Transitions - Sustainable Design: The Science of Sustainability and Green Engineering - page 123

as in soils (e.g., clays) with very slow rates of transport. In this way, engineers
and scientists must work closely with city and regional planners early in the site
selection phases. 12 As the Bhopal incident has tragically illustrated, human factors
must be considered along with physical factors. Planners, therefore, are an asset
to any green site selection team.
Intervention to Control the Exposure
We now enter territory familiar to conventional engineering. We need to establish
controls to prevent or at least reduce exposures to any pollutants that remain after
prevention steps have been taken. In other words, we need to design systems to
protect potential receptors.
The receptor of contamination can be a human being, other fauna in the
general scheme of living organisms, flora, or materials or constructed facilities.
In the case of humans, as we discussed earlier, the contaminant can be ingested,
inhaled, or dermally contacted. Such exposure can be direct with human contact
to, for example, particles of lead that are present in inhaled indoor air. Such
exposure also can be indirect, as in the case of human ingestion of the cadmium
and other heavy metals found in the livers of beef cattle that were raised on
grasses receiving nutrition from cadmium-laced municipal wastewater treatment
biosolids (commonly known as sludge ).
Heavy metals or chlorinated hydrocarbons can be delivered similarly to do-
mestic animals and animals in the wild. Construction materials also are sensitive
to exposure to released substances, from the “greening” of statutes through the
de-zincing process associated with low-pH rain events to the crumbling of stone
bridges found in nature. Isolating potential receptors from exposure to hazardous
chemicals, the engineer has an opportunity to control risks to those receptors.
The opportunities to control exposures to contaminants are associated directly
with the ability to control the amount of hazardous pollutants delivered to the
receptor through source control and siting of hazardous waste management fa-
cilities. One solution to environmental contamination could be to increase their
dilution in water, air, or soil environments. We discuss specific examples of this
type of intervention later in the chapter.
Intervention at the Point of Response
Most of the experience in addressing chemical contamination has been at the
point where the threat already exists. Something is already contaminated, so we
need to respond to the threat.
Opportunities for intervention at this point of response are grounded in basic
scientific principles, engineering designs and processes, and applications of proven