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Blog > Legal Marijuana: Where there’s Smoke there’s Sound September 19, 2017 |

Legal Marijuana: Where there’s Smoke there’s Sound

Massachusetts, like many other US states, is on the fast-track towards a legal framework for medicinal and recreational cannabis. The Regulation and Taxation of Marijuana Act 1 permits adults to possess and use marijuana. Further, after required licensing procedures, retail marijuana stores will be permitted to open beginning in July 2018.  With an annual sales forecast of about $1 billion in MA alone, commercial-scale production of cannabis presents numerous opportunities through the supply chain from the grower to the distributor. With these opportunities come challenges that need to be considered in the design of cultivation facilities. This blog post will discuss the potential for community noise impacts from such facilities.

A quick review of the popular literature tells us that cultivation facilities require careful regulation of temperature and humidity to maintain a suitable environment for cannabis plants, with typical targets in the range of 60°F to 80°F and 65% to 75% relative humidity. Because of these requirements, one of the main sources of noise at an indoor cultivation facility is heating, ventilating, and air-conditioning (HVAC) equipment. In a typical commercial building, this equipment can be run at reduced capacity during nighttime hours, which saves energy and reduces noise emissions. However, to provide appropriate conditions to support plants in both vegetating and flowering stages, HVAC equipment at a cultivation facility may be operated nearly continuously (24 hours per day).

Running the HVAC and process equipment requires an enormous amount of electrical power which can dictate the siting of a cultivation facility. Take a simple example: a typical facility requires about 80 W of electrical power for every square foot of cultivation area. For even a small-size facility with 6,000 sq ft (60 ft x 100 ft) under cultivation, the numbers work out to 480 kW. Were the facility to use this power continuously, the load would be about 12,000 kWh per day (about 350,000 kWh per month). When you consider that the average US household consumes about 1000 kWh per month, it quickly becomes clear that cannabis cultivation has the potential for serious environmental impacts if power is not generated sustainably and delivered efficiently.

Providing the sort of power demanded in the example above is neither simple nor inexpensive, and such considerations can be a deal-breaker for a cultivation facility. Typical practice is to deliver the electricity at high voltage (230 to 500 kV) to a transformer substation on the site of the facility, where the power is “stepped-down” to a more readily-usable voltage (110 or 220 V). The step-down transformers can generate a significant amount of noise, as anyone who has ever walked by an electrical substation can attest.

The main community issue with transformer noise is not the loudness, but rather the constant frequency hum (a result of the internal design of the transformer which generates strong tones at even multiples of the line frequency). We use 60 Hz (cycles per second) power in the US which produces strong tones at 120 Hz, 240 Hz and 360 Hz. Tonal sounds tend to be more disturbing to communities than sounds with many frequency components. If a hum (single tone) and a hiss (many frequencies) have exactly the same sound level, people will say the hum is louder and much more annoying. Interestingly, the human ear is very good at detecting tones, even the in the presence of other noise, which further increases the potential for community annoyance.

In addition to HVAC and power equipment, a third source of community noise is associated with transport of materials to and from the facility. Large quantities of CO2 gas are often used to boost production yields, and this gas must be delivered by tanker truck in most cases. Due to high demand, these deliveries could happen during off-hours when people in the community are sleeping. Backup alarms and revving of tractor engines have the potential to disturb and annoy the community.

So what is a good grower to do about these potential noise impacts? The first thing that should be considered is location, location, location! Siting a cultivation facility near an abundant source of power (hopefully far from where people live) is the ideal place to start. Once a suitable site has been selected, existing sound levels should be measured to establish a baseline. Our typical practice here at Acentech is to monitor ambient sound levels continuously for about a week to have confidence that we have thoroughly characterized the existing environment. A review of noise regulations should also be completed so that the facility does not exceed limits enacted by cities, towns, and states. With the baseline monitoring and code review complete, design goals for facility-generated sound at nearby sensitive receptors can be established.

Due to the potential number of sound sources and their various locations around a facility, computer modeling is a useful tool for estimating community sound levels. These models can incorporate complex topography and meteorological effects, and can account for the reductions produced by sound barrier walls and changing equipment load. Here are a few screenshots from a recent cultivation facility project. You can see the sound sources, the 3D terrain over which sound levels are calculated, buildings and barriers which block sound, and noise-sensitive receptors.

Pictured: 3D models of a prospective cannabis facility site, which are extremely useful for predicting community sound levels.

Putting the legal and political issues aside, with a thoughtful approach and effective noise control treatments, there is no reason why a cannabis cultivation facility can’t be as good a neighbor as any other industrial facility.

[1.] St. 2016, c.34 , as amended by St.2016, c.351 , effective December 15, 2016

Author: Andrew Carballeira

As a Senior Consultant in the Acoustics group, Andy is working on various projects involving educational, commercial and residential facilities. His areas of concentration include architectural acoustics, noise and vibration control,…

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