Treatment and Disposal of Milk House and Milking Parlor Wastes

Toilet Waste Treatment

Sewage discharged from the toilet facilities contains disease-causing organisms that cannot be discharged into the ground surface. Therefore, toilet wastes must not be discharged into the same plumbing system that handles the wastes from the wash water used for the floors and equipment. Toilet wastes must be discharged into a separate septic tank and then, if possible, discharged into a soil treatment system, preferably a drainfield trench. If soil conditions make subsurface drainage impractical, septic tank effluent can discharge into a lagoon. However, the lagoon cannot be used to irrigate crops for human consumption if this is done.

It is absolutely necessary that the waste water be separated into two plumbing systems, one for the water from washing floors and the milking equipment and the other for the wastes from the toilet facility.

The sewage treatment system for the toilet room consists of a septic tank and soil treatment unit. The septic tank separates the solids and allows the effluent to flow into the soil treatment unit, preferably a drainfield trench. Both the septic tank and the drainfield trench can be considerably smaller than those required for the home.

Septic Tank Construction

It is usually most economical to purchase a prefabricated septic tank. Precast is often the most economical and most suitable. Do not install metal tanks; they will corrode and begin to leak within 5 years. A septic tank can also be constructed in place using either curved or rectangular concrete blocks. If concrete blocks are used, they must be laid on a poured concrete base. The curved blocks can be laid without mortar, but must be given two coats of plaster cement after block placement. Rectangular blocks must be laid with mortar and given two coats of plaster cement on the inside of the tank. Fiberglass tanks are also available, though somewhat more expensive than precast concrete tanks. Fiberglass tanks weigh less and consequently are easier and less expensive to transport.

A septic tank must be watertight and must have proper inlet and outlet baffles of materials that won't corrode, manhole access, inspection pipes, a 3-inch drop from inlet pipe to liquid surface, plus many other necessary features. Prefabricated septic tanks are usually available. Check with your local zoning administrator to see if the tank you plan to buy meets specifications.

Sizing the Septic Tank

The septic tank allows the solids to separate from the liquids. In case of a toilet facility, which must be in a room separate from the milkhouse, most of the solids will be generated by the toilet stool. Any soap scum from the lavatory or shower will end up in the floating scum layer of the septic tank. The size of the septic tank will depend upon the type of toilet room and the number of people using it each day. If there is a shower, this may generate up to 30 gallons per use. An average toilet flush is about 5 gallons and 1 or 2 gallons of water are needed to wash hands and face.

Don't install a septic tank having less than 300 gallons of liquid capacity. Install a 500 gallon or larger tank if your daily estimated water use is more than 150 gallons. If you use a prefabricated concrete tank, you may not be able to purchase one much smaller than 500 gallons. A larger tank is usually an economical purchase since it has a greater volume to store the accumulated solids.

Tank Location and Access

The septic tank should be located at least 10 feet from the milkhouse and barn. It should be located at least 50 feet from any water supply well. Also, the tank should not be located where the milk truck or other heavy vehicles will drive over it unless the tank has a reinforced cover strong enough to withstand those loads. Many times it is difficult to locate a septic tank near a milkhouse because of a driveway. Locate the septic tank on the other side of the drive, and run a cast iron (for strength) sewer pipe under the driveway to the septic tank. The cast iron pipe can be relatively shallow since it will be carrying the warm sewage. If the sewer pipe is laid on a uniform grade of no more than 1 inch in 4 feet and no less than 1 inch in 8 feet, it will transport all of the sewage solids and normally will not freeze. As an additional protection against freezing, the 4-inch cast iron pipe can be encased in a 6-inch layer of clean rock, ¾-inch to 2½ inches in diameter. For additional insulation, a 2-inch thick by 2-foot wide sheet of styrofoam can be laid in the trench above the sewer before the soil is backfilled.

It is much better to run the raw sewage under a driveway than to run the effluent line from the septic tank under the driveway because the flow is much faster through the raw sewage line and the liquid is warmer.

When the septic tank is located 10 feet from the milkhouse and the snow cover is undisturbed over the sewer pipe, 12 inches of soil cover is enough to prevent the pipe from freezing. The sewer pipe can be suitable quality plastic, but be careful to lay it on an even grade and no flatter than 1 inch in 8 feet (1 percent).

The top of the septic tank usually should be close to the ground surface. Twelve inches of earth cover is sufficient to protect the tank from freezing. Allow snow to accumulate over the tank to provide some insulation. The septic tank should have manhole access within 6 inches of the ground surface. Cover the manhole with at least 6 inches of earth so that someone cannot accidentally open the manhole cover and fall into the tank. Inspection pipes should extend up from the inlet and outlet baffles. These will allow you to inspect the tank and remove any possible plugging. The inspection pipes should be flush with or above the final ground surface with tight-fitting caps.

Treatment and Disposal of Septic Tank Effluent

Federal standards on which Minnesota Grade A milk interpretations are based do not recommend discharging septic tank effluent into a livestock waste lagoon, except where soil conditions make subsurface drainage impractical. The water from a livestock waste lagoon receiving any human sewage cannot be used to irrigate any crops used for human consumption.

