LAND AS THE RESOURCE - Low Impact Development and Sustainable Stormwater Management - page 62

Figure 3-12 The Ford auto plant in Dearborn, Michigan, has become the industrial model
for sustainable building, with a vegetated roof, porous pavements, wetland channels, and
toxic soil remediation.
that constantly change the surface of our planet, but at a time scale beyond
our comprehension. For most of human history, human beings did not occupy
North America, and we did not arrive until some 8,000 years ago (as far as
we know). Human settlements were certainly guided by and followed geologic
constraints and opportunities, but for the most part Native Americans did little
to alter the land form or extract mineral resources (Figure 3-13). This changed
when Europeans arrived.
The United States can be considered as comprised of major physiographic
regions (Table 3-1) that reflect both the geologic formations that underlie and
form the land surface and the weathering processes that have shaped this surface
over millennia. Much of the middle portion of the United States was a shallow
sea during the Cretaceous period (200 million years ago), and the current coastal
regions were inundated by ocean waters during periods of sea-level changes
caused by warming and cooling cycles. The inland sea resulted in a thick layer
of deposited marine organisms that formed chalk (creta), and the other valleys
that were covered by ocean waters followed a similar process of marine organ-
ism deposition to form carbonate bedrock, or limestone. These rock types have
developed solution channels over hundreds of millions of years that hold vast
aquifer systems of groundwater, and provide abundant water capacity.
In the balance of the country underlain by older bedrock, groundwater is
contained in fractures in the rock and is generally limited to a few hundred feet