United States Department of Agriculture 635-CPS-1

NRCS, NHCP

July 2022

NRCS reviews and periodically updates conservation practice standards. To obtain the current 

version of this standard, contact your Natural Resources Conservation Service State office or 

visit the Field Office Technical Guide online by going to the NRCS website at 

https://www.nrcs.usda.gov/ and type FOTG in the search field. 

USDA is an equal opportunity provider, employer, and lender.

Natural Resources Conservation Service 

CONSERVATION PRACTICE STANDARD 

VEGETATED TREATMENT AREA 

CODE 635 

(ac)

DEFINITION 

An area of permanent vegetation used for agricultural wastewater treatment. 

PURPOSE 

This practice is used to accomplish one or more of the following purposes– 

• Improve water quality by using vegetation to reduce the loading of nutrients, organics, pathogens,

and other contaminants associated with livestock, poultry, and other agricultural operations 

CONDITIONS WHERE PRACTICE APPLIES 

This practice applies where: 

• A vegetated treatment area (VTA) can be constructed, operated and maintained to treat

contaminated runoff from such areas as feedlots, feed storage, compost areas, solid manure

storage areas, barnyards, and other livestock holding areas; or to treat process wastewater from

agricultural operations. 

• A VTA is a component of a planned agricultural waste management system to improve surface or

groundwater including downstream drinking water sources. 

CRITERIA 

General Criteria Applicable to All Purposes 

Size the total treatment area for the VTA on both the contributing site water runoff and vegetation nutrient

balances. 

• Water balance is the soil’s capacity to infiltrate and retain runoff within the root zone. Base the

runoff determination on the most restrictive soil layer within the root zone regardless of its

thickness. Use the soil’s water holding capacity in the root zone, infiltration rate, permeability, and

hydraulic conductivity to determine its ability to absorb and retain runoff. 

• Nutrient balance utilizes the nutrients from the waste runoff to meet the nutrient removal

requirements in the harvested vegetation. Base the nutrient balance on the most limiting nutrient

(i.e., nitrogen or phosphorus). 

Divert uncontaminated water from the treatment area to the fullest extent possible unless additional

moisture is needed to manage vegetation growth in the treatment area. 

Establish permanent vegetation in the treatment area. Use a single species or a mixture of grasses,

legumes, and other forbs adapted to the soil and climate. Select species to meet the current site

conditions and intended use. Selected species will have the capacity to achieve adequate density, vigor,
and yield within an appropriate time frame to treat contaminated runoff. Complete site preparation and

seeding at a time and in a manner that best ensures survival and growth of the selected species. 

Select vegetation that will withstand anticipated wetting or submerged conditions. Harvest vegetation as

appropriate to encourage dense growth, maintain an upright growth habit, and remove nutrients and other

contaminants that are contained in the plant tissue. 

Design the VTA based on the need to treat the runoff volume from the 25-year, 24-hour storm event from

the agricultural animal management facility. Infiltrate a portion or the entire volume of the design storm,

based on management objectives. Unless discharge is permitted by applicable regulations, store the

noninfiltrated portion of the design volume for utilization or treatment. 

Exclude all livestock, including grazing, from the VTA. 

Apply discharge into and through vegetated treatment area as sheet flow. To encourage sheet flow across

the treatment area, provide a means to disperse concentrated flow, such as a ditch, curb, gated pipe, level

spreader, or a sprinkler system. Complete land grading and install structural components necessary to

maintain sheet flow throughout the treatment area. 

Limit the natural or constructed slope of the VTA from 0.3 to 6 percent. The minimum entrance slope to the

VTA is 1 percent. 

Use NRCS Conservation Practice Standard (CPS) Code 632, Waste Separation Facility, to pretreat

influent with waste separation (i.e., settling basin) to reduce organic loading and nutrients to levels that are

tolerated by the VTA and to prevent excessive accumulation of solids in the treatment area. 

Utilize inlet control structures to control the rate and timing of inflow during normal operations and to

control inflow as necessary for operation and maintenance. 

Locate VTAs outside of floodplains. However, if site restrictions require location within a floodplain, provide

protection from inundation or damage from a 25-year flood event, or larger, if required by regulation. 

Install VTAs where the water table is either naturally deep or artificially lowered so that the infiltrated runoff

does not mingle with the groundwater at the bottom of the root zone. Subsurface drainage within the VTA

is not allowed. Subsurface drainage may be used to lower the seasonal high water table to an acceptable

level provided the subsurface drain lines are at least 10 feet away from the VTA boundary. 

Unless soil moisture can be maintained to prevent drying and cracking, do not plan infiltration areas where

soil features such as cracking will result in preferential flow paths that transport untreated runoff from the

surface to below the root zone. 

Ensure that appropriate erosion control measures and sheet flow control measures (i.e., gravel spreaders)

are adequately addressed over the entire length of the VTA. 

