Wastewater Management An Assessment of the Noise Generated from the Operations of the Bon air West Wastewater Treatment Plant, Trinidad. 1 Nabilla Seepersad, Health Safety and Environment Division, Water & Sewerage Authority of Trinidad and Tobago,(e-mail:nabillap@wasa.gov.tt) 2 Pramenath Narinesingh, University of the West Indies, Department of Civil and Environmental Engineering, St Augustine, (e-mail: pramenath.narinesingh@sta.uei.edu) ABSTRACT Environmental and occupational noise exposure from noise generated by commercial and industrial businesses continues to be a problem worldwide. The problem of noise generated from the Bon Air West Wastewater Treatment Plant (BAW WWTP) has been examined in this study. Although noise surveys have been conducted worldwide, there are negligible studies that have focused on utilities (water or wastewater). Occupational and Environmental noise measurement studies have been carried out on the facility and compared to environmental and occupational standards. A noise contour map was developed and was used as a holistic approach to aid in noise reduction. It has been found during the surveys that the noise levels detected from the BAW WWTP were in compliance with the Noise Pollution Control Rules (NPCR) 2001 as amended, however the levels were in excess of the 5dBA maximum above the background noise levels. It was also found that the operators on the facility were subjected to over 80dBA in certain areas of the compound. Although the levels to which they were exposed didn’t put them at risk for hearing loss, hearing protection devices should be used in these areas. These areas are seen on the noise contour map that was generated. Although the environmental noise detected was in compliance with the NPCR 2001 as amended it can be a nuisance to the neighbouring community causing general irritation. Key words: Wastewater Treatment Plant, Noise, Environmental noise, Occupational Noise, Noise Pollution Control Rules, Noise contours, Hearing Conservation Programme. INTRODUCTION Noise is said to be annoying if a person or group of persons who are exposed to noise, reduce, avoid or removes themselves from the noise Molini 1979. Communities are more frequently coming in close proximity to industries as improper land use practices are becoming more frequent. Also the construction of new housing developments requires that wastewater treatment plants or lift stations are incorporated to treat the wastewater generated by these developments, thus requiring examination of noise related problems. Emphasis has not been placed on noise pollution from the industrial and commercial practices, as such there are not many sound pressure level studies conducted within the field with special emphasis on water and wastewater services. In recent times in Trinidad and Tobago, industries have been subject to conducting mandatory routine noise surveys as part of the stipulations of issued Certificates of Environmental Clearances (CECs). However, the older industries were not subject to this practice and as such do not give due weightage to the problem of noise pollution as it does not jeopardize employee's life immediately after exposure and does not pose any immediate detrimental effects on the receiving environment GC KisKu 2006. Environmental noise is noise generated by activities such as transportation, industry and recreational activities. It may also affect persons within the area or receiving environment. Occupational noise is noise that person is exposed to relating to their job or profession. The following are the parameters which are measured for studies: Lpeak is the highest instantaneous sound level that the microphone detects. Unlike the Max Level, the peak is detected independently of the slow or fast response that the unit is set for. Leq – a notional sound level which in the course of the period of exposure would cause the same A-weighted sound to be received as that due to actual exposure. Lavg - the average sound level measured over the run time. This becomes a bit confusing when thresholds are used. Any sound below the threshold is not included in this average. Noise monitoring has been ongoing internationally and includes operations such as airport operations, dye and textile industries and monitoring on the premises of institutions to name a few. Studies have been conducted to determine whether there exists a correlation between noise exposures and certain illness such as increased blood pressure, heart beat acceleration and sleeping disorders.Lang, Fouriaud, and Jacquinetsalord 1992Abbasi, Marri, and Nebhwani 2011.Locally noise monitoring has been undertaken as a reactive approach in most instances or for legal requirements when applying for Certificate of Environmental Clearance or upholding the stipulations of the issued CECs/Noise Variations. The BAW WWTP is approximately twenty (20) years old and serves approximately one thousand two hundred and eighty six (1,286) lots (597372.72m2). The Plant is owned by the Water and Sewerage Authority of Trinidad and Tobago (WASA) which is the authority that provides water and sewage services to residents and communities throughout Trinidad and Tobago. The area surrounding the Bon Air WWTP is classified as a residential area consisting of mostly single storey dwelling houses. It is the Authority’s responsibility to ensure that legal requirements are met during all operations with respect to environmental and occupational standards. The Authority received complaints of noise disturbance generated from the BAW WWTP from the residents of the immediate community over the last ten (10) years and more so recently in 2012. The residents have indicated that the noise causes negative effects on their lives such as lowering their quality of life and well-being. Within the last year the operators have also indicated that the level of noise to which they are exposed has been disturbing and considered as being very loud. There have also been unofficial complaints from the operators on the facility about the excessive noise. Some remedial works have been conducted in an effort to reduce the noise levels generated. While this has helped in noise reduction, additional