BARRIER SYSTEMS for ENVIRONMENTAL CONTAMINANT CONTAINMENT and TREATMENT - PART 5 (end) ppsx

Theroles of subsurface verification in this process of acceptance are as follows: • Meet or exceed regulatory requirements • Verify performance of engineered barriers • Verify conceptual

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The design service life of a containment system can range from as little as

10 years for slurry walls to more than 1000 years for radioactive waste storagestructures The longer the service life of a containment system, the greater the

* With contributions by William R Berti, DuPont Central Research and Development, Newark, Delaware; Skip Chamberlain, U.S Department of Energy, Washington, DC; Thomas W Fogwell, Fluor Hanford, Richland, Washington; John H Heiser, Brookhaven National Laboratory, Upton, New York; John B Jones, U.S Department of Energy, North Las Vegas, Nevada; Eric R Lindgren, Sandia National Laboratories, Albuquerque, New Mexico; William E Lowry, Science and Engineering Associates, Inc., Santa Fe, New Mexico; Keri H Moore, National Research Council, Washington, DC; Horace K Moo-Young, Jr., Villanova University, Villanova, Pennsylvania; Michael G Serrato, Westinghouse Savannah River Company, Aiken, South Carolina; Matthew C Spansky, Westinghouse Savannah River Company, Aiken, South Carolina;

4040_C005.fm Page 287 Wednesday, September 21, 2005 12:28 PM

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288 Barrier Systems for Environmental Contaminant Containment & Treatmentprobability of system failure Because most components of containment systemsexist underground, direct visual inspection is not tenable as a monitoring method.Thus, several traditional and evolving techniques of indirect and direct observa-tions need to be employed to obtain performance data.

In terms of containment system effectiveness, two types of failure categoriescan be identified: structural failure and functional failure Structural failure canoccur without functional failure, although it can eventually lead to functionalfailure Thus, verification monitoring of barrier structural and/or functional fail-ures is essential over the life of the barrier Long-term monitoring is an importantaspect in determining the integrity of the barrier over the lengthy lifetimes ofmany contaminants This chapter discusses the state-of-the-art monitoring tech-nologies and recommends innovative methods such as in situ sensors to improveand reduce the cost of barrier monitoring

5.2 GOALS

Subsurface verification is integral to achieving acceptance of covers, permeablereactive barriers (PRBs), and subsurface barriers such as walls and floors Theroles of subsurface verification in this process of acceptance are as follows:

• Meet or exceed regulatory requirements

• Verify performance of engineered barriers

• Verify conceptual models of contaminant fate and transport

• Verify models for containment systems

• Conduct long-term performance monitoring

• Ensure identification of trigger levels for contingency actions

At present, there are no specific regulations under the Comprehensive ronmental Response, Compensation, and Liability Act (CERCLA) or theResource Conservation and Recovery Act (RCRA), and there is no regulatoryguidance on subsurface barrier integrity or performance validation The onlyregulatory standard for barriers is the RCRA requirement (40 CFR 264, Subpart

Envi-N, Landfills) of a 10–7 cm/s hydraulic conductivity at a thickness of 0.91 m.Additional standards may be added in the near term because the United StatesEnvironmental Protection Agency (USEPA) Office of Emergency and RemedialResponse has launched the Superfund Initiative on Long Term Reliability ofContainment (Betsill and Gruebel, 1995) The USEPA is scheduled to work withother U.S agencies to develop technical guidance and methodologies to evaluatecontainment technologies

The American Society for Testing and Materials International (ASTM) hasstandards pertaining to barrier monitoring Reference to these standards should

be made when considering potential methods The ASTM D18.21.02 committee,chaired by Lorne G Everett, on vadose zone monitoring standards is responsiblefor publishing the list of vadose zone standards provided in Table 5.1

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Subsurface Barrier Verification 289

5.3 VERIFICATION MONITORING

Monitoring plays a key role at all stages in environmental management — frominitial site discovery to site closure Monitoring programs are essential in facili-tating site characterization and risk assessment, adequately conducting experi-mentation and evaluation, producing the data necessary for the performanceevaluation, determining whether residual contamination exists that will preventsite closure, and verifying the effectiveness of containment structures The focus

of monitoring programs is necessarily site and time specific For example, a soilremedial action may primarily require sampling during excavation and immedi-ately after remediation work is complete (site closure) For sediment and ground-water remedial actions, longer-term monitoring programs might be developedthat have their roots in initial site characterization activities, continue throughremediation, and extend for significant periods of time beyond termination ofactive remediation In the case of groundwater, most sites begin with an inheritedset of monitoring points already established and so part of the monitoring designprocess also includes determining to what extent the existing network can beused or must be abandoned or expanded Depending on the selected remedialaction (Table 5.2), monitoring programs can represent the majority of remedialaction costs (e.g., monitored natural attenuation) or only a small percentage.Traditional characterization and verification monitoring programs tend to pre-specify sample numbers, locations, sampling frequency, and analytics (i.e., off-site laboratory analyses) This traditional type of data collection presents several

TABLE 5.1 ASTM International Vadose Zone Monitoring Standards

Vadose zone terminology (final) Soil pore-liquid monitoring (D 4696-92) Soil core monitoring (D 4700-91) Matrix potential determination (D 3404-91) Neutron moderation (D 5220-92/97) Soil gas monitoring (D 5314-93) Hydraulic conductivity (D 5126-90) Decontamination of field equipment (D 5088-90) Flux determination by time domain reflectometry (D 6565) Determining unsaturated and saturated hydraulic conductivity in porous media by steady- state centrifugation (D 6527)

Horizontal applications of neutron moderation (D 6031) Frequency domain capacitance (Z4302Z)

Field screening guidance standard (final) Water content determination (draft) Vadose zone borehole flow rate capacity test (draft) Air permeability determination (outline)

Thermalcouple psychrometers (outline)

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290 Barrier Systems for Environmental Contaminant Containment & Treatment

II Define what is to

be monitored

Demonstrate that natural attenuation is occurring according to expectations accomplished by including steps to:

1 Identify any potentially toxic transformation products; Determine if a plume is expanding (either downgradient, laterally or vertically)

2 Ensure no impact to down gradient receptors

3 Detect new releases of contaminants to the environment that could impact the effectiveness of the natural attenuation remedy

4 Demonstrate the efficacy of institutional controls that were put in place to protect potential receptors

5 Detect changes in environmental conditions (e.g., hydrogeologic, geochemical, micro- biological, or other changes) that may reduce the efficacy of any of the natural attenuation processes

6 Verify attainment of cleanup objectives

Site operator and regional administrator (USEPA or the state-implementing agency)

III Establish the time

period for

monitoring

Continue as long as contamination remains above required cleanup levels, continue for a specified period (e.g., 1–3 years) after cleanup levels have been achieved to ensure that concentration levels are stable and remain below target levels.

Regional administrator (USEPA or the state- implementing agency)

1 Specify methods for statistical analysis of data, e.g., established tolerances, seasonal and spatial variability

2 Establish performance standards:

• Information on the types of data useful for monitoring natural attenuation performance

in the ORD publications (EPA/540/R-97/504, EPA/600/R-94/162)

• EPA/600/R-94/123: a detailed document on collection and evaluation of performance monitoring data for pump-and-treat remediation systems

Site operator and regional administrator (USEPA or the state- implementing agency)

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limitations, particularly in the context of subsurface characterization and toring The costs are sometimes prohibitive, driven both by sample analyticalcosts and the capital investment required for monitoring wells High monitoringcosts, particularly for monitoring programs that extend over time, result in pres-sures to limit data collection Limited data collection, in turn, results in decision-making that relies on data sets too sparse to adequately address the inherentheterogeneities and uncertainties associated with subsurface barrier systems.Finally, by prespecifying sample numbers and locations and relying on off-site

moni-TABLE 5.2 (continued)

Progressive Monitoring Steps for a Remediation by Natural

Attenuation Program

• Standard test methods such as described in EPA SW-846, “Test Methods for Evaluating Solid Waste - Physical/Chemical Methods” or EPA publication, “Methods of Chemical Analysis for Water and Wastes”

3 Establish a time interval agreed upon by regional administrator or agency, including reporting maps, tabulation of data and statistical analysis, identification of trends, recommendations for changes in approach, evaluation of whether contaminants have behaved as predicted, and whether other remedies are required

V Define action

levels or process

to be observed for

monitoring

Establish metrics for the monitoring system:

1 Establish background levels

2 Define what criteria shows that a plume is expanding or diminishing

3 Define what criteria shows that the conceptual model is applicable to a site

4 Determine the metrics of cleanup objectives and effectiveness

Site operator and regional administrator (USEPA or the state- implementing agency)

2 Identify extent and nature of nonpredicted behavior (e.g., release)

3 Re-evaluate conceptual model and evaluate feasible corrective actions from previous and evolving contingency plan

Site Operator will provide details of the monitoring program; should be provided

to USEPA or the state-implementing agency as part of any proposed monitored natural attenuation remedy

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292 Barrier Systems for Environmental Contaminant Containment & Treatmentlaboratory analyses with long turnaround times for analytical results, traditionalcharacterization and monitoring programs are ill equipped to handle unexpectedresults Fortunately over the last several years, technological advances haveoccurred in sensors, field analytics, and sample collection technologies that canhelp to lower costs and/or increase the effectiveness of monitoring programs (seeBox 5.1) New approaches for designing and implementing environmental datacollection programs have also been developed A few of those innovative barrier-monitoring technologies are discussed in the subsections below.

