Innovative applications of subgrade biogeochemical reactors: Three case studies

Subgrade biogeochemical reactors (SBGRs) are an in situ remediation technology shown to be effective in treating contaminant source areas and groundwater hot spots, while being sustainable and economical. This technology has been applied for over a decade to treat chlorinated volatile organic compound source areas where groundwater is shallow (e.g., less than approximately 30 feet below ground surface [ft bgs]). However, this article provides three case studies describing innovative SBGR configurations recently developed and tested that are outside of this norm, which enable use of this technology under more challenging site conditions or for treatment of alternative contaminant classes. The first SBGR case study addresses a site with groundwater deeper than 30 ft bgs and limited space for construction, where an SBGR column configuration reduced the maximum trichloroethene (TCE) groundwater concentration from 9,900 micrograms per liter (μg/L) to <1 μg/L (nondetect) within approximately 15 months. The second SBGR is a recirculating trench configuration that is supporting remediation of a 5.7‐acre TCE plume, which has significant surface footprint constraints due to the presence of endangered species habitat. The third SBGR was constructed with a new amendment mixture and reduced groundwater contaminant concentrations in a petroleum hydrocarbon source area by over 97% within approximately 1 year. Additionally, a summary is provided for new SBGR configurations that are planned for treatment of additional classes of contaminants (e.g., hexavalent chromium, 1,4‐dioxane, dissolved explosives constituents, etc.). A discussion is also provided describing research being conducted to further understand and optimize treatment mechanisms within SBGRs, including a recently developed sampling approach called the aquifer matrix probe.     

Evaluation of natural attenuation at a 1,4‐dioxane‐contaminated site

1,4‐Dioxane entered the environment as a result of historic leaks and spills in the production area at an industrial facility in the southeastern coastal plain. The areal extent of the 1,4‐dioxane plume is several hundred acres and is largely contained on the site. Land use adjacent to the plant property is primarily undeveloped (wetlands or woods) or industrial, with a small area of mixed land use (commercial/residential) to the southwest and north. The surficial aquifer is a relatively simple hydrogeologic system with well‐defined boundaries and is comprised of a 50‐ to 70‐foot‐thick deposit of alluvial/fluvial sand and gravel that overlies an aquitard in excess of 100 feet thick. A groundwater flow model, developed and calibrated using field‐measured data, was used for the fate‐and‐transport modeling of 1,4‐dioxane. The flow‐and‐transport model, combined with the evaluation of other site geochemical data, was used to support the selection of monitored natural attenuation (MNA) as the proposed groundwater remedy for the site. Since the active sources of contamination have been removed and the modeling/field data demonstrated that the plume was stable and not expanding, the proposed MNA approach was accepted and approved by the regulatory agency for implementation in 2004. Subsequent accumulated data confirm that concentrations in the 1,4‐dioxane plume are declining as predicted by the fate‐and‐transport modeling. © 2008 Wiley Periodicals, Inc.     

In‐Canal Stabilization/Solidification of NAPL‐Impacted Sediments

In situ solidification (ISS) has been used with increasing frequency as a remedial technology for source area treatment at upland sites impacted with a variety of organic contaminants, including coal tar, creosote, and other nonaqueous phase liquids (NAPLs). With several large, complex, urban water ways and rivers impacted with NAPLs, ISS is more recently being considered as a technology of choice to help reduce remedial costs, minimize short‐ and long‐term impacts of mobile NAPL, and lower the carbon footprint. This article presents the results of a successful pilot study of ISS at the Gowanus Canal Superfund site in Brooklyn, New York. This represents the first major sediment ISS field demonstration project in a saline environment and the first project to evaluate large‐scale implementation of ISS from a barge and through overlaying sediment. ©2016 Wiley Periodicals, Inc.     

Chemical and Biological Reduction of PCE by Pneumatic Fracturing and Injection of ZVI in Saprolite

This article presents a case study of the source‐area treatment of tetrachloroethene (PCE) in a low‐permeability formation using zero‐valent iron (ZVI). Evidence of the stimulation of biological reduction processes within the treatment zone occurred. Pneumatic fracturing and injection of microscale ZVI slurry in the overburden and weathered bedrock zones was performed at a commercial brownfields redevelopment site in Maryland. A 20,000‐square‐foot source area impacted with PCE at concentrations greater than 15,000 µg/L was treated at depths ranging from 10 to 70 feet bgs. An average ZVI dosage of 0.0024 iron‐to‐soil mass ratio within the overburden zone led to a 75 percent decrease in PCE mass in less than one year. For the weathered bedrock zone, an average 0.0045 iron‐to‐soil mass ratio resulted in a 92 percent decrease in PCE mass during the same period. The reducing environment and hydrogen generated by the ZVI may have stimulated Dehalobacter populations, as evidenced by concentrations up to 10⁴ cells per milliliter measured within the treatment area despite a groundwater pH as high as 9. The biological reductive dechlorination of the chlorinated ethenes explains the temporary increase in trichloroethene and cis‐1,2‐dichloroethene concentrations. © 2013 Wiley Periodicals, Inc.     

