Form 4-C Instructions: Storage Volume Calculation Worksheet
The purpose of this form is to verify the adequacy of manure storages for containing manure and
wastewater through critical periods when manure and wastewater cannot be applied to cropland.
This verification—Do I have enough manure storage? —is required by all three Illinois agencies
and is an important component of environmental stewardship.
Several high-profile manure storage overflow cases have occurred in Illinois in recent years,
spotlighting the need not only for having adequate storage but also managing that storage
capacity as the facility enters critical time periods. This form can help point out problems of
insufficient storage and assist you in planning future construction or management changes to
address those problems.
HINT: You can do many of the calculations on Form 4-C using free software from NRCS,
called AWM (Agricultural Waste Management). Download it from the NRCS web site at
<http://www.wcc.nrcs.usda.gov/awm/awm.html>. The software is written for designing a new
manure storage, but you can check the sizing of existing storages with it as well. An especially
handy feature is its storm water runoff and evaporation calculator. You identify your county, and
the weather records load and calculate automatically. Animal manure production data are also
included.
If you have historical manure hauling records…
One of at least three scenarios will apply to any storage:
1. New facility, having no history of manure production for the facility
2. Existing facility, new storage, having no history of manure storage or hauling records for
the storage
3. Existing facility and storage, having partial or extensive manure hauling records.
For Scenarios 1 and 2 (new manure or wastewater storage), you should perform all the
calculations on Form 4-C, including the storm water (lines 19-30) if this is an outside uncovered
storage. If the storage is not exposed to precipitation and does not receive runoff, you may skip
lines 19-30.
For Scenario 3 (existing storage with manure hauling records), you may in some cases be able to
skip lines 6-30 and put your historical manure hauling record average in line 31. If there is doubt
about the accuracy of the historical data, perform the calculations on the entire form and compare
the results in line 31 with your data. The calculations are especially important if you do not have
enough years of records to encompass years of average and above-average rainfall.
Instructions
Enter the name of the manure storage (or series of similar storages if they are being treated as
one storage).
Line 1. Enter the working volume of the manure storage you calculated on Form 4-B, here and
on Line 32 “Working vol.” If a series of similar manure storages is being treated as one storage,
enter the sum of those storages.
Line 2. Enter the animal species and stage of production adding manure to this storage. There are
three columns provided to allow entry of more than one species/stage. Example: Swine
confinement, pit under building, grower and finisher pigs in two different rooms.
Line 3. Enter the average numbers of animals that apply to this storage. Keep in mind that the
average manure production will be calculated for the purpose of showing whether you have
adequate manure storage capacity, so use your best estimate of the animal numbers.
Line 4. Animal average weight. For growing animals, one easy way to estimate is to add the
weight going into the growth stage and the weight leaving that stage, and dividing by two.
Example: swine nursery, average weight in = 11 lb., average weight out = 35 lb., 11 + 35 = 46,
average weight for the growth stage is 46/2 = 23 lb.
Line 5. Start with your best estimate of the maximum number of days manure and wastewater
storage this structure or series of structures can hold. At the end of the worksheet you will verify
whether the calculated manure and wastewater production is less than the working volume (there
is adequate storage capacity) or greater (you must reduce the estimated storage period).
The critical months for the storage design contain a period when you are not able to apply
manure to cropland or otherwise empty the storage. If the storage is outdoors and uncovered, you
are required to provide storage to contain the precipitation and runoff from a design storm.
Check the appropriate box. For new poultry and swine facilities, the design storm is the 100-year
24-hour storm; for all others, the design storm is the 25-year, 24-hour storm. Example: A dairy
manure storage pond receives manure plus feedlot runoff. You estimate that the liquid manure
storage has five months (150 days) storage capacity. Manure is land applied in the fall after
corn silage harvest and in the spring before corn planting. Some permanent pasture is available
for manure hauling in the winter. There could be two critical periods: summer (April through
August) or winter (November through March). Since rainfall and precipitation vary by month,
you may have to calculate both periods to see which is more restrictive. You should check the
box for the 25-year, 24-hour design storm (existing dairy facility).
Storage design period versus annual: Lines 6-18
Illinois regulations require you to calculate the annual manure production in addition to the
storage design period manure production. For Lines 6-18, each of the three animal species
columns is divided into “storage design period” and “annual” columns. If your storage design
period is 365 days, the numbers in the two columns will be equal. For all other cases, we
recommend you fill in the “storage design period” columns first, then go back and multiply those
numbers by the appropriate factor to give the “annual” number.
