Remediation: Techniques and Cost - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 407

These contaminants included antimony, barium, beryllium, cadmium, copper, manganese,
nickel, selenium, silver, zinc, phenols, phthalates, other SVOCs, and asbestos.
Of the 280 sites evaluated

• 193% or 69% had soil contamination only.
• 87% or 31% had soil and groundwater contamination.
• 21% or 7% had significant free product.

All the sites were located on unconsolidated sediments consisting of glacial, fluvial, lacus-
trine, alluvial, or marine sediments composed of gravel, sand, silt, clay, or mixtures of
these materials.

11.10.1 Results

For the contaminant groups, Table 11.1 summarizes their frequencies of detection and
required remediation, and percent of the total cost. Table 11.2 contains the number of sites
where each contaminant group was detected, whether groundwater was affected, if free
product was present, as well as the cost of the remediations. The data in Table 11.1 indicate
that PAHs were the group of compounds most often detected but were remediated just one-
third of the time, and accounted for only 1% of the total cost. Although PAHs were often
detected, remediation was not always required, and, when remediation was required, the
costs were lower than anticipated (Table 11.2). As shown in Tables 11.1 and 11.2, LNAPL
VOCs had a frequency of remediation equivalent to PAHs, but at a much higher cost. Over
90% of the cost to remediate LNAPL VOCs was associated with free product.
Tables 11.3 and 11.4 show the number of sites and selected frequency of the remedial
technologies where soil and groundwater were remediated, respectively. As depicted in
Table 11.3, excavation of soil was the preferred remedial option, especially when the vol-
ume of soil was less than 5000 tons and there was no impediment to excavation. When
there was a large volume of impacted soil or excavation impediments existed, SVE was the
preferred remedial option for VOCs in course-grained soils.
A combination of alternatives including, risk assessment, institutional controls, capping,
and thermal treatment were the preferred alternatives for large volumes of fine-grained

TABLE 11.1
Summary of Frequency of Detection, Remediation, and Cost

Frequency of
Detection (%)

Frequency of
Remediation (%)

Percent of
Total Cost Contaminant

PAHs 83 26.6 1.1

LNAPL VOCs 60 25.9 44.4

DNAPL VOCs 33.4 24.1 37.7

Lead 20 9.0 1.3

PCBs 8.3 5.0 2.5

Chromium VI 10 4.5 10.0

Mercury 4 2.5 1.8

Perchlorate 0.7 0.8 0.3

Arsenic 5.4 0.8 0.8

Chlordane 1.5 0.8 0.1

Total 100 100