Geologic Vulnerability - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 209

TABLE 6.3
Description of Geology for Site 1

Geologic
Unit

Soil
Class

Moisture
Content Depth (m) Color Description

Fill 0-0.6 Gray to brown Fill Dry Fill material consisting of sand and silt,

and some construction debris
including brick and wood fragments.
Fill material ranges from 0.3 to 0.6 m
(1-2 ft) thick throughout the site and
is not present beneath the buildings.

Clay with
some silt

0.6-2.4 Light brown CL Dry to moist Light brown clay with occasional very

thin, discontinuous silt layers
indicating layered deposition. Silt
layers range in thickness from less
than a millimeter to not more than
two millimeters.

Clay 2.4-12 Light olive gray

to blue gray

CH Damp Blue to gray colored ground moraine

clay. Upper portions very plastic. No
visible signs of any silt or original
depositional structures to indicate
depositional layering of any sort. Very
consistent in lithology and color with
depth. No signs of larger grained
materials such as pebbles.
Groundwater was not observed at the
contact between the upper lacustrine
clay and the ground moraine lower
blue clay.

many of the soil borings, more than two soil samples were analyzed to gather data on the
vertical extent of contamination. The maximum depth of the soil borings was 4.6 m (15 ft)
beneath the surface in impacted areas, yet the vertical extent of contamination did not
exceed a depth of 1.5 m (5 ft). The monitoring wells indicated damp to moist soils existed
at some locations within very thin layers of silt. These silty layers were just a few milli-
meters thick and were also observed in soil samples collected from some of the soil bor-
ings drilled during investigative activities. After the monitoring wells failed to detect any
groundwater seepage, they were pulled from the ground and the boreholes sealed with a
bentonite clay grout.
Characterization of the geology at the site was accomplished by drilling a soil boring
to a depth of 12 m (40 ft) in a nonimpacted area. In general, the site was underlain by a
clay deposit from a Pleistocene age glacial lake that occupied the region more than 12,000
years before the present. Historical geological literature of the region indicates a ground
moraine or lodgment till deposit extended to depths of approximately 55 m (180 ft) beneath
the ground at the site. Table 6.3 details the geology between the ground surface and 12 m
(40 ft) beneath the site.
Other pertinent technical and geological information concerning the site included

• Storm sewers in the immediate vicinity did not intersect any of the contamination
• Surface water drainage was controlled by storm sewers
• No buried utilities intersected contaminated areas