CAFO Manure Storage Winter Capacity Planning Level Guidance

The guidance outlined in this document is to be used to determine the Manure Storage Winter Capacity Planning Level for CAFO operations. As outlined in the Pennsylvania Nutrient Management Program Technical Manual, NMP Summary, this information must be documented in the NMP Standard Format.

For determining the manure storage winter capacity planning level, winter is defined as December 15 to February 28 which equals 76 days.

The following criteria must be addressed when determining the Manure Storage Winter Capacity Planning Level.

  1. Freeboard is required at all times and is not part of the useable capacity of the manure storage facility. The required minimum freeboard for storage facilities in 25 Pa. Code 91.36(a)(6)(i-ii) are:
    • 6-inch minimum freeboard for all manure storage facilities not meeting the following two conditions:
      1. 12-inch minimum freeboard for manure storages facilities that are ponds
      2. 24-inch minimum freeboard for manure storage facilities that are exposed to rainfall and on an operation with over 1,000 AEUs that was new or expanded after January 29, 2000
  2. The 25-year, 24-hour precipitation on the surface, at the required design storage volume level, of the facilities for all operations (except swine, veal and/or poultry designed after April 14, 2003) -- 25 Pa. code 91.36(a)(1). This precipitation volume must include the surface area of the facility itself as well as all manure handling areas draining into the facility. County values for the 25-year and 24-hour storm rainfall are listed in Supplement 9.
  3. The 100-year, 24-hour precipitation on the surface, at the required design storage volume level, of the facilities for all swine, veal and/or poultry designed after April 14, 2003 -- 25 Pa. code 91.36(a)(5). This precipitation volume must include the surface area of the facility itself as well as all manure handling areas draining into the facility. This location-specific 100-year, 24-hour rainfall value can be found at the NOAA 14 website. If that resource is not available, use 8.8 inches as the100-year, 24-hour rainfall. This is the highest 100-year, 24-hour rainfall value in PA. The minimum 100-year, 24-hour rainfall is 4.9 inches and within county variation can be as high as 2.2 inches.
  4. Manure, wastewater and other wastes to be accumulated over the winter storage. The total volume of average daily manure production over the planned winter storage period should be used as calculated in Appendix 3 of the Nutrient Management Plan Standard Format. Manure storage volume calculations are listed in Supplement 8;
  5. Normal precipitation less evaporation on the surface area, at the design storage volume level, of the facility during the winter storage period -- NRCS Conservation Practice standard 313 (Waste Storage Facility). To assist with this calculation, monthly average rainfall, runoff and evaporation data, by county, are listed in Supplement 7;
  6. Normal stormwater runoff during the winter storage period from all areas that drain to the manure storage facility -- NRCS Conservation Practice standard 313 (Waste Storage Facility). To assist with this calculation, monthly average rainfall, runoff and evaporation data, by county, are listed in Supplement 7;

Note: For an additional margin of safety, it is recommended that the estimated Manure Storage Winter Capacity Planning Level not be adjusted by the volume of any winter manure applications authorized in the plan.

If the estimated Manure Storage Winter Capacity Planning Level is adjusted for the volume of manure authorized for winter spreading and the planned winter manure applications do not occur, this could result in exceeding the useable winter storage capacity and not meeting the required minimum freeboard for the storage facility.

