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Phytoremediation Using Poplar Trees as a Corrective Action at a UST Release

Located in Maybell, CO A Project Overview

Edward Fus, PE Higgins and Associates, LLCJane Bral State of Colorado Dept of Labor & Employment, Division of Oil and Public Safety

Anu Ramaswami, University of Colorado Denver

Abstract

A release from an Underground Storage Tank system located in the alluvial plain created by the YampaRiver in the high desert mesa of Northwest Colorado is being remediated using phytoremediation. Theproject is the first application of phytoremediation to address BTEX impacted groundwater under theColorado Division of Oil & Public Safety Petroleum Storage Tank Remediation Program. Sitecharacteristics including a shallow water table, remote location, distribution of hydrocarbons, and theestimated higher cost of alternatives suggested the potential for the selection of this remedial option. Aspart of the regulatory approval process, a pilot study was conducted and incorporated field data withlaboratory analyses using a hydroponic growth chamber at the University of Colorado, Denver (UCD,Ramaswami et al, 2001). The pilot test confirmed that poplar trees can be effective for phtyoremediation ofBTEX, that growth of poplar trees are not inhibited by BTEX concentrations found at this site, and that

phytoremediation using Poplar trees has a high potential for success. The UCD pilot study findings,supported by a favorable economic and technical analysis, resulted in State of Colorado approval of thecorrective actions proposed for this project. In June 2002, to implement the approved corrective actionplan, 300 Lombardy Poplar (Populus x Nigra Italica) saplings were planted. Groundwater characteristicsand tree monitoring data, collected prior to and during the first growing season, is presented. Theregulatory perspective, site characterization, hydrocarbon distribution, location of existing trees, strategybehind new plantings, planting methodology, and tree maintenance issues are also discussed.

Introduction

Phytoremediation is an accepted method to remediate inorganic and organic contaminants from soil orgroundwater. However, its consideration as a potential clean-up strategy for petroleum storage tankreleases at gasoline retail sites is unusual. The Maybell Store project is the first attempt to usephytoremediation to remediate such a release in the State of Colorado. Phytoremediation of a petroleumhydrocarbon release at the Maybell Store using Poplar trees has been pilot tested, approved by Stateregulators, and implemented. The following paragraphs detail the initial site conditions, regulatory path,pilot test results, implementation, and initial results of the Maybell Store project.

Site Setting

The Maybell Store is located in Maybell, Colorado in the high mesa environment of the northwest corner ofthe State. Maybell is approximately 30 miles west of the town of Steamboat Springs and 50 miles east ofthe Colorado-Utah border. The Yampa River, flowing to the west, is located approximately 1 mile to thenorth of the site.

The water table within the project area annually varies between 2-10 feet below ground surface asinfluenced by normal seasonal fluctuations and an irrigation canal located approximately 600 ft south of the

site. Depth to water during the summer months is typically 2 to 6 feet below ground surface. The climateis arid in that the area receives less than 12 inches of annual precipitation. The low precipitation over theinterior of the Yampa River basin provides little opportunity for groundwater recharge. However,groundwater does occur in the river alluvial deposits and is recharged by streams during high flows andfrom irrigation. Months of high water occur in the spring and early summer. Snowmelt is the principalsource of water supply in the basin.

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Site History

The site has a history of association with selling fuel for automobiles since at least 1971. It is known that 3underground storage tanks (USTs) were installed at the site in that year. The site also serves as thegrocery/general store for the town of Maybell and has existed since the 1920s. In 1995, all tanks, pumps,and lines were removed from a location near the southwest corner of the property and replaced with a newUST located near the southeast corner of the site. The removal of the 3 USTs and associated equipmentwas not conducted in a manner consistent with State of Colorado regulations. The release was likely to beevident at this time but the process of installing the new UST was finished and no environmentalmonitoring or assessment occurred.

As part of an effort to sell the property in 1997, the owner contracted others to conduct an environmentalinvestigation of the site. This investigation resulted in the identification of subsurface hydrocarbons atvarious locations on the Maybell Store property. Upon notification of the results of the investigation, theColorado Department of Labor and Employment, Division of Oil and Public Safety (OPS) requested theowner determine the extent of petroleum contamination. These investigations were conducted and theirresults follow.