In Situ solidification—A case study at a former manufactured gas plant in Macon,Georgia

In situ solidification (ISS) is a reliable, EPA‐recognized technology for the treatment of industrial and waste sites. ISS was employed at a former manufactured gas plant (MGP) site in Macon, Georgia, for the treatment of approximately 33,000 cubic yards of coal tar residues in the saturated zone soil. The site is regulated by the Georgia Environmental Protection Division (EPD) under the Hazardous Site Rehabilitation Act (HSRA) and is located approximately four blocks from downtown Macon. This article will review the technical and regulatory basis for the successful use of this technology, provide an overview of the treatability and pilot testing used to develop the design and implementation of the treatment process, and present the results of the application of ISS to an MGP site. The results of groundwater monitoring, pre and postremediation, will also be discussed. © 2004 Wiley Periodicals, Inc.     

Remediation of a Diffuse Trichloroethene Plume in an Urban Setting

During an environmental assessment of a former fleet vehicle maintenance facility located in Jacksonville, Florida, dissolved trichloroethene (TCE) concentrations exceeding the Florida groundwater standard (3 micrograms per liter) were detected at a depth of 40 feet (12 meters) below land surface (bls). A plume was delineated that measured approximately 600 feet (183 meters) by 150 feet (46 meters), extending across a major road and onto adjacent properties. Shaw Environmental, Inc., which was acquired by CB&I in February 2012, performed pilot tests with in situ oxygen curtain (iSOC), and the injection of Anaerobic Biochem Plus (ABC+), a mixture of lactates, a phosphate buffer, fatty acids, and zero‐valent iron. Based on the pilot‐test results, ABC+ appeared the more effective of the two methods and was selected for full‐scale implementation. In February 2011, Shaw Environmental, Inc. and a subcontractor used direct‐push technology to inject ABC+ in 120 borings. By September 2011, the treatment succeeded in lowering the concentrations of TCE to below the Florida standard in all impacted wells. Subsequent sampling events indicate that TCE concentrations have remained below the standard, but sampling continues for iron, which is decreasing but remains slightly elevated. © 2013 Wiley Periodicals, Inc.     

Successful unsaturated zone treatment of PCE with sodium permanganate

In situ chemical oxidation (ISCO) with permanganate has been widely used for soil and groundwater treatment in the saturated zone. Due to the challenges associated with achieving effective distribution and retention in the unsaturated zone, there is a great interest in developing alternative injection technologies that increase the success of vadose‐zone treatment. The subject site is an active dry cleaner located in Topeka, Kansas. A relatively small area of residual contamination adjacent to the active facility building has been identified as the source of a large sitewide groundwater contamination plume with off‐site receptors. The Kansas Department of Health and Environment (KDHE) currently manages site remedial efforts and chose to pilot‐test ISCO with permanganate for the reduction of perchloroethene (PCE) soil concentrations within the source area. KDHE subsequently contracted Burns & McDonnell to design and implement an ISCO pilot test. A treatability study was performed by Carus Corporation to determine permanganate‐soil‐oxidant‐demand (PSOD) and the required oxidant dosing for the site. The pilot‐test design included an ISCO injection approach that consisted of injecting aqueous sodium permanganate using direct‐push technology with a sealed borehole. During the pilot test, approximately 12,500 pounds of sodium permanganate were injected at a concentration of approximately 3 percent (by weight) using the methods described above. Confirmation soil sampling conducted after the injection event indicated PCE reductions ranging from approximately 79 to more than 99 percent. A follow‐up treatment, consisting of the injection of an additional 6,200 pounds of sodium permanganate, was implemented to address residual soil impacts remaining in the soil source zone. Confirmation soil sampling conducted after the treatment indicated a PCE reduction of greater than 90 percent at the most heavily impacted sample location and additional reductions in four of the six samples collected. © 2009 Wiley Periodicals, Inc.     

