worksop stw - sludge digestion

Worksop STW - Sludge Digestion

September 2011

Severn Trent Water

J686 DOC 001 A

C:\Documents and Settings\PeterM\Desktop\Worksop Report Cover.doc

16 August 2011


September 2011

Severn Trent Water

Mott MacDonald Bentley, One Supply Chain West, Lamledge Lane, Shifnal TF11 8SD, United Kingdom T +44(0) 1952 468210 F +44 (0)1756 798 068, W www..mottmac.com

Severn Trent Centre, 2 St John's Street, Coventry, CV1 2LZ


Mott MacDonald Bentley, One Supply Chain West, Lamledge Lane, Shifnal TF11 8SD, United Kingdom T +44(0) 1952 468210 F +44 (0)1756 798 068, W www..mottmac.com

��

Draft 26/08/2011 M Marsden M Forni G Hewson Draft for comment

1 27/09/2011 M Marsden M Forni G Hewson Version 1

Issue and revision record

This document is issued for the party which commissioned it and for specific purposes connected with the above-captioned project only. It should not be relied upon by any other party or used for any other purpose.

We accept no responsibility for the consequences of this document being relied upon by any other party, or being used for any other purpose, or containing any error or omission which is due to an error or omission in data supplied to us by other parties

This document contains confidential information and proprietary intellectual property. It should not be shown to other parties without consent from us and from the party which commissioned it.

J686/DOC//001/A 16 August 2011 C:\Documents and Settings\PeterM\Desktop\Worksop Report Cover.doc


��

Executive Summary i

1. Introduction 1

2. Guidance 2

3. Site Description 3

4. Results 5 4.1 Noise Survey ______________________________________________________________________ 5 4.2 Noise Criteria ______________________________________________________________________ 6 4.3 Noise Predictions ___________________________________________________________________ 7

5. Conclusion 10

Appendix A: Plant noise sources 1

Appendix B: Measurement Summary 1

Appendix C: Glossary of noise terms 2

Content

i 245212 Worksop Sludge Digestion Scheme September 2011 P:\Southampton\HWA\General\Noise\245212 Worksop WWTW 27 September 2011\v1


This report describes a noise assessment for the proposed Sludge Treatment Facility at the existing Severn Trent Water treatment plant located at Rayton, outside Worksop. The assessment has been made based on British Standard 4142 and Local Authority guidance. A noise survey was conducted to establish existing background noise levels during the proposed operating hours of the plant. Noise from the proposed plant has been predicted at the nearest noise sensitive locations. Noise mitigation measures have been recommended to meet the Local Authority noise criteria.

Executive Summary

1 245212 Worksop Sludge Digestion Scheme September 2011 P:\Southampton\HWA\General\Noise\245212 Worksop WWTW 27 September 2011\v1

Worksop Proposed Sludge Treatment Facility

Mott MacDonald Bentley has been commissioned by Severn Trent Water to undertake a noise assessment of the proposed sludge treatment facility Rayton, Worksop.

This assessment is in support of the planning application for the proposed site.

A noise survey has been conducted at the site to establish existing background noise levels at the nearest residential locations to the proposed works. Noise from the proposed sludge treatment facility has been predicted at the nearest noise sensitive locations. Based on British Standard guidance and Local Authority criteria a noise assessment of the extension to the existing works has been performed.

1. Introduction



British Standard 4142 ‘Rating industrial noise affecting mixed residential and industrial areas’ outlines guidance for assessing a new industrial noise source in mixed residential and industrial areas. This standard gives a means of assessing the likelihood of complaints from the introduction a new industrial noise source to an area. It applies a noise limit on proposed new plant relative to the existing level of background noise. If the new noise source is impulsive, intermittent or tonal in nature, then a correction of 5 dB is made.

The guidance in BS4142 sets a limit of 10 dB below the background noise level (LA90) at which point noise complaints are unlikely. At a level of 10 dB above the background noise, complaints are likely. BS4142 does not define specific criteria within this range. A noise level of 5 dB above the background noise is categorised as ‘of marginal significance’.

