REMEDY OPTIMIZATION and COST CONTROL for REMEDIAL DESIGN and REMEDIAL ACTION at the acmE SOLVENTS NPL SITE
B. Costello and B. Dotterrer
Nationwide Environmental Services, Inc., Denver, Colorado 80215, Phone: 303-232-2134, FAX: 303-232-1724
NES serves as the technical manager for the Acme Solvents site located south of Rockford, Illinois. The remedy selected for the site includes installation of an alternate water supply, groundwater extraction and treatment system, Low Temperature Thermal Stripping, SVE system, BVE system, off-site disposal of underground tanks and contents, and construction of a RCRA Cap. This paper presents the measures utilized to optimize the remedy during the RD/RA phase of the response action. The Acme Solvents PRPs realized savings of approximately $1.7 million during LTTS when NES identified a lower-cost alternative LTTS technology. Hydrogeologic conditions encountered during installation of the groundwater extraction system would have resulted in significant increase in costs if installed as originally designed. NES identified an alternative system with the design engineer and obtained approval from EPA Region V for design modifications which met the intent of the ROD and maintained project cost within the established budget. The ROD proposed a bedrock vapor extraction system tha was shown to be unnecessary, saving the PRPs over $1.5 to $2 million. NES submitted a request to the agency to exempt LTTS-treated soil from RCRA regulations with the intent of eliminating construction of the RCRA cap element of the remedy. This action presents a potential cost savings of $200,000.
Keywords: remedy optimization, cost control, LTTS, BVE, RCRA Cap
INTRODUCTION
The Remedial Investigation and Feasibility Study (RI/FS) stages of the CERCLA remedial response process frequently are performed without full knowledge of the extent of historical activities that have been conducted at any given site. Additionally, the time frame under which such work is to be completed is usually not adequate to obtain a thorough understanding of the impacts resulting from past activities. Lastly, as a matter of practicality, both the regulatory and regulated communities concur that the RI/FS phase of the CERCLA response Action should not be a "research project" to which unlimited resources are devoted for the purpose of precisely defining the extent of impacts at a given site. Consequently, the selected remedy often does not entirely address the scope of activities that may be necessary during the Remedial Design/Remedial Action (RD/RA) phase of the response action to achieve cleanup objectives established for the site in the Record of Decision (ROD).
A result of this condition is that significant potential exists for an expansion of RD/RA activities to occur, both under fund-financed cleanups and responsible party-led actions, causing project budgets to balloon and completion schedules to be cast aside. A diligent review of the site cleanup objectives relative to the actual site conditions during the RD/RA phase of the project should be performed periodically throughout the life of the project to identify opportunities to reduce the scope of site work or at a minimum retain the project scope within that initially anticipated.
The Remedial Design and Remedial Action (RD/RA) conducted at the Acme Solvents NPL Site (Site) was undertaken by the responsible parties with USEPA oversight. The RD/RA phase of the response action is near completion. Operation and maintenance activities have commenced for remedial components installed at the Site during the RD/RA phase and requiring long-term operational horizons to meet remediation goals established in the ROD. Measures taken to optimize design and construction activities, and control costs during implementation of the RD/RA phase of the project for Operable Unit 2 (OU2) are presented in the following paper.
General information related to the Site, including physical description, historical activities, and the selected remedy, are presented in the following section.
The Site covers 20 acres located in Winnebago County approximately five miles south of the city of Rockford, Illinois. Land use on properties adjacent to the Site consists of quarry operations for production of construction aggregate to the north, agricultural land to the east and south, and rural residential immediately to the west and a sanitary landfill farther to the west. The sanitary landfill has also been identified as a Superfund site by the USEPA. A map showing the location of the Site is presented in Figure 1, and a Site layout diagram is presented in Figure 2.
Topography in and around the Site is characterized by gentle to steep rolling upland hills. Soils on the Site are shallow and consist primarily of a sandy loam with low organic content. A highly weathered dolomite bedrock immediately underlies the thin soils and is exposed in areas along steep grades where persistent erosional pressures occur. An intermittent stream crosses the Site on the western third of the property and flows to the north forming a tributary to Killibuck Creek. Killibuck Creek flows north and west and enters the Rock River approximately two miles to the northwest. Natural vegetation supported on the Site includes native grasses and herb species typical of cleared agricultural lands in the climate regime, and second or third growth woody species along creek bottoms where moisture is abundant.
The Site served as a disposal location for residuals generated from the Acme Solvents Reclaiming Inc. facility in Rockford, Illinois, from 1960 to 1973. Spent degreasing agents and waste solvents were collected at the facility and subjected to a distillation process for subsequent reuse. The distillation bottoms as well as waste paints, oils, and general refuse were transported to the Site south of town and deposited in steel storage tanks, in earthen depressions created by previous quarrying operations, or in excavations constructed by the Site operator in native soils.
Upon inspection in 1972, the Illinois Environmental Protection Agency (IEPA) issued notice to the operator to clean up the Site. Subsequently, work was conducted by the IEPA and USEPA to investigate the extent of contamination there. The results of groundwater quality monitoring conducted for residential wells in proximity to the Site revealed that volatile organic compounds (VOCs) were present in some wells at concentrations exceeding the USEPA Health Risk Advisory levels. Additionally, Semivolitale Organic Compounds (SVOCs) and Poly-chlorinated Biphenyls (PCBs) were detected in soils at elevated concentrations. The USEPA placed the Site on the National Priorities List in 1984.
The USEPA issued the ROD for Operable Unit No. 1 (OU1) in 1985. The response actions identified in the ROD for OU1 included excavation and on-site incineration of an estimated 26,000 cubic yards of wastes and affected soils, providing an interim alternate water supply to local residents whose domestic wells were affected by contaminants migrating from the Site in groundwater, and implementation of additional studies to better define the extent of impacts at the Site.
The ROD for Operable Unit No. 2 (OU2) was issued by USEPA in December 1990 and addressed the removal of source materials remaining upon completion of OU1, construction of a permanent alternate water supply for affected residences, on-site thermal treatment of affected soils, installation of a groundwater extraction and treatment system, installation of a bedrock vapor extraction and soil vapor extraction system, and capping requirements for any treatment residuals and soil that may remain on-site above health-based risk thresholds upon completion of the remedy. The Group entered a consent decree with the USEPA and IEPA in 1992 which specified the terms and conditions under which the RD/RA tasks necessary to carry out the remedy selected for OU2 would be performed.
