WAIKATO POWER PLANT SH31, KAWHIA ROAD OTOROHANGA ASSESSMENT OF NOISE EFFECTS

Transcription

1 1/355 Manukau Road Epsom, Auckland 1023 PO Box Epsom, Auckland 1344 T: E: WAIKATO POWER PLANT SH31, KAWHIA ROAD OTOROHANGA ASSESSMENT OF NOISE EFFECTS Report No 9894 Prepared for: Nova Energy Wellington March 2016 Prepared by:. Nevil Hegley

2 2 CONTENTS EXECUTIVE SUMMARY INTRODUCTION DISTRICT PLAN NOISE REQUIREMENTS CONSTRUCTION NOISE CONSTRUCTION EQUIPMENT NOISE POWER STATION PLANT NOISE Basis of Assessment Noise Sources PREDICTING NOISE LEVELS Introduction Methodology Requisite Sound Reduction Enclosed Noise Sources External Noise Sources Predicted Construction Noise Power Station Operation Noise Conclusions Appendix A... 20

3 3 EXECUTIVE SUMMARY Nova Energy is proposing to develop a nominal 360 Megawatt (MW) open cycle gas turbine (OCGT) power plant at a proposed site located off State Highway 31, Kawhia Road, approximately 10km north of Otorohanga. The noise during the construction phase of the power station has been evaluated and will comply with the Otorohanga District Plan construction noise criteria. By implementing noise control treatment, including enclosure of most of the plant s noise sources, the noise level from the power station will comply with the requirements of the District Plan at all times; that is, 40dB L Aeq. The plant operation is steady state so by complying with the night time limit of 40dB L Aeq the 50dB L Aeq daytime limit and 75dB LAmax night time limit will also be achieved with a large factor of safety.

4 4 1 INTRODUCTION Nova Energy is proposing to develop a nominal 360 Megawatt (MW) open cycle gas turbine (OCGT) power plant at a proposed site located off SH31, Kawhia Road, approximately 10km north of Otorohanga, as shown on Figure 1. Proposed Station Figure 1. Location of SIte Figure 1. Location of Proposed Power

5 5 This report considers the noise 1 effects of the proposed power station and how the site will be developed to comply with the District Plan noise requirements to ensure the noise will be within a reasonable level for the neighbours. 1 Appendix A sets out a glossary of acoustic terms used in this report.

6 6 2 DISTRICT PLAN NOISE REQUIREMENTS The power station is located in a Rural Effects Area in the Otorohanga District Plan. The Land Use Chapter, section 14 sets the following relevant noise requirement for an activity in a Rural Effects Area at: 1. All measurements shall be taken at the boundary of the site receiving the noise except that in the Rural Effects Area the measurement shall be taken at the notional boundary of any rural site receiving the noise. 2. Noise from well drilling and testing from within the Renewable Electricity Generation Policy Area is to be measured from the Waipapa Noise Control Boundary provided that the noise standard for activities within the Renewable Electricity Generation Policy Area are complied with (see note 1 above). 3. Noise received by any habitable buildings located within the Waipapa Core Site Noise Control Boundary will not be taken to be residential buildings for the purpose of determining a notional boundary for noise generated within the Renewable Electricity Generation Policy Area, including well drilling and testing activities. 4. Day shall be defined as: Monday to Friday 7am to 10pm. Saturday 7am to 7pm. Sunday and public holidays 8am to 5pm. 5. Night shall be defined as: At all other times. 6. Where adjoining properties have frontage onto different orders of road or are located in different effects areas the most stringent noise standard shall apply at the receiving boundary. 7. Sound levels will be measured in accordance with the provisions of New Zealand Standard NZS 6801:2008 Acoustics Measurement of Environmental Sound and will be assessed in accordance with the provisions of New Zealand Standard NZS 6802:2008 Acoustics Environmental Noise. Standards 14A Noise Measurements shall not exceed:

7 7 Effects Area Road Order LAeq (Day) LAeq(Night) LAmax (Night) Rural Effects Area (excluding Waipapa Noise Control Boundary) 1, 2 & 3 50dB 40dB 75dB 14.3 Any construction, maintenance or demolition activity which complies with New Zealand Standard NZS6803:1999 Acoustics Construction Noise is a permitted activity.

