Agenda - Planning Commission - 02/04/2016

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• driveways, patios and other paved areas • sheds, gazebos, saunas, kennels, etc. • fences, retaining walls, etc. • swimming pools Situations and Considerations There are many and varied situations that may arise in the determination if a setback or restriction should be required. It is thought that these decisions could be better made on a case-by-case situation at the local level (except for the situations in the Mandatory situations section above). This section provides some guidance on the risks involved in making setback or restriction decisions. 1. Damage done to the superstructure of an existing BSLI from SSTS installation. In most situations, the installation of the SSTS could damage the superstructure of a BSLI. However, given that fact, it does not seem prudent to require a setback on all BSLI. It is recommended that careful consideration be given to possible damage during SSTS construction and require setbacks, restrictions or guidance based on possible risk and value of the BSLI. Examples in this area would include: • The damage caused if a sewage tank hits the superstructure when being placed into the excavation (tank swing). • The tail swing from excavation equipment hitting the superstructure. • Driving on paved areas with SSTS construction equipment not designed to carry a heavy load. 2. Damage to the in -ground structural integrity of an existing BSLI during installation of a SSTS (provided by Paul R. Heimkes, Minnesota Department of Labor and Industry; paul.heimkes@state.mn.us). There are requirements for the design of a buildings' footing and/or foundation that will require a designer to address how a sewage tank may affect the footing/foundation system. It should be remembered that foundations are designed and constructed of many different types of designs and/or materials. Examples include: piers, piles, wood foundations, pea -gravel footings, masonry blocks, geo-piers (piers usually drilled in and filled with larger compacted rock), timbers, etc. All of these types of materials can and will be affected differently by soil loading conditions, moisture, soil types, differential movement, or other bearing elements located adjacent to the structure(s). Below are seven items that must be reviewed and/or accounted for when considering the placement of a sewage tank next to a buildings' footing/foundation system: A. Frost depth and frost protection for the footing/foundation Soil is used to protect the building footing/foundation from frost/freezing and potential soil movement. In the southern part of the state, a minimum of 42 -inches of soil coverage is required. In the northern parts of the state, 60 -inches of soil coverage is required. Depending on soil conditions/types, even more could be required by the building designer. So placement of a sewage tank must not affect the soil coverage over the building footing or foundation. B. Minimum soil bearing capacity Minimum soil bearing capacity must be considered for the footing/foundation when an object encroaches into the required soil bearing area of the building. There is usually a minimum of a 2:1 ratio needed for soil bearing (projection area) under - and extending away from - a buildings' footing. Tanks or other elements that are placed in or below this area will require review of the standard footing/foundation design. Photo by LeRoy Janski — WI Dept of Commerce Subsurface Sewage Treatment Systems and Building, • wq-wwists4-47 • August 2011 MInne ota Pollution Structures and Lot Improvement Page 2 of 4 Control Aganty