Department of Health Seal

TGM for the Implementation of the Hawai'i State Contingency Plan
Section 19.7

19.7 Institutional and engineering Controls

Appropriate measures must be used to mitigate the environmental hazards posed by contaminated media left on site in restricted use closures. These measures are defined as institutional controls and engineering controls. Institutional controls are methods intended to prevent exposure to contaminated media by legal or procedural means (for example, environmental covenants), as opposed to engineering controls, which are methods of exposure prevention by physical means (for example, an active vapor mitigation system to prevent subsurface vapor intrusion into indoor air spaces).

Institutional controls alone are generally not sufficient to mitigate environmental hazards, with the exception of commercial or industrial zoned sites where representative sampling has demonstrated contaminant levels are above residential or unrestricted use EALs, but below applicable commercial/industrial use EALs. Engineering controls require institutional controls for their long-term management. Consequently, in most cases, institutional and engineering controls must be used together to adequately manage remaining environmental hazards at restricted use closure sites.

19.7.1 Institutional Controls

Institutional controls are legal or administrative measures that prevent exposure by influencing human behavior through laws, rules, permits, requirements, contracts, warnings, and advisories. Institutional controls help to minimize the potential for human exposure to contaminated media by controlling activities that may affect exposure. Institutional controls also restrict land use and on-site activity that might interfere with the containment of contaminated media left on site. Examples of institutional control measures include:

  • Prohibition on excavation of soil
  • Prohibition on use of groundwater
  • Prohibition on residential or other sensitive land use

HDOH's primary legal instrument for establishing institutional and/or engineering controls at a site is the site closure document. HDOH may, at its discretion, require an environmental covenant to provide additional long-term protection for sites with significant and persistent contamination (see Subsection 19.8.1).

19.7.2 Engineering Controls

Engineering controls are tangible measures that prevent exposure by physically preventing humans (or wildlife) from coming into contact with contaminated media left on site at restricted use closure sites. Institutional controls are required to ensure that engineering controls are properly managed. Examples of engineering controls include:

Soil Contamination

  • Capping systems – contaminated soil is covered with a cap to reduce surface-water infiltration and leaching, control gas and odor emissions, improve aesthetics, provide a stable surface over the contaminated soil, and prevent human exposure from direct contact. Caps can range from a simple native soil cover to single layer caps (e.g., asphalt/concrete and soil/bentonite/clay) to multi-layer cover systems (e.g., Resource Conservation and Recovery Act [RCRA] caps) to buildings or structures.

    Consideration must be given to the type, magnitude, and extent of contaminated soil when selecting the appropriate cap. A cap for soils contaminated with highly toxic and persistent contaminants should be highly durable and long lasting, such as a multi-layer cover system.

    Soil caps may be appropriate at certain sites where future development/construction is highly unlikely and institutional controls are used to restrict such land use. The soil cap thickness is determined considering site-specific factors but must be adequate to reduce or eliminate the environmental hazard(s). A visible marker, such as orange construction fencing, is generally used to mark the top of the contaminated soil layer. Soil caps are typically used for non-volatile contaminants where leaching is not a concern.

    If a structure is used as a cap, the permanence of the proposed building must be considered. For example, a high-rise structure designed and built for the long-term would be an appropriate "building cap" for significantly contaminated soils. The shorter life span of less durable structures must be taken into account when assessing long-term effectiveness of the cap.
  • On-site Encapsulation/Repository – for potentially mobile contaminants, soil is consolidated and encapsulated into a lined subsurface on-site cell or vault. Such systems are designed to eliminate or reduce surface-water infiltration and leaching, control gas and odor emissions, improve aesthetics, and prevent human and ecological exposure from direct contact. On-site repositories range from High Density Polyethylene (HDPE) liner encapsulation to subsurface concrete vaults. For non-mobile contaminants, unlined borrow pits may be adequate for on-site management.

Groundwater Contamination

  • Hydraulic Containment – measures are used to control the hydraulic gradient to minimize the spread of a groundwater plume. One example is the use of pumping wells to actively prevent the plume from spreading and reaching drinking water wells, surface water, or uncontaminated aquifers, etc. Another example is a slurry wall in which low permeability materials, such as grout, are injected into the subsurface to contain a groundwater plume. Institutional controls are necessary to restrict groundwater use.
  • Alternative Water Source – an alternative water source can be provided to an area where groundwater is contaminated and not suitable for ingestion. Institutional controls are necessary to restrict groundwater use.

Sediment Contamination

  • Capping systems - contaminated sediments are covered with a cap to eliminate erosion and dissolution into the water body, improve aesthetics, provide a stable surface over the contaminated sediment, and prevent human and ecological exposure from direct contact. An example is lining a streambed containing contaminated sediments with an impermeable material, such as HDPE liner, and then stabilizing the liner with highly durable materials, such as riprap and concrete.
  • Dredging - An ongoing dredging program can be used as an engineering control of contaminated sediments, as well.

Soil Vapor Contamination

  • Vapor barriers – impermeable materials are placed beneath a proposed building site to prevent subsurface vapor intrusion into indoor air spaces. Active vapor removal systems should be considered for sites with significant soil gas issues in which a gas collection system is placed beneath the barrier and connected to a suction fan, which may be vented above the roof of the building, or connected to a vapor treatment system such as a thermal oxidizer or granular activated carbon.