Manure Storage Winter Planning Level for Straight-Walled Circular Storages

  1. Determine the gallons of storage needed for the winter period.
    1. Winter is defined as December 15 to February 28 which equals 76 days.
    2. Gallons of winter storage from manure and waste production = (Daily manure production + Bedding + Washwater + Drainage area Normal Precipitation less evaporation) x 76 days. Do not include drainage area Normal precipitation less evaporation from drainage area if computed separately as outlined in step 7.b.
  2. Convert the needed gallons of winter storage from Step 1 to cubic feet.
    1. Cubic feet of winter storage = Gallons of winter storage (from Step 1.b.) ÷ 7.48
  3. Determine the volume per foot of storage.
    1. Volume per foot of storage (circular storages) = 3.14 (pi) x storage radius squared
  4. Determine the feet of storage needed for the winter period.
    1. Cubic feet of winter storage needed (Step 2.a.) ÷ Volume per foot of storage (Step 3.a.)
  5. Determine the appropriate freeboard.
    1. The freeboard varies by the type of farm. Refer to Manure Storage Winter Capacity Planning Level item 1 on page 1.
  6. Determine the appropriate design storm.
    1. The design storm varies by the type of farm and county. Refer to Manure Storage Winter Capacity Planning Level items 2 and 3 on page 1.
    2. Rainfall contribution to the manure storage from the appropriate design storm = Design Storm Rainfall ÷12
  7. Determine the depth effect on the storage from runoff from associated drainage areas for both the Design Storm Rainfall and from Normal precipitation less evaporation over the winter period. This second part may already be included in 1.b.
    1. Depth in the storage from the drainage area to the manure storage from the appropriate Design storm = (Drainage area x (Design Storm Rainfall ÷ 12)) ÷ volume per foot of storage (from Step 3.a.)
    2. Depth in the storage from the drainage area for Normal precipitation less evaporation over the winter storage period. Use Supplement 7 with appropriate county and surface type, typically paved and assuming evaporation. Prorate the December value by multiplying by 17/31 and add January and February. Depth on storage from Normal precipitation less evaporation from drainage area=(Drainage area x (((Net runoff for Dec. x 17/31) + Jan +Feb)) ÷12)÷ volume per foot of storage (from step 3)
  8. Summation: Depth of storage needed going into the winter period (As measured from top of storage)= Freeboard(step 5) + Rainfall Depth (step 6.a.) + Feet of storage needed for wastes (step 4.a.) + Drainage area Design Storm resulting Depth ( Step 7.a.) + Drainage area Normal precipitation less evaporation ( Step 7.b.), if not included in (Step 1.b.)
  9. Record this value in NMP summary.

Example Straight-Walled Circular Manure Storages

A Clearfield County dairy farm has a straight-walled circular manure storage with a diameter of 100 feet and a radius of 50 feet. This farm has a 3,000 ft2 paved drainage area contributing to the manure storage. The depth of storage is 10'. The site has < 1,000 AEU's.

  1. For the winter period, 200,000 gallons of usable storage is needed. This volume includes the following:
    1. Daily manure production + Bedding + Washwater
    2. Normal Precipitation less evaporation runoff volume from any drainage area
      1. This value included in 1.a.
  2. Using the 200,000 gallons from Step 1, determine the cubic feet of storage needed.
    Cubic feet of storage needed = 200,000 gallons ÷ 7.48 = 26,738 ft3
  3. Using the storage radius of 50 feet, determine the volume each foot of storage holds.
    Volume per foot of storage (circular storages) = 3.14 x (50 ft)2 = 7,850 ft3
  4. Using volume of winter storage needed (Step 2) and the volume per cubic foot of storage (Step 3), determine how many feet of storage are needed for winter period.
    Feet of storage needed at the winter period = 26,738 ft3 ÷ 7,850 ft3 = 3.41 ft
  5. Based on the site information and guidance.
    Feet of freeboard in storage = 0.50 ft
  6. Add required design storm feet requirements. Technical Manual Supplement 9 expresses all design storm rainfall as inches.
    1. 25 yr/24 hr rainfall for Clearfield County = 4.4 in. ÷ 12 = 0.37 ft
    2. Design storm depth contribution directly to the manure storage = 0.37 ft
  7. Depth contributions from associated drainage areas.
    1. Design storm volume contribution from the drainage area to the manure storage = 3,000 ft2 x 0.37 ft ( same as in step 6.a.) ÷ 7,850 ft3 = 0.14 ft
    2. Included in 1.b.
  8. Summation of required Feet of storage needed at the beginning of winter as measured from the top of storage = 3.41 ft + 0.50 ft + 0.37 ft + 0.14 ft = 4.42 ft
  9. Record in the NMP summary that the required depth from top of storage going into the winter period must equal or exceed 4.42 ft.

