PO.Box 1098, Bowral, NSW. 2576
Bowral NSW 2576.
AutoCAD SHX Text
IMPLEMENTATION OF EROSION AND SEDIMENT CONTROLS Works must be staged in the following order with the relevant erosion and sediment controls implemented prior to and during each phase of works as specified. Before commencement of clearing, topsoil stripping and earthworks in each phase of works, the site must be secured and the following erosion and sediment control measures installed in order except for Items marked (P) which must be undertaken progressively as required throughout all stages of works. Stripping and earthworks necessary to install the erosion and sediment controls are permitted but must be kept to a minimum. PHASE 1 – CONSTRUCTION ACCESS CONSTRUCTION ACCESS 1. Work on the Waste Rock Emplacement (WRE) must not begin until the Spring Work on the Waste Rock Emplacement (WRE) must not begin until the Spring Creek Haul Road is constructed; refer to SEEC Drawings 17000009-P02-ESCP-01 to ESCP11 for Erosion and Control requirements during those works. 2. Barrier fencing (or alternative measures) must be in place around the edge Barrier fencing (or alternative measures) must be in place around the edge of the construction boundary to restrict access and in any additional locations as required to minimise unnecessary disturbance - Refer to the 'Access Control' notes overpage. 3. Install sediment fence where shown and to the requirements of SD 6-8 and Install sediment fence where shown and to the requirements of SD 6-8 and the Sediment Fence Notes. 4. Install upslope clean water diversion drains where shown and following SD Install upslope clean water diversion drains where shown and following SD 5-6, stabilise the lands when done (Refers to options in Table 1). 5. Install the piped culvert that must take flow in clean water diversion drain Install the piped culvert that must take flow in clean water diversion drain CD7 (ESCP-05) where shown as early works, stabilise the works area when done (Table 1). 6. Begin construction of the access to the WRE and to the topsoil stockpile Begin construction of the access to the WRE and to the topsoil stockpile area. 7. Strip and stockpile soil to the requirements of the Soil Stripping and Strip and stockpile soil to the requirements of the Soil Stripping and Stockpiling Notes. 8. If significant rain is forecast (>50% chance of <10mm in 24 hours) install If significant rain is forecast (>50% chance of <10mm in 24 hours) install slope breaks at 25 m spacing on the disturbed subgrade and divert flow into U-Shaped sediment traps (refer to SD-UST-1 and SD-UST-2 on ESCP 10). 9. Construct the access roads and their drainage to the Engineer’s details. Construct the access roads and their drainage to the Engineer’s details. s details. Table drains must be installed on both sides of the roads and they must terminate in mitre (turn out) drains installed at 25m spacing. 10. Dust suppression to be carried out when required (Refer to the 'Dust Dust suppression to be carried out when required (Refer to the 'Dust Suppression' notes)(P). 11. Monitoring, Maintenance and inspections must be carried out regularly as Monitoring, Maintenance and inspections must be carried out regularly as required and in accordance with the 'Site Inspection and Monitoring' notes (P). 12. Stabilise all works areas when done; refer to the Stabilisation Notes, Table Stabilise all works areas when done; refer to the Stabilisation Notes, Table 1, SD 4-2 and SD 7-1 (P). 13. Temporary sediment structures and temporary diversion drains may be Temporary sediment structures and temporary diversion drains may be removed when the lands are stablilised to the requirements of Table 1. PHASE 2 – INSTALL DIVERSION DRAINS AND TEMPORARY SEDIMENT BASIN (WRES3) . INSTALL DIVERSION DRAINS AND TEMPORARY SEDIMENT BASIN (WRES3) . 1. Undertake the works in the following order. Undertake the works in the following order. 2. Install barrier fence to delineate the works area; refer to the Access Notes Install barrier fence to delineate the works area; refer to the Access Notes below. 3. Install clean water drains CD1, CD2, CD3, CD6 and CD7 where shown on Install clean water drains CD1, CD2, CD3, CD6 and CD7 where shown on ESCP-05 and to the requirements of SD 5-6 and Table 3. 4. Install a structure to equally split flow into the joint beginnings of CD6 and Install a structure to equally split flow into the joint beginnings of CD6 and CD7 (Location “X” on ESCP-05). X” on ESCP-05). on ESCP-05). 