Manly Lagoon Dredging Project - Manly Council - NSW Government

Manly Lagoon Dredging Project – Review of Environmental FactorsPrepared for Manly and Warringah Councilsof 125-500 microns) and well sorted (PBP, 2002). Surface samples from Burnt Bridge Creek(near its confluence with the Lagoon) comprised clean medium grained sands (PBP, 2003a).Table 5.2: Textural Properties of Sediment Samples from Vibrocores from within Manly Lagoon (After:PBP, 2002)Core Name andSample Depth*Description of Core Location % Gravel % Sand % Mud1/9 200-1000^ Nolan Reserve Trash rack 0.0 45.6 54.41/9 1550-2500 Nolan Reserve Trash rack 0.0 87.3 12.71/10 0-490^ End of Campbell Parade 0.0 100.0 0.01/10 490-1500^ End of Campbell Parade 0.0 34.1 65.91/11 0-700^ Adjacent to Manly Vale Bowling Club 0.0 65.8 34.22/5 200-600^ End of Riverview Parade 0.0 71.3 28.72/5 600-1350 † End of Riverview Parade 0.0 93.9 6.12/5 1350-2150 End of Riverview Parade 0.0 91.2 8.82/7 400-1100^ Upstream of Riverview Parade 0.0 65.3 34.72/7 1100-2000 Upstream of Riverview Parade 0.0 71.3 28.72/7 2000-2500 Upstream of Riverview Parade 0.0 93.1 6.9AVERAGE % BY WEIGHT OF ALL CORES 0.0 74.4 25.6AVERAGE % BY WEIGHT OF SELECTED CORES^ 0.0 63.7 36.6* The sample depth is expressed as the depth increment (mm), measured from the top of the core, over whichthe sample was taken.^ These cores samples are the ‘selected cores’ used for the second average calculation and can be consideredindicative of material that is to be dredged i.e. generally from the 0 to 1200mm depth range.† This core sample was not included in the ‘selected cores’ as it is not considered to be indicative of material tobe dredged, since dredging profiles in Appendix J show that approximately 500mm of material is to be removedat this location.It should be noted that calculations and dredging plans (Appendix J) show 97% of materialto be removed will be from the upper 1m of accumulated sediment, with the remaining 3%being from the 1-1.2m depth range.Acid Sulfate Soils (ASS)Potential acid sulfate soils (PASS) are naturally occurring soils containing iron sulfides(pyrite). They become ASS when they are dried, and the pyrite is exposed to air. In air, pyriteis oxidised, resulting in production of sulfuric acid (DECC, 2009a).An Acid Sulfate Soils Risk Map was generated using the NSW Government’s NaturalResource Atlas on 20 July 2009. According to this map, shown in Figure 5.1, there is a highprobability of occurrence of acid sulfate soils within Manly Lagoon. The map is supported byanalysis of samples collected in 2001, which identified collected sediments as having an acidsulfate generation potential (PBP, 2002).2 July 2010 Cardno (NSW/ACT) Pty Ltd 43H:\Doc\2010\Reports.2010\Rep2580v4.doc