Mt Piper Power Station Extension Environmental Assessment – SKM

18 September, 2009

Operational and Construction Noise Impact Assessment
Sinclair Knight Mertz


3.2. Intrusive Noise Criteria

A noise source is considered to be non-intrusive if:

  • the LAeq, 15 minute level does not exceed the RBL by more than 5 dB(A) for each of the day, evening and night-time periods,
  • the subject noise does not contain tonal, impulsive, or other modifying factors as detailed in Chapter 4 of the INP.

From 5HTable 2-2 the lowest RBL noise levels for day, evening and night the intrusive noise limits have been applied to the monitoring locations as the assessment criteria. The corresponding intrusive noise criteria for the day, evening and night time periods are presented in 56HTable 3-1.

The Industrial noise policy provides guidance in the application of setting the Rating Background Level in Appendix B – Applying the background noise policy. Part 3 of section B1.3 Analysis procedure, states in relation to an RBL:

Where this level is found to be less than 30 dB(A), the rating background level is set to 30 dB(A)”.

Although part of the noise policy, in rural areas this has the effect of setting the intrusive noise limit artificially higher than would be calculated using the background plus 5 dB(A) method. The assessment of the proposed extension has included the INP guidance for a minimum RBL of 30 dB(A) at sensitive receivers, thus making the lowest intrusive noise criterion LAeq, 15 minute 35 dB(A) at Locations B & C.

It is however cautioned that a blanket application of this policy is not always in the best interests of the project. In-house experiences with similar projects shows that noise emissions may comply with environmental criteria, however, noise impacts can still be the cause of ongoing tension with neighbouring residents. This report recommends the control of potential noise emissions from the extension through careful design that may provide lower intrusive noise emissions than those identified under the INP.


3.5 Low Frequency Noise Impacts

 Section 4 of the INP lists modifying factor adjustments to account for certain annoying characteristics of noise emissions from industrial premises. The low frequency adjustment requires that the difference between the predicted C weighted and A weighted levels is no more than 14 dB(A), without penalty. The average difference between the C weighted and the A weighted levels calculated for the Mt Piper extension project is in the order of 20 dB when calculated at a receiver location and therefore the current assessment includes a penalty for low frequency noise. In accordance with Table 4.1 of the INP, a 5 dB(A) penalty has been added to the predicted noise levels.

As discussed the amenity criteria are primarily designed to control long term noise through planning goals. The intrusiveness criteria are better suited to control noise impacts that may potentially cause annoyance at nearby residences. Due to the low existing background noise levels, the intrusiveness criteria for the day time and night time are the most stringent of the noise goals, and these will be used to assess the potential for noise impacts as the result of the proposed extension of Mt Piper Power Station. The day, evening and night time limits would apply to noise generated by the Power Station operations at any residential dwelling or sensitive receiver.


3.6. Sleep Disturbance Criteria

The DECC Environmental Noise Control Manual (ENCM) (NSW EPA 1994) provides guidance in assessing the likelihood of sleep arousal due to industrial noise impacts. The assessment of sleep disturbance varies between studies however it is commonly acknowledged that not all people are affected to the same degree or by the same noise exposure.

Findings from studies of sleep disturbance measured by an awakening, change in sleep state or after-effects, reflect the considerable variation in people’s response to noise. Suggested peak permitted noise levels vary from 45 to 68 dB(A), depending on ambient noise (Griefahn 1991), and disturbance is related to both the number and maximum level of noise events (Bullen et al. 1996). Appropriate internal design noise levels for various types of occupancy are detailed in the Australian Standard AS 2107-1987.

For assessment purposes, the ENCM uses the criteria based on LA1 noise level of the source being no more than 15 dB(A) above the LA90 (background) noise level, when measured outside a bedroom window. From the monitoring results in 60HTable 2-2 and based on the audibility of the power station at Location C the sleep disturbance noise criterion for the most affected sensitive receiver would be 38 dB(A).

Attended monitoring results indicate that the current noise environment not related to the Power Station may produce LAmax events at this location that exceed the sleep disturbance criteria by more than 10 dB(A). In addition noise emission from the power station is at a steady state and therefore not likely to generate noise that could cause sleep disturbance.


5.3. Sleep Disturbance 

For the proposed coal fired plant extension option the noise levels are expected to be constant in nature. As the predicted noise levels at the nearest residences are estimated to be nominally at the DECC INP noise criterion, it follows that, due to the steady state nature of the noise emissions from the Power Station and the infrequent stoppages, sleep disturbance impacts due to loud noise events are not likely to occur as the result of operations of the proposed extension.


6.1.2. Sleep Disturbance 

The nature of the gas fired Power Station means that stop/start noise influences can occur much more frequently that a coal fired power station. Due to the potential for noise impacts that are louder than normal operations to occur, an assessment of sleep impacts from start up and shut down noise sources has been undertaken for the CCGT. Based on estimated noise levels of 103 dB(A) at 20 metres, an assessment of the potential for sleep disturbance impacts has been made. These results are shown in Table 6-2.

(see downloadable document at bottom of page for Table 6-2 Predicted Sleep Disturbance Levels at Key Residential Locations) 

The noise level for peak events from the CCGT are expected to be significantly lower than the sleep disturbance criteria at all sensitive receiver locations.

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