5. Install level spreaders at the ends of clean water drains to the Install level spreaders at the ends of clean water drains to the requirements of SD 5-6. 6. Install sediment fence where shown on ESCP-05 to the requirements of SD Install sediment fence where shown on ESCP-05 to the requirements of SD 6-8 and the Sediment Fence Notes next sheet. 7. Install WRESB3 where shown on ESCP-05 and build its inlet and outlet Install WRESB3 where shown on ESCP-05 and build its inlet and outlet structures (refer to the 'Sediment Basin Management' notes below). 8. Install the dirty water drains D19 and DD10 where shown on ESCP05 and Install the dirty water drains D19 and DD10 where shown on ESCP05 and connect them to WRESB3. 9. When all the above works are installed, and the disturbed lands are When all the above works are installed, and the disturbed lands are stabilised to the required c-factor or % groundcover (Table 1), work on WRESB1 may begin (Phase 3) PHASE 3 – WRESB1 WORKS WRESB1 WORKS 1. Begin stripping the footprint of WRESB1 following the Soil Stripping and Begin stripping the footprint of WRESB1 following the Soil Stripping and Stockpiling Notes. 2. Ensure all dirty water is diverted to WRESB3. The sediment basin must be Ensure all dirty water is diverted to WRESB3. The sediment basin must be managed per the Sediment Basin Management Notes; dirty water trapped in WRESB3 must be managed per the Dirty Water Discharge Notes. 3. If works are being done between the months of October to March (inclusive) If works are being done between the months of October to March (inclusive) then special erosion control measures are required. If significant rain is forecast (>50% chance of <10mm in 24 hours) then all disturbed lands must be “locked down” by applying soil binder (e.g. Vital Stonewall or equivalent) locked down” by applying soil binder (e.g. Vital Stonewall or equivalent) by applying soil binder (e.g. Vital Stonewall or equivalent) at the manufacturer’s recommended rates. s recommended rates. 4. Note the requirement of Item 3 above is required all year on the Note the requirement of Item 3 above is required all year on the downstream face of WRESB1, notwithstanding the requirements, also, of Item 8 below. 5. The downslope face of WRESB1 must be stepped to form slope breaks at no The downslope face of WRESB1 must be stepped to form slope breaks at no more than 8 m spacing. Alternatively, install fibre rolls to break up the slope at 8m spacing (SD FR-01). 6. Dust suppression must be carried out when required (Refer to the 'Dust Dust suppression must be carried out when required (Refer to the 'Dust Suppression' notes)(P). 7. Monitoring, Maintenance and inspections must be carried out regularly as Monitoring, Maintenance and inspections must be carried out regularly as required, in accordance with the 'Site Inspection Monitoring and Maintenance' notes (P). 8. Undertake progressive stabilisation of lands as final earthworks are Undertake progressive stabilisation of lands as final earthworks are complete in each area rather than waiting until the completion of works. Final stabilisation must be completed in accordance with the 'Stabilisation' notes, Table 1, SD 4-2 and SD 7-1 (P). 9. WRESB3, its dirty water drains and its associated sediment and barrier WRESB3, its dirty water drains and its associated sediment and barrier fences may be removed when WRESB1 and its batters are complete and stable. PHASE 4 - WASTE ROCK EMPLACEMENT AREA - SITE PREPARATION Before commencement of stripping and earthworks the following erosion and sediment control measures must be installed in order except for Items 11 to 15 which are to be undertaken progressively as required throughout all stages of works (Refer to the Monitoring and Maintenance notes): 1. Establish a site office, toilet and parking area (alternatively existing Establish a site office, toilet and parking area (alternatively existing amenities can be used). 2. Barrier fencing must be installed around the edge of the construction Barrier fencing must be installed around the edge of the construction boundaries to restrict access and in any additional locations as necessary to minimise unnecessary disturbance. Refer to the 'Barrier Fencing' notes below. Delineate only those lands to be disturbed for the upcoming stage of waste rock emplacement. 