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Remaining Simulcast Questions and Answers from February 28, 2012

Question 1: How you can determine the maximun capacity of a plant can store a contaminat material? - International Participant; Ecuador

David Tsao: I would suggest conducting benchtop studies to determine this for your specific situation. If it is a volatile, you will need to have a setup that can capture volatile emissions (e.g. carbon traps) in order to get closer to a complete mass balance.

Question 2: Are any of the phytotechnology mechanisms listed on slide 20 employed on urban brownfield sites that are 1 acre or less in size? - State Government Participant; Saint Paul, MN, United States

David Tsao. yes, all of them. Actually, I think you mean applications rather than mechanisms. Area, of course, limits phyto-applications...just can't plant enough plants to do the containment or remediation needed in the small area. There are "pocket parks" that have been installed on small urban areas (Google or Bing it). these provide good phytostabilization covers; perhaps remediate residual organics (phytorem cover). There are landscape species that are better than others for remediation...we employed them at our retail sites for gasoline constituents. Generally, you are not going to get enough trees into a small area to do significant hydraulic control, but could be used to phytoremediate deeper soils.

Question 3: What is the potential for poplar trees to uptake groundwater with high concentrations of ammonia at the same time they hydraulically contain/control groundwater discharge to surface water? - Environmental Consultant; Ottawa, Canada

David Tsao: generally a decent potential. Will of course depend on concentration of ammonia, pH, other site-specific factors. I don't have direct experience with phytoremediating ammonia, but do know there has been some work done. I think Argonne National Lab (Dr. Negri) and U.Iowa (Dr. Schnoor) might have first hand knowledge.

Question 4: Slide 20: which is the fate of the wood, can be used as biomass in an incinerator under the states law or the US law? In Italy, that wood can't be considered as a resource in the sense that you have to pay the societies that incinerate biomass to take this wood (i am sorry but is what really happens and it is one of the major limit to this technology). - Regulator; Rome, Italy

David Tsao: agree that this can limit applicability. Do you have to harvest at all to make the remediation work? Or, is it simply an economics question. In the US it is state specific and depends on the contaminant (metals generally tend to be the issue more than organics). Generally it is the air emissions regulations that need to be considered.

Question 5: Slide 32: how can you evaluate if the "existing vegetation" is working properly in terms of reducing or immobilizing the contamination? I am referring particularly in the case that some vegetation is "sick" probably for the high concentration in a certain part of the site and some other is "health" because of low concentration in other part of the site (contaminated but not in the hot spot). - Regulator; Rome, Italy

David Tsao: depending on the contaminant, the target media/depth, etc., perhaps do tissue sampling looking for the contaminant or sample the rhizosphere. Ultimately you are trying to determine the phyto mechanism that is at play...phytoextraction, rhizodegradation, phytodegradation, etc. If you get confirmation that a specific mechanism is at play, then you can determine whether that is causing the plant responses (e.g. contaminant toxicity) or something else (e.g. poor nutrients).

Question 6: How do you determiine a plant harvest frequency for phytoextraction (i.e., how long will a plant extract)? - Environmental Consultant; Grand Rapids, MI, United States

David Tsao: this depends on many factors: climate (how many cropping cycles you can get in a season), plant species, growth cycle (when does the extraction take place in the plant growth cycle), whether the plant is an annual, biennial, or perennial, where in the plant is the contaminant stored once extracted, etc. I would consider conducting benchtop studies to get some answers. This is just from the "plant" side; there are also operational issues to consider: how fast can you harvest, what equipment, waste handling, etc.

Question 7: In a situation where plants seasonally die back (for example with seeding-annual or herbaceous-perennial plants). Are there site examples where the dead plant matter needed to be collected so that they didn?t re-contaminate the soil and groundwater? If so, how was this achieved? - Environmental Consultant; Melbourne, Australia

David Tsao: Most phytoextraction applications (e.g. for metals) require harvesting plant materials and removing from the site. This is done just before or shortly after the end of the growing season. Since you are considering grasses or herbaceous species, the harvesting would be generally easier using standard farming equipment. You should also consider this (what equipment, how to harvest) when you select your species in the first place.

Remaining Simulcast Questions and Answers from September 15, 2011

Question 1: If you're using phytotechnology and intend to use a specific technology (ex. rhizodegradation) to what extent do you have to account for another phytotechnology coming into play? - Community Stakeholder; Port Washington, NY, United States

David Tsao: The mechanisms such as rhizodegradation are generally inherent in any application of phyto as long as the specific contaminant can be influenced by the mechanism. For example, if you want to rhizodegrade a contaminant, but that contaminant can also enter into the plant (phytoextraction), then you will have to deal with both. However, the mechanisms occurring in the root zone (rhizodegradation) will occur first and could degrade sufficient contaminant that entry into the plant is negligible.

