remediation of heavy metal-contaminated farm soil using turnover and attenuation method guided with...

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ENVIRONMENTAL ENGINEERING SCIENCEVolume 25, Number 1, 2008© Mary Ann Liebert, Inc.DOI: 10.1089/ees.2006.0183

Remediation of Heavy Metal-Contaminated Farm Soil UsingTurnover and Attenuation Method Guided with a Sustainable

Management Framework

Ching-Ho Chen* and Ing-Jia Chiou

Department of Civil and Environmental EngineeringNanya Institute of Technology

Jungli, Taoyuan County, Taiwan, Republic of China

ABSTRACT

Remediation for contaminated farm soil had become an important task in Taiwan for the authorities becausemany farms had been contaminated with heavy metals due to illegal discharges of industrial wastewater. Acomprehensive and effective remediation methodology for heavy metal-contaminated farm soil was presentedin Taiwan, which integrated assessment of soil contamination and environmental characteristics, remediationtechnology, and performance assessment. Turnover and attenuation method was chosen and applied in this studybased on assessment criteria of social, technological, economical, and environmental feasibilities. However,there were some difficulties needed to be solved when turnover and attenuation method was applied becauseof great variation of environmental characteristics in Taiwan. A sustainable management framework based onManaging for Results method was therefore developed for guiding the accomplishment of the remediation tasks.Three contaminated sites had been successfully completed for the remediation tasks in this study by using theproposed integral methodology. The distribution of heavy metal concentrations in soils and environmental char-acteristics had been predicted using the proposed rule for determining adequate number and locations of sam-pling points and used to calculate the excavation depth for each area. The results of performance measurementsshowed that the farm lands had recovered their agricultural utility to meet the landowners’ request, heavy metalconcentrations in the soils had been reduced with proper attenuation ratio, remediation cost had been controlledin the range of the budget, and heavy metal concentrations in the soils and crops after remediation can meetthe regulatory limits. The comprehensive and effective remediation methodology could be employed to assurethe effectiveness and efficiency of the remediation tasks based on the principles of sustainable development,as observed from the analytical results of the three contaminated cases.

Key words: soil contamination and remediation; heavy metal; turnover and attenuation; managing for results;sustainable development

*Corresponding author: Department of Civil and Environmental Engineering, Nanya Institute of Technology, 414, Sec. 3, Chung-Shang E. Rd., Jungli, Taoyuan 320, Taiwan, R.O.C. Phone: 886-3-4361070 ext. 5141, 3303; Fax: 886-3-4563674; E-mail:[email protected]

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INTRODUCTION

LAND IS AN IMPORTANT RESOURCE for the subsistence anddevelopment of human beings. Land resources should

be allocated and used effectively to achieve sustainable use.Noncontaminated land should be protected and conserved,and contaminated land should be remedied and recovered.In Taiwan, due to the overdevelopment of the industry andtechnology, some factories illegally discharged untreatedheavy metal wastewater into nearby irrigation canals, con-taminating soil in many farms with heavy metal leading thatthe lands cannot normally be used by farmers. Heavy metalcontaminated soil was first reported in 1983. About 303hectares of farmland which had been contaminated by theheavy metal was found by 2003 [Taiwan Environmental Pro-tection Administration (TEPA), 2004].

Few control measures can be used to solve the problemsof soil contamination during the period, since the regula-tions for soil contamination control had not been legislatedby 2000. Meanwhile, farmers owning contaminated land fre-quently ask the authorities to recover the original use of theirlands. Because the problems, including farmers’ large areasof useless land, and the effect of land contamination on hu-man health and secondary contamination urgently needing

to be solved, the Taiwan Environmental Protection Admin-istration (TEPA) planned to start the first remediation taskfor heavy metal-contaminated farm soil in 1998, even if therelevant laws had not yet been legislated. The main purposeof this study is therefore to develop a comprehensive andeffective methodology which can be used to systematicallyaccomplish the remediation tasks.

The major concepts of remediation for contaminated soilin this study are shown in Fig. 1. Many remediation facili-ties are not suitable to be used because most of the farmlands were divided into small areas and contained lots ofclays, gravels, and groundwater in Taiwan. Furthermore,heavy metal concentrations and environmental characteris-tics (including soil characteristics, thickness of soil layer,gravel level, and groundwater flow) of each area in reme-diation sites are quite different. Effectiveness of remedia-tion tasks will be influenced by the foresaid factors. Hence,a systematical and effective sampling and analysis for heavymetal concentrations of the soil should be carried out first.Moreover, an investigation and assessment of environmen-tal characteristics are also necessary. Assessment results ofarea and degree of soil contamination can be used as a ba-sis to generate remediation strategies and plans. Precise pre-diction for distribution of heavy metal concentrations is im-

Figure 1. Major concepts of remediation of contaminated soil.

REMEDIATION OF HEAVY METAL-CONTAMINATED FARM SOIL

ENVIRON ENG SCI, VOL. 25, NO. 1, 2008

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portant for increasing effectiveness of remediation tasks. Arule for determining the adequate number and locations ofsampling points is necessary for decreasing the cost and timefor excessive sampling and investigation.

The farm lands contaminated with lower concentrations ofheavy metals (Cd � 5 mg/kg and Pb � 200 mg/kg) in Tai-wan were selected to be remedied first. The major remedia-tion methods for soil contamination include: washing, flush-ing, extraction, immobilization, degradation, attenuation, andreduction of volatilization [United States Environmental Pro-tection Agency (U.S. EPA), 1989; Rivett et al., 2002; Virku-tyte, 2002; Khan et al., 2004; Federal Remediation Tech-nologies Roundtable (FRTR), 2006]. The turnover andattenuation method was chosen and applied in this study basedon the assessment results of social, technological, economi-cal, and environmental feasibilities compared with other re-mediation methods, listed in Table 1. The remediation costof turnover and attenuation method is lower than those ofother remediation methods. Variations of soil characteristicsafter remediation by the turnover and attenuation method areless than those by other remediation methods. However, thismethod is suitable for low-contaminated land with enoughthickness of clean soil layer, indicating that this method can-not be applied for high-contaminated or thin-soil-layer lands.