Methods for barrier monitoring generally fall into broad classes such as ment of moisture change, collection of moisture and gas samples, temperature,flow/velocity, barometric pressure, and settlement An in-depth evaluation ofbarrier-monitoring science and technology is provided in the National Department

measure-of Energy Vadose Zone Science and Technology Roadmap [Idaho National ronmental Engineering Laboratory (INEEL), 2001]

Envi-5.3.1.1 Moisture Change Monitoring Methods

A number of methods are available for barrier-monitoring moisture change insoils (Everett et al., 1984; Wilson et al., 1995; Looney and Falta, 2000a,b) Many

of these measurement techniques require laboratory testing to develop calibrationcurves relating instrument output to soil moisture content Several of the morecommonly used methods are described below

BOX 5.1

Rapid Field Characterization of Sediments

Rapid field characterization techniques have been developed to speed assessment and reduce costs These are field-transportable screening tools that provide measurements

of chemical, biological, or physical parameters on a real-time or near real-time basis Specific advantages include the ability to get rapid results to guide sampling locations, the potential for high data mapping density, and a reduced cost per sample The

approaches do have limitations including the nonspecific nature of some tests,

sensitivity to sample matrix effects, and some loss in accuracy over conventional

laboratory analyses A variety of tools has been suggested for the rapid characterization

of sediments, as shown in the table below.

Screening-Level Analyses Recommended by the Assessment and Remediation

of Contaminated Sediments Program for Freshwater Sediments

X-ray fluorescence spectrometry (XRF) Metals

UV fluorescence spectroscopy (UVF) Polycyclic aromatic hydrocarbons (PAHs)

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• Neutron probe — The neutron probe contains a source of neutronsand detectors to measure backscattered neutrons The magnitude andenergy of backscattering is primarily a function of the hydrogen content

of the material surrounding the probe To take readings, the neutronprobe is lowered into the pipe and a continuous record of the response

is obtained Changes in the readings over time at a particular depthindicate changes in the number of hydrogen atoms, i.e., water content.The neutron probe must be calibrated for specific soils This method

• Time domain reflectometer — In this method, an electromagneticend of the cable, a portion of the signal is reflected The amplitude andtravel time of the reflected portion depend on the dielectric properties

of the soil, which in turn are strongly dependent on soil moisturecontent The output is typically monitored on an oscilloscope or cabletester These probes can be monitored remotely and have no directanalytical costs associated with them other than initial calibration Thistends to minimize life-cycle costs

• Thermocouple psychrometer — This instrument measures relativehumidity within the soil pores, from which soil water potential andtherefore moisture content can be calculated Humidity is determined

by the observed difference in temperatures between two ples, one of which is exposed to the humidity in the surrounding soiland experiences cooling; the other thermocouple is located adjacent tothe first but is isolated from the humidity Moisture content is deter-mined from relative humidity on the basis of laboratory calibration

thermocou-• Electromagnetic Induction (EMI) — EMI is a standard geophysicaltechnique (Chapter 4) that is used to measure the conductivity of soilmass At the ground surface, a transmitter coil generates an electro-magnetic field that induces eddy currents in the underlying subgrade.Secondary electromagnetic fields created by the eddy currents aremeasured by a receiver coil that produces an output voltage related tothe subsurface conductivity EMI is a rapid technique that is often used

to delineate contaminant plumes, buried wastes, and other features thathave conductivity contrasts with the surrounding soil

• Electrical resistivity tomography (ERT) — ERT is based on a largenumber of soil resistance measurements (Chapter 4) analyzed by math-ematical methods (e.g., finite difference models employing inversiontechniques) Each resistance measurement involves several electrodes,some to apply a current through the soil and some to measure thevoltage drop The location and spacing of the electrodes determinesthe soil volume being measured; in general, larger electrode spacings areused at greater depth Commonly, a linear series of electrodes is placed

on the ground surface or beneath a landfill An automatic monitoring

wave is transmitted along a transmission cable buried in soil At the

is discussed in more detail in Section 5.9.1.1

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294 Barrier Systems for Environmental Contaminant Containment & Treatmentsystem excites various pairs of electrodes according to a programmedsequence and measures the resistance between other pairs When alldesired combinations have been read, the resulting data are analyzed.The result is a two-dimensional contour map (i.e., a vertical or hori-zontal slice) of soil resistivity along the electrode line Changes inmoisture content over time appear as changes in resistivity Laboratorycalibration of subgrade soil is required to develop quantitative relation-ships High-resolution resistivity has shown particular merit in bothcap and subsurface liner monitoring but is not developed to a stagewhere it can be recommended in the near term.

• Fiber-optic cable — These systems could be considered as one of thelatest improvements in vadose zone sensor systems Fiber-optic sys-tems already are measuring strain, temperature, acoustics, moisture,

pH, flow, and chemicals Fiber-optic cable could be included in thefuture applications of a monitoring system The cable could bedeployed in the perforated stainless-steel tubing laid down below thebottom liner during construction Consideration could be given toincluding fiber-optic cable in the horizontal and vertical monitoringorientations The cost advantages expected with the use of fiber-opticsensors are substantial The risk of causing preferential flow pathsassociated with installing a very small diameter fiber cable is smallrelative to the other technologies

5.3.1.2 Moisture Sampling Methods

There are processes other than leakage through the barrier liner system that couldcause changes in moisture content of the vadose zone Examples include moisturerelease from the admix layer as it consolidates under the load of the waste, andvapor migration due to temperature changes caused by excavation, lateral mois-ture, or vapor movement into the trench (from outside the trench), and removal

of subgrade soils Moisture change resulting from such processes could be cult to distinguish from leachate In addition, those methods described above indissolved constituents as well as moisture content alone In spite of these limi-tations, in the case of a RCRA cap, which is designed as an impermeable cap,elevated moisture migration rates alone can be used as an indicator of increasedinfiltration through the cap

diffi-To determine whether moisture is the result of leakage through the barrierliner, samples are collected and analyzed for constituents known to occur in thewaste material A number of techniques are available and are described in theliterature (Everett, 1980; Everett et al., 1984; Wilson et al., 1995; Looney andFalta, 2000a,b)

• Suction lysimeter — The suction lysimeter consists of a porous cup

or plate attached to a small diameter tube leading to a sampling chamber.4040_C005.fm Page 294 Wednesday, September 21, 2005 12:28 PM

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The lysimeter is buried in the soil at the location where a sample isdesired, and the tubing leads to an accessible location To obtain asample, a reduced pressure is applied to the lysimeter Water in the soilmatrix is sucked into the lysimeter and accumulates in the samplingchamber There are various modifications utilizing additional tubes,check valves, and other components to allow samples to be retrievedfrom depth, but the basic operating principle is the same

• Absorbent pads — This method uses pads of absorbent material, such

as felt, to collect soil moisture One commercially available system(Flute) that has been used to collect samples beneath a radioactivewaste landfill at Los Alamos National Laboratory (New Mexico), uses

a cylindrical flexible membrane that holds the pads The membrane isinitially inside out, or inverted, and is everted as it is placed in theborehole so that the pads contact the borehole wall After a period oftime, when the pads have reached equilibrium with the surroundingmaterial, the membrane is withdrawn, being inverted again during thisprocess so that the pads are not contaminated In soil materials, where

an open borehole cannot be maintained over the long term, a permeablecasing is required

• Sodium iodide gamma detector — This is a radiation-measuringinstrument that is lowered down an access pipe Rather than returning

a sample to the ground surface, the detector measures the radioactivity

of the surrounding soil This method identifies contaminants that aregamma emitters in sufficient concentrations to be clearly detectable

