Flocculent Treatment Management Plan
4.
Dosing options 4.1 Introduction
There are three main forms of dosing: Rainfall Activated; Flow Activated; and Batch Dosing. In the rainfall activated process during rainfall the dosing system is automatically activated by rainfall to provide the appropriate volume of additive to the sediment laden surface runoff. In the flow activated process the dosing system is automatically activated by flow (typically pumped) to provide the appropriate volume of additive to the sediment laden inflows. The batch dosing process is typically undertaken to treat an impounded volume of sediment laden water, typically as the result of pumping. This is a manual process where the volume of impounded water is determined and from this the appropriate volume of additive determined, added and mixed. The sampling and testing of soils detailed in Section 3 of this FTMP will be utilised to determine the appropriate chemical and dose rate.
4.2 Rainfall activated dosing 4.2.1. Introduction Rainfall activated dosing will be utilised where the sediment retention devices receive runoff as a gravity surface flow. This system will typically be used in the early stages of the works with a transition to flow activated dosing as the excavation progresses and gravity surface flow decreases. The flocculation systems to be used will be designed in accordance with GD05. The basic design will be a rainfall activated system (typically) using Polyaluminium Chloride (PAC) to dose the Sediment Retention Pond (SRP). The layout of a typical PAC Rainfall Activated System is shown in Figure 4-1 below.
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