Questions to Consider Before Using PetroFix
How do I know PetroFix is working since it removes hydrocarbons from the groundwater and I can’t tell total reductions from simply monitoring groundwater?
From lab studies we know hydrocarbons, and specifically benzene is biodegraded by doing full-bottle extractions on batch experiments. After incubating with benzene, activated carbon, soil and water, an entire bottle is extracted with another solvent and we see all benzene is gone. In control experiments like this (killed/sterile bottles) the benzene can be recovered from the activated carbon at very high recovery percentages, showing biodegradation is the removal process. Regenesis PlumeStop technical bulletin 3.1 is available showing a post-sorption contaminant biodegradation lab study with benzene that documents benzene biodegradation on the activated carbon (PlumeStop and PetroFix use the same diameter carbon and this lab study is representative for PetroFix as well). In the field, we rely on multiple lines of evidence to show ongoing biodegradation after adsorption. The utilization of added nitrate and sulfate in the right pattern (nitrate first, sulfate second) is the first line. When we quantify microbial functional genes and specific bacteria associated with hydrocarbon degradation we do not see drastic changes even when groundwater hydrocarbon concentrations are reduced by 2 OOM or more. This is a very clear indicator that the microbes are still able to metabolize the adsorbed hydrocarbons. Finally, benzene is one of the weakest-bound petroleum contaminants, meaning if it isn’t consumed it will appear in the water again long before other contaminants. This doesn’t occur on treated sites, strongly suggesting it is being degraded.
Is it appropriate to use PetroFix on sites with observed light non-aqueous phase liquid (LNAPL)?
Yes, the issue is bulk floating petroleum. We believe using a rule-of-thumb that the presence of continuously measured floating LNAPL is an indicator of high mass that usually results in an exceedance of the desired performance range of PetroFix. High amounts of LNAPL could both overwhelm sorption sites on the PetroFix carbon and the rates of anaerobic degradation. Our goal for PetroFix is to provide sustained multiple-order of magnitude reductions of BTEX and TPH and to let our customers know of site conditions where we think attaining this goal would be challenged. If uncertain, we advise that you order a single drum of PetroFix and pilot test at your site.
Can PetroFix and PlumeStop both be used for a site with comingled petroleum and chlorinated hydrocarbon plumes?
PetroFix is specifically formulated for hydrocarbon plumes and while it could sorb both solvents and petroleum, its formulation will not promote anaerobic destruction of chlorinated products. In fact, PetroFix injected with its electron acceptors in an area targeted for reductive dechlorination treatment of solvents would be expected to repress reductive dechlorination until they are depleted and this would negatively delay solvent treatment. What we advise is that if you are concerned about overlap that you contact Regenesis for design assistance to evaluate an optimal treatment scenario.
Can PetroFix be injected at the same event as other Regenesis products such as RegenOx, or would it require an additional injection event?
We believe that PetroFix is compatible with RegenOx and PersulfOx chemistry and could be co-injected in the same areas as these products. However, these material should not be injected simultaneously in the same hole. Other constraints to consider would be the ability to get total volumes from both ISCO products and PetroFix in the ground simultaneously since both require high volumes and high effective pore space filled. We see PetroFix as a very strong option for post ISCO polishing as either a second subsequent injection or possibly simultaneous injection during a single mobilization. The practitioner would need to determine the optimal timing when PetroFix should be injected to coincide with the mass reduction goals of the ISCO injections and at which injection event PetroFix should be paired. Regenesis is happy to discuss such options and make recommendations.
Has PetroFix been tested at a fractured bedrock site and if so, what were the results?
We have had a project where PetroFix was distributed in a bedrock aquifer and distribution was better than expected because effective pore space is less than in soil. As long as fractures are interconnected and the aperture sizes of those fractures are large enough you would expect to be able to push PetroFix into the formation, potentially using larger ROI’s than what we normally estimate for direct push. In a fractured bedrock site with sufficient interconnectivity you also have the option to use a pump-pull arrangement using different wells to facilitate distribution in different directions. We would recommend a small pilot test using a drum of material to verify the deliverability of the product and validation of ROI.
Have you had any success delivering PetroFix via injection wells?