•

basin a few meters in dimension It is lined with a geomembrane andbackfilled with vadose zone soil The floor of the basin slopes to acollection point, and a pipe leads from this point up to the groundsurface When a sample is required, a sampling pump is lowered downthe pipe, where quantifiable measurements can be obtained

5.3.1.3 Vadose Zone Monitoring Considerations

To monitor flow and transport in covers, walls and floors, point-type probes such

as tensiometers, time-domain reflectometry probes (TDR), suction lysimeters,and thermistors can be used as well as geophysical imaging methods such asseismic surveys, ground penetrating radar (GPR), and three-dimensional (3-D)ERT (Hubbard et al., 1997) Point-type probes may or may not intersect singleflow paths (Figure 5.1) The shortcoming of point-type probe measurements isthe difficulty of combining their responses in a meaningful way, such as integrat-ing or volume averaging responses from a number of point measurements Geo-physical imaging methods complement point-type measurements by providing aspatially distributed view of subsurface conditions Each measurement represents

an average over space and time; however, the volume affected cannot be determined

Basin lysimeter — The basin lysimeter consists of a broad, shallowFor additional details, refer to the discussion in Section 5.5.2.1

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The shortcomings of geophysical methods are their lack of spatial resolution indetecting small barrier leaks, and the difficulty of correlating values such aselectromagnetic responses and seismic velocities to hydrogeologic parametersgoverning fluid flow Neither method can be used to observe flow in singlefractures of fluid movement at the fracture matrix interface in sufficient detail toaccurately represent transport through barriers

5.4 VERIFICATION SYSTEM DESIGN

One of the key issues discussed at the workshop was integrating the verificationsystem design into the overall barrier design The barrier must have a set ofperformance requirements that are site specific and risk based Without a risk-based performance objective, the barrier is either intact and good or breachedand unusable As stated previously, none of the regulatory agencies has a set ofcriteria for a barrier De facto, the regulators take a risk-based approach toapproving such structures Risk-based performance objectives are crucial to thesuccessful deployment of subsurface barriers

This fact is demonstrated when comparing two identical failures in a barrier

at distinctly different locations Suppose an obstruction blocks the flow of groutduring installation of a barrier wall, resulting in a 1 m2 hole in the barrier wall

In one case the hole occurs within 1.2 m of the uppermost (shallowest) region

of the barrier In the other case, the hole is located at the bottom region of thebarrier Water flux through the waste site would result in contaminant mobilization

FIGURE 5.1 Schematic of the performance of local-type and cross-borehole monitoring methods in a heterogeneous formation (In Situ Remote Sensors and Networks, 1999e).

1 Tenslometers, ER probes, TDR provide local (6–20 om) measurements

2 Vacuum water sampling and neutron logging aﬀect the 30–40 om near borehole

3 Cross-hole radar and 3D ER; tomography are eﬀective within the zone of up to 10–12 m

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and transport with the water Water flow would occur mostly in a vertical directiondue to gravity Near the surface of the barrier, horizontal spread would be minimaland the likelihood that water will transport out of a hole near the top of the barrier

is small At the bottom of the barrier, water would collect and any hole in thisregion would serve as a drain, similar to a bathtub These two nearly identicalflaws in the barrier have extremely different consequences One would requirerepair and the other could be ignored entirely

When designing a verification/monitoring system, it is crucial that a set offailure criteria be established This may necessitate implementing an iterativeapproach to barrier and verification designs Once the performance requirementsare established for the barrier and a conceptual model is developed, a conceptualverification system can be designed The conceptual barrier design may need to

be modified to accept the verification design (e.g., use of plastic componentsinstead of metal to allow for the use of ground penetrating radar) Once conceptualmodels for both have been developed, the failure mechanisms of the barrier need

to be identified Using risk assessment models, the failure scenarios can besimulated to determine what constitutes unacceptable failure of the barrier.Depending on the results, the verification/monitoring system may requirechanges, which can result in further modifications to the barrier design and soforth This process continues until an acceptable combination of barrier designand verification/monitoring system is achieved

5.5 MOVING FROM STATE OF THE PRACTICE

TO STATE OF THE ART

Subsurface verification suggests that containment design and implementationmove toward the state of the art rapidly from the current state of the practice In

1976, Everett et al recommended neutron probes and suction lysimeters for capand floor barrier monitoring Thirty years later, these same two techniques arestill primarily used for barriers in California The basic steps to accomplish thisbadly needed state-of-the-art transition are twofold:

1 Take a full system approach in which design, implementation, terization, and verification are iterative, inter-connected, and ongoing.This integrated approach includes optimizing the verification activities,defining the performance goals and action levels, and using methods

charac-to quantify uncertainty

2 Move implementation toward the smart structure approach now used

in buildings, bridges, roads, and other structures in which sensors andtelemetry are incorporated during construction This smart structureapproach will affect a lowering of cost through in situ analysis andhelp achieve the end state at many sites that are expected to have noon-site restoration personnel

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The technical process of total system performance assessment (i.e., integrationdesign, prediction, and data collection) may appear complex initially However,such processes are used in our everyday lives (e.g., buying a car, selecting anarea where to live, choosing a career) The approach here is to build on thefamiliar everyday aspects to develop a process that can be rigorously and defen-sibly applied to environmental remediation (Borns, 1997) The predictive toolsand data needs from subsurface monitoring programs for boosting long-termcontainment system performance are part of an integrated system of data collec-tion, decision analysis, and uncertainty analysis The engineering process ofdecision analysis and uncertainty analysis bridges the gap of predictive tools usedbetween the engineering design and the long-term performance assessment meth-ods (tens of years to thousands of years of performance) Decision analysis anduncertainty analysis also provide a basis for an integrated and interactive approachusing design, predictive models, and the analysis of the accumulated data atdifferent stages of the project

All projects, engineering and environmental, have built-in decision processesthat involve varying risk-reward scenarios (Lockhart and Roberds, 1996) Theseprocesses can be based on intuitive, analytic, numerical, and expert judgmentapproaches Developers, end-users, and stakeholders evaluating in situ stabilizationand containment systems are faced with a similar problem of selection However,the time periods of predicted performance are longer, and the consequences offailure are higher than these everyday examples of system prediction The pre-dictive tools and the data, which are used to ascertain long-term performance,are required to be rigorous, documented, and defensible Such predictions oflong-term performance are based on conceptual models of system design and thegeological environment (natural system) that encompasses the system Theseconceptual models and the adequacy of the performance prediction reflect theuncertainties and data quality that describe natural and designed containmentsystem performance

5.5.1.1 Links to Modeling and Prediction

An example of the important link among landfill design, modeling, and mance assessment is in the realm of permeable reactive barriers Morrison et al.(2001) described the importance of reaction path modeling to predict and verifyPRB performance Similarly, Roh et al (2000) demonstrated the importance ofmodeling the corrosion, precipitation, redox reactions, and sorption in predictingPRB material performance Hydrologic modeling was identified by Gupta andFox (1999) as essential for barrier design (including location, width, and materialselection) and for evaluating scenarios for performance predictions These sepa-rate modeling activities should be linked into a system with the data flowing fromthe subsurface or other verification activities The overall system can be linked

perfor-as in Figure 5.2

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5.5.1.2 Optimization

The integration of verification data and modeling permits another important step,which is the optimization of the integrated system An optimization approach forverification is a set of tools, at this time conceived to be computer programs, thattells the PRB user or designer where and how often measurements or samplesneed to be obtained to determine (1) whether the remedial system is operatingproperly, and (2) if risks have increased The goal is to monitor in space and time

to achieve the following:

• Meet regulatory requirements and/or assess residual risks using a imum number of monitoring stations located where the contaminant

min-or surrogate variable is most likely to be

• Sample at a frequency that captures contaminant movement to confirmthat all processes are operating effectively or trigger any necessarycontingency action

Gupta and Fox (1999) describe how hydrologic data combined with modelingdefine the optimal monitoring well locations and range of variation in flowdirection and flux needed for verification

5.5.1.3 Decision and Uncertainty Analysis

The decision analysis process (Figure 5.2) of Lockhart and Roberds (1996) can

be used as an example to identify the predictive tools and data needs for subsurfacecontainment projects This process also provides a basis for implementing anintegrated and interactive approach using design, predictive models, and theanalysis of the accumulated data at different project stages The tables are pro-vided to give an understanding of the types of parameters and processes that need

to be determined to apply risk decision analysis processes to a given problem.The evaluation of remediation sites demonstrates the difficulties in obtainingdata and the uncertainties of important parameters Water balance modeling,

FIGURE 5.2 The decision–analysis process of Lockhart and Roberds (1996) (Civil neering, April, 62–64).