Line 6. From the data source you checked in Form 4-B, Line 1, enter the amount of manure
produced per animal, in cubic feet per day. Example: MWPS-18 gives the manure production of
a 150-lb average finishing pig as 1.2 cubic feet per day. This includes waterer spillage.
However, the pigs in this finisher enter at 80 pounds and are raised to 270 pounds. The average
weight is (80 + 270)/2 = 175 lb. So we could increase the average production by multiplying
175/150*1.2 = 1.4 cubic feet per day.
Line 7. Most sources of manure production data include wastewater. Otherwise enter the
appropriate daily per-animal wastewater estimate.
Lines 8-10. In a bedded facility, the bedding takes up storage volume. Enter your estimate of the
pounds of bedding per animal per day on Line 8, and the unit weight of the bedding on Line 9.
Line 10 is the quotient, resulting in the volume of bedding that goes into the storage per day per
animal. Example: A dairy freestall barn uses an average of 50 pounds of sand bedding per day
per stall. The sand weighs 150 pounds per cubic foot, so enter 1/3 cubic foot of bedding volume
per animal per day in Line 10.
Line 11. Add the manure, wastewater, and bedding. This is the daily per-animal volume.
Line 12. Some unusual systems may remove part of the manure and wastewater stream so that it
does not contribute to this storage. You may also want to use this line in the case of a system
where part of the manure is deposited elsewhere by the animals. Example: A dairy heifer facility
has a bedded-pack barn and an outside feedlot. No feeding is done inside the barn, so you
estimate that only 1/3 of the manure is deposited in the bedded pack. In doing the storage volume
calculation for the barn, you could enter 2/3 of Line 6 in Line 12.
Line 13. Subtract Line 12 from Line 11 and enter on Line 13. This is the manure, wastewater,
and bedding production for each animal, for one day.
Line 14. If animals are present during the entire storage design period, enter the number of days
on Line 5. Otherwise subtract the number of days the facility will be empty during that period.
Example: A slatted-floor beef barn has a storage design period of 180 days but typically animals
are only present for 158 days. Enter 158 on Line 14.
Line 15. This is the total volume of manure, wastewater, and bedding produced by all the
animals that enters this manure storage during the storage design period.
Lines 16 and 17. Enter any other expected additions to, or removals from, this storage during
the design period.
Lines 18, 18a, and 18b. This is the point where you total the manure, bedding, and wastewater
inputs for the storage. On Line 18a, total across all the numbers in the “storage design period”
columns in Line 18. Do the same for the “annual” columns, and enter that on Line 18b.
Lines 19-30. Address storm water additions to the storage. These only apply to manure storages
that are outside and uncovered, and/or that receive runoff.
Line 19. Enter the measurement of all the runoff area that contributes storm water to the storage.
Note that if part of the area is paved or roofed, and part is unpaved, you may need to separate the
two for purposes of runoff calculations. This is because unpaved area has less runoff due to
infiltration.
Line 20. Enter the entire area of the manure storage. For earth-bermed structures, measure to the
top of the inside berm.
Lines 21 and 22. Draw a line through the boxes beneath the months that are not part of your
“design case period.” From the charts in the Appendix C, select the closest weather station in
IL-10C 32-36, “Illinois Normal Monthly Precipitation by City,” and enter the normal monthly
precipitation for the design case months on Line 21. Put the total for those months in box “T.”
Using the graphs in IL-10C 37-40, locate the appropriate region of the state and enter the runoff
percentages in the boxes for the months corresponding to your design case period. Notice one set
of graphs is for unsurfaced (dirt) feedlots, and the other set is for concrete (i.e. paved.) If you
have a significant proportion of both unsurfaced and concrete, you should consider doing the
runoff calculation twice. However, a conservative or safe figure will be obtained if you consider
all the feedlot “concrete.”
Line 23. Multiply each month’s precipitation by its corresponding feedlot runoff percentage, and
add the numbers across. Enter the sum in box “T” Example: A concrete feedlot near Mattoon has
a manure storage with a five-month design case period ranging from March through July.
