- Determine the cost ranges that might be encountered
in this application
The cost ranges that might be encountered in this—or any other application—depend on
the treatment technology which is applicable and chosen. Thus, with some 100,000 yd^3
(76,500 m^3 ) of soil to be treated, the cost ranges from Table 4 = 100,000 yd^3 x $/yd^3. For
biological land treatment, cost ranges = 100,000 x $30 = $3,000,000; 100,000 x $90 =
$9,000,000. For bioventing, cost ranges = 100,000 x $50 = $5,000,000; 100,000 x $120 =
$12,000,000. For biorector treatment, cost ranges = 100,000 x $150 = $15,000,000;
100,000 x $250 = $250,000,000. Thus, a significant overall cost range exists—from
$3,000,000 to $25,000,000, depending on the treatment technology chosen.
The wide cost range computed above shows why it is so important that the engineer
choose the most cost-effective system which accomplishes the desired cleanup in accor-
dance with federal and state requirements. With an estimated 2000 hazardous waste sites
currently known in the United States, and possibly several times that number in the rest of
the world, the potential financial impact on companies and their insurers, is enormous.
The actual waste site discussed in this procedure highlights the financial decisions engi-
neers face when choosing a method of cleanup.
Once a cleanup (or remediation) method is tentatively chosen—after the site investi-
gation and feasibility study by the engineer—the controlling regulatory agencies must be
consulted for approval of the method selected. The planned method of remediation is usu-
ally negotiated with the regulatory agency before final approval is given. Once such ap-
proval is obtained, it is difficult to change the remediation method chosen. Hence, the en-
gineer, and the organization involved, should find the chosen remediation method
acceptable in every way possible. - Evaluate the time requirements of each biological
treatment technology
Biological land treatment has been used for many years for treating petroleum residues.
Also known as land-farming, this is the simplest and least expensive biological treatment
technology. However, this method requires large amounts of land that can be dedicated to
the treatment process for a period of several months to several years. Typically, land
treatment involves the control of oxygen, nutrients, and moisture (to optimize microbial
activity) while the soil is tilled or otherwise aerated.
Bioventing systems, Fig. 22, are somewhat more complex than land treatment, at a
moderate increase in cost. They are used on soils with both volatile and nonvolatile hy-
drocarbons. Conventional vapor extraction technology (air stripping) of the volatile com-
ponents is combined with soil conditioning (such as nutrient addition) to enhance micro-
bial degradation. This treatment method can be used both in situ and ex situ. Relative to
land treatment, space requirements are reduced. Treatment time is on the order of weeks
to months.
Bioreactors are the most complex and expensive biological alternative. They can clean
up contaminated water alone, or solids mixed with water (slurry bioreactors). The reactor
can be configured from existing impoundments, aboveground tanks, or enclosed tanks (if
emissions controls are required). Batch, semicontinuous, or continuous modes of opera-
tion can be maintained. The higher cost is often justified by the faster treatment time (on
the order of hours to days) and the ability to degrade contaminants on difficult-to-treat
soil matrices.
Since time is not a controlling factor in this application, biological land treatment, the
least expensive method, will be chosen and applied. - Compute the net present value for alternative treatment
methods
Where alternative treatment methods can be used for a hazardous waste site, the method
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