Phytoremediation Technology Evaluation and Preliminary Design Chlorinated and Petroleum Hydrocarbon Groundwater Plume at Former Gas Liquids Extraction Facility, Colorado November 13, 2012 Dustin Krajewski MS Civil/Environmental Engineering Colorado State University
Agenda Introduction: Why? Site Conceptual Model: Where are we starting from? Remediation Objective: What defines success? Alternatives Evaluation: Will phytoremediation work? Preliminary Design: What do we do now? Long Term Monitoring: What s next? Additional Considerations: What else?
Introduction Why? Remediation Engineer (AECOM) Technologies include excavation, groundwater pump and treat, soil vapor extraction, etc. and more recently enhanced bioremediation including bioaugmentation Actual cleanup site client is innovative and interested Green and Sustainable Remediation (GSR) Integration of sustainable principles, practices and metrics into all phases of a remediation 1 Other projects: NAPL, VOCs, metals, PAHs, pesticides 2 Regulatory Acceptance Not common, but increasing acceptance and interest
Site Conceptual Model Background The Site is a former liquids terminal that operated from mid- 1970 s through 1995. Environmental investigation and remediation since 1992 Four areas containing confirmed impacts Area 1 PIG receivers, petroleum hydrocarbons (considered remediated) Area 2 Former dehydrator area, BTEX in soil and groundwater Area 3 Former compressor units, chlorinated compounds [tetrachloroethene (PCE) and daughter products] in groundwater Area 4 Condensate ASTs, BTEX in groundwater
Site Conceptual Model Site Layout
Site Conceptual Model Water Quality / Characteristics Groundwater Quality: Benzene, PCE, tetrachloroethene (TCE), cis-1,2-dichloroethene (cis 1,2-DCE) concentrations in groundwater exceed maximum contaminant levels (MCLs) at the Site Hydrology Depth to water: Shallow wells are 0.4 to 8 feet below ground surface (bgs) and deeper wells from 12 to 19 feet bgs (seasonal fluctuations) Flow: Flow direction is to the northeast with a calculated hydraulic gradient of 0.04 feet/foot Hydraulic conductivity: 3.81 x 10-6 cm/s to 1.04 x 10-3 cm/s (geometric mean of 4.30 x 10-5 cm/s) Estimated porosity: 0.25 Groundwater velocity: 0.02 feet/day or 7.1 feet/year
Site Conceptual Model Groundwater Conditions (Benzene)
Site Conceptual Model Groundwater Conditions (PCE)
Site Conceptual Model Groundwater Conditions (cis 1,2-DCE)
Site Conceptual Model Soil Quality / Characteristics Soil Quality: Recent soil samples indicate all results below regulatory cleanup levels in vadose zone Soil Characteristics Estimated porosity: 0.25 Lithology: Interbedded sands, silts, and clays with a claystone evident around 20 feet bgs Membrane Interface Probe (MIP): Determine vertical and horizontal extent of impacts (petroleum and chlorinated) Identified presence of a shallow confining layer with corresponding increased concentrations at that layer
Site Conceptual Model MIP Layout
Site Conceptual Model MIP Results
Remediation Objective Ultimate Objective: Achieve regulatory closure under the CDPHE Voluntary Cleanup Program Clean up Goals: MCLs 3 required at property boundary Risk based remediation approach allowed Other goals: Health and Safety (zero incidents) always Sustainability vacant lot, good opportunity for innovative solution Cost effective not a high profile site
Alternatives Evaluation Common Technologies 4 Air sparging: Pilot test conducted, results included high pressure, low flow Excavation: Requires excavation in saturated zones (groundwater dewatering, soil dewatering, increased waste, etc.) and ex situ soil treatment Bioremediation Injections Proven technology at similar sites using high fructose corn syrup and microbial cultures Sustainable but injectability an issue based on air sparge results
Alternatives Evaluation Phytoremediation Phytoremediation (+) Shallow groundwater, vacant property, nearby irrigation ditch (-) Soil types not ideal (silt and clay) Will the plant take up the contaminant and by-product? Yes: Log K ow PCE (3.4) 5, TCE (2.29) 6, cis 1,2-DCE (1.86) 7, Vinyl Chloride (0.6) 8, and benzene (2.13) 9 For uptake by organic contaminants = Log K ow between 1 and 3.5 10
Alternatives Evaluation Phytoremediation Decision Tree 10
Alternatives Evaluation Phytoremediation Decision Tree 10
Phytoremediation Preliminary Design Based on technology screening and decision trees, phytoremediation tree stand is chosen alternative Selected tree is poplar (proven technology for VOCs 10,11 ) Plant density based on 1 tree every 75 square feet 10
Phytoremediation Preliminary Design Phytotechnology mechanisms 10 Rhizodegradation (phytostimulation) Phytohydraulics Phytodegradation Phytovolatilization