Engi-Optimum decision

Implementation

& feedback Potential

Consequences Potential

Data Parameter Deﬁnitions

Mathematical Models

Conceptual Models

Sensitivity studies

Parameter Assessments

Potential consequences

Data Project description

Project alternatives

Decision criteria Screening &

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300 Barrier Systems for Environmental Contaminant Containment & Treatmentwhich is a significant component in transport modeling, provides an example ofthe difficulties in evaluation Such difficulties are due to the level of understanding

of the process and the adequacy of the data to support the evaluation For waterbalance modeling, it must be recognized that evaporation (or evapo-transpiration)cannot be reliably calculated in either humid or arid environments The bestestimates for the evaporation parameters are for humid environments Even forthe best of these estimates, a great deal of empirical judgment is required, andthe uncertainties are large The resulting recharge estimates are in error by asmuch as 100% or more It is virtually impossible to calculate evaporation for aridenvironments Errors of two to three orders of magnitude or more are not uncom-mon Because the understanding of processes is incomplete and because of thehigh degree of uncertainty for important parameters, there is no preferred code

or set of codes for hydrologic modeling at arid sites Hydrologic models for aridsites are still being tested and calibrated

As barriers have become more complex, there is an ever-increasing need to buildintelligence into them so that they can sense and react to environmental changesand impacts To achieve this, a nervous system is required that performs in amanner analogous to those living things sensing the environment, conveying theinformation to central processing unit (the brain), and reacting appropriately

A number of sensor technologies are being modified for use in verificationmonitoring systems for barriers These sensors can be embedded into the barriers

or in close proximity to the barriers, resulting in smart barriers with a built-innervous system These smart barrier systems offer the prospect of adding effectivemonitoring systems that are responsive to barriers but also are able to localizefailures and take appropriate action (Borns, 1997) Sensors incorporated intobarrier construction have the following advantages:

• They are inexpensive and can be placed in numerous positions wherepreviously only one data point was captured through expensive mon-itoring wells

• They can be designed to change out easily upon failure

• They reduce the sampling waste created in conventional monitoringprograms

• They can be placed in difficult to reach locations and possibly eliminateexposure to contaminated mediums for field workers who would nor-mally have to collect samples

• Through the iterative process, they improve the model

• Because most barriers will outlive most monitoring sensors, Everettand Fogwell (2003) have stressed the importance of long-term access

to critical subsurface monitoring locations These locations for capsand liners are discussed later in this chapter

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One of the most effective monitoring technologies currently being employed

is fiber optics Fiber-optic systems involve fiber-optic sensors and communicationlinks that allow the measurements of critical parameters of materials, structures,liquids, and gasses Surrogate parameters are good indicators of barrier perfor-mance and are easily achievable with fiber-optic sensors Surrogate measurementssuch as moisture, pH, temperature, flow/velocity, and barometric pressure aregood indicators of barrier failures The monitored moisture data facilitates site-specific understanding of the transport pathways and processes that influencecontaminant movement

The technical discussions of how fiber-optic sensors operate are not discussed

in this chapter because a number of manufacturing options exist Simply stated,fiber-optic sensors rely on the interaction of a light beam in the core of the fiber-optic cable with the parameter to be measured or some interaction thereof Thecladding on the fiber-optic cable can also be treated to produce the desired results.The advantages of this technology include lightweight systems, immunity toelectromagnetic interference, and the ability to be imbedded into hostile environ-ments with extremely high bandwidth capability Fiber-optic sensor systems cansense environmental changes within or around the barriers, interpret the measure-ments, and initiate an appropriate reaction to these changes Some of the param-eters that are being measured using this technology include strain, temperatures,acoustics, moisture, pH, flow, and chemicals (Udd, 1995)

Representative distributed fiber-optic sensors allow measurements of specificparameters and can help determine the location of where the measured-inducedchange occurs (Udd, 1995) Distributed chemical sensors can be constructed bycoating an optical fiber with indicator chemicals The chemical to be senseddiffuses into the cladding, modifying the absorption of the dye and accordinglychanging the attenuation of the fiber laser or light beam, which represents thechemical to be measured Additional information can be found in the bibliography

of Udd (1995)

For example, fiber-optic sensors have the potential to enable smart barriersthat would be difficult or impossible to implement using conventional electronictechnology High priority barrier-monitoring parameters discussed at the Long-Term Monitoring Sensor and Analytical Methods Workshop sponsored by theUnited States Department of Energy (USDOE) and its Characterization, Moni-toring, and Sensors Technology (CMST) Program include moisture content, mois-ture flux, and moisture potential (USDOE/CMST, 2001) Engineering goals forlong-term monitoring sensors include making the sensors easy to understand,install, calibrate, operate, and maintain with a capability to service Monitoringsystems could easily be automated with data transmission via telemetry for remotecontrol and data processing capability Many sensors that meet short-term needsfor barrier performance could be used as springboards for long-term monitoringsensor development Most costs would be significantly less than the currentbaseline cost for a deployable system with a replacement cycle every two years(USDOE/CMST, 2001)

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5.5.2.1 Long-Term, Post-Closure Radiation Monitoring

Systems (LPRMS)

An example of a new monitoring approach is the LPRMS that uses commerciallyavailable components in a reliable, low-cost, multipoint system for real-time,long-term, unattended monitoring of closed waste sites The system measures awide range of radionuclides and activity levels applicable to a large number ofUSDOE sites

The LPRMS is designed for gamma detection in subsurface soils The ation probe consists of a sealed assembly that contains a butt-coupled, thallium-doped sodium iodide NaI (TI) scintillator/photomultiplier tube (PMT) and amulti-channel analyzer (MCA) This assembly, termed the nanoprobe, can bedropped into polyvinyl chloride (PVC) casings that are pushed into the soil usingcone penetrometer technology (CPT) At the surface, solar-powered remote sta-tions (Figure 5.3) at each measurement location incorporate the system powersupply and a cell phone modem to communicate to an off-site host computer,which can be located hundreds or thousands of miles away A large number ofremote stations can each operate independently (Figure 5.4) and, without humanintervention, send their daily or weekly results to the host computer for analysis,

radi-FIGURE 5.3 Conceptual drawing of installed system (In Situ Remote Sensing and works, 1999a).

Net-6-17

System Architecture

1.5" × 6" NaI detector PMT and MCA

Power & digital

Communication

Cable

OFF-SITE HOST COMPUTER

Cell phone communication tower

PVC Pipe (installed using CPT)

Land line to host computer

Environmental enclosure

Enclosure to well cover

Deep cycle battery

Modem power switch

& RS485 to RS232 converter

REMOTE DETECTOR

STATION

Modem

Mast Battery

charge

controller

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data trending, and alarming If required, the nanoprobes are easily serviceablethrough retrieval from the PVC casing for repair or replacement

This system is designed to be capable of monitoring large numbers of manently installed probes over long-term periods The above ground location ofmost of the electronic components and the absence of below ground componentsthat require maintenance minimizes long-term costs

per-This technology can remain unattended for long time periods while providingautomated data generation, analysis, formatting, and reporting from many mon-itoring locations Additional advantages are as follows:

• Real-time detection of nine typical (within USDOE) radionuclides inthe media surrounding the sensor eliminates the long turnaround timeencountered with conventional sampling and laboratory analysis

• Sensor-based automated data generation, although not currently assensitive as typical laboratory analysis, reduces the potential for error

FIGURE 5.4 Schematic of System Components (In Situ Remote Sensing and Networks, 1999a).

Conceptual drawing of installed

system

Antenna

Cell phone communication tower Remote detector stations

Solar panel

Environmental enclosure

NaI detector and MCA PVC Casing 4040_C005.fm Page 303 Wednesday, September 21, 2005 12:28 PM

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304 Barrier Systems for Environmental Contaminant Containment & Treatmentfrom manual sampling, sample tracking, laboratory data generation,analysis, and reporting.