The remediation tasks should be done effectively and effi-ciently so as to let the results be accepted by the landownersand the public after the remediation method was determined.Furthermore, remediation strategies and plans should be cor-rect and complete to decrease the variations of heavy metalconcentrations and environmental characteristics in each con-taminated land. Finally, remediation performance is assessedand used to manage remediation tasks and report to the pub-lic. Therefore, a management framework integrating contam-ination assessment, remediation technology, and performance

assessment is necessary for guiding remediation tasks. Thisstudy conducted Managing for Results (MFR) method to de-velop a sustainable management framework to be used to ac-complish remediation tasks effectively and efficiently.

MFR is a future-oriented process that emphasizes de-ployment of resources to achieve meaningful results. Thedesired results are based upon identified needs of customersand stakeholders, and are used to improve the quality andcost-effectiveness of programs and services (Maryland StateGovernment, 1997). MFR was proposed by Drucker (1964),and was initially employed in enterprise management. In the1980s, MFR had become part of a global movement to makegovernment more efficient, effective, and accountable.Many developed countries, including the United States,United Kingdom, France and Canada, have accepted MFRas a good management practice [Organization for EconomicCooperation and Development (OECD), 1997; Office of theCity Auditor Portland Oregon, 2002]. In the United States,the Government Performance and Results Act (GPRA) waslegislated in 1993. Under the act, most agencies and localgovernments were to develop multiyear strategic plans, an-nual performance plans, and annual performance reports[United States General Accounting Office (USGAO) 1997;Maxwell School of Citizenship and Public Affairs of Syra-cuse University, 2002]. The United States EnvironmentalProtection Agency (U.S. EPA) also used MFR for manyagency-wide, national, and regional programs (USGAO,2001; U.S. EPA, 2002).

The first remediation task of this study was successfullycompleted in 1999 before the regulations were legislated,which was also the first remediation case in Taiwan. TheSoil and Groundwater Pollution Remediation Act was thenlegislated in the next year. This study continuously improvedthe methodology based on the Act, and used it in anothertwo contaminated sites for more verification in 2003–2004.The detailed methodology and results for the three remedi-ation cases are described below.

METHODOLOGY

The turnover and attenuation method is to mix the con-taminated soil about 30 cm below the surface with the cleanor low-contaminated soil in deeper layers, to remedy thelands with low heavy metal concentrations. There are somedifficulties needed to be solved when the turnover and at-tenuation method is applied in Taiwan: (1) there was no ex-perimentally feasible procedure that can be applied, becausethis study carried out the first remediation task in Taiwan;(2) the theoretical excavation depth is determined by themaximal ratio of heavy metal concentrations, but gravellevel is possibly higher than the bottom line of the theoret-ical excavation depth; (3) this study requested that contam-inated soil cannot be delivered out of the remediation site

Table 1. Assessment results of feasibilities of the turnover andattenuation method for the low concentration soil heavy metalcontamination.

Feasibility Assessment result of feasibility

Society The method slightly influences soil characteristics from the comparison with the other method. The farm lands can be easily recovered their agricultural utility and the landowners’ request can be met.

Technology The method can reduce the concentrations of heavy metals in soil since there is enough thickness of clean soil layer in remediation site to attenuate contaminated soil.

Economy Remediation cost for the method can be lowerthan those for other remediation methods.

Environment The concentrations of heavy metals in soils and crops after remediation can meet the regulatory limits.

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to avoid the secondary pollution, and attenuation soil shouldbe provided from the remediation site; (4) many remedia-tion facilities cannot be used because of topographic char-acteristics of farm lands in Taiwan.

This study developed a sustainable management frame-work for remediation of soil contaminated by heavy metalswith the turnover and attenuation method to overcome theabove difficulties, illustrated in Fig. 2. This framework con-sists of planning, implementation, and control stages, de-veloped based on the methods of MFR, management think-ing, and system analysis. Methods used in this study aredescribed with the framework as follows.

Planning stage

Identification of the system for the remediation of con-taminated soil. The system boundary can be identified based

on the area where the concentration is higher than the reg-ulative standards. The major components of the system iden-tified in this work include the soil, heavy metals, drainagecanals, and other substances on the land, such as plants andgravels.

The precise data of area and degree of soil contaminationare important bases for designing remediation strategies andaction plans. However, detailed sampling requires a greatdeal of cost and time. Therefore, an effective assessment ofarea and degree of soil contamination should be carried outin this step. The Kriging method has been applied in manyfields, including the spatial interpolation of pollutants incontaminated soil (Samra and Gill, 1993; Stein et al., 1995;Chien et al., 1997; Juang et al., 1999). However, the distri-bution of heavy metal concentrations in contaminated soilin Taiwan usually exhibits great variation. This phenome-

Figure 2. Sustainable management framework for remediation of heavy metal-contaminated farm soil.



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non shows that the predicted data of the area and degree ofsoil contamination by the traditional sampling method withordinary Kriging estimation are usually different from theactual condition. Hence, this study designed a procedure,shown in Fig. 3, to identify the adequate number and loca-tions for sampling based on technological and economicalconsiderations. Soil samples are taken in each 500-m2 gridsquare at first. Statistical data for heavy metal concentra-tions of the samples are used with the Kriging method topredict heavy metal concentrations in the contamination site.Three semivariogram models were tested in this study, in-cluding the exponential, spherical, and Gaussian models.The crossverification results indicated that the exponentialmodel was more adequate for this study than spherical and

Gaussian models. Different sample number, depth of soillayer, topography, and water flows were used to analyze andverify their influences on the precision of predicted resultsof heavy metal concentrations. Finally, the rule for deter-mining adequate number and locations of sampling pointscan be identified as follows.

