1/355 Manukau Road Epsom, Auckland 1023 PO Box 26283 Epsom, Auckland 1344 T: 09 638 8414 E: hegley@acoustics.co.nz

WAIKATO POWER PLANT

SH31, KAWHIA ROAD

OTOROHANGA

ASSESSMENT OF NOISE EFFECTS

Report No 9894

Prepared for: Prepared by: …………………….

Nova Energy Nevil Hegley Wellington March 2016

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CONTENTS

EXECUTIVE SUMMARY ............................................................. 3 

1  INTRODUCTION ...................................................................... 4 

2  DISTRICT PLAN NOISE REQUIREMENTS ......................................... 6 

3  CONSTRUCTION NOISE ............................................................ 8 

4  CONSTRUCTION EQUIPMENT NOISE ........................................... 10 

5  POWER STATION PLANT NOISE ................................................ 11 5.1 Basis of Assessment ....................................................... 11 5.2 Noise Sources ................................................................ 11

6  PREDICTING NOISE LEVELS ..................................................... 13 6.1 Introduction ................................................................... 13 6.2 Methodology .................................................................. 13 6.3 Requisite Sound Reduction ............................................... 14 6.4 Enclosed Noise Sources ................................................... 15 6. 5 External Noise Sources .................................................... 15

7  Predicted Construction Noise ............................................. 16 

8  Power Station Operation Noise ........................................... 16 

9  Conclusions ..................................................................... 19 

Appendix A ...................................................................... 20

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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 LAeq. The

plant operation is steady state so by complying with the night time limit of

40dB LAeq the 50dB LAeq daytime limit and 75dB LAmax night time limit will also

be achieved with a large factor of safety.

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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.

Figure 1. Location of SIte

Figure 1. Location of Proposed Power

Proposed Station 

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This report considers the noise1 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.

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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:

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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.

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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

Leq Lmax Leq Lmax Leq Lmax Weekdays 0630-0730 60 75 65 80 55 75

0730-1800 75 90 80 95 70 85 1800-2000 70 85 75 90 65 80 2000-0630 45 75 45 75 45 75

Saturdays 0630-0730 45 75 45 75 45 75 0730-1800 75 90 80 95 70 85 1800-2000 45 75 45 75 45 75 2000-0630 45 75 45 75 45 75

Sundays and public holidays

0630-0730 45 75 45 75 45 75 0730-1800 55 80 55 85 55 85 1800-2000 45 75 45 75 45 75 2000-0630 45 75 45 75 45 75

Where:

(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

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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.

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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 Sound Power (LWA) Caterpillar D8R bulldozer 112dB Komatsu PC710 excavator 105dB Caterpillar 825C compactor 107dB Mobile crane, 100 – 200kW 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.

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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 Numberwithin

building

Heightagl (m)

Sound Power Levels LWA

Gas turbine enclosure and base beam 2 4.5 97.9 Air filter house (two intake surfaces) 2 10.9 105.3

Air filter house silencer surfaces 2 10.9 96.3 Gas turbine room ventilation exhaust fan and duct

2 banks 8 95.7

Generator enclosure, gear box, and base

2 4.5 99.6

Generator room ventilation exhaust silencer, damper and exit

2 6 101.6

Generator room ventilation fan and shell surfaces

2 6 106.2

Variable bypass Valves exhaust duct and silencer

13 Part load and start up only

Auxiliary skid:

12

Including noise enclosure 2 2 98.3

Skid cooler and fan with acoustic louvers

2 2 84.9

Generator lube oil skid for generator/gear box

2 2 91.7

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 Numberwithin

building

Height agl (m)

SoundPower

Levels LWA GT Stack outlet 18 104.2

GT Stack Casing 0-18 90.8

Fin fan lube oil coolers 3 100.4

Gas turbine room ventilation discharge exit

11 84.7

Table 2. Plant Components to be Located Outside each Building

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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 200 – 300m. 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 7.1.2 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 (LAeq) 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 (LAeq) below the level predicted.

The cumulative noise has been predicted using the Brüel & Kjær Predictor

program version 11.00. This is a powerful environmental noise calculation

software package that uses a digital terrain model (with the ground contour

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Figure 2. 360MW Station Layout, No Noise Control

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

9613-1/2 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.

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.

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6.4 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/m3 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.

6. 5 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.

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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 NZS6803.

8 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.

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Figu

re 4

. P

redi

cted

Pow

er S

tation

Noi

se,

dB L

Aeq

18

Figure 5. Location of Closer Dwellings

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.

Location1 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

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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 (LAeq)

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.

* * *

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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

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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 (Lmax)

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.

L10

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.

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Background Sound L95

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 LAeq 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, Ldn

The day/night level (Ldn) 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 07.00 hours and

from 22.00 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 Lmax, L10, L95 and Leq

values when including all events over the 15 minute measurement period and

Figure A2 some typical noise levels.

* * *

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Figure A2