Chapter 5: Predicted Environmental Impact & Mitigating Measures

Transcription

1 Chapter 5: Predicted Environmental Impact & Mitigating Measures The Environmental Impact Assessment measures and analyses any permanent or temporary environmental impacts which may be created as a result of a proposed development. Section 14 of the Environment Protection Act requires the EIA report to discuss the following: 1. The direct or indirect effects that the undertaking is likely to have on the environment 2. The social, economic and cultural effect that the undertaking is likely to have on people and society This chapter will therefore aim at assessing the different impacts caused during the construction stage, the implementation and operation of the proposed residential project. Adverse impacts are hence identified and mitigating measures are listed for implementation. 5.1 Environmental Impacts of the proposed development Potential impacts The proposed undertaking may have direct or indirect impacts on the physical environment namely on soil, hydrology, geology, flora, fauna, air quality, water quality, noise and landscape. Socio economic impacts of the proposed undertaking should also be considered in terms of demography, the local community, transport and traffic, housing and employment. The different environmental impacts may be categorised as relating to the following: Air pollution Noise pollution Flora & Fauna Sewage treatment and disposal Storm water management Solid waste collection and disposal Production of effluents produced on site Machinery used will generate hydrocarbons as by-products. Socio economic impacts Traffic and transportation implications 46

2 Quantification of most likely environmental impacts caused by the proposed undertaking: I Impact of minimal significance II Impact of standard significance III Impact of large significance Environmental Impact Construction Phase Operation Phase Air quality II I Noise II I Solid waste disposal II II Flora I I Fauna I I Physical Effluents II I Geology II II Visual & aesthetic III II Excavation II I Hydrocarbon by-products III I Ground Water I I Surface Water II I Chemical wastes I I Traffic II II Human Machinery II I Economic III III Job Creation II II Housing II II Table : Environmental Impacts caused by proposed development Table shows the scoping matrix i.e. a Table indicating the main environmental impacts and attempting to quantify their respective effects. The environmental impacts have been grouped as affecting the physical environment and the human environment during the site clearing, the construction and operation stages. The construction stage involves the infrastructural works associated with the proposed development. The operation stage concerns the day-to-day running of activities within the project once the construction stage is completed. Based on the scoping matrix, the environmental risk may be evaluated using a simple linear equation: Risk = Probability of occurrence x Environmental impact quantification Based on the above equation, the project promoter, consultants and contractor will take the necessary precautions and enforce the necessary mitigating measures to minimise the adverse effects on the surrounding environment. The assessment performed in Table has been subdivided into the physical and human impacts onto two phases, i.e. the construction phase and the operation stage. It is therefore essential that mitigating measures be applied in order 47

3 to avoid nuisance and undesirable effects to local inhabitants. The landscape (visual and aesthetic aspect of the site) is also going to be altered enormously during that construction phase. In addition Table indicates the positive impacts the proposed construction of the new morcellement would bring in terms of job creation and increase in economic activities in the project surroundings. Other positive environmental/socio economic impacts of the project are listed below: Increase in housing standard/capacity for the local inhabitants in line with the Government s policy to provide un toit pour chaque famille. Creation of jobs during the construction and operation phase of the morcellement Regeneration of the Petite Riviere Noire area Air Quality Source of impact The air quality will be most affected during the construction phase with the emission of dust particles from machinery like excavators, electric grinders and equipment. For the construction phase, air quality will be mostly affected from heavy plant, logistic of workers and equipment. The impact receptors are likely to include site workers. The substance, which will most significantly contribute to air pollution, will be particulate matter (PM 10 ). Particulate matter (PM 10 ) may cause health hazards when inhaled in significant amounts and can also reduce the visibility. Most of those dust particles will come from basaltic dust particles. The Government authorities of Mauritius have published the maximum tolerable emission of particulate matter for industrial plant as 200 mg/m 3 - a value unlikely to be reached or exceeded during construction phase. Although the site is of large scale, the level of pollution is very unlikely to be above the normal tolerable level and hence does not require farreaching mitigating measures to be applied. Emission standards for other chemical pollutants (including fluorides, chlorides etc) have also been published by the Department of Environment. However chemical pollutants principally hydrocarbon by-products from the site will only be the result of normal vehicle operation (CO x and NO x ) and will hence not be considered during the course of this study since no 48