Normal monthly precipitation values and runoff percentages are: March 3.23 x 53% = 1.71
inches; April 3.88 x 53% = 2.06 inches; May 4.04 x 54% = 2.18 inches; June 3.75 x 60% = 2.25
inches; July 4.25 x 62% = 2.64. The total is 10.84 inches of runoff.
Line 24. New swine and poultry facilities must use the 100-yr, 24-hr storm event, and all others
use the 25-year, 24-hr event. Check the appropriate box for this storage. From the 100-yr, 24-hr
or 25-yr, 24-hr rainfall graphs in Appendix D, enter the precipitation for the design storm that
applies to your facility.
 For the 100-yr, 24-hr event, a conservative figure for virtually all of Illinois is 7.0 inches.
Northeastern counties can use 6.0 inches.
 For the 25-yr, 24-hr event, a conservative figure for virtually all of Illinois is 6.0 inches.
Northeastern counties can use 5.0 inches.
Line 25. The storage must not only contain the normal runoff, but must also have the capacity at
all times to contain the design storm runoff. Calculate the cubic feet of storm water for the design
storage period, including the design storm allowance. Add the feedlot runoff total in Line 23 and
the design storm in Line 24, multiply that result by the size of the watershed, and then divide by
12 to get the result in cubic feet. Enter the result on Line 25. Example: The beef feedlot in the
previous example is 2.2 acres in total area (2.2 x 43,560 = 95,832 square feet.) The 25-yr, 24-hr
design storm for Mattoon is between 5 and 6; use 5.5 inches. The total runoff depth is 10.84
inches plus 5.5 inches, or 16.34 inches. Storm water volume is 95,832 x 16.34 / 12 = 130,491
cubic feet; round it to 130,000 cubic feet.
Is evaporation an issue?
For most outside storages you should figure evaporation the same as from a pond or lake. Annual
Free Water Surface evaporation figures are available from various sources, but a single figure of
39 inches for the State is sufficiently accurate. However, if the storage has a floating crust that
impedes evaporation (common on dairy and beef manure storages), a conservative approach is to
not credit any evaporation.
Line 27. If you choose to account for evaporation from the storage, the monthly percentage
values from Urbana, IL (40°06' 88°14') are adequate. Draw a line through the boxes beneath the
months that are not part of your “design case period.” Winter month evaporation percentages for
Urbana are not available. For the spring through fall months enter:
April 9%; May 13%; June 15%; July 15%; August 14%; September 10%; October 7%;
November 4%. (Source: NRCS Ag Waste Management Field Handbook.)
As an alternative, the estimate for the months of April through October is 75% of the total
annual; and November through March, 25% of the total annual. Example: A swine feedlot near
Pana has a storage pond of 1.2 acres. The design storage period is November through March;
use 25% of the annual FWS evaporation for the total of those months.
Lines 28 and 29. Multiply the monthly percentages by the annual FWS evaporation and enter
the amounts in the boxes in Line 28. Add across and put the sum in the box “T”. Calculate the
precipitation minus evaporation for the storage surface (line 21 box “T” plus line 24 minus line
28, box “T”.) Put the result in Line 29. Example: Since the storage design period in our previous
example is November through March, use 25% x 39 inches or 9.75 inches of evaporation from
the storage surface. Note that we assume the surface does not have a floating crust. Normal
precipitation for the area is 14.6 inches, Nov-Mar. The design storm event for an existing swine
facility is the 25-yr, 24-hr event of about 5.5 inches. The sum is 20.1 inches; subtract 9.75 inches
evaporation for a difference of about 10.4 inches.
Line 30. Calculate the entire volume of the precipitation minus evaporation for the storage
surface (multiply line 29 by the area you calculated in line 20; divide the result by 12 to get cubic
feet.) Example: The storage pond in the previous example has a surface area, including the
inside of the berm, of 1.2 acres (1.2 x 43,560 = 52,272 square feet.) 52,272 x 10.4 / 12 = 45,300
cubic feet.
Line 31. Add the storm water and the manure, bedding, and wastewater together to get the total
storage volume requirement for the design case period. Enter here and on line 32, “Total vol.
required.” This is the point at which you can also compare historical manure hauling or pumping
records to the “book” values calculated in lines 6-31. Make sure your historical data are
corrected to include the same storage design period used in the calculations.
Line 33. Check the appropriate box—“adequate” if the total volume in line 32 is less than the
working volume, “inadequate” if the total volume is greater than the working volume.