REMEDIAL DESIGN and REMEDIAL ACTION
The RD/RA phase of the site response action under CERCLA involves implementation of the remedy selected for the site in the ROD. The RD element of the project normally involves extensive design activities for the individual remedy components with review by the regulatory agency at various completion stages (i.e., 30%, 95%, 100%). Pre-design studies in which additional site-specific information is acquired, are normally a part of the design phase. Results of the pre-design studies assist the design engineer in better defining parameters to be used in preparing the design for a given remedy component. The RA element involves construction of the remedy design and typically includes such activities as: excavation and transport of materials both on and off-site; construction of permanent structures on-site having both underground and aboveground components; installation of treatment equipment; provisions for permanent or temporary utilities to support the remedy construction; and incidentals such as acquiring permits or securing access to properties required to carry out the remedy but which are not under the immediate control of the responsible parties.
The RD/RA components involved in implementation of the remedy selected for the Site under the ROD OU2 are listed below. A discussion of the operational concepts for each of the RD/RA components selected for the Site as well as a description of the specific application of these remedial components is presented in the following sections.
Institutional Controls
Tank Removal and Disposal
Low Temperature Thermal Stripping (LTTS)
Alternative Water Supply System
Soil Vapor Extraction (SVE) System
Bedrock Vapor Extraction
Groundwater Extraction and Treatment (GWET) System
RCRA Cap and Soil Cover
A security fence was installed around the perimeter of the Site to satisfy institutional control requirements in the ROD. The fence is constructed of standard chain link, topped with barbed wire and is 5500 ft in length. Gates are located at various points along the fence length to permit access to off-site elements of the remedy such as groundwater extraction wells. A pivoting cross member arrangement with vertical tines is installed at three stream crossings to prevent access along stream channels while allowing debris collected in the channel unimpeded travel during high stream flow events.
The responsible parties have been granted control of the site during implementation of the remedy under a Consent Decree with the USEPA, but do not have ownership of the property. The provisions of the Consent Decree permit the responsible parties to: access the site for the purpose of carrying out and maintaining the remedy; establish terms and conditions under which access may be controlled; and designate uses for the site before, during, and after completion of the remedy.
Two steel underground storage tanks (> 10% volume below grade) were used at the Site for storage of solvent distillation residues and other waste residues prior to deposition in on-site excavations. The material remaining in the tanks at the time the RD/RA project commenced was removed from the tanks, solidified with a stabilizing agent, and transported off-site for disposal by incineration.
The tops of the tanks were cut off with a non-thermal shear to access the material inside. The material was then extracted from the tanks using a backhoe and placed in 30-cubic-yard roll-off containers with HDPE liners. Kiln dust was used as a solidifying agent for the tank material in order to meet RCRA moisture criteria for landfilling. The solidified waste was then transported off-site and incinerated at a TSCA permitted facility. The empty tanks were triple rinsed, cleaned, crushed with heavy equipment, and transported off-site for disposal at a RCRA Sub-title C landfill. Soil around the perimeter of the tanks was sampled and material which exceed soil cleanup standards for the Site was identified and marked for treatment under the on-site thermal treatment remedy component conducted later.
Six residential locations west of the Site were identified as having domestic well water affected by migration of VOC compounds in groundwater from the Site. An alternative water supply system was constructed to provide a clean source of permanent water to the affected residences. The alternative water supply system is comprised of an existing supply source, a pneumatic tank to maintain constant delivery pressure in the system, a six-inch service main 4400 ft in length, and two-inch service connections from the water main to residences served by the system. Water is supplied to the residences at an average pressure of 75 psi. Water meters were installed in all service connections to monitor water usage at each location. Existing domestic wells were abandoned upon installation of the new supply system.
Low Temperature Thermal Stripping
Distillation residues from the solvent reclaiming process were initially placed in existing excavations at the Site formed during historic quarrying operations or in excavations constructed by the Site operator specifically for waste disposal. Subsequently, the Site operator mixed waste residues in the excavations with native soils in an attempt to satisfy cleanup orders issued by the State of Illinois. Upon completion of the removal action for mixed wastes under OU1, 6000 tons of the affected soils remained at the site. This material was designated for treatment by Low Temperature Thermal Stripping (LTTS) under the ROD OU2 to meet cleanup goals established for affected soils. Contaminants of concern in soils included VOCs, SVOCs, and PCBs.
The objective of the LTTS process is to remove the target compounds from the medium in which they are contained (in this case soil) and concentrate them for subsequent disposal by condensation, or disposal by incineration in off-gas handling systems. Typically, the LTTS process involves indirect heating of the contaminated medium in a low-oxygen atmosphere and at temperatures sufficient to attain the boiling point of the compounds targeted for removal. Under these conditions, the target compounds are transferred from the liquid phase in the soil to the gaseous phase in the atmosphere within the process unit. The process is generally carried out using two stages, a heating stage where media transfer is achieved and an air handling stage where off-gases resulting from media transfer operations are processed for capture or disposal by incineration.
The process is normally operated in the range of 600-1000 degrees Fahrenheit to effect media transfer, with the actual operating temperature dependent on the boiling point of the target compounds, thermal transfer characteristic of the medium in which the compounds are contained, and cleanup objectives. The LTTS process at the Site was operated at 1000 F to meet the removal requirements for PCBs in soils. Heating of the soil medium was achieved by infrared heating bars positioned along a horizontal conveyor on which affected soil was placed and processed. It is important that conditions for combustion do not occur in the media transfer stage of the process due to the explosion hazards that may result, and in the case of material containing PCB, to eliminate formation of undesirable by-products (e.g. dioxins, dibenzofurans).
Capture of the target compounds released from the soil medium was achieved by applying a slight vacuum to the sealed heating chamber using an inductive fan on the air-handling train connecting the heating chamber to the off-gas collection equipment. Steam was used as a sweep gas in the heating chamber to maintain a low oxygen environment. The steam was evolved from vaporization of the moisture contained in the feed soils. If the moisture content of the feed soils was not sufficient for formation of the steam loading required, water was added to the feed soils. Upon removal from the heating chamber, the off-gas was cooled and the target compounds contained in the condensate were captured in liquid separation equipment for off-site incineration.