Often it is less expensive to treat the small amount of septic tank wastes in a drainfield trench than to run a pipe to the lagoon. If some lawn area and suitable soil is available reasonably close to the milkhouse, install a shallow drainfield trench. The amount of trench needed will depend upon the amount of water used in the toilet facilities of the milkhouse. Table 4 presents the amount of drainfield trench required for various water uses.

Drainfield Trenches

Suitable soil is an excellent filter for septic tank effluent. Soil with a percolation rate between 0.1 minute per inch and 60 minutes per inch will remove bacteria and fine sewage solids from the septic tank effluent.

Soil with a percolation rate foster than 0.1 minute per inch has large pore spaces which cannot effectively filter the sewage effluent. Soil with a percolation rate slower than 60 minutes per inch is an effective filter, but does not allow much liquid to pass through. Such a soil likely will have its natural structure damaged during construction so that it will accept little or no sewage effluent. On such soils, mounds or other alternative sewage treatment may be necessary.

Fine-textured soils also often have a high water table in the spring that will prevent the drainfield trench from treating any sewage. The bottom of the drainfield trench should be at least 3 feet above the highest level of the water table for satisfactory operation and proper sewage treatment.

Evaluate the soil in the area that could be used for a drainfield. Make soil borings and run a percolation test according to the procedure outlined in Extension Folder FO-0583, How to Run a Percolation Test. Estimate the daily water use of the toilet room and select the amount of trench bottom area from table 4. For example, if the soil percolation rate is between 31 and 45 minutes per inch and you estimate a water use of about 50 gallons per day, then 80 square feet of trench bottom area will be needed.

A drainfield trench can be no narrower than 1½ feet and no wider than 3 feet. A 30-inch (2½-foot) backhoe width is common. With this trench width, you will need 80/2.5 = 32 lineal feet of trench to treat 50 gallons of sewage each day.

If the soil is suitable, excavate a trench 24 to 30 inches deep with the bottom level throughout the trench length. Use a backhoe with raker teeth along the sides as well as on the tip of the bucket. Leave the soil bottom and sidewalls of the excavated trench rough so the soil will absorb sewage effluent easily. Smeared or compacted soil will not accept as much effluent as you have designed for the system. Never excavate a clay soil when it is wet and don't allow any equipment wheels or tracks in the bottom of the excavation. Don't walk in the bottom of the trench because you will pack the soil. Have them trench bottom and sidewalls in a natural soil condition before the trench rock is placed.

Place 12 inches of clean rock, ¾-inch to 2½-inches in diameter. in the bottom of the trench. The rock should be free of dust, dirt, and debris. Do not use crushed limestone because the sewage will dissolve it and it will clog the soil.

Place a 4-inch distribution pipe on the trench rock laid on a grade of 1 inch in 50 feet. Use plastic pipe with perforations at least ½ inch in diameter or agricultural drain tile in 1-foot lengths spaced ¼ inch apart. Don't use plastic drain tubing because the small holes will plug with sewage.

Perforated plastic pipe should be laid with one row of holes at the bottom. The ¼-inch space between drain tiles should be covered along the top of the tile by tarpaper strips to prevent soil from filtering down into the tile.

Use plastic distribution pipe with at least 1,200 pounds per lineal foot of crushing strength. Standard quality clay drain tile is suitable, but concrete tile must be of "special quality" grade or the sewage will break it down or dissolve it.

Cover the distribution pipe with 2 inches of the trench rock. Then place a 3- to 4-inch layer of loose hay or straw covered by untreated building paper on the rock to keep the soil backfill from filtering down into the rock.

Add 12 inches of top soil backfill over the top of the hay or straw layer. Mound the backfill 6 inches above the level of the original soil to allow for settling. You can pack the backfill by foot or with light equipment, but don't allow any heavy equipment on the trench after construction.

Let grass grow over the drainfield trench. It can be mowed as part of your lawn or clipped several times during the summer.

Don't let milk trucks, tractors, cars, or other heavy vehicles drive on the drainfield trench. In the winter, let snow accumulate naturally in the trench area. Don't compact the snow with snowmobile or foot traffic. Trenches with 6 to 12 inches of soil above the top of the trench rock won't freeze if there is a good grass cover and loose snow.

Septic Tank Maintenance

The purpose of the septic tank is to trap the solids and keep them out of the drainfield. Bacteria break down some of the solids, but a residue remains that must eventually be pumped out. If the septic tank is 300 gallons or larger and gets only the toilet wastes, the solids should not need to be removed for 3 to 5 years, possibly longer.

Have the milkhouse septic tank serviced when the house septic tank is serviced. There will likely be little, if any, additional cost, particularly if the tank manhole is easily accessible. The septic tank serviceperson will dispose of the septic tank solids properly so they will not endanger the public health or contaminate ground or surface waters.

Produced by Communication and Educational Technology Services, University of Minnesota Extension.

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