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LNAPL Meeting Agenda

LNAPL Reg Reform Discussion
February 16, 2012
1:00  – 3:00 am
MassDEP, One Winter Street, Boston, 2nd Floor


 1:00        Welcome and Introductions
1:10        Background on LNAPL MCP issues and regulatory/policy discussions to date
1:30        The definition, meaning and purpose of an Upper Concentration Limit (UCL)
2:00        Discussion of Regulatory provisions which better address LNAPL UCL concerns?


Under the provisions of 310 CMR 40.0996, “the presence of non-aqueous phase liquids (NAPL) having a thickness equal to or greater than ½ inch in any environmental medium is considered to be a level which exceeds Upper Concentration Limits (UCLs)” and hence which prohibits the attainment of a Permanent Solution.  In addition, 310 CMR 40.0006 states this thickness is “as a continuous separate phase as measured in a groundwater monitoring well or otherwise observed in the environment.”

As articulated in earlier MassDEP guidance, (Characterizing Risks Posed by Petroleum Contaminated Sites: Implementation of the MADEP VPH/EPH Approach; 2002):

The occurrence, detection and migration of non-aqueous phase liquids in the subsurface are a complex phenomenon.  Many investigators have attempted to develop theoretical and/or empirical methods to correlate the apparent thickness of NAPL, as measured in a monitoring well, to the actual thickness of that NAPL in the surrounding formation……..Unfortunately, none of the methods or approaches presented to date appears to be sufficiently reliable or reproducible at field sites, especially when significant fluctuations occur in the elevation of the groundwater table

Since 2002, improved LNAPL assessment techniques based on the fundamental principles of multi-phase fluid flow in porous media (FFPM, used for decades in the oil industry) have been developed and applied over the last several years to environmental applications.  A number of states and regulatory authorities, including MassDEP, have formed workgroups and are developing guidelines based on FFPM concepts to more accurately describe the nature, extent and behavior of LNAPL in the subsurface formation.  These efforts have considered similar works from Texas, Alaska, British Columbia, API, ITRC, U.S.EPA, and ASTM, among others.

Integrating these improved LNAPL assessment techniques into the overall MCP regulatory framework has proven to be a challenging task involving disparate and often conflicting opinions and approaches from among MassDEP’s LNAPL Workgroup.  However, consensus has emerged around the following:

  • The current MCP criterion of ½ inch of LNAPL is not an ideal metric for assessing compliance with a UCL and, in some cases, may be a barrier for sites’ otherwise meeting the requirements for a Permanent Solution.
  • The application of the fundamental principles of multi-phase fluid flow in porous media (FFPM) has been overwhelmingly accepted by the scientific and regulatory communities throughout north America, and it is clearly consistent with the Response Action Performance Standard 310 CMR 40.0191(2)(b) “use of accurate and up-to-date methods, standards and practices, equipment and technologies which are appropriate, available and generally accepted by the professional and trade communities conducting response actions…”

Questions?:  Ken Marra, kendall.marra@state.ma.us, (617) 292-5966


One Response

  1. Suggestion that MADEP eliminate the UCL for NAPL in any environmental medium at 310 CMR 40.0996(6). (Matt Hackman/LSP)

    The MCP Method 3 Upper Concentration Limit (UCL) listed at 310 CMR 40.0996(6):

    “(6) The presence of non-aqueous phase liquids (NAPL) having a thickness equal to or greater than 1/2 inch in any
    environmental medium shall be considered a level which exceeds Upper Concentration Limits.”

    has been problematic since its implementation, because the criterion, “(NAPL) having a thickness equal to or greater than 1/2 inch in any
    environmental medium” is not one that has a consensus on how this should be measured.

    “NAPL” is defined at 310 CMR 40.0006:

    “Nonaqueous Phase Liquid and NAPL each means oil and/or hazardous material that is present in
    the environment as a continuous separate phase as measured in a groundwater monitoring well
    or otherwise observed in the environment.”

    This UCL condition is often confused with the 72-hour notification condition listed at 310 CMR 40.0313(1):

    “(1) a release to the environment indicated by the presence of a subsurface Non-Aqueous Phase
    Liquid (NAPL) having a measured thickness equal to or greater than 1/2 inch;”

    which is inferred to mean measured in a monitoring well, although this is not explicitly stated. (This becomes more problematic when you

    consider that the thickness of “Light, Non-Aqueous Phase Liquid” (LNAPL) such as petroleum products, may vary inversely with the diameter of

    the monitoring well. For example, LNAPL may be observed at a thickness of several inches in a 3/4-inch diameted driven well, but, when

    overdrilled to a 4-inch monitoring well, the thickness may be <0.01 ft (approximately 1/8 inch). But I digress.)

