WASTE TREATMENT LAGOON (No.) s2

Field Office Technical Guide Section IV

Natural Resources Conservation Service Conservation Practice Standard

CONSTRUCTED WETLAND (Ac.) CODE 656

DEFINITION Creation) for creating a wetland on a site location which historically was not a wetland, or A wetland that has been designed and was a wetland with a different hydrology, constructed for the primary purpose of water vegetation type, or functions that occurred quality improvement. naturally on site.

PURPOSE CRITERIA

To reduce the pollution potential from both General agricultural and urban sites to water resources. All federal, state, and local laws, rules, and CONDITIONS WHERE PRACTICE APPLIES regulations governing the design, construction, and use of constructed wetlands shall be This practice applies where runoff is followed. contaminated by metals, pesticides, nutrients, or animal wastes to levels unacceptable for The Mississippi Department of Environmental downstream receiving waters and where: Quality has a “no discharge” policy for animal waste treatment systems. Therefore, treated  A constructed wetland is a component of a wastewater from a confined animal operation planned agricultural waste management that is discharged must meet discharge limits or system. either be collected and land applied or recycled.  Wastewater originates from livestock or aquaculture facilities. Location. Constructed wetlands shall be located  It is necessary to treat urban runoff. outside the limits of jurisdictional  It is necessary to treat cropland runoff. wetlands of any and all classifications.  It is desirable to treat acid mine drainage.  Nutrient levels must be reduced. The topography, soil, hydrology, and vegetative characteristics of the site and its contributing  Odors must be reduced. watershed shall be documented.  A constructed wetland can provide the intended water quality treatment. Constructed wetlands located within a floodplain shall be protected from inundation or damage This practice does not apply to: wetland from a 25-year flood event. restoration (Conservation Practice Standard 657, Wetland Restoration) intended to Constructed wetlands shall be located to provide rehabilitate a degraded wetland where the soils, sufficient separation distances so prevailing hydrology, vegetative community, and biological winds and landscape elements such as building habitat are returned to original conditions; arrangement, landforms, and vegetation will wetland enhancement (Conservation Practice minimize odors and protect aesthetic values. Standard 659, Wetland Enhancement) intended to rehabilitate a degraded wetland where Constructed wetlands shall be located with a specific functions and/or values are enhanced separation distance that will minimize the beyond original conditions; or wetland creation potential for ground water contamination. (Conservation Practice Standard 658, Wetland

Conservation practice standards are reviewed periodically and updated if needed. To obtain the current version of this standard, contact the Natural Resources Conservation Service.

NRCS, Mississippi January 2000 Type. Constructed wetlands shall be designed to handle the “first flush” volume shall have as surface flow systems consisting of adequate a minimum capacity to store 0.5 inches of seepage control, a suitable plant medium, runoff volume from the entire drainage area. rooted emergent hydrophytic vegetation, and the structural components needed to contain and 4. Surface area. The surface area control the design flow. requirements shall be determined using recognized and documented design Topography. Site topography shall procedures in consideration of aerial accommodate the requirements for loading, temperatures and the desired level length to width ratios on the wetland of treatment. cells and the number of cells needed for adequate treatment 5. Configuration. The length to width ratios for the overall wetland area shall be in the Design range of 4:1 to 10:1. Individual cells shall have a length to width ratio of 10:1 to 15:1. Design criteria in the standards and This ratio allows for plug flow kinetics The specifications for Dike (356) and Structure for wetland shall consist of at least two rows of Water Control (587) will be used as appropriate. parallel cells to facilitate treatment and Additional design information can be found in biomass removal during operation and the Engineering Field Handbook, Chapter 13, “ maintenance. Wetland Restoration, Enhancement, and Creation”, Chapter 6, “Structures” Constructed 6. Seepage control. The constructed wetland Wetlands for Animal Waste Treatment” and shall be located in soils with an acceptable other design guidance documents permeability that meets all applicable regulations or it shall be lined. Soil or In addition, the following design criteria shall synthetic liners shall meet the same design apply: and construction requirements of Practice Standard 359, Waste Treatment Lagoon. 1. Inlet. The structural design of the inlet shall allow control of the flow discharged to the 7. Flow depth. The design flow depth shall be wetland and the screening of the influent to based on the most severe season of prevent blocking by debris and bacterial operation, the desired level of treatment, slime. Criteria for NRCS Practice Standard and the required littoral zone of the plant 313, Waste Storage Facility, for fabricated species being used. The design flow depth structures shall apply as necessary. shall be a minimum of 0.33 ft. and a maximum of 1.5 ft. 2. Influent. The influent to the constructed wetland shall be pretreated to reduce Sites designed to handle the “first flush” concentrations of solids, organics, and volume of urban runoff shall have a nutrients to levels that will be tolerated by minimum capacity to store 0.5 inches of the wetland plants and not cause excessive runoff volume from the entire drainage area. accretion within the wetland. This may or The first flush must be released within 48 may not apply to the treatment of urban hours in preparation for receiving the next storm water runoff. storm event.

