Conducting Subsurface Environmental Investigations in Urban Watersheds - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 148

the methodology described in Table 4.3. To determine consistency using Table 4.3, a rep-
resentative sample of the soil or sediment is necessary; the recommended sample size is
approximately 5-10 cm 3 .
Moisture content should be estimated in the field using the criteria listed in Table 4.4.
Plasticity is the property of soil or rock allowing it to be deformed beyond the point of
recovery without cracking or exhibiting appreciable change in volume—its “plastic limit.”
Criteria for estimating plasticity of soil samples in the field are presented in Table 4.5
(OEPA 2006).
Pertinent information on each soil boring is recorded onto a boring log . Figure 4.20
shows a sample boring log (Iowa Department of Natural Resources 2002).
Additional physical parameters may be used to characterize subsurface solid materials,
but these cannot be reliably measured in the field and most often require determination at
a laboratory. These additional parameters include (ASTM 1996)

TABLE 4.3
Criteria for Describing Consistency

Description Criteria

Very soft Thumb will penetrate easily, typically more than 25 mm (1 in.)

Soft Thumb will penetrate approximately 25 mm

Firm Thumb will indent soil approximately 6 mm (0.25 in.)

Hard Thumb will not indent soil, but readily indented with thumbnail

Very hard Thumbnail will not indent soil

Source: Ohio Environmental Protection Agency, Technical Guidance for Ground

Water Investigations , Columbus, OH, 2006.

TABLE 4.4
Criteria for Describing Soil Moisture

Description Criteria

Dry Absence of observable moisture, dry to the touch

Moist Damp but no visible water

Wet Water is observed when sample is squeezed

Saturated Free water present without squeezing the sample

Source: Ohio Environmental Protection Agency, Technical Guidance

for Ground Water Investigations , Columbus, OH, 2006.

TABLE 4.5
Criteria for Describing Plasticity

Description Criteria

Nonplastic A sample cannot be rolled to an approximate diameter of 12 mm (0.5 in.)

Low plasticity A sample can be rolled, but is lumpy and difficult, and cannot be rolled when sample is

drier than the plastic limit

Medium plasticity A sample is easily rolled and not much time is required to reach the plastic limit

High plasticity A sample is very easily rolled and it takes considerable time to reach the plastic limit

Source: Ohio Environmental Protection Agency, Technical Guidance for Ground Water Investigations , Columbus,

OH, 2006.