    There was much discussion regarding how this UCL condition might be modified, but I give full credit to Ms Marilyn Wade for pointing out that,

    since this UCL condition is unnecessary and serves no purpose, the correct course of action is to eliminate it.

    The first question to ask is: "Why was this UCL condition included in the MCP?"

    MADEP staff appeared to have difficulty articulating the scientific and policy rationale for this UCL in 1993 when the MCP was first written.

    However, as I understand it, the rationale included the following points:

    1. As a public policy, MADEP feels that certain types, masses and concentrations of contaminants should not be left in the environment,

    even if it can be demonstrated that, under current and forseeable future conditions a condition of no significant risk exists, because not all future

    conditions are forseeable.

    2. Because NAPL is defined as "a continuous separate phase", at some aggregate amount, NAPL should be recoverable, and if it can

    be recovered, it ought to be, because that is preferable to leaving contamination in the environment, even if it poses no significant risk.

    (I point out that the most common form of LNAPL, in fact the most common "oil" released to the environment are petroleum products, specifically

    gasoline and diesel fuels and No. 2 though No. 6 heating oils. "Petroleum", literally "rock oil" is a naturally occurring material which is found in the

    subsurface of the earth, and then refined, i.e. separated and processed like other natural materials such as plant materials and minerals, into

    pvarious products of commerce. But I digress.)

    3. Because NAPL is a liquid phase, like groundwater, as opposed to a solid phase like soil, or solid hazardous wastes such as certain

    metallic componds, e.g. lead oxide, it has the intrinsic property of mobility. ("Liquid" is typically defined as a state of matter with the property to

    "flow.") This mobility means that this contaminant can move and thus its future location may not be the same as its current location. In particular,

    MADEP is concerned about the possibility of NAPL moving toward or into contact with sensitive receptors.

    4. As noted, petroleum products are the most common form of NAPL released to the environment, due to their ubiquity in our society and

    their importance to our way of life and society. Their use as motor fuels and heating fuels derives in part from their potential to volatilize into a

    vapor phase, since the combustion processes which release the energy of petroleum fuels to do useful work occurs in the vapor phase. (Liquids

    and solids typically do not burn, per se. They are heated until the compounds volatilize at which point, in the presence of an oxidizer such as the

    oxygen in ambient air, and a source of heat sufficient to ignite, an exothermic chemical reaction we call "fire" typically occurs. But I digress.) This

    property of volatilization means that NAPL is often a potential source of gas or vapor phase contamination, which is also mobile, and, in

    particular, represents a potential threat to indoor air. Thus the presence of NAPL in the environment near current or potential future buildings is a

    potential threat to human health that should be eliminated if possible. In particular, NAPL componds less dense than water, which tend to float on groundwater and volatilize directly to soil vapor, have the maximum possible diffusive driving force, and thus present a "worst case" source to soil vapor and potentially indoor air.

    These are all good points, and while the discussion above is necessarily oversimplified, I think there is generally consensus in society at large, as

    well as the regulated community, that the presence of uncontrolled/uncontained NAPL in the part of the environment where it can impact sensitive

    receptors such as humans, through dermal contact, inhalation or ingestion, or the "environment" (basically the upper portion of the earth's crust

    used by humans and most other life forms) should be minimized.

    So the next question is: "If we accept the rationale for the UCL as it was formulated in 1993, is 310 CMR 40.0996(6) achieving the stated

    objective?" The answer to this question appears to be no, for the following reasons:

    1. As mentioned above, there is no scientific, standard, agreed-upon means or method to measure the criterion "(NAPL) having a

    thickness equal to or greater than 1/2 inch in any environmental medium". Since this cannot be consistently determined, the requirement cannot

    be consistently applied or complied with.