3. Establish sediment fencing in the locations shown and following Standard Establish sediment fencing in the locations shown and following Standard Drawing SD 6-8 (Refer to the 'Sediment Fencing' notes). 4. Prior to stripping topsoil, gypsum is to be spread evenly over the ground Prior to stripping topsoil, gypsum is to be spread evenly over the ground surface at a rate of 5 tonnes/ha to be stripped up with the topsoil (Refer to the 'Soil Treatment and Stabilisation' notes). 5. Depending on the lift, dirty water diversion drains DD1 (A,B & C) and DD2 Depending on the lift, dirty water diversion drains DD1 (A,B & C) and DD2 (A,B & C) are to be formed and stabilised (Refer to Table 3 for all sizing and lining specifications). Energy dissipaters are to be installed at the outlets (Refer to Detail 2). (Refer to Drawing 17000009_P01_ESCP06 for locations and to Standard Drawing SD 5-4 for construction details). 6. The temporary waterway crossing within DD2-B is to be installed in The temporary waterway crossing within DD2-B is to be installed in conjunction with the construction of this drain and in accordance with Standard Drawing 5-1. 7. Establish the stockpile area within the location specified and following Establish the stockpile area within the location specified and following Standard Drawing SD 4-1 (Refer to the 'Soil Stripping & Stockpiling' notes). 8. Earthworks can now commence for the stage. Stockpile topsoil and subsoil Earthworks can now commence for the stage. Stockpile topsoil and subsoil separately and in accordance with the requirements on Standard Drawing SD 4-1 and the 'Stockpiling' notes next sheet. 9. Disturbed lands that grade more than 6% must be temporarily stabilised Disturbed lands that grade more than 6% must be temporarily stabilised with soil binder (e.g. Vital Stonewall) or other temporary ground cover if rain is forecast (more than 50% chance of more than 10mm in 24 hours), even if they are to be re-worked. To reduce the need for temporary stabilisation, minimise disturbed areas as much as possible by only removing grass and stripping soils for each lift of the rock emplacement. 10. Slope lengths across disturbed lands to be maintained at <80m during all Slope lengths across disturbed lands to be maintained at <80m during all rainfall events (Refer to SD5-5). 11. Dust suppression to be carried out when required (Refer to the 'Dust Dust suppression to be carried out when required (Refer to the 'Dust Suppression' notes)(P). 12. Treatment of dirty water is to be carried out as necessary in accordance Treatment of dirty water is to be carried out as necessary in accordance with the Sediment Basin Management and the other dirty water management' notes (P). 13. Monitoring, maintenance and auditing is to be carried out regularly as Monitoring, maintenance and auditing is to be carried out regularly as required, in accordance with the 'Site Inspection Monitoring and Maintenance' notes and the CEMP (P). 14. Apply soil binder to final exposed landform and re-apply ever 3 months. Apply soil binder to final exposed landform and re-apply ever 3 months. WASTE ROCK EMPLACEMENT 1. Once the Waste Rock Emplacement Area is prepared and all phases 1 to 4 are Once the Waste Rock Emplacement Area is prepared and all phases 1 to 4 are complete, waste rock may be brought in. 2. The notes 2 to 14 under “Waste Rock Emplacement Area - Site Preparation” The notes 2 to 14 under “Waste Rock Emplacement Area - Site Preparation” Waste Rock Emplacement Area - Site Preparation” generally apply. 3. Waste rock placement is to occur in three lifts - refer to Drawings Waste rock placement is to occur in three lifts - refer to Drawings 17000009_P01_ESCP06 to ESCP08 for lift footprints. 4. As waste rock is placed, grade the surface away from the embankment face so As waste rock is placed, grade the surface away from the embankment face so that water does not drain down it. 5. To facilitate this, place a stabilised windrow of soil along the top of the To facilitate this, place a stabilised windrow of soil along the top of the embankment (Refer to Table 3 - DB for details). This should be in place for the duration of the works. 6. Place waste rock in a manner that quickly reduces, and maintains, slope gradients Place waste rock in a manner that quickly reduces, and maintains, slope gradients to less than 6%. Disturbed lands that grade more than 6% must be stabilised with soil binder (e.g. Vital Stonewall) or other temporary ground cover if rain is forecast (more than 50% chance of more than 10mm in 24 hours), even if they are to be re-worked. 