The remediation site was divided into several divisionsbased on irrigation canals. If a division was larger than 2hectares, 12 sampling points would be suggested. Six andthree sampling points would be suggested for the divisionsof 1–2 hectares and less than 1 hectare, respectively. Addi-tionally, the number of sampling points should be increasedif the heavy metal concentration was higher than five timesthe regulatory limit. The locations of sampling points were

Figure 3. Procedure for developing the rule for determining adequate number and locations of sampling points.

determined by the location of the withdrawing point, waterflow line, and land shape. The area around the withdrawingpoint and water flow line were assigned more samplingpoints than the side areas of the land, because the heavymetal pollutants were carried by the irrigation water. Theanalytical results for sampling cost illustrated that the num-ber and locations of sampling points suggested in this studycan be used to predict the distribution of heavy metal con-centrations with a lower cost.

Soil characteristics, thickness of soil layer, gravel level,and groundwater flow were also investigated and assessedto be used to generate remediation strategies. Investigationpoints were preliminarily selected in each 10 � 10 m area.Conceptual description of environmental characteristics incontamination site, shown in Fig. 4, indicates that remedia-tion strategies and plans, including excavation depth anddrainage facility layout, should be carefully designed be-cause the environmental characteristics of the remediationsites are quite varied. Theoretical excavation depth for re-mediation area can be calculated by Equation (1).

H � Max. � 35 (cm) � 1.2 (1)

H: excavation depth (cm)

The ratios of investigated concentrations and regulatorylimits of heavy metal (Cu, Cd, Pb, Zn, Ni, and Cr) are cal-culated, and the highest one is used to determine the theo-retical excavation depth to ensure that the quantity of cleansoil is enough to attenuate all of the heavy metals. The thick-ness of contaminated soil layer was set as 35 cm, and a safetycoefficient of 1.2 was applied in this study. However, the-oretical excavation depth was modified when the actualthickness of soil layer was smaller than the foresaid depth.For example, Fig. 4 shows that thickness of soil layer atpoint 2 (TS2) is smaller than the theoretical excavation depth(Ht). Therefore, the practical excavation depth (Hp) will bedeeper than Ht. When thickness of soil layer at point 1 (TS1)

�Current conc.

(Cu, Cd, Pb, Zn, Ni, Cr)Regulatory limits

(Cu, Cd, Pb, Zn, Ni, Cr)�

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Water quality analysisDrainage

Groundwater flow

Lift pump

Ht � MaxHeavy metals conc. (Cu, Cd, Pb, Zn, Ni, Cr)

Regulatory value (Cu, Cd, Pb, Zn, Ni, Cr)*35(cm)*1.2

Ht : Theoretical excavation depth (cm)

Hp : Practical excavation depth (cm)

TS1 : Thickness of soil layer at point 1 (cm)

TS2 : Thickness of soil layer at point 2 (cm)

Pumping shaft

Gravel level

50cm

1m

TS1

TS2

Hp Ht

Heavy metals contamination area

Figure 4. Conceptual description of environmental characteristics in the contamination site.



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is larger than Hp, this area is verified that can provideenough clean soil to be attenuated. Hence, investigationpoints will be selected to identify the profile of gravel levelto determine practical excavation depth. If thickness of soillayer and gravel level are found with significant variation,more investigation points are also required.

Groundwater flow is also an important impact factor whenremediation tasks are carried out. For example, Fig. 4 illus-trates that groundwater flows from the gravel layer when thearea is excavated to Hp. Groundwater will cause the toomoist soil to be broken, stirred, and mixed. Therefore, pump-ing shafts will be constructed around the remediation areaif groundwater flow is found in the soil layer within the ex-cavation depth. Excessive groundwater that flows into thepumping shafts is removed via lift pumps so as to preventit from influencing the remediation tasks.

Identification of the mission, vision, goal, and objectivesof the remediation based on the principles of sustainable de-velopment. The mission, vision, goal, and objectives givethe remediation an explicit direction to proceed, encourag-ing people to accept its results. They can be identified byfollowing the principles of sustainable development and re-ferring to the public requirements. This study identifies themission as “to remedy the heavy metal contamination to en-sure the sustainable use of land resource.” The vision is “theclean and safe farms.” The goal is “to recover the originalland use of the contaminated farms.” The objectives are: (1)the farm lands can be recovered for their agricultural utilityto meet the landowners’ request as the social objective; (2)heavy metal concentrations in the soils can be reduced withproper attenuation ratio as the technological objective; (3)remediation cost for the method can be controlled in therange of the budget as the economical objective; and (4)heavy metal concentrations in the soils and crops after re-mediation can meet the regulatory limits of environmentalprotection and food safety as the environmental objective.

Strategies planning of remediation based on the objec-tives. This study could consequently designed remediationstrategies in detail based on assessment results of area anddegree of soil contamination and environmental character-istics described in the Identification of the system for theremediation of contaminated soil section (see before) to ef-fectively reduce heavy metal concentrations without exces-sive remediation cost. The required quantity of attenuationsoil and excavation depth for each remediation area is cal-culated based on Equation (1).

However, thicknesses of soil layer in some areas are evensmaller than their required excavation depths, meaning thatthey cannot provide enough attenuation soil. This study there-fore calculated the demands of attenuation soil for such areas.Moreover, this study showed that contaminated soil cannot bedelivered out of the remediation site to avoid the secondary

pollution, and attenuation soil should be provided from the re-mediation site. Consequently, some neighbor areas in the re-mediation site which have been assessed to have enough thick-nesses of soil layer should provide the required attenuation soil.

Using Fig. 4 as an example, the soil layer thickness wasassumed to be 100 cm, which was less than the required ex-cavation depth of 150 cm. The areas of the land and its neigh-bor land were 0.8 and 1.0 hectares, respectively. Hence, thedemand of attenuation soil for the land was:

8,000 m2 � (1.5—1) m � 4,000 m3

The initial excavation depth of the neighbor land (1.0hectare) was 120 cm and the demand of attenuation soil wasprovided from this neighbor land. The practical excavationdepth would therefore become:

(4,000 m3/10,000 m2) � 1.2 m � 1.6 m

Groundwater may flow from the gravel layer and hinder theremediation tasks. Therefore, this study built pumping shaftsaround some remediation areas based on the assessment re-sults of the distribution of the groundwater flow. Adequate liftpumps were used to remove groundwater from the pumpingshafts to avoid the influence of the the groundwater.

