Both audible and low frequency impulse noise can be produced by operating WTGs. The noises produced and their impacts will differ according to machine design and size, and site specific characteristics such as topography. Noise has not been a primary issue where wind farms are in isolated locations. However, some counties are beginning to receive complaints about noise where wind development is occurring near populated areas. Alameda County has received a substantial number of complaints about the noise levels from residents near the Altamont Pass. If new wind farms are to be located near existing residences or businesses, mitigation measures for noise may be necessary. Such mitigation measures can include testing of the wind turbines(s) prior to installation to determine the level of audible and impulse noise generated by operation, monitoring of noise levels as individual WTG's come on-line, and requiring compliance with local noise standards or ordinances.
The aesthetic impact of wind farm development is very difficult to evaluate and resolve. As more wind farms are constructed, counties are beginning to receive complaints from some residents. Some of the best winds are along or just below ridge tops and placing wind machines in these locations makes them extremely visible. In addition, construction on hillside locations results in vegetation loss and visible scarring of the landscape by roads and turbine pads.
Whether aesthetics becomes a major issue will depend upon the extent of actual damage, the viability of mitigation measures, the local political climate, and how vocal local residents are to changes in existing views resulting from WTG installations. In the San Gorgonio Wind Resource Study, Riverside County and the U.S. Bureau of Land Management have established a number of guidelines or mitigation measures, based on topography and the types and number of wind turbines being proposed, which can be implemented to reduce visual impacts in siting wind farms. These guidelines require that developers avoid slopes over 25 percent to prevent disturbance and degradation of landforms, and to limit visual scarring by cut and fill, retaining walls, trenching, and vegetation removal. The document also discusses appropriate set-backs from scenic highways and key viewpoints, spacing and clustering of various sized turbines, placement of turbines with unusual designs such as the Darrieus "eggbeater" turbines, and using colors that blend with the particular environment.