Manly Lagoon Dredging Project - Manly Council - NSW Government

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Manly Lagoon Dredging Project – Review of Environmental FactorsPrepared for Manly and Warringah CouncilsParameter(s)Water Quality andHydrologyMitigation Measures› Any disturbed areas on the lagoon banks should be remediated at theearliest possible opportunity to minimise dust generation;› All heavy vehicles and machinery should be regularly maintained tominimise exhaust emissions;› An Odour Management Plan should be prepared for the proposed works,incorporating a communication strategy with potentially affected residentsand a range of mitigation measures as a contingency measure in the eventthat odour is generated during the dewatering process;› Regular, subjective monitoring of odour will be undertaken by the sitesuperintendent or an independent external person. This will consist of dailychecks at three local receptor locations, with the results of all observationsbeing maintained in a log.› Prior to the commencement of works, a complaints telephone line dedicatedto taking calls from the public will be established, and will be advertised tolocal residents and by the use of site signage.› The ESCP will mitigate any impacts associated with sedimentation ofdownstream water area within Manly Lagoon using silt curtains. Primary siltcurtains will be implemented approximately 25m upstream and downstreamof the area where dredging works are taking place, across the full profileand depth (at high tide) of the Lagoon, to prevent the movement of anydisturbed silt outside the works area. In addition, a secondary downstream‘back-up’ silt curtain will be deployed approximately 15m downstream of theprimary curtain;› Silt curtains will be designed to be able to withstand a 5 year ARI floodevent, however the design shall also consider any circumstances underwhich the silt curtains may need to be removed to allow passage of floodwaters;› Full scale dredging will be preceded by a controlled ‘calibration period’,during which dredging will be undertaken for short periods in which allimpacts are carefully observed. Before full dredging can proceed, thecontractor must demonstrate that the process is operating as designed, thatall mitigation measures are working as intended, and that the resultingwater and treated sediment quality is as expected (Section 2.6);› An approved contractors work method statement must be in place prior tothe commencement of dredging;› Measures should be in place to contain overburden water from thedewatering process until testing has confirmed the water is acceptable forreturn to the lagoon;› Containment of overburden water within the bund should provide forexposure of the water to sunlight in order to promote die-off of anyEnterococci present within the water;› No water will be returned to the lagoon until testing has confirmed that thewater has a pH in the range of 7.0-8.2, and that the turbidity has fallen to alevel shown by regression analysis to be equivalent to 50mg/L suspendedsolids. (Section 5.3.1);› Overburden water must be discharged back into the lagoon through a pipeand in a controlled manner to minimise turbidity and erosion at the point ofdischarge;› A Water Management Plan should be prepared incorporating the WaterQuality Monitoring Program pre, during and post dredging to be undertaken2 July 2010 Cardno (NSW/ACT) Pty Ltd 116H:\Doc\2010\Reports.2010\Rep2580v4.doc
Manly Lagoon Dredging Project – Review of Environmental FactorsPrepared for Manly and Warringah CouncilsParameter(s)Mitigation Measuresby Cardno Ecology Lab (2010);› Should any significant increase in nutrient levels, or visual evidence ofincreased algal growth be observed in the lagoon, dredging works willcease until findings have been reviewed and management plans, workinstructions and mitigation measures have been amended as required;› The potential impact of fuel spills, polymer or lime spills at the proposed siteshould be managed by conducting the refuelling of machinery and thedosing and liming of dredged material in defined bunded areas only;› All materials including fuel, oil, polymer and lime are to be securely storedwithin a bunded area which prevents the possibility of release followingvandalism;› In relation to bunding and containment, the contractor will be required toensure that:oooooooooAll bunds will be constructed such that the minimum crestheight is at 2.3m AHD (shown by the Manly Lagoon FloodStudy to correspond to the 5 year ARI (MHL, 1992));All bunds must be sufficiently strong to withstand flood flows;The bunds will be adequate in terms of size and strength tohold the sediment and water if the bags break;The area inside the bunds is of a sufficient size to hold thewater and the geobags;The bunds can hold the water for long enough to wait for theresults of any required laboratory analysis to be returnedfrom the laboratory;In order to ensure exposure of any enterococci in the bundwater to sunlight, the bunds will be sited away from shade,and the depth of water within the bunds will be maintained ata level which allows penetration of sunlight;The bags, and all associated infrastructure can withstandexpected pH levels;The potential for spontaneous combustion in the bags hasbeen fully considered;Any processes likely to be initiated while the sediment/wateris in the bag that may affect the quality of the water or thesediment (for example, water becoming deoxygenated priorto release back into the lagoon, etc) have been fullyconsidered.› In the event of a significant spill in a non-bunded area, a spill kit should bedeployed and DECCW representatives should be advised immediately. TheHazards Management Plan should contain details on how to manageaccidental spills on site and the employed method of clean up for accidentalspills of ULTIMER 7757 must be in accordance with the methods prescribedin the Product Safety Data Sheet (Appendix I).› In the event that any flood or spill event occurs which may lead to adeterioration in water quality, the closure of Queenscliff beach (locateddownstream) will be considered as a precautionary measure;› The dredging plans in Appendix J have been developed to remove thevolume of sediment which has accumulated since the MHL (1992) survey.This ensures that the material to be removed is comprised solely ofsediments which have accumulated by natural processes since this date,and thereby significantly reduces the likelihood that contaminated sediment,2 July 2010 Cardno (NSW/ACT) Pty Ltd 117H:\Doc\2010\Reports.2010\Rep2580v4.doc
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Manly Lagoon Dredging Project - Manly Council - NSW Government

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