The Local Authority (Bassetlaw District Council) have confirmed that the following criteria should apply to the site:

• Daytime (0700-2300 hours) LA90 +10dB(A)

• Night-time (2300-0700 hours) LA90 +5dB(A)

2. Guidance



The current Severn Trent Water site is located in Rayton, east of Worksop. The nearest noise sensitive locations to the proposed scheme are as follows:

• Location 1: Rayton Farm Cottage

• Location 2: Edge of the Worksop town

• Location 3: Properties south of the Retford Road (Manton Villas/Forest Lane)

Figure 3.1 shows the site layout indicating the noise sensitive locations in addition to the location of the proposed works.

The new treatment works are proposed to the east of the existing treatment works at the Severn Trent Water site.

The treatment plant is located on the outskirts of Worksop in a relatively sparsely populated area. Just north of the Retford road is an industrial area.

Figure 3.1 – Attended noise monitoring locations

3. Site Description

3

1

2



Figure 3.2 – Data logger noise monitoring location



��

Attended noise measurements were made in the vicinity of the site on the 23rd June between 13:00 and 06:00 on the 24th June 2011. Noise was monitored at the three locations identified in Figure 3.1. The data logger was left at Rayton Farm, as shown in Figure 3.2 between 13:00 on the 23rd June 2011 and 28th June 2011.

Noise at the data logger location was monitored over 5-minute intervals. Measurements were made of the ambient noise level (LAeq) and a number of statistical indices including the background noise (LA90). The measurement details are presented in Appendix A. In addition, a glossary of the measurement terms are given in Appendix B.

Two instruments were used: Larson Davies 820 and CEL 593 sound level meters. Before and after the measurement period, the calibration was checked on each meter using a Larson Davis CAL200 Precision Acoustic Calibrator. No significant drift in calibration was noted.

Each microphone was supported using a tripod between 1.2 and 1.5 metres above the ground and fitted with a windshield.

Throughout the measurement period the weather was cloudy with occasional showers. Also there was a light breeze during the survey.

The results of the measurement at the data logger location, location 1 are shown in Figure 4.1. The LA90 descriptor is commonly used to describe the background noise level.

4. Results



The dominant noise source at location 1 from wind in the nearby trees.

The noise source at location 2 was affected by a combination of sources including noise from children in the adjacent school yard, distant traffic and birdsong.

Generally, location 3 was dominated by road traffic noise. Also there was occasional noise from the golf course and birdsong.

At all locations, noise from the wastewater treatment plant was inaudible during the noise survey.

��

The proposed operating hours of the proposed scheme are on a 24 hour basis. Note that it is anticipated that the loader will operate only during the daytime. Based on the long term measurement location, at the nearest location to the proposed plant, the quietest background

Figure 4.1 – Data logger Noise Measurement Results

20

30

40

50

60

70

80

90

13:3

0:00

16:0

0:00

18:3

0:00

21:0

0:00

23:3

0:00

02:0

0:00

04:3

0:00

07:0

0:00

09:3

0:00

12:0

0:00

14:3

0:00

17:0

0:00

19:3

0:00

22:0

0:00

00:3

0:00

03:0

0:00

05:3

0:00

08:0

0:00

10:3

0:00

13:0

0:00

15:3

0:00

18:0

0:00

20:3

0:00

23:0

0:00

01:3

0:00

04:0

0:00

06:3

0:00

09:0

0:00

11:3

0:00

14:0

0:00

16:3

0:00

19:0

0:00

21:3

0:00

00:0

0:00

02:3

0:00

05:0

0:00

07:3

0:00

10:0

0:00

12:3

0:00

15:0

0:00

17:3

0:00

20:0

0:00

22:3

0:00

01:0

0:00

03:3

0:00

06:0

0:00

08:3

0:00

11:0

0:00

13:3

0:00

16:0

0:00

18:3

0:00

LAeq LAmaxLA10LA90



noise measured noise measured during the daytime and nighttime are as follows:

