How to Handle Seepage From Farm Silos
|Last Reviewed:||November 2018|
|History:||Replaces OMAFRA Factsheet 04-031, of the same name|
|Written by:||S. Clarke, P.Eng., and D. Hilborn, P.Eng|
PDF Version - 2.74 MB
As part of providing accessible customer service, please email the Agricultural Information Contact Centre (firstname.lastname@example.org) if you require communication supports or alternate formats of this publication.
Table of Contents
- Seepage is an Environmental Problem
- Rate and Volume of Seepage Production
- Managing Silo Seepage and Precipitation Runoff
- Management of Seepage
- Site Locations for Seepage Collection Tanks and vegetated Flow Paths
- Sizing of Small Seepage Tanks
Silage seepage presents two concerns for the agricultural industry - water pollution, and corrosion and deterioration caused by the silo silage juices.
When silage is harvested and stored at low moisture contents less than 70% for horizontal silos and 60% for tower silos, there is minimal corrosion and pollution threat. Above this moisture level, significant flow of silage juices (or seepage) from silos may occur (Table 1 and Figure 1). Corrosion happens where the seepage is trapped for a period of time.
The production of seepage can be reduced or eliminated through cropping techniques and harvest timing (see the OMAFRA Factsheet, Harvesting Corn Silage at the Right Moisture).
However, there are conditions where seepage can't be avoided. For example, weather conditions may force a farmer to harvest wet silage or ensile by-products such as sweet corn materials. Both will result in seepage production.
Figure 1. Horizontal silo - seepage production based on silage moisture content.
Most of the environmental problems associated with silage/haylage seepage on farms come from improper or inadequate collection and retention of the seepage draining from the silos. An adequate collection and storage/treatment system is essential if seepage is anticipated.
Table 2 provides information on the acids in silage seepage that cause silo corrosion. Detailed information on silo corrosion is available in the OMAFRA Factsheet, Deterioration of Concrete Tower Silos.
normally less than 1%
Source: Cornell University 1994 and OMAFRA
In 2013, farmers in Ontario made 5 million tonnes of corn fodder, producing in the process over 20 million L of silage seepage effluent. Silage seepage in an undiluted form has extremely high BOD (biochemical oxygen demand) values, ranging from 12,000-90,000 mg/L (Table 3), which is approximately 60-450 times stronger than domestic sanitary sewage. Even a small discharge of seepage into a watercourse can remove enough oxygen for a fish kill to occur. Reports from Pennsylvania, New York and Ontario have linked silage seepage to fish kills. In addition, cases of silage seepage contaminating wells in Ontario and the U.S. have been reported.
Table 3 shows that seepage contains significant nutrient concentrations (similar to liquid dairy manure). Seepage is an excellent nutrient source for growing crops if properly applied to land. However, similar to other nutrients, seepage can become a pollutant if it enters surface water or groundwater.
Rate and Volume of Seepage Production
The greatest percentage of silage seepage is produced within 5-10 days of storage loading. For normal silage and haylage production, the remaining seepage is usually produced within the following 30 days. The volumes produced are dependent on the vertical pressure in the silo and the initial moisture content of the crop (Figure 1). The addition of acid additives to silage facilitates higher crop moisture, which can result in a higher initial rate of silo seepage.
The ensiling of wetter materials such as sweet corn by-products or corn silage for biogas facilities results in much higher seepage production. This can occur throughout the entire period that the crop is stored.
Seepage flow out of vertical silos is the greatest during the first month of storage. In silos with good internal drainage (i.e., a network of floor drains to carry out leachate), it tapers off after that. Where internal drainage of the silo is poor (or the ensiled material is higher moisture), flow will occur throughout the total storage period as the silo is being emptied. Rainwater on uncovered silage can produce additional effluent.
For horizontal silos, the rain runoff or snow melt from the floor area inside the storage and feed preparation area adds more effluent to the collection system. The highly concentrated effluent base flow will be increased on occasion by rainstorms and snowmelt.
It is important that all the base flow from the silo along with the first flush of precipitation runoff is collected and stored, since this material has higher concentrations of organic matter and nutrients.
Figure 2. Horizontal silo front-flow seepage system - diluted liquid to vegetated area.
Figure 3. Low-flow collection system diagram. (Source: AEM)
Figure 4. Low-flow collection system.