Assessment Regulations

Requirements for assessment of UST petroleum release sites in Colorado can be found in the ColoradoCode of Regulations (CCR) 1101-14. Additional details of site assessment requirements are presented inthe OPS document Colorado Owner/Operator Guidance Document (February 1999). In Colorado,assessment of petroleum releases is based on the identification of contaminated media (soil, groundwater,vapors), and determining and assessing the most likely pathways of exposure as follows:

Surficial soil - direct contact with contaminated soil via exposure to skin, ingestion orinhalation of vapors

Subsurface soil - leaching to groundwater

Soil vapor to indoor air - inhalation of vapors emanating from soil

Groundwater to indoor air - inhalation of vapors emanating from groundwater

Groundwater ingestion

The potential for human exposure to petroleum contaminants via these pathways at potential receptor sitessuch as surface water, groundwater, water supply wells, structures, utilities and sensitive environments isassessed. The process and regulatory criteria are based on a risk-based approach using Risk-BasedScreening Levels (RBSLs) for the Chemicals of Concern (COCs). The RBSLs were determined by OPSspecific to the environment most typical of Colorado. The extent of soil contamination must be definedboth horizontally and vertically (to the water table) within and surrounding the source area. The extent ofgroundwater contamination must be defined by monitoring wells placed up gradient, down gradient andcross-gradient of the source area and within the source area. OPS is concerned with evaluating potentialimpacts to nearby receptors, such as residences or businesses, that do not dispense petroleum fuels.Additionally, assessment of soil vapors may be required if the contamination is found to extend to or underany of these structures at concentrations that exceed the groundwater to indoor air RBSLs.

Assessment of petroleum releases in Colorado must define the extent of the COCs - benzene, toluene, ethyl

benzene and total xylenes (BTEX) and total petroleum hydrocarbon (TPH) in soil, BTEX in groundwater,and benzene in soil vapor. These COCs must be defined to levels at or below the OPS RBSLs and TPHthreshold for soil (equal to 500 mg/Kg), the RBSLs for BTEX in groundwater (equal to the EnvironmentalProtection Agency Maximum Contaminant Levels for BTEX) and the OPS RBSL for benzene in soilvapor. Table 1 provides the RBSLs for the various exposure pathways considered by OPS.

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Table 1

Tier 1 Risk-Based Screening Levels (RBSLs)

Media ExposurePathway

Land Use Benzene Toluene Ethylbenzene

Xylenes

Surficial

Soil(mg/kg)

Ingestion,

dermal,inhalation

Residential

Industrial

4.1

12

4,100

28,000

2,100

15,000

36,000

250,000

SubsurfaceSoil(mg/kg)

Leachate togroundwater

N/A 0.26 170 200 1,900

Soil Vapor(g/m3)

Indoor airinhalation

Residential

Industrial

2,700

35,000

>VP*

>VP*

>VP*

>VP*

>VP*

>VP*

Groundwater(mg/l)

Indoor airinhalation

Residential

Industrial

0.015

0.39

6.9

490

18

>Sol**

14

>Sol**

Groundwater(mg/l)

Groundwateringestion

N/A 0.005 1.0 0.68 10

* >VP denotes that even at a concentration equal to the vapor pressure of the chemical, a hazard quotient of1 is not exceeded.

**>Sol denotes that even at a concentration equal to the solubility of the chemical, a hazard quotient of 1 isnot exceeded.

Assessment requirements follow standard industry practices for soil sampling, monitoring wellconstruction, groundwater sampling and water level and/or phase-separated petroleum hydrocarbon (PSPH)measurements. Site-specific data are required for calculating hydraulic conductivity using slug tests orpumping tests. Determination of the groundwater flow direction from a water level contour map isrequired, along with calculation of the groundwater flow velocity. Additional soil and aquifercharacteristics may be collected and used (fraction organic carbon, bulk density, porosity, etc.) if site

specific RBSLs for soil using a Tier 1A or Tier 2 model will be determined, or if a groundwater flow andtransport model will be used.

