1、API PUBLr463L 95 E 0732290 0555453 589 American Petroleum Institute *P Ew.irnaaid S,iYs 1 Rvrmnbrp re+. Petroleum Contaminated Low Permeability Soil: Hydrocarbon Distribution Processes, Exposure Pathwavs and In Situ Rgmediation Technologies Health and Environmental Sciences Department Publication Nu
2、mber 4631 September 1995 API PUBLm4631 95 m 0732290 0555454 415 m Stratgrer for Todayk Environmental Partner documenting performance improvements; and communicating them to the public. The foundation of STEP is the API Environmental Mission and Guiding Environmental Principles. API ENVIRONMENTAL MIS
3、SION AND GUIDING ENVIRONMENTAL PRINCIPLES The members of the American Petroleum Institute are dedicated to continuous efforts to improve the compatibility of our operations with the environment while economically developing energy resources and supplying high quality products and services to consume
4、rs. The members recognize the importance of efficiently meeting societys needs and our responsibility to work with the public, the government, and others to develop and to use natural resources in an environmentally sound manner while protecting the health and safety of our employees and the public.
5、 To meet these responsibilities, API members pledge to manage our businesses according to these principles: To recognize and to respond to community concerns about our raw materials, products and operations. To operate our plants and facilities, and to handle our raw materials and products in a mann
6、er that protects the environment, and the safety and health of our employees and the public. To make safety, health and environmental considerations a priority in our planning, and our development of new products and processes. To advise promptly, appropriate officials, employees, customers and the
7、public of information on significant industry-related safety, health and environmental hazards, and to recommend protective measures. To counsel customers, transporters and others in the safe use, transportation and disposal of our raw materials, products and waste materials. To economically develop
8、 and produce natural resources and to conserve those resources by using energy efficiently. To extend knowledge by conducting or supporting research on the safety, health and environmental effects of our raw materials, products, processes and waste materials. To commit to reduce overall emission and
9、 waste generation. To work with others to resolve problems created by handling and disposal of hazardous substances from our operations. To participate with government and others in creating responsible laws, regulations and standards to safeguard the community, workplace and environment. To promote
10、 these principles and practices by sharing experiences and offering assistance to others who produce, handle, use, transport or dispose of similar raw materials, petroleum products and wastes. API PUBL*4631 75 m 0732270 0555455 352 Petroleum Contaminated Low Permeabi I ity Soi I: Hydrocarbon Distrib
11、ution Processes, Exposure Pathways and In Situ Remediation Technologies Health and Environmental Sciences Department API PUBLICATION NUMBER 4631 EDITED BY: TERRY WALDEN BP OIL COMPANY 4440 WARRENSVILLE CENTER ROAD CLEVELAND, OH 441 28-2837 AUGUST 1995 American Petroleum Ins titute API PUBL*463L 95 0
12、732290 0555456 298 = FOREWORD API PUBLICATIONS NECESSARILY ADDRESS PROBLEMS OF A GENERAL NATURE. WITH RESPECT TO PARTICULAR CIRCUMSTANCES, LOCAL, STATE, AND FEDERAL LAWS AND REGULATIONS SHOULD BE REVIEWED. API IS NOT UNDERTAKING TO MEET THE DUTIES OF EMPLOYERS, MANUFAC- TURERS, OR SUPPLIERS TO WARN
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14、 FOR THE MANU- FACTURE, SALE, OR USE OF ANY METHOD, APPARATUS, OR PRODUCT COV- ERED BY LETTERS PATENT. NEITHER SHOULD ANYTHING CONTAINED IN ITY FOR J“GEMENT OF LETTERS PATENT. THE PUBLICATION BE CONSTRUED AS INSURING ANYONE AGAINST LIABIL- Copyright Q 1995 American Petroleum Institute ii - API PUBL*
15、4631 95 0732290 0555457 124 = ACKNOWLEDGMENTS THE FOLLOWING PEOPLE ARE RECOGNIZED FOR THEIR CONTRIBUTIONS OF TIME AND EXPERTISE DURING THIS STUDY AND IN THE PREPARATION OF THIS REPORT API STAFF CONTACT Harley Hopkins, Heaith and Environmental Sciences Department MEMBERS OF THE THE SOIL AND GROUNDWAT
16、ER TECHNICAL, TASK FORCE 4% MEMBERS OF THE GW-30 PROJECT TEAM R. Edward Payne, Mobil Oil Corporation (Project Team Leader) Vaughn Berkheiser, Amoco Corporation Tim Buscheck, Chevron Research and Technology Company Steve deAlbuquerque, Phillips Petroleum Company Lesley Hay Wilson, BP Oil Company Bob
17、Hockman, Amoco Corporation Victor J. Kremesec, Amoco Corporation Al Liguori, Exxon Research and Engineering Company Jeff Meyers, Conoco, Inc. John Pantano, ARCO Exploration and Production Technology Adolfo Silva, Petro-Canada, Inc. David Soza, Pennzoil Company Terry Walden, BP Oil Company API acknow