7. Ensure all dirty water drains to the sediment basin. Temporary dirty water drains Ensure all dirty water drains to the sediment basin. Temporary dirty water drains will be formed by the fill. Connect them to DD1 (A,B,C) & DD2 (A,B,C,). 8. Progressively stabilise the active embankment faces (batters) as the fill proceeds; Progressively stabilise the active embankment faces (batters) as the fill proceeds; Refer to Table 1 for options and timing. 9. As Lift 1 is completed and Lift 2 begins, Lift 1 will begin rehabilitation; although As Lift 1 is completed and Lift 2 begins, Lift 1 will begin rehabilitation; although stabilisation of the active embankment face is to be progressively undertaken - refer to Note 15. 10. As Lift 2 is completed and Lift 3 begins, Lift 2 will begin rehabilitation; although As Lift 2 is completed and Lift 3 begins, Lift 2 will begin rehabilitation; although stabilisation of the active embankment face is to be progressively undertaken - refer to Soil Treatment & Stabilisation Notes. 11. All access to the waste rock emplacement area must be confined within the All access to the waste rock emplacement area must be confined within the designated footprint. ACCESS CONTROL ACCESS CONTROL Install barrier fences or suitable administrative controls to define project works and clearing limits. Barrier fencing can simply be made from tape wound around star pickets or stakes. Alternatively, sediment fence, site fence or chain wire fences can be used for this purpose if so desired. Existing site fences can also be used where they are present in the relevant locations. Barrier and sediment fencing must be used to ensure that all vehicles entering and leaving the site pass over a stable access point to minimise bogginess in these areas and minimise sediment tracking. Barrier fencing must be used to delineate all 'no go' areas. Barrier fencing must be used at the discretion of the site manager to delineate other 'no go' areas. The soil erosion hazard on the site must be kept as low as practicable by minimising land disturbance. Some ways of doing this are outlined in Table 2. All access must be via the Haul Road. SOIL STRIPPING AND STOCKPILING Ideally, strip topsoil when it is moist, not too wet or too dry. Take care when stripping topsoil not to strip subsoil with the topsoil profile. Topsoil and subsoil should be managed separately. Stockpile areas must be established within approved locations and as specified by the site manager. Stockpiles must be established and maintained in accordance with SD 4-1 (ESCP09). Mulched vegetation, topsoil and subsoil must be stockpiled separately. Sediment fencing must be installed around the lower edge of stockpiles as per SD 4-1, unless the stockpile is immediately adjacent to a suitable alternative control such as a sediment basin. A diversion drain/bund must be installed on the high side of stockpiles if run-on from upslope lands could impact on the stockpile. Stockpiles are not to be positioned within 5m of possible concentrated water flow (includes table drains). Stockpiles must be sited at least 50m from any watercourse, natural drainage line or creek and at least 2m from any trees to be retained. Stockpiles must not be located on flood prone lands below the 2-year flood level. Stockpiles must be positioned within the approved project construction boundary and away from protected areas (e.g. native vegetation). Wherever possible site stockpiles on gently-sloped lands. Inactive stockpile faces must be provided with at least 60% cover within 10 days of formation. Stabilisation measures on stockpiles must be employed as per the requirements set out in Table 1. Stabilisation of stockpiles can be achieved by seeding and spraying with a soil stabiliser (e.g. Vital P47), covering with geotextile or matting or equivalent (note seeding is not required for stockpiles if are to be in place for less than 3 months or if they have an existing seedbank (non-weeds)). Stockpiles of topsoil or mulch should be constructed to no more than 2 meters in height; stockpiles of subsoil may be higher. Stockpiles faces must be no steeper than 2:1 (H:V). DUST SUPPRESSION Dust suppression should be carried out whenever necessary to minimise sediment becoming air borne due to wind erosion. An appropriate water source for dust suppression and/or dust suppressant management