The treated soil residues from the LTTS process were stockpiled, tested for compliance with cleanup goals, and backfilled on-site in the excavations from which the affected soil was removed. Grab samples from the treated soil stockpiles were composited for analytical determination.
Soil Vapor Extraction (SVE) System
Upon release to the ground, materials classified as volatile organic compounds (VOCs) may reside in the voids between soil particles in both the liquid and gaseous phase. The extent to which VOCs are retained in any particular soil matrix is dependent on the physio-chemical characteristics of the medium. For example, soils with high clay content are known to have a higher potential to retain VOCs than sandy soils due to increased surface area, reduced permeability, and high adsorptive capacity of clay particles.
If a groundwater source is present in proximity to the VOC-affected soil, VOCs may contribute to groundwater pollution by migrating through the soil medium and any underlying strata into the groundwater. The purpose of the soil vapor extraction (SVE) system is to remove VOCs from the soil through transfer and subsequent release to the atmosphere or capture and treatment in airhandling equipment. Removal from the soil medium of the gaseous VOCs is accomplished by application of a vacuum across the affected soil volume and collection of the soil gas removed by the vacuum in air-handling equipment. Various means exist to supply the vacuum to the soil column.
The SVE system installed at the Site consists of air-injection wells installed perpendicular to the ground surface, an underground network of perforated piping installed six ft below ground surface (bgs), a vacuum pump, and air condensation collectors. The vacuum pump creates a negative pressure in the underground piping network and VOCs in the soil air spaces are drawn into the piping and then through the condensate collectors. The air is then exhausted to the atmosphere. Clean ambient air is introduced into the affected soil column through the air wells to maintain air flow through the soil at a rate which maximizes the vacuum source operation.
Conceptually, a Bedrock Vapor Extraction System performs the same function as an SVE system. A negative pressure is applied to the medium for the purpose of removing VOCs residing in voids for subsequent release to the atmosphere or capture and treatment. In that significant differences may exist in the physio-chemical makeup of bedrock and soils, similar differences are expected to occur between the design of a BVE system and SVE system.
The ROD OU2 contains provisions for the performance of a BVE pilot test to evaluate the feasibility of implementing a full-scale BVE system at the Site. The intent of the ROD in requiring consideration of a BVE system is to limit the contribution of VOCs that may exist in bedrock to the aquifer immediately underlying the Site. On a practical basis, the function of a BVE system at the Site would be to capture the incremental mass of VOCs that may be present in the bedrock that is not released to media subject to capture by either the SVE system or the Groundwater Extraction and Treatment System.
Groundwater Extraction and Treatment (GWET) System
Domestic water wells at residences located down gradient of the Site, with respect to groundwater flow, were found to contain VOCs, and to a limited extent, SVOCs in concentrations that exceeded health standards established by USEPA. Although a permanent alternative water supply was provided to residences with affected wells, CERCLA requires that existing or potential groundwater supplies be protected for future use. The ROD OU2 required the design and construction of a system to extract affected groundwater migrating off the site and treatment of the removed ground water to satisfy surface waster discharge standards. The purpose of the GWET system was to restore the quality of groundwater in the affected aquifer to levels suitable for future use.
The GWET system component constructed at the Site consists of two elements: a groundwater extraction system to capture and remove groundwater exceeding groundwater cleanup standards, and a water treatment plant to treat removed groundwater to levels that meet surface water discharge standards. A layout of the groundwater extraction system and the groundwater treatment facility is presented in Figures 2 and 3, respectively.
The groundwater extraction system design consists of sixteen extraction wells (EXW). Five are mass removal wells (EXW-1 through EXW-5) located within or immediately down gradient of waste disposal source areas at the Site. The western alignment of the extraction well capture system is comprised of five wells (EXW-6 through EXW-10) located west and down gradient of the Site source areas. The southern alignment of the extraction system consists of six extraction wells (EXW-11 through EXW-16) located to the south of the Site source areas. Extraction wells EXW-1 through EXW-14 have been installed in accordance with project design specifications. The installation of extraction wells EXW-15 and EXW-16 was not completed due to subsurface conditions that prevented the wells from being installed in accordance with the project design.
The groundwater treatment element of the GWET system consists of numerous unit processes for removal of target compounds contained therein, and structures and controls for housing and operation of the unit process equipment. The primary compounds targeted for removal by the GWET consist of VOCs and SVOCs. The natural chemistry of the groundwater within the aquifer to be restored required that certain secondary compounds be targeted for treatment, to allow the unit processes for primary target compounds to operate effectively. The secondary target parameters included mineral content and biological activity.
The unit processes utilized for removal of VOCs and SVOCs include air stripping and carbon adsorption. As in the SVE system, mass transfer of the VOCs in the liquid phase to the gaseous phase is the primary means of removing the target compounds from the affected media. At the Site, air stripping is accomplished in a vertical tray unit in which ambient air is introduced into the bottom of the sealed stripper vessel. Groundwater removed from the extraction system is introduced at the top of the vessel and falls through a series of vertically aligned perforated trays in the unit. The groundwater falls by gravity through the stacked trays while the air flows to the top of the sealed unit and is released through a vent at the top. This arrangement allows the water to be treated to contact a large volume of air within the vessel. The removal efficiency for VOCs in the air stripper unit is dependent not only on the volume of air contacted by the groundwater but the surface area of the introduced air medium. A larger surface area, achieved by reducing the size of the air bubble in the water matrix, will enhance the mass transfer rate of VOCs from the liquid phase to the gaseous phase.
Following removal of VOCs in the air strippers, SVOCs in the groundwater are targeted for removal by carbon absorption. Carbon absorption is accomplished in sealed vessels in which the groundwater is introduced at the top of the vessel and flows by gravity through activated carbon beds. The activated carbon has a high affinity for VOCs and SVOCs; thus it is essential to remove VOCs to the maximum extent possible in the air strippers so that the absorptive capacity of the carbon beds for SVOC removal is maximized. Upon becoming saturated, the activated carbon in the units is replaced and the spent carbon sent off-site for re-activation.
