United States Department of Agriculture 627-CPS-1

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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 

WASTEWATER TREATMENT, MILK HOUSE 

CODE 627 

(no)

DEFINITION 

The physical, mechanical, and biological treatment of dairy milk house wastewater. 

PURPOSE 

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

• Improve water quality by reducing nutrients in surface and ground water 

• Improve air quality by reducing odors 

CONDITIONS WHERE PRACTICE APPLIES 

This practice presents a conservation alternative that applies to milking operations where milk house

wastewater is generated. Milk house wastewater is the greywater from the cleaning of milking equipment. 

This practice does not apply to treatment of large quantities of waste whole milk, which should be pumped

directly to a liquid waste storage structure. 

This practice does not apply to human waste or backwash from a water softener. 

CRITERIA 

General Criteria Applicable to All Purposes 

Treatment system performance and capacity 

Design the capacity of the milk house wastewater treatment system to treat the milk house greywater

collected at the maximum daily volume of wastewater produced. Ensure the wastewater treatment system

design can handle the specific total solids and nutrient content of the waste stream. 

Laws and regulations 

Plan, design, and construct the milk house wastewater treatment system to meet all Federal, State, Tribal,

and local laws and regulations that can affect the installation, placement, and use of the milk house

wastewater treatment system. 

Location 

Locate and design the waste treatment system such that it is outside the 100-year floodplain unless site

restrictions require locating it within the floodplain. If located in the floodplain, protect the facility from

inundation or damage from a 25-year flood event. Additionally, follow the policy found in the NRCS

General Manual (GM) (Title 190), Subpart B, Section 410.25, “Flood Plain Management,” which may

require providing additional protection for milk house wastewater treatment components located within the

floodplain. 
Collection of milk house wastewater 

Design sump traps, grates, and screens in the milk house to remove solids from collected wastewater.

Minimize milk solids and fat content of the wastewater by diverting waste milk and emergency spills of the

milk supply away from the collected wastewater. 

Wastewater characteristics 

Ensure the wastewater treatment system design can handle the specific total solids and nutrient content

of the waste stream. 

Design components 

The milk house wastewater treatment system consists of five components. Components 1 through 4 listed

below are required on all systems. Component 5, the final treatment, has options for implementation

based on the site conditions and management alternatives. Example shown in figure 1. 

1. Pretreatment tank component, reduces the total solids and nutrient content of the inflow up to 50

percent by clarifying the wastewater. The pretreatment tank design requires a specific hydraulic

retention time to reduce the solids content by settling separation, and the detergents, fat, oil, and

grease (FOG) content by flotation separation. 

2. Storage tank for the clarified wastewater after pretreatment. 

3. Transfer component, typically a pump system to distribute the stored pretreated wastewater. 

4. A distribution system to uniformly apply the wastewater to the final wastewater treatment

component. 

5. A final wastewater treatment component that processes the nutrient content and utilizes the

wastewater. Based on the site conditions, different strategies can be used for the final wastewater

treatment component. 

• Onsite Soil Wastewater Treatment Component.—Used where the natural surface soil microbial

population treats the wastewater and is referred to as the “land treatment area.” Sites must

have a sufficient depth of unsaturated soil, appropriate ground slope, adequate treatment area,

and no ground water quality risks. 

• Soilless Media Wastewater Treatment.—Where a treatment system is designed and

constructed to process the wastewater with soilless media. The wastewater is then utilized after

the wastewater final treatment component. This strategy is for sites that have resource

concerns of soil quality, ground water quality, or both. Example sites can be where the— 

• Ground water table is within 2 feet of the soil surface. 

• Site has less than 2 feet of soil over bedrock. 

• Site has soils that mobilize metal elements into soil water. 

• Site has high-risk karst topography and potential sink holes. 

• Associated conservation practice standards for vegetative treatment can be used as the final

treatment component. The milk house wastewater treatment design includes the criteria for

components 1 through 4, so in this case, the associated conservation practice is installed as

component 5 for the final treatment component. Vegetative treatment practices are applied

according to NRCS Conservation Practice Standard (CPS) Nutrient Management (Code 590),

Vegetated Treatment Area (Code 635), or Constructed Wetland (Code 656). 

Figure 1. Example of storage tank with submersible pump configuration. Pump is

located a minimum of 6 inches off the bottom of the tank to avoid moving solids to the

final wastewater treatment component. *In-situ soil land treatment area with biofilter.

