land disturbing pollution prevention mitigation measures

LAND DISTURBING POLLUTION PREVENTION MITIGATION MEASURES (LDP2M2) FOR TRANSFER STATION

CHAPTER 3: SITE ASSESSMENT

JUNE 2015 3-6

3.2 SEDIMENTATION Soil erosion during the construction stage may result in the discharge of suspended sediment into the existing watercourses and can lead to the deterioration of the water quality of the affected small streamlets and downstream river. The sediment yields from the Project Site have been estimated using MUSLE equation:

Y=89.6(VQp)0.56(K.LS.C.P)

Where Y = Sediment yield per storm event (tones)

V = Runoff volume in cubic meter Qp= peak discharge in m3/s K = Soil erodibility factor LS = Slope/length factor related to overland flow C = Cropping management factor P = Erosion control practice factor

In terms of sediment output, the sediment yields during pre-development have been calculated to be 0.74 tonnes/storm (Table 3-2). During site preparation without mitigation, sediment yields have increased significantly to 6.57 tonnes/storm event. However, with the mitigation measures, sediment yields reduced significantly to 3.28 tonnes/storm event. Sediment yields during post-development have been calculated to be 0.61 tonnes/storm event.

Table 3-2: Sediment Yield

Calculation of sediment yield

Existing 1

V (m3) QP (m3/s) (V*QP)0.56 K LS C P Sediment Yield

tonnes

362 0.11 7.49 0.008 0.69 0.2 1 0.74

Site preparation – uncontrolled 1


tonnes

604 0.16 13.28 0.008 0.69 1 1 6.57

Site preparation-controlled

1


tonnes

604 0.16 13.28 0.008 0.69 1 0.5 3.28

Operational stage


tonnes

1087 0.30 25.65 0.008 0.22 1 1 0.61


CHAPTER 4: DESIGN AND MAINTENANCE OF BMPS

JUNE 2015 4-1

4 LAND DISTURBING POLLUTION PREVENTION MITIGATION MEASURES

The land clearing and site preparation phase can lead to the considerable soil erosion and sediment delivery into the water body. This will deteriorate the water quality downstream of the Project site. The objectives of the erosion and sediment control plan are to minimise erosion and sedimentation during site preparation activities and to implement soil conservation measures. The Land Disturbing Pollution Prevention d Mitigation Measures (LDP2M2) will details out all temporary measures that will be implemented during the site preparation phase. The overall LDP2M2 is given in Figure 4-1.

The LDP2M2 plan has been prepared to meet the following principles:

Minimising soil erosion.- The north-western part of the project site is preserve and maintained as green area. Apart from that buffer strip on the western and eastern part of the Project site will be maintained as green area.

Preserving Top Soil and Other Assets; - topsoil removed from the site clearing will be stockpiles within the site and protected from erosion for reuse in landscaping and turfing.

Access route and site management - One access route is provided for the Project.

The construction entrance connecting to the existing road will be stabilised and paved (10m) and equipped with wash through.

Runoff control and management – Runoff from the undisturbed area at the northern

part of the Project site will be collected by inceptor drain and diverted into the existing drain without additional treatment. Temporary earth drains will be provided along the boundary of Project site. A temporary drain network will be provided to collect runoff from disturbed areas

Earthwork and Erosion control - Erosion control is provided via vegetation cover. At

the final slope, turfing will be provided. After earthwork is completed, areas not involved in construction are to be provided with close turfing

Sediment prevention control -.Silt trap is provided to control sediment delivery into

the watercourse. The site perimeter is temporary secured by earth bank to avoid sediment leakage from the site.

Slope stabilization; - All final slope within the site are provided with proper engineering

stabilization and protected with turfing.

Site maintenance – All BMPs structures are designed for minimal maintenance requirements.



JUNE 2015 4-3

The LDP2M2 component for the project consists of five aspects namely erosion control, runoff control, sediment control, site planning & management and general construction control. The proposed BMPs are tabulated in Table 4-1.

Table 4-1: Proposed Best Management Practices (BMPs)

No.

