensions are
the barrier width, Y, and
the barrier length, X, along the direction of groundwater flow, and
the effective vertical thickness, Z.
In barriers, contaminated water needs to be in contact with the oil for a certain amount of time.
Past experience in lab and field studies indicates that 2 - 4 months is needed for satisfactory treatment of chlorinated solvents.
Contact times greater than 4 months may be needed when
contaminant or background electron acceptors are very high or
there's a high K zone that somehow got missed in the site characterization.
Once you specify the contact time, the design tool will then calculate the minimum allowable length along the direction of groundwater flow.
When required, the design tool will specify more than one row of injection wells to achieve the specified contact time.
In low velocity aquifers, the minimum contact length can be so small that it just doesn't make sense. In these cases, you may want to specify a minimum allowable length.
In source areas, contact time typically isn't an issue, so contact time is not included as a design criteria.
In the design tool, we use a ‘Base Treatment Volume' as a standard treatment zone around each well to scale up our design calculations.
For area treatment, the BTV is equal to a rectangular prism with dimensions equal to the well spacing times the row spacing times the effective thickness
For barrier treatment, the BTV is equal to the volume of a cylinder surrounding each well where the cylinder diameter is equal to the well spacing.
We also use two scaling factors in the design calculations.
The volume scaling factor is equal to the volume of water and oil injected divided the pore volume of the Base Treatment Volume.
The mass scaling factor is equal to the amount of oil injected per well divided by the maximum oil retention in the BTV.
When we first started working with emulsified oils, we recommended that people inject one pore volume of water and enough oil to fill up all the attachment sites within the treatment zone.
This is essentially the same as using volume and mass scaling factors of one.
However, many people noticed the emulsions were transported through the aquifer much more quickly than expected.
In many cases, monitor wells would turn milky white indicating emulsion breakthrough after injecting only 0.2 pore volumes.
This rapid break is probably due to rapid transport of emulsion through higher permeability layers.
Since the emulsion was obviously being transported much more rapidly than expected, many people started injecting less oil and less water.
This is equivalent to using mass and volume scaling factors less than one.
In later model simulations, we will look at the effect of injecting less oil and water on contact efficiency.
To determine the amount of water required, you multiply the Base Treatment Volume times effective porosity times the Volume Scaling Factor.
Higher values of the volume scaling factor typically result in higher contact efficiencies. In later slides you'll see how to select this design factor.
The maximum oil retention by the sediment is one of the most important parameters in your design.
Unfortunately, it is also one of the most poorly understood.
From what we know, oil retention is a function of the droplet characteristics, surfactant type and soil type.
The oil droplets need to be smaller than the sediment pores, or they will be rapidly strained out. For many commercially prepared emulsions, this is not a significant issue since the average droplet size is much smaller than most soil pores.
Silts and clays have more charged sites on their surfaces so they hold more oil droplets.
The type of surfactant used to prepare the emulsion seems to be important since this controls the affinity of the oil droplets for sediment surfaces.
Emulsions prepared with non-ionic surfactants seem to have a lower oil retention.
Emulsions prepared with ionic surfactants generally have a higher retention.
The table on this slide shows measured values of Oil Retention for a few different soils.
As you can see, there is a tremendous range in the data.
If you are designing a small pilot test, picking a value off this table might be acceptable.
If you are designing a larger project, you really need to measure oil retention on samples collected from your site.
There is an SOP is in an appendix to the Design Tool Manual that describes a pretty simple procedure to measure oil retention.
I really encourage you to make some actual measurements on samples from your site using the same emulsion you are going to use in the field.
You would never design a remediation system based on permeability values you looked up in a hydrogeology textbook.
Don't try to design an emulsified oil project based on values you pick off a table or suggested by a vendor.
To determine the amount of oil required, you multiply the Maximum oil retention for the soil times the Base Treatment Volume times bulk density times a Mass Scaling Factor.
Higher values of the mass scaling factor typically result in higher contact efficiencies. However, this also increases costs. In the next few slides, you will see how the scaling factor effects contact efficiency.
Now I want to talk about where the mass and volume scaling factors came from.
As part of developing this design tool, we conducted a bunch of computer simulations using MODFLOW and RT3D.
Details of this work are presented in Chapter 2 of the Design Tool Manual.
Model simulations were generated for a range of values including
injected oil mass,
injected fluid volume,
well spacing and
injection sequence.