3. Runoff. The design of a constructed wetland 8. Embankments. Height of the constructed system to treat wastewater from a confined wetland perimeter embankment shall be the animal operation shall not allow for the direct sum of the following: or indirect runoff from the surrounding watershed. Criteria for NRCS Practice  Design flow depth Standard 356, Dike and 587, Structure for  Wetland accretion—a minimum of 1 inch Water Control shall apply as necessary. per year for the design life  25-year, 24 hour precipitation To treat urban storm water runoff the  Ice cover- 25 year thickness wetland shall be designed to contain the  12 inches of freeboard direct rainfall and contributing runoff from a 2-year, 24-hour storm event. Sites designed The height of the wetland’s interior

NRCS, Mississippi January 2000 656-3 embankments shall be the minimum of the sum of the following:

NRCS, Mississippi January 2000 656-4

 Normal design flow Livestock should be excluded from the wetland  Wetland accretion—minimum of 1 inch per site. year for the design life PLANS AND SPECIFICATIONS Both perimeter and interior embankments shall have top widths conducive to Plans and specifications shall be prepared in maintenance and vegetative control. All accordance with the criteria of this standard and embankment side slopes shall be a shall describe the requirements for applying the minimum of a 2 horizontal to 1 vertical. practice to achieve its intended use. Plans shall include construction sequence, vegetation 9. Overflow device. An ungated overflow establishment, and management and device designed to operate when 25-year, maintenance requirements. 24-hour precipitation is exceeded without infringing on the wetland perimeter OPERATION AND MAINTENANCE embankment. An operation and maintenance plan shall be 10. Vegetation. Rooted emergent hydrophytic developed that is consistent with the purposes of plants suitable for local climatic conditions the practice, its intended life, safety and tolerant of wastewater constituents requirements, and the criteria for its design. shall be used. Operational requirements should include:

11. Water budget. A water budget that evaluates  Maintenance of water levels in wetland cells wastewater volume, precipitation, appropriate for vegetation and treatment. evapotranspiration, wastewater utilization,  Flow control according to the water budget and constituent concentrations shall be used  Monitoring of system performance to determine the required hydraulic  Effluent analysis prior to utilization detention time for primary and secondary treatment facilities. Maintenance requirements should include:

12. Outlet. Constructed wetlands will discharge  Repair of embankments to storage facilities to allow for land  Vegetation control application in accordance with requirements  Fence repair of Conservation Practice Standard 590-  Maintenance of wetland vegetation Nutrient Management. The discharge may  Biomass removal also be recycled through the waste  Repair of pipelines management system. REFERENCES CONSIDERATIONS Constructed Wetlands for Animal Waste Locate constructed wetlands as near the source Treatment, A manual on Performance, Design, of the water or wastewater to be treated as and Operation with Case Histories, USEPA Gulf practicable and downslope if at all possible. of Mexico Program Recycle effluent back through the waste Engineering Field Handbook, Chapter 13, management system as process water to dilute “Wetland Restoration, Enhancement, and BOD and TSS, decrease odor potential, and Creation.” increase DO to enhance nitrification of influent.

The soil used for the planting medium should soil characteristics necessary for good plant growth and survival. Soil amendments may be necessary.

NRCS, Mississippi January 2000