Design of action plans of remediation based on the strate-gies. A systematical and practical remediation procedure,shown in Fig. 5, was first developed in Taiwan based on theassessment results of area and degree of soil contaminationand environmental characteristics to overcome the foresaiddifficulties. The surface of the contaminated site was cleanedup first. The drainage canals and settlement tanks were alsobuilt. The resulting waste and wastewater were properlytreated and disposed to prevent secondary contamination.

The contaminated areas was dug to the practical excava-tion depth based on assessment results of area and degreeof soil contamination and environmental characteristics. Thedug soil and gravel were then separated and adjusted. Theearthwork and gravel were backfilled, leveled, and firmlypressed. The soil block was broken, stirred, mixed, andsieved to attenuate the heavy metal concentrations. The pre-liminary verification for heavy metal concentrations wasthen carried out to quickly measure the heavy metal con-centrations in soil and the effect of diluting and mixing. Thenumber of samples was determined based on the assessmentresults of area and degree of soil contamination and envi-ronmental characteristics.

This study designed and applied some special facilities tocarry out remediation tasks by using the turnover and atten-uation method according to the requirement of the remedia-tion procedure and environmental characteristics of each ofthe remediation sites in Taiwan. Lots of clays and gravelswere contained in the remediation site, and the area of eachdivision of the site is small. Therefore, a multifunctional fa-cility for breaking and sieving the soil blocks to improve the

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Figure 5. Remediation procedures developed based on assessment results of area and degree of soil contamination and environmen-tal characteristics.



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efficiency of soil stirring and mixing was designed and ap-plied in this study, shown in Fig. 6 as an example.

When the heavy metal concentrations in the mixed soilcould meet the regulatory limits, the mixed soil was back-filled and firmly pressed layer by layer. The tests of XRF,flatness, and compactness were carried out when the landwas completely backfilled to ensure that the soil character-istics are suitable for cultivation.

The surface of the soil was then turned over and loos-ened. Lime and organic fertilizer were added to improve thesoil fertility. The tests of germination, fertility, and cropplanting were carried out when the foresaid works were doneto ensure the agricultural utility of the land can be recov-ered. The contaminated sites can be remedied via the sys-tematical steps consisting of assessment, remediation, andperformance tests.

Establishment of performance measures of remediationbased on the action plans. This study identified eight indica-tors, listed in Table 2, to assess whether remediation tasks canachieve the expectative results and performance or not. Theseindicators can be classified into five types: input, output, out-come, efficiency, and quality. Furthermore, they can be usedto assess the achievement of objectives in the environmental,social, economical, and technological phases. The followingindicators were used to assess whether the agricultural utili-ties of the farm lands could be recovered or not.

1. Heavy metal concentrations in soils. The concentra-tions of heavy metals after remediation in the soils shouldmeet the regulatory limits announced by the environmental

protection authority in order to allow agricultural utility ofthe remediation farms to be recovered. Heavy metal con-centrations in the soils are measured in two phases: the pre-liminary verification during turnover period, and the verifi-cation executed by impartial organization. The preliminaryverification undertaken by the constructor can adopt the U.S.EPA SW-846 Method 6200 (1998), the portable X-Ray Flu-orescence Analyzer (XRF) method, to quickly measure theeffect of diluting and mixing. The XRF method also matchesthe method stipulated by the TEPA. The sampling methodused by an impartial organization follows TEPA NIEAS102.60B (2001). The remediation standards for the con-centrations of the heavy metals in soil were Cd � 1 mg/kgand Pb � 40 mg/kg before the Soil and Groundwater Pol-lution Remediation Act was legislated. The soil treatmentstandards were announced in 2001 based on the above Act:Cu � 200 mg/kg, Zn � 600 mg/kg, Cr � 250 mg/kg, Ni �200 mg/kg, Cd � 5 mg/kg, and Pb � 500 mg/kg.

2. Compactness. Undesirable changes such as sinking,shrinking, or demoisturizing of the soil after being excavatedand turned over should be avoided to influence agriculturalutility of the remediation farms. The compactness test wasperformed on the spot according to American Society forTesting and Materials (ASTM) D1556 (1984), the sand-conemethod, to ensure that the undesirable changes will not oc-cur. The practical requirement for compactness in cultiva-tion is generally about 80–90%.

3. Flatness. Turnover and attenuation of the soil involvesexcavating a large area of farmland, and therefore changes

Figure 6. Multifunctional facility for breaking and sieving the soil blocks to improve the efficiency of soil stirring and mixing.

the original elevation, flatness, and drainage pathway. Thecanals must be reconstructed and the land must be prop-erly leveled to ensure that the farmlands can normally drainwithout water accumulation after remediation. Flatness testis then undertaken to check whether the farm lands areproperly leveled or not. Water is withdrawn into the farmlands as a horizontal reference for the test. The waterdepths and the drainage pathway were then recorded. Thedifference between the maximal and minimal water depthsin the farm lands after remediation must be less than 10cm, which indicates that irrigation water can be normallydrained.

Germination percentage. Farm lands after remediationshould be suitable for growth of the crops. The germina-tion test was hence carried out after the soil was backfilled.The germination percentage is calculated using formula

(2) in accordance with the standard germination testingmethod of the International Seed Testing Association(ISTA, 2005).

Germination percentage of seeds (%)

� � 100% (2)

This study selected spoon cabbage and Chinese cabbagefor the experiment. The time limit for observing the seedgermination was set to 21 days. This study also employedthree parameters—the initial germination percentage, thetime for highest germination percentage, and the highest ger-mination percentage—to be evaluated with this indicator.The germination percentage of the remedied soils should bemore than 85%, which represents that the remedied soils canbe suitable for growth of the crops.

Number of germinating seedsNumber of seeds for test

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Table 2. Types of performance measure and performance indicators.