BMPs Number / Design Description

Site Planning & Management Control

1 Preserve existing trees and vegetation

Buffer strip along the drain and boundary will be maintained.

2

Stockpiles Topsoil To make use of the existing site sources materials for erosion and sediment control which may minimize cost and time in the materials procurement.

Erosion Control

1 Protection of Cut and Fill slope

To stabilised the cut and fill slope

2 Erosion Control Mattress including hydroseeding

To protect slope from eroded. Immediately applied after final slope

3 Mulching by using available material on site

Woodchip from oil palm trees can be used

Runoff Control

1

Temporary Earth Drain with check dam

2 years ARI design storm Side slope: 2 : 1 or flatter

To direct runoff into temporary silt trap. Check dam help to reduce velocity of flow and also can trap sediment laden

2

Silt Fence The silt fence does not filter runoff, but acts as a linear barrier creating ponding which allows soil particles to settle out thereby reducing the amount of soil leaving a disturbed area.

3

Temporary / permanent diversion channel permanent measures

2 years ARI design storm Side slope: 2 : 1 or flatter

To divert off-site runoff around the construction site, divert runoff from stabilised areas

4

Earth bank A temporary ridge of compacted soil constructed immediately above a new cut or soil fill slope or around the perimeter of disturbed area. To divert storm runoff from upslope drainage areas away from unprotected disturbed areas and slope to a stabilised outlet. To divert sediment-laden runoff from disturbed area to a silt trap.

Sediment Control

1

Silt Trap 1 unit The silt trap is a temporary measure. To be maintained until the site area is permanently protected against erosion



JUNE 2015 4-4

No.

BMPs Number / Design Description

2

Stabilised Construction Entrance/Exit

1 A temporary gravel, construction entrance/exit is a stabilised pad of crushed stone located at any point where traffic enters or leaves a construction site onto a public road

3 Wash Through 1 To reduce off-site sedimentation by

eliminating the tracking or flowing of sediment onto main road.

General Construction Control

1 Water Browser

2

Secondary Containment System

A second containment wall or embankment constructed with concrete or pre-fabricated metal that fencing around any petroleum base products with the containment capacity of 110 % the capacity of the said vessel or tank. To failsafe the primary containment (vessel or tank wall) that leaks or spills from flowing out further into drainage way or watercourses before recovering action to be taken.

3

Designated Schedule Wastes Storage Area

To minimize or eliminate the discharge of pollutants from construction site generating hazardous waste to the storm drain system or to watercourses.

4

Sanitation Temporary or portable toilet at all construction site to prevent sanitary and septic waste material directly to the storm drain system or to watercourses without any treated first to standard requirement and compliance.

All the mitigation measures are subject to change, depending on the actual site condition. Prior to site clearing and earthworks activities, environmental protection installations (BMPs) shall be carried out. This is to mitigate potential erosion and sedimentation impacts to the surrounding area. Mitigation Measures for Soil Erosion and Sedimentation:

The Project Proponent to ensure that the appointed contractor shall implement all mitigations measures as proposed in the LDP2M2;

Site clearing shall be limited to the project area. Vegetation cover should not be cleared until earthworks are ready to begin. In order to reduce soil erosion;

Site clearing and earthworks should be carried out during the dry season to reduce the impact of rainfall on exposed land;



JUNE 2015 4-5

Stabilize disturbed areas as soon as possible to minimize erosion;



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4.1 SITE PLANNING AND MANAGEMENT CONTROL 4.1.1 Preserve existing trees and vegetation Vegetation provides erosion control, strormwater detention and aesthetic value to a site during and after construction activities. Preserving layers of trees, shrub and ground cover plant help will help control runoff during site preparation. Existing vegetation along the watercourse shall be preserved. The norther-western part of the Project site where there is no construction activity will be preserved and maintained as natural vegetation. 4.1.2 Stockpile Topsoil Topsoil shall be removed from areas of cuttings, stockpiles for re-use for soiling the slope and for the provision of beds for cultivation of trees and shrubs. Excavated topsoil shall be stockpiled at a designated area and may be covered with geotextile or plastic covers to avoid wind and water erosion. 4.2 EROSION CONTROL

