Verification of Methods for Assessing the Sustainability of Monitored Natural Attenuation

ER-200824

Objective

The overall objective of the proposed project is to demonstrate/validate an integrated methodology for assessing the long-term sustainability of monitored natural attenuation (MNA) that was developed through Strategic Environmental Research and Development Program (SERDP) project ER-1349 (Integrated Protocol for the Assessment of the Long-Term Sustainability of MNA of Chlorinated Solvent Plumes). The method, which captures the full range of natural attenuation (NA) processes (diminishing source mass flux, dilution and dispersion, biological and abiotic transformations, volatilization, and evapotranspiration) was developed as an enhancement to Sequential Electron Acceptor Model, 3D (SEAM3D), also a product of a SERDP-funded project (ER-1062). The three main technical objectives of the proposed effort are to (1) Validate a methodology for calculating bioavailable organic carbon (BOC) by establishing correlations with field-measured dissolved oxygen (DO) and chloroethene concentrations, concentrations of natural organic carbon compounds present in aquifer sediment, and rate and extent of reductive dechlorination; (2) Verify the upscaled source zone depletion (SZD) function using site contaminant concentration data for a range of source zone geometries; and (3) Validate short term sustainability (STS) using BOC and DO concentration data and demonstrate long term sustainability (LTS) of MNA using SEAM3D v.2.1 at four sites where time of remediation (TOR) is estimated using the SZD function.

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Technology Description

Under SERDP project ER-1349, a methodology for assessing MNA sustainability at chlorinated solvent sites was developed. The methodology uses the comprehensive numerical model SEAM3D version 2.1 to assess sustainability by integrating effects of dense nonaqueous phase liquid (DNAPL) source depletion, advection, dilution, dispersion, volatilization, abiotic reactions, and microbial transformations. At chloroethene sites, reductive dechlorination is typically the critical attenuation process in MNA-based remedial strategies. Sustainable reductive dechlorination is controlled by fluxes of electron acceptor and donor species from recharge, dispersion from upgradient groundwater, and dissolution of solid phase organic carbon within the aquifer at sites where only indigenous carbon is present. Long-term MNA sustainability is determined by computing the net plume behavior in response to the stoichiometric balance between electron donors and acceptors and transport processes using SEAM3D. This proposed approach utilizes a simple but novel method to quantify BOC and a field-scale SZD function to estimate contaminant fluxes and remediation time frame. This project is designed to validate the BOC method by demonstrating correlations with the rate and extent of reductive dechlorination for a wide range of sites (10-12 total). The SZD function and the overall MNA sustainability framework will be demonstrated and validated using data from four sites exhibiting a range of hydrologic and source characteristics. Uncertainty in sustainability predictions will be explicitly evaluated.

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Benefits

This project will demonstrate/validate a framework and methods as well as provide an interactive computational tool to assess the long-term sustainability of MNA-based remediation strategies. DoD remedial project managers (RPM) need a comprehensive methodology for assessing MNA sustainability that has been validated at sites that exhibit a range in the level of reductive dechlorination. This approach will be useful and expedient for RPMs. With the demonstration of the MNA sustainability framework to make reliable, defensible estimates of MNA sustainability at a variety of sites, the use of MNA can be improved, resulting in direct savings in capital and operations and maintenance (O&M) costs. DoD faces remediation of 1,400 to 3,000 chlorinated plume sites. The Air Force Center for Environmental Excellence's (AFCEE) natural attenuation protocol estimated that 20% of all sites would be amenable to MNA. Assuming that 20% of DoD sites are amenable to natural attenuation, implementation of MNA could potentially save DoD an estimated $11.6 to $25 billion over chemical oxidation and/or thermal treatment over the next 30 years. (Anticipated Project Completion - 2011)

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Project Documents

Points of Contact

Principal Investigator

Ms. Carmen Lebr�n

Naval Facilities Engineering Command Engineering Service Center

Phone: 805-982-2907

Fax: 805-982-4304

Program Manager

Environmental Restoration

SERDP and ESTCP

Project Documents

Document Types

  • Fact Sheet - Brief project summary with links to related documents and points of contact.
  • Final Report - Comprehensive report for every completed SERDP and ESTCP project that contains all technical results.
  • Cost & Performance Report - Overview of ESTCP demonstration activities, results, and conclusions, standardized to facilitate implementation decisions.
  • Technical Report - Additional interim reports, laboratory reports, demonstration reports, and technology survey reports.
  • Guidance - Instructional information on technical topics such as protocols and user’s guides.
  • Workshop Report - Summary of workshop discussion and findings.
  • Multimedia - On demand videos, animations, and webcasts highlighting featured initiatives or technologies.
  • Model/Software - Computer programs and applications available for download.
  • Database - Digitally organized collection of data available to search and access.