Regenesis - Resources - faq

1. Can ORC be injected via re-injection wells?
Yes, if the following conditions are met: 1) the wells are constructed properly; 2) the aquifer is capable of accepting the planned volumes of low % solids ORC slurry (range of 10-20%); 3) if the wells are flushed with sufficient clear water chaser (we suggest a minimum of 1-2 well volumes or until the water present is clear); and 4) post-injection clearing of the well screen using a steel wire brush. NOTE: it is critical that all ORC be removed and flushed from the well screen post-ORC injection. Failure to follow these guidelines may result in a reduction in well pack permeability and reduced percentage of well screen openings. For more information on the use of ORC in monitoring wells, please refer to Technical Bulletin 2.3.4: Use in Existing Monitoring Wells.

2. Can ORC be used to treat the vadose zone?
Yes, if a well-defined vadose zone contaminant mass is present and there is sufficient soil moisture to activate the release of oxygen from ORC. Additionally, there must be enough moisture to support biological activity. Typically, bacteria are located in thin films of water and contaminant that coat soil, and these thin films must have enough area to provide good contact between bacteria, oxygen, and contaminant.

ORC application in the vadose zone consists of a series of closely spaced injection points to which a dilute slurry of ORC and water is delivered. The dilute ORC/water mixture is used to mound and spread the ORC and provide moisture to the vadose zone.

3. How do I know when ORC is exhausted?
To evaluate if ORC is exhausted, contaminant concentrations and dissolved oxygen (DO) should be measured. Use of dissolve oxygen (DO) alone as an indication of ORC exhaustion may mislead you. The measure of DO is a function of the DO in excess of what is consumed by the aquifer (i.e. the aquifer's capacity to process DO). When DO consumption in the aquifer is high due to biological activity DO measurements will be low. Thus, contaminant levels should also be used as an indicator of ORC longevity.

If ORC application was within the previous 6-9 months, TPH/BTEX remains low, and little or no DO is present, ORC is most likely releasing oxygen, and it is being consumed in contaminant biodegradation. However, if TPH/BTEX has increased to the original, baseline levels or has reach a plateau that lasts for several months, and it is beyond the 6-9 month release period, ORC has probably been exhausted and new contaminant influx or desorption has occurred. As with all contaminants a careful review of groundwater elevation changes should be factored into any of the above issues. A significant change in groundwater elevation typically affects the concentration of contaminants in groundwater.

4. Can ORC be used with nutrients?
Yes, but the successful application of nutrients to subsurface systems is a complex issue that usually requires significant knowledge of the site and possibly even microcosm experiments in the laboratory. When properly applied, nutrients may increase rates, but the cost and additional work may not be worth the benefits. Injection of nutrients without site knowledge and analysis can give negative results such as nutritional imbalances, microbial fouling of the aquifer, and deterioration of local water sources. Our extensive experience with the application of ORC shows that has probably never failed as a direct result of insufficient nutrients. Typically, oxygen is the limiting factor in contaminant biodegradation, not nutrients like nitrogen or phosphorus. Thus, a lack of nutrients does not prevent biodegradation when ORC is used. For more information on the use of nutrients, we suggest a review of Cookson's discussion on nutrient addition. This discussion can be found in Appendix B of Bioremediation Engineering: Design and Application by John T. Cookson. However, note that the material on nutrients in this reference was intended for biopiles or composting and might not be sophisticated enough for use in the subsurface.

5. How frequently do I need to reapply ORC?
Over the past 7 years Regenesis has reviewed, in detail, hundreds of ORC projects (out of 7500 total sites with ORC application ) and the typical longevity for ORC is 6-9 months. Shorter (3-6 months) or longer (9-12 months) time frames occur for under specific conditions, but the vast majority of sites fall into a range of 6-9 months. ORC will release oxygen faster at sites with high contaminant or organic loading and rapid groundwater velocity (> 0.5 ft/day) than at sites without these characteristics. For more information on the longevity of ORC, please refer to Technical Bulletin 1.1.1: Laboratory Studies.

6. Can I inject ORC slurry into bedrock?
We have injected a thin slurry of ORC (less than 10% solids) at a few sites where the bedrock was very fractured and weathered with good success. However, a reduction in permeability may result, if multiple injections of ORC are made, and the bedrock is not porous enough. ORC socks can be a more effective way to treat bedrock. Please contact our applications engineers if you would like technical information on the use of ORC in bedrock.