4.2.1 Protection for Cut and Fill Slope Slopes above the platform must be cut according to the design specified by the geotechnical engineer and based on tested soil parameters to minimize erosion.. Stabilization and protection of such soil slopes must be also be carried out according to the specification by the geotechnical experts. For the prevention or reduction of sediment flow, the temporary embankment should be well compacted to ensure that the soil particles is not readily eroded by runoff. Upon completion of the cut slope, turfing should be carried out to protect it from being eroded. The excess earth from cut activity, if any, should be stored temporarily at the designated stockpile area. The stockpile should be protected from erosion using temporary measures such as plastic sheets before being transported to the fill areas. The fill area should be laid in horizontal layers and the faces of fill slopes be maintained as filling progresses. In addition, fill areas should be compacted and graded so the runoff diverts into the temporary drains, which leads to the sedimentation ponds. The fill materials should be compacted properly in order to prevent excessive soil wash down during heavy rains. 4.2.2 Turfing All cut and fill slopes will be turfed. The main turfing will be carried out at sloping areas. Turfing will be carried out immediately upon completion of earthworks at the exposed areas in order to act as buffers along contours to reduce runoff velocity and to minimise erosion. In the event that turfing is not possible, temporary measures such as plastic sheets should be used to cover the exposed slopes to reduce erosion until turfing is carried out. The cut slopes should preferably be covered with a permanent erosion prevention mat where applicable/ practicable with a permanent root reinforcement system, which provides permanent root / stem reinforcement for vegetation to grow and collects sediments prior to vegetation establishment. Once vegetation is established, the grass has to be watered and fertilized regularly to ensure proper and rapid growth.



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4.2.3 Mulching Mulching is a temporary ground covering to protect the exposed soils during land clearing and earthworks from the rainfall impacts. Existing vegetation such as palm oil, rubber trees, and coconut trees can be used. The tree trunks can be cut into small pieces by tree eaters. The wood chip will be used to protect and control soil erosion. 4.3 RUNOFF CONTROL Surface runoff from the Project site shall be managed properly to reduce its potential for erosion. The flow direction, volume and velocity of the surface runoff shall be control by BMP’s to direct runoff from the exposed areas. 4.3.1 Temporary Drain A temporary drainage is used to divert runoff or channel runoff to silt trap, thereby reducing the potential for erosion and off-site sedimentation. Temporary drains shall be constructed to channel surface runoff prior to commencement of land clearing. The size of temporary drain is depending on the catchment area. The bigger the catchment area, the bigger the size of temporary drain 4.3.2 Check Dam Check dam is a temporary barrier constructed across a drainage ditch or area of concentrated flow. The purpose of check dam is to minimise erosion rate by reducing the velocity of water in areas of concentrated flow. Check dam will be installed along the temporary drainage system to control flow velocity and to capture larger soil particles and reduce sedimentation. 4.3.3 Silt Fence Silt fences can be constructed to intercept drainage and surface flow prior to entering nearby waterways or rivers. Silt fence does not filter runoff but acts as a linear barrier creating upstream ponding which allows soil particles to settles out thereby reducing the amount of soil leaving a disturbed area. 4.3.4 Temporary Silt Trap Surface runoff volume will be increase during the development of the project site. Runoff will be managed by providing one silt trap The design of temporary silt trap shall be based on the Urban Storm Water Management Manual for Malaysia, published by the DID. 4.3.5 Diversion Channels / Earth Bank Runon from the undisturbed area at the northern part of the Project site should be intercepted and diverted from the disturbed area to an existing drain. Interceptor drain and earth bank will be provided at the northern part of the project site.



