Environmental Engineering Reference
In-Depth Information
were higher and Cu concentrations significantly higher (t
16
= −3.0, p = 0.009) in
treatment sub-catchments after the E&E program.
Discussion
No reduction in accumulated pollutants was apparent after immersion by storm
flows at the Heatherton sub-catchments on Nov 1 and 15. Although further testing
is required for performance validation, this observation suggests monitoring during
moderate rainfall is feasible.
The association between Cu and catchment age suggests an indirect relationship
with vehicle use. Cu pollution in urban catchments has been linked to vehicle use
[8]
, hence higher Cu concentrations in new sub-catchments may be related to the
prevalence of larger property parcels with bigger car parks.
Increased Cu concentrations after the E&E program in the Settlement treatment
group of sub-catchments was influenced by high Cu concentrations at sub-catchment
S6. Stormwater pipes draining areas outside this sub-catchment were discovered
after sampling had commenced, casting doubt on the boundary integrity of this
sub-catchment. If properties outside the E&E program delivery boundary contrib-
uted stormwater to this outfall, Cu concentrations at S6 may not reflect the E&E
program's performance in this sub-catchment.
The positive association with rainfall and even distribution of Zn concentrations
between sub-catchments suggests the major inputs of this metal were structural
rather than point-source. Galvanized roofing, atmospheric deposition and road
surface materials have all been implicated as sources of Zn in urban runoff
[9, 10]
.
Therefore, more frequent rainfall was a likely factor contributing to increased pol-
lutant concentrations in 2007, particularly Zn.
Although hydrocarbon pollution has been linked with catchment features such
as roads and parking lots
[11]
, diffuse sources cannot reasonably account for the
degree of hydrocarbon pollution observed in this study. TPH pollution was epi-
sodic, with low base loads punctuated by occasional pollution events. This observa-
tion is consistent with poor stormwater management such as machinery wash-down
to stormwater, inadequate work shop waste storage, or even deliberate dumping of
waste oil. The E&E program was specifically designed to address stormwater man-
agement practices. The reduction in TPH concentrations in most treatment sub-
catchments, particularly those with the highest TPH loads, suggests it was at least
partly effective.
The reduction in TPH compared to Zn and Cu suggests that changes in property-
level stormwater management had a greater impact on pollution by hydrocarbons
than heavy metals. The reduction in Zn concentrations in Heatherton and Dunlops
A treatment catchments suggest that changing stormwater management practices
can reduce heavy metal pollution, although not to the same extent as hydrocarbons.
The association of Zn with rainfall is consistent with evidence that structural
features such as galvanized iron roofing can contribute significant quantities of
Zn to stormwater
[9]
. At the time of follow-up sampling not all E&E program