7. Can ORC be used in a saline or brackish aquifer system?
Yes, but the release profile of ORC may be accelerated slightly because of catalysis of the oxygen release reaction by metal ions in the solution. Please refer to Technical Bulletin 2.4.3.2: Performance in Regions of Higher Salinity for more information.

8. Can ORC be used on a separated MTBE plume?
Yes, provided site conditions are adequately understood and a proper design is implemented. MTBE biodegrading bacteria are generally widespread (although absent from a few notable sites), and MTBE bioremediation does not require BTEX to be present to be successful. The effect of BTEX compounds on MTBE biodegradation is being elucidated. In many cases, microbes that degrade both BTEX and MTBE will preferentially use the BTEX before degrading the MTBE. Thus, the presence of BTEX can be inhibitory to MTBE biodegradation. Additionally, without a supplementary oxygen source, BTEX biodegradation can deplete all oxygen in the system leaving the MTBE not degraded. On the other hand, BTEX biodegradation in the presence of oxygen can stimulate the production of enough biomass to rapidly degrade the MTBE and some bacteria actually need a small amount of BTEX (or other fuel hydrocarbons) to be present to induce MTBE-degrading enzymes. Overall, the likelihood for significant MTBE biodegradation increases under highly aerobic conditions (such as those produced by ORC), low groundwater velocity to ensure retention of MTBE in the biologically-active area, and decreasing BTEX concentrations due to biodegradation.

Regenesis reported some of the first field observations of MTBE biodegradation under aerobic conditions (see Technical Bulletin 2.2.3.1: Potential for the Bioremediation of Methyl Tertiary Butyl Ether and Technical Bulletin 2.2.3.2: Does Competitive Inhibition Play a Role in MTBE Bioremediation?). We also have several case histories on ORC applications that describe successful MTBE treatment, and good MTBE bioremediation with ORC was reported by Landmeyer et al. (2001) Environmental Science and Technology, Vol. 35, No. 6, p. 1118. Our records show that ORC has been applied to approximately 500 sites with MTBE contamination (with and without BTEX contamination). We monitored the results from the 30 MTBE sites that were in the finishing stages of treatment and found 25% had excellent results, 50% were moderately successful, and 25% had poor results at the time of analysis. Although some of the poor result sites occurred because they were poorly characterized or poorly designed, the most likely reason for the 25% of sites with a poor result is low numbers (or complete absence) of the appropriate MTBE-degrading microbes at the site. This conclusion stems from statistics on the thousands of ORC sites that show that 3% of sites fail because poor site characterization, bad design, or other factors intrinsic to the site (high organic matter, high reduced metals). The difference between the 25% of MTBE sites with poor results and the 3% of all ORC sites with poor results may be due to a lack of MTBE biodegrading organisms or their presence in low numbers. If they are present in low numbers, giving t dhe site more time and more oxygen can result in MTBE biodegradation.

9. How much oxygen will ORC provide?
ORC will release a full 10% of its weight as dissolved biologically available oxygen.

10. What concentrations of dissolved oxygen can I expect to see at a site after ORC application?
Unlike air sparging (which uses atmospheric air), ORC provides pure oxygen. Thus, the concentration of oxygen from ORC can build up in groundwater to very high concentrations (up to about 45ppm) before leaving solution in the form of a bubble. This gives ORC technology a tremendous advantage over air sparging in that the high concentrations of oxygen dramatically increase the rate of oxygen diffusion through the subsurface. Thus, ORC has the potential to impact a much greater area around an application point by simple diffusion than can be expected by applying atmospheric air.

It should be recognized however that dissolved oxygen concentrations do not always have the opportunity to build up in the groundwater. If ORC is applied into contaminated groundwater there exists a biological oxygen demand that is using the oxygen – this is the effect you are trying to achieve where the indigenous microbes are aerobically degrading the pollutant. If the contaminant concentration is actively being reduced, the oxygen is being consumed and therefore may not build up to high dissolved levels. Once contamination in the area around the application point is degraded, the biological oxygen demand in this area is reduced and one can then expect to see a buildup of dissolved oxygen.

11. Can ORC be harmful to the aquifer?
ORC is a non-toxic compound with no potential adverse effects to the aquifer. The by-products of ORC's reaction with water are oxygen and ordinary magnesium hydroxide, which is virtually insoluble. Thus, ORC liberates only oxygen into the aquifer. The magnesium hydroxide is insoluble and either remains as an inert faction of the soil or, in the application of filter socks, the magnesium hydroxide is contained within the cloth and is removed from the well. It should be noted that magnesium peroxide and magnesium hydroxide are safe for human consumption as they are both used as anti-acids in common drug store products.