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4.4 SEDIMENT CONTROL 4.4.1 Silt trap Silt trap shall be constructed to collect and store sediment from areas cleared during land clearing and construction stage and minimise the amount of sediment leaving the Project area into rivers and stream. It should help in removing coarse sediment from runoff. The silt trap is a temporary measure, and is to be maintained until the site area is permanently protected against erosion by vegetation and/or structures. The silt trap must be inspected weekly and after each rainfall. Desilting should be carried out when the sediment storage zone is not more than 300 mm high. For this project, designs for the sedimentation pond shall be based on the Urban Storm Water Management Manual for Malaysia, published by the DID. The size of the silt trap shall be adequately designated to cater for the maximum soil loss and sediment yield during the platform formation stage. The proposed location of silt trap is shown in Appendix A. 4.4.2 Stabilised Construction Entrance/Exit

Access road may severely eroded and unstable for the construction traffic created by heavy vehicles. A stabilized construction entrance / exit shall be provided at the access road connecting main road to the construction site. 4.4.3 Wash Through Wash trough can reduce or eliminate the amount of sediment transported onto the main road by construction vehicles. Dust on the public road would be dispersed by wind during dry weather. Wash trough should be install at the access to the Project site to ensure that tires any vehicles are free from earth dirt and sediment before entering the main road. 4.5 GENERAL CONSTRUCTION CONTROL 4.5.1 Water Browser Water browser should be use to spray regularly on haulage road to suppress the dust. 4.5.2 Secondary Containment System Bulk fuel storage tanks are commonly used at the construction site for refuelling construction vehicles and generator set. Spillage and improper refuelling may cause potential environmental and safety impacts that must be address at an early stage. These tanks should be place in one location only and within the maintenance yard. Containment bund should be provided around the storage tanks to contain the contents of the tank in the event of spillage. The buns-wall around the storage tanks should have a capacity to contain worst spillage condition i.e. 110% capacity of the largest containers.



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4.5.3 Schedule Waste Storage Area A designated schedule waste storage area should be provided at the designated area within the maintenance yard to minimise or eliminate the discharge of pollutants from construction site to the watercourse. 4.5.4 Sanitation Temporary or portable toilet at all construction site to prevent sanitary and septic waste material directly to the storm drain system or to watercourses without any treated first to standard requirement and compliance. 4.6 MONITORING 4.6.1 Total Suspended Solid (TSS) Regular inspection and maintenance will be carried out to ensure that the temporary drains and silt trap are operating efficiently. Monthly TSS monitoring shall be carried out at discharge outlets of the silt trap during both the site clearing and earthworks works period. Water discharge from the silt trap should not contain suspended solid load exceeding 50 mg/l as stipulated by the DOE`s standard. It should be noted that the TSS monitoring for the active silt trap should be carried out on a monthly basis. The following measures and procedures should be adhered to during silt trap sampling and monitoring:

i. Sampling of the discharge is done at the discharge outlet. Where a pipe or distinctive discharge point is not accessible, the sample is to be collected from any convenient point immediately;

ii. Collection of the sample from the direct outlet or pipe is into the sample bottle while from shallow streams or flow paths, a suitable scoop can be used but care to be taken that bottom sediment or sand is not taken during sampling;

iii. Sampling is not to be carried out during or immediately after a rain or storm event. When rain had occurred, a minimum time interval of two hours is recommended after the rain or storm event before sampling;

iv. All samples must be collected in the appropriate plastic bottles and after collection or filled to the brim, be firmly capped and if possible, sealed with masking tape;

v. The quantity of sample must not be less than 1 liter; vi. All samples must be clearly marked, either on the bottle or on labels, the location

or ID of the sampling station, the date and time of sampling and the person taking samples. Where labels are used, care must be taken to ensure that these do not come off during the transportation to the laboratory;

vii. A Chain of Custody (COC) form (with details on number of samples, type of analysis required, date of collection and date of dispatch) to be filled and forwarded with the samples to the accredited laboratory; and

viii. Although discharges from silt traps are tested only for Total Suspended Solids, the samples should be sent as soon as possible to the laboratory for analysis to avoid any possible interference from decomposition of organic material.



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4.6.2 Sediment and Erosion Control Best Management Practices (BMPs)

The effectiveness of Sediment and Erosion Control BMPs should be monitored based on the presence of silt behind or within control devices, the presences of silt downstream of the site, and sign of erosion in stabilized areas after a storm level. The system may be deemed ineffective if:

i. Silt is present outside the control area; ii. Structural controls are breached or fail under storm events of minor intensity; iii. Evidence of silt buildup in downstream strom water drains and waterways is

apparent; and iv. Controls are not maintained in accordance with design guidelines.