• Minimal long-term manpower is required to operate the LPRMS whencompared with the baseline conventional sampling program

5.5.2.2 Environmental Systems Management, Analysis,

and Reporting (E-SMART™) Network

Another example of an intelligent new verification system is the E-SMARTnetwork The E-SMART network installation includes the application of sensorsthat detect and measure contaminants in groundwater and soil gas as well asphysical parameters such as barometric pressure, pH, and temperature

Conventional monitoring systems suffer from limited expandability The goal

of the E-SMART network is to eliminate these incompatibilities by defining anopen standard for constructing modular monitoring networks This vision ofcompatible environmental sensors, sampling devices, control systems, and dataanalysis systems is shown in Figure 5.5

The E-SMART network integrates diverse monitoring and control gies by using a modular, “building block” design approach to allow for flexiblesystem configuration The network treats each smart device — whether a sensor,sampler, or actuator — as a black box that obeys the standard communicationprotocols and electrical interfaces for the network This approach allows multiplevendors to produce different sensors that meet the same functional specificationand that can be interchanged without impacting operation

technolo-Each E-SMART sensor or actuator contains its own microprocessor brainthat provides it with a means of storing calibration, control, status, and quality

FIGURE 5.5 E-SMART Vision (In Situ Remote Sensing and Networks, 1999b).

Workstation

Plume Smart sensors

Sampler

E-Smart network management system

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assurance data This brain communicates using the network protocol, managesdata, and controls operation of the smart device Because the sensor manufacturerembeds the sensor-specific information within the smart device, the E-SMARTuser is not required to develop calibration or control programs for specific sensors

5.5.2.3 Direct Push Technologies

Direct push technologies have proven to be effective site characterization andverification tools in recent demonstrations at the USDOE Hanford site (Wash-ington) and U.S Air Force sites at Harrison Air Force Base (AFB) (Indiana)(closed since 1995), Misawa Air Base (Japan), and Kirtland AFB (New Mexico).CPT has met refusal in some geologies before being advanced to the desireddepths at dense nonaqueous phase liquid (DNAPL) sites A sonic CPT systemcombines the speed and high penetration capabilities of sonic drilling with theeconomic, continuous data logging of CPT, thus allowing access through difficultstrata An important application of CPT is to install monitoring points Percussion-driven probes have been enhanced by integration with a laser-induced fluores-cence spectrometer and other sensors, providing a less expensive and more easilydeployed system Successful integration of real-time DNAPL chemical sensingand geophysical instrumentation with horizontal directional drilling technologywill allow characterization of DNAPL-contaminated strata without introducing avertical conduit to underlying formations and other obstacles such as buildingsand barrier floors Direct push technology is an excellent platform for makingcontinuous measurements of contamination: it is useful in pushing sensing sys-tems into the subsurface; for installing monitoring wells and points; and forobtaining gas, water, and soil samples for environmental testing

CPT-associated sensor technologies such as soil strength stain gauges, tivity, soil moisture, pore pressure, gas chromatography/mass spectrometry(GC/MS), multi-gas and organic vapor monitoring, and laser-induced fluores-cence (LIF) (Kram et al., 2001a,b), provide enhanced site characterization, and,while still on-site, can quickly and cost efficiently install monitoring wells.Kram’s group (Kram and Keller, 2004a,b; Kram et al., 2004) has optimizedseveral laser excitation sources for specific carbon ranges using LIF, allowingreal-time profiling of petroleum hydrocarbon and some DNAPLs By including

resis-a CPT well instresis-allresis-ation component during verificresis-ation, plume delineresis-ation effortscan be accomplished within one field mobilization When compared with con-ventional approaches, this seamless method of optimizing well placement reducestime and avoids additional data review, permitting, and mobilization/demobiliza-tion costs Recent work by the U.S Navy (Kram and Keller, 2004a,b; Kram et al.,2004) compares conventional well performance with pre-packed direct-push wellinstallations If successful, this approach referred to as a Site Characterizationand Analysis Penetrometer System (SCAPS) and shown in Figure 5.6 will result

in significant verification monitoring cost savings

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Data processing space VEHICLE

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5.5.2.4 Nanotechnology Sensors

Nanotechnology enables the creation of functional materials, devices, and systems

by controlling matter at the atomic and molecular scales to exploit novel

prop-erties and phenomena Most chemical and biological sensors, as well as some

physical sensors, depend on interactions occurring at these levels Potential

appli-cations under development include chemical sensors and probe tips

Nanotech-nology such as carbon nanotechNanotech-nology will impact almost every aspect of our

lives including fuel cells, portable X-ray machines, extremely lightweight strong

fabrics, and artificial muscles The discovery of carbon nanotubes (CNT) —

extremely narrow, hollow cylinders made of carbon atoms — by Sir Harold Kroto

(Florida State University Nobel laureate) and his colleagues initiated an entirely

new field of chemistry research aimed at understanding the properties of these

unusual molecules The characteristics of and the ability to grow CNTs at specific

locations and manipulate them afterward make it likely that the tubes will have

considerable impact on electronics and sensors (Smith and Nagel, 2003)

High levels of integration made possible by nanotechnology give the sensor

the ability to be the device and possibly also the system Nanotechnology takes

the complexity out of the system and puts it into the material Fluorescence and

other means of single molecule detection are being developed Nanotechnology

will enable the design of sensors that are much smaller, less power hungry, and

more sensitive than current micro- or macro-sensors Sensing applications will

thus enjoy benefits far beyond those offered by micro-electromechanical systems

(MEMS) and other types of micro-sensors The ability to install hundreds of

sensors in a small space allows malfunctioning devices to be ignored in favor of

the remaining good ones, thus prolonging a system’s useful lifetime

Examples of current work include development of a miniaturized gas

ioniza-tion detector that could be used for gas chromatography Nanotube hydrogen

sensors have been incorporated in a wireless sensor network to detect hydrogen

concentrations in the atmosphere In addition, a chemical sensor based on CNT

has been developed for gaseous molecules such as nitrogen dioxide (NO2) and

ammonia (NH3)

Nanotechnology is certain to improve existing sensor applications and be a

strong force in developing new ones Nanoscale materials and devices are

begin-ning to be integrated into real-world systems, and the future looks bright in

particular for integrating the wireless smart sensors into hazardous waste barriers

and containment systems

Toshiba Corporation is providing technical coordination to an international

con-sortium of academic institutions and companies working to develop AEMS, a

continuous, automated monitoring of groundwater pollutants The consortium

seeks to bring the know-how of its member organizations to the development and

commercialization of a system providing enhanced monitoring and identification

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of pollutants in the groundwater and subsoil below manufacturing facilities,

including pharmaceutical, chemical, and food-processing facilities AEMS is

expected to detect and identify leaks of contaminants at the source and in real

time to support the very earliest deployment of measures to clean up polluted

groundwater and soil In practical applications, AEMS will comprise an array of

on-site biosensor systems installed in wells drilled around a monitored barrier

These wells feed groundwater samples to the systems and provide the means for

continuous monitoring of groundwater contamination around the designated area

The biosensor is bio-mimetic and consists of two layers of artificial lipid

mem-branes that are used to evaluate the toxicity of chemicals in the groundwater The

membranes generate specific responses to different types of organic compounds

in pollutants, allowing identification of hazardous substances The sensitivity of

the biosensor has been improved to the point where it is capable of detecting

hazardous substances, such as trichloroethylene (TCE), in concentrations as low

as one part per billion (10–9 or 0.001 milligrams per liter)

Under the direction of Dr Thomas W Fogwell, Scientific Director at Fluor

Hanford, Richland, Washington, a modification of the transport modeling code,

STOMP (Subsurface Transport Over Multiple Phases), is in development in

support of surface barrier designs The need for a new code is driven by design

requirements for approximately 200 new surface barriers needed to close many

of the waste sites on the Hanford Central Plateau Several different surface barrier

designs have been proposed based on a graded approach that fits degree of

protection with site risk There is a clear need to be able to evaluate and compare

design alternatives, while considering waste site-specific needs in view of

tech-nical, regulatory and economic issues Because all of the designs cannot be built

and evaluated over the appropriate spatial and temporal scales, computational

models offer an opportunity to perform side-by-side comparisons over the design

life for a range of conditions The overall objectives of this work are as follows:

• Extend the plant-soil atmosphere dynamics module to 3-D space

• Add capabilities to analyze the effects of dynamic structural and

hydrau-lic properties that may result from deformation (This will require the

addition of algorithms for static and dynamic localized grid refinement.)

