United States Solid Waste and Directive: Environmental Protection Emergency Response 9283.1-2FS April Agency (OS-220) 1989 A Guide On Remedial Actions For Contaminated Ground Water GOAL The goal of Superfund ground-water remediation is to protect human health and the environment by restoring ground water to its beneficial uses within a time frame that is reasonable, given the particular site circumstances. This fact sheet summarizes the key issues in the development, evaluation, and selection of ground-water remedial actions at Superfund sites. For more detailed information, consult Regional Ground-Water Forum members or the Interim Final “Guidance on Remedial Actions for Contaminated Ground Water at Superfund Sites,” (Ground-Water Guidance) December 1988, OSWER Directive No. 9283.1-2. REQUIREMENTS OF CERCLA
The approach outlined in this fact sheet is • Satisfy the preference for remedies that • Remedial actions that restore ground designed to ensure that ground-water reme employ treatment that permanently and water are to be federally funded until cleanup ial actions will meet the following require significantly reduces the mobility, toxicity, or levels are achieved or up to 10 years, ents of CERCLA: volume of hazardous substances as a principal whichever comes first. However, if the • Protect human health and the environ element or provide an explanation in the ROD purpose of the ground-water remedial action ment (121(b)) for why the preference was not satisfied is to provide an alternate water supply, for • Comply with applicable or relevant and (121(b)). In addition, the following provisions example, but not to restore ground water, appropriate requirements (ARARs) of Fed of CERCLA may or may not be pertinent to then the Federal government will pay capital ral and State laws (121(d)(2)(A)) or warrant groundwater remediation, depending on and startup costs only (104(c)(6)). a waiver under CERCLA Section 121(d)(4) site-specific circumstances: • A review must be conducted at least • Be cost-effective (121(a)) • Alternate concentration limits (ACLs) from every 5 years if wastes are left onsite (121(c)) • Utilize permanent solutions and altern otherwise applicable or relevant and above health- or environment based levels to ative treatment technologies or resource appropriate requirements can only be used for verify that the remedy continues to provide recovery technologies to the maximum determining offsite cleanup levels under special adequate protection of human health and the extent practicable (121(b)) circumstances (121(d)(2)(B)(ii)). environment.
SCOPING GROUND-WATER SITE MANAGEMENT PLANNING REMEDIAL ACTIVITIES Site management planning identifies the An operable unit is a portion of an overall Before collecting any data, it is useful to response approaches that will be taken to response action that, by itself, eliminates or conduct two planning activities: address the site problems. Two response mitigates a release, a threat of a release, or approaches can be taken to remediate ground an exposure pathway; it may reflect the • Site management planning (See right), water at Superfund sites: final remediation of a defined portion of a which involves identifying the types of site. At many sites, it is appropriate to analyses and actions that are appropriate to • Removal actions implement an operable unit as an interim address site problems and their optimal • Remedial actions, which can be final, or action. Interim actions may be implemented sequence. interim actions to prevent exposure to contaminants or • Project planning (See next prevent further degradation of ground page),which includes such activities as Removal actions are authorized for any water (by remediating hot spots, for scoping data collection efforts, initiating release that presents a threat to public health, example) while the overall remedial identification of ARARs, and work plan welfare, or the environment. CERCLA limits investigation (RI) and feasibility study (FS) preparation. Superfund-financed removal actions to $2 are being conducted. Interim actions million and 12 months unless the criteria for involving pumping can also provide critical granting an exemption to the statutory limits information for evaluating the final remedy. are satisfied. Remedial actions are sometimes addressed as operable units.
Word-searchable version – Not a true copy Characterization Characterization of of the Hydrogeology Contamination
Describe, the geology using geophysical meth- Consider selecting one or more chemicals for ods and sediment samples collected during monitoring to reduce analytical costs and drilling of soil borings and monitoring wells. simplify modeling. These chemicals may be Present the information using geologic cross selected on the basis of toxicity, exposure, sections and fence diagrams. mobility, persistence, treatability, or volume of contaminants. If appropriate, however, Assess the ground-water movement by using nontoxic constituents or chemical classes, water level measurements from wells screened such as total volatile organic compounds, at various depths. Present a contour map of could also be monitored. each aquifer to determine recharge and discharge and identify the direction of ground- Determine the horizontal and vertical extent of water flow. the contaminant plume through monitoring at various locations and depths. Understand the Evaluate data over time to detect seasonal or relationship of the source to the ground tidal fluctuations. water. Contaminant levels should be monitored over time to identify migration and Aquifer tests may be used to determine the degradation patterns. Note the density of hydraulic properties of the aquifers and contaminants to aid in assessing their aquitards, and to evaluate the performance and behavior in the ground water. effectiveness of the extraction system. Aquifer tests can be used in conjunction with Assess contaminant/soil interactions to aid in modeling. assessing the effectiveness of a ground-water extraction system. Laboratory analysis of contaminant partitioning behavior in the saturated soil may be critical to the development of the remedy and the determination of whether ground-water extraction is practicable.
