U.S. EPA Contaminated Site Cleanup Information (CLU-IN)


U.S. Environmental Protection Agency
U.S. EPA Technology Innovation and Field Services Division

Solidification

Guidance

The S/S process involves the incorporation of binders, and depending upon the waste or binder, additives and/or water with contaminated media to produce a material with improved physical and chemical properties. The overall process commonly includes (a) the establishment of material performance specifications based on remediation goals, (b) treatability studies intended to develop an appropriate mix design of reagents and additives that addresses material performance specifications and refines implementation techniques and construction performance specifications, (c) mobilization of field equipment and implementation of the S/S mix design at field scale, and (d) monitoring of material performance after the remediation process is completed (ITRC 2011).

Additional Information

Amending Soils with Phosphate as Means to Mitigate Soil Lead Hazard: A Critical Review of the State of the Science (Abstract)
Scheckel , G.L. Diamond , M.F. Burgess , J.M. Klotzbach , M. Maddaloni , B.W. Miller, C.R. Partridge, and S.M. Serda.
Journal of Toxicology and Environmental Health, Part B: Critical Reviews 16(6):337-380(2013)

Phosphate amendments have been studied as a means to mitigate risks from exposure to Pb in soil by promoting the formation of highly insoluble Pb species, such as pyromorphite. The formation of insoluble Pb species thereby reduces the risk of Pb leaching through soils into drinking waters and absorption by soil biota, and may make it less bioavailable during physiological transport in the human gastrointestinal tract following incidental ingestion. This paper provides a detailed description of phosphate chemistry and the goal of converting Pb into pyromorphite. Slides by Scheckel et al. (2013)Adobe PDF Logo

Adobe PDF LogoEngineering and Design: Treatability Studies for Solidification/Stabilization of Contaminated Material
U.S. Army Corps of Engineers. ETL 1110-1-158, 38 pp, 1995

Furnishes information and guidance on scoping a treatability study for S/S of contaminated material.

Adobe PDF LogoGuidance on the Use of Stabilisation/Solidification for the Treatment of Contaminated Soil
Bone, B.D., L.H. Barnard, and C.D. Hills.
Environment Agency, UK, Science Report SC980003/SR1, 103 pp, 2004

Examines the use of hydraulic binder systems that are usually designed to provide both leaching and physical improvements to the contaminated material. Strongly recommends treatability studies (bench-scale tests) to evaluate and validate the performance of the mixes for a particular site.

Adobe PDF LogoInnovative Site Remediation Technology Design and Application, Volume 4: Stabilization/Solidification
Conner, J.R. et al.
EPA 542-B-97-007, 234 pp, 1997

This document addresses innovative stabilization/solidification technologies that were sufficiently developed at the time of compilation to be used in full scale applications. It addresses in detail all aspects of the technologies including application, design, and implementation.

Screening Tests for Assessing Treatability of Inorganic Industrial Wastes by Stabilisation/Solidification with Cement
Stegemann, J.A. and Q. Zhou.
Journal of Hazardous Materials 161(1):300-306(2009)

Treatment by S/S is complicated by the fact that the presence of impurities, such as the contaminants and bulk matrix components present in industrial wastes, can have deleterious effects on cements. To avoid technology failures, careful laboratory development and testing of S/S formulations is required prior to full-scale application, including problems with handling and contaminant retention. This paper proposes a series of test methods and performance thresholds for use in evaluating the treatability of industrial wastes by S/S and optimizing S/S formulations: measurement of S/S product workability, bleeding and setting time (for flowable mixtures) or Proctor compaction (for compactable mixtures), together with unconfined compressive strength, leachability in a batch extraction with distilled water, and hydraulic conductivity.

Adobe PDF LogoStabilization and Solidification of Contaminated Soil and Waste: A Manual of Practice
Bates, E. and C. Hills.
Hygge Media, 603 pp, 2015

This "Manual of Practice" has been designed as a practical reference for regulators, site owners, engineering firms, and others involved in selecting, designing, bidding, and providing oversight for the remediation of hazardous waste sites using S/S. This book provides guidance on applicable contaminants, site characteristics, project planning, equipment capabilities, production rates, performance specifications and the quality assurance of S/S treated materials. Included are references to numerous case studies and an extensive reference list of completed projects that successfully employed S/S.