Evaluating a Site for Natural Attenuation: EPA Region IV's New Guidance

Natural attenuation has recently been recognized by the U.S. Environmental Protection Agency (EPA) as an appropriate remedy for sites contaminated with chlorinated solvents. Because natural attenuation does not require active remediation, it is considerably less expensive than other groundwater remedies. However, as laid out in EPA's recently released guidance, careful, systematic evaluation of natural attenuation must be conducted to ensure that the remedial approach is appropriate for a given site. The guidance requires that data be collected to demonstrate that natural attenuation is occurring and a fate-and-transport model must be conducted to estimate the extent to which a contaminated plume will ultimately migrate. Finally, the proponent of natural attenuation must be prepared to conduct long-term groundwater monitoring to verify that natural attenuation is controlling plume migration and that human health and the environment are not adversely affected.     

Remedial Process Optimization and Ozone Sparging for Petroleum Hydrocarbon‐Impacted Groundwater

A former natural gas processing station is impacted with total petroleum hydrocarbons (TPH) and benzene. Remedial process optimization (RPO) was conducted to evaluate the effectiveness of the historical air sparging/soil vapor extraction (AS/SVE) system and the current groundwater extraction and treatment system. The RPO indicated that both remedial activities offered no further benefit in meeting remediation goals. Instead, an in situ chemical oxidation (ISCO) system was recommended. Ozone was selected, and the results of a bench test indicated that the ozone demand was 8 to 12 mg ozone/mg TPH and that secondary by‐products would include hexavalent chromium and bromate. A capture zone analysis was conducted through groundwater flow modeling (MODFLOW) to ensure containment of the injected oxidant using the existing groundwater extraction system. Results of a pilot study indicated that the optimum frequency of ozone sparging is 60 minutes in order to reach a maximum radius of influence of 20 feet. TPH concentrations within the treatment zone decreased by 97 percent over two months of ozone sparging. Concentrations of hexavalent chromium and bromate increased from nondetect to 44 and 110 mg/L, respectively, during the ozone sparging but attenuated to nondetectable concentrations within three months of system shut down. ©2016 Wiley Periodicals, Inc.     

Enhanced anaerobic bioremediation of a TCE source at the Tarheel Army Missile Plant using EOS

EOS, or emulsified oil substrate, was used to stimulate anaerobic biodegradation of trichloroethene (TCE) and tetrachloroethene (PCE) at a former Army‐owned manufacturing facility located in the Piedmont area of North Carolina. Previous use of chlorinated solvents at the facility resulted in soil and groundwater impacts. Ten years of active remediation utilizing soil vacuum extraction and air sparging (SVE/AS) were largely ineffective in reducing the TCE/PCE plume. In 2002, the Army authorized preparation of an amended Remedial Action Plan (RAP) to evaluate in situ bioremediation methods to remediate TCE in groundwater. The RAP evaluated eight groundwater remediation technologies and recommended EOS as the preferred bioremediation alternative for the site. Eight wells were drilled within the 100 × 100 feet area believed to be the primary source area for the TCE plume. In a first injection phase, dilute EOS emulsion was injected into half of the wells. Distribution of the carbon substrate through the treatment zone was enhanced by pumping the four wells that were not injected and recirculating the extracted water through the injection wells. The process was repeated in a second phase that reversed the injection/extraction well pairs. Overall, 18,480 pounds of EOS were injected and 163,000 gallons of water were recirculated through the source area. Anaerobic groundwater conditions were observed shortly after injection with a corresponding decrease in both PCE and TCE concentrations. Dissolved oxygen, oxidation‐reduction potential, and sulfate concentrations also decreased after injection, while TCE‐degradation products, ferrous iron, and methane concentrations increased. The reduction in TCE allowed the Army to meet the groundwater remediation goals for the site. Approximately 18 months after injection, eight wells were innoculated with a commercially prepared dechlorinating culture (KB‐1) in an attempt to address lingering cis‐1,2‐dichloroethene (cis‐DCE) and vinyl chloride (VC) that continued to be observed in some wells. Dehalococcoides populations increased slightly post‐bioaugmentation. Both cis‐DCE and VC continue to slowly decrease. © 2007 Wiley Periodicals, Inc.     

