Environmental Remediation Program
Address
Division of Environmental Quality
P.O. Box 176
Jefferson City, MO 65102-0176
United States
Email
Introduction
Missouri regulations 10 CSR 26-2.075 and 10 CSR 26-5.020 require tank owners/operators who experience a release of petroleum to remove as much free product as practicable. The Department of Natural Resources determines whether this requirement has been met and what documentation is required to demonstrate compliance. This technical bulletin is intended to aid practitioners in complying with this requirement.
“Free product” is defined in 40 CFR 280.12 as “a regulated substance that is present as a non-aqueous phase liquid.” As knowledge in the field has advanced, practitioners have come to understand non-aqueous phase liquid may exist in the environment in either a mobile or immobile state. In this technical bulletin, “light non-aqueous phase liquid” (LNAPL) is used to mean both mobile and immobile non-aqueous phase petroleum, while “free product” refers only to the mobile portion of LNAPL.
LNAPL Conceptual Site Model (LCSM)
Development of an LCSM will aid the consultant in establishing LNAPL remediation objectives and selecting a remedial technology.
Per the Interstate Technology & Regulatory Council’s (ITRC) “Evaluating LNAPL Remedial Technologies for Achieving Project Goals,” the LCSM is similar to a conceptual site model, which identifies the source(s), pathway(s) and receptor(s), but the emphasis in the LCSM is on the contaminant source (i.e., the LNAPL). Hence, additional information to consider when LNAPL is present includes the following:
- Is there an ongoing LNAPL release?
- What is the LNAPL spatial distribution?
- Are there risk and exposure issues attributed to the presence of the LNAPL?
- Are there potential explosivity issues associated with the LNAPL?
- What is the free product recoverability?
A well-developed LCSM will usually include some or all of the following scientific and technological information (please see the documents referenced at the end of this technical bulletin): Site setting (historical and current)—including land use, groundwater use, presence and proximity of receptors, etc.:
- Geological and hydrogeological information/setting – including cross-section diagrams, analysis of boring/well logs and a review of historical fluctuations in groundwater elevations and/or gradient.
- LNAPL physical properties (density, viscosity, interfacial tensions, vapor pressure) and chemical properties (constituent solubilities and mole fractions).
- Spatial distribution of the LNAPL, including if available, LNAPL distribution over time (vertical and horizontal delineation).
- LNAPL mobility and stability information.
- Associated dissolved-phase and vapor-phase plume information.
The LCSM will assist in planning field activities and data collection. For example, the location and number of monitoring wells needed for dissolved-phase delineation may not suffice for LNAPL body spatial delineation, product testing or transmissivity testing.
ITRC’s document titled “Evaluating LNAPL Remedial Technologies for Achieving Project Goals” (December 2009) and ASTM E2531-06 (Reapproved 2014) “Standard Guide for Development of Conceptual Site Models and Remediation Strategies for Light Non Aqueous-Phase Liquids Released to the Subsurface” are recommended resources for developing LCSMs, evaluating applicable remedial options, and determining performance metrics for remediation of a petroleum tank release. Each evaluation will be site-specific and product-specific.
Evaluation of ‘As Much As Practicable’
Demonstrating that as much free product has been recovered as practicable can be done quantitatively and/or qualitatively.
A quantitative analysis is more typical for a relatively recent release and typically includes documentation to show:
That an active free product recovery method has been or is being employed.
- That the active free product recovery method is/was appropriate for the site-specific conditions.
- That the method’s ability to recover free product has reached asymptotic and/or technological limits (e.g., decline curve analysis or similar method).
- That the remaining free product is not migrating and is not feeding a vapor-phase or dissolved-phase plume and/or causing it to migrate into previously uncontaminated areas.
A qualitative analysis is more typical for older releases where various recovery methods have been attempted, such as excavation of soil or other source removal techniques, and sufficient historical data have been collected. The department will entertain qualitative arguments, which can include (but are not limited to) discussion of the following items. Each site is different and the department will evaluate each site based on its specific merits. Examples of information that may be used in a qualitative analysis include:
- Groundwater elevations vs. free product occurrence.
- Seasonal variations in free product presence and volume.
- The frequency with which free product has been observed in wells and at what thicknesses.
- Free product mobility and dissolved-phase contaminant migration, or lack thereof.
- An evaluation of each recovery method attempted, why that recovery method was used, its results, and a discussion of whether that method was appropriate for the site.
- If a remedial method was used and was not effective, an evaluation of why that method was not effective.
- The spatial extent of free product.
- Whether the product is physically accessible for recovery (e.g., might not be accessible if under a roadway).
- The portion of the LNAPL mass that is comprised of free product
- A discussion of LNAPL remedial objectives
- A discussion of Natural Source Zone Depletion.
Summary
The type and amount of information needed to determine and document that free product has been recovered as much as practicable will vary from site to site and will be based on the type and spatial extent of the LNAPL body and the site conditions. While a detailed LCSM will greatly aid in the analysis, there is no one technique or approach suitable for every site and petroleum release. Documenting compliance with this requirement is the responsibility of the tank owner/operator and his consultant; the final determination whether this requirement has been met will be made by the department.