Doty, Carolyn B.

English

Colorado Law

University of Colorado Law SchoolColorado Law Scholarly CommonsUncovering the Hidden Resource: GroundwaterLaw, Hydrology, and Policy in the 1990s (SummerConference, June 15-17)Getches-Wilkinson Center Conferences,Workshops, and Hot Topics6-17-1992Groundwater Cleanup: Is It Worth It?Carolyn B. DotyFollow this and additional works at: http://scholar.law.colorado.edu/groundwater-law-hydrology-policyPart of the Environmental Health and Protection Commons, Environmental Law Commons,Hydraulic Engineering Commons, Natural Resources Law Commons, Natural ResourcesManagement and Policy Commons, Science and Technology Commons, Water Law Commons, andthe Water Resource Management CommonsReproduced with permission of the Getches-Wilkinson Center for Natural Resources, Energy, and the Environment (formerly the Natural ResourcesLaw Center) at the University of Colorado Law School.Citation InformationDoty, Carolyn B., "Groundwater Cleanup: Is It Worth It?" (1992). Uncovering the Hidden Resource: Groundwater Law, Hydrology, andPolicy in the 1990s (Summer Conference, June 15-17).http://scholar.law.colorado.edu/groundwater-law-hydrology-policy/38    Carolyn B. Doty, Groundwater Cleanup: Is It Worth It?, in UNCOVERING THE HIDDEN RESOURCE: GROUNDWATER LAW, HYDROLOGY, AND POLICY IN THE 1990S (Natural Res. Law Ctr., Univ. of Colo. Sch. of Law 1992).  Reproduced with permission of the Getches-Wilkinson Center for Natural Resources, Energy, and the Environment (formerly the Natural Resources Law Center) at the University of Colorado Law School.  GROUNDWATER CLEANUP:IS IT WORTH IT?Carolyn B. DotyPolicy and Risk AnalystAutomated Sciences Group, Inc.Oak Ridge, TNUncovering the Hidden Resource:Groundwater Law, Hydrology and Policy in the 1990sUniversity of Colorado at BoulderNatural Resources Law CenterJune 15-17, 1992GROUNDWATER CLEANUP: IS IT WORTH IT?I.	 I NTRODUCTI ONA. SummaryDuring the past decade, many decisions have been made to restore aquifers todrinking water standards using the pump-and-treat approach. However, until recently,little data have been available with which to evaluate the effectiveness of thisremedial approach. Recent theoretical studies and field experience have indicatedthat aquifer restoration using the pump and treat approach is not as feasible as wasoriginally predicted. Evidence suggests that groundwater pumping is ineffective forpermanently reducing levels of aquifer contamination to meet health-based goals forgroundwater. The primary contributors to the ineffectiveness of pumping are factorsassociated with the physical and chemical processes that affect the behavior ofcontaminants in the subsurface environment. This discussion focuses on thelimitations and costs associated with aquifer restoration, and outlines considerationsfor selecting approaches for managing contaminated aquifers.B. General ReferencesDoty, C. B. and C. C. Travis. 'The Effectiveness of Groundwater Pumping as aRestoration Technology," Risk Analysis Section, Center for Risk Management, OakRidge National Laboratory, Oak Ridge, TN, ORNLTM-11866 (1991).Doty, C. B., A. G. Crotwell, and C. C. Travis. "Cost Growth for TreatmentTechnologies at NPL Sites," Risk Analysis Section, Center for Risk Management,Oak Ridge National Laboratory, Oak Ridge, TN, ORNL1TM-11849 (1991).Freeze, R. A. and J. A Cherry. "What Has Gone Wrong?" Groundwater, 27(4), 459-464.McCarty, Perry. "Scientific Limits to Remediation of Contaminated Soils and GroundWater," Proceedings of the National Research Council Water Sciences TechnologyBoard Colloquium, Washington, DC (1989).U. S. Environmental Protection Agency. "Considerations in Ground WaterRemediation at Superfund Sites," Office of Solid Waste and Emergency Response,Directive No. 9355.4-03, Washington, DC (October 1989).U. S. Environmental Protection Agency. "Suggested ROD Language for VariousGround Water Remediation Options," Office of Solid Waste and EmergencyResponse, Directive No. 9283.1-03, Washington, DC (October 1990).U. S. Environmental Protection Agency. "Evaluation of Groundwater ExtractionRemedies," Office of Solid Waste and Emergency Response, EPA/540/0289/054,Washington, DC (1989).II. INDICATORS OF PUMP AND TREAT EFFECTIVENESSA. The primary indicators of effectiveness of a pump and treat system in restoring anaquifer to a specified cleanup level are permanent reduction of aquifer concentrationsover time and reduction of the contaminant mass in the aquifer.B. The ideal scenario would be a steady decrease in contaminant concentrations until thetarget level is attained.III. PUMP AND TREAT PERFORMANCE RECORDSA. Although concentrations may drop initially, this decline is followed by a leveling ofconcentrations with little or no further decrease in concentrations.B. At sites where the plume appears to be well-contained, concentrations have leveledafter average VOC concentration reductions of approximately 60% to 90% in onsitewells, with large masses of contamination (at least 50%) remaining in the aquifer.C. At all sites where contaminant concentrations have leveled, the concentrations remainwell above the target levels, even at sites where cleanup goals were established abovedrinking water standards.D. When pumps are turned off, the concentrations rise again, often to levels greater thanthe initial concentrations.IV. PRIMARY FACTORS INFLUENCING EFFECTIVENESSA. If not fully remediated, contaminated soils serve as the primary source ofcontamination.B. Even if soils are remediated, immobilized contaminants in the vadose zone andsubsurface continue to serve as secondary sources of contamination.1. Contaminants sorbed into the aquifer material matrix. The mass ofcontaminant sorbed to the aquifer material is generally significantly greaterthan the mass in solution.2. Immobile contaminants in the non-aqueous phase. The mass ofcontamination in the non-aqueous phase may be considerably greater than inthe dissolved phase.3. Contaminants trapped in zones of low permeability or fractured bedrock.Even highly soluble contaminants may be trapped in the finer pore structure.2V. FEASIBILITY OF AQUIFER RESTORATIONA. Pumping is generally effective for plume containment.B. Evidence to date suggests that eliminating secondary sources of contamination withina reasonable time frame is technically infeasible, and this factor will continue to bethe primary contributor to the ineffectiveness of pump and treat systems, even aftersoil remediation is complete.1. Little success has been achieved in locating dense NAPLs (DNAPIs).2. Mobilizing DNAPLs is currently not feasible.3. Contaminant desorption rates are extremely slow, and contaminants appearto irreversibly sorbed in some cases.VI. COSTS AND REMEDIAL TIME FRAMESA.	 Inadequate consideration of the presence of continuous secondary sources ofcontamination has resulted in underestimation of remedial time frames.1. Recent modeling studies estimate pump and treat time frames of 100 to 1,000years for VOC-contaminated sites.2. Remedial time frames for aquifer restoration are underestimated by at leasta factor of three.3. Estimates of contaminant retardation are essential for determining remedialtime frames.4. Site-specific retardation factors cannot be obtained because the mechanismsthat control contaminant desorption are not fully understood.B.	 Underestimation of remedial time frames has resulted in the gross underestimationof costs of remediation.C. The ineffectiveness of pumping to achieve aquifer restoration results fromfundamental chemical and physical processes. Therefore, spending more money onsite characterization, completing source remedial actions, and modifying pump andtreat system designs will not ensure successful remediation.

Groundwater Cleanup: Is It Worth It?

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Groundwater Cleanup: Is It Worth It?

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