4 mitigating measures are required. It should also be noted that the above-mentioned impacts would vary depending on: Number of vehicles operating at a particular time Wind regime, temperature and rainfall Atmospheric pressure Duration of earthworks The general guidelines for air quality standards for Mauritius and as recommended by the World Health Organisation (WHO) are listed in Table : POLLUTANT MAURITIUS WHO Averaging Time PM μg/m3 50 μg/m3 70 μg/m3 1-h 24-h Annual SO μg/m3 200 μg/m3 50 μg/m3 350 μg/m3 125 μg/m3 50 μg/m3 1-h 3-h 24-h Annual NO2 200 μg/m3 400 μg/m h 24-h μg/m3 CO μg/m μg/m3 1-h Table : Air quality standards From the above standards and based on the duration and the location of works on site, it is unlikely that the above threshold value will be exceeded. Bag filters will be used to reduce PM 10 concentrations while sulphur dioxide emissions may be reduced using diesel with low sulphur content Mitigating Measures In order to minimise the effects of particulate emissions during the site clearing and the construction phase, the selected contractor will be required to: Spray both the earthworks with water depending upon the atmospheric conditions and the number of workers present on site. Ensure the protection and well being of his employees by minimising their vulnerabilities to falling objects or dust generated by the machinery on-site. The contractor shall use an appropriate shift system and take care that his workers wear necessary protection like masks, safety glasses, and ensure that the necessary and standard precautions are rigorously followed to prevent loss of human life. Make sure that a mechanical team is present during site works to control PM 10 emissions generated by the machinery. 49

5 Reduce dust particles that might be carried away by the wind - a shelter will be used to stock the resources. Properly stack dust mounts, concrete rubbles and wooden wastes. Maintain access to site and internal roads in good condition to minimise dust propagation. Adequate buffer zones will be allowed between the site and existing built up areas. Some pollution may however be unavoidable during the construction phase Assessment of Flora and fauna Source of impact The proposed site for development is predominantly used as hunting grounds. All plants and trees of ecological interest will be preserved as far as possible so as to blend with the morcellement project Noise Pollution and vibrations Source of impact Some noise pollution will be unavoidable, especially during the construction phase. The noise involved during the construction phase will be the result of operation of excavators, lorries and heavy machinery like electric grinders.. Noise is measured in decibels and is considered to be a nuisance when the following conditions are all met: 1) The combined expected maximum noise level exceeds 68dB (A), L10 (18 hour). 2) The relevant noise is at least 1.0dB above the prevailing noise level 3) The contribution to the increase in noise level of the new or altered development is at least 1.0dB (A). A relates to weighting according to an average person L10 relates to noise level exceeded 10% of the time. During the construction of the infrastructural services, significant vibrations may take place. The noise involved during the construction phase will be the result of building of roads, walls, drains and water reticulation network. The effects of such vibrations will be minimised by ensuring infrastructural works take place in daytime during weekdays. 50

6 Mitigating Measures It is expected that both the construction and the infrastructural works for the project will take place during daytime and weekdays, hence causing minimum disruption. Works on public holidays, weekends and during overtime will be minimised to ensure noise is kept low. The construction engineers should make sure to use machinery equipped with latest sound-reduction technology. Presence of vegetation and green spaces surrounding the proposed site is likely to reduce the noise experienced. Buffer zones between the site and existing built up areas will be provided to reduce noise propagation Effects of altering the landscape and visual impact Source of impact All efforts have been made to create and design a new morcellement following guidelines and recommendations provided by the Planning Guidelines published by the Ministry of Housing and Lands, the National Development Strategy and the Outline Planning Scheme for Black River District Council Area. A change in landscape from a sloppy terrain to a fairly terraced morcellement may be regarded as abrupt. Successful developments generally blend landscaping and architecture to achieve a consistent, unified and unique project character. In terms of thematic design, the use of boulders, rock outcrops and local trees can provide both a sense of enclosure and integration with the existing landscape. Appropriate designs will be used to ensure the above is feasible. Adequate projected open spaces will also promote enormously each and every visitor s experience. Good design around existing vegetation and landforms, planting pockets shall offer elements of texture, shadows, fragrances and colour where the purists shall take pleasure socializing. It should also be noted that the visual appearance of the site may be unpleasant during the construction stage due to stockpiling of blocks, aggregates, pipes and other building materials. However such a situation will only be temporary and no mitigating circumstances need to be established. The visual impact is generally classified as an obstruction or an intrusion. An obstruction may be defined as some feature which obscures the view and is categorized as high, moderate or slight. An intrusion is essentially subjective and is the impact on the visual impression of 51