12. Does ORC elevate the pH?
Moderate pH levels are maintained when ORC is used in bioremediation. The pH of magnesium peroxide is 8.5. After it is hydrated and begins to form magnesium hydroxide the pH rises to 10. However, due to the insoluble nature of ORC (the solubility factor is 1.8 x 10^-11) and the end product magnesium hydroxide, any pH increase in the subsurface remains highly localized. Thus, at a very short distance from the ORC application the pH will return to background levels.

13. Will ORC foul the aquifer?
No. The use of ORC combats the problem of biofouling by generating a highly localized, elevated pH. Hence, microbial growth is inhibited in the immediate area of the application. Regenesis has never received notice of ORC fouling in-situ conditions within an aquifer such as a noticeable reduction in hydraulic conductivity, etc.

Iron fouling is minimized because of the slow, gentle release of oxygen which diffuses out into the aquifer. In fact, ORC has been used in aquifers with elevated iron when air sparging was not possible because of high levels of iron hydroxide precipitated in the vicinity of the sparge points.

14. What is the radius of influence of ORC?
The movement of oxygen from an ORC particle is governed by the laws of mass transport. The commonly used advection-dispersion equations, derived from these laws, are used to understand the phenomenon.

The principal factor governing the transport of oxygen is groundwater advection. If a project site has significant groundwater flow, the radius of oxygen movement from an ORC application point will be distorted in the downgradient direction. A very fast moving aquifer will result in a narrow band of oxygen moving downgradient with very little lateral spreading.

In the event that there is very little to no groundwater flow at a site, the force of diffusion will dominate the oxygen transport process. In this case, the outward movement of the oxygen is more radial in geometry and is driven primarily by the oxygen concentration gradient. Thus in a low-flow situation such as a low permeability aquifer material (silt and clay), oxygen released from ORC will move outward into the polluted groundwater from the area of high concentration near the ORC particle to the surrounding areas of low concentration in the polluted aquifer matrix. Pressurized ORC slurry injections typically distribute ORC in a radial fashion about 4 to 5 feet from injection points in fine grain aquifers. Consequently, ORC slurry injections have proven to be highly effective means of overcoming the limited mass transport processes inherent in low permeability materials. Using 8 to 10 foot injection point spacing in a grid based slurry injection, the effective distance over which dissolved oxygen must be transported is often reduced from feet to inches, which can easily be achieved through diffusion alone.

15. What are the advantages to using ORC as opposed to other remediation options?
When considering alternatives for remediation of a dissolved phase contaminant plume, ORC is generally the most cost effective treatment option. Due to the accelerating effect that oxygen has on in-situ biodegradation processes, ORC is often used to expedite, and therefore reduce the cost of natural attenuation approaches to site remediation. The process of using ORC to reduce the cost of natural attenuation and expedite site closure has been termed &Accelerated Natural Attenuation" by the environmental engineering industry.

Because ORC is a passive treatment technology, O&M costs are substantially reduced as compared with other mechanical remediation technologies such as pump and treat or air sparging with SVE.

16. Can ORC be used to remediate chlorinated hydrocarbons?
Yes, if the compound is aerobically degradable. The most visible of these applications is for vinyl chloride treatment. Vinyl chloride is a highly carcinogenic degradation product of perchloroethene (PCE) and trichloroethene (TCE), which is often associated with dry cleaning operations and landfills. Unlike its more highly chlorinated parent compounds which require treatment by anaerobic dechlorination, the vinyl chloride is aerobically degradable, and thus is rapidly degraded by indigenous microbes in the presence of ORC. If you are interested in the treatment of more high chlorinated compounds such as PCE and TCE, we encourage you to consider the use of Hydrogen Release Compound (HRC®) which was developed specifically for the treatment of these compounds.

17. Have regulatory agencies approved the use of ORC?
Yes. ORC has been approved for use in all 50 states of the US. In addition it has been used in many other countries including Canada, UK, Germany, Poland, Netherlands, Denmark, France, Italy, Japan, Korea and Australia.

18. Are there any disposal issues with the spent ORC?
No. The ORC powder, if injected into the aquifer for plume treatment, remains in place after treatment, becoming an innocuous part of the soil matrix. In the Filter Sock form, the socks are not considered a hazardous waste unless perhaps they have been allowed to absorb large amounts of phase separated chemicals. Thus, if used properly, the socks can simply be disposed of as non-hazardous waste.