system must be identified prior to starting construction works. Temporary stabilisers (e.g. Vital P47), geotextile, jute matting or equivalent can be used in non-trafficked areas to assist with dust control. SOIL TREATMENT AND STABILISATION Prior to stripping topsoil, weeds are to be sprayed and gypsum is to be spread evenly over the ground surface at a rate of 5 tonnes/ha to be stripped up with the topsoil. Disturbed lands that grade more than 6% must be temporarily stabilised with soil binder or other suitable product if rain is forecast (more than 50% chance of more than 5mm), even if they are to be re-worked. Undertake progressive stabilisation of disturbed ground surfaces as they are completed rather than at the end of the works program (Refer to Table 1). Final stabilisation is to achieve the C-factors outlined in Table 1. Stabilisation of batters and general surfaces can be achieved by: 1. Shallow ripping gypsum into the subgrade at a rate of 5 tonnes/ha and to a Shallow ripping gypsum into the subgrade at a rate of 5 tonnes/ha and to a depth of 50-100mm to break up hardsetting surfaces. 2. Placing treated topsoil over the ripped subgrade surface (see Standard Placing treated topsoil over the ripped subgrade surface (see Standard Drawing SD 4-2 and SD 7-1 for instructions regarding topsoil replacement). 3. Seeding, then placing placing locally sourced native mulch over the soil . Seeding, then placing placing locally sourced native mulch over the soil . Alternatively, topsoil can be placed then hydromulched (with seed) or seeded and sprayed with Vital P47 (or equivalent). 4. Mulch, hydromulch or soil binders and additional seed might need Mulch, hydromulch or soil binders and additional seed might need re-application if adequate vegetation is not achieved. Appropriate seedbed preparation should be carried out when stabilising lands (See Standard Drawing SD 7-1). Diversion drains, bunds and table drains are to be stabilised as indicated in Tables 1 and 3. Stockpiles are to be stabilised as per the requirements of Table 1 and as shown in Standard Drawing SD 4-1 and in the stockpiling notes. As surfaces are stabilised and permanent drainage measures are installed, temporary water management structures can be removed (e.g. diversion drains). Sediment basin inlets/outlets must be stabilised in accordance with Table 1 and as detailed on the plan and within the 'Sediment Basin Sizing Table'. Laydown/storage areas, access tracks must be stabilised where necessary and as much as practicable with suitable trafficable measures (e.g. with aggregate, crushed rock, road base or a heavy duty trafficable soil stabiliser). Wherever possible, re-use cleared/mulched vegetation for either temporary or permanent stabilisation of disturbed areas. SEDIMENT FENCING Install sediment fences or (alternatively) mulch filter berms in the locations shown. Install all sediment fencing in accordance with SD 6-8 (ESCP09). Sediment fences must be firmly trenched into the ground for their entire length. Sediment fences must include small 'returns' at maximum 20m intervals (see SD 6-8) to minimise the risk of water flowing along them rather than through them. Mulch filter berms/bunds must be minimum 0.75m high and must be installed in accordance with the IECA standard fact sheet for Mulch Filter Berms (SD MB-01, sheet ESCP09). Checks (returns) must be provided at maximum 20m intervals on the high side of mulch berms to minimise the risk of water flowing along them rather than through them. Mulch berms on slopes > 10% must be lined/wrapped with permeable jute matting, geotextile or equivalent. SEDIMENT BASIN MANAGEMENT WRESB3 Sediment basin location and sizing is shown on the following drawings. Dirty water accumulating in excavations/cut sections can be pumped or carted to WRESB3 providing adequate capacity is available and the basin won't overflow as a result. Note that the 5-day maintenance requirement for the basin to be emptied still applies (see below). Within 5 calendar days of the conclusion of any rainfall causing runoff, WRESB3 must be empty, ready for the next rainfall event. If rainfall (causing runoff) occurs again within 5 days of the previous rain event, the 5-day requirement re-sets. Dirty water accumulating in WRESB3 can be used onsite for dust suppression or construction purposes without treatment. Note that the 5-day maintenance requirement for basins to be emptied still applies. The design