8 8 3 CONSTRUCTION NOISE As set out above, all construction activities must comply with the requirements of NZS6803:1999 The Measurement and Assessment of Noise from Construction, Maintenance and Demolition Work. Table 2 of NZS6803:1999 sets the noise limits when measured approximately 1m from the most exposed façade of a dwelling for different durations of the construction noise. The actual levels set are: Time of week Time period Typical duration (dba) Short term duration Long term duration L eq L max L eq L max L eq L max Weekdays Saturdays Where: Sundays and public holidays (a) "Short-term" means construction work at any one location for up to 14 calendar days; (b) "Typical duration" means construction work at any one location for more than 14 calendar days but less than 20 weeks; and (c) "Long-term" means construction work at any one location with a duration exceeding 20 weeks. As it will take longer than 20 weeks to construct the power station the long term duration construction limits will apply to the total project. These levels are shown shaded in the above Table. Noise from construction equipment would depend on the emission of noise from individual items of equipment, the distance from site boundaries and any

9 9 screening that may be present to shield the noise from the receiver position, which for construction noise is 1m from the façade of the dwellings. The site preparation would include general earthworks using excavators, bulldozers and compactors. During the construction of the building and installation of plant the additional equipment likely to contribute to the noise during the installation includes mobile cranes, air compressors, mobile welding machines and miscellaneous hand held power tools such as skill saws and grinders. Construction equipment such as two or three 20-65t cranes has been included for general power station construction with larger cranes expected to be used for specific items of equipment (such as the turbine and generator). It has been assumed that concrete for the foundations and buildings would be imported using ready-mix trucks. Although installing the machinery would be a major part of the construction phase it is not a noisy activity. The major source of potential noise would be increased traffic flows delivering equipment to the site. Heavy truck traffic at construction sites is generally evenly distributed during the working day, while the majority of light vehicles are related to the work force arriving and leaving the site. Although there may be major machinery deliveries at night, the noise from traffic related to the proposed power station development is not expected to have any adverse effects for the neighbours.

10 10 4 CONSTRUCTION EQUIPMENT NOISE A summary of the sound power levels of typical construction equipment to be used on site, based on field measurements of plant operating, is: Plant Caterpillar D8R bulldozer Komatsu PC710 excavator Caterpillar 825C compactor Mobile crane, kW Sound Power (LWA) 112dB 105dB 107dB 107dB Three of each of the above items of plant operating at any one time has been assumed in the calculations. Other construction equipment, such as trucks, portable generators, impact wrenches, saw benches, etc are quieter than the above plant so will not have any cumulative noise events to the predicted station plant noise. It is expected piles will be required to support the heavy rotating gas turbine generator and/or the GSU transformer. Assuming precast concrete pipes driven with a drop hammer, which is noisier than bored piles, this work will have a sound power level of 118dB LWA. The construction of the access road will be undertaken with equipment such as scrapers, bulldozers, excavators, graders, trucks and compactors. The noise from this work will be similar to the noise generated by the site preparation for the power stations. During the construction and laying of the supply gas pipelines, which are assembled above ground, equipment will include trucks, pipes being prepared using a portable grinder (110dB LWA) and welding using a portable generator (93dB LWA) to provide the power for the welding and laying lengths of pipe (stringing) in trenches using a mobile crane.

11 11 5 POWER STATION PLANT NOISE 5.1 Basis of Assessment This assessment has been undertaken using noise emissions data for a nominal 50MW gas turbine (LM6000) generator package. However other gas turbine generator packages are potentially available for the project, including turbines of a nominal 60MW capacity and these are being considered (hence the total nominal capacity of 360MW). The noise emissions characteristics of these packages, once enclosed in a building are very similar, and can be appropriately treated in a similar manner to that described for the nominal 50MW gas turbine package to meet the same off-site noise standards. Such equipment would require a noise management design for the particular package and layout selected but would still meet the required standards. 5.2 Noise Sources To ensure the proposed power station will comply with the lower night time noise limits, it is proposed to locate the turbines within acoustically-treated buildings, two turbines in each building. The following noise sources will be located in each building: Noise Source Number within building Height agl (m) Gas turbine enclosure and base beam Air filter house (two intake surfaces) Air filter house silencer surfaces Gas turbine room ventilation exhaust fan and duct Generator enclosure, gear box, and base Generator room ventilation exhaust silencer, damper and exit Generator room ventilation fan and shell surfaces Variable bypass Valves exhaust duct and silencer Auxiliary skid: 2 banks Sound Power Levels L WA 13 Part load and start up only

12 12 Including noise enclosure Skid cooler and fan with acoustic louvers Generator lube oil skid for generator/gear box Table 1. Plant Components to be Located within each Building The following noise sources will be located outside the buildings and will be in addition to the noise sources in the building enclosure as set out above: Noise Source Number within building Height agl (m) GT Stack outlet GT Stack Casing Fin fan lube oil coolers Sound Power Levels L WA Gas turbine room ventilation discharge exit Table 2. Plant Components to be Located Outside each Building

