EPA/600/R-17/293 September 2017 Best Practices for Environmental Site Management: A Practical Guide for Applying Environmental Sequence Stratigraphy to Improve Conceptual Site Models Michael R. Shultz1, Richard S. Cramer1, Colin Plank1, Herb Levine2, Kenneth D. Ehman3 BACKGROUND CONTENTS This issue paper was prepared at the request of the Background 1 Environmental Protection Agency (EPA) Ground Water Forum. The Ground Water, Federal Facilities, and Engineering Forums I. Introduction - The Problem of Aquifer were established by professionals from the United States Heterogeneity 3 Environmental Protection Agency (USEPA) in the ten Regional Impact of Stratigraphic Heterogeneity on Offices. The Forums are committed to the identification Groundwater Flow and Remediation 4 and resolution of scientific, technical, and engineering Sequence Stratigraphy and Environmental issues impacting the remediation of Superfund and RCRA Sequence Stratigraphy 4 sites. The Forums are supported by and advise the Office II. Depositional Environments and of Land and Emergency Management's (OLEM) Technical Facies Models 7 Support Project, which has established Technical Support Facies models for fluvial systems 10 Centers in laboratories operated by the Office of Research Glacial geology and related depositional systems 10 and Development (ORD), Office of Radiation Programs, and the Environmental Response Team. The Centers work closely III. Application of Environmental Sequence with the Forums providing state-of-the-science technical Stratigraphy to More Accurately assistance to USEPA project managers. A compilation of issue Represent the Subsurface 12 papers on other topics may be found here: Phase 1: Synthesize the geologic and depositional setting based on regional geologic http://www.epa.gov/superfund/remedytech/tsp/issue.htm work 12 Phase 2: Formatting lithologic data and The purpose of this issue paper is to provide a practical guide identifying grain size trends 16 on the application of the geologic principles of sequence Phase 3: Identify and map HSUs 19 stratigraphy and facies models (see "Definitions" text box, page 2) to the characterization of stratigraphic heterogeneity Conclusions 22 at hazardous waste sites. References 24 Application of the principles and methods presented in this Appendix A: Case Studies A1 issue paper will improve Conceptual Site Models (CSM) and provide a basis for understanding stratigraphic flux and Appendix B: Glossary of terms B1 associated contaminant transport. This is fundamental to designing monitoring programs as well as selecting and This document was prepared under the U.S. Environmental Protection Agency implementing remedies at contaminated groundwater sites. National Decontamination Team Decontamination Analytical And Technical Service EPA recommends re-evaluating the CSM while completing the (DATS) II Contract EP-W-12-26 with Consolidated Safety Services, Inc. (CSS), 10301 Democracy Lane, Suite 300, Fairfax, Virginia 22030 site characterization and whenever new data are collected. Updating the CSM can be a critical component of a 5 year 1Burns & McDonnell 2U.S. EPA review or a remedy optimization effort. 3Chevron Energy Technology Company Application of Environmental Sequence Stratigraphy DEFINITIONS and facies models benefit groundwater remediation projects by improving the ability to: Sequence Stratigraphy: The study of sedimentary deposits in the context of their 1. Interpret lateral continuity between borehole depositional environments and changes data and correlate site data in three dimensions; in relative sea-level, sediment supply, and 2. Identify groundwater flow paths and available sediment storage areas. preferential contaminant migration pathways; 3. Map and predict contaminant mass transport Facies Model: Conceptual construct describing (high permeability) and matrix diffusion- the processes acting in a particular depositional related storage (low permeability) zones; environment to transport, deposit, and preserve sediment, usually presented as a 4. Identify data gaps and assess the need and three-dimensional block diagram illustrating cost benefit of high resolution site the organization of sedimentary bodies in the characterization; stratigraphic record. 