7 the area. A preliminary assessment of the visual impact of the proposed development has been performed using the following techniques: 1) Calculation of the solid angle subtended by the future dwellings from various view points 2) Assessment of the visual envelope i.e. a plot of the area from which the project site may be seen Mitigating measures To minimise the landscape and visual impact, the following mitigating measures will be considered: The morcellement has been designed with an integrated approach in such a way that limits have been imposed on the height of the houses. All developments within the morcellement will be done in accordance with a strict cahier de charges. The individual plots will be oriented and blended in the natural setting to ensure no adverse visual impact from the sea. All houses roofs will be of same colour and material in order to ensure a harmonious appearance Surface runoff Source of Impact In a study conducted by the Water Resource Unit (WRU) in 1997, it was shown that the whole island receives an annual rainfall of 2100mm which constitutes approximately 3900Mm 3 of rain water annually. It was found that 30% of the water is lost due to evapotranspiration, 60% is converted to surface run off and the net groundwater recharge is equal to 10%. The implementation of the proposed development is likely to alter the surface run off of the site at several exposed areas of the site after rainfall. Surface runoff is generally caused by the erosion of soil in areas where the soil has been sloppily piled. In the proposed development, surface runoff will also depend on the month within which the construction will take place. The intensity of the run off will depend on the extent of site clearing, role played by vegetation prior to clearing and month during which works are effected. In Les Sols de Maurice by Willaime (1983), it was shown that the most prominent factor of erosion is no doubt rainfall, provided it is considered in both angles quantitative (global volume) as well 52

8 as qualitative (intensity). However land erosion does not depend solely on the abundance or aggressiveness of rainfall; they are also dependant on ground relief, soil permeability, vegetation and land use. Based on the contour lines, percolation tests carried out and data gathered on the rainfall intensity at Riviere Noire from the meteorological station, an assessment of the increase in surface run off can be predicted using Fournier s equation: C 2 p P where C is the erosive capacity p is the rainfall in the month receiving the highest rainfall P is the height of the annual rainfall This indicator has been calculated for Saint Antoine, Medine, Vacoas and Union Park. Values obtained vary between 35 and 80 indicating less erosive climates at Saint Antoine and Medine. It is also generally assumed that 30% of the site surface will produce run off. The amount of run off may then be estimated by linear interpolation using Table Rainfall (mm/d) Run off volume ( m / d Table : Amount of run-off volume ) Mitigating measures Reducing the effects of surface run off can be performed using one of or a combination of the following techniques: Increasing infiltration of water into soil Controlling excessive storm run off Controlling soil erosion Using the run off for useful purposes To cater for the water being driven away by surface runoff, the following measures will hence be taken into consideration: 53

9 A storm water drainage network will be required to account for this change in absorption capacity of the site. An adequate storm water drainage network will be designed in accordance with the regulations currently in force. Planned creation of green spaces with gardens, trees and vegetations that will be present in the new morcellement project will help in minimizing soil erosion. The landscape architects will ensure that the designs of gardens not only improve the aesthetic aspect of the terrain but also help in decreasing major surface runoffs. Excavations carried out during the construction phase should be done sequentially in such a way that the minimum possible strips of land are left exposed simultaneously Solid waste Source of impact Solid waste is likely to be generated in significant amount during the construction phase of the development. Appropriate measures therefore need to be taken to cater for the adequate disposal of such solid wastes. Improper solid waste disposal may also lead to skin diseases. Moreover solid waste will attract vermins, rats and deteriorate the general aspect of the site and its surroundings. Organic wastes will comprise mainly of domestic refuse like food and garden debris like fallen leaves, broken branches and lawn mowing. During the construction phase, the inorganic waste likely to be generated will include: Concrete rubbles and blocks Cement sheets Wooden and metallic beams Paper, plastic, cartons Blocks, rocks, boulders Broken tiles, glass debris Metal debris, cans and tins Wood, straw and timber remains Organic waste generated during the construction stage will be minimal and shall include leaves, branches, food consumed by workers on site Mitigating measures Mitigating measures adopted to account for the generation of solid waste during the construction stage include the following: 54