Question 2: Is there a reference that IDs which plants are good for which contaminants? - Environmental Consultant; Vernon Hills, IL, United States

David Tsao: check the slide I presented with the various databases. One of those is Appendix B in the PHYTO-3 document. It's dated, but it's a place to start. Unfortunately, there is no single comprehensive phyto database available although I had recent discussions with those working in the field to develop one. Also US EPA has developed some guidance documents with specific focus (i.e. phyto of chlorinateds) which contain selected species.

Question 3: Do you control the technology used by plant selection and contaminant at issue only or are there other factors? How often does a secondary technology (planned or not) come into play? - Community Stakeholder; Port Washington, NY, United States

David Tsao: Not sure I understand this question completely, but there are many factors that "control" the technology. Some are within actual human control (irrigation, fertilization, weed control, use of boreholes to access deeper, etc.) and some outside of our control (i.e. weather, predation, infestation, etc). We can try to address some of the outside factors, but usually only in reactive mode. Another ability to "control" is species selection...appropriate depth, growth rate, biomass production, suitable to the climate/altitude, etc. The second part of the question is probably a "depends" answers (depends on the specific situation at your site). Based on my portfolio of sites where phyto has been applied (several dozen), only a handful (count on one hand) have switched from phyto to some other technology at a later date or added something to supplement.

Remaining Simulcast Questions and Answers from May 10, 2011

Question 1: At a project site, a fungus claimed the life of almost all hybrid poplar trees planted as part of a phyto-remediation project. When selecting trees for hydraulic control/remediation purposes, do you recommend a diversity of species to reduce the likelihood of such devastation? - Environmental Consultant; Laramie, WY, United States

DTsao: yes, 2 to 3 species within the Salicaceae Family such as a mix of poplars and willows can be enough diversity. I have some sites with up to a dozen species including climax (oaks, cypresses, etc.)

Question 2: Have these species of plants used ever become invasive species in the larger area beyond the site ? - Participant; Milwaukee, WI, United States

DTsao: I will never say never, but typically the hybrids that are available commercially are sterile clones. Commercial growers don't want their stock replicated. If that is a potential issue, then incorporate that into the species selection process and also consult local ag extension service for advice on noxious/invasive species.

Question 3: Slide 59; Can mechanical barriers be used to keep animals like the beavers out? ? Participant; Milwaukee, WI, United States

DTsao: Not 100% sure what is meant by a "mechanical barriers". Fencing can be considered a mechanical barrier. So can a gun (that's a quote from a wildlife specialist I once received - also known as acute lead poisoning at military cleanup sites). Individual trunk guards around trees need to be flexible to allow the trunk to expand, need to also allow some sunlight and moisture to pass through (trapped moisture will rot the tree and promotes fungal infections - see Q1). Some have suggested trapping and relocating larger animals such as beavers.

Remaining Simulcast Questions and Answers from January 27, 2011

Question 1: How is the identification and mapping used with this remedial option? - Environmental Consultant; Taylorsville, KY, United States

Question 2: I am in region 2 (Orange County, NY) and am looking for types of plants or trees known to absorb lead. We are in the city of Newburgh and the children I work with are interested in community gardening around an old armory. - Local government participant; Newburgh, NY, United States

Question 3: Just for clarification, the goal of hydraulic control is to direct groundwater flow and not to directly remove the contaminant? - Student; Hampton, VA, United States

Question 4: Are soil amendments or soil augmentation needed for any of these options? - Participant

Question 5: Is the depth of bedrock, 5-10 feet below ground surface, be a limiting factor in the effectiveness of phytoremediation in treating impacted groundwater? - Participant

Question 6: For the arsenic phyto using ferns, you indicated the plant matter caused the arsenic to be in a more toxic form. Do they have to handle that material as Haz waste? The data indicates reduction to about 100 or 150 ppm, do you know if it has been able to reduce levels to near background levels (5 ppm)? - Environmental Consultant; Plymouth, WI, United States

Question 7: Is there any evidence that a phytotechnology might alter groundwater chemistry such that it affects pre-existing natural biodegradation? For example, could tree roots exude sufficient oxygen to increase oxygen levels in groundwater such that pre-existing anaerobic biodegradation is reduced or aerobic biodegradation is enhanced? - Environmental Consultant; Manchester, NH, United States

Question 8: Resources for case studies? - Environmental Consultant; Portland, OR, United States

Question 9: What is time frame for cleanup using phyto? - Environmental Consultant; Portland, OR, United States

Question 10: In temperate climates, does inactivity during the winter (4 months?) prevent regulatory consideration and approval of phytoremediation as a groundwater containment method? I imagine it depends on the hydrogeologic situation. - Environmental Consultant; Plymouth, WI, United States