Adobe PDF LogoStabilization/Solidification of CERCLA and RCRA Wastes: Physical Tests, Chemical Testing Procedures, Technology Screening and Field Activities
Arozarena, M.M. et al.
EPA 625-6-89-022, 79 pp, 1989

Discusses in depth the physical testing methods used to characterize solid and hazardous wastes before and after S/S and contains an overview of leaching mechanisms, leach test methods and applications, factors affecting results, and selection and interpretation of leach tests.

Adobe PDF LogoTreatability Study Report for In Situ Lead Immobilization Using Phosphate-Based Binders
Bricka, R.M., A. Marwaha, and G. Fabian.
ATC-9137195, ESTCP Project ER-0111, 195 pp, 2008

Phosphate-based binders marketed by four vendors were evaluated at Camp Withycombe, OR, for immobilization performance of Pb in small arms firing range soil. Variability in Pb stability was observed in all four soil treatments.

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Performance Monitoring

Material performance specifications are design targets developed based on the material performance goals. These design targets are used during treatability studies to evaluate whether a developed treated material will meet the material performance goals established at the start of the S/S design and implementation process.

Construction performance specifications are developed for use during field operations. These implementation targets are established at the conclusion of treatability testing or after field/pilot studies have identified appropriate specifications for the implementation of a designed S/S formulation. Performance specifications are used to verify that the treated material created in the field is consistent with the material developed and characterized during treatability testing; thus, the intent of testing is not to predict the performance of the material but rather to ensure that field materials behave in the same manner as the materials tested in the laboratory.

Post-treatment testing requirements vary from project to project depending on the regulatory agencies involved. Post-treatment testing consists of both chemical and physical tests. Required chemical testing often consists of performing the Toxicity Characteristics Leaching Procedure (TCLP) and chemically analyzing the extract. Physical parameters tested will vary from project to project and may include unconfined compressive strength, permeability, and durability (USACE 1995).

The frequency of sampling freshly treated material depends on the overall size of the S/S project, the daily treatment rate, the observed consistency of mixing by the remediation contractor, observed changes in the contaminated material properties, and other factors. A higher frequency of sampling is generally performed during the pilot phase and/or the start of S/S production to develop a test-results data set. The sampling process further assesses the variability of the material to be treated and the variability expected in the test results. The data set can be used to confirm the ability to meet the performance criteria. While the sampling frequency for a specific project is determined by the designer and/or the regulator, as a general guideline, performance sampling of treated material is recommended in consideration of the following circumstances (ITRC 2011):

  • Sample at least once per day of production and once per shift (if there are multiple shifts) and any time the batch plant or mixing equipment operator changes.
  • Sample every 400-800 m3 (500-1000 yd3) of treated material. Alternate frequencies may be appropriate based on overall volume to be treated for a site, anticipated contaminated material characteristics heterogeneity, and review of test results as the project progresses.
  • Sample any time the contaminated material or blended material physical characteristics appear to change significantly (e.g., greater contaminant level, significant variation in moisture content, significant variation in material gradation).

Leaching Testing

The most commonly specified chemical test is the TCLPAdobe PDF Logo. The TCLP is applied because it is linked to regulations in EPA's RCRA program; however, there has been discussion about the appropriateness of applying TCLP to S/S-treated waste when the treated waste is managed other than in a municipal landfill. The TCLP procedure relies on extracting sample waste with a diluted organic acid, thus simulating conditions of mixed waste (including organic waste) disposal, such as in a municipal landfill. Many S/S-treated wastes are disposed of in monofills or treated in situ and left in place. The TCLP procedure may not be the appropriate simulation of these disposal scenarios. To address this concern, the Synthetic Precipitation Leaching Procedure (SPLPAdobe PDF Logo) might be applied in place of the TCLP. The SPLP is designed to simulate waste exposure to acid rain. The final disposal environment intended for the treated waste is an important consideration when determining the appropriate test (Barnett et al. 2009).

