Manly Lagoon Dredging Project - Manly Council - NSW Government

Manly Lagoon Dredging Project – Review of Environmental FactorsPrepared for Manly and Warringah Councilswater samples collected on 30 July 2009, as part of the water quality monitoringprogram (Cardno Ecology Lab, 2010; Appendix H) indicated a large range in values(61 to 2433 CFU/100mL), with the higher values being upstream of the trial location;Interpretation of the PBP (2007) report, and practical experience whilst working in thelagoon suggests that the amount of fine material with which metals, nutrients andbacteria (i.e. enterococci) are associated is likely to be greatest in the uppersediment layers such as those removed during the dredging trial, while the actualdredging program will remove sandier sediments to a depth of up to 1.2m. Hence theresults of the dredging trial are likely to show higher concentrations of the parametersassociated with the fine materials than we expect to be encountered during the actualdredging program; andResidual flocculant in dredge spoil is characterised as having low potential humanhazard. It is not classified as hazardous or carcinogenic, nor are any of its ingredients(Nalco, 2009).In summary, the Trial Dredging 2 report concluded that the treated dredge spoil from the trialwas chemically suitable for application to land and that the overburden water collected fromthe geobags during dewatering would not cause any identifiable environmental harm ifreturned to Manly Lagoon in a controlled manner. The trial concluded that the dredgedsediments from the lagoon will require dosing with lime to neutralise acid sulfate potential(Cardno Ecology Lab, 2009c). There are other parameters that were not tested, includingsalinity and the presence of gross pollutants, which may affect the suitability of the treateddredge spoil for land application.2 July 2010 Cardno (NSW/ACT) Pty Ltd 28H:\Doc\2010\Reports.2010\Rep2580v4.doc