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(Figure from the University of Minnesota Extension publication M1207, with permission

to use and modifiy as shown.) 

Wastewater design volume 

Wastewater treatment systems must be designed to meet the maximum daily volume of wastewater

produced. When the maximum daily volume of wastewater produced is not known, flow meters can be

used in gathering real-time data to determine the design volume. Use existing records of wastewater

volume, a minimum of 2 months of collected flow meter data, or a minimum of 5 gallons per wet cow

based on annual maximum, plus wash water required for all tanks and equipment. 

Tank components 

Evaluate the pretreatment and storage tank sites for the depth to seasonal high ground water or perched

ground water conditions that would require special design considerations for tank buoyancy. 

Locate pretreatment tank and storage tank at least 10 feet from any structure. 

Use a State-approved prefabricated concrete, steel, or plastic septic tank, or a tank design that meets the

materials and structural design requirements for ASTM C1227, “Standard Specification for Precast

Concrete Septic Tanks.” Tanks must be designed to be watertight and buried below grade. Steel or plastic

tanks must meet acceptable septic industry standards. 

The following attributes are required on the milk house wastewater tank components: 

• Tank must be suitable for the site conditions. Site conditions include vehicular traffic loads, soil

backfill loads, corrosion of wastewater, ground water floatation, and frost action. 

• All riser joints, access openings, and pipe connections must be watertight. 

• Install a sanitary trap or air gap ahead of the inlet of the pretreatment tank to prevent gases from

flowing into the milk house from the pretreatment system. 

• Specify baffles at both the inlet and outlet location on the pretreatment tank. 

• Do not use a pretreatment tank with multiple compartments separated by a mid-tank baffle wall.

Mid-tank walls cause turbulence flow preventing the clarification processes. 

• Include a commercial size effluent screen or filter at the outflow of the pretreatment tank, prior to

the storage tank and distribution pump, if required by pump manufacturer or distribution treatment

system. Use a filter rated at two times the daily wastewater flow capacity (2 X volume wastewater,

gpd). Commercial effluent filters with 1/16-inch wide slit type filter or 1/16-inch circular filter holes, or

their equivalent have been found to work. 

• Include a warning system in tanks to detect overfull conditions from solids and FOG buildup,

clogged filter, or failed pump. 

• Select tank manhole covers that aid safety and maintenance. 

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• In cold climates, install pretreatment and storage tanks with a minimum of 2 feet of soil cover over

the top to protect from freezing, or insulate the top. 

• Bury tanks with no more than 4 feet of soil cover at riser for tank cleanout equipment accessibility. 

Pretreatment tank (Component 1) 

The minimum hydraulic retention (storage) time for the wastewater pretreatment component to settle out

the solids and float FOG out of suspension is 3 days. Design the minimum pretreatment tank volume for

three times the daily volume of wastewater produced. 

The clarified liquid design depth within the tank must be a minimum of 4 feet. 

Figure 2. Example of pretreatment tank component configuration. (Figure from the University of

Minnesota Extension publication M1207, with permission to use and modify as shown.) 

Storage tank (Component 2) 

Clarified wastewater from the pretreatment tank must be stored in the storage tank until final treatment.

The storage tank volume supplies the wastewater for distribution to the final treatment component. 

Size the storage tank for a minimum capacity of 1 day of the design volume of wastewater produced or

500 gallons, whichever is greater. Size the storage tank larger when the final treatment (component 5)

needs a larger dosing capacity or multiday rest periods between wastewater application treatments. 

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Figure 3. Example of storage tank with submersible pump configuration. Pump is located a

minimum of 6 inches off the bottom of the tank to avoid moving solids to the final wastewater

treatment component. 

Transfer component (Component 3) 

The wastewater treatment transfer component design must include the slope and length of wastewater

transfer pipeline. Use gravity flow where feasible only from the milking center to the pretreatment tank and

pretreatment outflow to the storage tank. Uncontrolled gravity flow from the storage tank to the final

wastewater treatment is not allowed. 

For pressure systems, size pumps to transfer the wastewater to the distribution system for the final

treatment component at the required pressure head and flow rate. The pressure requirements must

include elevation change, transfer pipe pressure losses, and the required distribution pressure at the pipe

holes plus a minimum of 2 feet of (water head) pressure at the end of the distribution pipeline. 