    2. Because the criterion cannot be measured, a number of surrogate measurements have been used instead, the most common of which

    is the measurement of the thickness of NAPL (either light, non-aqueous phase liquid or LNAPL, or dense, non-aqueous phase liquid or DNAPL,

    where "light" means less dense than water and "dense" means more dense than water) in a monitoring well, which is something that a standard

    and widely available tool ("interface probe") exists to measure, and can measure reproducibly. (As noted above, the use of the term "monitoring

    well" is problematic since the thickness of NAPL may vary depending on the diameter of the monitoring well, among other properties.)

    3. Even if a 1/2 inch of LNAPL, for example, is observed in a monitoring well, this alone doesn't fully communicate whether or not this is a

    potential threat to human health or the environment. For example, if a two-inch monitoring well is observed to have three inches of LNAPL, and

    this LNAPL is removed, and no LNAPL is subsequently observed in that monitor well after one year, this is likely no significant risk. On the other

    hand, if the LNAPL returns and is again measured at three inches after one hour, this is likely a potential significant risk. Thus it is not just the

    presence of NAPL in a certain thickness, or its observed movement, (in this case into the monitoring well) but the rate of that movement, in this

    case within an hour or not even within a year.

    4. One person noted that the UCL was based on the mass of NAPL present. However, the mass alone is not a sufficient determinant of

    risk. 1,000 gallons of No. 2 fuel oil adsorbed in fine sand/clay soils well below the MCP Method 1 concentration for TPH and VPH and EPH

    ranges may indeed have "NAPL" at the microscale in the microscopic pores of the soil matrix, but is clearly immobile and a condition of no

    significant risk. However, 10 gallons of No. 2 fuel oil released immediately adjacent to the fieldstone basement wall of a single family residence,

    say from the coppor tubing running from their underground storage tank to the furnace, could be a significant risk and possibly a substantial or

    imminent hazard. Thus mass or volume alone is not a sufficient criterion.

    5. I note that literally millions of gallons of NAPL are currently present in the shallow (less than 15 feet below grade) soil in Massachusetts,

    as part of the network of fuel and heating oil underground storage tank systems, and these generally function very well at containing NAPL. Thus

    the concern is not volume underground, but whether or not that NAPL is controlled, for example by being contained in an underground storage

    tank system.

    Thus we start to see that the real concern with regard to the potential threat of uncontained NAPL in the environment is an aggregation of the

    properties of mass/volume, concentration and mobility. To be mobile, there needs to be a sufficient concentration of NAPL, exceeding the

    saturation concentration of the soil it is in. To be mobile for any significant distance, that concentration of NAPL needs to be present over a fairly

    large area, for example, at least a cubic yard, and more typically several or tens of cubic yards.

    Rather than try to continue to "tweak" this UCL, and risk falling afoul of the "lipsick on a pig" scenario, the next question we can ask is: "Are there

    other mechanisms, features, requirements, etc. of the MCP that already address the human health and environmental risk and public safety and

    welfare that this UCL was formulated to address?

    I believe the answer is yes.

    First we consider the general requirements listed at 310 CMR 40.0190. The RP is required to achieve a permanent solution and a condition of

    No Significant Risk if feasible, and to reduce concentrations of oil and hazardous material to background if feasible. They must consider both

    current and reasonably forseeable future uses of the release site and the surrounding environment.

    We then go to the following section 310 CMR 40.0191: ResponseAction Performance Standard, specifically 310 CMR 40.0191(3):

    "(3) The application of RAPS shall be protective of health, safety, public welfare and the
    environment and shall include, without limitation, in the context ofmeeting the requirements of
    this Contingency Plan, consideration of the following:
    (a) technologies which reuse, recycle, destroy, detoxify or treat oil and/or hazardous
    materials, where feasible, to minimize the need for long-term management of contamination
    at or from a disposal site;
    (b) containment measures as feasible Permanent Solutions only where reuse, recycling,
    destruction, detoxification and treatment are not feasible;
    (c) remedial actions to reduce the overall mass and volume of oil and/or hazardous material
    at a disposal site to the extent feasible, regardless of whether it is feasible to achieve one or
    more Temporary Solutions and/or Permanent Solutions or whether it is feasible to achieve
    background for the entire disposal site and not include the dilution of contaminated media
    with uncontaminated media; and
    (d) response actions to restore groundwater, where feasible, to the applicable standards of
    quality within a reasonable period of time to protect the existing and potential uses of such

    But what about the concern that not all future uses are forseeable? Fo this we go to MADEP's policy #WSC-04-160 "Conducting Feasibility