rainfall event for WRESB3 is 42.4mm (5-day, 85th %'ile). Therefore, it is assumed the basin will overflow in an event of more than 42.4 mm over any 5-day period. If the basin overflows implement the Level 4 response in Table 7.5 in the Water Management Plan. The sediment basin must include a weir overflow/spillway sized to have a capacity to pass the 100 year peak flow. Outlet must be onto stable lands or into a waterway. Additional volume can be provided in the sediment basin for storing water if so desired (i.e. it can be made bigger than is required by this ESCP). A marker(s) must need to be installed within the basin to indicate the various volumes. Gypsum should be included in the sediment basin walls and at inlets to promote sediment settling. A marker peg (or similar) must be included in the basin showing the top level of the Sediment Storage volume. Sediment basin must be de-silted whenever sediment accumulates to more than 60% of the Sediment Storage Volume. Sediment removed from the basin can be taken to a stockpile area, buried onsite or used as general fill. Ensure sediment removed from basin is not placed where it could wash, blow or fall offsite. Sediment basin must achieve at least 3:1 length:width from its inlet to its spillway (SD 6-4 on ESCP09). If this is not achieved through the natural shape of the basin, a baffle must be included. Consider using an automatic flocculation system. WRESB1 Generally manage WRESB1 as per WRESB3 with the exception that basin management period is increased to 10 days. WRESB1 is designed for the 95th percentile 10 day rainfall depth which is 110.4mm OTHER DIRTY WATER MANAGEMENT Water accumulating in localised excavations or in any other low points (including incomplete WRESB1) onsite can either be: o Re-used for dust suppression or construction purposes, as long as those Re-used for dust suppression or construction purposes, as long as those lands drain back into a sediment capture system; or o Infiltrated onto well vegetated lands that drain back to the sediment Infiltrated onto well vegetated lands that drain back to the sediment basin; or o Pumped into a tank or truck and released into WRESB3. Pumped into a tank or truck and released into WRESB3. Water in WRESB3 must be irrigated onto well vegetated lands within the project boundary at least 40m away from any waterway, swale or drainage line. Ensure water is applied slowly and in a manner to avoid concentrated surface runoff and/or erosion. Refer to the CEMP or the Project’s Flocculation and Discharge s Flocculation and Discharge Management Plan for details on irrigation balance calculations. SITE INSPECTION, MONITORING AND MAINTENANCE 24 hours prior to forecast significant rainfall (more than 50% chance of more than 10mm in 24 hours) the following must occur: o The site environment manager (or their representative) must inspect the The site environment manager (or their representative) must inspect the condition of all erosion and sediment controls and action any urgent repair, maintenance or improvement works. They must keep a record all findings (including details of actions and their close outs); o Slope breaks must be pushed up or cut in across large (>80m slope length) Slope breaks must be pushed up or cut in across large (>80m slope length) exposed areas to slow down flows and minimise erosion; and o Exposed lands must be treated with soil binder as detailed in Items 3 and Exposed lands must be treated with soil binder as detailed in Items 3 and 4 of the Phase 3 works instructions above. Regular site inspections must be conducted by the site environment manager (or their representative): o At least weekly during normal construction hours; and At least weekly during normal construction hours; and o Prior to forecast rainfall (see above); and Prior to forecast rainfall (see above); and o Daily during rain events (if safe to do so); and Daily during rain events (if safe to do so); and o Within 24 hours of the cessation of a rain event that causes runoff. Within 24 hours of the cessation of a rain event that causes runoff. Additional erosion and sediment controls must be installed as necessary to ensure satisfactory outcomes in keeping with the project conditions and best-practice Blue Book guidelines. Progressive ESCPs must be updated and/or prepared as required. After rainfall, sediment accumulated in trapping devices (e.g. basin, sediment fence) must be removed to a secure