Department of Health Seal

TGM for the Implementation of the Hawai'i State Contingency Plan
Section 13.5
STEPS TO ENVIRONMENTAL HAZARD EVALUATION

13.5 STEPS TO ENVIRONMENTAL HAZARD EVALUATION

It is important to begin to identify potential environmental hazards at a site as soon as initial soil, groundwater and other data are received. As discussed above, this is used to guide completion of the site investigation as well as to identify hazards that may require additional attention. Questions that should be asked and addressed as part of the Environmental Hazard Evaluation include:

  1. Of the initial list of COPCs, which contaminants could pose potential environmental hazards under uncontrolled site conditions?
  2. What are the specific environmental hazards posed by the targeted COPCs?
  3. Are additional site data needed to better define the extent and magnitude of contamination or the specific environmental hazards identified?
  4. Is an advanced evaluation of a specific environmental hazard warranted?
  5. What is the distribution of potential environmental hazards across the site?
  6. Is a response action required to address identified hazards?

These questions are discussed in more detail in the following sections. As discussed in Section 3, the initial Conceptual Site Model should be continually refined as additional data are collected and a greater understanding of site conditions is gained.

13.5.1 IDENTIFY KEY COPCS

Preliminary COPCs are selected based on the known or assumed past use of hazardous chemicals at the site. This is an important part of the Phase I assessment of the site and the subsequent preparation of a sampling and analysis plan. For example, if gasoline was stored at the site then the target COPCs should be TPH-gasoline, benzene, toluene, ethylbenzene, and xylenes (BTEX), lead and fuel oxygenates. If the site was used to mix pesticides then the specific types of pesticides should be identified. Related contaminants such as arsenic, lead, mercury and dioxins should also be considered COPCs. Additional guidance for pesticide and petroleum contamination is provided in Section 9. Refer also to the HDOH Screening for Environmental Hazards at Sites with Contaminated Soil and Groundwater guidance document (HDOH, 2016).

The list of COPCs can be quickly narrowed down once initial data are obtained by a comparison of data to the Tier 1 EALs. If the representative concentration of a contaminant does not exceed the respective Tier 1 EAL, then it can be reasonably assumed the contaminant does not pose a significant environmental hazard. If the Tier 1 EAL is exceeded, then additional evaluation of that contaminant is warranted. Contaminants that exceed the Tier 1 EALs should continue to be considered COPCs and carried through the environmental hazard evaluation process.

13.5.2 DETERMINE REPRESENTATIVE CONTAMINANT CONCENTRATIONS

As discussed in Sections 3 and Section 4, sites should be subdivided into individual decision units (DU) and the representative concentration of target COPCs within each DU determined. For groundwater and soil gas samples, direct reference to reported concentrations of COPCs in single monitoring wells or soil gas collection points is appropriate.

For soil, the use of Multi-increment sample data to determine representative contaminant concentrations is preferred over discrete sample or judgmental sample data (see Section 4). Multi-increment samples provide better coverage of DUs and better estimates of representative contaminant concentrations in comparison to discrete sample data, especially in cases where only a limited number of discrete sample points (e.g., <30) are located within a target DU. Multi-increment is a registered trademard of Envirostat, Inc.

Discrete soil sample data can also inject an unnecessary distraction into the site investigation process due to a tendency to focus on "maximum" contaminant concentrations reported at a single sample point location. Identification of the maximum concentration of a contaminant at any given point within a DU is not an objective of the site investigation or environmental hazard evaluation process. As discussed in Section 4, the concentration of a contaminant at any given sample point location in itself has little importance. This is because direct exposure or other potential environmental hazards must be evaluated for the DU as a whole, rather than at any given point within the DU. In typical environmental contaminant evaluations, the question is:

"What is the representative contaminant concentration across the DU as a whole?" not "What is the maximum contaminant concentration across the DU as a whole?"

13.5.3 IDENTIFY POTENTIAL ENVIRONMENTAL HAZARDS

If the representative concentration of a contaminant is verified to exceed Tier 1 EALs then the specific environmental hazard(s) posed by the contaminant should be identified. A detailed, site-specific evaluation of each possible environmental hazard on a site-specific basis would be an arduous and time-consuming task. Fortunately, this level of effort will rarely be necessary. A simple comparison of site data to the detailed action levels used to develop the Tier 1 EALs offers a relatively rapid and cost effective alternative. As discussed in subsection 13.3.3, use of the EAL Surfer to identify specific environmental hazards makes this process relatively simple and is highly recommended.