The risk-based approach adopted by OPS allows the calculation of site-specific RBSLs for soil for thevarious exposure pathways, based on site-specific conditions and risk using either the Tier 1A or Tier 2models. The Tier 1A model is a simple analytical model that assumes the contaminated soil is in contactwith groundwater. The Tier 2 model is a more complex numerical model that allows for separationbetween the contaminated soil and the groundwater. If the site assessment data demonstrates conditions atthe site are less conservative than those considered by OPS in the calculation of the soil RBSLs, potentiallyhigher RBSLs could be calculated for the site, thus allowing soil with higher concentrations of the COCs toremain onsite. Likewise, by using a numerical groundwater fate and transport model to evaluate risk, if sitespecific data are used in the model and the model demonstrates that the COCs in groundwater will notimpact the property boundary (or another closer receptor), closure of the site may be possible with

groundwater concentrations exceeding the RBSLs.

Assessment Results

As part of the assessment required by OPS, a total of sixteen direct-push sample points, eighteenmonitoring wells and three vapor monitoring points were installed and sampled. Water for the MaybellStore and irrigation, supplied by two different wells (Store Well and Irrigation Well) installed into a deeperaquifer were also sampled. Results of monitoring and sampling these locations indicated the following:

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1. Groundwater flow is most often to the northeast. However, when the irrigation canal is running,

occasional flow to due north has been observed. The groundwater gradient is estimated to be0.003 ft/ft.

2. Groundwater is at its highest level in May after the irrigation canal begins to flow and snowmelthas already caused the water table to rise. Depth to water has been observed as little as 1.34 ftbelow ground surface during this time period as irrigation can cause a 5-6 ft rise in groundwatertable elevation.

3. In general, near surface soils encountered during the investigation are silty sand with a claycontent that often increases with depth. Below the silty sand surface, silty sandy clay and claylayers ranging in thickness from 0.5 to 5 feet were observed. At approximately 5-8 feet belowground surface, sandy gravel was encountered. Sandy gravel was observed extending to themaximum depth explored (15 ft) at all locations.

4. Impacts of petroleum hydrocarbons are generally found in a narrow fan shape emanating from thesource area near well MW-7 extending to the north at well MW-13 and the northeast at well MW-1. The maximum adsorbed benzene concentration found in a soil sample was near the source areaat MW-7 (30 mg/kg benzene and 774 mg/kg BTEX). The maximum dissolved benzeneconcentration (1,500 g/l) and BTEX (7,200 g/l) was found in groundwater collected from wellMW-5. Vapor samples were collected and have undergone laboratory analysis but have yieldedonly non-detectable results. A copy of a BTEX, TPH, & MTBE in Groundwater Map (Figure 1)

follows and reflects pre-planting concentrations of these parameters.5. The on-site Store water supply and Irrigation wells extend to a deeper aquifer and are not impacted

by the hydrocarbon release.6. The area impacted by dissolved BTEX in groundwater is approximately of an acre. A large

smear zone created by wide fluctuations in water table elevation has likely contributed to soilimpacts that approximate acre in size.

Corrective Action Plan

The OPS corrective action process is based on the preparation and approval of a Corrective Action Plan(CAP). The CAP presents and compares the technical and economic feasibility of a minimum of threeremedial methods that may be applicable for remediation of soil and groundwater (and vapor if necessary)at the site. Pilot testing of the most feasible method is required unless other reliable information

confirming the success of the chosen method is available. If pilot testing is successful and remediationobjectives are predicted to be met within a reasonable time frame and with reasonable costs, OPS willapprove the CAP. Following CAP implementation, monitoring of groundwater (and vapor if necessary)and soil sampling is performed to observe the success of the selected remedial method. If the expecteddecreases of the concentrations of the COCs in soil, groundwater and vapor quality are not observed, aCAP modification may be requested for enhancements to the selected remedial method, or for analternative remedial method to be proposed.

The use of innovative new technologies, such as Phytoremediation, for the remediation of petroleumreleases is encouraged by OPS. This is especially true when the technology has been shown to be bothtechnically and economically feasible, ultimately resulting in savings to the Colorado Petroleum StorageTank Reimbursement Fund (the Fund). The Fund provides reimbursement to owners/operators of OPSregulated petroleum storage facilities where a release has occurred and the owner/operator is performing

the remediation. The site owner at Maybell has been determined eligible to receive reimbursement fromthe Fund.

Due to the shallow groundwater table, soil vapor extraction was not considered a viable remedialalternative. Air sparging, although technically feasible, would likely cause a concern for fugitivehydrocarbon vapors impacting the Maybell Store, the elementary school, or other nearby public buildings.Thus, two mainstream remedial approaches to site restoration were eliminated from consideration.