The unit processes utilized for removal of secondary target compound involve reductions in the Biochemical Oxygen Demand (BOD) of groundwater removed from the mass extraction wells (EXW1-EXW5) and pH adjustment to precipitate metals followed by filtration to remove suspended matter. BOD removal is required to prevent biomass colonization and growth in the inclined plate separator employed downstream in the treatment process for suspended solids removal. BOD removal is achieved in a fixed-film reactor in which biomass is grown on fixed plates in the reactor unit and as a consequence of respiration, fixes (oxidizes) organic content in the groundwater influent. The concentration of organic matter is thus reduced in the flow to downstream unit processes. Precipitation of mineral content in the extracted groundwater and removal of resulting suspended solids is accomplished using an inclined plate separator followed by a sand filter. Solids generated from the fixed-film reactor and the inclined-plate separator are transferred to a solids-accumulation vessel and subsequently de-watered in a plate-and-frame-filter press. Final solid waste products are transported off-site for disposal by landfill.
Groundwater processed in the treatment facility is discharged to the intermittent stream channel located on the Site. The water treatment plant effluent is sampled quarterly to ascertain the status of the discharge relative to surface water quality standards.
Affected soils to be remediated at the Site under the ROD OU2 are generally located in or adjacent to former waste management areas. The LTTS process was employed for soils in areas having higher concentrations of contaminants of concern and which posed the major potential for continued contribution to groundwater. The SVE system was installed for remediation of soils which contained contaminants of concern at relatively lower concentrations but still in excess of Site cleanup standards. The BVE remedy component was selected for application in areas of the Site where VOC concentrations in bedrock were considered to present a potential threat for continued release to groundwater. Under the ROD OU2, a RCRA compliant cap was selected for installation over areas of the Site where soil and bedrock remediation measures did not meet cleanup levels established for protection of groundwater.
The cap consists of a composite layer design which incorporates a foundation layer, compacted clay layer, flexible membrane liner (FML), geo-textile cushion layer, drainage layer, geo-net layer, and vegetative soil cover. A cross-section of the cap design is provided in Figure 4. There is no provision in the cap design for off-gas capture since the organic content of the material to be capped is low and the potential for methane generation is likewise very limited. The intent of the RCRA compliant cap is to intercept direct precipitation and divert it from contact with the underlying soil and bedrock medium, the effect of the cap being to minimize the volume of aqueous solution that could solubilize VOCs contained in the subsurface media and transfer them to groundwater.
Typically, a work plan is developed by the lead agency as part of the CERCLA process which identifies the specific tasks to be performed during the RD/RA phase of the response action. Although, the work plan stage provides an opportunity to narrow the scope of activities at a site, in most instances the work plan provides no better definition of the scope of activities required to implement the remedy than is contained in the ROD, since the site-specific information relied upon for preparation of both documents is the same. This was the case for the Site discussed herein. The work plan served simply as a reiteration of the language contained in the ROD. Therefore, during the RD/RA phase of the remedy, the potential existed for a significant amount of interpretation to be applied to remedy implementation plans.
Provided such leeway, a significant opportunity existed for limiting the scope of activities to only those necessary to carry out the Site remedy and achieve cost savings during the RD/RA phase of the project. By the same means, the potential also existed for significant expansion in the remedial action to occur. The language presented in the ROD and the relationships among the various remedial components contained therein were carefully considered over the duration of the RD/RA project to identify and implement opportunities for limiting project scope and, thereby, attain cost savings. The measures that were implemented to achieve these goals are presented in the following section. The major items of the RD/RA project that were addressed to this end are listed below.
RD/RA Organizational Structure
ARARS Analysis
Remedial Components
RD/RA Project Organization Structure
CERCLA response actions implemented by responsible parties, pursuant to a Consent Decree with the lead agency, frequently involve representation by a diverse group of members. Divergent objectives may therefore exist among the individual members of the responsible party group with respect to activities involved in meeting the ROD. For example, certain members of the group may still be adverse to the remedy required under the ROD and therefore may not promote a cooperative environment in matters involving the regulatory agency such as during design reviews or project schedule revisions. Another complicating condition is that litigation among members seeking contribution or with insurers for coverage may result in a tendency to over manage the project or create an impasse with respect to decision making. Though internal strategies of the group members are intended to achieve the lowest cost for each individual member, more often the cumulative effect is to divert attention from the practical aspects of the remedy and impair the ability to complete the project in the most cost-effective manner for all involved.
The organizational structure developed by the responsible parties for managing the remedy is therefore a central aspect to achieving cost control which ultimately serves to benefit all group members. The organizational structure utilized by the responsible parties at the Site proved to be well-suited for completing the RD/RA phase of the project in a cost-effective manner. A description of the RD/RA project organization follows.
A technical manager was contracted to consult with the parties on technical issues and was assigned responsibility for day-to-day activities associated with performance of the remedy.
A design engineer was contracted to design and warrant the individual remedy components and oversee field construction.
Major remedy construction work was contracted directly to remediation contractors.
A technical committee served to represent the group in matters involving technical decisions.
An executive committee served to manage internal group matters and approve expenditures.
The analysis of Applicable or Appropriate and Relevant Requirements (ARARs) relative to the selected remedy is an important aspect to consider for completing the remedy consistent with cost control objectives. A thorough and accurate analysis of the ARARs will result in the ability to develop a remedy implementation plan that minimizes the potential for performance of unnecessary tasks or inefficient utilization of design and construction resources. Further, a well performed ARARs analysis may result in the identification of efficiencies where multiple components are required as part of the remedy which involve adherence to multiple state and federal regulatory requirements. The three general categories of ARARs that may apply to CERCLA response actions are as follows:
Chemical specific requirements. Health, risk or technology-based numerical standards for air, water, or waste media.
Action-specific requirements. Standards that are related to the performance of a particular activity.
Location-specific requirements. Standards that are related to the performance of activities in relation to their geographical location.
The specific actions and benefits that were derived from the ARARs analysis performed for the Site are summarized below.
Off-site response actions requiring permits from local, state, or federal agencies were identified and the necessary permits acquired in advance of site activities, preventing delays in RD/RA project schedules and construction contractor down time.