13.5.4 ADVANCED EVALUATION OF ENVIRONMENTAL HAZARDS

Potential environmental hazards flagged by comparison of site data to Tier 1 EALs (or approved alternative action levels) may or may not exist at the site. The Tier 1 EALs assume uncontrolled site conditions, with the potential for contaminated soil to be exposed at the surface at some point in the future under a residential land use scenario. The models used to develop the soil action levels assume a fresh release and maximum contaminant mobility. Screening soil data at this level allows unrestricted use of the property. Actual site conditions could differ and contaminants could pose a much lower threat to human health and the environment than a simple screening level evaluation might imply. If warranted by potential cleanup costs or other factors (including requirement by the HEER Office), a more advanced and site-specific evaluation of targeted hazards can be carried out.

Advanced approaches for evaluation of environmental hazards discussed earlier are presented in the HDOH guidance document Screening for Environmental Hazards at Sites with Contaminated Soil and Groundwater ["EHE guidance" (HDOH, 2016)]. A summary of commonly used approaches is provided in Tables 13-3 and 13-4.

The need to carry out more advanced evaluations of tentatively identified environmental hazards must be assessed on a case-by-case basis. Exceeding action levels for specific hazards does not necessarily indicate the contamination poses a significant threat to human health and the environment, only that additional evaluation is warranted (see Section 13.3). In many cases the most cost-effective action to address a tentatively identified environmental hazard is to simply remove all contamination that exceeds Tier 1 EALs (e.g., excavation and disposal of a small area of lead-contaminated soil). In cases where cleanup costs could be substantial or full cleanup is otherwise not technically feasible, a more detailed evaluation of tentatively identified environmental hazards may be warranted. For petroleum-related contamination in particular, soil gas data often indicate a much lower vapor intrusion hazard than predicted by simple comparison of soil or groundwater data to HEER Office action levels. The additional data could negate the need for remedial actions at some sites to address this hazard. In other cases, soil gas data can help identify the presence of contamination that was not detected in earlier soil and groundwater sample collection.

Preparing a traditional human health risk assessment or ecological risk assessment as described in the following sections does not fulfill the need to prepare an initial Environmental Hazard Evaluation. As discussed in Section 13.7, a traditional risk assessment focuses on toxicological risks associated with direct exposure to contaminated soil, groundwater, or air. While this is important, direct exposure is only one of several potential environmental hazards that must be addressed in a more comprehensive Environmental Hazard Evaluation. Action levels specifically developed to screen for potential direct exposure concerns are incorporated in the Tier 1 EALs. Exceeding Tier 1 EALs does not necessarily indicate that the contamination does in fact pose direct-exposure hazards, only that potential risks to human health need to be considered in subsequent actions at the site. This could include preparing a more detailed human health risk assessment (see Section 13.7).

Table 13-3 Commonly Used Approaches for Evaluating Environmental Hazards in Groundwater

Environmental Hazard

Example Site-Specific Evaluation Approaches

Contamination of drinking water resources

·    Identification and monitoring of nearby, groundwater supply wells and guard wells

·    Long-term monitoring of groundwater to evaluate plume migration potential

·    Use of groundwater plume fate & transport models in combination with long-term monitoring to evaluate plume migration potential

Vapor Intrusion

·    Collection of soil gas data (strongly recommended) and subsequent evaluation of risk to human health (site-specific vapor intrusion model)

Impact to Aquatic Habitats

·    Use of groundwater data to evaluate plume expansion and migration over time

·    Use of fate and transport models to predict long-term migration potential of groundwater contaminant plumes

·    Preparation of a site-specific, ecological risk assessment, which can include aquatic bioassay testing, an evaluation of species diversity and/or sediment studies

Gross contamination

·    Check groundwater for free product

·    Check discharge areas for sheen and other gross contamination concerns




Table 13-4 Commonly Used Approaches for Evaluating Environmental Hazards in Soil

Environmental Hazard

Example Site-Specific Evaluation Approaches

Direct Exposure

·    Use of Multi-increment sample data to evaluate direct exposure concerns in targeted decision units

·    Use of HDOH Tier 2 Direct Exposure Spreadsheet to calculate alternative action levels (available from HEER Office web page)

·    Use of laboratory arsenic bioaccessibility tests to better evaluate arsenic toxicity

·    Preparation of a site-specific human health risk assessment that considers engineered and institutional controls to eliminate or minimize exposure pathways, alternative exposure assumptions, alternative target risks, etc.