Types ofperformancemeasure Indicator Description Objective

Input Remediation cost Cost spent for remediation tasks in Economyeach site (dollar)

Output Remediation areas Areas that have been remedied Environment(hectare)

Outcome Land areas after Areas after remediation which can Environmentremediation which meet meet the following standards (hectare) & Societythe standards and recover (1) Heavy metal concentration in soil Environmentthe agricultural utility (1) (mg/kg): Cd � 1, Pb � 40 (before & Society

(1) 2001); Cu � 200, Zn � 600,(1) Cr � 250, Ni � 200, Cd5, Pb � 500(1) (after 2001)(2) Compactness 80–90% Environment

& Society(3) Flatness (cm) � 10 Environment

& Society(4) Germination percentage �85% Environment

& Society(5) Fertility Environment

& Society(6) Heavy metal concentration in Environment(1) crops (ppm): Cd � 0.5, Hg � 0.5, & Society(1) Pb � 0.2

Efficiency Remediation cost per unit Remediation cost per hectare of land Economyland area (US$/hectare)

Remediation cost per unit Remediation cost per cubic meter of Economysoil volume soil (US$/m3)

Remediation time per unit Days needed for remediation per Societyland area hectare of land (day/hectare)

Quality Acceptance rate of the Acceptance rate of the public for the Societypublic remediation result (%)

Attenuation of heavy Attenuation percentage of heavy Environmentmetal metal concentration (%)



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Fertility. Farm lands after remediation should be fertileto cultivate the crops. However, the fertile, loose, and softsurface soil will be mixed with the poor, sticky, hard, andlow-permeability soil in deep layers. The mixed surface soilmay be hard to cultivate because of insufficiency of phos-phorous and potash as well as low permeability. Hence, thesurface soil was loosened, broken, and added lime and or-ganic fertilizer to improve its fertility. Fertility tests wereundertaken before and after the foresaid works done to ver-ify whether the lands can recover their agricultural utility ornot. The test items are in accordance with recommendationof the Taiwan Council of Agriculture, including pH value,electric conductivity, total organic carbon, nitrogen, phos-phorous, and potassium.

Heavy metal concentrations in crops. The heavy metalconcentrations in the crops that were planted on the reme-died lands should meet the regulatory limits announced bythe food safety authority. Some selected area of the farm-land was planted crops in four continuous stages, and theheavy metal concentrations in the crops were analyzed ac-cording to the method of test for heavy metals in foods—test of cadmium [Taiwan Council of Agriculture (TCOA),2003]. The growth and yield of the tested crops were alsorecorded and compared with those of nearby uncontami-nated farmland. The analyzed results of the concentrationsof cadmium and mercury in the crops should be less than0.5 ppm, and that of lead should be less than 0.2 ppm, whichillustrates that the farm lands can be normally cultivated.

Implementation stage

The action plans are carried out during the implementa-tion stage. Furthermore, the tasks of the control stage arealso undertaken simultaneously to ensure that the remedia-tion results can reach the objectives.

Control stage

The performance measures are tracked, monitored, andreported during the remediation process. The reported per-formance indicator values can be used by the decision mak-ers to evaluate whether the management results for remedi-ation tasks can meet the anticipated goals and objectives.

RESULTS AND DISCUSSION

This study used the turnover and attenuation method withthe proposed sustainable management framework for reme-diation of heavy metal-contaminated farm soil in TaoyuanCounty (Chen et al., 1999), Hsinchu City (Chen et al.,2004a), and Changhua County (Chen et al., 2004b) in Tai-wan, shown in Fig. 7. The applied results are discussed be-low.

Assessment results of area and degree of soil contamination

Sampling and analysis of heavy metal concentrations insoils based on the rule developed as shown in the Identifi-

Figure 7. Locations of the three heavy metal contaminated sites in Taiwan.

cation of the System for the Remediation of ContaminatedSoils section were carried out for the three contaminated ar-eas. The concentration contours were drawn using Surfersoftware (Golden Software Inc., 2004) in this work basedon the above results for each item in each site.

The concentration contours of Cu in the contaminated area

in Hsinchu City, which were sampled in 2003, are shownas an example in Fig. 8. The sampling and analyzing resultsthat TEPA carried out in 2002 were also presented. The farmland on the left and bottom in Fig. 8 could be divided basedon irrigation canals. The area of the foresaid farm land was1.44 hectares, which was between 1 and 2 hectares. The

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Figure 8. Cu concentrations of the contaminated site in Hsinchu City before and after remediation.



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number of sampling points was preliminarily suggested assix, based on the first part of the proposed rule. However,the highest concentration was 1,480 mg/kg in this case,which was higher than five times the regulatory limit (200mg/kg), meaning that more sampling points were required.The adequate number of sampling points was therefore de-

termined as nine based on the second part of the proposedrule. Five sampling points were selected around the with-drawing point and water flow line, while four samplingpoints were selected in the side areas of the land.

Figure 8 shows that the heavy metal concentration at thewithdrawing point of the irrigation canals was the highest

Figure 9. Remediation tasks carried out in this study.

because factories have illegally discharged heavy metalwastewater into the irrigating canals. The concentrationsthen decreased along the water flow direction, and the con-centrations in the side areas of the land were the lowest. Thedistribution of heavy metal concentrations had been pre-dicted via the proposed sampling rule.

Soil characteristics, thickness of soil layer, gravel level,and groundwater flow were also investigated and assessed.The areas where the soil layers were not thick enough toprovide attenuation soil were located. The required attenu-ation soil for the foresaid areas were calculated and providefrom the other areas in the same remediation site. The ar-

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Figure 9. (Continued)



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eas that were found with groundwater flow within the ex-cavation depth were also recorded. The drainage canals andpumping shafts were built around the foresaid areas.