Variations in oil mass and fluid volume were represented by variations in the Scaling Factors.
We then calculated a volume contact efficiency for a target treatment zone between a set of injection wells.
The flow contact efficiency was calculated for water migrating through an emulsified oil barrier.
Water was considered ‘contacted' if it passes through a zone where the oil concentration is greater than 5% of the maximum oil retention.
The figure at the top of this slide is an example permeability distribution for a cross-section through the simulation area.
The darker red areas are higher permeability zones, while the lighter pink areas are low K zones.
This permeability distribution was generated using a statistical procedure based on measured permeability distributions at a number of different sites.
Emulsified oil is injected into this hypothetical aquifer through the two wells identified at the bottom.
The bottom figure shows the simulated oil distribution using a mass and volume scaling factor of 0.78.
This means that the total mass of oil injected is equal to 78% of the maximum oil retention in the treatment zone, and
the total volume of oil and water injected is equal to 78% of the pore space in the treatment zone.
In the middle of the simulation grid between the two injection wells, there is a mixture of contacted and uncontacted zones.
The oil contacted zones are high permeability layers where the oil is rapidly transported.
The uncontacted zones are typically lower permeability regions.
While the oil distribution shown above is not perfect, it should still result in fairly rapid biodegradation and should be very effective in preventing downgradient migration of dissolved contaminants.
In the oil contacted zones, the oil will ferment to hydrogen and acetate resulting in the most rapid biodegradation.
Hydrogen and acetate produced in the oil contacted zones will also diffuse into the uncontacted zones, stimulating biodegradation. However, biodegradation rates will probably be lower in the uncontacted areas because of the lower electron donor concentrations.
Over time, contaminants will also diffuse out of the lower K zones, coming in contact with oil.
Since the high K zones are effectively contacted and the high K zones also transmit the most contaminants, the oil distribution shown in this slide should be very effective in controlling the downgradient flux of dissolved contaminants.
In later slides, we show the effect of varying the amount of water and oil injected on contact efficiency.
Volume contact efficiency is calculated for the region between the two injection wells.
You need to be aware that contact efficiency is NOT the same as treatment efficiency, since contaminants can be degraded by dissolved hydrogen and acetate released from entrapped oil.
That said, higher contact efficiency can generally be expected to result in higher treatment efficiency.
As I described on the last slide, we ran a series of simulations where we varied the amount of oil and water injected.
For each simulation, we determined the flow contact efficiency through a barrier consisting of a line of injection wells, and the volume contact efficiency for the region between injection wells.
Simulations were run for aquifers with low, medium and high levels of heterogeneity.
As expected, the average contact efficiencies were some what better for the more homogeneous aquifers and somewhat poorer for the high heterogeneity simulations.
However, the results were reasonably similar for all permeability distributions, so we have only presented results for the medium heterogeneity distributions.
Shown on this slide is a three dimensional surface relating flow contact efficiency through a barrier to the mass and volume scaling factors.
Injection of more oil is represented by an increase in the mass scaling factor.
Injection of more water is represented by an increase in the volume scaling factor.
When we first developed this process, we recommended that people inject 1 pore volume of water and enough oil to fill the maximum oil retention for the treatment zone.
This is equivalent to using mass and volume scaling factors of 1
Based on the curve show above, this should result in a flow contact efficiency of about 80%.
Increasing the amount of oil and water injected by 50% increases the mass and volume scaling factors to 1.5.
This should increase the flow contact efficiency to over 90%.
However, this will also significantly increase the cost for oil and labor to implement the injection.
The flow contact efficiencies shown in this figure are pretty high because most groundwater flows through the high permeability zones and the high permeability zones are most effectively treated by the emulsified oil.
When using this relationship to estimate contact efficiency, please be aware that this curve was generated for a ‘medium' heterogeneity aquifer.
The actual contact efficiency at your site will undoubtedly be somewhat higher or lower.
However, the general trends shown here will probably hold for most sites.
Injecting more water and more oil will generally lead to higher contact efficiencies.
This figure is repeated in the design tool along an equation that allows users to calculate the range of expected contact efficiencies for specified values of the mass and volume scaling factors.
This slide shows the three dimensional surface for volume contact efficiency during area treatment of a medium heterogeneity aquifer.
This figure assumes the well spacing equals the row spacing.
This slide shows the volume contact efficiency when the row spacing equals two times the well spacing in a medium heterogeneity aquifer.