Manure Storage Winter Planning Level for Straight-Walled Rectangular Storages

  1. Determine the gallons of storage needed for the winter period.
    1. Winter is defined as December 15 to February 28 which equals 76 days.
    2. Gallons of winter storage from manure and waste production = (Daily manure production + Bedding + Washwater + Drainage area Normal Precipitation less evaporation) x 76 days. Do not include drainage area Normal precipitation less evaporation from drainage area if computed separately as outlined in step 7.b.
  2. Convert the needed gallons of winter storage from Step 1 to cubic feet.
    1. Cubic feet of winter storage = Gallons of winter storage (from Step 1.a.) ÷ 7.48
  3. Determine the volume per foot of storage.
    1. Volume per foot of storage (rectangular storages) = storage length x storage width
  4. Determine the feet of storage needed during the winter period.
    1. Depth of storage = Cubic feet of winter storage needed (Step 2.a.) ÷ Volume per foot of storage (Step 3.a.)
  5. Determine the appropriate freeboard.
    1. The freeboard varies by the type of farm. Refer to Manure Storage Winter Capacity Planning Level item 1 on page 1.
  6. Determine the appropriate design storm.
    1. The design storm varies by the type of farm and county. Refer to Manure Storage Winter Capacity Planning Level items 2 and 3 on page 1.
    2. Rainfall contribution to the manure storage from the appropriate design storm = Design Storm Rainfall ÷ 12
  7. Determine the depth effect on the storage from runoff from associated drainage areas for both the Design Storm Rainfall and from Normal precipitation less evaporation over the winter period. The second part may already be included in 1.b.
    1. Depth in the storage from the drainage area to the manure storage from the appropriate Design storm = (Drainage area x (Design Storm Rainfall ÷ 12)) ÷ volume per foot of storage (from Step 3.a.)
    2. Depth in the storage from the drainage area for Normal precipitation less evaporation over the winter storage period. Use Supplement 7 with appropriate county and surface type, typically paved and assuming evaporation. Prorate the December value by multiplying by 17/31 and add January and February. Depth on storage from Normal precipitation less evaporation from drainage area = (Drainage area x ((Net runoff for Dec. x 17/31 + Jan +Feb)) ÷12) ÷ volume per foot of storage (from step 3.a.)
  8. Summation: Depth of storage needed going into the winter period (As measured from top of storage)= Feet of storage needed for wastes (step 4.a.) + Freeboard(step 5.a.) + Rainfall Depth (step 6.b.) + Drainage area Design Storm resulting Depth ( Step 7.a.) + Drainage area Normal precipitation less evaporation ( Step 7.b.), if not included in (Step 1.b.)
  9. Record this value in NMP summary.

Example Straight-Walled Rectangular Manure Storages

A Clearfield County farm has a straight-walled rectangular manure storage with a length of 80 feet and a width of 50 feet and a depth of 10 feet. This farm has a 3,000 ft2 drainage area contributing to the manure storage that was installed after the original NMP was developed. The site has < 1,000 AEU's.

  1. For the winter period, 200,000 gallons of usable storage is needed. This includes the following:
    1. Daily manure production + Bedding + Washwater
    2. Normal Precipitation less evaporation runoff volume from any drainage area
      1. The drainage area did not exist when the plan was done and this value will be computed in 7.b.
  2. Using the 200,000 gallons from Step 1, determine the cubic feet of storage needed.
    Cubic feet of storage = 200,000 gallons ÷ 7.48 = 26,738 ft3
  3. Using the storage length and width, determine the volume each foot of storage holds.
    Volume per foot of storage depth = 80 ft x 50 ft = 4,000 ft3
  4. Using volume of winter storage needed (Step 2) and the volume per cubic foot of storage (Step 3.a.), determine how many feet of storage are needed for winter period.
    1. Feet of storage needed for winter period = 26,738 ft3 ÷ 4,000 ft3 = 6.68 ft
  5. Determine the appropriate freeboard.
    1. Feet of freeboard in storage = 0.50 ft
  6. Add required design storm feet requirements. Technical Manual Supplement 9 expresses all design storm rainfall as inches.
    1. 25yr/24 hr rainfall for Clearfield County = 4.4 in. ÷ 12 = 0.37 ft
    2. Design storm requires 0.37 ft of depth in the storage
  7. Associated depths from drainage area
    1. Design storm volume contribution from the drainage area to the manure storage = (3,000 ft2 x 0.37 ft) ÷ 4,000 ft3 = 0.28 ft
    2. Depth on storage from Normal precipitation less evaporation from drainage area = 3,000 SF x ((1.17 x 17/31 + 0.79 + 0.94) ÷12)÷ 7,850 ft3 = 0.08 feet
  8. Summation: Depth of storage needed going into the winter period (As measured from top of storage) = 6.68 + 0.5 + 0.37 + 0.28 + 0.08 = 7.46 ft
  9. Record in the NMP summary that the required depth from top of storage going into the winter period must equal or exceed 7.46 ft.