Assessment of Design Evaluation of Parameters for Plume Movement Consideration of Potential Treatment and Response Technical Uncertainty Technologies
Consider modeling the ground Identify sources of uncertainty, e.g., pre- Identify several likely remedial water as a tool to guide the dicting the nature, extent, and movement of technologies during scoping to placement of monitoring wells, contamination; determining contaminant focus data collection activities. predict concentrations of movement through the vadose zone; Consider data needs for screening contaminants at exposure points, estimating the rate and direction of the out inappropriate technologies and estimate the effect of source control ground-waterflow; and estimating the cost for designing workable systems to actions, and evaluate the expected of remedial alternatives. Assess the provide a sound basis for selecting a performance of the ground-water magnitude of uncertainty from each of remedy and reducing implementation remedial action. these sources, and weigh the costs and time. Consider the costs and benefits benefits of reducing uncertainty by of conducting a treatability study. collecting additional information.
Word-searchable version – Not a true copy REMEDIAL ACTION OBJECTIVES Remedial action objectives include cleanup levels, the area of attainment, and the restoration time frame.
Cleanup Levels Cleanup levels will generally be set at Table 1 For systemic (noncarcinogenic) basis of factors related to exposure, Restoration Time Frame aquifer testing or saturated soil core health-based levels, reflecting current toxicants, cleanup levels should be set at technical limitations, and uncertainties. analysis may be warranted. Potential ARARs The restoration time frame is defined as and potential use and exposure. For levels to which humans could be the period of time required to acheive ground water that is a current or • Maximum contaminant levels exposed on a daily basis without Alternate concentration limits (ACLs) cleanup levels in the ground water at all Once technical limits to achieving potential source of drinking water, (MCLs) experiencing appreciable adverse effects may be established in some situations locations within the area of attainment. cleanup levels have been assessed, maximum contaminant levels (MCLs) during their lifetimes. To determine where remediation of the ground water restoration time frames for remedies can • Promulgated State standards For drinkable ground water, at least one under the safe drinking water Act or aggregate effects from systemic is not practicable. CERCLA Section alternative should reach cleanup levels be evaluted relative to this limit on the more stringent State standards devised Other Potential ARARs and TBCs toxicants, the hazard index is used. 121(d)(2)(B)(ii) places restrications on in the minimum time frame technically basis of the following considerations: to protect drinking water generally are the use of ACLs. The ground water must • Proposed MCLs achievable. Technical limits to ARARs. If an MCL or State standard For carcinogens, cleanup levels should discharge to nearby surface water and extracting contaminants that will tend • Feasibility of providing an alternate does not exist for a contaminant, then • Risk-specific doses reflect an individual excess lifetime cause no statistically significant to increase the restoration time frame water supply – including schedule, cost, other potential ARARs and criterai that cancer risk of 10-4 to 10-7 ; that is, increase of contaminants in the surface quality, reliability, and yield. Also, • Reference doses include contaminant/soil interactions, are not ARARs but are to-be-considered aggregate cancer risk levels should fall water. In addition, provisions for the presence of dense nonaqueous phase whether the alternate water supply is -4 -7 (TBC) should be identified. The most • Lifetime Health advisories within the 10 to 10 risk range. The enforceable institutional controls that liquids, continued migration form itself irreplaceable should be considered. common ARARs and TBCs are 10-4 aggregate excess lifetime cancer risk prevent access to the contaminant plume Readily available alternate water • Maximum contaminant level goals sources, widely spread plumes, and summarized in Table 1. This is level is considered the starting point for must be made. poorly transmissive aquifers. Because supplies will increase the flexibility to consistent with the Ground Water • Water quality criteria analysis, but other risk levels between these conditions are not generally select longer restoration time frames. -4 -7 Protection Strategy which differentiates 10 to 10 may be supported on the addressed in plume migration models, ground water on the basis of use, value, • Potential use and value of the ground and vulnerability. water – including the timing of anticipated demand, the magnitude of Area of Attainment Figure 1 the demand, the need (drinking, The area of attainment is the area outside irrigation), and the availability of other the boundary of any waste remaining in Sample Remediation Process- water sources. If there is a high demand place and up to the boundary of the Ground-Water Remedy for the ground water, shorter time frames contaminant plume. Generally, the are warranted. boundary of the waste is defined by the source control remedy. If the source is • Effectiveness and reliability of removed, the entire plume is within the institutional controls – effective area of attainment. But, if waste is controls restricting use or access to managed onsite, the ground water contaminated ground water may increase directly beneath the waste management the flexibility to select a remedy with a area is not within the area of attainment. longer restoration time frame. Examples of institutional controls include licensing of well drillers, well construction permits, well quality certification, and regulations of new development and property transactions.