Vapor Intrusion

·    Collection of soil gas data (strongly recommended) and subsequent evaluation of risk to human health risk (site-specific vapor intrusion model)

Leaching

·    Collection of groundwater data

·    Use of HDOH laboratory batch test guidance to evaluate contaminant mobility and estimate concentrations in source area leachate

Impacts to terrestrial habitats

·    Field inspection to determine the presence or absence of potentially significant terrestrial ecological habits

·    Preparation of a detailed ecological risk assessment.

Gross contamination

·    Field inspection of petroleum-contaminated soil to evaluate potential gross contamination concerns (especially in existing or planned residential areas)

Additional guidance is provided in the HDOH EHE guidance document (HDOH, 2016).

13.5.5 COMPLETE THE SITE INVESTIGATION

The identification of potential environmental hazard(s) and completion of the site investigation is an iterative process. Basic site investigation activities can be considered complete when the vertical and lateral extent of contamination above Tier 1 EALs (or acceptable alternatives) is determined. In some cases (e.g., investigation of commercial/industrial areas with land use restrictions), the delineation of contamination to higher action levels will be acceptable. The need for additional site data to complete the investigation should be continually reviewed as initial data is screened for potential environmental hazards.

For example, if direct exposure to contaminated soil is flagged in the EAL Surfer as a potential hazard, then site data should be reviewed to ensure that the limits of contamination are adequately identified. Estimating representative contaminant concentrations across exposure areas (e.g., residential yards, commercial lots) rather than more specific areas is generally acceptable. This is because it is assumed a person would have equal access to all parts of the exposure area (i.e., decision unit), not just the contaminated areas. For large, industrial complexes, the property may need to be divided into smaller decision units based on specific exposure areas (e.g., specific work areas at an industrial site). The use of Multi-incrementsampling to better estimate exposure point concentrations for specific exposure areas should be considered (see Section 4). The collection of arsenic bioaccessibility data for arsenic-contaminated soil is recommended when the concentration of total arsenic exceeds the Tier 1 EAL of 20 mg/kg. This is used to better evaluate direct exposure concerns.

If soil leaching hazards are identified then specific spill areas should be identified and treated as separate decision units. This is because the spill area, not the site as a whole, is the target where the "receptor" of concern is the groundwater directly underneath the contaminated soil. If Tier 1 soil action levels for leaching concerns are exceeded, then batch test data should be collected for the target contaminants and a more advanced evaluation of leaching concerns carried out. Keep in mind that soil data are not necessarily good indicators of potential groundwater contamination. This is especially true for chlorinated solvents. Releases of wastewater contaminated with solvents may not leave an identifiable smear zone in vadose-zone soil due to the low sorptive capacity of the solvent compounds, even though the release results in significant contamination of groundwater.

Soil or groundwater data flagged for potential vapor intrusion almost always indicates that soil gas samples should be collected at the site. The model used to develop the soil and groundwater actions levels for vapor intrusion hazards estimates the concentration of a volatile contaminant in shallow soil gas based on assumed chemical and soil properties. The models are considered to be conservative, especially for highly biodegradable chemicals like TPH and BTEX. Active soil gas data (e.g., collected in a summa canister) are much more reliable for evaluation of this hazard. The collection of methane data is also useful at sites with heavy petroleum contamination to address the potential for explosion hazards, especially where confined spaces are present or may occur after redevelopment.

The results of the site investigation should be summarized on to-scale maps and, as needed, cross sections of the site that clearly delineate the lateral and vertical extent of contamination above Tier 1 EALs (or approved alternative action levels). The same maps can be used to identify areas of specific environmental hazards and assist in development of appropriate response actions, as discussed below. A recommended format and content requirements for site investigation reports is presented in Section 18

13.5.6 PREPARE ENVIRONMENTAL HAZARD MAPS

Documentation of the distribution of environmental hazards across the site is an important step in the conceptual site model. Examples of issues to consider include: 1) What areas of the site pose potential direct exposure or vapor intrusion hazards? 2) What areas of the site pose potential leaching hazards? and 3) In what areas will grossly contaminated soil likely be encountered during future subsurface activities? Understanding the site in terms of environmental hazards rather than just contaminant concentrations is important because this serves as the basis for cleanup as well as long-term management plans. The most appropriate response action can vary, depending on the environmental hazards posed by the targeted contaminants.

