Colorado State University

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

CSU

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?

CSU

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 remediation1

Other projects: NAPL, VOCs, metals, PAHs, pesticides2

• Regulatory Acceptance

Not common, but increasing acceptance and interest

CSU

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

CSU

Site Conceptual Model Site Layout

CSU

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

CSU

Site Conceptual Model Groundwater Conditions (Benzene)

CSU

Site Conceptual Model Groundwater Conditions (PCE)

CSU

Site Conceptual Model Groundwater Conditions (cis 1,2-DCE)

CSU

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

CSU

Site Conceptual Model MIP Layout

CSU

Site Conceptual Model MIP Results

CSU

Remediation Objective

• Ultimate Objective: Achieve regulatory closure under the CDPHE Voluntary Cleanup Program

• Clean up Goals:

MCLs3 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

CSU

Alternatives Evaluation

Common Technologies4

• 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

CSU

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 Kow 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 Kow between 1 and 3.510

CSU

Alte

rnativ

es E

valu

atio

n

Ph

yto

rem

ed

iatio

n D

ecis

ion

Tre

e1

0

CSU

Alte

rnativ

es E

valu

atio

n

Ph

yto

rem

ed

iatio

n D

ecis

ion

Tre

e1

0

CSU

Phytoremediation – Preliminary Design

• Based on technology screening and decision trees, phytoremediation tree stand is chosen alternative

Selected tree is poplar (proven technology for VOCs10,11)

Plant density based on 1 tree every 75 square feet10

CSU

Phytoremediation – Preliminary Design Phytotechnology mechanisms10

Rhizodegradation (phytostimulation)

Phytohydraulics

Phytodegradation

Phytovolatilization

CSU

Phytoremediation – Preliminary Design Phytodegradation and Phytovolatilization

• Model uptake of contaminant based on Transpiration Stream Concentration Factor (TSCF)10,12 – ratio of xylem / external solution

equation12

• Mass of VOC removed by plant uptake

UptakeVOC12 = (TSCF)(CVOC)(T)(f)

• CVOC = 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

CSU

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 (3.71x105); TCE (1.85x105); DCE (3.71x105); benzene (2.36x106)

• 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)

CSU

Phytoremediation – Preliminary Design Rhizodegradation

• Use first order decay function based on current attenuation rates:10 C(t) = C0e

-kt

Evaluated TW-16 (highest DCE concentration)

• PCE = N/A (cleanup level achieved)

• TCE = 35.3 years [C(t) = 5 ppb, C0 = 14 ppb]

• DCE = 89.3 years [C(t) = 70 ppb, C0 = 950 ppb]

TCE y = 74.148e-8E-05x

R² = 0.2388

cis 1,2-DCE y = 20.317e-3E-05x

R² = 0.2881

1

10

12/6/99 5/24/02 11/9/04 4/28/07 10/14/09 4/1/12

Ln

TC

E a

nd

1,2

-DC

E C

on

cen

tra

tio

n

(pp

b)

Time (Date)

Ln TCE and 1,2-DCE Concentration over time at TW-16

TCE

DCE

CSU

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 aerobic10,

• Enhanced anaerobic13 (PCE→TCE→cis 1,2-DCE→VC→ethane/ethene)

• Estimated capital cost10

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

CSU

Phytoremediation – Long Term Monitoring10,14

• 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

CSU

Phytoremediation – Additional Considerations

• Implement small scale pilot study/treatability study in area of highest impacts (1st 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 acre10

CSU

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.

.

CSU

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.)