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At Maybell, the remedial methods considered in the original CAP were enhanced bioremediation using

oxygen release compound (ORC) ($350,000) or biosparging ($175,000), excavation and disposal ofcontaminated soil with groundwater pumping and treatment ($236,000) and phytoremediation ($200,000).Phytoremediation was determined to be the most technically and economically feasible method. OPSdisapproved the original CAP because no pilot study confirming the likely success of the selected remedialoption had been performed. In addition, OPS knew of no other petroleum sites in the state of Colorado that

had intentionally used phytoremediation as a remediation method. Earlier, OPS had been introduced to Dr.Anu Ramaswami at the University of Colorado at Denver (UCD) who, along with graduate students, wasperforming research related to remediation of petroleum hydrocarbons using phytoremediation. OPS sawan opportunity to assist with Dr. Ramaswamis research and enable a pilot test of a potentially technicallyand economically effective remediation method. OPS requested the site owner to contact Dr. Ramaswamiabout performing a pilot investigation of the technical feasibility of phytoremediation. Thus the resultingpilot test ensued.

Pilot Test

Phytoremediation using poplar trees had been proposed in the original CAP. However, a literature searchindicated that although much information is available on BTEX degradation in the rhizosphere of grasses,not much information detailed the interaction of BTEX compounds with poplar trees, either in terms oftoxicity of BTEX compounds to the growth of the poplar tree, or a quantitative assessment of the degree of

BTEX uptake by poplar trees. Because of the above data needs, a pilot scale was initiated at the UCD CivilEngineering Department to assess the effectiveness of BTEX phytoremediation test using poplar trees. Theobjective of pilot test was to:

Investigate if BTEX is toxic to poplar trees at the levels found at the site;

Conduct a hydroponic test to evaluate plant-BTEX interaction parameters; and,

Conduct a preliminary field assessment on existing trees at the site to evaluate the effect ofphytoremediation at this site.

The first phase of the pilot test consisted of a toxicity assessment, which showed that water containing mid-levels (700 g/l) to high levels (1400 g/l) of each of the BTEX compounds did not adversely affect thegrowth of poplar tree saplings over a 2 month period (See Figure 2). These results indicate that poplar treescan effectively be used for phytoremediation of BTEX plumes at 1400 g/l concentration levels.

Figure 2

Average increase in stem diameter of Poplars exposed to BTEX irrigation water

The second phase of the study quantified the degree of uptake of BTEX by poplar saplings (Populusdeltoids x-nigra), separating active plant uptake of BTEX from passive volatilization losses. Phase 2studies utilized hydroponic systems with initial BTEX concentrations in water of approximately 3000 ppb.Results of Phase 2 tests indicated more than 90% removal of BTEX mass from water in planted systems

0.0000

0.0200

0.0400

0.0600

0.0800

0.1000

0.1200

0.1400

0.1600

Control Mid Level High Level

IncreaseinDiameter(inches

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over a 1 week test period, compared with unplanted control systems that lost approximately 50% BTEXmass due to volatilization (See Figure 3). A graphical technique (Ramaswami and Rubin, 2001) showedgood correlation between the mass of BTEX removed from water and the volume of water transpired by thepoplar saplings, from which the Transpiration Stream Concentration Factor (TSCF) was computed. TheTSCF indicates the ratio of BTEX concentration in the plant transpiration water to that in groundwater.Favorable TSCFs ranging from 0.66 to 0.92 were obtained for three of the BTEX compounds indicatingthat plants uptake BTEX at efficiencies ranging from 66% to 92% from the surrounding waters.

The third phase of the study was a field site visit to quantify typical poplar tree transpiration rates in thehigh mesa conditions of Maybell, CO and to assess movement of BTEX from groundwater into treescurrently existing on site. Based on 4 days of data collected using a Dynamax TDP Flow Velocity meterin August, 2001 the average transpiration rate of a young poplar tree (2.5 inch trunk diameter) at theMaybell site was observed to be approximately 7 Liters per day. Groundwater samples from wells MW-5and MW-7, along with vegetation in the vicinity of these wells, werealso screened to assess current BTEXlevels. Low-levels of BTEX (100 g/l) were observed in vegetation, a favorable indicator forphytoremediation since BTEX uptake and degradation by plants appears to be occurring already at the site.

