## 3 Results and Discussion
### Noise Measurement in Residential Areas
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Residential** & **Residential** & **L\({}_{\text{eq,A}}\) [dB]** & **Original Condition** & **L\({}_{\text{Aeq,P}}\)** & **U [dB]** \\  & **House** & & **Altitude [m]** & **[dB]** & **U [dB]** \\ \hline  & A & 59.2 & 179.2 & & \\ I & B & 60.2 & 179.2 & & \\  & C & 61.3 & 179.2 & & \\ \hline  & D & 64.5 & 179.2 & & \\ II & E & 54.1 & 179.2 & & \\  & F & 56.9 & 179.2 & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Measured noise values in residential areas. The second stage involved extension of the measures already implemented to reduce noise from the traffic route and production facilities. The design of the solution was based on the need to ensure that the proposals were feasible and did not interfere with existing technology. The proposed measures were as follows:  
* VL2 traffic roads improvement,
* closure of production facilities from the side of residential area I. Based on experimental measurements, the result of implementation of additional measures resulted in a further reduction in the noise level generated by the sandy gravel processing. Detailed results are given in Table 4. The noise values measured did not exceed 60 dB, however, they still did not comply with the permissible noise level in accordance with [19]. Thus, the above measures were also assessed as insufficient. Based on this, further research attention, in the third stage, was focused on another noise source--noise generated by the technological equipment used, which resulted in its replacement. A more detailed specification of the measures investigated is as follows:  
* removal of obsolete cone crusher and its replacement with a new type at VL1,
* replacement of four low-capacity screeners with two high-capacity screeners at VL2,
* VL1 traffic roads improvement. The measurement results after the implementation of the third stage of noise-reducing measures showed a further decrease in the noise propagation into the outdoor environment. Nevertheless, the permissible noise levels for residential houses B, D and F were exceeded (see Table 4). The measures were assessed as partially effective, however, still insufficient. Therefore, a further series of measures, designated as the fourth stage, was proposed:  
* installation of CETRX slabs, 30 mm thick, in lengths of 182.6 m on the original noise barrier,
* construction closure of the burker conveyor belt junction with DURISOL blocks at VL2,
* construction of noise barrier made of DURISOL blocks and MALCIT cover plates on the side of residential area I,
* replacement of conveyor belt drive gearboxes. After the implementation of the fourth stage of noise-reducing measures, noise measurements in residential areas I and II were carried out only at the three critical locations:  
* residential house B,
* residential houses D and F.  
After the last stage, the required noise levels were reached at all monitoring points. Detailed results of the measured values of noise levels in residential areas I and II before and after the implementation of the four stages of noise-reducing measures are given in Table 4. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Residential Area**} & \multirow{2}{*}{**Residential House**} & \multicolumn{5}{c}{**Leq,A [dB]**} & \multirow{2}{*}{**Leq,p [dB]**} & \multirow{2}{*}{**U [dB]**} \\ \cline{3-3} \cline{5-8}  & & & **Original Condition** & & & **Stage 1** & **Stage 2** & **Stage 3** & **Stage 4** \\ \hline \multirow{3}{*}{I} & A & 59.2 & 56.2 & 52.9 & 48.0 & - & \multirow{3}{*}{50.0} & \multirow{3}{*}{\(\pm\)2.3} \\  & B & 60.2 & 59.7 & 57.1 & 53.0 & 48.4 & & \\  & C & 61.3 & 55.7 & 53.6 & 47.2 & - & \\ \hline \multirow{3}{*}{II} & D & 64.5 & 58.5 & 56.5 & 54.0 & 49.8 & \\  & E & 54.1 & 52.2 & 50.8 & 44.4 & - & \\ \cline{1-1}  & F & 56.9 & 51.8 & 50.2 & 49.8 & 49.3 & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Noise values measured in residential areas.