• Daytime(0700-2300): LA90 32 dBA

• Nighttime (2300-0700): LA90 28 dBA

Based on the above measurements and the local authority criteria (10 dB above the daytime background and 5 dB above the nighttime background), the following noise criteria apply to the proposed development:

• Daytime(0700-2300): LAeq 42 dBA

• Nighttime (2300-0700): LAeq 33 dBA

�� !��

The main items of plant and their associated noise levels are detailed in Appendix B. A layout of the proposed site is shown in Figure 4.2. The main stages in the processing of the proposed treatment works are as follows:

(1) Sludge Screens

(2) Sludge Thickening

(3) Acid Phase Digestion

(4) Mesophillic Digestion

(5) Sludge Dewatering

(6) Sludge cake pad and sludge recycling

In addition to the fixed items of plant, it is proposed that there will be sludge imports to the site. It has been assumed that there will be up to 90 loads to the site per week in articulated tankers. For the purpose of this assessment it has been assumed that each of these deliveries will take half an hour to unload. Also, there will be a loader which is used to move cake from the day pad into the storage bays. This loader is also used to load the lorries. The loader has been assumed to operate during the daytime only.



In addition, it is anticipated that collections of the sludge cake will occur one week each month for 3 trips each day.

Noise from the proposed dewatering works have been predicted using a 3-D CadnaA noise model. The prediction method is based on ISO 9613:2006 Attenuation of sound during propagation outdoors. Noise was predicted at each of the noise sensitive locations, represented by the noise monitoring locations 1-3. The unmitigated calculations have included for the low level wall (1.5m) around the cake pad area. It has been assumed that noise from the plant is

Figure 4.2 – Proposed plant

4m high noise barrier



steady and no correction has been made to account for the tonal, intermittent or impulsive nature of the sound. A summary of the predicted noise levels are shown below

Table 4.1: Predicted noise level

Description Freefield noise level [LAeq, dB ] Location

1 2 3

Predicted noise level with no mitigation dB(A) Daytime Nighttime

37 36

31 30

32 31

Daytime Noise criteria 42 42 42

Nighttime Noise criteria 33 33 33

Exceedance of criteria without mitigation (Daytime) -4

-10

-9

Exceedance of criteria without mitigation (Nighttime) +4

-2

0

Predicted noise level with mitigation 33 30 31

As the table above demonstrates, noise levels predicted from the proposed plant will meet the Local Authority criteria during the daytime at all locations. Also the predicted noise from the proposed scheme will meet the Local Authority criteria with the proposed scheme at the properties to the west of the site during the daytime and nighttime.

Some mitigation is needed to meet the criteria during the nighttime at properties east of the site at Rayton Farm.

The following noise mitigation scheme is proposed:

• Two 4m high reflective noise barriers to be located around the main items of plant as shown in Figure 4.2.

• 4m high reflective noise barrier to be located by the tanker loading area.

This is based on the assumption that the noise source of is located at a height of 1.5m.



Noise from the proposed sludge dewatering plant has been predicted and assessed using the Local Authority criteria. The proposed scheme meets the Local Authority criteria at all locations during the daytime and nighttime proposed operating hours, with the exception of the properties at Rayton Farm.

The properties at Rayton farm require the following noise mitigation measures to meet the nighttime noise criteria:

• Two 4 m high noise barriers to be located around the main items of plant, as shown in Figure 4.2

• A 4m high noise barrier to be located around the tanker unloading area.

With the above measures in place noise from the proposed sludge treatment works are predicted to be within the Local Authority criteria.

5. Conclusion



Table A.1: Summary of Manual Measurements

Location Date/Time LAeq LA90 LA10 LAmax Comments

1 13:25 51.3 43.0 53.0 71.4 Wastewater treatment plant inaudible, noise controlled by wind in poplar trees

2 14:00 47.6 42.0 50 69.6 Noise from wind in trees, children in nearby school yard, wastewater treatment plant inaudible.

2 14:20 47.0 42.0 49.0 70.1 Wind in trees, children in nearby school yard, wastewater treatment plant inaudible.

Survey Temporarily abandoned due to rain.