Additional Criteria for Pressure Dosing Systems 

Distribute the effluent over the VTA through sprinkler irrigation or other pressure dosing system. Match the

application rate of sprinkler nozzles to the most restrictive soil infiltration rate or other factors to prevent

effluent from discharging from the VTA. 

CONSIDERATIONS 

Additional nutrient and infiltration design guidance in Vegetated Treatment Systems for Open Lot Runoff,

(Koelsch, et. al., 2006). 

When near sensitive areas such as impaired watersheds (nutrients and pathogens concerns) or close

proximity to housing developments (odor concerns), consider adding additional screening or additional

bedding management and manure solids removal from livestock areas in conjunction with the VTA to

-CPS-2

NRCS, NHCP

635

July 2022
reduce nutrient and pathogen loads being treated by the VTA and thereby further reducing the likelihood of

odor or water quality concerns.

Provide more than one vegetated treatment area to allow for resting, harvesting vegetation, and

maintenance, and to minimize the potential for overloading. 

Provide additional storage in the basin collection area to minimize or eliminate discharge into the VTA

during rainfall events. Delay application until rainfall has ended to improve infiltration and nutrient uptake. 

To maximize nutrient uptake, use warm and cool season species in separate areas to ensure that plants

are actively growing during different times of the year. 

Supplement water as necessary to maintain plants in a condition suitable for the treatment purpose. 

Direct contaminated effluent to a waste storage facility during excessively wet or cold climatic conditions. 

Consider suspension of application to treatment area when weather conditions are not favorable for

aerobic activity or when soil temperatures are lower than 39° F. When soil temperatures are between 39°

F and 50° F, consider reducing application rate and increasing application period while maintaining a

constant hydraulic loading rate. 

Manage the VTA to maintain vegetative treatment effectiveness throughout the growing season. Time the

harvest of the VTA plants so vegetation can regrow to a sufficient height to effectively filter effluent late in

the growing season. 

Install a berm around the lower end of the VTA to contain excess runoff that may occur. 

Effluent from the VTA may be stored for land application, recycled through the wastewater management

system, or otherwise used in the agricultural operation. 

Install fences or other measures to exclude or minimize access of the VTA to humans or animals. 

Install a pumping system at the bottom of the VTA to either recirculate the effluent to the top of the VTA or

transfer to a waste storage facility. 

PLANS AND SPECIFICATIONS 

Prepare plans and specifications that describe the requirements for applying the practice to achieve its

intended use. 

As a minimum include: 

• Critical construction perimeters, necessary construction sequence, vegetation establishment

requirements, level spreader mechanism requirements, associated practices and agronomic

nutrient removal. 

• Plan view showing the location of the VTA. 

• Details of the length, width, and slope of the treatment area to accomplish the planned purpose

(length refers to flow length down the slope of the treatment area). 

• Herbaceous species, seed selection, and seeding rates to accomplish the planned purpose. 

• Planting dates, care, and handling of the seed to ensure that planted materials have an acceptable

rate of survival. 

• Site preparation sufficient to establish and grow selected species. 

OPERATION AND MAINTENANCE 

Develop an operation and maintenance plan consistent with the purposes of the practice, its intended life,

safety requirements, and the criteria for its design. 

-CPS-3

NRCS, NHCP

635

July 2022
Include the following items as appropriate: 

• Control undesired weed species, especially state-listed noxious weeds, and other pests that could

inhibit proper functioning of the VTA. 

• Inspect and repair treatment areas after storm events to address gullies, reseed disturbed areas,

and prevent concentrated flow. 

• Apply supplemental nutrients and soil amendments as needed to maintain the desired species

composition and stand density of herbaceous vegetation. 

• Maintain or restore the treatment area as necessary by periodically grading or removing excess

material when deposition jeopardizes its function. Reestablish herbaceous vegetation. 

• Routinely dethatch or aerate a treatment area used for treating runoff from livestock holding areas

in order to promote infiltration. 

• Conduct maintenance activities only when the surface layer of the VTA is dry enough to prohibit

compaction. 

Monitor treatment areas in arid or semiarid regions that potentially could be affected by high salinity or

sodium content for excessive salt and sodium buildup. Take corrective action if excessive salt or sodium is

found. 

Monitor all treatment areas to maintain optimal crop growth and environmental protection. Ensure that

neither phosphorus is accumulating in the soil profile, nor nitrogen is leaching below the root zone. 

REFERENCES 

USDA/NRCS, National Engineering Handbook, Part 651, Agricultural Waste Management Field

Handbook. 

Koelsch, R., B. Kintzer, and D. Meyer. (ed.) 2006. Vegetated Treatment Systems for Open Lot Runoff - A

Collaborative Report. USDA, NRCS. 

Koelsch, R., J. C. Lorimor, and K. R. Mankin. 2006. Vegetative Treatment Systems for Management of

Open Lot Runoff: Review of Literature. Applied Engineering in Agriculture, Volume 22, pages 141-153.

-CPS-4

NRCS, NHCP

635

July 2022