Department of Health Seal

TGM for the Implementation of the Hawai'i State Contingency Plan
Section 13.1


Table 13-1 Target Environmental Hazards by Media

Environmental Hazard


Contaminated Groundwater

Human Health Risk


- Drinking Water

Toxicity concerns related to contamination of groundwater that is a current or potential source of drinking water

- Vapor Intrusion

Emission of volatile contaminants from groundwater and intrusion into overlying buildings

Aquatic Habitats

Discharges of contaminated groundwater and toxicity to aquatic organisms. Includes contamination of fish and shellfish used for human consumption.

Gross Contamination

Includes taste and odor concerns for contaminated drinking water supplies, free product, sheens and odors on surface water, general resource degradation, etc.

Contaminated Soil

Human Health Risk


- Direct Exposure

Exposure to contaminants in soil via incidental ingestion, dermal absorption and inhalation of vapors or dust in outdoor air.

- Vapor Intrusion

Emission of volatile contaminants from soil and intrusion into overlying buildings


Leaching of contamination from soil by infiltrating surface water (rainfall, irrigation, etc.) and subsequent contamination of groundwater resources

Terrestrial Habitats

Toxicity to terrestrial flora and fauna

Gross contamination

Includes potentially mobile free product, odors, aesthetics, explosive hazards, general resource degradation, etc

Contaminated Soil Gas


An explosion hazard can exist if accumulation of unstable gases such as methane or Total Volatile Hydrocarbons (TVH) occurs in confined spaces.

Vapor Emissions

Emission of volatile contaminants from soil or groundwater into overlying buildings and/or outdoor air.


Figure 13-2. Summary of Environmental Hazards Considered in Action Levels. The four target media tested to evaluate these potential hazards are groundwater, soil, soil gas and indoor air.

A summary of common environmental hazards that should be initially screened for at contaminated sites is given in Table 13-1 (see also Figure 13-2)):

The potential for one of more of these environmental hazards to be present at a site should be evaluated in an EHE, which should include screening sample data if available. As discussed in Section 3, preparation of a conceptual site model that summarizes current site conditions is an important part of the EHE process.

Note that some of the environmental hazards listed above are not necessarily "risk-based," at least in the traditional toxicological use of this term with respect to dose and response. For example, soil that is grossly contaminated with petroleum may not pose a toxicological risk to future residents, but it could pose significant odor and nuisance concerns and in some cases even result in explosive levels of vapors in soil gas. Although it may seem counterintuitive, it is quite possible for soil that is flammable to be considered "nontoxic" in a standard human health risk assessment. Even so, the fact that the soil is flammable is important to call out in the Environmental Hazard Evaluation. Gross contamination can also complicate future construction or subsurface utility activities that require disturbance of heavily contaminated soil or groundwater.

Leaching of contaminants from soil is also important to consider, even though this is rarely included in traditional risk assessments. Discharges of contaminated groundwater or free product into nearby surface water bodies, either naturally or via leakage into storm sewers or through site dewatering activities, can pose significant environmental hazards to aquatic habitats. When large plumes of impacted groundwater threaten fisheries, the discharge of contaminated groundwater to surface water and subsequent uptake of contaminants into seafood may also be of concern. This includes the biomagnification of contaminants up the food chain and risks to human or ecological health if contaminated fish or shellfish is ingested.

The environmental hazard that drives the potential need for remedial action at a contaminated site is closely tied to the toxicity and mobility of the targeted contaminants. Concerns posed by soil contaminated with chemicals that are highly toxic to humans and relatively immobile are generally driven by direct exposure hazards (e.g., arsenic, lead, polychlorinated biphenyls [PCBs]). Vapor intrusion typically drives environmental hazard for soil contaminated with volatile carcinogens, although direct exposure and leaching hazards are not far behind (e.g., benzene, tetrachloroethylene [PCE], TPH gasoline, methane). Leaching hazards will often drive cleanup of soil contaminated with noncarcinogenic chemicals that are highly mobile (e.g., TPH gasoline or diesel, toluene, xylenes, chlorinated herbicides). Soil contaminated with pesticides or metals that are relatively non-toxic to humans and immobile could still pose significant toxicity hazards to terrestrial flora and fauna (e.g., barium, copper, nickel).

Drinking water toxicity hazards are almost always identified for contaminated aquifers. Potential vapor intrusion hazards will also usually be identified for groundwater contaminated with carcinogenic, volatile chemicals. Chemicals that have a low taste and odor threshold may not pose toxicity concerns but can still pose gross contamination hazards for drinking water resources (e.g., TPH, ethylbenzene, toluene, xylenes). A number of pesticides pose aquatic toxicity hazards at concentrations well below drinking water standards. This can drive remedial actions if discharge of contaminated groundwater into a sensitive aquatic habitat is possible. Free product could pose both toxicity and gross contamination hazards if allowed to migrate offsite and discharge into a surface water body. Free product also poses potential vapor intrusion hazards for nearby buildings as well as potential explosive, subsurface vapor hazards.

Other potential environmental hazards may require attention at some sites, including exposure of construction workers to contaminated groundwater and the potential uptake of contaminants in garden produce. The need to include additional environmental hazards in the site assessment must be determined on a site-by-site basis.