2 17:34 46.6 37.0 50.0 65.0 Some rain, distant traffic, pigeons cooing, birds, individual cars on nearby streets, wastewater treatment plant inaudible.

3 18:02 60.7 49.0 65.0 68.9 Traffic noise, radio in car at Bristol Street Motors, wastewater treatment plant inaudible.

2 20.40 44.2 37.0 47.2 63.2 Voices on golf course, striking ball, pigeons cooing, wastewater treatment plant inaudible.

3 21.04 58.2 44.0 63.0 70.7 Intermittent traffic, running water in drain 39dBA, high altitude aircraft, wastewater treatment plant inaudible.

2 05:31 45.2 37.0 48.0 61.6 Distant traffic 36dBA, Pigeons cooing 45dBA, wastewater treatment plant inaudible.

3 05:58 51.7 43.0 63.0 72.8 Traffic, very faint mains hum, birds wastewater treatment plant inaudible.

Appendix A: Plant noise sources



Reference location

(refer to planning drawing B356SLPB20104)

Plant Description

Number of items of plant

Sound Power Level [dB] of item

of plant

(1) Sludge screens

Motorised pumps

2 (of 4) to operate at any one time 881

Mixer pump 1 94 2

Gravity belt thickener feed

pumps 2

912

(Assumed additional 10 dB reduction

in noise due to building)

(2) Sludge Thickening

2 thickened primary sludge transfer pumps 2 881

Feed pumps 3 882

Sludge recirculation

pumpsets 4 881

Gas compressors 2 932

(3) Acid Phase Digestion

Sludge transfer pumps 2 881

Digestor feed pumps 2 881

(4) Mesophillic Digestion Digester sludge

recirculation pumps 4 881

Motor from Belt press

dewaterer to sludge cake

day pad 2 962

(5) Sludge Dewatering

Conveyors 2 881

Deliveries: Sludge imports

90/week

109 3

(6) Sludge cake pad and sludge recycling

Loader 1073

Table B.2: Corrected LAeq Measurements 1. Data has been estimated 2. Data calculated based on measurement data of similar plant 3. Data based on data in BS5228 Code of practice for control of noise and

vibration on open and construction sites

Appendix B: Measurement Summary



The Decibel Noise levels are usually quoted in decibels (dB). The decibel scale is a logarithmic (rather than linear) measure of sound intensity relative to a reference value. The threshold of hearing is zero dB while, at the other extreme, the threshold of pain is 120 dB. In practice, these limits are seldom experienced and typical levels lie within the range of 30 dB(A) - a quiet night-time level in a bedroom, to 90 dB(A) – that at a kerbside of a busy street.

The A-Weighting

In addition to its non-linear amplitude response, the human ear also has a non-linear frequency response. It is less sensitive at low and high frequencies and most sensitive in the range 1000 to 4000Hz (cycles per second). The A-weighting characteristic is applied so that these levels correspond more closely to the subjective response. A-weighted levels are usually expressed in dB(A).

Statistical Sound Level Indices, LAN

Noise from road traffic and other sources fluctuates continuously, both on a short and long-term basis. It is therefore necessary to use indices which involve a statistical averaging over the appropriate time period. The A-weighted level LAN is the level exceeded for N% of the measurement period. Thus the LA90 is the level exceeded for 90% of the measurement period, usually used to determine the background noise. The LA10 is the level exceeded for 10% of the measurement interval, usually used to measure road traffic noise.

The LAeq Index

The equivalent continuous sound level LAeq is the level of a notional steady sound, which at a given position and over a defined period of time, would deliver the same A-weighted acoustic energy as the fluctuating noise.

Free-Field Sound Level

The sound level which is measured or calculated in open space, without any reflections from nearby surfaces.

Facade Sound Level

A facade sound level is that determined 1m in front of the most exposed window or door in a facade. Sound is reflected from hard surfaces in a similar manner to light by a mirror and the effect is to produce a slightly higher (2.5 dB) sound level than would occur if the building was not there.

Appendix C: Glossary of noise terms