Environmental Monitoring and Assessment (2005) 101: 23–38
c Springer 2005
EFFICIENCY OF AN INFILTRATION BASIN IN REMOVING CONTAMINANTS FROM URBAN STORMWATER
G. F. BIRCH∗ , M. S. FAZELI, and C. MATTHAI
Environmental Geology Group, School of Geosciences, The University of Sydney, NSW, 2006, Australia (∗ author for correspondence, e-mail: gavin@es.usyd.edu.au)
(Received 19 December 2002; accepted 28 January 2004)
Abstract. The efficiency of a Stormwater Infiltration Basin (SIB) to remove contaminants from urban stormwater was assessed in the current investigation. The SIB, installed in an urban suburb in eastern Sydney (Australia), was monitored over seven rainfall events to assess the removal efficiency of the remedial device for total suspended solids (TSS), nutrients (TP, TKN, Nox , TN), trace metals (Cd, Cr, Cu, Fe, Mn, Ni, Pb, Zn), organochlorine pesticides and faecal coliforms (FC) from stormwater. The weighted average concentration (WAC) of TSS in the stormwater effluent from the SIB was reduced by an average of 50%, whereas the WAC of Cu, Pb and Zn were also reduced by an average 68%, 93% and 52%, respectively. However, the WAC of Cr, Fe, Mn and Ni displays either similar concentrations as the stormwater influent (Cr and Mn), or substantially higher concentrations (Fe and Ni), due possibly to leaching of fine-grained zeolite clay particles in the filtration bed. The mean removal efficiency of the SIB for total phosphorus (TP) and total Kjeldahl nitrogen (TKN) was 51% and 65%, respectively. In contrast, the average WAC of oxidisable nitrogen (nitrate and nitrite nitrogen or Nox ) is about 2.5 times greater in the effluent (1.34 ± 0.69 mg L−1 ) than in the incoming stormwater (0.62 ± 0.25 mg L−1 ). The WAC of total nitrogen (TN) was similar for stormwater at the in-flow and out-flow points. The SIB was very efficient in removing FC from stormwater; and the WAC of almost 70 000 cfu (100 mL)−1 at inflow was reduced to 0.05.
The removal efficiency of organochlorine pesticides and PAHs could not be established from the data because concentrations of these contaminants in the stormwater were below detection for most analytes. Although no work was conducted to quantify the partitioning of trace metals between dissolved and solid phases, it is likely that the majority of trace metals are associated with the suspended particulate matter in the stormwater. This assumption is supported by strong and significant correlations between trace metals and TSS in the stormwater runoff (R2 : 0.44−0.87; p 0.80) in stormwater runoff at the SIB site include Fe:Cr, Cr:Mn, Cr:Ni, Fe:Mn, Fe:Ni and Mn:Ni (Table V).
4. Conclusions The current study has shown that the SIB constructed in Eastern Sydney, is moderately to highly efficient in removing suspended particulate matter and the trace metals Cu, Pb and Zn from stormwater. FC contents in treated stormwater effluent are substantially reduced. In addition, concentrations of TP and TKN (Norg + Nam ) are also moderately reduced by infiltration of stormwater through the SIB filter bed. However, the SIB was ineffective in reducing the concentrations of total nitrogen (TN) in treated effluent, although a conversion of TKN to NOx was observed. Concentrations of Cr, Fe and Ni were higher in stormwater effluent than influent possibly due to leaching of clay minerals from the SIB filter bed, however the concentrations of these elements are only moderately above recommended ANZECC guidelines for freshwater quality.
EFFICIENCY OF AN INFILTRATION BASIN
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Acknowledgements This work was funded by the New South Wales Stormwater Trust and administered and supervised by the New South Wales Environment Protection Authority and Leichhardt Council. The authors thank staff from the latter organisations for their assistance.
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