Storage and Treatment of Silage Seepage
Collect the seepage and runoff in a small storage at the silo site and transfer it to an outdoor liquid manure or runoff storage on the farm. Do not contain silage leachate in an under-barn storage (located below animals), because dangerous gases may be produced when the effluent and manure are mixed. Where outdoor liquid manure or runoff storages are not available on the farm, provide a separate storage to contain seepage plus runoff material. During the cropping season, apply seepage on land in the same way as you would apply manure. If seepage is applied to the land, account for the nutrients in the seepage in the Nutrient Management Plan.
Another means of handling and treating seepage involves collecting and storing only the low-flow rates of concentrated leachate from the silo in a storage tank (Figure 2). Allow the diluted high-flow rates of material to flow to a vegetated flow path. Use a low-flow collection system (Figures 3 and 4) to separate the concentrated low-flow seepage.
Reduction of Seepage
Harvest silage/haylage at low moisture:
- <65% moisture content for tower silos less than 12 m (40 ft) deep
- <60% moisture content for tower silos over 12 m (40 ft) deep
- <70% for horizontal silos
Planting shorter-season varieties of corn will result in a drier crop, lowering seepage production. Avoid ensiling wet by-products such as sweet corn residue.
Bunker Silo Sealing/Covering Systems
Using a bunker silo sealing or covering system will reduce silage infiltration by air and water. A sealing system consists of a layer of white or black plastic used as a cover and seal. Old tires are placed edge to edge over the surface of this plastic to help seal the silage.
Figure 5. Tarpaulin and sausage bag system for silage protection.
Figure 6. Sausage bag placement.
New Silo Sealing System - "No Tires Used"
In this system, traditional plastic sheeting is covered with a second layer. Instead of tires, sausage-bags filled with sand or gravel anchor the cover in place (Figures 5 and 6). The advantages of this system are the added protection, improved sealing, flexibility, and ease of installation and storage of the sandbags.
- A polyethylene sleeve holds together several of the sausage-bags across the width of a silo. This product reduces the chance of air infiltration between the sausage bags. Figure 6 shows sausage bag placement.
- Use the sausage bags directly on the silo plastic, to reduce the cost and replace the use of tires. This is a good solution if birds or animals tear the plastic seal.
- Adding absorbents designed to take up excess moisture will result in very low or no seepage production. Materials include oatmeal, dried sugar beet pulp, dried corncobs, ground corn and hay cubes. To be effective, add enough material to absorb the anticipated seepage. Proper use of these materials is necessary. It may be possible to feed these materials, however, first get proper advice on how to make sure the material is safe as a feed source.
- On many occasions it may not be possible to wilt the forage adequately or harvest at the desired dry matter content. If the forage is too wet, seepage is likely. Add absorbent materials to "absorb" this seepage. Table 4 lists the water-holding capacity of various materials.
Source: University of Minnesota (1980)
Figure 7. Tower silo seepage storage system.
Recommended practices for managing silo seepage include:
- Cover the silo - this prevents precipitation from entering and leaching through the silage/haylage.
- Divert all surface water away from the silo site, as this is considered clean water and does not require collection and storage.
- For new silos where any seepage is expected, install a seepage collection and storage system as shown in Figures 2, 7 or 8.
- Inspect the interior silo surface each time the silo is empty for signs of corrosion. Wherever corrosion is severe, recoat the inside of the silo.
- For horizontal silos, there are several options to manage seepage:
- Existing horizontal silos: Place a 100-mm (4-in.) tile drain on the floor where the wall meets the silo floor (Option A, Figure 9)
- New silos: Form holes in the wall to drain silo seepage to an outside drain (Option B, Figure 9.) CAUTION: Protect steel from silage acids with adequate (75 mm (3 in.)) concrete cover.
- Existing or new horizontal silos with good floor drainage to the front of the silo: Install a catch basin that collects seepage and drains to a long-term storage tank (Figures 3, 4 and 10).
- Flow may occur throughout the total storage period as the silo is emptied. Diluted flow or flow in periods where seepage is not collected must not directly enter a watercourse or catch basin or run across land with shallow bedrock (Figure 2).
Figure 8. Horizontal silo seepage floor-drain collection system.
- Install cross drains 75 mm x 75 mm (3 in. x 3 in.) on 6-m (20-ft) spacing, filled with 20 mm (7?8 in.) of clear stone. Drain should pick up seepage and first flush of rain runoff.
- Drain cross drains to storage tank with header drain 100 mm x 100 mm (4 in. x 4 in.).