Implementation of remediation strategies and action plans

The excavation depth for each remediation area was cal-culated using the concept of Fig. 4 and Equation (1) basedon the predicted distribution of heavy metal concentrations.The demands of attenuation soil for the areas that were foundas insufficient thicknesses of soil layer by the foresaid in-vestigation were then calculated based on the foresaid re-sults of the excavation depth. Furthermore, the supplies ofthe attenuation soil and required excavation depth for the ar-eas that were found as sufficient thicknesses of soil layer by

the foresaid investigation were also calculated. All of the at-tenuation soils were then provided from the remediationsites. The remediation cost could be controlled without ex-cessive attenuation soils. Moreover, all of the contaminatedsoils had not been delivered out of the remediation site andthe secondary pollution was prevented. Therefore, the diffi-culties mentioned in the Methodology section can be effec-tively overcome. The following schedules were used to con-trol the implementation of remediation tasks:

1. The engineering steps, engineering diagrams, and re-quired cost were designed into the action plans in 2months. Remediation costs for the sites in TaoyuanCounty, Hsinchu City, and Changhua County were 160,650, and 490 thousand dollars, respectively.

2. The remediation areas were delimited in 2 months. The

Table 3. Measured results of performance indicators for three remediation sites.

Types of Remediation Remediation Remediationperformance site in site in site inmeasure Indicator Taoyuan County Hsinchu City Changhua County

Input Remediation cost 160 650 490(thousand dollars)

Output Remediation areas (hectare) 8.9 32.8 30Outcome Land areas after 8.9 32.8 30

remediation that meet thestandards and recover theagricultural utility (hectare)(1) Heavy metal Cd: 0.98, Cu: 183, Ni: Cu: 185, Ni:(1) concentration in soil Pb: 25.5 193, Cr: 216, 153, Cr: 112,(1) (mg/kg) Zn: 285 Zn: 307(2) Compactness 80–90% 80–90% 80–90%(3) Flatness (cm) 10 10 10(4) Germination — 87.5% —(1) percentage(5) Fertility Fertility of Fertility of —

remedied soil remedied soilhas been has beenrecovered recovered

(6) Heavy metal Cd: 0.29, — —(1) concentration in crops Pb: 0.10(1) (ppm)

Efficiency Remediation cost per unit 18,000 20,000 16,000land area (US$/hectare)

Remediation cost per unit 5.2 5.6 4.7soil volume (US$/m3)

Remediation time per unit 28.9 11.4 12.2land area (day/hectare)

Quality Acceptance rate of the 78% 90% 90%public

Attenuation of heavy Cd: 85% Cu: 90%, Ni: Cu: 45%, Ni:metal 32%, Cr: 67%, 56%, Cr: 37%,

Zn: 43% Zn: 33%

required depth of turning over the soil, the soil quantityof stirring and the concentrations of heavy metals afterdiluting were drawn up for each area in accordance withthe concentrations of heavy metals and the thickness ofthe soil layer in each area, and the required time for theabove task was marked out during the same period.

3. The facilities for safety, environmental health, and pol-lution control were planned within 1 month after theabove task was finished.

4. The turnover and attenuation tasks were carried out bythe scheduled time limits, which were 10, 12, and 12months for Taoyuan County, Hsinchu City, andChanghua County, respectively.

Remediation tasks for the site in Taoyuan County werefirst carried out, shown in Fig. 9, which exactly followedthe procedures developed in the Design of action plans ofremediation based on the strategies section (Fig. 5). Thisstudy, based on the action plans, finished the remediation ofabout 8.9 hectares of farmland from May 1998 to January1999. Later, from July 2003 to June 2004, the remediationwas conducted in Hsinchu City and Changhua County in

contaminated places, completing about 32.8 hectares and 30hectares of the farmland remediation, respectively.

Performance assessment of remediation tasks

The remediation results are expressed with performanceindicators for each item as follows. Table 3 lists the perfor-mance indicator values for the remediation in the three sites.This study yielded lots of data. Among the data of heavymetal concentration in soil, flatness, and heavy metal con-centration in crops, only the highest value of each indicatoris chosen and listed in Table 3. Meanwhile, only the lowestvalue of the germination percentage indicator is chosen andlisted. Performance indicator values for input indicate thatremediation costs are controlled within the budgets. Perfor-mance indicator values for output show that the areas of thecontaminated sites had been completely remedied. Addi-tionally, performance indicator values for outcome, effi-ciency, and quality are discussed as follows.

Performance indicator values for outcome. Indicator val-ues illustrate that 100% of the land area can meet the stan-dards and recover the agricultural utility after remediation

CHEN AND CHIOU 26

Figure 10. Cu and Cr concentrations before and after remediation of the contaminated site in Hsinchu City.



27

in all three sites. The measured results for the indicators arediscussed as follows.

Heavy metal concentrations in soils. The concentrationsin the remedied soils from the monitoring data by the methodin the Heavy Metal Concentration in Soils section clearlyindicate that the regulatory standards can be met. This in-vestigation has illustrated all the monitoring results with the

concentration contour. Figure 8 shows the concentration ofCu in a remedied region in Hsinchu City. Figure 10 illus-trate the concentrations of Cu and Cr before and after re-mediation of the contaminated site in Hsinchu City. For ex-ample, the highest concentration of Cu is 974 mg/kg beforeremediation. The average concentration after remediation ofCu is 86.7 mg/kg, with the standard deviation of 17.8 mg/kg.Furthermore, the highest concentration of Cu is 183 mg/kg,

Figure 11. Ni concentrations of the contaminated site in Changhua County before and after remediation.

which is lower than the control standard of 200 mg/kg. Fur-thermore, the concentrations of Cu and Cr before and afterremediation of the contaminated site in Changhua Countyare shown in Fig. 11. The concentrations of Cd after reme-diation of the contaminated site in Taoyuan County are listedin Table 4. Furthermore, the proposed assessment methodof area and degree of soil contamination is verified to be ad-equate and effective with the measured results. Hence, theconcentration of heavy metal in the soil after remediationcan meet the standards.

Compactness. The compactness of the remedied landclearly illustrates from the test data by the method in theCompactness section to be between 80 and 85%, and satis-fies the requirements for agricultural cultivation.

Flatness. The test data by the method in the Flatness sec-tion indicated that the terrain relief of the remedied landswas less than 10 cm, meeting the needs of irrigation anddrainage of farmlands.

