305.630.  Noise mitigation — requirements — roads, relocation of highways — effect of plan on floodplain. — 1.  Any area surrounding an airport as defined in section 305.600 which is to be expanded, and which has a noise level rating of seventy-five LDN or greater shall be purchased by the airport authority or owner of such airport for purposes of noise mitigation within a reasonable period of time after the determination of such noise level.  Noise level monitors shall be placed in locations surrounding the airport in such a manner as to ensure that an accurate noise level reading may be made in any given area, and such noise level monitors shall be maintained in proper working condition.  Upon the request of at least ten percent of the residents of a neighborhood, the airport authority or other owner of the airport shall install noise level monitors in such neighborhood and maintain them in proper working condition, if any portion of such neighborhood is located within three miles of the airport.

  2.  Whenever property is purchased or otherwise taken for airport use, as required by subsection 1 of this section, or pursuant to any powers authorized by law, a plan shall be prepared to establish a perimeter zone of not less than one thousand feet distance from the proposed airport boundary.  Any area within one thousand feet from the proposed airport boundary in which the noise level rating is less than sixty-five LDN may be exempted or excluded from the perimeter zone required by this subsection.  Residences within this area shall be purchased by the airport authority provided the majority of property owners agree to such a purchase plan.  Nothing in this subsection shall be deemed to prohibit any airport buy out program that is agreed to by the residents of any area involved in such a program or to prohibit any resident from requesting the airport to purchase such resident's property for conditions other than noise abatement.  Whenever a perimeter zone of not less than one thousand feet distance from the proposed airport boundary is established, the owner of the airport shall landscape such buffer to provide a visual barrier to air traffic activities and airport operation.

  3.  Any airport expansion which affects roads to any neighborhood shall also provide for the relocation of such access roads, rather than simply providing for the elimination of such access roads.  Any airport expansion which affects any highway which is maintained or regulated by the state transportation department shall provide that the highway is to be relocated and the costs of such relocation shall be the responsibility of the airport authority or other owner of the airport, except that the cost of an expansion of such highway may be shared by the transportation department.  Any such relocation shall be under the supervision of the transportation department.

  4.  In any airport expansion performed pursuant to any powers authorized by law, any land which is purchased for noise mitigation purposes shall be developed so that existing structures no longer used for their original purpose are demolished and the land is cleared of debris and allowed to return to its natural condition within six months after such property is vacated.

  5.  The airport authority or other owner of the airport shall file a plan of its proposed expansion with the department of natural resources.  The department shall approve the proposed expansion plan if such plan will not adversely affect the floodplain of any areas in the vicinity of the airport to such a degree as to cause significant risk of damage from floodwaters to any such area.