• Calibrate and validate the model using data from Pacific Northwest

National Laboratory’s (PNNL) Field Lysimeter Test Facility (FLTF),

the prototype Hanford Barrier, and other selected experimental

capil-lary barriers in the western U.S

• Perform a sensitivity analysis to determine the influence of key

param-eters and model discretization on model predictions, and identify the

key model parameters

• Provide a barrier design tool as well as technical guidance and

docu-mentation to support the preconstruction performance evaluation of

candidate barriers

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New code to modify STOMP was completed at the end of fiscal year 2003

The code was calibrated in January and February 2004 and scheduled to be ready

for application by October 2005

5.6 DRIVERS FOR IMPLEMENTATION

OF NEW APPROACHES

A major issue in verification monitoring technology development is identifying

what motivates stakeholders, end users, and regulators to move from state of the

practice to state of the art Such drivers are often a reduction in risk and a reduction

in cost In the realm of subsurface verification, the drivers for change are cost

and development of methods that enable the desired end states for remediation

sites Only recently has the USDOE begun to design verification systems that

meet or exceed the regulatory requirements for barriers Most communities still

use old state-of-practice barrier verification systems This chapter discusses

sub-surface verification and monitoring for several types of barriers: landfill covers,

PRBs, and walls and floors The discussion here begins with landfill covers, which

to date are the most common containment barrier in use But first, the drivers for

implementation of new approaches must be explored

For the 30 years or more life span of some sites that use covers or other barriers,

long-term monitoring costs can be larger than the initial barrier implementation

costs The system approach described in Section 5.4.1 allows several opportunities

to affect life-cycle costs of remediation

This first of these opportunities is optimization Optimization, with its

imbed-ded use of predictive tools, permits (1) the selection of the parameters to measure,

(2) the selection of the sensitivities of sensors, (3) the location and timing of

monitoring, and (4) the selection of appropriate action criteria With optimization,

the appropriate actions for a given site can be made, and, therefore, a

cookie-cutter approach need not be followed

The other major cost opportunity in applying state-of-the-art approaches is

in situ physical and chemical analysis In the mid-1990s, the USDOE was

spend-ing more than $200 million on chemical analysis to support its environmental

management and remediation activities As an example, the USDOE Savannah

River site (Aiken, South Carolina) requires 40,000 groundwater samples a year

at $100 to $1,000 per sample for off-site analysis (i.e., a total of $4 million to

$40 million per year) (Ho and Lohrstorfer, 2001)

Environmental remediation has begun to move toward different end states such

as brownfield rather than greenfield use (reapplication of the remediated lands

for industrial use), wildlife preserves, or other forms of public/private lands

INEEL led an inter-agency effort to develop the Long-Term Stewardship Science

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310 Barrier Systems for Environmental Contaminant Containment & Treatmentand Technology Roadmap (2001) that suggests that remediated sites will betransferred to locations that are minimally staffed with remediation personnel ornonmanned These sites will be required to be remotely monitor waste movement

by relying on in situ sensors.

5.7 COVERS

This section discusses some potential deployments of the barrier verificationdeployment methods is not meant to be exhaustive, but represents some of thepossible configurations to move from state of the practice to state of the art Thedata quality objectives (DQO) of the monitoring systems would need to be clearlyidentified, and the methods applied would provide a means of monitoring a landfillafter closure in lieu of certain groundwater monitoring In addition to this dis-cussion, two USDOE case histories are portrayed: one in New Mexico and another

to collect quantifiable results A typical design would be a basin lysimeter made

up of 100-mil high-density polyethylene (HDPE) installed under the bottomsump The lysimeter can extend 1.52 m beyond the perimeter of the bottom sumpand can be designed with an access pipe that allows the removal of any liquidcollected Due to the lateral flow patterns normally generated near capillarybarriers and those that exist at the interface between contrasting soil textures,such a basin lysimeter could be expected to detect most leaks in the bottom liner

of a landfill

Time-proven technologies like neutron moderation can be considered belowthe barrier liner systems of cells As new technologies are developed and oldtechnologies improved, consideration should be given to deploying or improvingthese new options Particular reference could be made to emerging volume-integrating technologies like high-resolution resistivity and cross-borehole ERT.This strategy of being prepared to employ future technologies as they developcould be facilitated by installing access tubing (probably perforated) beneath thebottom liners of new construction, providing a relatively inexpensive method ofaccommodating new technologies as they become available Of the new technol-ogies, those giving volumetric information seem to be the most promising Themain advantage of such a tubing network would be that ERT methods could beused to provide a spatial distribution of any detected leakage

methods mentioned in Section 5.3 that are applicable to covers This list of

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Even with today’s technologies, horizontally emplaced perforated accesstubes could be used for measuring parameters such as soil moisture movement,gamma detection, soil pore water sampling, and soil gas The perforated toolaccess tubes should span the entire length of a cell buried in a 1.22- to 1.83-mdeep trenches along the bottom of each cell and located in areas of potential linerfailure The multi-purpose, perforated access tubes could use the following types

of barrier-monitoring technologies in measuring the above-mentioned parameters:

a neutron probe, a sodium iodide gamma detector, and absorbent pads for uating soil pore water quality The value of this monitoring approach is that itrepresents a cost-effective graded method that would allow spatial monitoringbelow the landfill in order to locate liner failure positions Soil moisture alonecould be used as a cost-effective sentinel parameter, which could be supportedwith other parameters if required Perforated casing below the landfill mightpermit the collection of soil gas samples and could be used as part of a leakage

eval-or perfeval-ormance check of both the barrier liner and the caps

5.7.1.2 Verification Measurement Systems

Vertically emplaced perforated access tubes (open-holed at bottom) can beinstalled (for measuring soil moisture movement, gamma detection, and for col-lecting soil pore water samples) The access tubes can extend from the surface,through the barrier closure cover and the waste, but not through the bottom liner.These access tubes can be used for detecting vertical moisture changes throughoutthe waste, function as an access port for various other types of geophysical tools(e.g., neutron and gamma logging tools), provide access for absorbent pads, andpermit access for direct soil sampling through the open hole at the bottom It isimperative that a good seal be completed around the perimeter of the access tubes

to prevent preferential flow between the access tubes and soil material Thefollowing are other sensors that can be used with such a vertical tube system:

• TDR probe monitoring stations for each vertical access casing can beinstalled for measuring volumetric soil moisture

• Heat dissipation probe monitoring stations (co-located with the TDRprobes) can be installed on each of the vertical access casings tomeasure matrix potential, which is the driving force for unsaturatedmoisture movement

• Suction lysimeters in a vertical profile can be installed to collect soilpore water samples for chemical and radiological analysis

5.7.1.3 Barrier Cap Monitoring

At closure, instruments should be installed in the final barrier cover to measureits effectiveness of the cover in restricting moisture movement There are manypotential designs Some involve instrumentation of just the cap and some schemesinvolve vertical neutron access tubes installed in the cover and through the waste4040_C005.fm Page 311 Wednesday, September 21, 2005 12:28 PM

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to the bottom of the trench Therefore, meaningful, post-closure, verificationbarrier-monitoring data should not be relied upon until a baseline has beenestablished and moisture equilibration has stabilized Once stabilization has beenachieved in the post-closure monitoring system, it is anticipated that much of thegroundwater monitoring specific to a facility could be eliminated or reduced inscope

Settlement is an important long-term risk associated with the barrier mance of both the liner and the cap A system of determining settlement by usingeither survey stakes, topographic remote sensing, fiber-optic cables, GPR forsettlement plates, or visual inspection should be considered A time-consistenttopographic survey of the cap should be generated to identify such items assettlement depressions, erosion features, and vegetative features that may developover time This survey can also serve to give early warning to possible (but notcertain) future water leaks The indication of subsidence can trigger monitoring

perfor-in more localized areas

The mixed waste landfill in Albuquerque, New Mexico, was established in 1959

as a disposal area for low level radioactive and mixed waste generated by researchfacilities of Sandia National Laboratory The landfill accepted low level radioac-tive and mixed waste from March 1959 through December 1988 Approximately30,480 cubic meters of low level radioactive and mixed waste containing approx-imately 6300 curies of activity were disposed of in the landfill For the landfillcover design, Sandia National Laboratory and the state elected to use RCRASubtitle C facilities regulations as guidance The goal of the USEPA-recom-mended design of final covers for RCRA Subtitle C facilities was to minimizethe formation of leachate by minimizing the contact of water with waste, minimizefurther maintenance, and protect human health and the environment consideringfuture use of the site

The USEPA accepts alternative cover designs that consider site-specific ditions, such as climate and the nature of the waste, that meet the intent of theregulations An alternative cover design consisting of a thick layer of native soilwas developed as the closure path for the mixed waste landfill The design relies

con-on soil thickness and evapo-transpiraticon-on to provide lcon-ong-term performance andstability and is inexpensive to build and maintain because of the availability ofsuitable soils in the area The cover meets the intent of RCRA Subtitle C regu-lations because of the following:

• Water migration is minimized through the cover

• A monolithic soil layer minimizes maintenance

• Erosion control measures minimize cover erosion

• A “soft” design accommodates subsidence

• Permeability of the cover is less than or equal to that of natural subsoilspresent