Germination percentage. This study included a step toloosen the surface soil and add organic fertilizer in the re-mediation procedure (Fig. 5) to improve the permeabilityand fertility of remedied soil. Table 5 and Fig. 12 presentthe experimental results in Hsinchu City as examples by themethod shown in the Germination Percentage section. Thetimes of initial germination before and after the remediation

for spoon cabbage were both 3 days, while those for Chi-nese cabbage were 4 days and 3 days, respectively. The high-est germination percentages before and after the remedia-tion for spoon cabbage were 81.5 and 89.5%, while thosefor Chinese cabbage were 88.0 and 87.5%, respectively. Thehighest germination percentages after the remediation wereboth higher than 85%, which indicate that the remedied soilwas suitable for growth of the crops.

Furthermore, the time for reaching the highest germina-tion percentage after the remediation for spoon cabbage was8 days, which is much shorter than that before the remedi-ation (18 days). The time for reaching the highest germina-tion percentage after the remediation for Chinese cabbagewas 8 days, which is also shorter than that before the re-mediation (10 days). The experimental results reveal that theforesaid step can improve the permeability and fertility ofremedied soil, which is even more suitable for agriculturalapplication than the soil before remediation.

Fertility. Indicator value of fertility is also used to verifythe effectiveness of the foresaid step. Table 6 lists the av-erage data for 41 investigation data of soil fertility inHsinchu City as examples by the method in the Fertility sec-tion. The electric conductivity, phosphorous, and potassiummoderately increased, while the total organic carbon and ni-trogen somewhat decreased. The investigation results illus-trate that the foresaid step can improve the fertility of reme-died soil, which can reach the similar fertility of soil beforeremediation.

CHEN AND CHIOU 28

Table 4. Cd concentrations after remediation of the contaminated site in Taoyuan County.

Depth ofTypes of soils soils (cm) Zone 1 Zone 2 Zone 3 Zone 4 Zone 5

Before remediation 0–30 3.25 � 1.14 2.72 � 1.16 3.04 � 1.32 3.61 � 1.32 3.31 � 1.22(sampled in 1998)

After remediation 0–15 0.29 � 0.26 0.28 � 0.12 0.56 � 0.33 0.55 � 0.20 0.43 � 0.31(sampled in 1999)

Note: Unit: mg/kg.

Table 5. Germination parameters of spoon cabbage and Chinese cabbage.

Parameters Vegetables After remediation Before remediation

Initial germination time Spoon cabbage 3 � 0 3 � 0(day) Chinese cabbage 3 � 0.5 4 � 0

Time to reach the Spoon cabbage 8 � 1 18 � 2maximum germination Chinese cabbage 8 � 1 10 � 1(day)

The maximum Spoon cabbage 89.5 � 1.5 81.5 � 1.5germination ratio (%) Chinese cabbage 87.5 � 0.5 88.0 � 0

Note: Three repetitions of experiments were carried out.



29

Heavy metal concentrations in crops. The experimentedresults of the heavy metal concentration in crops in theTaoyuan County were used as examples. The rice yield ofremedied farmlands was found to be 70–80% of that of theneighboring farmlands without contamination in the firstround of experimental planting. Table 7 shows the Cd con-centrations in the soil and rice by the method shown in theHeavy Metal Concentrations in Crops section. Some Cd con-centrations in the rice planted in the contaminated farms thathad not been remedied were higher than the regulatory limit(0.5 ppm). In the remedied farmland, the cadmium concen-trations in the topsoil (0–15 cm) and the subsoil (15–30 cm)were 0.43–0.92 mg/kg (average 0.59 mg/kg) and 0.48–0.78mg/kg (average 0.63 mg/kg), respectively. Cadmium wasnot detected in all test samples of rice. Compared with otherreport (Chen, 1991), the result is slightly different from thatwhen the Cd content in the soil exceeded 1 mg/kg, whichcould make the Cd concentrations in the rice exceed 0.5ppm.

To understand the long-term change of heavy metal con-tent in rice that was planted on the remedied farmlands, fourcontinuous stages of paddy rice in 2 years were planted onthe same farmlands about 0.1 hectare. The Cd contents ofthe rice in the test plants, listed in Table 8, were lower thanthe food safety standard of 0.5 ppm. The experimented re-sults indicate that the remediation tasks were successful to

let the heavy metal concentration in crops be controlled inregulatory limits.

Performance indicator values for efficiency. The assess-ment results of performance indicators for efficiency indi-cate that the remediation cost and time via the comprehen-sive and effective remediation methodology in this studywere efficient. The detailed information is listed below:

Remediation cost per unit land area. After subtracting thesampling, analysis, and improvement verification costs, thenet remediation costs using the comprehensive and effectiveremediation methodology of this study were 18,000 $/hect-are, 16,000 $/hectare, and 20,000 $/hectare in TaoyuanCounty, Changhua County, and Hsinchu City, respectively.The cost of soil covering method, which is also suitable forremedying the low concentration of heavy metal farmlands,is 277,000–857,000 $/hectare. The other costs of solidifica-tion, extraction and plant extraction are 249,000–543,000,686,000–829,000, and 54,000–223,000 $/hectare, respec-tively (Neidorf, 1996; Khan et al., 2004).

Remediation cost per unit soil volume. If an exchangedsoil depth of 35 cm is applied as the basis of conversion,then the costs for the remediation based on the comprehen-sive and effective remediation methodology developed in

Figure 12. Relationship between Germination percentage and growing time for spoon cabbage and Chinese cabbage.

Table 6. Effect of turnover and attenuation on soil properties.

Types of soils Conductivity (ds/m) TOC (%) N (kg/ha) P (kg/ha) K (kg/ha)

Before remediation 1.42 � 0.13 1.58 � 0.11 108 � 8 265 � 15 169 � 7(investigated in 2003)

After remediation and 1.70 � 0.21 1.29 � 0.09 87 � 4 275 � 12 214 � 9fertility improvement(investigated in 2004)

Note: Three repetitions of experiments were carried out.

this study are 4.7–5.6 $/m3. The cost of soil covering methodis 97–390 $/m3. Additionally, the costs of solidification, ex-traction and plant extraction are 87–190, 240–290, and19–78 $/m3, respectively (Neidorf, 1996; Khan et al., 2004;FRTR, 2006). The comparative results indicate that the re-mediation performed by the proposed remediation method-ology is cost-efficient.

