Geologic Vulnerability - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 214

TABLE 6.5
Description of Geology for Site 2

Geologic
Unit

Soil
Class

Moisture
Content Depth (m) Color Description

Sand 0-7.9 Medium orange SW Dry to 3.0-3.6 m,

then saturated

Medium- to coarse-grained sand
with occasional pebbles. Evidence
of bedding present. Thickness of
bedding layers ranges between a
few millimeters to 3 cm.

Clay with
some silt

7.9-9.1 Light brown SM Saturated Fine-grained sand. Immediately

grades into blue clay. Sharp
contact. Evidence of clay
intraclasts in lower portion of
sand indicating an erosional
surface.

Clay 9.1-23 Light olive gray

to blue gray

CH Damp to dry 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
or any sort. Very consistent in
lithology and color with depth.
No signs of larger grained
materials such as pebbles.

• Potable water was supplied by the municipality and the source was more than
24 km (15 mi) away. However, some local residences used groundwater within the
same aquifer for irrigation purposes
• Contaminated groundwater extended beyond the property boundary approxi-
mately 365 m (1200 ft)

A complex groundwater flow pattern existed at the site. The site was located on a ground-
water divide where groundwater flowed to the east and slightly north in the northern por-
tion of property, but flowed toward the southeast on the southern portion of the property.
Figure 6.6 shows the on-site groundwater flow pattern.
The types of contaminants detected at the facility included

• VOCs including
• DNAPLs commonly referred to as chlorinated solvents used to degrease and
clean metal surfaces
• LNAPLs used as solvents, paint thinners, and cleaning products, and are com-
mon constituents in fuels such as gasoline
• PCBs used in electrical equipment

The specific chemical compounds with their highest concentrations detected and esti-
mated contaminant mass remediated are listed in Table 6.6.
The highly permeable soil and shallow groundwater depth (i.e., the vulnerable geol-
ogy) allowed VOCs to rapidly infiltrate and migrate to groundwater. In addition, the high