• Ability to monitor and control contaminant movement – complex flow patterns, for example in fractured bedrock or karst areas, and unusual distributions of contaminants may increase the benefits of shorter restoration time frames.
Word-Searchable Version - Not a True Copy GENERAL RESPONSE ACTIONS
After developing remedial action objectives, soil vapor extraction, in situ vitrification, and controls; and (2) wellhead treatment or general response actions are identified. others. provision of an alternate water supply with General response actions for contaminated institutional controls, when complete ground water include active restoration, Plume containment seeks to minimize the restoration to cleanup levels is not plume containment through hydraulic spread of a plume through hydraulic gradient practicable. control, and limited or no active response, control, which can be either active or passive. combined, if appropriate, with institutional Containment is appropriate where active Factors that may cause active restoration to controls to protect human health. These are restoraton is not practicable or where the be impracticable or not cost-effective include: discussed below. beneficial uses of the ground water do not warrant it. In addition, plume containment • Widespread plumes such as at industrial Active restoration is useful when there are may be combined with active restoration or areas, mining sites, and pesticide sites mobile contaminants, moderate to high natural attenuation to achieve cleanup levels. • Hydrogeological constraints such as hydraulic conductivities in the contaminated with fractured bedrock, or where the aquifer, and effective treatment technologies Limited or no active response includes two transmissivity is less than 50 square feet per available for the contaminants in the ground remedial scenarios: (1) a natural attenuation day water. Innovative technologies for active alternative that eventually achieves cleanup • Contaminant-related factors such as the restoration may include biorestoration, soil levels throughout the area of attainment and presence of dense nonaqueous phase liquids flushing, in situ stream stripping, includes monitoring and institutional • Physical/chemical factors such as partitioning to soil or organic matter. FORMULATING REMEDIAL ALTERNATIVES
A range of remedial technologies can be Treatment options include biological, drinking water supply. Finally, there are combined under a particular general chemical, physical, thermal, or in situ various options for containment, response action. Process options for methods. Treated ground water can be monitoring effectiveness, and institutional extraction include: extraction wells, discharged to surface water or a controls. Alternatives are developed by ext raction/injection systems, and publicly-owned treatment works, combining these various process options interceptor drains and trenches. reinjected to the aquifer, or used as a into a comprehensive response approach. DETAILED ANALYSIS OF ALTERNATIVES AND SELECTION OF REMEDY
CRITERIA AND BALANCING prevent exposure? limitations on POTWs receiving discharge The analysis of remedial actions for ground • Reduction of mobility, toxicity, and waters? What uncertainties exist with the water is made on the basis of the following volume : What reductions are achieved treatment process considered? evaluation criteria. Considerations that are through treatment in any phase of the • Cost unique to ground water are noted. remediation process? This includes initial Threshold criteria treatment of ground water and subsequent Modifying criteria: • Overall protection of human health and treatment of resulting residuals. Special note • State Acceptance the environment: Will the remedy achieve should be given to remedies that transfer • Community Acceptance and maintain clean-up levels? Are all contaminants from ground water to air If the alternatives will achieve the same long exposure pathways controlled; e.g., discharge without treatment of the air releases, term goals, the primary balancing criteria will points, points of use? especially if risk through the air pathway be implementability, cost and short term • Compliance with ARARs: Will the exceeds 10-6 . effectiveness. remedy attain MCLs or state standards in • Short-term effectiveness: What is the potentially drinkable ground water or justify restoration time frame? What cross-media DOCUMENTATION a technical impracticability waiver? Are impacts occur as a result of ground-water In addition to the standard documentation, a ARARs met for the treated ground water and treatment or construction of a containment ROD for a ground-water action should any treatment residuals that are generated? facility? How much farther will the plume include the following components: Balancing criteria spread before the remedy is completed? • Remedial action objectives defined in the • Long term effectiveness and • Implementability: What permitting FS for each alternative: i.e., the cleanup permanence: Remedies that achieve the requirements must be met for discharge of levels, the area of attainment, and the cleanup levels will be comparable with treated ground water? Are there access restoration time frame. respect to this criteria. For remedies that will problems with installation of the remedy--e.g., • A description of the technical aspects of not restore ground water, how reliable are the extraction wells and slurry walls--in terms of the selected remedy that will form the basis of engineering or institutional controls used to resources required? Are there capacity design for the system, such as the following:
