At its ultimate capacity of 100 million gallons per day, the Aguas de Rosarito facility, near Tijuana, Mexico, will be the largest desalination plant in the Western Hemisphere, providing a much-needed new source of drinking water to the coastal communities of Baja California. The planned reverse osmosis facility, to be constructed in two phases at an estimated cost of US$ 550 million is a project developed and financed by an international consortium in a public-private partnership with local governments.
Environmental Noise Assessment
HGC Engineering was retained by ERM, a global provider of environmental resources management services to undertake an environmental noise assessment of the proposed desalination plant. There are existing communities bordering the project site on three sides, with noise-sensitive residences, schools and places of worship.
The purpose of this study was to:
- Employ predictive analysis to determine the anticipated offsite sound levels in the neighboring residential communities, resulting from the future operations of the facility
- Evaluate the anticipated sound levels with respect to the environmental noise assessment criteria of the Inter-American Development Bank (“IADB”) (which adopts the guidelines of the International Finance Corporation (“IFC”) of the World Bank Group) and applicable Mexican Federal noise guidelines
- Identify whether noise control measures may be needed, and develop recommendations and specifications for such measures, as appropriate.
To the benefit of the project, the financing and design teams knew to consider environmental noise issues and bring in HGC Engineering early in the design process. All too often noise control is neglected until after the design has advanced or after construction has begun, when the options are limited, and mitigation is costlier and less effective.
World Bank Environmental Noise Guidelines
The challenge, though, was that many of the equipment selections were not yet finalized, and manufacturer’s noise data were not yet available. Drawing from our extensive database of measured sound emissions from similar past projects, and our experience in assessing large facilities to IADB noise standards, we were able to develop a predictive inventory of noise sources, based on the power ratings, flow rates, capacities, and rotation speeds of the multiplicity of pumps, compressors, fans, blowers, motors, and substation transformers.
Predictive Acoustical Computer Model
While the outdoor equipment was a primary concern, the majority of the equipment was located indoors and was nevertheless a potentially significant source of noise. In that respect, sound transmission through the building walls was considered in the analysis. These source levels were used along with geometrical and topographical information about the site and surrounding area to develop a predictive acoustical computer model, in order to determine the offsite sound levels in the neighboring community.
HGC Engineering visited the site and surrounding vicinity in May 2019, to investigate the existing acoustical environment. We conducted automated monitoring of the background sound for 96 hours (two weekdays and two weekend days), in order to establish the applicable sound level limits in accordance with the IADB environmental noise assessment guidelines. In addition to the continuous monitoring, attended sound level measurements were conducted during both daytime and nighttime hours during the week and weekend, in order to investigate the sound levels at additional locations, and to gather anecdotal information about the dominant sources of background sound.
The measurements, predictive modelling and established IADB/Mexican Federal noise limits were used to develop maximum sound level specifications for key items of equipment and investigate additional options for engineered noise control measures.