Select a type of pump suitable for operating in the corrosive environmental conditions of milk house

wastewater. 

Locate pump intake a minimum of 6 inches off the bottom of the tank to avoid moving solids to the final

wastewater treatment component. 

Base the requirements for pump installation, anchoring, and connecting appurtenances on manufacturer’s

recommendations. 

NRCS CPS Pumping Plant (Code 533) can be utilized. 

For siphon-dosing systems, the system must transfer wastewater at the volume and rate as designed

for the final treatment component. 

Distribution system (Component 4) 

Design the distribution pipe with pipe material intended for wastewater systems. Specify hole sizing and

spacing as a function of pipe diameter, length, pumping pressure, and flow for uniform distribution to the

final treatment. Specify valve and control equipment intended to be used in wastewater treatment. 

Design the installation to be suitable for the weather conditions at the site. When an operation is planned

for cold weather, install the piping system on a slope to drain back to the pump to prevent freezing (thus

no check valve), settling of solids, or both in the pipelines. Systems using sprinkler heads in cold weather

should drain back to the pump and have flexible nozzles. 

Protect transfer and distribution pipes from freezing and damage by livestock or machinery. 

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NRCS CPS Waste Transfer (Code 634) can be utilized. 

Final treatment (Component 5) 

Locate the final wastewater treatment outside any established rights-of-way such as roads, legal drains,

utilities, and pipelines. Table 1 lists setback distances required for identified landscape and physical

features unless State, Tribal, or local rules and regulations require a larger separation distance. 

Table 1. Minimum Setback Distance for Storage and Treatment Areas for Horizontal Isolation of

Soil Water Flow. 

Soils investigation for the final wastewater treatment component 

Determine the size of the final wastewater treatment component of the selected wastewater treatment

system. Perform the soil investigation outside the planned footprint area. Confirm the soil texture and

depth to any seasonal high ground water or restrictive layers. 

Vegetative treatment 

If vegetative treatment is used for the final wastewater treatment component, require year-round plant

growth. Vegetation must be dense to provide effective treatment. Use criteria from NRCS CPS Vegetated

Treatment Area (Code 635) or Constructed Wetland (Code 656). 

Additional Criteria for Onsite Soil (Component 5), Wastewater Treatment Process, Land Treatment

Area 

Locate treatment systems where favorable soil characteristics and geology exist for the dispersal,

infiltration, and assimilation of wastewater. Select a site away from future grazing, manure spreading,

animal traffic, or vehicle traffic. 

A minimum separation distance of 2 feet is required between the wastewater application surface and any

seasonal high ground water, perched ground water, impermeable soil, or bedrock. 

The area required for the design of the final wastewater treatment component is based on the most

restrictive organic loading rate for the site soil texture properties identified. See additional document for

this practice: “Wastewater Treatment—Milk House, Worksheet: Sizing Land Treatment Area.” 

Decommission or reroute existing drainage tile located within the land treatment area footprint, plus an

offset of half the drainage tile spacing specified in the soil drainage guide, or follow the appropriate soilspecific State guidance for drainage tile separation beyond the land treatment area footprint. Drainage tile

may be used in the land treatment area if it has been designed in a parallel system to the dispersal

system so as to maximize the expected soil treatment process. 

Exclude offsite surface water runoff from entering the land treatment area. Use NRCS CPS Diversion

(Code 362) or Roof Runoff Structure (Code 558) to divert surface water away from the land treatment

area. 

Wastewater distribution systems for a land treatment area can include the following distribution

component alternatives: 

• Surface Application to a Land Treatment Area.—Distribution systems that include other design

Feature Setback Distance (ft.)

Property line 10

Building foundation 20

Top of slope dropoff 20

Private well 50

Wetlands 50

Public water supply well 75

Surface water 100 

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features to meet the treatment application site criteria. 

• Surface application on a land treatment area under a bark bed biofilter. 

• Land treatment area dosing with wood chip biofilter. 

• Gravel spreader surface infiltration area. 

• Other designs that meet the treatment application criteria. 

• Sprinkler Irrigation Area.—Match the application rate of sprinkler nozzles to the most restrictive soil

infiltration rate to prevent wastewater discharging from the land treatment area. Ensure the

wastewater is applied at agronomic rates for nutrient removal and meeting an approved

comprehensive nutrient management plan. 