Fate of waste residues generated during implementation of the various response actions was identified prior to initiation of the remediation activity, and waste acceptance procedures for off-site disposal was completed prior to implementation of reducing cost for waste storage containers and shortening project completion schedules.
Alternative measures for meeting the ROD requirements for the BVE and RCRA Cap remedy components were identified and implementation strategies for remedial actions impacting implementation of identified alternatives was revised.
The requirements of the ROD were constantly reviewed throughout the life of the RD/RA project and efforts were devoted to identification of measures to control cost of the response action. Changes or revisions to the response actions which occurred during design and construction activities to achieve cost objectives are described in the following section. In certain instances, the need for revisions resulted from the existence of site conditions that became known only upon completion of pre-design studies or implementation of the remedial action.
Phase 1 Source Control-LTTS
The intent of this remedy component was to remediate an estimated 6000 tons of affected soils located in former waste areas in order to remove the potential for contribution of contaminants contained therein to groundwater and lessen health risk posed by direct contact. The material to be remediated was identified to consist of a mixture of soil (non-solid waste) and RCRA F001-F005 listed waste constituents. Soils exceeding established screening levels for contaminants of concern listed in the ROD were excavated and stockpiled for treatment. Excavated soils were then treated by the LTTS process to remove VOCs, SVOCs, and PCBs to levels meeting RCRA Treatability Variance Standards for soil and debris and health-based VOC cleanup standards listed in the ROD. LTTS-treated soils that contained metals in concentrations exceeding TCLP-cleanup criteria were treated by solidification and stabilization in order to be exempted as characteristic waste under 40 CFR 261.24. The LTTS-treated soils were elected to be backfilled on-site, and thus had to be managed as a RCRA hazardous waste under the USEPA "contained in" policy for mixtures of non-solid waste and RCRA-listed hazardous wastes.
The LTTS system processed soils and sludges at rates up to ten tons per hour with moisture contents ranging from 8 to 20% percent during full-scale operation. Upon completion of the LTTS remedial component, 7180 tons (wet weight) of soil were actually excavated from the designated waste areas and processed through the LTTS unit. The soils were processed in 35 lots of 200 tons each (nominal). In addition to the 7180 tons of mixed soil treated during full scale LTTS, 508 tons of soil were treated in the equipment shakedown and proof-of-process test phase of the project prior to commencement of full-scale treatment. A total of 2777 tons (wet weight) of treated LTTS soils contained lead in concentrations exceeding TCLP thresholds and were subsequently treated by the solidification/stabilization (S/S) process. Approximately 100 tons of material were treated off-site by incineration due to concentrated amounts of VOC and SVOC constituents along with high lead levels. Remedy optimization and cost control measures that were pursued during implementation of this remedial component are described below.
Technology Identification
A treatability study was performed to ascertain the capability of available full-scale processing equipment in meeting the cleanup standards established for the targeted material. The technologies tested during the treatability study consisted of equipment which utilized a rotating drum design for movement of material through the process and indirect heating supplied by gas burners. The equipment arrangements tested demonstrated that they were capable of meeting cleanup goals for the soil mixture but the cost for treatment was considered to be relatively high.
A third equipment arrangement was subsequently identified for LTTS application which utilized a conveyor system to move material through the process and indirect heating provided by infra-red heater bars. This process equipment had a greater processing rate, and required much less air flow through the heating unit thus less off-gas handling requirements. As a result, more consistent treatment of the soil mixture was achieved. The cost to apply this equipment arrangement was significantly less than the other technologies evaluated during the treatability study. As a further measure of assurance that the technology would be successful, the construction services contract specified that the remediation contractor was responsible for excavating all soils designated for treatment by LTTS and transporting them off-site for incineration at the same price as the on-site LTTS treatment cost, should the system fail to perform.
Air Emissions Permit
An air permit application was submitted to the Illinois EPA (IEPA) to satisfy ARAR air emission requirements for the LTTS process. Upon review of the air emission ARAR submittal, the IEPA issued a letter of conditional concurrence with the air-emission parameters and respective limits identified in the application, pending successful completion of the proof-of-process demonstration.
The USEPA Region V TSCA Group provided a recommendation for approval to process soils containing PCBs in the selected LTTS process unit. The TSCA group initially maintained that the 99.9999% DRE criteria for incinerators should be applied as an ARAR to air emissions from the LTTS unit. In response to application of the 6-9s DRE, it was stated that application of incinerator DRE criteria to the LTTS process was inappropriate since combustion did not occur in the unit. In addition it was stated that the major portion of the affected soil at the site would need to be treated in order to demonstrate attainment of the 6-9s criteria due to the low concentration of PCBs present in site soils.
In further discussions with USEPA on this issue, it was pointed out that though historic site data indicated maximum concentrations of PCBs in soils to be 290 mg/kg, recent site data revealed PCB soil concentrations to be much lower. The decision was made to apply the human-health-risk-based standard established for the site (1x10-5) to establish the acceptable level of PCBs in emissions from the LTTS unit. Air emissions dispersion modeling was subsequently performed to (1) estimate air emissions, (2) verify compliance with applicable regulations, and (3) estimate off-site concentration impacts. Air modeling demonstrated that the health-based risk standard would provide an appropriate level of protection and could be met by the LTTS process.
Off-Site Disposal
Paint sludges were found to exist in certain areas where soils were to be excavated for remediation by LTTS. The determination was made that it would be more efficient to transport these materials off-site for disposal by incineration rather than process them through the LTTS unit. Processing this material would result in dilution of the concentrated material and then re-concentration in the off-gas capture system. A request for issuance of a ESD to the ROD was submitted to the USEPA to allow off-site transport and disposal of the paint sludge material. An ESD was issued by the USEPA for this action.
Process Modifications
Changes to the original design of the LTTS process were made prior to and during full-scale treatment operations. The design changes involved material handling procedures, process equipment rearrangements, and sampling procedures. The design changes that were made are presented below.
The treatment of soils of low moisture content (<10%) and high total hydrocarbon content (>5%) may have contributed to a shortened life of the electric heater bars in the unit. In order to address this problem, a number of design modifications (including, among others, the application of special coatings to the heater bars and enclosing the heater bars in protective tubing) were evaluated. This experimentation showed that injecting steam at the feed end of the heating chamber to dilute the concentration of hydrocarbons in the heating chamber internal atmosphere extended heater bar life. This procedure was used during subsequent operations.