18、ledges Terry Walden, BP Oil Company, as prime contractor for APIs Low Permeability Soil Research Program, and for his role in the development and editing of the papers included in this report. API acknowledges Dr. Richard Johnson, Oregon Graduate Institute, for his contributions to the project. iii
19、ABSTRACT Remediation of hydrocarbon contaminated sites having silty or clayey soils poses special technical challenges to site managers because such low permeability soils typically resist remediation with conventional technologies. Recognizing the limited information available to field practitioner
20、s charged with evaluating remediation options for low permeability soil, API initiated a multi-year program to consolidate information on the topic and conduct research on technologies that show promise for removing, or enhancing the removal, of contaminants in this media. The goal is to increase ou
21、r understanding of the need and ability to remediate such soils in-situ. This report presents a set of ten papers focusing on light non-aqueous phase liquids (LNAPLs) in low permeability soils. Collectively, the papers address four key topics: (1) processes affecting the migration and removal of LNA
22、PLs; (2) exposure potential posed by clay soil hydrocarbons via a soil, groundwater or air pathway; (3) available models for predicting LNAPL removal and (4) techniques presently available to remediate or enhance remediation. Each of the techniques discussed are capable of facilitating removal of hy
23、drocarbons from low permeability soil. However, it is important to evaluate the degree to which human exposure can be further reduced given the effort and cost associated with applying these remediation approaches. TABLE OF CONTENTS Summary of Processes, Human Exposures and Technologies Applicable t
24、o Low Permeability Soils Terry Walden, BP Oil Company, Cleveland, Ohio 1 Relevant Processes Concerning Hydrocarbon Contamination in Low Permeability Soils David B. McWhorter, Colorado State University, Fort Collins, Colorado . A-1 Assessment of Human Exposure Posed by LNAPLS in Low Permeability Soil
25、s Terry Walden, BP Oil Company, Cleveland, Ohio David B. McWhorter, Colorado State University, Fort Collins, Colorado . B-1 Soil Vapor Extraction in Low Permeability Soils Frederick C. Payne, ETG Environmental Inc., Lansing, Michigan . C-1 Bioventing in Low Permeability Soils Robert Hinchee, Battell
26、e Memorial Institute, Columbus, Ohio D-1 Hydraulic and Im ulse Fracturing for Low Permeability Soils Larry Mur B och, University of Cincinnati, Cincinnati, Ohio E-1 Pneumatic Fracturing for Low Permeability Soils John R. Schuring, New Jersey Institute of Technology, Newark, New Jersey F-1 Thermal Te
27、chnologies in Low Permeability Soils Kent S. UdeIl, University of California, Berkeley, California G-1 Surfactant-Enhanced Soil Flushin6 in Low Permeability Media Thomas M. Ravens and Philip M. Gschwend Massachusetts Institute of Technology, Cambridge, Massachusetts . H-1 Mixed Region Vapor Strippin
28、g and Chemical Oxidation for In-Situ Treatment Of NAPLS in Low Permeability Media R. L. Siegrist, O. R. West, and D, D. Gates Oak Ridge National Laboratory, Oak Ridge, Tennessee 1-1 Modeling Issues Associated with Fractured Media Marian W. Kemblowski, HydroGaia Inc., Logan, Utah . J-1 API PUELS463L
29、75 m O732270 0555460 719 m SUMMARY OF PROCESSES, HUMAN EXPOSURES AND TECHNOLOGIES APPLICABLE TO LOW PERMEABILITY SOILS Terry Walden, BP Oil Company Cleveland, OH ABSTRACT This paper summarizes a series of ten focus papers on the topic of light non-aqueous phase liquids (LNAPLs) in low permeability s
30、oils. Collectively, the papers address four key issues: (1) physical and chemical processes affecting the migration and removal of LNAPLs; (2) available models for predicting this behavior; (3) exposure potential posed by clay soil hydrocarbons via a soil, groundwater or air pathway; and (4) techniq
31、ues presently available to remediate or enhance remediation. The goal is to provide guidance and understanding on the need and ability to remediate such soils in-situ. The focus is primarily on the vadose zone of petroleum-contaminated sites. Section 1 INTRODUCTION Recognizing the limited options av
32、ailable to field practitioners charged with remediating sites with silty or clayey soils, the API initiated a three-year program beginning in 1992 to consolidate information on the topic and conduct research on technologies that show promise for removing, or enhancing the removal, of contaminants in
33、 this media. A multi-discipline group was assembled under the umbrella of the API to address the four phases of the problem referenced above. These individuals agreed to work as a team and write focus papers on their areas of API PUBL*4631 95 0732290 0555YbL b55 expertise, which included topics in t
34、he process, modeling, exposure and technology areas. The team included the following: Topic Process Issues Modeling Issues Exposure Issues Soil Vapor Extraction Bioventing Thermal Processes In-Situ Soil Mixing Hydraulic Fracturing Pneumatic Fracturing Surfactant Flushing Author David McWhorter Maria