Additional Criteria for Soilless Media (Component 5), Wastewater Treatment Process 

The soilless media treatment processes can be used if site soils have inadequate unsaturated depth or

are composed of chemicals containing arsenic or metals that become soluble with wastewater biological

oxygen demand (BOD). Soilless media treatment systems incorporate an aerobic microbial treatment with

imported media in a designed structure prior to final treated water infiltration or utilization. After the final

treatment process, wastewater can be recycled for cleaning the holding area, transferred to storage, or

infiltrated. The planning and design for a soilless media wastewater treatment system must include the

final utilization steps for the treated wastewater. 

Wastewater treatment systems may include any of the following alternatives: 

• Aerobic Treatment Unit and Subsurface Absorption System.—Refer to “Milk House Waste, Aerobic

Treatment Unit – A Milk House Wastewater Treatment Option” (Christopherson et al., 2007). 

• Filter Mound.—Refer to “Design Guide: Michigan Filter Mound for Treating Milking Center

Wastewater” (Michigan Livestock Wastewater Treatment Workgroup, 2012). 

• Gravel Vertical Flow Contactor.—Refer to “Gravel Vertical Flow Contactor, Michigan (Pea) Gravel

Contactor for Treating Milking Center Wastewater” (Michigan Livestock Wastewater Treatment

Workgroup, 2018). 

Other waste treatment systems must follow the criteria in NRCS CPS Waste Treatment (Code 629). 

Additional Criteria for Reducing Odors 

The wastewater pretreatment (component 1) decreases odor-related concerns. Use the criteria from

NRCS CPS Air Filtration and Scrubbing (Code 371) where additional reduction of ammonia and volatile

organic compounds (VOC) compounds evaporating from the wastewater are needed. Biofilters are

typically a mixture of wood chips or wood shreds piled such that air moves passively through the filter. The

natural microbial population on the carbon-sourced material will reduce odors of ammonia and VOC

compounds evaporating from the wastewater. 

CONSIDERATIONS 

Consult with the landowner/operator for their consideration of the management and maintenance aspects

of alternative treatment and distribution systems before selecting the system to be installed. 

Consider the weather at the location where the wastewater distribution system will function to ensure

year-round operations. Consider vehicle access, wind direction, proximity of streams and flood plains, and

visibility. 

For milk house wastewater facilities producing over 500 gallons per day of wastewater, consider a

wastewater storage system better suited to economically treating large volumes of liquid waste. 

Consider elevation and distance from various components to take advantage of gravity flow to tanks. 

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Consider the alternative types of tank manhole covers. Quick-release manhole covers accommodate easy

access for maintenance. Lockable manhole covers prevent unwanted access. 

If designing a land treatment area for component 5, consider a distribution system and treatment area

layout that has a longer, narrower footprint. That layout can be more accessible for construction and

maintenance. 

Consider designing more than the minimum number of system treatment zones to add flexibility for

maintenance and operational tasks. Vegetative treatment systems can require resting periods and

management seasons for vegetation removal. 

Consider including wastewater source production and management strategies to reduce solids and the

organic loading rate on the wastewater treatment system. 

Consider methods to separate sand and manure solids from parlor floor wash down, holding area, or

influent drains collected. Scrape solids separated to main manure collection system. 

Consider management alternatives for reducing waste milk collected in the milk house wastewater.

Examples include— 

• Diverting waste milk directly to the manure collection system. 

• Collecting the first rinse water from milking equipment containing a higher quantity of milk and add it

to the long-term manure storage. 

• Feeding waste milk, the first rinse water, or both to farm animals that can utilize the residual milk

nutrients. 

Consider testing the milk house wastewater for organic strength (5-day biological oxygen demand

(BOD5)). Representative sampling of the wastewater BOD5 can provide operating information to prevent

pretreatment and treatment system overloading and wastewater treatment failure. Wastewater treatment

system designs based on site-specific wastewater organic strength data will more likely meet the practice

life. 

Consider continued monitoring of a water supply flow meter to inform the dairy of potential management

concerns about capacity. Milk house management adjustments may be needed, or adjustments in the

wastewater treatment system operation and maintenance plan may be required to address capacity

changes. 

PLANS AND SPECIFICATIONS 

Prepare plans and specifications for waste treatment facilities according to the criteria of this standard and

good engineering practices. 

