Understanding Chlorinated Hydrocarbon Behavior in Groundwater: Guidance on the Investigation, Assessment and Limitations of Monitored Natural Attenuation RR-699 October 2014 This document is intended solely as guidance and does not contain any mandatory requirements except where requirements found in statute or administrative rule are referenced. Any regulatory decisions made by the Department of Natural Resources in any matter addressed by this guidance will be made by applying the governing statutes and administrative rules to the relevant facts. The Wisconsin Department of Natural Resources provides equal opportunity in its employment, programs, services, and functions under an Affirmative Action Plan. If you have any questions, please write to Chief, Public Civil Rights, Office of Civil Rights, U.S. Department of the Interior, 1849 C. Street, NW, Washington, D.C. 20240.This publication is available in alternative format (large print, Braille, etc.) upon request. 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Box 7921, Madison, WI 53707 · dnr.wi.gov, search “brownfield” THIS PAGE INTENTIONALLY LEFT BLANK Understanding Chlorinated Hydrocarbon Behavior in Groundwater: Investigation, Assessment and Limitations of Monitored Natural Attenuation TABLE OF CONTENTS CHAPTER 1 ........................................................................................................................... 1 PURPOSE & INTRODUCTION .................................................................................................. 1 1.1 PURPOSE ........................................................................................................................................................... 1 1.2 INTRODUCTION ................................................................................................................................................. 1 1.3 APPLICABILITY.................................................................................................................................................. 3 1.4 LIMITATIONS ..................................................................................................................................................... 3 1.5 REGULATORY REVIEW OF SUBMITTALS ............................................................................................................ 4 1.6 DISCLAIMER...................................................................................................................................................... 4 1.7 OTHER RELEVANT GUIDANCE DOCUMENTS ..................................................................................................... 5 CHAPTER 2 ........................................................................................................................... 7 LAYING THE BASIS FOR MNA: ............................................................................................... 7 CHLORINATED HYDROCARBON BEHAVIOR, SITE INVESTIGATION .................................. 7 AND MONITORING NETWORK ................................................................................................ 7 2.1 OVERVIEW OF CHLORINATED HYDROCARBON BEHAVIOR IN THE SUBSURFACE .............................................. 7 2.1.1 Physical behavior of chlorinated hydrocarbons ................................................................... 7 2.1.2 Degradation processes affecting chlorinated hydrocarbons ............................................. 12 2.1.2.1 Reductive dechlorination .............................................................................................................. 12 2.1.2.2 Oxidative destruction .................................................................................................................... 12 2.1.2.3 Abiotic destruction ........................................................................................................................ 13 2.1.3 Chlorinated hydrocarbon movement in the subsurface .................................................... 13 2.2 SITE INVESTIGATION ...................................................................................................................................... 13 2.2.1 Identifying soil and groundwater contamination ............................................................... 14 2.2.1.1 Degree & extent of contamination ................................................................................................ 14 2.2.1.2 Hydrogeologic and geochemical framework ................................................................................. 15 2.2.1.3 Define potential receptors and exposure pathways. ..................................................................... 15 2.2.2 Predictions of contaminant fate & transport ...................................................................... 17 2.2.3 Site investigation report ........................................................................................................ 17 2.3 SELECTING AND EVALUATING REMEDIAL ACTIONS ....................................................................................... 18 2.4 LONG-TERM MONITORING WELL NETWORK................................................................................................... 19 2.4.1 Identify primary contaminant flow paths ........................................................................... 19 2.4.2 Monitoring plume behavior ................................................................................................. 20 2.4.2.1 Locating monitoring well transects ................................................................................................ 20 2.4.2.2 Defining the plume vertically ......................................................................................................... 21 2.4.2.3 Defining the plume horizontally..................................................................................................... 21 2.4.2.4 Sentinel wells................................................................................................................................. 22 CHAPTER 3 ..........................................................................................................................25 TOOLS TO ASSESS NATURAL ATTENUATION OF CHLORINATED HYDROCARBONS ....25 i 3.1 ENVIRONMENTAL CONDITIONS NECESSARY FOR DEGRADATION OF CHLORINATED HYDROCARBONS .......... 25 3.1.1 Microorganisms capable of degrading contaminants ........................................................ 25 3.1.2 Oxidation-reduction (redox) capacity of groundwater ...................................................... 26 3.1.3 Availability of a carbon source (electron donors) .............................................................. 26 3.1.4 Absence of competing electron acceptors ........................................................................... 27 3.2 ASSESSING PATTERNS OF NATURAL ATTENUATION IN GROUNDWATER ......................................................... 27 3.2.1 Geochemical footprints ......................................................................................................... 27 3.2.1.1 Evidence of specific natural attenuation mechanisms ................................................................... 28 3.2.1.2 Establish effectiveness of the groundwater monitoring networks. ................................................. 30 3.2.2 Patterns of contaminant degradation .................................................................................. 30 3.3 DETERMINING NATURAL ATTENUATION RATES ............................................................................................. 31 3.3.1 Establishing steady state ....................................................................................................... 33 3.3.1.1 Plots of monitoring data ................................................................................................................ 33 3.3.1.2 Non-parametric statistics .............................................................................................................. 33 3.3.1.3 Mass loss calculations .................................................................................................................. 34 3.3.2 Estimating decay rates .......................................................................................................... 36 3.3.2.1 First order decay at a point in the plume (Temporal Analysis) ...................................................... 37 3.3.2.2 First order decay along the plume centerline (Spatial Analysis) ................................................... 37 3.3.2.3 First order decay in the source area (Temporal Analysis) ............................................................ 38 3.3.2.4 Buscheck and Alcantar procedure (Spatial Analysis) ................................................................... 38 3.3.2.5 Decay rates using mass flux measurements (Spatial Analysis).................................................... 39 3.4 DATA EVALUATION ......................................................................................................................................... 39 CHAPTER 4 ..........................................................................................................................41 MONITORING MNA REMEDY .................................................................................................41