With the available data on transpiration rates together with the TSCF for Benzene which was found to be0.9 (See Phase 2), a rough computation of the uptake rate of benzene by trees was made. Assuming a 90%reduction in groundwater benzene is required down-gradient of Well MW-7, the time for achieving such a

degree of reduction can be estimated as:

dVolumeAquiferunitperRateionTranspiratTSCF

NeededTime 4001)9.01ln(

=

=

The above computation assumes average transpiration rates by young poplar trees of 10 L water per day, aspacing of 1.5 meters between trees and an average aquifer thickness of 2 meters, with porosity of 0.35.The active growing season in Maybell was assumed to be 100 days, hence an average of 4 years is requiredto reduce groundwater benzene levels from the current 250 g/l to 25 g/l (90 % removal). The aboveestimate of time required for 90 % benzene removal is based upon tree transpiration alone, with theassumptions stated above. It is anticipated that, in addition to plant activity, microbial degradation ofbenzene as well as volatilization losses will also contribute to benzene removal from groundwater, whilesorption may sequester benzene in soil. Thus, the UCD pilot test provided information on key mechanisms

affecting phytoremediation of BTEX at the Maybell site.

Figure 3

Removal of BTEX from water by poplar saplings tested in a hydroponic system

Final BTEX Aqueous Concentrations

0

500

1000

1500

2000

2500

3000

3500

4000

Initial Control Plant

Concentration(ug/L)

Benzene

Toluene

Ethylbenzene

o-Xylene

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Implementation

A second CAP was submitted to OPS recommending phytoremediation, with the results of the successfulpilot test included. Implementation costs were estimated at $207,000 including the pilot test, with time tocleanup estimated to be 3 to 5 years. OPS approved this CAP on April 19, 2002 and the CAP wasimplemented during the summer of 2002.

Tree Acquisition

Because of the liability associated with non-approved purchases for Fund reimbursement, the purchase ofthe saplings could not proceed until OPS approved the CAP. This reality limited tree acquisition options.Further, the window of opportunity to plant and establish the trees in 2002 required their expeditedpurchase. Contacts with the Colorado State Forester, Colorado Nurserymens Association, and othersources provided trees that would result in higher expenses or delayed planting. Ultimately, a commercialgrower based in Montana was identified with a selection of available Poplar trees that would be suitable foruse in Maybell, CO.

Three hundred dormant Lombardy Poplar (Populus x Nigra Italica) trees were purchased and delivered tothe site on May 31, 2002. Lombardy Poplars were selected due to their perceived ability to easilyacclimate to the Maybell environment, overall tree size, quantity of available trees, and total cost. The trees

were bare-root, of conservation grade (not aesthetic grade), and ranged in size from approximately 1.5 to 4feet in height (height of the above ground portion of the tree and thus does not include the root system).The trees were removed from their shipping container and placed in buckets of water overnight.

Tree Planting and Layout

On June 1, the trees were planted in an pattern that encompassed the BTEX impacted area. The attachedExisting and New Trees Map (Figure 4) shows the approximate location of all trees located on the MaybellStore site. The saplings were planted in a matrix containing 24 north-south columns and 17 east-west rows.Trees were planted on ten foot centers until the majority of the impacted area was occupied. The drivewayisland in the center of the property was not planted due to limitations presented by existing trees and trafficpatterns of large vehicles using the driveway. After the available planting area was filled using ten footcenters, certain areas were planted using five foot centers. These more densely planted areas include the

portion of the site near the original release (the former pump island location near MW-7 and immediatelynorth), the vicinity just north of well MW-5, and along the south edge of the driveway near well MW-6.Areas selected for denser planting correspond to historic data suggesting higher concentrations of dissolvedhydrocarbons.

The trees were planted using an eight-inch auger mounted on the rear of a tractor. The auger created athree foot deep hole which had remaining loose soil removed by hand using a standard post-hole digger.One tree was placed into each hole at an elevation such that a minimum of one foot of the sapling wasabove ground surface (this procedure maximized the amount of the tree located below ground surfaceallowing for greater potential rooting). The hole was then backfilled by hand to near the original groundsurface with native material previously removed from the hole. After mild compaction of soil into the hole,a moat was formed around the base of the tree and a layer of wood-chip mulch was placed on top of thesoil, and the location thoroughly irrigated. The Tree Planting Diagram attached as Figure 5 illustrates the

planting method.

