Closure of Animal Waste Lagoons John W. Worley
Lagoon Closure • What is required? • What are options for managing an inactive lagoon? • What does an inactive lagoon contain?
What Is Required? • New or existing CAFO’s (1,000 Animal Units or more) • Notify EPD within 3 months of the date lagoon ceases to be used. • Close within 24 months (18 if closed involuntarily)
What Is Required? • Remove all waste from lagoon • Land apply at agronomic rates • Do not allow discharge to surface waters
What Is Required? • Rules refer throughout to the NRCS Field Office Technical Guide for guidance in acceptable practice. • Conservation Practice Standard 360, Closure of Waste Impoundments
Options for Closing a Lagoon • Complete Closure and Fill (reclaim land surface) • Breach the Lagoon Berm • Convert to Farm Pond • Livestock Watering • Irrigation Storage • Fish Pond
All Options • Remove conveyances (Fill pipes) • Remove as much waste as practical by conventional pumping methods • Agitate, pump, refill, repeat • Use dredge or similar device to remove sludge • Pump liquid, remove sludge mechanically • Some sludge may remain if it “will not pose a threat to the environment”
Close and Fill • Remove berms and restore land to approximate original shape • Excavated (Cut) Impoundments • Mound soil inside pond to allow for settling and encourage surface water runoff • Establish vegetation to prevent erosion
Breach the Berm • Embankment (Fill) Impoundments • Breach berm (embankment) with side slopes of breach no more than 3:1( or more depending on soil material) • Deep enough to prevent ponding • Establish vegetation in all areas to prevent erosion. 1 3
Conversion to Pond • Must meet structural requirements for final use • Must remove “all” sludge • Test water for safety. For livestock watering, Nitrate N below 30 ppm, Dissolved Oxygen more than 3 ppm (3 mg/L).
Other Considerations • If sludge is allowed to dry, it will decompose releasing odors and nutrients (can last for years) • Safety (fencing, signage) should be considered throughout the process • Poultry lagoons will contain oyster shells that are very difficult to remove by agitation
What does an Inactive Lagoon Contain? • Liquid Layer • Initially relatively high rates of N, P, K, organic matter (i.e. 500 ppm nitrogen) • Low nutrient and OM levels after 2 to 3 years (usually less than 100 ppm nitrogen)
What does an Inactive Lagoon Contain? • Sludge Layer • High nutrient content, especially P, K • Fairly high organic matter • High ash (undigestible material) • relatively unchanged over time as long as it remains wet
What does Sludge Removal Cost? • Wide variation • Ranges from $0.01 to $0.05/gal • For 1-million gallon lagoon (1/2 acre 6-feet deep)- $10 to $50 thousand • Average Cost $42,000 per acre to close lagoon by NRCS standards (Based on 1995 North Carolina Data) • 2-acre swine lagoon recently converted for approx. $15,000 in South Georgia • Recent estimate for 4-acre lagoon - $100,000
Geotubes for Sludge Removal • Provides flexibility in time and space • Solids can be stored in tube until ready to use • Solids are more transportable • Liquid can be returned to lagoon to remix and repump • More expensive than pumping on a nearby field IF that is an option