Although not always needed or required, post-cleanup "as built" environmental hazard maps that clearly depict the extent and nature of environmental hazards at a site can be very useful. As discussed in the previous sections, this can be accomplished by comparison of site data to HEER Office action levels (or acceptable alternatives) for targeted hazards. Maps that summarize the extent and magnitude of contamination can be converted to environmental hazard maps by basing contaminant isoconcentration contours on action levels for specific hazards.

Example environmental hazard maps are provided in Figures 13-6 and 13-7.

In Figure 13-6, soil contaminated with dioxins and arsenic poses direct exposure hazards across a large portion of the site. Soil contaminated with chlorinated herbicides (e.g., ametryn, atrazine, diuron, etc.) in a smaller area of the site poses an additional leaching hazard. In a third area, soil contaminated with chlorinated solvents poses vapor intrusion hazard, a direct exposure hazard and a leaching hazard. In a fourth area, soil contaminated with heavy petroleum poses only gross contamination concerns. Note that highly toxic and mobile contaminants often pose a combination of several environmental hazards, including vapor intrusion, direct exposure and leaching (e.g., PCE).

The environmental hazard map in Figure 13-6 can now be used to guide selection of the most appropriate remedial alternative. Complete removal of contamination is obviously preferable. Assuming that this is not achievable for the example, a well-managed soil cap can be adequate to eliminate direct exposure hazards. Areas that pose a leaching hazard and cannot be cleaned up in a relatively short time frame will, in contrast, require some type of impermeable cap. Subslab vapor mitigation systems will be required for new buildings placed within the vapor intrusion hazard area. Indoor air studies may be needed for existing buildings located in this area.

Documenting where grossly contaminated soil and groundwater will be left in place at a site is also important (e.g., Figure 13-7). Gross contamination hazards often drive the cleanup of contaminated soil and groundwater, not direct exposure or even leaching hazards. Over time, grossly contaminated soil and groundwater can generate methane and related explosive hazards. Although the contamination may not pose environmental hazards under current site conditions, the unexpected discovery of grossly contaminated soil and groundwater during subsurface construction or utility activities can result in significant delays and project costs. Foreseeing and documenting these concerns in an Environmental Hazard Management Plan is important (see Sections 18 and Section 19).

Figure-13-6

Figure 13-6. Environmental Hazard Map for Hypothetical Site with Soil Contamination. Hypothetical hazards include pesticides, dioxin, arsenic, solvents and heavy oil. Areas delineated by comparison of site data to HDOH action levels for the noted hazard (or approved alternatives). Remedial options could vary with respect to the specific environmental hazard(s) posed in a given area of the site including capping, vapor mitigation systems, offsite disposal, etc. (see text).




Figure-13-7

Figure 13-7. Environmental Hazard Map for Hypothetical Site with Groundwater Contamination. Hypothetical site contaminated with petroleum. Areas delineated by comparison of site data to soil screening levels for the noted hazard. Aggressive remediation should focus on removal of vapor intrusion hazard so property can be redeveloped. Aggressive remediation of groundwater that poses acute aquatic toxicity hazards and gross contamination (odors, sheens) within 50 meters of the shoreline is also recommended. Long-term monitoring of remaining groundwater contamination required (see text).

13.5.7 RECOMMENDED FOLLOW-UP ACTIONS

Based on the results of the Environmental Hazard Evaluation, provide recommendations for additional actions at the site. This could include additional fieldwork, additional analyses of existing samples, further evaluation of targeted environmental hazards, evaluation of remedial alternatives, preparation of an Environmental Hazard Management Plan, etc. If all contamination above Tier 1 EALs (or approved alternatives) is removed or if otherwise warranted by site conditions, then a recommendation of no further action should be made. The most appropriate response to address environmental hazards at contaminated sites depends on a number of site-specific factors, including the presence or absence of hazards under current conditions, planned future site use, the regulatory acceptability and cost-benefit of immediate cleanup as opposed to the use of engineered and institutional controls, natural attenuation of contaminants over time, etc. When practicable, full cleanup of contaminated soil and groundwater to permit future, unrestricted use of the property is desirable. A detailed discussion of site closure considerations is presented in Section 19.

When full cleanup is not feasible, the extent and magnitude of remaining contamination must be summarized and the potential environmental hazards posed by the contamination under uncontrolled conditions clearly described. The need for institutional and engineered controls must then be evaluated. This could include restrictions on future use of the property, installation of vapor mitigation systems under buildings, capping of contaminated soil to prevent exposure or leaching, long-term monitoring of groundwater, etc. These actions must be described in a site-specific EHMP. The preparation of an EHMP is discussed in more detail in Sections 18 and Section 19.