Acid Sulfate Soils & Dewatering Management Plan, plus Groundwater Monitoring

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MDW Environmental Services was engaged to complete an Acid Sulfate Soil (ASS) and Dewatering Management Plan (DMP) to manage Potential Acid Sulfate Soil (PASS) and dewatering issues arising during the replacement of a 210m section of sea wall in the Perth metropolitan area.

An ASS investigation was completed to determine whether or not ASS was present. Seven soil cores at a depth of 4.5 metres along the site were taken. Results indicated there was Potential ASS onsite; therefore management procedures were put in place to ensure there was no environmentally significant adverse impact to receiving waters resulting from the disturbance, treatment, and reuse of ASS/PASS materials.

Dewatering was required to keep the site dry so construction could take place. Throughout the dewatering process, daily monitoring and weekly sampling was completed on both discharge points. Samples were taken to a NATA accredited laboratory for analysis.

All field monitoring and analysis was compared against ANZECC Freshwater Ecosystem trigger values and DEC trigger values. Where laboratory results exceeded the corresponding trigger values appropriate treatment was put in place to ensure water was managed appropriately.

Excavations were placed in a limestone bund before being removed and treated at a licensed treatment facility. Soil was treated as per the ASS DMP.

Results of all monitoring conducted during the sea wall construction were successful in minimising the effect on the surrounding environment.