BIOAUGMENTATION CONSIDERATIONS - Bioaugmentation for Groundwater Remediation - page 145

this range. However, volatile fatty acids and carbonic acid are produced during electron donor
fermentation and hydrochloric acid (HCl) is generated through reductive dechlorination; both
of these processes can cause a decrease in pH. Thus, reductive dechlorination in source zones
with high VOC concentrations can be associated with extensive localized dechlorination and
production of HCl, whereby the soil's natural buffering capacity can be exceeded (Robinson
and Barry, 2009 ). In these instances, it is important to supply enough buffer to compensate for
acid production to maintain suitable conditions for Dhc . It should be borne in mind that other
processes can act to increase the pH of the aquifer. These processes include sulfate reduction,
iron (III) oxide reduction, acetate fermentation, calcite dissolution and proton exchange on
clays (Robinson et al., 2009 ).
If the natural aquifer pH is not in the 6-8.3 range, then the aquifer pH can be adjusted
through the addition of buffers. Three commonly used buffers or buffer-containing products
include sodium bicarbonate, AquaBupH TM (EOS Remediation, Raleigh, NC, USA), and
Neutral Zone # (RNAS, Brooklyn Center, MN, USA). These products are discussed below.
Sodium Bicarbonate is an inexpensive, readily available buffer, which has been widely used to

buffer groundwater for bioremediation/bioaugmentation applications. The disadvantage of
using sodium bicarbonate is that it is soluble and can wash out of the treatment area, thereby
requiring multiple, often time-consuming, applications. For recirculating systems, sodium
bicarbonate can be metered in and distributed throughout the target area. For passive systems,
the buffer solution can either be made up in tap water (which may need to be pre-reduced prior
to injection and may cause localized plume dilution) or the contaminated groundwater can be
extracted, buffered and re-injected, which may be subject to permitting or regulatory barriers
and is time-consuming, especially for low permeability aquifers. The addition of sodium
bicarbonate also can increase the sodium concentration of the groundwater significantly, and
may alter the geochemical conditions enough to cause some mineral species to precipitate,
which can lead to aquifer clogging.
AquaBupH

TM is a mixture of an “alkaline buffering” suspension, emulsified vegetable oil, and
a proprietary food additive. It is designed to provide a long-term source of buffer through the
distribution of particulate buffer (median particle size of 2.5 micrometer [ m m]) in the vicinity of
the injection point and has a low sodium content ( < 0.4%). This product can be used for
bioremediation/bioaugmentation applications requiring the addition of both buffer and elec-
tron donor. The vendor recommends that the acid demand of the aquifer matrix and ground-
water be determined and then the amount of AquaBupH TM needed to achieve the desired pH
can be calculated. This approach may mean that additional injections of emulsified vegetable oil
(without buffer) may be required initially and subsequently to provide sufficient electron
donor. AquaBupH TM is injected like an emulsified vegetable oil, with the product metered
into an injection line. EOS Remediation provides a design spreadsheet to assist in estimating the
appropriate dose of AquaBupH TM ( www.eosremediation.com ). The spreadsheet accounts for
the HCl produced from dechlorination, the carbonic acid produced through substrate fermen-
tation, and the hydroxyl released from electron acceptor reduction.
Neutral Zone

# is a colloidal suspension of calcium carbonate and is designed to remain in
place and not wash out of the targeted treatment zone. According to the vendor, it will not
cause adversely high pH because the base is liberated by the acid it will neutralize and not by
dissolution in water. The advantage of Neutral Zone # is that it can be added independently of
the amount of electron donor added. Neutral Zone # is significantly more viscous and dense
than emulsified vegetable oil. Therefore, the vendor recommends that the product be diluted
5-10 fold with water and then injected with a proportional feed system into multiple points
(permanent wells or direct-push points) simultaneously.