Contact efficiencies are lower than in the previous slide because you are using half as many wells.
Oil consumption in a barrier is determined based several different factors including
the amount of background electron acceptors
the contaminant concentration
the amount of dissolved organic carbon released to the downgradient aquifer, and
the amount of oil used to produce dissolved iron, manganese and methane.
Field monitoring results from emulsified oil barriers indicates that treatment efficiency is fairly constant when excess oil is present.
However as the oil begins to be depleted, treatment efficiency will gradually decline.
In the design tool, we account for this decline in treatment efficiency using a substrate scaling factor.
The substrate scaling factor is equal to the fraction of oil consumed when treatment declines below acceptable levels.
At this point, you would typically inject more oil to rejuvenate the barrier.
Past experience suggests that treatment efficiency will drop significantly once 30 to 60% of the injected oil has been consumed.
The theoretical life of a single group of injections is mass of oil injected divided by the mass of oil consumed per year.
Oil consumed per year is the water flux per year through a barrier times the oil consumed per liter of water.
The reinjection interval is the theoretical life times the substrate scaling factor.
When groundwater flow velocities are low, this calculation can result in an unreasonably long time between reinjections.
For example, in a low velocity aquifer, this calculation might indicate that you only need to inject additional oil once every 20 years.
In this case, the user can specify a maximum reinjection interval that overrides this calculation.
This slide provides an overview of the design tool structure.
Users first enter input data on the site characteristics and costs.
The design tool then leads the user through a series of calculations to design either barriers or area treatments.
As part of the design process, users must enter information on the treatment zone dimensions and scaling factors.
The design tool then generates estimates of contact efficiency, capital and life cycle costs as a function of well spacing.
This slide shows the introductory table of contents page.
Users navigate through the tool by clicking on a button.
Each subsequent page has buttons to go forward, go back or return to table of contents.
If users want to erase everything and start over, they click on the reset page.
Normally you start with the aquifer description.
When you click on the button for site characteristics, this screen will appear.
On it you enter the general site characteristics including site name, aquifer characteristics, etc.
Spaces outlined in red must be filled out.
Spaces outlined in black can be left blank and it will not effect any of the calculations.
We have provided the blank spaces so the user can document important site characteristics, even if they are not used in the calculations.
For example, the site name is not used in any calculations. However, you would want to type this in for future reference.
On these two sheets, users enter information on contaminant concentrations and background electron acceptors.
This information will be used to calculate substrate demand.
Users also enter information related to drilling and injection costs by either direct push injection, injection through direct push wells or conventional wells.
Through a series of calculations, the costs for each injection approach are summarizes as:
a) total fixed cost;
b) total cost per injection point or well;
c) injection rate per well; and
d) total cost per day of injection.
These costs are later used to calculate capital costs for different injection well spacings.
Once you enter the barrier design worksheet, you enter information on
the treatment zone dimensions,
required contact time, expected carbon release rate,
and scaling factors.
The three dimensional surface functions developed from the numerical modeling are then used to estimate expected contact efficiency.
Using results from the barrier design page, the design tool computes capital cost as a function of well spacing.
For the example shown here, the lowest capital cost occurs for a 15 ft well spacing.
Users enter information on life cycle costs including monitoring and engineering costs for future injections.
The design tool then computes total life cycle Net Present Value as a function of well spacing.
At this point, the user needs to select a well spacing to be used in the design.
In this example, a 20 ft well spacing has a slightly lower NPV than the 15 ft well spacing
However, a user might want to go with the 15 ft well spacing because of it's lower capital cost or just personal preference.
This next page shows a breakdown of yearly costs for monitoring, well installation, substrate, labor for injection, and fixed costs.
Cumulative net present value versus time is also shown.
The last page in the design tool allows the user to print out a summary of the final design for their records.
This concludes our overview of the emulsified oil design tool.
We recommend that you now open the design tool and begin working through the example problem included as a tutorial in the manual appendix.
You should also read through the users manual.
There is a lot of good information on how the tool works.
Chapter 2 of the manual includes an extensive discussion on the effect of different design parameters on contact efficiency.
If you have not already done so, you should consult the guidance documents and protocols describing the use of emulsified oil for anaerobic bioremediation.
If you have any suggestions on how we might improve this tool, please send them to Bob Borden at the email address shown on the title slide.
Thank you very much.