Tree Maintenance

Approximately one week after planting, leaf buds began to break and shoot development occurred.Watering of the saplings was performed by the owner using a regular garden hose. This task requiredapproximately 4 hours per watering event. Watering during the summer of 2002 was conducted on an as-needed basis and was performed 26 out of 30 days in June, 19 out of 31 days in July, 14 out of 31 days in

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August, and 4 out of 30 days in September. Thus, water was provided the saplings 63 out of a possible 122days during the first growing season.

Grass and weeds were prevented from competing with the saplings by the use of mulch and regularmowing. Hand mowing was performed by the owner on an as-needed basis. Other maintenance issueshave included mending trees knocked over by children and adding mulch when necessary.

Economics

The economics of most UST projects in CO are dominated by the rules, regulations, and policies of theFund. Reimbursement by the Fund requires that the owner comply with various requirements (i.e.registration of tanks, leak detection, reporting, etc). Non-compliance with regulations results in establishedpenalties that reduce reimbursement amounts or may prohibit reimbursement altogether. The owner of the

Maybell Store was determined to be eligible for reimbursement with a 10% reduction in all requests due tothe lack of environmental oversight during the original UST removal phase.

The Fund allows for owner/applicants to perform work on projects and be reimbursed for their timeprovided that the work would have to be conducted by the consultant or other contractor anyway. Becausethe owner is retired and has the time and ability to perform the work, the Fund has been utilized to buyowner project labor at favorable rates rather than opting for mechanical means or other labor reducingalternatives. Some tasks that are owner performed include tree planting, site inspections, tree irrigation,mowing, and groundwater elevation monitoring.

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Since the cost to assess and perform the remedial investigation/feasibility study process differs with everyproject, these costs will not be discussed. However, other costs including the pilot study, cost of trees,planting and other first year costs are shown below in Table 2. Future costs associated with the project areshown in Table 3. The cost of water has not been included in either table.

Table 2

Actual First Year Costs

Item Units Quantity Rate ($) Subtotal ($)

Pilot Study Total 1 15,000 15,000

Purchase Trees

300 Trees w/shipping Total 1 250 250

Planting

Labor Hours 48 15 720

Tractor w/operator Hours 16 55 880

Mulch Total 3 50 150

Tree Maintenance

Watering Hours 250 15 3,750

Other Hours 50 15 750

Total = 21,500

Table 3

Estimate of Future Costs

Operations & Maintenance Items Units Quantity Rate ($) Subtotal ($)

Utilities Year 5 350 1,750

Site Maintenance

Labor Months 20 750 15,000

Equipment/Materials Months 20 150 3,000

Sampling & Analysis

Sampling Quarters 16 3,000 48,000

Analytical Quarters 16 2,500 40,000Reporting

Labor Quarters 16 3,000 48,000

Disposal Costs

Miscellaneous Total 1 2,500 2,500

Water Gallons 1 500 500

System Closure

Labor Hours 200 60 12,000

Well Abandonment Wells 27 300 8,100

Tree Removal total 1 2,000 2,000

Total = 180,850

Preliminary Findings

A total of 17 newly planted trees were selected for monitoring of growth in overall height. Trees wereselected by random except for an effort to scatter the monitoring points throughout the planted area.Results indicate that an average of 16.65 inches of growth in total tree height occurred from 6/6/02 to9/2/02. The results of tree growth monitoring for the 2002 growing season through bud break in early May2003 are shown in Table 4. Measurements collected on May 2, 2003 show shorter trees than the previousSeptember due to deer damage.