EPA has collaborated in efforts to develop additional leaching methods within the Leaching Environmental Assessment Framework (LEAF). The framework is based on the measurement of intrinsic leaching properties of a material in conjunction with mathematical modeling to estimate release under field management scenarios. LEAF represents a considerable shift in leaching assessment methodology from current approaches, which typically are based on single-point pH tests that are not necessarily reflective of management conditions. As part of its LEAF participation, EPA prepared a document (Garrabrants et al. 2010Adobe PDF Logo) that provides the background required to understand the development, application, and use of four test methods. The document includes an overview of the leaching process, selection of test parameters, and estimates of the time, material, and costs required.

In late 2012 EPA published two new leaching tests. Method 1313Adobe PDF Logo, Liquid-Solid Partitioning as a Function of Extract pH Using a Parallel Batch Extraction Procedure, is a leaching characterization method that is used to provide values for intrinsic material parameters that control leaching of inorganic and some organic species under equilibrium conditions. This test method provides a means for obtaining a series of extracts of a solid material (i.e., the eluates), that can be used to estimate the LSP (e.g., solubility and release) of constituents as a function of pH. Method 1316Adobe PDF Logo, Liquid-Solid Partitioning as a Function of Liquid-to-Solid Ratio in Solid Materials Using a Parallel Batch Procedure, is a leaching characterization method used to provide intrinsic material parameters that control leaching of inorganic species under equilibrium conditions. This test method allows a means for obtaining the eluate of a solid material to use in estimating the solubility and release of inorganic constituents.

As of November 2012, two other leach tests were in the draft stage: Method 1314, Liquid-Solid Partitioning as a Function of Liquid-Solid Ratio, and Method 1315, Mass Transfer Rates in Monolithic and Compacted Granular Materials, a method for mass transfer rate controlled release (i.e., diffusion) from monolithic or compacted granular materials.

Long Term Monitoring

A gradual release over time through diffusion and/or leaching of contaminants of concern is anticipated in S/S remedies. The remedy is designed so that the contaminant flux is low enough to achieve remedial action objectives. Typically monitoring the quality of downgradient groundwater is performed. The usual parameters tested for are the contaminants of concern or a suitable subset to ensure RAOs are being met and, if the S/S material can be affected by the groundwater, groundwater quality parameters such as pH, conductivity and major anions (e.g., sulfate and chloride). Although the direct periodic testing of the S/S material's structural integrity can be done, it is not recommended unless site specific circumstances dictate it (ITRC 2011 Bone et al. 2004).

If the S/S material remedy has ancillary components such as an engineered cover, these will generally need periodic inspection to determine if they are functioning as designed.

References:

Barnett, F., S. Lynn, and D. Reisman. 2009. Technology Performance Review: Selecting and Using Solidification/Stabilization Treatment for Site Remediation. EPA 600-R-09-148.

Bone, B.D., L.H. Barnard, D.I. Boardman, P.J. Carey, C.D. Hills, H.M. Jones, C.L. MacLeod, and M. Tyrer. 2004. Adobe PDF LogoReview of Scientific Literature on the Use of Stabilisation/Solidification for the Treatment of Contaminated Soil, Solid Waste, and Sludges. Environment Agency, UK, Science Report SC980003/SR2, 343 pp, 2004.

Garrabrants, A.C., D.S. Kosson, H.A. van der Sloot, F. Sanchez, and O. Hjelmar. 2010. Adobe PDF LogoBackground Information for the Leaching Environmental Assessment Framework (LEAF) Test Methods. EPA 600-R-10-170.

ITRC. 2011. Development of Performance Specifications for Solidification/Stabilization. 162 pp

USACE. 1995. Adobe PDF LogoEngineering and Design Treatability Studies for Solidification/Stabilization of Contaminated Material. ETL 1110-1-158.