location where it can't wash or blow offsite (preferably to an active stockpile). Weather conditions must be monitored onsite and daily rainfall must be recorded. A daily rainfall gauge must be installed at the site. Safe storage areas for wastes, fuels, excess concrete and other potential contaminants must be delineated by the site manager. Adequate supplies of erosion control measures (e.g. geotextile rolls, jute matting, and hydraulic soil binders) must be maintained in the site compound for rapid deployment as required. If required water treatment chemical(s) and equipment must be maintained onsite. Dust suppression must be undertaken as required to minimise the risk of offsite dust impacts. Refer to the Dust Suppression notes for details. BACKGROUND INFORMATION EROSION AND SEDIMENT CONTROL DESIGN The details shown within this plan are for construction stage erosion and sediment control requirements only. This Erosion and Sediment Control Plan (ESCP) has been prepared in accordance with Blue Book Volume 1 (Landcom, 2004) and project approval conditions. An erosion hazard assessment has been completed for all areas within the proposed works. The predicted soil loss across all site areas has been determined in accordance with the following: A = R x K x LS x C x P Where A = Annual soil loss due to erosion (t/ha/yr) = Annual soil loss due to erosion (t/ha/yr) R = Rainfall erosivity factor = Rainfall erosivity factor K = Soil erodibility factor = Soil erodibility factor LS = Topographic factor derived from slope length (L) and slope gradient (S) = Topographic factor derived from slope length (L) and slope gradient (S) C = Cover and management factor = Cover and management factor P = Erosion control practice factor = Erosion control practice factor The following values have been used: R : 2410 : 2410 K : 0.06 (assumed for all soils) : 0.06 (assumed for all soils) L : 80m : 80m : 80m S : 13% : 13% LS : 5.55 : 5.55 C : 1.0 (Construction stage - i.e. no soil surface protection or ground : 1.0 (Construction stage - i.e. no soil surface protection or ground 1.0 (Construction stage - i.e. no soil surface protection or ground cover applied) P : 1.3 (for general construction areas - assumes smooth and compacted) : 1.3 (for general construction areas - assumes smooth and compacted) Based on the above data, the potential soil loss is 1044 t/ha/yr (Soil Loss Class 6 – Very High). Sediment basins are required if the site’s potential soil loss is > 200 t/yr s potential soil loss is > 200 t/yr (Landcom, 2004); therefore, a sediment basin is required. SEDIMENT BASIN (WRESB3) DESIGN ASSUMPTIONS IFD: 2-year, 6-hour storm intensity = 10.5mm/hr Volumetric runoff coefficient (CV) = 0.9 (assuming Hydrologic Group D runoff coefficient - low infiltration, high runoff) Design rainfall depth: 5-day 85th percentile rainfall depth = 42.4mm Total disturbed site area = 1.4ha (approx.) OTHER DESIGN DATA Site is in Rainfall Zone 7 (Landcom, 2004) Rainfall runoff coefficient (C10) (cleared and compacted lands) = 0.9 Rainfall runoff coefficient (C10) (un-cleared lands) = 0.55 THE SOILS Details of soils across the Project Site are contained in Part 8 of the Project's EIS (available at http://www.unitymining.com.au/approvals/). Recommendations for their management are given at Section 8.8. In summary, soils within the Project Site have the following characteristics: Coarse to medium-grained, weakly-structured topsoils with sandy-clay subsoils. Initial drainage into topsoils is rapid, although subsoils have imperfect drainage. As such, infiltration rates would decrease rapidly as soils approach maximum water holding capacity. Soils are moderately erodible but are significantly dispersible (i.e. Type D according to the classifications in Landcom, 2004). A conservative K-Factor of 0.06 is adopted. Sub Soils are inorganic, highly plastic clays and are prone to significant shrinking and swelling as they wet and dry. Soils are prone to tunnelling and slumping and might not be inherently suitable for use in earth structures (e.g. dam walls or embankments). Refer to the geotechnical engineering report/design. Soils are: o non-saline, non-saline, o strongly to very strongly acidic (topsoil = pH 4.6 to 5.4) and strongly to very strongly acidic (topsoil = pH 4.6 to 5.4) and o relatively infertile. relatively infertile. Liming rate to achieve pH = 6.5 will be approximately 300 to 400 gsm. Recommended gypsum rate is 500 to 1000 gsm.