    Evaluations under the MCP." Here we find:

    " Remediation of Degradable (Nonpersistent) Contaminants

    It is DEP’s position that achieving or approaching background can be deemed
    infeasible for degradable/nonpersistent contaminants regardless of media
    classification, except for small quantities of petroleum-contaminated soil considered
    accessible for remediation as described in Section 9.3.1. The benefits of additional
    remedial actions to achieve or approach background for degradable/nonpersistent
    contaminants would be considered insufficient to justify the costs of those actions.
    For example, for benzene, this policy supports a finding that it is infeasible to
    achieve or approach background since this compound would be expected to readily
    degrade in most environmental settings."

    (Note that petroleum compounds, except No. 6 oil, are categorically defined as "degradable/nonpersistent".)

    Referring to section 9.3.1:

    "9.3.1 Conditions of Categorical Feasibility

    For a limited number of pollutants, it is DEP’s position that remedial actions to achieve or
    approach background are almost always feasible, i.e., the cost of conducting a remedial
    action would be modest and exceeded by the benefit or risk reduction.
    It is DEP’s position that it is categorically feasible to remove small quantities of petroleum contaminated
    soil. Specifically, for the purposes of achieving Presumptive Certainty pursuant
    to this policy, it is DEP’s position that it is feasible to achieve background at a site where a
    condition of NSR has been reached, the remaining contamination is limited to 20 cubic yards
    or less of soil contaminated solely by petroleum products, and where such soil:
    􀂃 is located less than three feet below the ground surface;
    􀂃 is not covered by pavement or a permanent structure;
    􀂃 is not located within a sensitive environment (e.g., wetlands); and
    􀂃 is not located in an area where removal activities will substantially interrupt public
    service or threaten public safety (See Section"

    Thus, if complying with the MCP requirements, it is difficult to see what additional benefit the UCL for NAPL at 310 CMR 40.0996(6) confers, at

    least for the most common form of NAPL, i.e. LNAPL petroleum fuels. Given that there is literally no scientifically defensible or consensus standard of measuring the criterion of "(NAPL) having a thickness equal to or greater than 1/2 inch in any environmental medium", this UCL appears to be serving no purpose.

    But what about other forms of NAPL, specifically No. 6 oil, and other DNAPL such as halogenated solvents? Is this UCL condition still serving

    some purpose regarding these oils or hazardous materials? No. 6 oil is generally denser than water and thus is also a DNAPL material. DNAPL has the property of sinking through the water table and potentially reaching bedrock fractures which might allow travel over longer distances than through the soil matrix. However, the fact that the bedrock surface is typically topographically non-uniform, unlike the surface of groundwater, means that measurement of the 1/2-inch thickness in an environmental medium is even more problematic. Due to depth and generally non-uniform distribution in the subsurface to to the topographic factors discussed above, it is generally significantly more difficult to recover DNAPL than to recover LNAPL, although this can be accomplished in some cases.

    But most importantly, DNAPL is moving away from many of the most sensitive receptors such as occupied buildings and surface water.

    The primary concern regarding DNAPL is the movement toward bedrock fractures, because most groundwater supply wells, particularly public water system water supply wells, are located in bedrock, primarily to avoid drawing water that might be contaminated from surficial activity.

    In addition, DNAPL such as halogenated solvents tend to have significant solubility in water, and also tend to have the characteristic of volatility, both from the DNAPL phase and the dissolved phase. True, because these compounds sink through groundwater, the DNAPL phase is rarely the direct source to soil vapor or indoor air, but the inter-media transfer from DNAPL to dissolved phase in groundwater can be mobile both horizontally, primarily by groundwater advection, and vertically, primarily by diffusion.

    So, I don't have a good answer to whether or not it is useful to have a UCL specifically for DNAPL such as No. 6 oil and halogenated solvents.

    In summary, I think is has been demonstrated that the UCL for NAPL at 310 CMR 40-0996(6) has no additional value beyond the existing requirements of the MCP when considering LNAPL, particularly petroleum fuels (gasoline, diesel and No. 2 through No. 5 heating oil).

    If there is still a concern that the MADEP can articulate regarding the need for a UCL for DNAPL compounds such as No. 6 oil and halogenated solvents, then such an alternative UCL criterion should be formulated.

    Thus 310 CMR 40.0996(6) should be deleted from the MCP.

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