The vapor phase carbon piping in the emission control system was modified to allow the use of either 55-gallon drums containing 140 lb of carbon each or cells containing 1800 lb of carbon. This modification was also related to processing soils with high hydrocarbon content. Frequency of carbon change out was reduced by the use of larger carbon cells.
A filter press was installed in the off-gas treatment train to de-water solids captured in the oil water separator in order to achieve volume reduction of this waste stream.
Phase 2-Affected Media Remediation
Phase 2 remedial actions discussed in the section below, include the BVE system, the GWET system, and the RCRA Cap.
Bedrock Vapor Extraction System
A sampling program was conducted to demonstrate that the cleanup goals intended in the ROD for the BVE remedy component had been met and that design and construction of a BVE system was not required to satisfy requirements of the ROD. A description of the rationale and sampling program is presented below. The result of this action was to forego design and construction of the BVE system and proceed with installation of site-cover requirements for areas designated for remediation by BVE.
The USEPA agreed with NES during the ROD negotiations that pilot testing for the purpose of ascertaining the feasibility of a full-scale BVE system in meeting VOC removal capability would provide the most relevant information if accomplished when the groundwater extraction and treatment system and SVE system are in full operation and the bedrock media is maximally stressed. Evaluating the performance of the BVE pilot-scale testing under a fully stressed system (i.e., when the saturated and unsaturated zones are being fully subjected to remediation systems) allowed a more representative assessment of the incremental VOC removal attributable solely to BVE.
Pursuant to the ROD, the BVE pilot test was scheduled in two stages. The first-stage pilot test is designed to acquire information to be used in making an initial evaluation of the feasibility of implementing a full-scale BVE system and the necessity for a second-stage pilot test. Performance of a second-stage pilot test is based on USEPA's determination that a BVE system is potentially feasible. Should a determination be made that a second-stage pilot test is necessary, the results obtained from such testing were to be used in conjunction with the first-stage pilot test results to assess the overall feasibility of a full-scale BVE system. If USEPA determined that a full-scale BVE system is feasible, a full-scale BVE system would be installed and operated until BVE cleanup standards are attained.
No cleanup standards for VOCs in bedrock were established in the ROD. The ROD indicates that bedrock vapor cleanup standards are to be developed by the responsible parties and provided to USEPA in a report containing the BVE pilot test results. The suitability of such standards were to be considered in the overall BVE system feasibility determination made by USEPA. As stated in the ROD, the purpose of the BVE pilot test program is to generate data to "determine the feasibility of and design parameters for a BVE system" however a BVE pilot test is not required for the development of bedrock vapor cleanup standards. Therefore, cleanup standards for VOCs in bedrock were proposed which were developed in accordance with the ROD using existing Site data that considered health-based risk thresholds and media specific criteria.
As a first step, Bedrock vapor samples were collected from existing angled coreholes to assist in the design of the BVE pilot tests. Comparison of the historical results obtained during the site investigation phase to these pre-design study results indicated that a significant decrease in bedrock vapor VOC concentrations had occurred. In fact, the samples collected from certain coreholes showed no detection of VOCs. The only location where VOCs were detected was from a deep sample collected from a single corehole. Further, the VOC concentrations detected in the sample collected from this location were estimated because the values were below the method reporting limit.
The bedrock vapor cleanup standards proposed for the Site are the USEPA approved soil cleanup standards established in the ROD. The Site soil cleanup standards were developed by USEPA on the basis that if the VOC concentrations in soil were mobilized, the resulting VOC concentrations in groundwater would not exceed a 1 x 10 -5 carcinogenic risk level. Therefore, the use of site soil cleanup standards as BVE cleanup standards was appropriate since the same mechanism that would mobilize VOCs from soil would also mobilize VOCs from bedrock.
Applying site soil cleanup standards required that bedrock VOC concentrations be known. However, it is not feasible to obtain a bedrock sample with representative VOC concentrations because the VOCs volatilize or are otherwise rendered unrepresentative during the intrusive process of drilling and obtaining a core sample. Therefore, it is necessary to use calculated bedrock VOC concentrations for comparison of actual VOCs in bedrock to the site soil cleanup standards.
The calculated bedrock VOC concentrations were shown to be less than the cleanup standards established for both a multi-media cap and the soil cover alternatives, with the exception of tetrachloroethene (PCE) for the soil cover. The calculated bedrock VOC concentrations represented the highest expected concentration and the actual concentration was expected to be lower because of the conservative assumptions used in the calculation, natural microbial degradation, and dehalogenation reactions occurring in the bedrock.
Analytical results for the design study samples collected from angled coreholes were compared to reasonably developed bedrock media cleanup criteria, based on USEPA standards and guidance. The results of this comparison showed that the VOC site cleanup criteria had been achieved for a soil cover. Based on the measured VOC concentrations present in bedrock vapor, the incremental VOC mass contribution to the aquifer was considered to be negligible. Thus, the site condition intended to be achieved under the ROD in which the contribution of VOCs in bedrock to the aquifer is limited for the practical purpose of lessening the burden of groundwater restoration efforts was shown to exist. Further, the groundwater extraction and treatment system and SVE system as designed and operated are capable of capturing any residual VOCs that may be contributed from bedrock media.
On the basis of 1) the proposed BVE cleanup standards, 2) the results of the comparison of calculated bedrock VOC concentrations to the proposed BVE cleanup standards, and 3) the continued operation of the groundwater extraction and treatment system and the SVE system, the responsible parties requested approval to install a 12-inch soil cover over the former waste areas, excluding LTTS residuals areas, in lieu of a RCRA cap. The installation of a 12-inch soil cover in the former waste areas where bedrock and soil cleanup standards are met is consistent with the intent of the ROD in that the same level of protection (1 x 10 -5 carcinogenic risk level) to the aquifer is achieved.
Groundwater Extraction and Treatment System
Modifications were made to the GWET system during design and construction of this remedy component. The modifications were necessitated by actual field conditions that were different than those used in design of the system. The net effect of the modifications was to reduce the overall cost of constructing the remediation system compared to that which may have resulted without review of available alternatives and subsequent negotiation with the USEPA. A discussion of the need for the system modifications and the resulting changes is presented below.