5. Determine appropriate locations and screen intervals for monitoring and remediation wells, and; These methods are applicable to sites underlain by 6. Improve efficiency of remediating and clastic sedimentary aquifers (e.g., intermixed gravels/ monitoring of contaminated groundwater. sands/silts/clays). The scientific principles and methods presented in this document bring clarity The first two sections (I and II) present the technical to the challenges posed by lithologic heterogeneity basis of Environmental Sequence Stratigraphy. thereby facilitating successful site management Section III presents a three phase process for practical strategies. Lithologic heterogeneities can be application of Environmental Sequence Stratigraphy, characterized by the use of high resolution site ending with stratigraphic “rules of thumb” developed characterization (HRSC) techniques (http://www. through experience in a wide variety of environments cluin.org/characterization/technologies/hrsc/). The of deposition from outcrop and subsurface data sets application of sequence stratigraphy can be applied worldwide. Appendix A presents six case studies to new site investigations as well as existing site data of various applications of Environmental Sequence to update the Conceptual Site Model (CSM). These Stratigraphy and Appendix B is a glossary of terms methods allow the practitioner to place environmental used in the document. subsurface data in a geologic and hydrogeologic context, and predict the geology where subsurface data are absent. 2 GW Issue Best Practice for Improving Conceptual Site Models A Practical Guide for Applying Advanced Stratigraphic Concepts to Contaminated Groundwater Sites I. INTRODUCTION – The Problem of Aquifer Heterogeneity Permeability heterogeneity is inherent in the and provided a degree of hydraulic containment of subsurface and interacts with regional groundwater same. However, stratigraphic heterogeneity and gradient to control groundwater flow and contaminant associated issues including matrix diffusion, transport. In clastic sedimentary aquifer systems (i.e., (e.g., Sale and Newell, 2011) make groundwater gravel, sand, silt, and clay deposits), this permeability site cleanups particularly challenging. For sites heterogeneity is primarily due to lithologic and where sedimentary aquifers are impacted, detailed grain-size heterogeneity in three dimensions, termed understanding of stratigraphic heterogeneity at all “stratigraphic heterogeneity”, with post-depositional scales is required to inform future site management changes (bioturbation, compaction, cementation, decisions. alteration, etc.) as contributing factors. Stratigraphic heterogeneity is imparted by the physical processes As with the groundwater remediation industry, acting to transport, deposit, and bury sediments and problems related to subsurface fluid flow arising from is present at all scales from pore (microscale) through stratigraphic heterogeneity have long challenged the regional (macroscale) (Figure 1). petroleum industry, impacting exploration success and field production. Tools such as sequence stratigraphy While the impacts of stratigraphic heterogeneity on and facies models were developed to address these groundwater flow and contaminant transport have problems and to make predictions in between long been recognized (e.g., Koltermann and Gorelick, individual wells regarding reservoir continuity and 1996; Puls and Barcelona, 1996; EPA, 2004, Weissman, heterogeneity. This paper provides instruction on et al., 1999), the treatment of aquifers as isotropic and application of these tools to contaminated aquifers. homogeneous porous media remains commonplace The concepts presented herein are equally applicable in groundwater remedy design and implementation. to the unsaturated zone, including prediction of At many legacy sites, pump and treat remedies were contaminant and vapor migration pathways. applied, which served to recover contaminant mass Figure 1. Scales of stratigraphic heterogeneity in clastic aquifers. Facies models and sequence stratigraphy are applicable across all scales. (Modified from Krause et al., 1987). AAPG©1987 Reprinted by AAPG whose permission is required for further use. Best Practice for Improving Conceptual Site Models GW Issue 3 A Practical Guide for Applying Advanced Stratigraphic Concepts to Contaminated Groundwater Sites Impact of Stratigraphic Heterogeneity on practice in the petroleum industry for delineating Groundwater Flow and Remediation reservoir geometry and continuity. These methods are equally applicable to groundwater systems and As emphasized in this paper, groundwater flow related groundwater contaminated sites. directions can vary greatly from regional groundwater gradient due to anisotropy resulting from lithologic The deposition of sediment in a particular location heterogeneity. In many cases, sand and clay elements is controlled not only by the depositional processes are not deposited as a “layer cake” with one unit operating, but also by the interplay of multiple factors. stacked upon the other, but rather deposited in a These factors include sea-level change (magnitude and “shingled” or “laterally offset” fashion. This common rate), amount of sediment being delivered, climate, phenomenon spans a