Remediation time per unit land area. The contaminatedareas in Taoyuan County, Changhua County, and HsinchuCity were 8.9, 28.9, and 32.8 hectares, and the remediationtimes for these sites were 257, 365, and 365 days, respec-tively. Therefore, the remediation time per unit land areawas 11.4–28.9 day/hectare. The remediation times for so-lidification, extraction, and plant extraction methods were6–9 months, 8–12 months, and 18–60 months, respectively(Neidorf, 1996; Khan et al., 2004; FRTR, 2006). The com-pared results reveal that the remediation performed by theproposed remediation methodology is also time efficient.

Performance indicator values for quality. Most people ap-proved the remediation through the comprehensive and ef-fective remediation methodology because the remediationtimes were short and the remedied lands could recover theiroriginal utility. Additionally, the remediation achieved agood heavy metal attenuation rate. The evaluated resultsshow that the quality of the remediation work was good.

Acceptance rate of the public. In the first remediation casein Taoyuan County, 31 in all the 40 landowners (78%) ap-proved the remediation. In 2003, 160 in all the 176 landown-ers (91%) in Hsinchu City and 111 in all the 123 landown-ers (90%) in Changhua County approved the remediation.

The analytical results reveal that the turnover and attenua-tion method guided with the sustainable management frame-work could be widely accepted by people.

Attenuation rate of heavy metal. The remediation resultsof the contamination site in Taoyuan County are consideredas an example. Figure 13 shows the Cd concentrations ofthe soils sampled each 15-cm depth up to 75 cm before andafter remediation. The Cd concentrations in the contami-nated soil decreased from 2.28 � 0.42 mg/kg to 0.35 � 0.10mg/kg after remediation, indicating an attenuation rate of85%. The concentration in the bottom soil (60–75 cm) isslightly higher than those in other depths because the soilswere not completely well mixed. However, the differencesof concentrations are acceptable. Furthermore, the attenua-tion rates in Hsinchu City and Changhua County were in therange of 32 to 90%, indicating that the average concentra-tions of the heavy metal in the soil apparently decreased.The analytical results illustrate that the turnover and atten-uation method guided with the sustainable managementframework successfully blended the soil evenly.

CHEN AND CHIOU 30

Table 7. Concentrations of Cd in soil and rice.

Sample Topsoil (0–15 cm) Subsoil (15–30 cm) RiceType of soils no. (mg/kg) (mg/kg) (ppm)

Before 1 2.61 2.81 1.33 � 0.11remediation 1.94 1.34

2 0.87 0.87 0.49 � 0.321.04 0.78

3 0.15 0.17 ND0.11 0.22

4 4.51 3.97 1.23 � 0.073.89 3.15

5 0.99 0.60 ND0.40 0.24

After 6 0.43 0.46 NDremediation 0.45 0.49

7 0.57 0.57 ND0.57 0.66

8 0.68 0.72 ND0.82 0.79

9 0.92 0.74 ND

Table 8. Cd concentrations in rice after remediation.

Land no. 1st test 2nd test 3rd test 4th test

A ND NDB ND ND 0.21 � 0.02C ND ND 0.20 � 0.01D ND 0.29 � 0.04 0.17 � 0.02E ND 0.26 � 0.01

Unit: mg/kg; standard: 0.5 mg/kg.



31

CONCLUSIONS

A comprehensive and effective remediation methodologyfor heavy metal-contaminated farm soil was presented in thisstudy, which was the first applied methodology in Taiwan.The proposed methodology integrated assessment of soilcontamination and environmental characteristics, remedia-tion technology, and performance assessment to achieve ef-fectiveness and efficiency of remediation tasks. Turnoverand attenuation method was chosen and applied in this studybased on the assessment results of social, technological, eco-nomical, and environmental feasibilities.

A management framework based on MFR was developedfor guiding the remediation tasks, composed of assessmentprocedures for soil contamination and environmental char-acteristics, remediation procedures suitable for environ-mental characteristics of Taiwan, and performance indica-tors to assess remediation results. This study developed arule for determining the adequate number and locations ofsampling points to be used to predict the various distribu-tions of heavy metal concentrations in soils and environ-mental characteristics. The remediation results showed thatthe proposed sampling rule, calculation method, and inte-gral remediation methodology can be used to ensure that theheavy metal concentrations in soils meet the regulatory lim-its without excessive attenuation soils.

The remediation tasks of three contaminated sites had

been successfully accomplished in this study by using theproposed methodology. The performance measurements ofthe three remediation cases were explicitly illustrated thatthe requirements of the public and the authorities have beenboth met, indicating that the proposed management frame-work could be used to keep the remediation being effective.Furthermore, the remediation costs per unit land area, re-mediation costs per unit soil volume, and remediation timesof the above cases were more efficient than those of otherremediation works listed in literatures. The proposedmethodology and management framework had been there-fore used to improve the efficiency of remediation.

The social, technological, economical, and environmen-tal objectives were all met in the above cases. Therefore, theproposed integral methodology was successfully used to en-hance the performance of remediation for heavy metal-con-taminated farm soil based on the principles of sustainabledevelopment. There are still many contaminated areas re-quired to be remedied in Taiwan. Hence, this study recom-mends the authorities that the proposed methodology can beapplied in other contaminated sites in Taiwan.

ACKNOWLEDGMENTS

The authors would like to thank the Environmental Pro-tection Bureau of Taoyuan County Government, the Envi-

Figure 13. Cd concentration in the soil before and after remediation of Taoyuan County.

ronmental Protection Bureau of Hsinchu City Government,the Environmental Protection Bureau of Changhua CountyGovernment, Taiwan, R.O.C., and Apollotech Inc. for fi-nancially supporting this research.

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