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State Unveils Draft Policy On Natural Attenuation of Contaminated Sites

Written by: Gregory H. Smith

A singularly important new policy has been released in draft by the New Hampshire Department of Environmental Services (DES). The new policy will guide selection of natural attenuation as a groundwater remediation measure at hazardous waste and petroleum sites. The policy is a reflection of evolving regulatory reorganization of the cost-effectiveness of appropriate natural attenuation remedies. While evaluation and monitoring costs may be higher at the outset than active remediation, capital costs are generally much lower, resulting in overall savings.

The "Draft Guidelines for Selection of Natural Attenuation for Groundwater Restoration" recognizes that remediation through natural attenuation, or RNA, has been utilized historically at many sites. The new DES guidance policy for RNA will promote consistency in the way the Department evaluates RNA proposals received from parties responsible for remediating contaminated sites.

RNA includes any natural process that reduces contaminants in the environment in terms of mass, toxicity, mobility, volume and/or concentration. Some examples provided by DES include biodegradation, dispersion, dilution, sorption, volatilization and chemical and biological stabilization or destruction. The draft guidelines do not limit responsible parties to specific RNA techniques, but do identify various methods for demonstrating the adequacy of proposed remedies in ensuring that "Ambient Groundwater Quality Standards" (AGQS) are met in reasonable time and with minimal risk to the environment and public health. The guidelines do not alter specific remediation standards but will certainly expand the means of achieving them.

To consider a natural attenuation remedy, DES will require a site specific Remedial Action Plan (RAP). The RAP must (1) prevent further release of contaminants into groundwater; (2) establish a Groundwater Management Zone and administrative controls to ensure that groundwater within the zone is not consumed; and (3) restore groundwater quality to meet specific criteria.

Parties who wish to propose RNA in their RAP must demonstrate its effectiveness. DES has identified six major criteria that should be met. Foremost among these is that human health and the environment will be adequately protected pursuant to Env-Ws 410. Also, the time to achieve remediation goals must be "reasonable." While acknowledging that no definition of reasonableness can fit every site, DES has established 10 years as a default value, and will increase or decrease this time based on the information it receives regarding specific site characteristics. The burden will be on the applicant to justify a variance from the 10 year default, based on factors such as its ability to fund long-term monitoring and evaluation and the intrinsic value of the affected resources.

Responsible parties must also demonstrate that RNA will not result in increased risk to receptors, that is plants, animals and people who might be affected by the contamination. The plume, or extent of contamination, must be shown to be stable or receding. Both the regulated contaminants and the byproducts of RNA must be clearly decreasing over time. Finally, the RAP must show that biodegradation or some other destructive process is occurring at the site.

A thorough hydrogeological evaluation must be submitted to aid DES in evaluating whether RNA will be effective at the site. Evidence that RNA is occurring at the site and will be an effective remediation method can be primary, secondary, or tertiary. Primary evidence includes evaluation of contaminant and byproduct concentrations over time and distance from the source of the plume, thereby providing a basis to conclude that RNA will succeed in a reasonable time. In some cases where it is not possible to obtain useful primary evidence, secondary evidence will be required such as analytical or numerical modeling. Tertiary evidence, such as generalized scientific studies, may also be resorted to depending on the availability of primary and secondary evidence. DES has suggested several analytical models that may be useful. It proposes to require a minimum of four rounds of sampling over a sufficient period of time in support of any proposal for RNA. Specific requirements for sampling are included in the draft guidelines.

RNA will not be approved as a sole remediation method unless there are no uncontrolled sources of contamination at the site, except in cases where the applicant can show that the source(s) will be short lived and will not expand the plume. RNA may be used, of course, in conjunction with other remediation methods.

Any proposal including RNA must include a contingency plan detailing other methods of remediation that could be applied should RNA fail to meet remediation objectives, or if a change in local land or groundwater use results in a negative impact on RNA, or increased risk to receptors. A monitoring plan must be included in any RAP that proposes RNA, in order to detect changes in the plume over time. Monitoring wells must be installed to provide ongoing data regarding the progress of the remediation and to identify any new or increased risks. The draft guidelines provide detailed suggestions for the location and operation of monitoring wells.

DES has taken the position in the draft guidelines that RNA, if demonstrated to be effective within a reasonable time period, is the preferred method of remediation at petroleum contaminated sites, and in fact proposes to require that RNA be evaluated in any RAP for such a site. It recommends that, for non-petroleum contaminated sites, responsible parties or their consultants confer with the Hazardous Waste Remediation Bureau at the site investigation phase to explore the possibility of using RNA. In some circumstances RNA may even be approved without a RAP.

In summary, RNA can present in many instances a cost-effective alternative to active remediation of contaminated groundwater sites. DES’ proposed policy provides detailed guidance for evaluating RNA as an alternative and for preparing a plan that will give the Department the information it needs to make an informed decision on approval. Responsible parties and their consultants should review the draft guidelines and consider whether RNA is a viable and economically sound choice for their contaminated sites.

DES is seeking comments on its draft policy. A copy can be obtained by calling the NHDES Waste Management Division at (603)271-2900. Comments should be directed to Rich Levergood at (603)271-2183 or via e-mail at [email protected]

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