10 Wastes shall neither be disposed in any water course or bareland nor be burnt on site Appropriate fence should be used to prevent propagation of the debris via strong winds Inorganic waste, which can be re processed, will be catered away in properly equipped vehicles to the nearest transfer stations for an eventual transfer to a landfill site After the construction, the morcellement will operate as follows: The houses: carton boxes, food waste, paper, cans, plastic etc Administration offices: carton boxes, used computer parts, stationery etc Gardens and landscaped areas: grass, vegetal clippings, leaves, branches Strict guidelines will be put in place in order to manage the solid waste production during the operational phase of the development. The main goals of the guidelines will be to ensure adopting recycling techniques and encouraging sorting of solid waste at source into organic and inorganic wastes. Due to the high volume of solid waste generated, recycling and composting techniques will be encouraged to reduce amount of solid waste which will be carted away. As such the following mitigating measures are proposed: Sorting at source will be encouraged to separate organic and inorganic solid wastes. Materials such as plastic and glass may be sent to factories for recycling purposes Hazardous materials (if any) will also be collected, stored and transferred to a neighbouring landfill. Bins will be placed at various locations in the morcellement to collect paper, plastic, cans etc Using the above techniques, the promoter expects to keep risks of contamination low and volume of solid waste to a minimum. The compost from the on site facility may be used for the landscaped areas and reduce the amount of fertilizers used Effluents Source of impact During the construction phase, the main source of effluent will occur when staff and workers will be present on site. The amount of sewage generated will obviously depend on the number of staff present on site. However it is expected that the rate of generation will be at a 55

11 maximum of 10 m 3 /day. In order to account for the above, the selected contractor will be required to provide an adequate mobile toilet facility for the duration of works on the proposed site for development. Moreover food leftovers if allowed to decay will also produce leachate while sludge will need to be removed on a regular basis from the septic tank during the operational phase. The above effluents cannot be disposed of in the environment since their bacterial concentrations exceed the threshold set by the authorities. The Wastewater management authority has published standards regarding various concentrations for substances to be discharged. Parameter Standards COD 120 Total KJELDAHL Nitrogen (TKN) 25 NH4 Nitrogen 1 Nitrate 10 Total Phosphate 10 Total Suspended Solids (TSS) 45 PH 5 9 Table : Discharge standards The untreated discharge of domestic wastewater from the individual houses will be above the standards set by the authorities in Mauritius (Table ). These effluents may therefore have adverse impacts on the ecology and the surrounding environments if not treated. Hence adequate measures must be taken to ensure the safe collection and treatment of domestic effluents from the individual houses and other facilities within the morcellement. The primary objectives of an effective waste water system should ensure that: No contamination of the drinking water supply occurs by waste water No public health hazard occurs No pollution of ground and surroundings occur In order to cater for the treatment of waste water of the new morcellement, each house will be equipped with a septic tank and absorption pit/leaching field Mitigating measures The mitigating measures proposed for the collection and treatment of waste water are: The sewage system will not be connected to the surface run off system The design of the septic tank and absorption pit/leaching field will take into consideration the nature of the soil and percolation rate. 56

12 It is recommended that the septic tanks be de-sludged every 3-5 years to prevent clogging of the absorption system Hydrocarbon wastes Source of impact Diesel will be used to power most of the plants during the construction phase. Hydrocarbon wastes might occur through spillage from mechanical breakdown and servicing of vehicles, equipment and machinery. During heavy rainfall, surface runoffs will occur and might carry away the hydrocarbon wastes through the existing water storm drainage system. Spillage might also occur from work with pitch or tarmac. As part of the selection criteria, the contractor should have the contractual obligation to ensure the following: All equipment used by the contractor during infrastructural works should be properly serviced and possess necessary ISO standards where applicable The contractor should provide hydrocarbon collection facilities on site. It is only at such designated locations that servicing of equipment can take place. Properly trained personnel will carry out the servicing of equipment Mitigating measures Good maintenance of vehicles, equipment and machinery: Vehicles, equipment and machinery shall be maintained properly to prevent leakage of hydrocarbons and other automotive fluids. All maintenance shall occur in designated areas located away from waterways. Accessibility to spill prevention and response equipment: Spill prevention and response equipment including drip pans, drop cloths, and absorbent materials shall be kept at all designated maintenance and fueling areas. Steel sheet-piling will also be used as an effective secondary containment for any potential surface spill. Trace fueling areas as a means of mitigating the risk of water contamination: Waste generated during project activities shall be stored in designated waste collection tanks away from waterways. Steel sheet-piling used, in the vicinity of the project area, will extend above the ground surface to prevent the possibility of any spilled hydrocarbons from reaching surface water adjacent to the site. 57

