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Final Phytoremediation Treatability Study
Section 6 - Recommendations
There are several recommendations for further evaluation of phytoremediation of soils at CSSA if further pursued. Additional study should focus on the phytoextractable lead availability in multiple crop harvesting. Phytotech assumed that removal rates remains consistent throughout each growing season. This seems unlikely due to the drop in availability of phytoextractable lead. Additional issues recommended for further study are listed below:
Site-specific risk based cleanup levels. This technology is not likely to meet RRS1 (background) criteria; therefore, determination of risk-based cleanup levels may be appropriate. After site-specific risk-based levels are determined, historic data should be re-evaluated to confirm contaminants requiring remediation. Further recommendations below assume lead is the primary contaminant of concern; however, additional metals may require further evaluation.
Potential movement of metals within the soil matrix. The potential movement of lead within the soil matrix to move below the capture zone should be evaluated. That is, when the amendments are applied or conditioning of soil between crops by plowing or rotating, is the lead mobilized below the root zone, therefore minimizing the availability of mobile lead.
Suitability of phytoremediation in the central Texas climate.
Likelihood of deer and other animals to eat the Indian mustard plant.
Additional evaluation of costs. The potential costs associated with full scale implementation of the phytoremediation includes disposal of the plant biomass and particulate lead removal by density separation, all of which need further investigation. If the concentration of lead in soils to be removed is 1,000 mg/kg and phytoremediation generates plant biomass material at 3,000 mg/kg, the resulting biomass material being dispersed is 660 lbs. for every ton of soil treated. This cost of disposal will likely be more than the cost of growing and harvesting the plants.
Additional information is also needed to optimize the time of harvest. Plants should be harvested when the rate of metal accumulation in plants declines. This will minimize the duration of each growth cycle and allow more crops to be harvested in a growing season.