Environmental Engineering Reference
In-Depth Information
the soils metal investigation, i.e., the Cu-fabricating facility, several industrial properties
with extremely high concentrations of a particular metal, the Pb smelter, several chrome-
plating facilities, and a gun range. In addition, the three sites eliminated previously
because the near-surface soil was considered fill material of an unknown age and origin
were also eliminated here. They were not included because the shallow groundwater
occurring beneath these sites was not believed to be in a naturally occurring geologic
formation.
This screening resulted in a final dataset of 1140 groundwater samples collected from
126 sites, with the high sample-to-site ratio helping to ensure the replication of results. The
selected sites included parks, elementary and high schools, community colleges, churches,
banks, new residential developments as well as older residences, courthouses, a town hall,
law firms, malls, golf courses, vacant property, and industrial properties. Samples were
collected over a period of 10 years from 1990 to 2000, which helped average the variability
of metal concentrations caused by the constantly changing urban region.
Each of these sites was then classified with respect to land use and designated as resi-
dential, commercial, or industrial. The metals evaluated for this study included As, Ba, Cd,
Cr, Cu, Pb, Hg, Ni, Se Ag, and Zn. Table 9.6 shows the number and percent of sites within
the land use categories as well as the distribution of the samples obtained within each
geologic unit.
Shallow groundwater within the study area flows toward and discharges into the Rouge
River (Rogers and Murray 1997; Rogers 1997b; Murray and Rogers 1999). Inspection of the
groundwater flow direction at each site revealed a good correspondence with the direction
of surface water flow.
Monitoring wells were typically installed using a drilling rig equipped with an 11 cm
inner-diameter hollow stem auger. Monitoring wells were constructed and sampled
according to procedures outlined by USEPA (1986, 1990). In the laboratory, analysis of
the groundwater samples for dissolved metals was accomplished using USEPA 6000
or 7000 series methods (USEPA 1983) and following all USEPA protocols (SW 846 test
methods).
TABLE 9.6
Site and Sample Distribution
Number of
Sites
Percent of
Sites
Number of
Samples
Percent of
Samples
Land use
Commercial
70
56
580
51
Industrial
32
25
438
38
Residential
24
19
122
11
Total
126
100
1140
100
Geologic unit
Outwash
4
3
26
2
Moraine
6
5
17
2
Sandy and Silty Clay
16
13
189
17
Sand
50
39
364
32
Silty Clay
30
24
195
17
Clay
20
16
349
30
Total
126
100
1140
100
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