4.1 The approach presented in this guide is a practical and streamlined process for determining the appropriateness of remediation by natural attenuation and implementing remediation by natural attenuation at a given petroleum release site. This information can be used to evaluate remediation by natural attenuation along with other remedial options for each site.
4.2 In general, remediation by natural attenuation may be used in the following instances:
4.2.1 As the sole remedial action at sites where immediate threats to human health, safety and the environment do not exist or have been mitigated, and constituents of concern are unlikely to impact a receptor;
4.2.2 As a subsequent phase of remediation after another remedial action has sufficiently reduced concentrations/mass in the source area so that plume impacts on receptors are unlikely; or
4.2.3 As a part of a multi-component remediation plan.
4.3 This guide is intended to be used by environmental consultants, industry, and state and federal regulators involved in response actions at petroleum release sites. Activities described in this guide should be performed by a person appropriately trained to conduct the corrective action process.
4.4 The implementation of remediation by natural attenuation requires that the user exercise the same care and professional judgement as with any other remedial alternative by:
4.4.1 Ensuring that site characterization activities focus on collecting information required to evaluate and implement remediation by natural attenuation;
4.4.2 Evaluating information to understand natural attenuation processes present at the site;
4.4.3 Determining whether remediation by natural attenuation is the most appropriate and cost-effective remedial alternative with a reasonable probability of achieving remedial goals; and
4.4.4 Monitoring remedial progress.
4.5 Application and implementation of remediation by natural attenuation is intended to be compatible with Guide E1739 or other risk-based corrective action programs.
4.6 This guide does not address specific technical details of remediation by natural attenuation implementation such as site characterization (see Guide E1912), sampling, data interpretation, or quantifying rates. For additional discussion and guidance concerning these technical issues for remediation by natural attenuation see Appendix X1 through Appendix X7.
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