Environmental Engineering Reference
In-Depth Information
100
80
Restoration credit
+ 2500 SAY
60
Baseline
services
Historic and
residual deficit
-1500 SAYs
Habitat disturbance
-500 SAYs
40
Remediation option: Dredge “hot spots”
and perform restoration on nearby
habitats
20
Start
Years
FIGURE 7.14
NEBA-derived hot spot removal with restoration contaminated sediment remediation.
identified nutrient (primarily nitrogen) enrichment causing noxious algal
blooms as the primary impairment in the Green River. The sources of nitro-
gen identified and the associated loads were:
r Regional wastewater treatment plant (WWTP) - 2 kg N/day
r Urban storm water - 3 kg N/day
r Agricultural runoff - 4 kg N/day
r Feed lots - 6 kg N/day
r Total load - 15 kg N/day
The TMDL evaluation determined that a daily load of 12 kg N/day, a 3 kg
N/day reduction from the current load, was all the river could assimilate
without producing noxious algal blooms that ultimately compromised the
beneficial uses of the river.
The initial plan was to apply best practical treatment (BPT) requirements
to each nitrogen source as part of their Clean Water Act-mandated National
Pollutant Discharge Elimination System (NPDES) permit (Figure 7.15).
However this was very expensive ($13 million) with the bulk of the cost
($10 million) falling on the regional WWTP (Figure 7.16). Yet the reduction in
nitrogen load from the WWTP (1 kg N/day) was only half the total reduction.
The operators of the WWTP felt it was not equitable that they should pay
77% of the cost ($10 million out of $13 million) when they only represented
13% of the problem (2 kg N/day out of 15 kg N/day). Thus, they sought a
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