1.   Visible Emissions.  The visible emissions from any stationary source shall not exceed the percent opacity permitted below.  The percent opacity shall be determined by use of Environmental Protection Agency (EPA) Reference Method 9 (40 CFR Part 60, Appendix A).  In all zones, the percent opacity from any stationary source shall not exceed twenty percent (20%).

2.   Particulate Matter.  The emission of particulate matter from any operation or activity shall comply with the Iowa Department of Natural Resources (DNR) Air Quality Regulations.

3.   Toxic Air Pollutants.  The release of toxic air pollutants from any existing source, operation or activity shall not exceed the fractional quantities permitted below the Threshold Limit Values adopted by the American Conference of Governmental Industrial Hygienists.  If a toxic substance is not listed, verification that the proposed level of toxic air pollutants will be safe and not detrimental to the public health or injurious to plant and animal life will be required.  The measurement of toxic air pollutants shall be the average of any 24-hour sampling period.

   A.   In all C Zones and in the OBP Zone, the release of toxic air pollutants beyond lot lines shall not exceed 1/8 of the Threshold Limit Values.

   B.   In the I Zones, the release of toxic air pollutants shall not cause airborne concentration to exceed 1/8 of the Threshold Limit Values beyond zone boundary lines.

4.   Odorous Emissions.  The emission of offensive odorous air contaminants from any operation or activity shall not exceed the odor threshold concentration.  The odor threshold concentration is defined as the level which will just evoke a response in the human olfactory system when measured as set forth below.

   A.   In all Interim Development (ID) and C Zones and in the OBP Zone, when measured beyond lot lines at ground level or habitable elevation, odorous air contaminants shall not exceed the odor threshold concentration.

   B.   In the I Zone, odorous air contaminants shall not exceed the odor threshold concentration beyond zone boundary lines at ground level or habitable elevation.

5.   Glare.  Glare or light from any operation and all lighting for parking areas or for the external illumination of buildings or grounds shall be directed or located in a manner such that direct or indirect illumination from the source of light shall not exceed one and one-half (1½) foot-candles at lot lines in any R Zone or C Zone where a residential use is located.

6.   Sewage Wastes.  Sewers and sewage discharge shall meet the requirements of the appropriate regulations and guidelines established by one or all of the following:

   A.   The Clear Lake Sanitary District

   B.   Iowa Department of Natural Resources

   C.   Cerro Gordo County Board of Health

7.   Storage.

   A.   The open storage of materials and equipment shall not be permitted in any zone except I-1 and I-2 Zones, provided that the following requirements are met:

      (1)   Storage of materials and equipment shall be completely screened from view as required in Subsection (i) below.

      (2)   All combustible material shall be stored in such a way as to include, where necessary, access drives to permit free access of fire fighting equipment.

   B.   The bulk storage of flammable liquids and chemicals, when stored either in underground or above-ground tanks, shall occur no closer to the lot line or any principal building than the distance indicated by the following table:

 

The distance may be reduced to not less than 10 feet for a single container of 1,200-gallon water capacity or less, provided such a container is at least twenty-five (25) feet from any other container of more than 125-gallon water capacity.

8.   Screening.  Where a lot occupied by a commercial or industrial use abuts or is across a street, highway, alley or railroad right-of-way from an R or OBP Zone, a school or a recreational area, including a park, playground, Outlet Creek, Willow Creek or Clear Lake, screening shall be preserved, planted or constructed and maintained by the owner of the commercial or industrial use in accordance with the provisions set forth below.  In the instance where a lot occupied by a manufactured housing use abuts or is across the street from an RR-1 or RS-5 Zone, screening, in accordance with the provisions set forth below, shall also be provided by the owner of the manufactured housing use.

   A.   Location:

      (1)   Except for a use in the OBP Zone, screening shall be provided along lot lines or street right-of-way in a manner sufficient to effectively obscure the commercial or industrial use from view at ground level within the lot lines of a residential or OBP Zone, or school, abutting or located across the street from said commercial or industrial use.

      (2)   In an OBP Zone where parking is located within 60 feet of an R, OBP or ID Zone boundary, screening shall be provided in a location and manner sufficient to effectively obscure all off-street parking and loading, storage or other such areas of activity from view within the lot lines of the residential zone or school.

      (3)   In an RM Zone, screening shall be provided along lot lines or street right-of-way in a manner sufficient to effectively obscure the manufactured housing use from view within the lot lines of residential development in an RR-1 or RS-5 Zone.

      (4)   In all instances where street right-of-way, which acts to separate the lots on which said uses are located, is one hundred (100) feet or wider, screening shall not be required.

   B.   Screening Materials:

      (1)   An evergreen planting screen at least three (3) feet high when planted and spaced four (4) feet on center, may be used.  Other plant varieties may be incorporated into the evergreen planting screen if approved by and spaced according to the Building Official.  The planting bed shall have a minimum dimension of five (5) feet, be free of any impervious surface and be separated from streets, drives and parking areas by an unmountable curb or barrier in such a manner that sand and saltwater runoff will not damage the screening.

      (2)   Where a planting screen cannot be expected to thrive because of intense shade, soil and other site conditions, a solid fence of durable construction, an earthen berm covered with grass or low shrubs and/or other acceptable materials which provide maximum visual obscurity to a height of six (6) feet at maturity may be used, if approved by the Building Official.

   C.   Time of Installation:

      (1)   If a lot proposed for a commercial or industrial use is located adjacent to or opposite an existing residential use or subdivision in an R Zone, or a school, screening as required herein shall be installed prior to occupancy or commencement of a use.  The Building Official may grant a delay to the seasonal calendar dates of June 1 or November 1, whichever comes first.  Similarly, if a lot or space intended for the placement of a manufactured housing use is located adjacent to, or across the street from an existing residential development in an RR-1 or RS-5 Zone, the owner of the manufactured housing use shall provide screening as described herein.

      (2)   If (1) above is not the case, screening need not be provided until within six (6) months after a building permit is issued for a residential use or a school in an R Zone, a final plat of residential subdivision is approved, or a recreational area is available for use on adjacent or opposite land.

   D.   Exceptions:

      (1)   Where a proposed or existing commercial or industrial use is or will be located adjacent to or opposite a City recreational area, screening may be waived upon the granting of a conditional use from the Board of Adjustment for the following reasons:

(a)   If adequate existing or proposed landscaping within the recreational area is or will be provided.

(b)   If the nature of a use and the building occupied by the use are not objectionable to the purpose of the recreational area.

      (2)   Screening may be waived by the Building Official where the view is or will be blocked by a change in grade or by the natural or manmade features as determined by the Building Official.

   E.   Maintenance.  The owner shall keep all screening properly maintained, free of trash and litter, and all plant materials pruned in such a manner as to provide effective visual obscurity from the ground to a height of at least six (6) feet.