Development Application part 2 OF 2 All of CD, Information in notes - MCU12/0216

CSR Building Products Limited                                                                                                  Page 19
West Ridge Quarry
Site Based Management Plan


3.1.3        Implementation Strategy/Mitigation Measures
      Land disturbance is to be minimised to that which is absolutely necessary.
      Land disturbance is to be minimised during periods of high soil erosion risk (December to March), where practicable.
      Any vegetation clearing is to be staged as far as practical in line with the proposed extraction sequence.
      Conceptual Stormwater and Sediment Control Plans for the proposed quarry development are provided as Figure 9 –
      Conceptual Stormwater and Sediment Control Plan.
      The stormwater control principles for the system comprise of:
      -   a general philosophy that any overland flow from disturbed areas is considered to be contaminated with
          sediment/suspended solids, therefore requires treatment prior to release;
      -   capturing overland flows from the disturbed areas within the quarry area in the quarry pit, sediment basin or
          sediment trap for treatment by settlement prior to discharging (pumped or naturally) as concentrated flow into an
          adjacent drainage line or re-use for irrigating on the surrounding pasture land;
      -   designing the extraction pit to retain overland flow up to and including a 24 hour, 5-year annual recurrence
          interval (ARI) event;
      -   constructing all stormwater drainage works to meet 1-in-10 year peak flow design standard;
      -   managing stormwater by use of preventative procedures such as using a perimeter bund and diversion banks,
          containment, gravel filters, recycling, treatment and by use of corrective procedures such as maintenance, de-
          silting and revegetation of disturbed areas;
      -   diverting overland flow from clean catchments around and away from disturbed areas to the extent practicable
          using a diversion bank and natural contours where practicable;
      -   directing overland flow from paved or gravelled hardstand areas to a settling pit and gravel filter prior to
          discharging into the adjacent drainage pathway;
      -   constructing internal access and haul roads with an in-fall drainage is the preferred method, however out-fall
          drainage will be utilised where the road runoff can sheet evenly off the road;
      -   installing cross drainage structures within haul roads wherever reasonable and practicable to allow stormwater to
          shed from sloped unsealed access roads/ramps at regular intervals (typical spacing approximately 15 m for
          gradients of greater than 8%);
      -   maintaining similar water velocities through any temporary watercourse or diversions around a work area to pre-
          work velocities during such diversions, and must be re-instated once quarrying is completed.
      Various options of low-gradient techniques that may be used on-site are provided in Table 10 – Low Gradient
      Drainage Techniques below.

                                             Table 10 – Low Gradient Drainage Techniques

Technique                          Symbol    Typical Use
Catch Drain                        CD            The catchment and diversion of sheet flow across a slope or around soil disturbance.
                                                 Best used in non-dispersive soils, otherwise the drain must be lined with non-
                                                 dispersive soil (minimum 100 mm thick) prior to placement of a channel liner.
Diversion Channel                  DC            Diversion of large concentrated flows.
                                                 Permanent flow diversion channels.
Flow Diversion                     DB / PB       Diversion of minor flows when in situ subsoils are dispersive or otherwise highly
Banks/Perimeter Bund                             erodible.
(earth, sandbags, etc)                           Flow diversion at the base of hill slopes.
                                                 Cross drainage on unsealed roads.
Chute                              CH            Discharge of concentrated flows down steep slopes.
                                                 Control of flow into sediment basins.
Level Spreader                     LS            Conversion of minor flows back to ‘sheet’ flow.
                                                 Discharge of ‘sheet’ flows down grassed slopes or into bushland.

Stormwater Contamination Management
      Measures to be taken to minimise the potential for contamination of stormwater overland flow from Site are as follows:
      -  constructing access road(s) to freely drain at or near ground level using compacted base coarse, where
         necessary;


December 2012 / file ref. 1271_610_001                                                                              GROUNDWORK p l u s