The ROD required groundwater containing chemicals of concern exceeding site cleanup standards to be captured by a groundwater extraction system and treated on-site in a water treatment plant. Chemicals of concern were found at concentrations exceeding cleanup standards in groundwater samples obtained from on-site source monitoring wells, off-site down-gradient monitoring wells, and two residential wells west of the Site. Information obtained by the design engineer during the pre-design study revealed that the groundwater flow gradient in the area of the Site was predominately northeast to southwest and that a groundwater capture system placed west and south of the Site source areas would achieve capture of groundwater migrating from the area.
The groundwater extraction system element of the GWET system consists of 16 extraction wells designed to capture contaminated groundwater from site source areas and areas down gradient of the Site, and transfer it to the water treatment plant for removal of VOCs, SVOCs, and metals. A site plan showing the layout of the extraction system and water treatment plant is provided in Figure 2. There are five mass removal wells (EXW-1 through EXW-5) located within or immediately down gradient of site source areas. The western leg of the down gradient capture alignment is comprised of five extraction wells (EXW-6 to EXW-10) spaced at intervals of 200 linear ft. The southern leg of the extraction system capture alignment consists of six extraction wells (EXW-11 to EXW-16) which are also spaced at intervals of 200 linear ft. Extraction wells EXW-1 to EXW-14 have been completed in accordance with the project design. Extraction wells 15 and 16 were drilled but not completed due to geologic conditions encountered that precluded these wells from being installed as designed. These wells were subsequently abandoned and no replacement wells drilled.
Water production testing was required by the GWET project specifications for each extraction well to verify that the flow rates necessary to achieve groundwater capture in the field were consistent with information used in the extraction system design. The design engineer performed the well production testing in March 1995. In brief, water production test results revealed that the rate of groundwater extraction necessary to attain capture along the western alignment (EXW-1 to EXW-10) was consistent with the extraction system design information. Higher than expected production rates from EXW-6, EXW-7 and EXW-10 were balanced by lower production rates in the mass removal wells EXW-1 through EXW-5, and EXW-8 to EXW 9 along the western alignment. The water production test results for EXW-11 to EXW-14 revealed that groundwater would need to be withdrawn at a much higher rate (20-60 gpm) than the 5 gpm maximum assumed in the design to achieve capture along the southern alignment. No production data was obtained from EXW-15 and EXW-16 since they were not completed.
Based on the initial production test results, it was determined that additional data was needed from those wells that demonstrated higher than expected flow rates in order to calculate the flows needed to achieve capture along the alignment. Extended production testing was performed on EXW-7 and EXW-13. The results of the extended production testing confirmed that groundwater at EXW-11 through EXW-14 would need to be extracted at flows rates up to 60 gpm in order to achieve sustained capture along the southern alignment.
The groundwater treatment plant was designed to operate at an average flow of 80 gpm (16 wells at 5 gpm), and a peak flow of 120 gpm. A combined steady state flow of 60 gpm is expected to result from operation of EXW-1 through EXW-10 at groundwater removal rates necessary for capture in the source areas and along the western alignment. The extraction wells along the southern alignment were expected to contribute an additional 80-240 gpm to the treatment plant, based on recent production test results, resulting in a potential maximum total flow of 300 gpm. If EXW-15 and EXW-16 were required to be installed and produce water at the rates experienced in EXW-11 through EXW-14, the total flow to the treatment plant could have been as high as 420 gpm, exceeding the design capacity by 350%.
Four alternatives were developed for completing construction and operating the groundwater extraction and treatment systems in a manner that accommodates the differing groundwater flow conditions encountered, and meets the intent of the groundwater cleanup component of the Site remedy. The alternatives ranged from modification of extraction well pumps and associated mechanical and electrical connections for operation of the treatment plant at 120 gpm at an estimated cost of $100,000, to increasing the extraction system and water treatment plant capacity to 420 gpm at an estimated cost of $2.5 million.
Implementation of the modified extraction system alternative was selected for completing construction and operating the groundwater extraction system and water treatment plant. This alternative was considered to be the most practical approach to meet the intent of the GWE/SVE remedy component and accommodate unknown conditions encountered during installation of the extraction system. Selection of the modified extraction system alternative resulted in progress toward achievement of the following goals, while obtaining long-term performance information.
Remove contaminated groundwater from site source areas.
Achieve capture of groundwater migrating off the Acme Site along the western perimeter.
Remove VOCs in source area soils, thus reducing potential contribution to groundwater
Obtain information on the actual behavior of groundwater flow within the dolomite system.
The modified GWET system was approved by the agency with the knowledge that actual field conditions encountered during installation and operation of the extraction system may differ from those used in the Final Design. As a result of the unexpected field conditions, it was acknowledged that further system modifications may be necessary. The rationale considered in approving the modified extraction system alternative are presented below.
Sources of groundwater contamination have been removed.
SVE system will further reduce contaminant loading to groundwater from site soils.
Mass extraction wells remove the majority of contaminant mass from groundwater.
The concentrations of chemicals of concern in extraction wells along the southern alignment are close to or below cleanup standards based on recent analytical results.
Operation of extraction wells along the western alignment will provide long-term performance data for pumping in the dolomite formation.
The alternative water supply was extended south along Lindenwood Road to eliminate the potential for any exposure of residents to groundwater planned for natural attenuation in areas south of the site.
RCRA Cap
The ROD OU2 states that a 12-inch soil cover may be placed over the treated soil resulting from implementation of the Low Temperature Thermal Stripping (LTTS) remedial action in lieu of a RCRA Compliant Cap, if this material is exempted from regulation as a RCRA hazardous waste. The LTTS-treated soils at the Site were found to satisfy the criteria necessary to exempt the material from regulation as a RCRA hazardous waste; thus, a final soil cover was proposed for installation for this material to satisfy the Site cover requirements identified in the ROD. The result of this action will be to reduce the cost of the remedy by an amount commensurate with the cost of constructing the RCRA Cap. A description of the activities pursued to exempt the LTTS-treated soil from exemption as a RCRA hazardous waste are presented below.