Remaining Simulcast Questions and Answers from November 16, 2010

Question 1: Are the plant databases listed on slide 38 available publicly? - Participant from private sector; Milwaukee, WI, United States

Remaining Simulcast Questions and Answers from September 16, 2010

Question 1: Is there a list of plants that work best for some of the phytotechnologies? - Participant from US EPA; Kansas City, KS, United States

Question 2: What are the considerations regarding the potential for the transport of COCs through plant tissues? ex. shed leaves, consumers feeding on plant tissues, etc? - Consultant; Houston, TX, United States

Question 3: Does evidence exist that photo-degradation occurs in above-ground plant tissues? If so, could the presenters offer references regarding this issue? Asking specifically about PHOTODEGRADATION (degradation by light). - Consultant; Houston, TX, United States

Question 4: Do you have any information on Native Species that work for Phytoremediation? - Participant from US EPA; Kansas City, KS, United States

Question 5: Question about how to sell this as a partial solution when no in place allowed due to a recent federal agreement. No in place allowed meaning that the recent historic agreement for the Santa Susana Field Lab here stipulates presumptive remedy approach skipping risk assessment where no in place treatment is specifically on the agreement. That was there due to the effort by RPs to potentially create onsite landfill solution. But we want to use these technologies so we don't just fill other landfills. It's a landmark deal here in California that just happened last friday. - Participant; West hills, CA, United States

Question 6: What must be considered regarding the lifetime of a phytosequestration remedy? I.e. If persistent COCs are locked into the rhizosphere during the life of the plant, what happens at the end of the plant's life? - Consultant; Houston, TX, United States

Question 7: Do any of the presenters have experience implementing phytotechnology for remediation of PCB impacted soil? - Consultant; E. Brunswick, NJ, United States

Remaining Simulcast Questions and Answers from June 15, 2010

Question 1: What relevance, if any, does phytoremediation have to DNAPL cleanup? - Participant from U.S. EPA; Crystal City, VA, United States

Question 2: Have any of the speakers worked directly with perchlorate remediation or other phytotechnologies? - Environmental Consultant; Hockessin, DE, United States

Question 3: Is there any evidence that when trees drop their leaves in winter, the surface soil could potentially become re-contaminated with the targeted analyte which has now become stored in the plant tissue? thanks - Environmental Consultant; Hockessin, DE, United States

Question 4: As for shallow groundwater, how to determine the groundwater flow rate is suitable for phytoremediation? And how to determine the optimal distance for tree planting? - Environmental Consultant; Athens, GA, United States

Question 5: Would the speakers recommend working alongside a landscaping company to ensure good plant selection, longevity and develop a maintenance plan? - Environmental Consultant; Hockessin, DE, United States

Question 6: If we know that groundwater is at 3 feet, can we plant cottonwood whip in a 9 foot hole and have the roots grow at that depth without rotting?

Question 7: Any experience with the beneficial affects of shallow ponds with cat tails created by determined and pesky beavers?

Question 8: If we are using phytotechnologies to control the shallow groundwater gradient, what type of information do we need to collect to construct a water balance equation? - Environmental Consultant; Houston, TX, United States

Question 9: In your opinion how applicable is phytotechnology to Alaska where a cold climate and muskeg conditions exist? Is a constructed wetland treatment system or some other form of phytotechnology viable if these conditions exist at a mine where tailings and waste rock can produce acid mine drainage and at closure leachate will contain high concentrations of zinc, lead, cadmium and other metals? - Alaska State Regulator; Juneau, AK, United States

Question 10: What plants species are able to take up zinc, lead and cadmium in Alaskan conditions? If possible can you point to any studies where phytotechnology has been used in Alaska. - Alaska State Regulator; Juneau, AK, United States

Remaining Simulcast Questions and Answers from February 25, 2010

Question 1: Does Ele have any more examples of phyto projects implemented as part of the VCP here in Texas -- Environmental Consultant; Austin, TX, United States

Question 2: what volume of groundwater can the average tree "pull up"? Is it species dependent? -- New York State Regulator; Avon, NY, United States

Question 3: For the assessment phase, is there a plant-selection reference available that cross-references plants to USDA plant-hardiness zone maps? -- Private Sector Participant; Houston, TX, United States

Question 4: Do you know any successful story to tell about removal of cadmium and zinc from vadose soil with phyto? thanks -- Environmental Consultant; Milan, Italy

Question 5: Will regulators allow the use of contaminated groundwater to irrigate the remediation plantings in areas with insufficient precipitation. Are there concentrations that will stress the plant sufficiently to prevent remediation -- Private Sector Participant; Wilsonville, OR, United States