- Rain runoff from top of storage may be considered as clean water and will not reach the collection system.
- Collect, store and spread rain runoff from inside of the storage on cropland.
- Treat diluted rain runoff using an approved vegetated filter strip.
Figure 9. Outside-drain collection system for existing horizontal silo.
- (A) 100-mm (4-in.) diameter tile drains placed on silo floor.
- (B) Holes in silo walls lead to an exterior covered drain. Collect, store and spread rain runoff from inside storage on cropland. Treat diluted rain runoff using an approved vegetated filter strip.
Figure 10. Bunker seepage and clean water run-off system.
Caution: Never mix silage effluent in enclosed tanks, especially tanks within barns, because silage effluent mixed with manure slurry will accelerate the release of hydrogen sulphide gas. Add seepage only to uncovered outdoor storages.
Management of Seepage
Concentrated seepage may have to be mixed with the same amount of water (1:1) for application directly onto crops. Seepage is considered a nutrient, and the amount being applied must be accounted for in the Nutrient Management Plan.
Seepage is also used as a supplementary feed. Due to its high potassium and nitrate levels, only feed seepage after getting expert advice.
Seepage can also be used as an input for a digester system. To avoid operational issues, make sure it is introduced slowly.
Release any dilute material or runoff to a vegetated area. Do not do this if the vegetated area is on shallow bedrock. Make sure adequate distance to surface water or tile drain inlets exists.
As a good management practice, the Environmental Farm Plan recommends:
- locating seepage collection tanks at a distance of 60 m (200 ft) or greater from surface water (i.e., streams, ditches, ponds or tile inlets)
- setting separation distances between seepage tanks and wells at 23 m (76 ft) or greater for a drilled well and 46 m (151 ft) or greater for a bored/dug well
Locate storage sites for bagged, wrapped or tubed haylage (baylage) at least 9 m (30 ft) from surface water sources and field drainage tiles to reduce the risk of contamination.
Install additional storage to deal with wet years when seepage production is higher. Size the storage to include expected seepage volumes and runoff calculated at 0.0015 m3/m2/day (0.005 ft3/ft2/day) for the period of time that the flow is directed to the tank. Often the tank is sized to collect seepage for 1-2 months after the last filling of the silo occurred.
If the material in the seepage storage tank is not used immediately, leave enough freeboard in the tank for direct rainwater entry. Often, a 240-day period is used, requiring 0.6 m (2 ft) of freeboard.
- If the crop is stored at >80% moisture, size the storage for 10 m3/100 tonnes (320 ft3/100 ton) of crop storage.
- If the crop is stored at 70%-80% moisture, size the seepage storage for 3.1 m3/100 tonnes (100 ft3/100 tons) of crop stored.
- If the crop is stored at <70% moisture, use 1.55 m3/100 tonnes (50 ft3/100 tons) of crop stored.
Size a storage to contain seepage and runoff from a horizontal silo measuring 12 m x 30 m x 3.5 m (40 ft x 100 ft x 12 ft) for a 1-month period. Feed preparation apron area is 12 m x 6 m (40 ft x 20 ft). Crop moisture content is 75%. See Tables 5, 6 and 7.
Storage Capacity (T)
T70 = 980 tonnes (1,080 tons) (see Tables 5, 6 and 7)
(storage capacity at 70% moisture)
T75 = 0.3 (T70)/(1-M) (storage capacity at 75% moisture)
= 0.3 (1,080)/(1-0.75)
= 1,180 tonnes (1,296 tons)
Seepage Storage Volume
Seepage = 3.1 m3/100 tonnes x 1,180 tonnes
(100 ft3/100 tons x 1,296 tons)
= 36.5 m3 (1,296 ft3)
Rainfall Storage Volume
= 0.0015 m3/100 tonnes (0.005 ft3/ft2/day)
x 30 days x (area of silo m2 (ft2) + apron area m2 (ft2))
= 20 m3 (720 ft3)
Required Storage Size
= 3.65 m3 + 20 m3 (1,296 ft3+ 720 ft3)
= 56.5 m3 (2,016 ft3)
Seepage and Precipitation Storage Size 614 m3
Use Table 9 to find the dimensions of the required storage capacity = width x length x height
57 m3 (2,016 ft3) = 4.3 x 4.9 x 2.7 m (14
x 16 x 9 ft)
In addition, a flow path or vegetated area must be available to manage flows during the 11-month period when seepage is not expected. Do not design the flow path over tiles or shallow bedrock.