Yes, this product can be applied in injection wells and more so for sites where the wells were specifically design for pressure injection at targeted intervals. However, achieving distribution would have to take into consideration the limited ROI and distribution potential for pressure injection of PetroFix and whether a large number of injection wells makes economic sense over direct push. We realize there may be situations where distribution in deep aquifers or the hybrid use of both direct push injection and injection wells may be desired at a site. Ideal well construction would have 30-slot screen with 8/16 or 6/9 sand pack and if using schedule 40 PVC you would have a maximum operating pressure of 166 psi for a 2-inch well. We anticipate that most injections would require pressures well under this maximum operating pressure. However, it is possible that depending on depth and type of soils higher pressures could be realized without initiating fracturing and you may want a higher rated well material such as schedule 80 PVC which has a maximum operating pressure of 243 psi for a 2-inch well. We recommend that the injection screens be positioned at the target injection zones and that the screen doesn’t go above the water table. We also recommend strategic use of solid sections of pipe and bentonite grout seals as needed to maintain discrete injection intervals and pressures. Given the relatively high cost to install injection wells it would be worth performing a well injection pilot test before full scale. For higher permeability environments one could consider pump-and-pull well arrangements for enhanced distribution.
Do you have rules-of-thumb for how many pounds of PetroFix are needed per pound of hydrocarbon?
We do not have rules-of-thumb for how many pounds of PetroFix are needed per pound of hydrocarbon. Because we use independent carbon isotherms for each hydrocarbon compound and because different soil types alter carbon loading calculations using our isotherms we perform independent calculations for each site to get the best estimate for PetroFix dosage.
Any kick back from regulators when PetroFix gets in surrounding monitor wells?
We have not had projects stopped thus far from this concern and are aware of the reasons why it might be a concern. In comparison to high pressure fracking of PAC products, the activated carbon particles in PetroFix are very small that allows for distribution through soil and aquifer pores under natural flow conditions. By simply applying a PetroFix suspension through wells or direct push points, the PetroFix particles simply flow with groundwater through existing flux zones, coating the aquifer material surface with PetroFix particles. No artificial preferential pathways are formed in the which could irreversibly pack the well with powered activated carbon.
During injection to the subsurface PetroFix may flow into nearby monitoring wells, as evidenced by sampling the well and finding the water color to be black. This occurrence is not uncommon and is simply the result of the PetroFix material flowing out into the natural flux zones of the subsurface.
The injection of PetroFix is intended to coat the contaminated aquifer matrix with the PetroFix particles. Much of this process occurs immediately are the process of having all particles drop from suspension and binding to the aquifer matrix may take up to 1-3 months. To ensure that PetroFix entering monitoring wells at the time of injection does not drop from suspension within a monitoring well bore and filter pack, the material can be flushed from impacted wells upon completion of injection activities. This simply pushes any PetroFix suspended with in the monitoring wells back out into the aquifer where the particles will drop form suspension. This step helps to preserve the integrity of the monitoring well and ensures that water samples obtained from the well in the future are representative of groundwater within the aquifer itself. Regenesis can provide specific instructions for the flushing of monitoring wells.
Can I have REGENESIS develop a PetroFix design for me instead of my own involvement? When can REGENESIS do this?
PetroFix ideally is designed for self-design and self-application of the product. However, there are situations where the combined use of PetroFix with other technologies is appropriate and in those situations REGENESIS can become more involved in the design process. An example would be if preliminary ISCO activities were proposed ahead of PetroFix for mass reduction of LNAPL followed by PetroFix as a polish. REGENESIS can provide design services for these scenarios. Please contact REGENESIS if you have questions.
How do you recommend addressing data from PetroFix-impacted monitoring wells?
As long as free PetroFix is visibly suspended within the well water it is best to wait until the well clears up naturally. This can be facilitated by flushing clear water into the well which will push free particles back into the aquifer. Wait a reasonable period of time before sampling and purging to ensure that the sample volume collected is indicative of aquifer waters. In the event that you cannot wait to sample before clarification, it is possible to filter PetroFix out of samples to get a true dissolved phase concentration. Please contact Regenesis if you need help with this.
Furthermore, PetroFix is not like powdered activated carbon products that disrupt the filter pack around the well screen, irreversibly filling the filter pack pores with powdered activated carbon. PetroFix particles are small enough to move freely into and out of the filter pack with the natural flow of groundwater. PetroFix entering the filter pack material will coat that portion of the filter pack adjacent to the flux zone with a thin layer of PetroFix particles. In many cases, due to the much lower surface area available within the filter pack material, however, the amount of PetroFix retained there should be substantially less than would have been left behind on the native aquifer material had the well not been present. Please also refer to the answer to question 16.