Environmental Engineering Reference
In-Depth Information
to the occurrence and distribution of metals in the soils of an urban environment (move-
ment of water; location of industry) are closely tied to drainage patterns. Consequently,
the watershed concept has become a key factor in modern urban planning (RRRAP 1994;
Murray and Rogers 1999).
Specific objectives of this study were to determine if there are significant differences
between the metal concentrations: (1) in surface and near-surface soils (<0.5 m in depth),
the shallow subsurface soils (0.5-10.0 m in depth) and in soils at depths greater than 10.0 m;
(2) among the various soil types related to the glacial history of southern Michigan; and
(3) among major land use designations, such as residential, commercial, and industrial
properties. Another important goal of the study was to simply evaluate the background
concentration of metals in the soil of an urban environment. Sites selected for this study
included parks, elementary and high schools, community colleges, churches, banks, new
residential developments as well as older residences, courthouses, town hall, law firms,
malls, golf courses, vacant property, and industrial properties. As shown in Table 2.4, the
geology of the Rouge River watershed is sufficiently similar to many other urban areas to
be considered a model. Consequently, the results of this study have implications for many
cities, especially Cleveland, Chicago, Saint Louis, Salt Lake City, Seattle, and Los Angeles,
which are sufficiently similar geologically. Internationally, cities such as London, Paris,
and Mexico City are also in this category.
The data used in this study were derived from several sources including project files
compiled by the Michigan Department of Environmental Quality (MDEQ), now the
Department of Natural Resources and Environment (DNRE), which oversees the investiga-
tion and cleanup of hazardous waste sites in Michigan. Files from more than 3000 known
or suspected sites of environmental contamination were reviewed at the MDEQ southeast
Michigan district headquarters. Although soil samples were analyzed for contaminants
at the vast majority of the 3000 sites, only a few hundred sites met the rigorous standards
established for inclusion in this study. The methodology used in this study to characterize
urban metal concentrations in the soil relied on samples collected over a period of 10 years.
This feature of the study helped average the variability of metal concentrations caused by
the constantly changing near-surface urban soils versus the more stable subsurface soils.
Each site was carefully evaluated and screened to eliminate obvious data bias. Specific
sites excluded from the study included those with restricted access (a copper fabricating
facility) and industrial properties with extremely high concentrations of a particular metal,
for example, a lead smelter, a chrome-plating operation, and a gun range. Three sites were
eliminated because the near-surface soil was considered fill material of an unknown age
and origin. Performing this type of careful evaluation and screening was covered in detail
in Chapter 4.
This screening resulted in a final dataset of 3786 soil samples analyzed for heavy metals
at 171 sites. Each of these sites was then classified with respect to land use and designated
as residential, commercial or industrial. The metals evaluated for this study included anti-
mony, arsenic, barium, beryllium, cadmium, chromium, copper, lead, mercury, nickel,
selenium, silver, thallium, and zinc. Figure 9.1 shows the location of the 171 sites in the
study watershed where samples were collected from the three land-use categories.
Table 9.1 shows the total number of sites classified as residential, commercial, or indus-
trial and the number of samples collected from each of the soil units. The total number of
sites located on the various soil units exceeds 171 because some sites contained more than
one soil unit, and they were collected from soil borings that may have come from deeper
soils, which were texturally distinct from the surface soil. Table 9.1 also indicates the per-
centage of sites in each land use and soil unit category.
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