02-22-1988 - Agenda Packet City Council - regular meeting

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Throughout the study area only 10% of the develop, are conforming in lot area. The bulk of the development. 'ed prior to adoption of the 1975, 2-acre lot size requirement. 2. Factors Limiting Long -Term Use of On -Site Systems in Stubbs Bay a. Lot size is perhaps the most critical limiting factor for on -site sewage treatment in the most densely developed parts of the Stubbs Bay Study Area. Where lot sizes are 1/2 acre or less, often there is not a suitable location meeting the minimum required sanitary setbacks in whic;, to locate a new or replacement septic system (see Exhibit D). b. High water tables due to low elevations near the lakeshore limit many properties to either mound systems or holding tanks, since the 3' required vertical separation between drainfield and water tables can't be maintained. C. Heavy clay loam soils fc ind on most of the high ground in the study area, have slow percolation rates (requiring relatively more drainfield per gallon of effluent) and often create perched seasonal water tables which affect the functioning of trench drainfields. The Hennepin County Soil Survey Map indicates that the soils in the Stubbs Bay Study Area generally are not suited for trench systems (see Exhibit E). Mound systems are often suitable on these soils where slopes are 6% or less, and where adequate usable space is available. However. the small lot sizes and steep slopes eliminate the capability of installing a mound system on many lots within the study area. d. Surface drainage can have a limiting effect on the functioning of drainfields, especially where drainfield systems were placed in low drainageways in order to avoid use of a pump. e. Aside from the physical limitations and small lot sizes, other factors appear to have historically rnntributed to septic system failures in Stubbs Bay as will as in other areas, and observed failures in many cases may be attributed to one or more of the these factors: 4