13 13 6 PREDICTING NOISE LEVELS 6.1 Introduction It is generally recognised that the weather can have an effect on the level of noise that we hear and this becomes noticeable where the sound transmission path is greater than m. The closest house is located approximately 300m to the east of the power station. Of the various meteorological effects on the noise that will be received, wind and temperature inversions have the most noticeable impact on the received noise levels. The District Plan requires the use of NZS 6801:2008 Acoustics Measurement of Environmental Sound to assess noise. The meteorological conditions adopted in clause of NZS6801:2008 Acoustics - Measurement of Environmental Sound are: To demonstrate compliance, measurements should include or be appropriately adjusted to slightly positive propagation conditions, which are the upper limits of the meteorological window. Therefore when predicting sound levels it is recommended that slightly enhanced propagation is assumed. 6.2 Methodology When taking the above into account the cumulative noise levels from the proposed power station have been predicted based on a slightly positive meteorological effect on the transmission of noise from the proposed power station site. This means that if there is a light wind plus a strong temperature inversion the resulting noise may increase by as much as 2-3dB (L Aeq ) at the closer houses under these conditions. Should the wind strength increase to more than approximately 4m/s (8kts) the wind is expected to mask the noise from the power station. If the wind is blowing in the opposite direction (from the houses towards the power station), with or without a temperature inversion, the noise will be reduced by a minimum of 5dB (L Aeq ) below the level predicted. The cumulative noise has been predicted using the Brüel & Kjær Predictor program version This is a powerful environmental noise calculation software package that uses a digital terrain model (with the ground contour

14 14 interval at 2m) and considers the noise sources at the various locations on the ground. Calculations are undertaken in accordance with the requirements of ISO /2 Acoustics Attenuation of Sound during Propagation Outdoors. The analysis has adopted the ground absorption of grass land and with a slightly positive meteorological effect to calculate the ground contours. To determine any noise control that may be necessary to ensure the power station complies with the District Plan limits, the noise was first predicted without any noise control treatment. Figure 2 shows the layout for the nominal 300MW power station. The red shading on these figures shows the location of the surfaces radiating noise and the points are the location of specific items of plant on site. Figure MW Station Layout, No Noise Control 6.3 Requisite Sound Reduction From this work the minimum sound reduction required to comply with the lower night time noise limit is 17dB LAeq when assuming there are no special audible characteristics to the received noise.

15 Enclosed Noise Sources To achieve the design limits the noise sources identified in Table 1 will be enclosed. One design that will achieve the acoustic requirements (alternative designs are also available) is to use 100mm precast concrete walls, a metal clad roof with 6mm compressed fibre cement board installed on the underside of purlins plus a minimum of 75mm 14kg/m 3 fiberglass insulation in the ceiling cavity. To control the reverberation times within the building (echo effect) an absorptive material will be included on the surfaces exposed to the inside of the building, such as on walls where the material will be well clear of potential damage from day to day activities or on the ceiling. The ventilation may be provided via louvres and to optimise the sound reduction the louvres will be located facing away from the closer houses. In the event this is not practical to achieve for all ventilation, the louvres may be replaced with short silencers without presenting a specific design issue. It is noted that no provisions for windows or natural light have been made to optimise the acoustic performance External Noise Sources As part of the noise control some of the noise sources external to the buildings, as set out in Table 2, will be located so the buildings act as a screen to the closer dwellings. An example of where this approach has potentially significant benefits is with the positioning of the fin fan coolers; if additional noise reduction is needed, an engineered solution can be implemented to achieve the requisite acoustic performance.

16 16 7 PREDICTED CONSTRUCTION NOISE The proposed power station site is located approximately 350m from the closest dwelling. At this distance the noise from the site preparation will not exceed 56dB LAeq. It is expected that piling will be required for the heavy rotating gas turbine generator and/or the GSU transformer. Based on driving precast concrete piles this work will generate a level of up to 59dB LAeq at the closest dwelling. It has been assumed the noise will not be screened by the existing topography. These levels are well within the daytime 70dB LAeq limit of NZS6803:1999 Acoustics Construction Noise. As all other stages of construction work will be quieter than the earthworks and piling the noise from all aspects of the construction work will be well within the District Plan requirements to comply with NZS POWER STATION OPERATION NOISE The noise from the power station radiated into the neighbourhood from operation of the power station (at maximum development) when assuming enclosure of the plant components identified in Table 1, and that with a mild temperature inversion and a positive wind blowing from the source to the receiver position, has been predicted at 5dB LAeq intervals. The predicted noise contours are shown on Figure 4.

