ECONOMICS AND VALUATION OF BIOAUGMENTATION - Bioaugmentation for Groundwater Remediation - page 318

Case 3) is 30 years. NPV calculations were conducted using a discount rate of 3% for annual
costs. This discount rate is derived from Department of Defense (DoD) guidance on using
economic analyses in decision-making (DoD, 1995 ). This discount rate is based on current
Office of Management and Budget (OMB) data and assumes a 5% nominal return is available
on U.S. Treasury Notes and Bonds and an annual inflation rate of roughly 2%. This real
discount rate is appropriate for government entities, while a higher discount rate may be more
appropriate for private parties who can obtain higher returns on investments.
11.5.3 EISB Remediation Technology Description
For the purposes of this analysis, emulsified vegetable oil (EVO) will be used as the electron
donor to promote reductive dechlorination of TCE to ethene in the residual source area (Case 1)
and in the barrier configurations (Cases 2 and 3). The advantages of this donor include
longevity and ease of distribution in the subsurface relative to other slow-release donors. The
costs for laboratory treatability testing to verify that EISB will be effective at the site and to
ensure that EVO is a suitable donor have been included in the design phase.
It is possible to implement EISB applications by circulating groundwater between perma-
nent wells while injecting a soluble electron donor in a semi-passive approach rather than using
direct push of EVO in a passive approach. The different approaches to adding electron donors
are discussed in more detail in an earlier monograph in this series on in situ bioremediation of
perchlorate (Stroo and Ward, 2009 ). The semi-passive approach would require more frequent
addition of electron donor (e.g., every 6-8 months) but fewer injection locations are required
and the costs for electron donor are typically less, so the overall costs are generally similar to
the passive approach. The overall costs of the passive (EVO injection) and semi-passive
approaches are similar and the choice between one versus the other is unlikely to significantly
impact the cost analysis of bioaugmentation presented below.
In Case 1, the EVO will be applied through a series of 15 injection wells spaced on 5-m
(16.4 ft) centers distributed across the 250 m 2 (2,690 ft 2 ) source area. A groundwater model will
be used in the design phase to help specify the injection sequence and ensure the amendment
will contact the entire source zone. The 5-cm (2-inch) diameter injection wells will be screened
across the saturated zone and developed prior to EVO injection. Pre-design injection testing is
included in the cost analysis to establish the injection rate, which is assumed to be 10 L/min
(2.6 gal per minute [gpm]). The costs include the addition of 185 kg (407 lb) of a commercial
EVO solution to each injection point, along with 9,000 L (2,376 gallons [gal]) of fluid (dilute
EVO and chase water) to ensure complete distribution of the EVO. EVO will be metered
through a dosimeter pump connected to a nearby water source, and a manifold will be used to
allow injection into as many as five injection wells simultaneously. Each injection line will
contain a pressure gauge and flow totalizer, to allow accurate measurements of the fluid
injections into each well. The injections will be performed by a two-person crew requiring
11 days of labor, including set up and breakdown.
Bioaugmentation will be conducted along with the first injection of electron donor to
provide maximum distribution of the initial culture and minimize additional costs for injection.
Culture will be delivered to the site in stainless steel vessels and one liter of culture will
be injected into each of the 15 injection points based on a cell density of 10 10 -10 11 cells/L.
The culture medium will be transferred to the injection point using argon gas to pressurize the
culture vessel and displace the media into the injection point. Because the injection of culture
will be conducted along with the injection of electron donor, the additional labor for culture
injection will be minimal. Cost for the culture medium and the additional costs for labor and
equipment to inject the culture are included in the cost estimate.