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Additional Information on Performance

Amending Soils with Phosphate as Means to Mitigate Soil Lead Hazard: A Critical Review of the State of the Science (Abstract)
Scheckel , G.L. Diamond , M.F. Burgess , J.M. Klotzbach , M. Maddaloni , B.W. Miller, C.R. Partridge, and S.M. Serda.
Journal of Toxicology and Environmental Health, Part B: Critical Reviews 16(6):337-380(2013)

Phosphate amendments have been studied as a means to mitigate risks from exposure to Pb in soil by promoting the formation of highly insoluble Pb species, such as pyromorphite. The formation of insoluble Pb species thereby reduces the risk of Pb leaching through soils into drinking waters and absorption by soil biota, and may make it less bioavailable during physiological transport in the human gastrointestinal tract following incidental ingestion. This paper provides a detailed description of phosphate chemistry and the goal of converting Pb into pyromorphite. Slides by Scheckel et al. (2013)Adobe PDF Logo

Leaching Behaviour of Magnesium Phosphate Cements Containing High Quantities of Heavy Metals
Buj, I., J. Torras, M. Rovira, and J. de Pablo.
Journal of Hazardous Materials 175(1-3):789-794(2010)

Aside from compliance test results, little information is available about metals retention by magnesium potassium phosphate cements matrices. To investigate, several pastes were prepared by reaction between low grade MgO and KH(2)PO(4) in the presence of different heavy metal nitrate solutions (containing Cd(II), Cr(III), Cu(II), Ni(II), Pb(II) or Zn(II)). In all cases, the initial metal content of the dissolution was 25 g dm(-3) and the oxide-phosphate ratio of the pastes was 50:50 in weight. Four different leaching tests were conducted on magnesium potassium phosphate cement pastes: simple batch test, equilibrium leaching test, availability test, and acid neutralization capacity test. The metal leachate concentration was determined by means of ICP-MS. Metals stabilization was successful in all cases, although the immobilizing system showed a better behavior for Pb(II) and Cr(III) under acidic or neutral conditions.

Long-term Performance of Aged Waste Forms Treated by Stabilization/Solidification
Antemir, A., C.D. Hills, P.J. Carey, K.H. Gardner, E.R. Bates, and A.K. Crumbie.
Journal of Hazardous Materials 181(1-3):65-73(2010)

While there are a number of leaching tests available, currently accepted testing of S/S soils is based on short-term performance tests (TCLP and SPLP) that are used to infer their long-term stability. To test the long term stability assumption, this study evaluated S/S material that was extracted from full-scale remedial operations and examined the material using a variety of analytical techniques to evaluate long term field performance. The microstructure of retrieved samples was found to be analogous to other cement-based materials, but varied according to the soil type, contaminants present, treatment applied, and field exposure conditions. Key microstructural features from the US and UK are summarized. This work shows satisfactory performance of the S/S wastes during 16 years of service.

Adobe PDF LogoPhysical Performance of Cement-Treated Silty Sand Soil under Cycles of Freezing/Thawing
Jamshidi, R.J., C.B. Lake, C. Barnes, C.D. Hills, and P. Gunning.
Proceedings of the 2011 Pan-Am CGS Geotechnical Conference, October 2-6, 2011, Toronto, Ontario, Canada. 8 pp, 2011

Current design of S/S remediation systems to resist freeze/thaw (f/t) cycles is based on tests available for soil-cement, which considers sample integrity (rather than its hydraulic properties) as the resistibility indicator. This paper studies the effect of f/t cycles on physical performance of a silty sand soil solidified by addition of 10% Portland cement. Changes in the hydraulic conductivity, dynamic properties, and microstructure of the specimens were monitored after exposure to different levels of f/t. Results show a considerable amount of damage to the structure of the monolith after 7 cycles of f/t, with an increase of up to two orders of magnitude in the hydraulic conductivity of the specimens. Changes in the dynamic properties of the specimens suggest the proposed technique might be suitable for detection of performance change due to f/t exposure.

Adobe PDF LogoTreatability Study Report for In Situ Lead Immobilization Using Phosphate-Based Binders
Bricka, R.M., A. Marwaha, and G. Fabian.
ATC-9137195, ESTCP Project ER-0111, 195 pp, 2008

Phosphate-based binders marketed by four vendors were evaluated at Camp Withycombe, OR, for immobilization performance of Pb in small arms firing range soil. Variability in Pb stability was observed in all four soil treatments.