Monitored Natural Attenuation 5.0

MONITORED NATURAL ATTENUATION 5.0

5.1 OVERVIEW

It may be necessary for the owner or operator to gather additional data to determine the appropriate role for monitored natural attenuation (MNA) in the remediation plan for the site. If the owner or operator is able to establish the necessary lines of evidence, the bureau may allow MNA to be incorporated into the remediation plan. This evaluation applies to sites with dissolved phase plumes.

For releases from underground storage tanks, monitored natural attenuation means a methodology for remediation that relies upon a variety of naturally occurring chemical, physical and biological processes to achieve target concentrations. MNA is applicable at sites where it is equally protective of public health, safety and welfare, and the environment as other more active methods, and is generally accompanied by a program of sampling to document the progress and results of the above mentioned processes.

In general, it is not necessary or feasible to quantify the contribution of each of the various chemical, physical and biological processes resulting in an observed decrease in magnitude and extent of contaminants of concern. The bureau does, however, require that some lines of evidence be established supporting the assumption that biological processes are at work at the site. It is through the biological processes that contaminants are actually broken down into less toxic products. The intent of this chapter is to provide acceptable ways to establish the lines of evidence.

The bureau has approved the American Society for Testing and Materials (ASTM) Guide for Remediation by Natural Attenuation at Petroleum Release Sites (E1943-9) as its preferred method for assessing and monitoring sites for remediation by natural attenuation. If a need for supplemental guidance is identified, it will be added to this section at a later date. in this chapter. Owners, operators and their consultants should work with the bureau to develop the data and procedures to be used in assessing sites for and monitoring remediation by natural attenuation. The bureau will also be adhering to any department policy on monitored natural attenuation applicable to remediation under its various corrective action programs.

5.2 REFERENCES

Information regarding this subject is available in the following documents.

 American Society for Testing and Materials (ASTM) Guide for Remediation by Natural Attenuation at Petroleum Release Sites (E1943-98). Copies of this standard may be purchased through ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, telephone 610 832-9585, Web site www.astm.org.

5.0 Monitored Natural Attenuation 5-1 03/13/00  Ground-water Microbiology & Geochemistry, Francis H. Chapelle, John Wiley & Sons, Inc.; 1993.

 Use of Monitored Natural Attenuation at Superfund, RCRA Corrective Action, and Underground Storage Tank Sites, US Environmental Protection Agency, OSWER Draft Interim Final Directive 9200.4-17 (1997).

5.0 Monitored Natural Attenuation 5-2 03/13/00