strategies need to be put into place. The paper reports on the noise generated from the plant under normal working conditions and evaluate the compliance with NPCR 200, the Occupational Safety and Health Hearing Conservations Standards and the American Conference of Governmental Industrial Hygienists Standards. SCOPE The site is predominantly flat land with single unit dwelling houses. The layout of the WWTP is such that the structures and equipment are concentrated to the shouter side of the compound. The south perimeter of the compound is bordered by the Priority Bus Route which is used by vehicles that provide public transportation. The western side of the compound is bordered by Hosein Street, where there are single dwelling houses. The eastern perimeter of the compound is bordered by houses and the Lopinot Main Road while the northern perimeter is bordered by single dwelling houses. The measurements to be taken during the monitoring sessions include environmental and occupational monitoring. The parameters recorded for the environmental monitoring include Lpeak and Leq levels over a thirty minute period, one minute logging interval. The occupational parameters recorded during the monitoring sessions include Leq and Lavg for the duration of a shift. LITERATURE REVIEW Many studies have been conducted to determine the occupational risk of noise pollution in comparison to environmental noise studies. Previous studies on desalination plants have indicated the source of noise in these operations is high pressure pumps and turbines. It was also noted that it is not well suited for large plants to be situated at the centre of population without technological means and noise level control strategiesRachel Einav 2002. Studies conducted on the Holcim Cement Plant (Croatia) focused on four (4) major activities as most of the processes involved in cement production emitted noise pollution at a level which was a major environmental concern
timac and Eng 2005. The Production capacity is comparable to that of the Trinidad Cement Limited. The Main components of the study included environmental survey, noise mapping, establishment and implementation of noise reduction strategies and auditing of action implemented. Measurements were taken using a sound level meter to record Lpeak and Leq. The data collected was used to identify the noise sources and software from Bruel & Kjaer 2001was used for the calculation of the noise map. The noise map of the Holcim Cememt Plant and the Koromacno village showed a concentration of high levels of noise (80-90 dB(A) concentrated on the cement plant around certain machinery and further away from the plant the noise decreased. The noise map was used to prioritize the establishment of action plans through noise reduction measures. The noise map is beneficial in determining the sources of noise and locations where workers would be exposed to levels above the prescribed limits. It can also be used to determine which type of noise mitigation measures would be more efficient. Studies have been conducted in Sivas, Turkey at concrete, cement, iron, steel and textile industries to determine the effects of the noise generated from these industries on employees. Two hundred and fifty six (256) employees participated in the survey, the study focused on determining the physical, physiological and psycho-social impacts of the noise on humans. The results showed that the employees were exposed to levels well above 80 dBA. 74% of the employees were disturbed from noise in their workplaces, 61% complained about negative impacts on their nervous system (nervousness) and 31 % from hearing problems such as tinnitus and hearing lossE. Atmaca 2005. In Trinidad and Tobago environmental noise surveys have been conducted by industrial companies such as oil and gas companies. WASA has conducted surveys on some facilities which they have received noise complaints from neighbouring residents. The standard method used to conduct environmental and occupational monitoring by WASA. Occupational studies conducted incorporated the use of either a dosimeter or an integrated/logging sound level meter configured for the Occupational Safety and Health Hearing Conservation standards. Occupational Figure 1: Google image showing monitoring sites at the BAW WWTP which is represented by pins. METHOD An integrating/logging sound level meter was used to record the environmental noise generated. The meter was configured according to the NPCR 2001 (“A” weighting, fast response, Exchange rate of 3dB, Threshold set at zero, 1 minute logging interval). Thirty (30) minute studies were conducted at six (6) points, one (1) offsite to determine the background noise and five (5) on the compound of the plant to determine the noise generated). Meteorological conditions were also recorded at each monitoring site as they can manipulate sound. Environmental noise monitoring was conducted to represent daytime and night time noise levels. An edge 4 dosimeter was used to record the noise levels that the operators were exposed to during a twelve (12) hour shift. The dosimeter was configured to the OSH HC and ACGIH settings. Occupational noise was recorded over a six (6) days period for both day and night shifts where practical. A noise contour map was developed by plotting a grid of five (5) meters around the facility and using an integrated/logging sound level meter configured to OSH HC settings. Fifteen (15) second readings were taken at each grid point and contours were manually drawn. One of the main purposes of contour maps is to show the extent and location of noise problem areas. Each contour line has a corresponding number which indicates the noise level exceeded within that contour. Noise mapping studies have been conducted in Birmingham City by the UK Government’s Department of Transport in 2000; subsequently the study was updated in 2004. Additionally, studies have been undertaken in Croatia with respect to the application of noise mapping techniques. RESULTS AND DISCUSSION Evaluations on the environmental noise surveys were based on Leq limits from the NPCR 2001 as amended 80 and 65 dB(A) for daytime and night time levels and Lpk