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The proposed mixed waste landfill alternative cover incorporates a redundantinfiltration monitoring system that includes both baseline neutron probe accessholes and advanced distributed fiber optics The cover infiltration monitoringsystem is coupled with a shallow vadose zone monitoring system deployeddirectly beneath the landfill The shallow vadose zone monitoring system consists

of three neutron probe access holes drilled at 45° to a depth of 43.28 m belowground surface The close-coupled cover and shallow vadose zone monitoringsystem, in essence, functions as an early warning system, providing early detec-tion of a potential threat to groundwater, and allows corrective action to beinitiated before significant contaminant migration occurs This redundant moni-toring approach was designed to protect groundwater resources and was imple-mented because of its simplicity, low cost, and long-term viability

The close-coupled monitoring system is monitored closely The frequencyand duration of post-closure monitoring was established in consultation with thestate and formally documented in the mixed waste landfill long-term care plan.The cover and vadose zone monitoring system provides infiltration and perfor-mance information and early detection of potential contaminant migration fromthe landfill, as well as establishing background and trend analysis information.The close-coupled cover and shallow vadose zone monitoring system is a simpleyet robust system designed to meet the intent of long-term RCRA and USDOEperformance requirements: reducing labor-intensive, long-term groundwatermonitoring and allowing substantial cost savings

5.7.2.1 Cover Infiltration Monitoring

The landfill alternative cover will contain six vertical neutron probe access holes,two in each of the original disposal areas Each access hole will extend throughthe cover and an additional 2 ft into original landfill soils Aluminum casings will

be installed after cover construction is complete by hand auguring diameter boreholes through the cover and driving the aluminum casing to properdepth Each casing will be fitted with a perforated, tapered drive-tip A 0.3 m by0.3 m concrete pad will be placed at the collar of each casing to prevent prefer-ential flow down the annulus The cover will also contain a distributed fiber opticsinfiltration monitoring system that will be deployed in two lifts The lowermostdeployment will be on the prepared sub-grade surface The uppermost deploymentwill be 0.45 m above the prepared sub-grade surface between the third and fourthnative soil lifts The uppermost fiber-optic grid will be transposed 90° from thelower grid to maximize spatial resolution and increase monitoring efficiency

6.25-cm-5.7.2.2 Neutron Moisture Monitoring

The neutron moisture probe is increasingly being applied to address ization and infiltration issues at environmental sites undergoing long-term care.Neutron moisture monitoring has become the industry standard for soil moisturemeasurement, and its operation and data interpretation is well established The4040_C005.fm Page 313 Wednesday, September 21, 2005 12:28 PM

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character-314 Barrier Systems for Environmental Contaminant Containment & Treatmentprincipal advantages of this technique are repeatability, precision, and long-termviability Nothing is permanently installed downhole, which allows for periodiccalibration of the neutron probe Practical considerations and knowledge ofvadose zone hydrologic processes guide the number and location of neutron probeaccess holes.

5.7.2.3 Fiber Optics Distributed Temperature

Moisture Monitoring

The distributed fiber-optic infiltration monitoring system proposed for the cover

is based on the observation that a change in soil-water content causes a sponding change in soil thermal conductivity When constant power is dissipatedfrom a line heat source (in this implementation, an electrically conducting wirebundled with the optic fiber), the temperature increase near the heat sourcedepends on the thermal conductivity of the surrounding medium As soil-watercontent increases so does its thermal conductivity The temperature increase asmeasured by the fiber optic will be reduced because of the conduction of thethermal energy away from the heat source Measurement accuracy is ±1°C with

corre-a resolution of corre-approximcorre-ately 1 m over the entire length of the ccorre-able The opticcorre-alfiber and line heat sources are bundled in a hermetically sealed stainless-steelcable that is 0.6 cm in diameter

An important advantage of fiber-optic sensors is their ability to providepassive sensing of a wide variety of physical parameters This not only meansthat the sensor operates without the need for electrical power, but the overallsystem (including the input-output fibers that serve as the telemetry links) is alsoelectrically passive, and, thus, the entire system exhibits low intrinsic suscepti-bility to the effects of electro-magnetic interference Experience to date in envi-ronmental monitoring indicates that electrically based sensors are extremelysusceptible to electrical storms, particularly in the semi-arid and arid west andsouthwest Therefore, issues of electrical passivity are of paramount importancewhen a sensor is required for long-term monitoring and performance in anelectrically noisy environment

5.7.2.4 Shallow Vadose Zone Moisture Monitoring

Three angled, 11.4-cm outside diameter, 0.5-cm inside diameter access holes will

be installed in the shallow vadose zone directly beneath the mixed waste landfill:two to the west and one to the east of the cover The vadose zone access holeswill be spaced at equal increments: the east access hole bisecting the two westaccess holes The access holes will be installed under separate contract usingresonant sonic drilling Resonant sonic is the preferred drilling technique because

it literally fluidizes and displaces the surrounding soil as the drill string advances,creating a very tight fit between the drill string and the formation No cuttingsare generated, and no fluids are used to advance the drill string Backgroundvalues for the soil volumetric moisture content will be measured during installation4040_C005.fm Page 314 Wednesday, September 21, 2005 12:28 PM

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of the neutron probe access holes Each access hole will be collared approximately

3 m outside of the toe of the cover side slopes Each access hole will be drilled

60 m at 45˚ to a true vertical depth of 42 m As each access hole is completed

at 60 m, the 11.4-cm sonic drill string will be left in place down-hole andunscrewed at the surface leaving about 0.6 m of stickup Each sonic drill stringwill remain open to the vadose zone A protective cover constructed of steel pipewill extend 0.6 m below grade and 0.9 m above grade Each protective cover will

be fitted with locking caps and secured with locks

5.7.3 CASE HISTORY: FERNALD ON-SITE DISPOSAL FACILITY

The Fernald Environmental Management Project (FEMP), located 29 miles west of Cincinnati, Ohio, is constructing an aboveground on-site disposal facility(OSDF) that is used to isolate low level radioactive waste generated by plantremediation activities The disposal facility design allows for the construction ofnine cells filled with a total of 1.9 million m3 of low-level radioactive soil andconstruction debris from cleanup activities at the site The disposal cells aredesigned to remain stable for 1000 years to the extent reasonable and, in anycase, no less than 200 years

north-Each of the OSDF cells has a bottom liner system, including a leachatecollection system that is approximately 1.52 m thick It is composed of multiplelayers of clay and gravel (Figure 5.7) and a geosynthetic liner that is designed

to protect the underlying Great Miami Aquifer The cap of each cell is a component cover approximately 2.68 m thick with components to limit water

multi-FIGURE 5.7 Multiple-layer system.

Vegetation (typ) Erosion mat

Vegetative soil layer Biointrusion barrier Cover drainage layer

Granular ﬁlter Top soil

Compacted clay cap

Protective layer

Leachate collection system (LCS) drainage layer

Leak detection system (LDS) drainage layer

Compacted clay liner Subgrade

0.15 m 0.53 m

2.65 m

Primary geomembrane liner (80-ml)

Secondary geomembrane liner (80-ml) Secondary Geosynthetic clay liner

Primary Geosynthetic clay liner

Geomembrane cap (60-ml) Geosynthetic clay cap Geotextile cushion Geotextile cushion

Geotextile cushion Geotextile ﬁlter

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316 Barrier Systems for Environmental Contaminant Containment & Treatmentinfiltration (geomembrane) and biointrusion (cobblestones) (Kumthekar et al.,2002) As of September 2003, Cell 1 was filled and capped with the monitoringsystem in place; Cell 2 was filled with capping planned for 2003; and Cells 3,

4, and 5 were partially filled

The objective was to create a monitoring system that generates data on thephysical conditions of the cell cover This objective was selected because engi-neering experience with final covers incorporating composite barriers indicatesthat physical stability is the most important factor affecting long-term perfor-mance The following five critical monitoring parameters were established based

on the functional requirements and design criteria of the OSDF:

1 Pore water pressure in the drainage layer — Buildup of water pressure

in the drainage layer must be kept below a critical value to maintainphysical stability

2 Total and differential settlement — Settlement must be kept at a imum so as not to impact barrier performance, hydraulic gradients, andthe free flow of moisture throughout the drainage layer Distortionsmust be limited to less than 10%

min-3 Soil-water content and soil-water potential — These elements are ical to the health of the root zone within the vegetative layer, whichprotects all other layers and must remain in place for other layers toretain effectiveness

crit-4 Soil temperature above barrier layer — To function properly, the barriersystem must not freeze