Prior to construction, instruct the contractor to locate all buried utilities applicable to the project area,

including drainage tile and other structural measures. Plan the site construction to protect natural

resources and accommodate existing utilities. 

As a minimum, provide— 

• Layout and installation details of livestock facilities, waste collection points, waste transfer

components, and waste treatment and storage facilities, and with supporting documentation. 

• Map showing the location of the final treatment areas if the treatment involves land spreading that is

variable. The map should include the locations of any specified setback distances. 

• Location of all inflow and discharge pipelines, pipeline materials, diameter, slope, and

appurtenances. 

• Required properties of any locally sourced materials such as sand or gravel used in the treatment

processes. 

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• Details of structural support systems for all components of the treatment facility. 

• Fencing and signage as appropriate for safety purposes. 

• Required tests of the treated waste as appropriate for confirmation of treatment effectiveness. 

• Other plans to manage the system, including a nutrient management plan for proper land

application of byproducts if applicable. 

OPERATION AND MAINTENANCE 

Develop an operation and maintenance (O&M) plan for this practice. The O&M plan must meet the

purpose of the practice, its intended life, safety requirements, and the treatment system criteria for the

design. Maintenance of transfer equipment, pretreatment and storage tanks, pumps, distribution system,

and treatment media will be required throughout the year and expected life of the practice. 

Prepare operation guidelines as needed for the treatment system to prevent harsh chemicals, drain

cleaners, pharmaceuticals, manure solids, or other inappropriate substances from entering the milk house

wastewater drain. The guidelines can include, but are not limited to, management strategies for the milk

house to reduce wastewater produced. Include a plan in the guidelines to manage emergency spills or

unexpected waste milk disposal to ensure waste milk does not reach the wastewater treatment system. 

Include instructions to monitor the pretreatment and storage tanks (weekly for the first 6 months) for

separated solids and floating material. Check the space of clarified liquid of the pretreatment tank near the

outlet for the required 4 feet of depth. Schedule cleanout of the sludge and scum if buildup is found to be

more than 25 percent of the tank volume. Determine the schedule for regular tank clean-out, which could

be monthly to annually. Determine a schedule for regular inspection and cleaning of filters or screens. 

Limit vehicle and animal access on any wastewater land treatment area to avoid damage to the

wastewater transfer and distribution system, equipment, and treatment area site soil surface. Vegetative

treatment systems must plan for scheduled vegetation management and harvest. 

REFERENCES 

ASTM Standard C1227. 2020. Standard Specification for Precast Concrete Septic Tanks. ASTM

International, West Conshohocken, PA. DOI: 10.1520/C1227-20. https://www.astm.org/

Christopherson, S.H., D.R. Schmidt, and K.A. Janni. 2007. Milk House Waste, Aerobic Treatment Unit – A

Milk House Wastewater Treatment Option. University of Minnesota. 

Holmes, B.J. 2009. Milking Center Wastewater Guidelines, A Companion Document to Wisconsin NRCS

Standard 629. University of Wisconsin-Madison Extension, Department of Biological Systems

Engineering. 

Michigan Livestock Wastewater Treatment Workgroup. 2012. Design Guide: Michigan Filter Mound for

Treating Milking Center Wastewater. 

Michigan Livestock Wastewater Treatment Workgroup. 2018. Gravel Vertical Flow Contactor, Michigan

(Pea) Gravel Contactor for Treating Milking Center Wastewater. 

Morin, S., Whalen, J.K., Barrington, S., and Lin, X. 2007. Soil Nutrient Load and Drain Water Quality in

Seepage Fields Receiving Milk House Wastewater. Water, Air and Soil Pollution, Vol. 181, Issue. 1-4, pp.

51-63. 

Schmidt, D., S. Christopherson, P. Fryer, and K. Janni. 2005. Design Recommendations for Milkhouse

Wastewater Treatment Systems. Paper presented at 2005 ASAE Annual International Meeting, Tampa,

FL, United States. 

Schmidt, D.R., K.A. Janni, and S.H. Christopherson. 2008. Milk House Wastewater Design Guide,

Publication No. M1207. University of Minnesota Extension. 

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Wright, P.E. and R.E. Graves. 1998. DPC 15, Guideline for Milking Center Wastewater. Northeast

Regional Agricultural Engineering Service.

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