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Table 4

Tree Growth Data

(data reported as inches of tree height above ground surface)

Tree IDNumber

Treeheight on6/6/2002

change Treeheight on7/30/2002

change Treeheight on9/2/2002

change TreeHeight on5/2/2003

1 19 11 30 7 37 -5 32

2 17.5 10.5 28 23 51 -13.5 37.5

3 24 -12 12 0 12 -1.5 10.5

4 34 16 50 16 66 -3 63

5 11.75 4.25 16 36 52 -4 48

6 18 20 38 7 45 -9 36

7 26 -9 17 13 30 -1 29

8 25 15 40 9.5 49.5 -2 47.5

9 22 12 34 6 40 -1 39

10 11.5 9.5 21 5.5 26.5 -3.5 23

11 23 9 32 3 35 -5.5 29.5

12 21.75 11.25 33 1 34 -1 33

13 26.5 5.5 32 1.5 33.5 NA Dead14 34 9 43 5 48 -2 46

15 29.5 11.5 41 4.5 45.5 -3 42.5

16 19.75 11.25 31 5 36 -3.5 32.5

17 27.75 5.25 33 0 33 -2.5 30.5

Average 23 +8.24 31.24 +8.41 39.65 -3.43 36.22

NA = not applicable

Groundwater sampling and analyses conducted just prior to planting and quarterly thereafter have yet toindicate a reduction in BTEX concentrations due to phytoremediation. It is anticipated that groundwatersamples collected during the 2003 growing season will provide the necessary data to begin to evaluate thesuccess of the project. This evaluation will compare the effects of phytoremediation against the estimatedrate of natural attenuation established prior to planting.

The progress of phytoremediation at Maybell is being closely monitored by OPS. If results indicate themethod is successful and cost effective, phytoremediation will potentially have applicability at otherlocations within the State of Colorado.

References:

Colorado Department of Labor and Employment, Division of Oil and Public Safety. February 1999. Petroleum Storage TankOwner/Operator Guidance Document. Denver, Colorado.Summit Environmental Services, 2000, Site Characterization Report,Summit Environmental Services, 2001, Corrective Action PlanSummit Environmental Services, 2002, Corrective Action Plan RevisedA. Ramaswami, L. Johnson, K. Morrison, 2001,Phytoremediation Pilot Test for the Maybell Site, Dept of Civil Engineering,University of Colorado-DenverE. Rubin & A. Ramaswami, 2000,Phytoremediation of Methyl Tertiary Butyl Ether (MTBE), Dept of Civil Engineering, University ofColorado-DenverC. Frick, R. Farrell, & J. Germida, December 29, 1999,Assessment of Phytoremediation as an In-Situ Technique for Cleaning OilContaminated Sites, Petroleum Technology Alliance of CanadaPhytoremediation Resource Guide USEPA, EPA 542-B-99-003, 1999Underground Tank Technology Update, March/April 2001,Phytoremediation Basics, Vol 15, No 2Personal Contacts by Mr. Fus with Dr. Anu Ramaswami, Assistant Professor, Dept of Civil Engineering, University of CO-Denver;Mr. Randy Moench, CO Dept of Forestry, Nursery Manager, Colorado State University Campus, Ft. Collins, CO; Ms. Shary Draper,Soil Conservation Service, Craig, CO; and, various members of the Colorado Nursery Association.

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Author Biographies and Contact Information

Mr. Fus directs corporate engineering services and manages the Portland, OR office for Higgins andAssociates, LLC.Edward J. Fus, PEHiggins and Associates, LLC Higgins and Associates, LLC8749 NW Marshall Street 8200 S. Akron Street, Suite 117Portland, OR 97229 Centennial, CO 80112(503) 296-7859 voice (303) 708-9846 voice(503) 296-0499 fax (303) 708-9848 faxefus@higgins-and-associates.com

Ms. Bral is an Environmental Protection Specialist with the State of Colorados Division of Oil & PublicSafety.Jane M. Bral, PGColorado Department of Labor and Employment-Division of Oil & Public Safety1515 Arapahoe StreetTower 3, Suite 610Denver, CO 80202-2117(303) 318-8543 voice

(303) 318-8546 faxjane.bral@state.co.us

Dr. Ramaswami is a Civil Engineering professor at the University of Colorado, Denver and is currentlycompleting a book on phytoremediation.Anu Ramaswami, PhDAssistant Professor of Environmental EngineeringDepartment of Civil EngineeringUniversity of Colorado, DenverCampus Box 113, PO Box 173364Denver, CO 80217(303) 556-4734 voice(303)556-2368 - fax

aramaswa@carbon.cudenver.edu

Acknowledgement:

We are grateful for the help of Lisa Johnson who assisted Dr. Ramaswami during the completion of thepilot study. Ms. Johnson has since been employed by the USEPA Region VIII.