Bioremediation of a former dry cleaner using potassium lactate

Chlorinated solvents were released to the surficial groundwater underneath a former dry cleaning building, resulting in a groundwater plume consisting of high concentrations of trichloroethene (TCE) and cis‐1,2‐dichloroethene (cis‐1,2‐DCE) and low concentrations of tetrachloroethene (PCE) and vinyl chloride. The initial remedial action included chemical oxidation via injection of 14,400 gallons of Fenton's Reagent in March 2002, and an additional 14,760 gallons in April 2002. A sharp reduction of contaminant concentrations in groundwater was observed the following month; however, rebound of contaminant concentrations was evident as early as October 2002. A source area of PCE‐impacted soils was excavated in June 2004. Following the excavation, Golder Associates Inc. (2007) implemented a biostimulation plan by injecting 55 gallons of potassium lactate (PURASAL® HiPure P) in September 2005, and again in February 2006. Comparing the preinjection and postinjection site conditions, the potassium lactate treatments were successful in accomplishing a 40 to 70 percent reduction in mass within four months following the second injection. Elevated vinyl chloride concentrations have persisted through both injection events; however, significant vinyl chloride reduction has been observed in one well with the highest total organic carbon (TOC) concentrations following each injection. © 2008 Wiley Periodicals, Inc.     

Optimizing remediation strategies for a former dry‐cleaner site

Residual tetrachloroethene (PCE) contamination at the former Springvilla Dry Cleaners site in Springfield, Oregon, posed a potential risk through the vapor intrusion, direct contact, and off‐site beneficial groundwater uses. The Oregon Department of Environmental Quality utilized the State Dry Cleaner Program funds to help mitigate the risks posed by residual contamination. After delineation activities were complete, the source‐area soils were excavated and treated on‐site with ex situ vapor extraction to reduce disposal costs. Residual source‐area contamination was then chemically oxidized using sodium permanganate. Dissolved‐phase contamination was subsequently addressed with in situ enhanced reductive dechlorination (ERD). ERD achieved treatment goals across more than 4 million gallons of aquifer impacted with PCE concentrations up to 7,800 micrograms per liter prior to remedial activities. The ERD remedy introduced electron donors and nutrient amendments through groundwater recirculation and slug injection across two aquifers over the course of 24 months. Adaptive and mass‐targeted strategies reduced total remedy costs to approximately $18 per ton within the treatment areas. © 2010 Wiley Periodicals, Inc.     

Pilot Scale Demonstration of the Electrochemical Peroxidation Process at a Petroleum Spill Site

In a pilot test experiment involving approximately 200,000 gallons of groundwater, Electrochemical Peroxidation (ECP) was used to degrade aqueous phase volatile organic compounds (VOCs) including benzene, toluene, ethylbenzene, and xylene (BTEX) compounds and methyl tertbutyl ether (MTBE) from a petroleum spill. ECP involves a form of the Fenton's Reagent reaction, which uses electrochemically generated iron and dilute hydrogen peroxide (<30 mg/L) to break down organic molecules through oxidation to carbon dioxide and water. This article discusses a pilot scale demonstration of the ECP technology and its application to aqueous phase organic contaminants. The remedial approach used at the pilot test site involves three phases: (1) ex‐situ chemical oxidation, (2) in‐situ oxidation by reinjection of treated effluent near the plume origin, and (3) reestablishment of aerobic biodegradation as the residual hydrogen peroxide discharged to a series of upgradient wells degrades to oxygen. Analytical results of the pilot demonstration indicate that the ex‐situ chemical oxidation reduced total BTEX concentrations in groundwater from over 1,000 ppb to undetectable concentrations (<1 ppb). © 2000 John Wiley & Sons, Inc.     

Insufficient source area remediation results in the rebound of TCE breakdown products in groundwater

In the early 1990s, a soil removal action was completed at a former disposal pit site located in southern Michigan. This action removed waste oil, cutting oil, and chlorinated solvents from the unsaturated zone. To contain groundwater contaminant migration at the site, a groundwater pump‐and‐treat system comprised of two extraction wells operating at a combined flow of 50 gallons per minute, carbon treatment, and a permitted effluent discharge was designed, installed, and operated for over 10 years. Groundwater monitoring for natural attenuation parameters and contaminant attenuation modeling demonstrated natural attenuation of the contaminant plume was adequate to attain site closure. As a result of incomplete contaminant source removal, a rebound of contaminants above the levels established in the remedial action plan (RAP) has occurred in the years following system shutdown and site closure. Groundwater concentrations have raised concerns regarding potential indoor air quality at adjacent residential properties constructed in the past 9 to 10 years. The only remedial option available in the original RAP is to resume groundwater pump‐and‐treat. To remediate the source area, an alternate remediation strategy using an ozone sparge system was developed. The ozone sparge remediation strategy addresses the residual saturated zone contaminants beneath the former disposal pit and reestablishes site closure requirements without resumption of the pump‐and‐treat system. A pilot study was completed successfully; and the final system design was subsequently approved by the Michigan Department of Environmental Quality. The system was installed and began operations in July 2010. As of the January 2011 monitoring event, the system has shown dramatic improvement in site contaminant concentrations. The system will continue to operate until monitoring results indicate that complete treatment has been obtained. The site will have achieved the RAP objectives when the system has been shut down and meets groundwater residential criteria for four consecutive quarters. © 2011 Wiley Periodicals, Inc.     