Monitoring should also take into consideration on any change(s) in drainage patterns and the extent of the change(s) in which it need to be address accordingly. The areas undergoing active construction are stabilized as quickly as possible through the use of vegetation, mulch, erosion control matting, or structural methods within 7 calendar days of the last construction activity. If construction or other site conditions do not allow stabilization within 7 days, alternative control approaches should be taken such as the use of water bowser trucks to wet the access roads and the use of plastic sheets near the slopes. 4.7 SITE INSPECTION The key to controlling erosion and sedimentation is the effective implementation and maintenance of LDP2M2s and this is the best achieved by undertaking a regular site inspection to ensure the LDP2M2 is always operating in accordance with its design intent. Hence the inspection will be performed as part of a regular construction inspection programme. The personnel in charge of site inspections for the proposed Project would be the Environmental Officer who will be in charge of the overall implementation of the LDP2M2 and monitoring of day to day of site operations. The results of the inspection and assessment will be recorded in writing. The report will include the date of inspection, the person (s) who performed the inspection and the observations. The site inspection will enable the new BMPs and adjustment to be carried out effectively through the tracking of changes.



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4.7.1 Frequency of Inspections Inspections should be undertaken;

i. During any storm event that threatens to exceed the available capacity in silt trap and permanent water quality control status;

ii. After any storm event with substantial runoff; iii. Daily, during hot or dry weather when grass cover is less than 100% on vegetated

areas; iv. Weekly as a matter of site routine for all site work particles; v. Before site closure or any other time when it might be otherwise left unattended for

more than 72 hours; and vi. From the site access in a fixed direction, which allow others (replacement worker,

DOE or consent authority officers) to follow the recorded inspection routine. 4.7.2 Overall Program Activities The site inspection program will consist of the following activities;

i. Inspection of earth drains and slope drains. Initiate cleaning if required; ii. Removal of any stockpile material or sediment that has encroached within 2 m

of surface drain; iii. Restoration of low spots in earth banks and diversion drains to their original height

and compact; iv. Where necessary, a construction of extra earth drains and/or diversion drains that

help separate on-site dirty waters from other waters; v. Install any new erosion and sediment control measures that have become

necessary since previous inspections because of severe storms or progress in the site’s development;

vi. Checks to ensure that all earth banks, and waterways are operating within the safe limits for the surface conditions by noting any evidence in scour; and

vii. Ensure that any construction work at site since previous inspection has not diverted sediment and water away from any site work practice.

4.7.3 Inspection of Silt Trap The silt trap must be inspected after each rain or storm event and on a regular basis at least twice a week especially during active earthworks is in progress or work areas cleared and permanent protective measures e.g. turfing or retaining wall has yet to be carried out. The inspection must cover the following:

i. Amount of silt/sediment retained - not more than 2/3 of the depth of the silt trap or 66% i.e. if a silt trap is 3 m deep, the amount of silt must not exceed 2 m and the depth of water remaining must not be less than 1 m;



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ii. Integrity of side walls and bund - there must be no leaks or breaches of the bund walls where water can bypass the bund wall or the pipe outlet;

iii. The aggregate material surrounding the perforated pipe should be inspected to ensure that these are not compacted with settled silt; and

iv. Presence of vegetative debris or construction waste material washed into the silt trap.

