CTMP Revision 0 Activities in the Auckland Region (GD05) as the Waikato Regional Council (WRC) guidelines do not currently address chemical treatment. Preliminary soil samples and bench testing has been undertaken as part of early site investigations (refer to the Chemical Analysis and Reactivity Test (CART) Report, Appendix A) which indicates significant improvement of clarity and turbidity with the use of chemical treatment. Ongoing soil sampling and bench testing will also be required as the earthworks progress. In this regard protocols have been established and are set out in Section 5. Any sampling for bench testing of sub-soils (below topsoil) that is necessary will be taken from the contributing catchment of sediment controls devices to determine the optimum chemical response and dosing rate, balanced within an acceptable pH range. Ongoing sampling will also be required as the earthworks progress. Bench tests of soil samples will be undertaken using the following two chemicals supplied by IXOM Chemicals: 1. Polyaluminium Chloride (PAC - [Al(OH)aClb(SO4)c]n), The most common chemical widely used throughout New Zealand, a polymer originally tested and documented by the Auckland Regional Council during the construction of the ALPURT motorway extension development1. 2. Superfloc – A blench of PAC and PolyDADMAC (Polydiallyldimethylammonium chloride– [C8H16NCl]n). GD05 states the recommended chemical and dose rate will be that which achieves the best settlement rate within the acceptable pH range of 5.5 to 8.5 and will not change the baseline pH beyond +/-1. To align with the conditions of consent the pH range, 6.0 to 9.0 will be adopted as part of this Project. 3 Implementation The CART Report provided in Appendix A confirms the efficacy of chemical treatment of typical site soils, based on the testing methodology described below and in the CART. A SSESCP will be prepared for each works area. Each SSESCP will identify and provide the sizing calculations and drawings for all ESC measures to be implemented in the corresponding area. Once a SSESCP has been certified by WRC, the ESC measures will be constructed in that works area. If the works are within an area or soil type already sampled and reported on in the CART, the chemical treatment systems will be initially set up based on the CART recommendations. If the works area is not within the extent of the CART report, additional soils sampling and bench testing will be undertaken in accordance with this CTMP. Confirmation of the recommended chemical, dose rates, roof tray sizes and header tank outlet spacings for each device will be submitted to WRC with the as-built certification of the devices and Appendix D of this CTMP will be updated with the recommended dose rates for that SSESCP area. The relationship of the various management plans and procedures that apply to the chemical treatment system is shown in Figure 1. 1 Auckland Regional Council Technical Publication 227 – ‘The Use of Flocculants and Coagulants to Aid the Settlement of Suspended Sediment in Earthworks Runoff : Trials, Methodology and Design’ June 2004
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