35、n Kernblowski Terry Walden Fred Payne Robert Hinchee Kent Udell Robert Siegrist Larry Murdoch John Schuring Philip Gschwend Affiliation Colorado State Univ. Utah State Univ. BP Oil ETG, Inc. Battelle Memorial Inst. Univ. of Cal. at Berkeley Oak Ridge National Lab Univ. of Cincinnati N JIT MIT Sectio
36、n 2 PROCESS ISSUES Low permeability soil refers to silts or clays whose saturated hydraulic conductivity is generally below 10-5 cm/s. These soils can be encountered in three distinct types of geologic settings. The first is a massive clay formation where the permeability is very limited and in fact
37、 dominated by secondary fractures normally the result of a desiccation or weathering process. The second is a layered or stratified formation where silt or clay layers are interspersed within sandy or higher permeability layers. The third can be considered a subset of the second and consists of silt
38、 or clay lenses that tend to be discontinuous and of a limited lateral and vertical extent within a sandy matrix. Fluid (including contaminant) migration is distinct in each setting and the remediation strategies differ accordingly for each media. In massive clay formations containing natural fractu
39、res in non-arid regions, the fractures a short distance above the water table are generally air-filled while the adjoining solid matrix blocks between fractures are water-saturated due to capillary pressure forces. What this means is that should a hydrocarbon spill occur, the LNAPLs will fill the fr
40、actures in the soil and bypass the matrix blocks, traveling downward until they encounter the capillary fringe (the area just above the water table), at which point they will spread laterally in cross-cutting fractures. The large 2 API PUBL*4631 95 W 0732290 0555462 591 entry pressures required to p
41、ush the LNAPL into the matrix will tend to keep these separate phase hydrocarbons in the fractures. Although separate phase product (i.e. LNAPL) invasion into the water-saturated matrix will not occur to any great extent, its constituents will eventually appear in the matrix as a result of the proce
42、ss of diffusion, i.e. movement resulting from the existence of concentration gradients. This is an aqueous phase - not a separate phase - process. The soluble constituents in the LNAPL will dissolve and a concentration gradient will be established between the dissolved hydrocarbon components in the
43、fracture and the uncontaminated pore water in the matrix. The more soluble components will partition out of the LNAPL phase first, and over a period of weeks to months, part or all of the LNAPL mass in the fractures will diffuse into the matrix, with equilibrium established when the matrix storage c
44、apacity (including both dissolved and adsorbed phases) is reached. The process of diffusion has a rather significant impact on remediation strategy. Diffusion is a slow process, and a phrase that is commonly heard is that if it takes x amount of years to diffuse into the soil, it will take x amount
45、of years to get out. In fact, this is extremely optimistic. Simple diffusion calculations indicate that the time to achieve 85% mass recovery is nearly 10 times as long as the time the contaminant is in the ground before remediation begins. So if a spill were to occur 2 years before remediation (def
46、ined as an air or liquid flushing system which sweeps the fractures free of contamination), it may take 20 years to get 85% of the mass out, and 200 years to achieve 95% removal, under the conceptual assumptions that were made (see McWhorter, this volume). These long remediation periods are the resu
47、lt of disparate concentration gradients. High gradients drive the contaminants quickly out of the fractures, whereas only low gradients exist when the fractures are cleared, establishing a slow process of reverse diffusion out of the matrix. It is apparent that technologies that rely strictly on dif
48、fusion-controlled fluid movement will take a long time to achieve success (if ever) and could therefore have high life cycle costs. An important example of this concept is in the application of soil vapor extraction. The remediation literature has numerous examples where high vacuum systems (some ap
49、proaching 25 inches of mercury or 0.8 atm) have been used for clay soils, presumably to improve the zone of influence of the induced air flow around the extraction wells. Air will likely, however, flow through the fractures in a massive 3 API PUBLX463L 95 0732290 0555463 428 clay formation, or the sandy layers in a stratified formation, and use of the term radius - in implying uniform flow through the subsurface - is misleading in this regard. If the mass transfer of contaminants is diffusion-limited, the air flow rate through the fractures or high permeabili