Manure Storage Winter Planning Level for Sloped-Walled Storage

The volume of storage per unit of depth changes for sloped waste storage facilities. This makes the calculation for the required depth of storage going into the winter period more complicated than for straight-walled storages. Follow the steps below for the most direct method for determining the Manure Storage Winter Planning Level. This method assumes that the inside top dimensions can be determined and a Stage-storage curve was developed for the storage facility or that one can be developed by contacting the "Engineer of record" for the facility. If that information is not available, your engineer may choose to use site specific engineering calculations or use the excel spreadsheet option that will provide the required information.

  1. Determine the gallons of storage needed for the winter period.
    1. Winter is defined as December 15 to February 28 which equals 76 days.
    2. Gallons of winter storage from manure and waste production = (Daily manure production + Bedding + Washwater+ Drainage area Normal Precipitation less evaporation) x 76 days. Do not include drainage area Normal precipitation less evaporation from drainage area if computed separately as outlined in step 5.b.
  2. Determine the appropriate freeboard.
    1. The freeboard varies by the type of farm. Refer to Manure Storage Winter Capacity Planning Level item 1 on page 1.
  3. Determine the appropriate design storm.
    1. The design storm varies by the type of farm and county. Refer to Manure Storage Winter Capacity Planning Level items 2 and 3 on page 1.
  4. Determine the contributing volume directly on the storage from both the Design Storm Rainfall and from Normal precipitation less evaporation over the winter period.
    1. Volume (in gallons) on the storage from the Design storm to the manure storage = Inside top width x inside top length x (Design Storm Rainfall ÷ 12) x 7.48
    2. Volume (in gallons) on the storage for Normal precipitation less evaporation over the winter storage period. Use Supplement 7 with appropriate county and surface type, typically paved and assuming evaporation. Prorate the December value by multiplying by 17/31 and add January and February. Volume (in gallons) on the storage from Normal precipitation less evaporation from drainage area = Inside top width x inside top length x (((Net runoff for Dec. x 17/31) + Jan +Feb)) ÷12) x 7.48

    Note: When designing a storage these events are normally shown as vertical distances subtracted from the top, however, when the storage is only partially full, the effect on the vertical depth can be significant due to the sloping sides, thus they are converted to volumes.

  5. Determine the contributing volume on the storage from runoff associated with drainage areas for both the Design Storm Rainfall and from Normal precipitation less evaporation over the winter period.
    1. Volume (in gallons) to the storage from the drainage area to the manure storage from the appropriate Design storm = Drainage area x (Design Storm Rainfall ÷ 12) x 7.48
    2. Volume (in gallons) to the storage from the drainage area for Normal precipitation less evaporation over the winter storage period. Use Supplement 7 with appropriate county and surface type, typically paved and assuming evaporation. Prorate the December value by multiplying by 17/31 and add January and February. Volume (in gallons) to the storage from Normal precipitation less evaporation from drainage area=Drainage area x (((Net runoff for Dec. x 17/31) + Jan +Feb) ÷12) x 7.48
  6. The total volume of storage needed for the winter period = Volume (step 1.b) + Volume (step 4.a.) + Volume (step 4.b.) + Volume (step 5.a.) + Volume (step 5.b.)
  7. Go to the Stage-storage curve for that facility. Starting at the top of embankment elevation or maximum depth and subtract the required freeboard from step 2.a. At that elevation read the associated volume available and record it.
  8. Determine maximum depth or elevation required at beginning of winter period.
    1. Volume (step 7) - Volume (Step 6) = Maximum volume allowed going into winter period.
    2. Read associated elevation or depth from previous step 8.a. This is the maximum elevation or depth entering the winter period.
  9. Determine the required vertical depth from top of embankment.
    1. Minimum vertical depth entering the winter period = total depth or top to dam elevation and minus the depth or elevation at the maximum allowed volume.
    2. Minimum slope distance entering the winter period = minimum vertical depth (step 9.a.) x inside slope ratio of the storage
  10. Record the minimum required vertical depth and slope distance in the NMP summary.