Microbially Mediated In Situ Desorption Accelerates Remediation of Large Gasoline Product Plume

Remediation of a large separate‐phase hydrocarbon product and associated dissolved‐phase gasoline plume was accelerated by coupling multiphase extraction with in situ microbial stimulation. At the beginning of remediation activities, the separate‐phase hydrocarbon plume extended an estimated seven acres with product thickness measuring up to 2.1 feet thick. Within 18 months after beginning extraction, reduction of gasoline constituents in groundwater became asymptotic and measureable product disappeared from the upgradient source area. At that time, the remediation team initiated a program of limited in situ anaerobic bioremediation with the goal of stimulating production of natural surfactants from native microbes to release petroleum from the soil matrix. Groundwater concentrations of gasoline constituents increased gradually over the next three years, improving recovery without biofouling the pump‐and‐treat infrastructure. Using this approach, the groundwater component of the remedy was completed in less than five years, substantially less than the 10 years to 15 years predicted by modeling. This strategy demonstrated a more sustainable approach to remediation, reducing electrical usage by an estimated 800 megawatt hours, reducing infrastructure requirements, and preserving an estimated 150 million gallons of groundwater for this arid agricultural area. © 2014 Wiley Periodicals, Inc.     

Use of mixed technologies to remediate chlorinated DNAPL at a Brownfields site

A former chlorofluorocarbon manufacturing facility in northern New Jersey was purchased for redevelopment as a warehousing/distribution center as part of the New Jersey Department of Environmental Protection's Brownfields redevelopment initiative. Soil and groundwater at the site were impacted with dense nonaqueous‐phase liquids (chlorinated organic compounds) and light nonaqueous‐phase liquids (petroleum hydrocarbons). The initial remedial strategy (excavation and offsite disposal) developed by prior site owners would have been cost‐prohibitive to the new site owners and made redevelopment infeasible. Mixed remedial technologies were employed to reduce the cost of remediation while meeting regulatory contaminant levels that are protective of human health and the environment. The most heavily impacted soils (containing greater than 95 percent of the contaminant mass) were excavated and treated onsite by the addition of calcium oxide and lime kiln dust coupled with physical mixing. Treated soils were reused onsite as part of the redevelopment. Residual soil and groundwater contamination was treated via in situ injections of emulsified oil to enhance anaerobic biodegradation, and emulsified oil/zero‐valent iron to chemically reduce residual contaminants. Engineering (cap) and administrative (deed restriction) controls were used as part of the final remedy. The remedial strategy presented in this article resulted in a cost reduction of 50 percent of the initial remedial cost estimate. © 2008 Wiley Periodicals, Inc.     

In-Situ Fenton-Like Oxidation of Volatile Organics: Laboratory,Pilot, and Full-Scale Demonstrations

Laboratory, pilot, and full-scale experiments were used to evaluate and optimize the ISOTEC^SM remedial process at a warehousing facility in Union, New Jersey. Based on modified Fenton's oxidative chemistry, the ISOTEC^SM process uses a proprietary catalytic agent that delays formation of reactive hydroxyl radicals. This allows adequate dispersion of the hydroxyl radicals, which is an oxidizing agent, throughout a contaminant plume. Ground-water at the site was contaminated with high levels of gasoline and waste oil constituents, principally BTEX and MTBE. Bench scale microcosm studies were used to evaluate the appropriate site-specific stoichiometric relationships between catalyst, stabilizers, and oxidizers; the effect of contaminant type and concentration; and the pH optima. Based on results of the laboratory studies, a pilot-scale study was performed at the site. One injection point for catalyst, stabilizers, and oxidant was installed in the contaminated zone at the site, with one hydraulically connected downgradient well used for monitoring. A single treatment of the reagents in the optimal stoichiometry determined from the laboratory study was injected in-situ over a period of three days. A 98.5 percent reduction in volatile organics was observed in the area treated, with the radial extent of treatment estimated to be approximately 20 feet, based on the presence of hydroxyl radicals detected in hydraulically connected areas and at the surface. The full-scale process employed six injection points and three treatment cycles over a three-month period. Subsequent to treatment, contaminant levels were either nondetectable or were reduced to below applicable New Jersey groundwater standards, with regulatory closure on the site achieved in less than one year.     

