Noise and traffic

Where the plant's noise comes from

We found no noise study for this project. At biogas plants studied in other countries, the noise comes from the combined heat and power engines, the compressors and the gas upgrading unit, fans, pumps, the flare, the machines that move the feedstock and reversing alarms[5][7].

• A combined heat and power engine in a container: 65 dB at 10 m, according to the maker[5].
• Tipping feedstock in a reception hall: 117 dB(A) of sound power[5].
• A pre-treatment unit: 76 dB at 5 m, with peaks of 84 dB[7].
• The hum of engines and compressors is tonal; Portuguese law adds a 3 dB(A) penalty to it[14].

We found no sound power figures for grid-injection compressors, biofilter fans, shredders or wheel loaders.

Adding up the equipment, we estimate 104⚑(Assumption) dB(A) of sound power for the whole plant (central scenario, low confidence). At 1 km that gives ≈ 29 dB(A), close to the typical night background (28 dB(A)⚑(assumption: typical rural values, not measured in the villages), not measured in the villages). The trucks pass much closer to the houses.[5][7][14][6][7][8]

What the law says

The General Noise Regulation (RGR) has two rules for a permanent noisy activity such as this plant[14].

• Zone limits. The 1st revision of Guarda's municipal plan (PDM, Aviso n.º 30765/2025/2) classes rural settlements (aglomerados rurais) as mixed zones[15]: there, noise may not exceed Lden 65 dB(A) or Ln 55 dB(A)[14]. The revision only takes effect once the REN delimitation for the municipality is published, and we have not confirmed that this has happened[15]. Where zones are not yet classified, the RGR applies Lden 63 dB(A) and Ln 53 dB(A)[14]. We have also not checked on the PDM maps whether either village is classed differently.
• Annoyance criterion. Noise with the activity running may not exceed the noise without it by more than 5 dB(A) by day, 4 in the evening and 3 at night[14].

The annoyance criterion does not apply when outdoor ambient noise is 45 dB(A) or less (art. 13(5))[14]. In a quiet village, the typical rural background is 28 to 35 dB(A) (typical values, not measured in the villages)[7][8], far below 45: this rule is likely not to protect residents. This is a reading of the text of the law, not a legal opinion.

For trucks on public roads, the RGR sets limits for the road and leaves each vehicle's noise to type approval; we found no explicit rule on whether the traffic a plant generates counts as part of the activity[14].

In short: a plant that complies with the law can still be clearly heard in the villages.

Health: the WHO values

For road traffic noise, the WHO recommends Lden below 53 dB and Lnight below 45 dB[11]. Lden is a 24-hour average that weighs the evening (+5 dB) and the night (+10 dB) more heavily[11].

An average hides the peaks. Waking up depends on each pass: the 2009 night guidelines put the awakening threshold at about 42 dB(A) peak inside the bedroom[16]. A window left ajar takes about 15 dB off the façade level[7], so a truck at the door stays far above that threshold.

Traffic noise is linked to annoyance, disturbed sleep and cardiovascular disease. In Europe, the European Environment Agency estimates about 66,000 premature deaths and 50,000 new cases of cardiovascular disease a year linked to transport noise[17].

Trucks at other plants

The plant's capacity and the number of trucks have not been disclosed[2]. These UK plants have public heavy-vehicle traffic figures (each movement is one pass, in or out):

In Portugal, the environmental impact studies for Torres Novas, Abrigada and Sousel exist, but we could not read their truck numbers[19][20][21]. Digestate (what is left after digestion) also leaves by truck and is counted separately[18]. Our 25 loads a day ⚑(Assumption) are a conservative figure, probably on the low side: comparable UK plants have 60–95 truck movements a day[10][9]. A smaller plant would need fewer: at 30,000 t/yr, the feedstock would come to about 3 loads a day (our estimate ⚑(Assumption)).

Road, vibration and emissions

• Road wear. Pavement damage grows very fast with axle weight: the classic rule is the fourth power, so an axle twice as heavy does about 16 times the damage[22]. More recent studies suggest exponents between 2 and 4, depending on the pavement[22].
• Vibration. Truck vibration comes mostly from potholes and patches in the road and grows with load and speed; it can be felt indoors[23]. Studies have not shown structural damage to sound houses, but they were mostly done on modern buildings[23]. A survey of cracks in the houses before and after is a reasonable request.
• Village streets. Each route runs through about 750 to 780 m of village street[1]. In Ireland, a 90,000 t/yr plant was refused partly because the local road was too small[24].
• Emissions and dust. We found no per-kilometre emission factors (nitrogen oxides, particles) we could cite for these trucks, and no data on the dust they raise.

What to ask

Ask the Câmara and the promoter:

• How many loads a day, counting feedstock and digestate, on normal days and at peaks?
• On which roads? Do the trucks go through Avelãs de Ambom, Pêra do Moço or both?
• At what times? Will trucks run at night or at weekends?
• Is there a traffic study and a noise assessment? With background noise measured in the villages, by day and at night?
• Which equipment stands outdoors? Which measures cut the noise: closed buildings, broadband reversing alarms, working hours?
• Who checks the noise once the plant is running, and how do you make a complaint?

You can ask the Câmara for these documents under the law on access to administrative documents (LADA): request template.