13 Notify the guilty parties: The guilty parties shall be notified immediately in the event of an unintentional spill to ensure clean up and disposal of the spilled material. This will also act as a measure to protect hydrocarbon wastes from being spilled. Necessary response teams: Provision should be made for the necessary response teams and equipment to be available so that they can give an adequate response to emergencies such as a spill of hydrocarbons resulting from work with pitch or tarmac Increased Demand on Public Utilities The construction of the morcellement project will automatically require connection to the national water, electricity and telecommunication networks. In addition the project will generate additional traffic. Each of the main additional requirements from the utilities is listed hereunder Potable Water Source of impact The potable water demand for the residential development has been estimated to be approximately 402m 3 /day (refer to Section 4.3). In no case will the potable water from the Central Water Authority (CWA) be used for irrigation purposes. The National Development Strategy (NDS) recommends the need for judicious use of water resources on the island while the National Physical Development Policy sets out clearly defined guidelines for efficient use of water resources: Policy No U.1: Reduction of losses in water supply systems Policy No U.3: Water Source Development Policy No U.5: Augmentation of Service Reservoir Storage Capacity Policy No U.6: Rehabilitation and Strengthening of Water Distribution Networks Mitigating measures The proposed mitigating measures to reduce pressure on water resources in the Petite Riviere Noire region include the following: Encourage harvest of rain water for irrigation purposes In no circumstances make use of potable water for irrigation purposes 58

14 Ensure no leakage occurs in the potable water distribution network within the morcellement Encourage residents within the morcellement not to waste water. Setting up of a monitoring system to ensure water losses are kept to a minimum Storm water will be channeled towards landscaped areas to make efficient use of rainwater Electricity Source of impact The electrical power demand for the proposed development has been estimated to be about 800KW. The Central Electricity Board (CEB) has been informed of the power needs and necessary contributions will be paid by the promoter. All works will be done in accordance with the requirements of the CEB Mitigating measures Encourage use of solar based power Encourage local residents to minimise electrical power waste Setting up of an underground electrical network to minimise risks of electrical power losses and cuts during tropical storms. Minimize effects of magnetic fields within the internal electrical network of the morcellement to reduce electrical power losses. 59

15 5.2 Impacts on the Human Environment The assessment of the environmental impact of the proposed development in relation to the human environment will be assessed in terms of employment jobs created or lost, housing the necessity for new accommodation, population changes in demography Assessment of Employment The proposed undertaking will in the first instance create jobs within the construction industry. The construction of the internal roads, drains, water reticulation network etc over the entire realisation of the project will have the following positive impacts in terms of employment: 1) Direct and indirect creation of employment 2) Creation of demand for building materials 3) Local industry and its labour force 4) Suppliers and manufacturers of raw materials such as rocks, concrete, pipe-works etc More specifically, during the construction phase, the project will have the following positive impacts: Job creation for consultants i.e. engineers, surveyors, architects, draughtsmen etc Provide work for a period of approximately 18 months to semi skilled labour i.e. masons, carpenters, builders, electricians, plumbers etc Increase construction industry related products i.e. wood, cement, bricks etc. During the operation phase of the project, the project will have the following positive impacts: Creation of new jobs which will directly benefit the local community Creation of further employment in the following sectors: car hiring and taxis, restaurants, small scale industries, tour operators etc Such activities in the region will create dynamism within several industries and will boost up the level of income at a local and regional level while enhancing job opportunities through the multiplier mechanism. Hence the proposed development has the potential to contribute to improving the standard of living in the region. 60