Word-searchable version – Not a true copy (Detailed Analysis-- Continued from pre implementing authority ground-water extraction until cleanup levels are vious page) Since performance of remedies for restoring attained, or groundwater extraction until an – Number of extraction wells contaminated ground water can often be equilibriumis reached and contaminant mass is – Treatment process eval-uated only after the remedy has been no longer being removed at significant rates, at – Control of cross-media impacts implemented and monitored for a period of which time portions of the plume that remain – Expected pumping and flow rates time, remedial action objectives should be above cleanup levels should be monitored and – Management of residuals presented as ranges to accommodate institutional controls established to prevent – Gradient control system reasonable degrees of change during design access to contaminated ground water. – Type of institutional controls and the and implementation. An option is to include two possible scenarios in the remedy, e.g.,
EVALUATING PERFORMANCE AND MODIFYING REMEDIAL ACTIONS
Performance evaluations of the full-scale After evaluating whether cleanup levels remedial action are conducted periodically to have or will be achieved in the desired time compare actual performance to expected frame, the following options should be performance. Conducting performance considered: evaluations and modifying remedial actions is • Discontinue operation part of a flexible approach to attaining • Upgrade or replace the remedial action remedial action objectives. to achieve the original remedial action objectives or modified remedial action Figure 2 represents a decrease in contaminant objectives concentration over time for three • Modify the remedial action objectives ground-water remedial actions of varying and continue remediation, if appropriate. effectiveness. Line A represents a remedial Performance monitoring should ensure that action that is meeting design expectations, residual contamination has been removed. and the desired cleanup levels are predicted This will generally require monitoring to be reached within the anticipated time. Line ground-water concentrations after active B represents a remedial action that is measures have been completed to allow predicted to achieve the cleanup levels, but contaminant concentrations in the soil and the action will have to be operated longer ground water to re-equilibrate. than anticipated. Line C represents a remedial action that will not achieve the desired cleanup levels for a long time, if ever, without modifying the remedial action. MULTIPLE SOURCES STRATEGY At sites where there are multiple sources of storage facilities located at or upgradient of ground-water remedies. Superfund resources ground-water contamination, some of which the area of contamination. may be used to provide an alternate water are Superfund sites, it may be appropriate to supply if an NPL site is a significant implement a multiple-source strategy. The Superfund will implement appropriate contributor to the plume and if the need to Superfund program should work remedial actions related to National Priorities alleviate the public health threat does not cooperatively with other responsible entities List sites once an RI/FS is initiated. At this allow for identification and involvement of to achieve comprehensive remedies, and may point, the Regional Administrator, in other parties at that time. Actions to prevent accept primary responsibility for coordinating consultation with the Assistant or minimize spread of contaminants from the all involved parties during the source Administrator of OSWER, should evaluate source are often implemented at multiple identification phase of work. the appropriateness of the Superfund source groundwater sites before completing program retaining primary responsibility for plume characterization, which can be lengthy The Superfund program should coordinate an coordinating the ground-water response and complicated at these sites. initial scoping plan for source identification action for all sources. This decision may be that would include limited sampling. determined by factors such as the The amount of Superfund resources used to Locations of possible sources may be contribution of Superfund sources relative to address ground-water contamination will determined through two surveys: (1) a survey other sources, as well as the availability and derive primarily from the extent to which the of contributors to and users of the affected willingness of other involved parties to overall contamination can be attributed to the ground water (termed a “contributor/user initiate action. Superfund site. It will also depend on the assessment”) that will help identify the other willingness and capability of the other parties that must be involved in the Response actions generally fall into three involved parties to take actions to address formulation of an effective remedy; and (2) a categories: provision of alternate water the contamination for which they are survey of potential sources such as solvent supply, source control measures, and responsible.
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