Manly Lagoon Dredging Project - Manly Council - NSW Government

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Manly Lagoon Dredging Project – Review of Environmental FactorsPrepared for Manly and Warringah Councilsanalyses requested, with the exception of enterococci tests in soil. These tests were doneusing the ASTM D6503-99 Standard Test Method for Enterococci in Water Using Enterolert,and all controls passed the appropriate quality control tests (Cardno Ecology Lab, 2009c).3.3.2 Testing of Runoff WaterTwo samples of the runoff water resulting from dewatering of the sediment and a ‘reference’lagoon water sample were analysed for the following parameters, as listed in CardnoEcology Lab (2009c): Physical Parameters, including Total Dissolved Solids, Total Suspended Solids(TSS) and pH; Total Metals, including Arsenic (As), Cadmium (Cd), Chromium (Cr), Copper (Cu),Lead (Pb), Nickel (Ni), Zinc (Zn) and Mercury (Hg); Nutrients, including Total Nitrogen (TN), Total Phosphorus (TP) and other nitrogenspecies; Pesticides, including organochlorine and organophosphorous pesticides; Phenolic Compounds; PAHs; BTEX; TPHs, including TPH (C6 – C36); and Enterococci.A single ‘reference’ water sample was collected prior to any disturbance from the backhoe,from within the silt curtains to provide a sample showing levels of the various parameterslisted above prior to disturbance (Cardno Ecology Lab, 2009c).The first runoff water sample (‘first flush’) was collected during initial filtration through thegeotextile bag. The second runoff water sample (‘second flush’) was collected towards theend of the filtration processes and hence represents the runoff once the dewatering processhas stabilised (Cardno Ecology Lab, 2009c). All water samples were also dispatched to ALSlaboratories.3.3.3 Trial Dredging ResultsComprehensive results of water and sediment/ASS testing can be found in Tables 1 and 2respectively in the full Cardno Ecology Lab (2009c) report (Appendix C).The results from Trial Dredging 2, using polymer ULTIMER 7757 at 25ppm, indicated thefollowing (Cardno Ecology Lab, 2009c):SedimentsAll metal species in untreated and treated samples were below their respectiveNAGD (1999) levels (i.e., unlikely to cause biological effects), and below investigationlevels for use in recreational open space;Fluoride was reduced in treated sediments compared to untreated sediments;2 July 2010 Cardno (NSW/ACT) Pty Ltd 26H:\Doc\2010\Reports.2010\Rep2580v4.doc
Manly Lagoon Dredging Project – Review of Environmental FactorsPrepared for Manly and Warringah CouncilsCyanide, styrene, naphthalene, phenolic compounds, benzene, toluene and relatedcompounds could not be detected in either treated or untreated sediments;Organochlorine and orthophosphate pesticides and PCBs could not be detected ineither treated or untreated sediments; andTPHs were detected at very low levels, which were, in total an order of magnitudebelow the guideline for use on open spaces.Acid Sulfate SoilsSediments have the potential to produce acid run off and would require a liming rateof 10 kg per tonne dry weight to neutralise acidity. It should be noted that this is alower rate than reported by Patterson Britton and Partners (Appendix E).Runoff WaterSecond flush water showed a 22% decrease in suspended solids compared to firstflush water, indicating that the geobag and ULTIMER 7757 polymer functioned asintended;Suspended solid levels of 171 mg/L in the overburden water were significantly higherthan those in the undisturbed water column, and appropriate mitigation measures,including discharge in a controlled manner within the area of the silt curtains areincluded in Section 5.3. Data on the effects of suspended sediments on estuarinefish suggest that levels greater than 600 mg/L may cause fish mortality (Wilber andClark 2001), and hence 171 mg/L of suspended solids in the overburden water isunlikely to negatively impact on estuarine fish species;The concentrations of metals did not differ significantly in the first flush compared tosecond flush samples, but were higher compared to the reference sample for allmetals (Appendix C). This indicates that sediments were significant sources of allmetals except copper, which was present in both water and sediments. Residualmetal levels exceeded ANZECC (2000) guidelines for chromium, copper, lead andzinc. However, this was also the case for some of the results obtained during waterquality monitoring in July to September 2009 at various locations within the lagoon(see Appendix H);Concentrations of Ammonia, Nitrite and Nitrate (NOx), TN and TP were similar toresults obtained during water quality monitoring in July to September 2009 at variouslocations within the lagoon (see Appendix H), however levels exceeded ANZECC(2000) guidelines for protection of aquatic ecosystems for slightly disturbedecosystems. Comparison to the reference sample indicates that sediments were asignificant source of nutrients for most nutrient parameters;Organochlorine and organophosphorous pesticides, phenols, PAHs and BTEXcompounds were not detected in either first flush or second flush water;Second flush water had 29% lower levels of enterococci bacteria compared to firstflush water, indicating that the flocculant acted to reduce enterococci that weresuspended in the dredge slurry. However, residual bacterial counts exceededguidelines for both primary and secondary contact. Results for enterococci levels in2 July 2010 Cardno (NSW/ACT) Pty Ltd 27H:\Doc\2010\Reports.2010\Rep2580v4.doc
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Manly Lagoon Dredging Project - Manly Council - NSW Government

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