4.8 MAINTENANCE PROGRAM Maintenance work should be carried out based on the site inspection. All erosion and sediment control measure on a construction site must be checked periodically and maintain sufficiently to ensure proper performance during every stage of development. In view of that, an inspection and maintenance plan should be prepared by the personnel in charge in regards to maintaining the erosion and sediment control measures. This would be carried out by the Construction Manager and/or subcontractor(s) appointed at that respective work areas. 4.8.1 Silt Trap Maintenance / Desilting Procedure Based on the site inspections, especially after each runoff event, arrangements will be made for the removal of sediments and other pollutants. This will include the removal of sediment from silt traps and disposal in compliance with local regulations as well as the clearing trash racks of all bulky and floatable material to avoid any clogging of drainage system and onsite flooding. The silt trap must be maintained at regular intervals depending on the rain conditions to achieve minimal efficiency. In any case, inspection of the silt trap should be carried out after every storm event. The maintenance work for the silt trap is as follows:

i. When the silt trap is filled with sediment greater than 2/3`s of the depth, de-silting works to remove the accumulated sediment must be carried out immediately to maintain the functionality of the silt trap.

ii. De-silting can be carried out by a backhoe but care must be taken not to damage and breach the bund wall or the pipe outlet.

iii. The sediment removed from the silt trap must not be placed next or near to the silt trap or within water flow channels where the possibility of the sediment washing back into the silt trap is likely especially during the next rain or storm event. The removed sediment should be removed for dumping at the approved dump site.

iv. All breaches of the bund wall or must be repaired or replaced as soon as possible to maintain the functionality of the silt trap.

v. Vegetative debris or construction waste material washed into the silt trap must be removed immediately to prevent any blockage and also damage to the bund wall or outlet pipe.

vi. A maintenance log to be completed with details of silt trap in terms of silt trap identification no (ID) number, location, date of inspection, type of maintenance or repair work, date of maintenance and repair including the person responsible.



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4.8.2 Maintenance of Vegetative Surface The re-vegetated surfaces should be observed to ascertain if they are progressing as planned. In the event where they are not progressing, the following action is recommended but not limited to:

i. Seek professional agricultural advice where necessary. ii. Consider the following remedial action:

Additional irrigation (watering); Application of fertilizers; Reseeding; Mulching; and Weed control.

4.8.3 Repairing of Damaged and Breached Structures Inspections should be carried out by the respective construction team managers on all structures for damage especially after any significant rainfall, and where necessary, take the following remedial actions:

i. Repair, re-pin, or replace torn, detached or otherwise damaged liners, biodegradable blankets, geo-fabric, etc;

ii. Fill and compact any low spots and breaches in earth banks and diversion drains where vehicles of other factors have reduced the design height or stability; and

iii. Repair (destabilize) any areas of soil erosion to reduce further erosion. 4.8.4 Record Keeping Record keeping of all inspections, compliance certifications, and non-compliance reporting are to be retained until the Project completed. The use of photographs may be useful. It is also highly recommended to keep records for any BMPs that are “action” in nature such as housekeeping as opposed to BMPs that can be gauged by physical changes such as turfing. Such “action” based BMPs can only be gauged and demonstrated through record keeping. For instance, a record keeping on the silt trap desilting activity will provide insight on how soon it takes for the trap to fill. 4.8.5 Logbook Effective record keeping can be done through the use of a logbook. A logbook should always be kept on site for inspection by DOE or Local Authority Officers with entries made weekly on;

i. Dates of installation and removal of site work practices; ii. Repair of any damage to site work practices;



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iii. Rainfall depths, durations, and times; iv. Storage capacity available in pollution control structures; v. Condition of site work practice structures and stabilized surfaces; vi. Time, date, volume, and type of additions of flocculation; vii. Estimates of water volumes discharges; and viii. Estimates of pollutant volumes removed.

4.8.6 Plan Review and Modifications The LDP2M2 should be reviewed and modified if any unanticipated changes occur on site that may significantly affect the existing plan. This would include changes to the Project schedule, the phasing, staging area modifications, off-site drainage impacts, and repeated failures of designed controls. During the preparation and review of the modified/revised LDP2M2, construction works may continue with temporary modifications to the erosion and sediment control BMPs. A revision to the LDP2M2 is also required when properly installed system are ineffective in preventing silt transport off the site. This may be due to the unforeseen site conditions or construction techniques, which adversely affect the system as designed. Another occasion whereby a revision is required is when there is a new relocated activity that could result in the discharge of significant amounts of pollutants.

land disturbing pollution prevention mitigation measures

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