5 Overall condition of cover — This parameter includes institutionalcontrols such as maintenance of signage within the buffer area, as well

as ecological controls such as the monitoring of biotic intrusionthroughout the cover system Erosion must be prevented through themaintenance of a healthy vegetative layer, which in turn ensures thatthe biointrusion layer remains functional

A monitoring system was designed to monitor these critical parameters aswell as the following four criteria to maintain the OSDF for at least 200 years(Table 5.3): (1) long-term performance, (2) availability for deployment in nearterm (within 12 months), (3) remote access and control, and (4) capability tointegrate into a data management system It was also essential to develop a systemthat was easily accessible for equipment maintenance and technology updates asnew cells are built and filled

The monitoring system for Cell 1 was installed to address these criteria.Sensors were installed in a series of nests at the most appropriate area to monitorbarrier stability There are 10 soil-water status nests that measure soil-water contentand potential, seven pressure transducer risers that monitor pore water pressure

in the drainage layer, seven settlement plates and rods, and eight sets of GPRthat monitor total and differential settlement (Figure 5.8) There are three waterstatus nests on each of the west, east, and northern slopes of Cell 1 and one at4040_C005.fm Page 316 Wednesday, September 21, 2005 12:28 PM

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the top of the cell to observe conditions at the highest point and the shallowestslope Each soil-water status nest has four content reflectometers and four soil-water potential probes equally spaced in the vegetative layer (Figure 5.8)(Kumthekar et al., 2002) Seven pressure transducer risers were installed along

TABLE 5.3

Critical Parameters and Selected Monitoring Technologies in the OSDF Final Cover System

Drainage layer Pore water pressure in

drainage layer

Submersible pressure transducers

Surface and internal

cover grades, barrier

Routine topographic survey Web cam

Visual and/or remote sensing

Hazardous Waste Management.

FIGURE 5.8 Layout of instrument nest on the final cover for Cell 1.

Soil water status nest Pressure Transducer Cabling

Fiber optic GPR plate

Cover perimeter Settlement plate

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318 Barrier Systems for Environmental Contaminant Containment & Treatmentareas of Cell 1 where the slopes are the longest and pore water pressures are thehighest: one on top of the cell and two each down the northwest slope, northslope, and northeast slope Along each slope, one of two transducers was placednear a drainage layer where high pore pressure could be expected if the layerbecame obstructed Transducers were placed at the top and middle of the slope

to monitor the distribution of pressure along the slopes Each transducer allowsunimpeded flow of water through the riser and is constructed with schedule PVCpipe to prevent damage and aid in the longevity of the riser Geotextile is usedalong the riser pipe to prevent plugging of the pipe, movement of barrier materialsbetween layers, and material from entering the well The geotextile also serves

as a cushion to prevent any damage to the geomembrane below it The settlementplates and rods were installed alongside of the pressure transducer risers Plateswere installed on the surface of the drainage layer with the rods extending to theground surface The GPR plates were installed on the west and east slopes andtwo each along the northwest, north, and northeast slopes

A subterranean vault was installed at the top of the cell to house both thedata logger and multi-plexers Within the sealed vault, humidity sensors monitorthe atmosphere for changes that could damage the equipment To allow for easyaccess and equipment repair with minimal manpower, the vault can be raisedwithout difficulty above ground The data logger is connected to a radio trans-mitter via a fiber-optic cable, allowing data to be uploaded to a managementsystem

It is expected that modification to this design will be made to subsequentcells based on lessons learned from the installation and subsequent monitoring

of this system

5.7.4 VERIFICATION NEEDS

Verification needs for covers were established at the workshop through the PRBwork group and the subsurface verification subgroup and were as follows: (1) waterbalance (e.g., storage, percolation, soil moisture, flux, flow rates), (2) gases andvapor transport (e.g., methane, oxygen, radon), (3) physical state (e.g., stiffness,cracks), and (4) long-term monitoring trends (i.e., space and time) Wilson et al.need that appears is the verification of the water balance within the cover system.Both the vadose zone science and technology roadmap and the long-termstewardship science and technology roadmap strongly suggest that the compo-nents of subsurface verification be incorporated within the remediation designfrom the onset (INEEL, 2001; USDOE, 2002) This is a full system design Fullsystem designs interactively incorporate prediction with optimization, sensorplacement, and approaches to trend analysis

from the state of the practice to the state of the art with end user and regulatoryacceptance In this example, the monitoring approach was incorporated in theconstruction design of the cover The monitoring approach is a combination of

The case history described in Section 5.4.1 provides an example of moving(1995) identified additional needs for covers (Table 5.4) The dominant verification

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tradition neutron probes and new applications of distributed fiber-optic sensors.Both approaches are aimed at measuring the water balance within the cover

5.7.4.1 Optimization and Trend Analysis

Site closures involving residual contamination and engineered remediation tems such as covers require monitoring relevant pathways to protect human health

sys-TABLE 5.4

Data Needs for In Situ Containment and Stabilization of DOE Sites

A Understanding of how data can be

applied to different scales

B Spatial and temporal heterogeneity

A Effective porosity

B Mass water content

C Volumetric water content

D Infiltration capacity

E Saturated hydraulic conductivity

F Soil-water characteristic curves

G Conductivity/pressure head relationship

IV Parameters related to climate

F Chemical degradation rates

G Radioactive decay rates

H Organic matter content

a Modified from Wilson, L.G et al (1995) Handbook of Vadose Zone Characterization and

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320 Barrier Systems for Environmental Contaminant Containment & Treatmentand the environment and to ensure that remediation systems are operating prop-erly Uncertainties in conceptual models, key parameters controlling importantfluxes, and forcing functions require a statistically-based monitoring networkcharacterized by the zone of influence (support) of the sensors/sampling device,the spacing between sensors, and the extent of the domain/site that needs to bemonitored Initial applications will use tools for each pathway, air, surface, andsubsurface, because models and approaches that consider coupled systems arecurrently limited However, as research proceeds, a coordinated monitoringapproach can be built.

Tools that optimize monitoring systems will lead to a 50% cost reduction anddecrease uncertainty by a factor of five over systems based on judgment or regulargrid systems An optimized monitoring system will allow risks and the uncertaintyassociated with risks to be assessed more accurately at all remediation sites.Over the life of a remediation project, monitoring costs can be substantialand can even exceed the costs of the remediation system The capability to reducemonitoring while retaining the critical information for either the site or theengineered barrier will lead to enhanced efficiency

5.7.4.2 Sensors and Other Hardware

Water balance is the critical verification need for covers The technical baselinefor subsurface sensors utilized for this need was described by Scanlon et al.(1997) Further information regarding the sensor types that can be used is provided

in Tables 5.5–5.8

TABLE 5.5

Toolbox: Water Balance

The water balance equation can be solved for any individual component

Advantage: Useful at early stage of site characterization Disadvantage: Field measurements are time consuming

Prediction of response of near surface groundwater levels to other parameters of the hydrologic cycle

Advantage: Useful for sites that want to avoid pump test that bring contaminants to surface Disadvantage: Shallow aquifers

Measure specific yield

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5.8 PRBS

Since the 1995 International Containment Technology Workshop sponsored byDuPont, the USEPA, and the USDOE, the interest in PRB technology has greatlyincreased, along with the number of sites where this technology is the selectedremediation method (USEPA, 2002) The use of PRBs to remediate halogenatedhydrocarbons (Gillham and O’Hanneisin, 1994) and metals (Morrison et al., 2002)

TABLE 5.6

Toolbox: Baseline In Situ Chemical Sensors

Advantage:

Undisturbed real-time measurements

Detect a contaminant plume

Calibration

Detect the presence of specific ions

a detector; an excitation signal from the light source is transmitted down the cable to the FOCS and the sensor fluoresces and provides a constant intensity light source that is transmitted back up the cable and detected as

a return signal

Advantage: Selective real-time

measurement, eliminate chain of custody

Disadvantage:

Equipment not readily available

Detect presence of specific organic compounds in water and vapor phase

Solid fibers: BTEX, DCE, TCE, carbon tetrachloride, chloroform, JP-5, gasoline Porous fibers: Humidity, pH, ammonia, ethylene, CO, hydrazine, and BTX

Tiêu đề	Barrier Systems for Environmental Contaminant Containment and Treatment - Part 5 (End)
Tác giả	David J. Borns, Carol Eddy-Dilek, John D. Koutsandreas, Lorne G. Everett
Trường học	Florida State University
Chuyên ngành	Environmental Engineering
Thể loại	Chapters
Năm xuất bản	2005
Thành phố	Tallahassee

Định dạng
Số trang	70
Dung lượng	2,28 MB