Phytoremediation Preliminary Design Phytodegradation and Phytovolatilization Model uptake of contaminant based on Transpiration Stream Concentration Factor (TSCF) 10,12 ratio of xylem / external solution equation 12 Mass of VOC removed by plant uptake Uptake VOC 12 = (TSCF)(C VOC )(T)(f) C VOC = Average groundwater concentration T = cumulative volume of water transpired per unit area per year f = fraction of the plant water needs met by contaminated groundwater
Phytoremediation Preliminary Design Phytodegradation and Phytovolatilization Plume sizes (square feet) PCE (5,250); TCE (2,625); DCE (33,300); benzene (9,000) # of trees based on plume size and 1 tree per 75 square feet PCE (70); TCE (35); DCE (444); Benzene (120) Volume of impacted groundwater (liters) PCE (3.71x10 5 ); TCE (1.85x10 5 ); DCE (3.71x10 5 ); benzene (2.36x10 6 ) Mass of contaminant in groundwater (grams) PCE (2); TCE (43); DCE (542); Benzene (147) Mass per year of transpired contaminant based on transpiration stream concentration factor (TSCF) and uptake calculations (g/year) PCE (0.42); TCE (10.24); DCE (144.11); benzene (37.14) Estimated time to remove contaminant mass through transpiration (years) PCE (4.4); TCE (4.2); DCE (3.8); benzene (3.9)
Ln TCE and 1,2-DCE Concentration (ppb) Phytoremediation Preliminary Design Rhizodegradation Use first order decay function based on current attenuation rates: 10 C(t) = C 0 e -kt Evaluated TW-16 (highest DCE concentration) PCE = N/A (cleanup level achieved) TCE = 35.3 years [C(t) = 5 ppb, C 0 = 14 ppb] DCE = 89.3 years [C(t) = 70 ppb, C 0 = 950 ppb] 10 Ln TCE and 1,2-DCE Concentration over time at TW-16 TCE y = 74.148e -8E-05x R² = 0.2388 TCE DCE cis 1,2-DCE y = 20.317e -3E-05x R² = 0.2881 1 12/6/99 5/24/02 11/9/04 4/28/07 10/14/09 4/1/12 Time (Date)
Phytoremediation Preliminary Design Summary 444 trees required to completely remove cis 1,2-DCE through transpiration (probably excessive) Assumes complete removal, not just to MCL Does not include enhanced attenuation through rhizodegradation only natural attenuation Enhanced aerobic 10, Enhanced anaerobic 13 (PCE TCE cis 1,2- DCE VC ethane/ethene) Estimated capital cost 10 Bare-rooted stock ($10 or less each) Potted stock (up to 10 gal) ($10 - $100 each) Larger stock ($100 - $500 per tree) Assume $250/tree x 444 = $111,000
Phytoremediation Long Term Monitoring 10,14 Sampling and Analysis Monitor same primary lines of evidence as other alternatives (groundwater concentration trends, hydrology, soil effects, etc) Secondary lines of evidence may be plant analysis (risk and mass balance) Plant tissue Volatilization O&M costs decrease as plantation becomes established O&M includes replanting as necessary (10 15% of initial plants) Other O&M include irrigation, fertilization, weed control (mowing, mulching, or spraying), and pest control
Phytoremediation Additional Considerations Implement small scale pilot study/treatability study in area of highest impacts (1 st year / 2 years?) Assess actual remediation mechanisms Evaluate rhizodegradation Confirm contaminant removal rates State regulatory requirements Air Water Prairie grasses Reduced cost? $100/pound and approximately 10 pounds required to cover 1 acre 10
Thank you Dustin Krajewski dustin.krajewski@aecom.com. References 1. Interstate Technology and Regulatory Council (ITRC). Accessed November 12, 2012. Green and Sustainable Remediation. http://www.itrcweb.org/teampublic_gsr.asp. 2. AECOM. 2012. Phytoremediation Services Brochure. 3. USEPA. Accessed November 12, 2012. Drinking Water Contaminants Maximum Contaminant Levels. http://water.epa.gov/drink/contaminants/index.cfm. 4. ITRC. Accessed November 12, 2012. Guidance Documents. http://www.itrcweb.org/gd.asp. 5-9. USEPA. 2012. Technical Fact Sheets on PCE, TCE, cis 1,2-DCE, VC, and Benzene. 10. ITRC. February 2009. Phytotechnology Technical and Regulatory Guidance and Decision Trees, Revised. 11. Longley, Kirsi. June 2007. The Feasibility of Poplars for Phytoremediation of TCE Contaminated Groundwater: A Cost-Effective and Natural Alternative Means of Groundwater Treatment. 12. McCutcheon, S. and Schnoor, J. 2003. Phytoremediation: Transformation and Control of Contaminants. 13. Van Den Bos, Amelie. August 2002. Phytoremediation of Volatile Organic Compounds in Groundwater: Case Studies in Plume Control. 14. National Risk Management Research Laboratory. February 2000. Introduction to Phytoremediation.
Questions 1) What are active phytoremediation mechanisms presented in this approach? 2) What are some long term monitoring requirements/strategies that could be implemented with this approach? Answers 1) Rizodegradation (Phytostimulation), Phytohydraulics, Phytodegradation, and Phytovolatilization 2) Groundwater sampling (contaminant, dissolved oxygen, other nutrients, etc.), plant tissue analysis, transpiration air analysis, transpiration water analysis, O&M (plant quality/replacements, weeds, pests, etc.)