17 17 Figure 4. Predicted Power Station Noise, db LAeq

18 18 In addition, the noise has been predicted at the notional boundary of each of the closer houses as shown on Figure 5 and the results are shown in Table 3. Figure 5. Location of Closer Dwellings Location 1 Predicted Noise 1 35dB 2 35dB 3 40dB 4 33dB 5 32dB 6 30dB 7 31dB 8 31dB 9 29dB 1 Figure 5 Table 3. Predicted Power Station Noise, db LAeq

19 19 9 CONCLUSIONS It is proposed to develop a nominal 360 Megawatt (MW) open cycle gas turbine (OCGT) power plant at Kawhia Road located to the north of Otorohanga. The analysis shows that any construction noise will comply with the requirements of NZS6803:1999 Acoustics Construction Noise at all times with a large factor of safety. To predict the noise level from the proposed power station a computer noise prediction model has been developed and the noise predicted at 5dB (L Aeq ) intervals. In addition, the noise has been predicted at the notional boundary of the existing dwellings in the area during the power station operation. Based on the predicted levels at the existing houses around the power station the noise can be controlled to within the permitted activity requirements of the Otorohanga District Plan for the lower night time noise limits. When taking into account the noise level from the proposed power station and the requirements of the Otorohanga District Plan, the noise effects from the power stations will be controlled to within a reasonable level at the notional boundary of all dwellings in the area. * * *

20 20 Appendix A Guide to Noise Terms The following sets out an explanation of the acoustic terms that will be referred to throughout this report. The aim is not to necessarily provide technical definitions, but to enable a basic understanding of what is meant. The setting of specific noise levels to control any adverse effects does not necessarily mean that noise will not be heard. Audibility depends on the level of a sound, the loudness of the background sound and any special frequency composition or characteristics that a sound may have. Research suggests that a small number of people (approximately 10%) will find any noise not of their own making unacceptable. Conversely, there are approximately 25% of the population that are essentially immune to any noise. Neither of these two extremes is normally designed for. In establishing the appropriate noise levels the aim is to try and represent the typical expected community reaction, this will generally be approximately 90% of the people. In order to reflect community response to noise it is necessary to establish a measure that reflects our attitude to the sounds that we hear. Due to the variability of many sounds (level, tone, duration, intrusiveness above the existing sound, etc) no single descriptor will totally describe the potential community reaction to a sound. For this reason there are a number of terms that need to be understood. dba The basic unit to quantify a sound is the decibel. The A-weighted sound level, or dba, is a good environmental noise descriptor because of the similarity between A-weighting and the frequency response of the human ear at moderate sound levels. It can also be measured easily. However, it provides no indication of

21 21 tonal frequency components or unusual frequency distributions of sound that may be the cause of annoyance. Where appropriate, this must be assessed separately. We can hear a change in sound pressure that varies from 1 (taken as the threshold of hearing) through to 1,000,000,000,000 (taken as the threshold of pain). In order to bring these numbers to a more manageable size a logarithmic scale is normally adopted. This reduces the above values to 0 and 12 respectively. The decibel is then described as 10 times the logarithm of the ratio of the pressure level of interest, to a reference pressure level. Thus the scale becomes 0 to 120dBA. Some typical subjective changes in noise levels are: A change of 3dBA is just perceptible A change of 5dBA is clearly perceptible A change of 10dBA is twice (or half) as loud Because we use a logarithmic scale care must be taken when adding sound levels. Two equal noise sources raises the level of one source by 3dBA. It takes 10 equal noise sources to raise the level of one source by 10dBA. ie 60dBA + 60dBA = 63dBA and 60dBA x 10 = 70dBA. Maximum Sound Level (L max ) This unit equates to the highest (maximum) sound level for a defined measurement period. It is adopted in NZS6802:1991 Assessment of Environmental Sound, mainly as a method of protecting sleep. L 10 The sound level which is equalled or exceeded for 10% of the measurement time. This level is adopted in NZS6802:1991 Assessment of Environmental Sound to measure intrusive sound. This level may be considered as the average maximum sound level.

22 22 Background Sound L 95 The sound level which is equalled or exceeded for 95% of the measurement time. This level is adopted in NZS6802:1991 Assessment of Environmental Sound to measure the background sound. This level may be considered as the average minimum sound level and is the component of sound that subjectively is perceived as continuously present. Equivalent Sound Level (LAeq) The L Aeq may be considered as the continuous steady noise level that would have the same total A-weighted acoustic energy as a fluctuating noise over the same time period. Day Night Level, L dn The day/night level (L dn ) is defined as the time-average sound level in decibels (re 20µPa) over a 24 hour period from midnight to midnight) with the addition of 10dB to nighttime levels during the period from midnight to hours and from hours to midnight, to take account of the increased annoyance caused by noise at night. Notional Boundary The notional boundary is defined as a line 20 metres from the facade of any rural dwelling or the legal boundary where this is closer to the dwelling. Figure A1 shows a noise trace with the relationship of L max, L 10, L 95 and L eq values when including all events over the 15 minute measurement period and Figure A2 some typical noise levels. * * *

23 23

24 24 Figure A2