Figure 11. NMAN source material information for silo seepage.
Seepage Calculations in Software
OMAFRA has a software program called Agrisuite that includes the
ability to complete silo seepage calculations. This information
is in the MStor worksheet of this software. Figure 11 shows an MStor
calculation for information described in Example 1.
Agrisuite is available from the OMAFRA website. Search for Agrisuite.
- If the crop is stored at >70% moisture, size the seepage storage for 3.1 m3/100 tonnes (100 ft3/100 tons) of crop stored.
- If the crop is stored at/or below 70% moisture, use 1.55 m3/100 tonnes (50 ft3/100 tons) of crop stored.
- The design criteria will give a minimum of 2 days of storage for the seepage material. Provide up to 1 year of storage with very low-moisture crops (i.e., <60% moisture).
- Cover tower silos with roofs to keep out rain.
Size a seepage tank based on the following criteria:
- tower concrete silo measuring 6 m x 21 m (20 ft x 70 ft)
- alfalfa silage at 70% moisture
- see Table 8 for capacity
= 640 tonnes (703 tons)
Required seepage storage size
= 1.55 m3/100 tonnes x 640 tonnes (50 ft3/100
tons x 703 tons)
= 10 m3 (352 ft3)
Storage size (10 m3 (352 ft3))
= width x length x height
Use Table 9 to find the dimensions of the required
10.5 m3 (384 ft3)
= 2.5 m (8 ft) x 2.5 m (8 ft) x 1.7 m (6 ft)
If the tank is not covered, an additional 0.6 m (2 ft) of depth is required for direct rainfall entry.
The following tables list the approximate wet tons capacity for a number of common silo sizes. The tables take into account a 1:2 sloping front face. Widths given are inside to inside and do not include space taken up by posts and planking. When using these tables, calculate the daily feed removal to ensure enough feed is removed to prevent spoilage. For capacity in Tonnes, multiply figures shown by 0.91.
|Average Silage Density (lbs/cu ft)||Silo Height (ft)||Silo Width (ft)||Removal Rate (tons/day)||Silo Capacity (tons)
Silo Length (ft)
The following table lists the approximate wet tons capacity for a number of common silo sizes.
Source: OMAFRA Factsheet Tower Silo Capacities, Order No. 88-033.
|Silo Diameter X Settled Depth (ft)|| Corn Silage
|55% m.c.||60% m.c.||65% m.c.||70% m.c.|
|12 x 30||47||54||62||74|
|12 x 40||66||75||87||102|
|12 x 50||85||97||111||132|
|14 x 40||92||106||121||143|
|14 x 50||121||136||157||185|
|14 x 55||134||153||175||206|
|16 x 50||163||184||210||246|
|16 x 60||200||227||259||303|
|16 x 65||220||248||284||330|
|18 x 50||210||238||272||317|
|18 x 60||261||293||334||388|
|18 x 70||311||349||397||461|
|20 x 60||328||369||419||486|
|20 x 70||393||439||498||576|
|20 x 80||457||510||579||668|
|24 x 60||486||543||616||712|
|24 x 70||582||649||734||844|
|24 x 80||678||754||850||977|
|24 x 90||774||860||968||1110|
|30 x 80||1088||1280||1477||1628|
|30 x 90||1242||1475||1702||1877|
|30 x 100||1397||1672||1929||2127|
|30 x 110||1552||1871||2158||2382|
Source: OMAFRA Factsheet Tower Silo Capacities, Order No. 88-033.
Silo seepage can be a pollutant or safety hazard if managed incorrectly. The methods to properly manage silo seepage include collection, storage and use of the nutrient rich source on the farm and elimination of the liquid seepage.
This Factsheet was revised by Don Hilborn, P.Eng., By-Products Engineer, OMAFRA, Woodstock, and Steve Clarke, P.Eng., Energy & Crop Engineer, OMAFRA, Kemptville.
Do you know about Ontario's Nutrient Management Act?
The provincial Nutrient Management Act (NMA) and the Regulation 267/03 regulate the storage, handling and application of nutrients that could be applied to agricultural cropland. The objective is to protect Ontario's surface and groundwater resources.
Please consult the regulation and protocols for the specific legal details. This Factsheet is not meant to provide legal advice. Consult your lawyer if you have questions about your legal obligations.
Factsheets are continually being updated, so please ensure that you have the most recent version.
For more information:
Toll Free: 1-877-424-1300