Under the USEPA "contained in" policy, mixtures of non-solid waste (soils) and hazardous waste are regulated as a RCRA hazardous waste as long as the mixture "contains" a listed hazardous waste. The material may be exempted from regulation as a RCRA hazardous waste if it can be demonstrated that the material no longer "contains" the listed hazardous waste. For RCRA listed wastes, the condition under which the mixture no longer "contains" the hazardous waste has been determined to be at levels which are below human health risk thresholds established for the constituents of concern.
As stated in the ROD, material introduced to the LTTS process unit consisted of a mixture of a non-solid waste (soil) and certain constituents of the RCRA F001-F005 listed waste category. Therefore, treated soils from the LTTS process must be managed as a listed hazardous waste having the waste codes F001-F005, under the Agency's "contained in" policy for mixtures of a non-solid waste and a listed hazardous waste. However, the ROD provides for installation of a 12-inch soil cover over areas where LTTS-treated soil is back-filled on-site in lieu of a RCRA Cap, if the residuals are exempted from regulation as a RCRA hazardous waste. The LTTS-treated soil may be exempted from regulation as RCRA hazardous waste by demonstrating that the material no longer contains the F001-F005 constituents above health-based levels and otherwise does not meet the definition of a characteristic waste as provided in RCRA at 40 CFR 261.3.
The F001-F005 listed waste contaminants of concern that were identified in affected soils at the Site are listed below. These contaminants of concern were identified in the ROD based on the results of site-wide sampling activities conducted during in the investigation phase of the Site response action.
1,1,1-trichloroethane
tetrachloroethylene
trichloroethylene
ethylbenzene
total xylenes
benzene
No specific USEPA guidance currently exists on the selection of criteria to be used for exemption of RCRA hazardous waste under the "contained in" policy. In general, the exemption criteria are to be selected on a case by case basis. As no clear guidelines exist for selection of criteria to be used in demonstrating that a mixture of a non-solid waste and listed waste no longer "contains" the listed waste, Risk-Based Concentration Levels (RBCs) developed by USEPA Region III were determined to be the appropriate exemption criteria for the purpose of demonstrating that the LTTS-treated soil no longer "contains" the F001-F005 contaminants of concern. The RBCs represent the most comprehensive concentration-based levels available and were developed specifically for use in establishing concentrations of contaminants in soil that are protective of human health.
Comparison of the 95 % Upper Confidence Level (UCL) calculation for the LTTS-treated soil results to the exemption criteria demonstrated that the concentrations for F001-F005 contaminants of concern, identified to be present in soil treated in the LTTS process unit, are below the respective risk-based concentrations derived for the transfer of contaminants from soil to groundwater. The LTTS treated soil was thus shown to no longer "contain" the F001-F005 listed hazardous waste and may be exempted from regulation as RCRA-listed hazardous waste.
Additionally, the LTTS-treated soil did not exhibit any of the waste characteristics identified in 40 CFR 261.3 and is therefore not a RCRA-characteristic waste. Total concentrations were used for the organic compounds and the "20x rule" for screening total concentration relative to TCLP concentrations was applied. The TCLP analysis was used for the analysis of metals in the LTTS-treated soil.
As stated in the ROD, "If no residuals are landfilled on-site (or if residuals can be delisted under RCRA), and if SVE is successful in treating VOCs to levels at or below the standards set forth for the soil cover, a 12-inch soil cover may be placed on the site rather than a RCRA compliant Cap." Delisting is not the appropriate means for exempting the LTTS-treated soil from RCRA regulation since this material consists of a mixture of a non-solid waste and constituents of a RCRA-listed waste (F001-F005). The appropriate means for exempting the LTTS-treated soil is through application of the "contained in" policy, whereby the material no longer has to be managed as a hazardous waste if it is demonstrated that the material no longer "contains" the listed hazardous waste at levels above health-based criteria. As shown, the concentrations of F001-F005 contaminants of concern in the LTTS-treated soil were below the health-based criteria developed by USEPA, thus a soil cover may be placed over the LTTS treated soils in place of a RCRA-compliant cap.
The remedy selected for implementation at CERCLA sites often does not fully address the scope of activities that may be necessary during the RD/RA phase of response action to achieve cleanup objectives established for the site in the ROD. Consequently, significant potential exists for an expansion of RD/RA activities to occur, both under fund-financed cleanups and responsible party-led actions, causing project budgets to balloon and project schedules to become obsolete. Knowledge that the probability for changes in the remedy to occur are great at the outset of the project is an important element of the project planning process and provides opportunities to optimize the project scope and control costs.
The Remedial Design and Remedial Action (RD/RA) conducted at the Acme Solvents NPL Site (Site) was undertaken by the responsible parties with USEPA oversight. A diligent review of the site cleanup objectives relative to the actual site conditions was performed throughout the life of the RD/RA project to identify opportunities to reduce the scope of site work necessary to meet the ROD. Measures taken to optimize design and construction activities, and control costs during implementation of the RD/RA phase of the project for Operable Unit 2 (OU2), included: evaluation of the RD/RA project organizational structure, ARARs analysis, and changes to the design and construction of the remedy that were identified as the project progressed. The specific optimization measures that were implemented during the RD/RA phase of the project are listed below.
Alternative LTTS technology was identified and implemented for affected soils at the site. This action resulted in a significant reduction in the cost to complete this remedial component.
A demonstration was made that the BVE component element of the remedy was not required to meet site cleanup goals.
The groundwater extraction and treatment system was modified to reduce the volume of water requiring extraction and treatment under the original design. This action resulted in a significant cost savings in construction and long term operation and maintenance costs.
A demonstration was made that LTTS-treated soils are exempt from regulation as a
RCRA hazardous waste and ARARs requiring installation of a RCRA-compliant to
cover this material no longer apply.
Figure 1. Site Location Map - Acme Solvents Reclaiming, Inc., Site
Winnebago County, Illinois, Date: 11/91
Figure 2. Site Plan - Acme Solvents Reclaiming, Inc., Site
Winnebago County, Illinois, Date: 3/96
Figure 3. Treatment facility plan - Acme Solvents Reclaiming, Inc.
Winnebago County, Illinois
Figure 4. Acme Solvents reclaiming final RCRA cap and 1-foot soil cover design.
Sections and Details.
Winnebago County, Illinois