Specific System Design Criteria
All of the treatment systems discussed in this guide require a primary septic tank with inlet and outlet baffles, figure 1. These tanks should meet all state-specific standards for construction or placement. The primary septic tank reduces settleable solids, fats, and grease, and also serves as a buffer between the final treatment system and the bulk tank should the entire bulk tank need to be dumped due to contamination. Because of these criteria, the primary septic tank should be sized for a minimum three-day Hydraulic Retention Time (HRT), the volume of the bulk tank, or 1000 gallons, whichever is greater. The recommended procedure for dumping a contaminated bulk tank is outlined below. Effluent from the primary septic tank is pumped or flows by gravity into a second septic tank or to the specific treatment system.
Primary septic tank installation
All septic tanks must meet the minimum design specifications outlined in MN Rules Chapter 7080 and be installed with a minimum of two feet and a maximum of four feet of soil cover over the top. See Section 7 of the University of Minnesota Onsite Sewage Treatment Program Manual for more information on septic tanks. If the site conditions do not allow for two feet of soil cover, two inches of insulation should be placed over the top of tank before being covered. The insulation reduces the chance of the system freezing in cold weather. At times the site elevations may require an initial sump be installed to move the effluent from the milk house to the first septic tank.
A commercial size effluent filter should serve as the last baffle before exiting the septic tank. This will help reduce any suspended material from exiting the tank. This effluent filter should be checked monthly after installation and cleaned with water if needed. If monthly inspections show no signs of sludge buildup filter inspections can be done quarterly.
Dumping a Bulk Tank
If the bulk tank milk is contaminated and needs to be dumped, the septic tank can be pumped and then the bulk tank drained into the septic tank and the septic tank (with the waste milk) can be pumped again. This waste milk can be land applied. Contact your milk cooperative for alternative methods of disposing of this waste milk.
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