Example Slope-Walled Manure Storages

A Lebanon County dairy farm has a sloped-HDPE lined manure storage. The inside slope ratio for the storage is 2.5. The storage system has three stages. Stage 3 will provide the winter storage. The inside top dimension are 153' by 247' with a usable depth of 12'. There is a 8,400 ft2 of drainage area contributing to the manure storage from a sandlane and sand recovery area. This > 1,000 AEU's CAFO was built in 1998. The evaluation is on the system for the 600 cow dairy barn. A Stage-Storage curve was provided for Stage 3 as shown in Figure 1 at end of example.

  1. Determine Winter Storage Volume
    1. From the original design printout the manure+wastewater+bedding was 2,795,575 gallons for 180 days.
    2. Daily production = 2,795,575 ÷ 180 days = 15,531 gallons/day
    3. Winter Storage Volume = 15,531 x 76 days = 1,180,356 gallons
    4. Drainage area Normal precipitation less evaporation will be addressed in 5b.
  2. The freeboard for this site is 1 foot.
  3. The design storm for this operation is the 25yr-24hr. event of 5.7 inches.
  4. Determine Design storm and Normal Precipitation less evaporation volume over storage.
    1. Design storm volume = 153'x247' x (5.7"/12) x 7.48 = 134,271 gallons
    2. Normal Precipitation less evaporation volume = 153' x 247'x (((2.34x17/31)+3.1+2.42) ÷12) x 7.48 = 160,259 gallons
  5. Determine Design storm and Normal Precipitation less evaporation volume over 8,400 SF drainage area going to the storage.
    1. Design storm volume = 8,400 x (5.7"/12) x 7.48 = 29,845 gallons
    2. Normal Precipitation less evaporation volume = 8,400 x (((1.7x17/31)+1.58+1.28) ÷12) x 7.48 = 19,856 gallons
  6. Total volume needed for winter period = 1,180,356 + 134,271 + 160,259 + 29,845 + 19,856 = 1,524,587 gallons
  7. From Figure one, subtract 1' of freeboard from the total depth of 12' and read across at 11' and then read down at 2,150,000 gallons.
  8. The maximum depth is as follows.
    1. 2,150,000 (step 7) - 1,524,587 (step 6) = 625,413 gallons
    2. Go to Figure 1 and read up from 625,413 and across for a depth of 4.1'*.
  9. Required vertical depth or slope length from top of embankment at the beginning of the winter period.
    1. Required Vertical depth = 12 - 4.1 = 7.9'
    2. Required Slope length = 7.9' x 2.5 = 19.75'
  10. Record values shown in step 9 in your NMP summary

*These values vary slightly with the spreadsheet method due to interpretation.

Storage Curve

Figure 1. Stage - Storage Curve for the farm's manure storage with readings

Manure Storage Winter Planning Level for Sloped-Walled Storage, Excel Spreadsheet Option

This method will generate a stage-storage curve for a typical sloped waste storage facility based on inside top length and width of the facility, along with knowing total depth and inside slope ratio. It will still require looking up net rainfall values and determining manure and other waste volumes over the winter period. Once all the data is inputted, it will allow the user to vary one input until the required storage matches. The output will show the required vertical depth going into the Winter Storage Period. This will only work on storages that have the same interior slopes on all sides. No credit is given to exterior type ramps. Sites that have multiple slopes require using actual As-built data to generate a Stage-storage curve.

January 1, 2013