Environmental Engineering Reference
In-Depth Information
2000
1800
1600
1400
1200
1000
800
600
400
200
0
2004
2005
TEPA-1C/D
2006
2007
2008
2009
2010
TEPA-2C/D
TEPA-5C/D
TEPA-6C/D
FIGURE 8.3
Alkalinity trends along transects within PRB.
(Hedin et al., 1994). Pb is thus expected to be one of the first metals pre-
cipitated out under sulfate reducing conditions followed by Cd and Ni. Pb
concentrations entering the PRB showed significant temporal and spatial
variation since monitoring activities at the site were first initiated. The high-
est average Pb concentrations entering the PRB (based on the average of the
A + B locations along each transect between 2006 and 2010) were reported at
TEPA-5, where concentrations averaged 93.6 μg/L (Table 8.2). The most recent
data (2010) showed that the average of the A + B concentrations entering the
PRB ranged from 8.8 μg/L at TEPA-2 to 29.6 μg/L at TEPA-5. With the excep-
tion of one location within the PRB (at TEPA-2D where a Pb concentration of
1.46 μg/L was measured in 2010), Pb was consistently treated to concentra-
tions less than 1.0 μg/L at all locations and to less than 0.5 μg/L at 5 of the
8 locations monitored within the PRB. The low Pb concentrations (<1 μg/L)
were also maintained downgradient of the PRB along all four transects at the
H locations near the creek.
The Cd concentrations entering the PRB far exceeded Pb concentrations
and similar to Pb, have also shown significant temporal and spatial varia-
tion. The average Cd concentrations entering the PRB ranged from 136 μg/L
at TEPA-6 to 461 μg/L at TEPA-2. The most recent data (2010) indicated that
cadmium concentrations entering the PRB ranged from 17.0 μg/L (TEPA-6)
to 470 μg/L (TEPA-2). Within the PRB, nearly 100% treatment was achieved
based on Cd concentrations being reduced to less than 0.3 μg/L along all
four transects. As in the case of Pb, Cd concentrations remained at low con-
centrations (<0.4 μg/L) downgradient of the PRB system.
Average Ni concentrations entering the PRB since 2008 ranged from 213 μg/L
at TEPA-1 to 409 μg/L at TEPA-6, while Ni concentrations entering the PRB in
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