limits of 120 and 115dB(A) for daytime and night time levels. Leq levels were in compliance with the maximum levels of for daytime and the night time periods and were highest at Site B (behind the blower room) and C (south perimeter bordered by the priority bus route). However, LEQ levels were in excess of the maximum 5dB(A) allowable over the background noise levels at site B and C.The Lpk readings were also in compliance with the maximum levels of 115 and120 dB(A) for daytime and night time levels respectively. Overall a noise map was developed on the basis of the data collected (Figure 2). This is a comprehensive study which incorporated both the environmental and occupational aspects of noise. As can be seen from the noise map the lowest levels of noise are located to the north of the compound 60 dB(A), which is furthest away from the source of noise. The noise levels progressively increased moving south of the facility closer to the structure which housed equipment such as blowers and pumps. Namely in the vicinity of the blower room the noise level was observed at 85 dB(A). Anomalies observed such as sharp bends in the contours may be attributed to meteorological conditions such as wind speed, wind direction, humidity and temperatureinc. 2008. These conditions alter noise levels through a process called refraction. The main sources of noise indicated by the contour map are the equipment from the blower room and the wet well. This coupled with the general wind direction (NE) is the main reason for high levels of noise south west of the facility. The noise map can be used to develop mitigation measures that can be used to ensure compliance with both environmental and occupational noise standards, thus ensuring the safety on the employees and reduced negative impact on the receiving environment. Figure 2: Noise contour map for the Bon Air West Wastewater Treatment Plant Figure 3: Summary graph of operator noise exposure during shift The noise exposure experienced by the operator during each shift shows that neither the Leq nor the Lavg have exceeded the Permissible Exposure Limit (PEL) set for both standards (Figure 3). The night shifts readings are lower than the day shift readings. The Leq and Lavg values are an average for the shift period recorded based on the ACGIH and OSH HC respectively. Figure 4: Graph showing percentage of shift time the employee is exposed to levels above prescribed maximum limits The percentage for each shift that the operator is exposed above the limit can be seen in Figure 4. The limits used for each standard are the Action Levels, 80dB for ACGIH and 85dB for OSH HC standards. According to the OSH HC standards, the operator was exposed noise levels over 85dB for up to 2.5% of the shift. According to the ACGIH standards, the operator was exposed noise levels over 80dB ranging from 1% to 18% of the shift. The night shifts showed lower percentages of exposure. The noise dose recorded with meter 1 (ACGIH) standards are higher than values recorded with meter 2 (OSH HC) standards. ACGIH standards allow for more protection of the employee as the configuration is more stringent. Based on the results from the occupational data collected and the ACGIH and OSH HC limits, the operators are not exposed to levels that will cause harm or hearing impairment. This is due to the levels of noise they are exposed to and the duration which is well below the prescribed levels by OSH HC and ACGIH (8 hour period). CONCLUSION The Environmental noise surveys indicated that the Leq and Lpk levels were within the permissible levels for both day and nighttime readings. However the Leq levels were in excess of the maximum 5dBA allowable over the background noise levels. The highest Leq levels were recorded at the monitoring site located behind the blower room and the monitoring site which is bordered by the Priority Bus Route. The Bon Air Wastewater Treatment Plant is not in breach of the Noise Pollution Rules 2001 as amended. The occupational noise survey indicated that the operators were not exposed to noise levels that were deemed to be harmful by the ACIGH or OSH HC standards. The noise dose obtained from both meters did not indicate over exposure when compared to the PEL. The Leq, Lavg, Lpk and dose was notably lower during the night shift. The noise contour map identified the zones of the Bon Air West Wastewater Treatment Plant that exhibited high sound pressure levels (over 80dBa) as at the blower room and a maximum of ten (10) meters southwest of the blower room. Further away from the source of noise the noise levels were lower; while closer to the source of noise the noise levels were higher. RECCOMMENDATIONS The noise generated from the Bon Air West Wastewater Treatment Plant causes a nuisance to the residents to the west (downwind) of the plant. Additional measure should be implemented to reduce the level of noise generated. A short term option for the reduction of the noise is the replacement of the perimeter chain link fence immediately behind and around the blower room with a solid wall. Additionally, the blowers may be retrofitted with the appropriate silencers to aid in noise reduction. Consideration may be given to fitting the room with appropriate acoustic enclosures and ventilation systems to reduce noise levels without having the blower motors over heat. The level of risk of hearing loss and or damage is low, it is recommended that the operators should be issued appropriate hearing protection devices such as ear plugs or ear muffs. These devices should be worn when carrying out tasks in zones of high noise levels. A hearing conservation programme should be established to ensure that the operators do not compromise their hearing. REFERENCES Abbasi, Aitbar Ali, Hussain Bux Marri, and Murlidhar Nebhwani. 2011. "Industrial noise pollution and its impacts on workers in the textile based cottage industry: An empirical study." Mehran Unversity Research Journal of Engineering & Technology no. 30 (1). E. Atmaca, I. Peker, A. Altin. 2005. "Industrial Noise and Its Effects on Humans." Polish Journal Of Environmental Studies no. 14 (No 6):721-726. 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