Biogeochemical gradients as a framework for understanding waste‐site evolution

The migration of biogeochemical gradients is a useful framework for understanding the evolution of biogeochemical conditions in groundwater at waste sites contaminated with metals and radionuclides. This understanding is critical to selecting sustainable remedies and evaluating sites for monitored natural attenuation, because most attenuation mechanisms are sensitive to geochemical conditions, such as pH and redox potential. Knowledge of how gradients in these parameters evolve provides insights into the behavior of contaminants with time and guides characterization, remedy selection, and monitoring efforts. An example is a seepage basin site at the Savannah River Site in South Carolina where low‐level acidic waste has seeped into groundwater. The remediation of this site relies, in part, on restoring the natural pH of the aquifer by injecting alkaline solutions. The remediation will continue until the pH upflow of the treatment zone increases to an acceptable value. The time required to achieve this objective depends on the time it takes the trailing pH gradient, the gradient separating the plume from influxing natural groundwater, to reach the treatment zone. Predictions of this length of time will strongly influence long‐term remedial decisions. © 2008 Wiley Periodicals, Inc.     

Seven‐year performance evaluation of a permeable reactive barrier

In June and July 2001, the Massachusetts Department of Environmental Protection (MassDEP) installed a permeable reactive barrier (PRB) to treat a groundwater plume of chlorinated solvents migrating from an electronics manufacturer in Needham, Massachusetts, toward the Town of Wellesley's Rosemary Valley wellfield. The primary contaminant of concern at the site is trichloroethene (TCE), which at the time had a maximum average concentration of approximately 300 micrograms per liter directly upgradient of the PRB. The PRB is composed of a mix of granular zero‐valent iron (ZVI) filings and sand with a pure‐iron thickness design along its length between 0.5 and 1.7 feet. The PRB was designed to intercept the entire overburden plume; a previous study had indicated that the contaminant flux in the bedrock was negligible. Groundwater samples have been collected from monitoring wells upgradient and downgradient of the PRB on a quarterly basis since installation of the PRB. Inorganic parameters, such as oxidation/reduction potential, dissolved oxygen, and pH, are also measured to determine stabilization during the sampling process. Review of the analytical data indicates that the PRB is significantly reducing TCE concentrations along its length. However, in two discrete locations, TCE concentrations show little decrease in the downgradient monitoring wells, particularly in the deep overburden. Data available for review include the organic and inorganic analytical data, slug test results from nearby bedrock and overburden wells, and upgradient and downgradient groundwater‐level information. These data aid in refining the conceptual site model for the PRB, evaluating its performance, and provide clues as to the reasons for the PRB's underperformance in certain locations. © 2008 Wiley Periodicals, Inc.     

Smart Characterization—An Integrated Approach for Evaluating a Complex 1,4‐Dioxane Site

Smart characterization approaches apply the latest high‐resolution site characterization methods to find the contaminant mass flux, by integrating relative permeability mapping, classical hydrostratigraphy interpretation, and high‐density groundwater and saturated soil sampling. The key factor that makes Smart characterization different is the application of quantitative saturated soil sampling in less permeable slow advection and storage zones to diagnose plume maturity and understand its implications for remedy selection and performance. Because direct sensing tools like the membrane interface probe are capable of providing screening‐level assessments for hydrocarbons and chlorinated solvents in storage zones, but not 1,4‐dioxane, the recommended Smart approach involves application of specialized high‐capacity mobile laboratories or rapid turn‐around using fixed commercial labs. In addition to the benefit of rapidly characterizing sites, Smart characterization facilitates a flux‐based conceptual site model, which allows stakeholders to focus remedies on the mobile portion of the contaminant mass or, in effect, the mass that matters. Through systematic planning and implementation, predesign characterization can be completed to optimize source and plume remedy strategies, balancing investment in Smart characterization with reductions in total life‐cycle costs to ensure that an appropriate return on investigation is obtained.  © 2016 Wiley Periodicals, Inc.