**1. Introduction**

This case study is based on postgraduate research by Cobo Dorado [1]. It refers to a limestone calcination plant to produce powdered lime, which is located in a rural area. The industrial plant has dense forest areas in parts of its perimeter, which were planted for landscape purposes.

The main sources of noise in the plant are the crushers, the sifter, and the coal processing mill. The latter is the object of this study.

There are four receivers on the perimeter of the property where the sound pressure levels (SPL) are regularly measured; two of them, called P1 and P2, will be considered for this study.

One of the main discussions regarding barrier options to mitigate the effect of noise caused by industrial plants is whether the plant barriers such as eucalyptus

plantations could effectively behave as acoustic barriers. Thus, the goal of the study was to evaluate if the presence of a eucalyptus plantation located between the coal processing mill (sound source) and P1 collaborates on reducing the SPL in P1. The main objectives were finding the best fit for the depletion law of the main noise source to better evaluate the acoustic behavior of the tree barrier comparing the accuracy of the results achieved by using four different equations to calculate the insertion loss (IL) of the green barrier under study and concluding about the possibilities of using general equations for obtaining the IL of a green barrier.

In order to carry out this research, measurements of SPL were taken, based on protocols of the National Environmental Authority. All measurements were taken with time weighting Fast at the sonometer, at a height of 1.5 m above the ground. They had a minimum duration of 15 minutes. The measurements on different days were considered.

A set of SPL measurements taken when the coal mill was the only operating source was selected. The measurements in the receivers were taken monthly. The equivalent continuous SPL (Leq) was recorded each second in scale A (LAF,eq), in scale C (LCF,eq), and in octave bands (LZF,eq). The background SPL at P1 and P2 were measured during the shutdown of the plant, and their frequency spectra were also obtained.

Based on the literature review (see Section 2) and the general characteristics of the eucalyptus plantation, it appears that it could attenuate the SPL in P1.

This paper is structured in six sections. First, a theory background (Section 2) and the case study basic information (Section 3) are presented; all the relevant measured spectra are also shown in Section 3. Section 4 points out the applied methodology. Section 5 presents the calculation process; at first, the sound depletion law of the source was studied and then, the SPLs in the receiver P1 were found without studying the green barrier. For explaining the difference between the measured and calculated figures, the acoustic performance of the tree plantation was obtained four ways: two of them were for solid acoustic barriers and the other two for tree barriers. The last sections for this chapter are devoted to discussing the results and present our conclusions.
