This publication discusses subsurface soil dispersal systems and the basic documentation needed to help determine if converting to a subsurface soil dispersal system would change regulatory jurisdiction.However, this is not intended to address specific design criteria, nor is it meant to answer all possible questions. To better understand jurisdiction for domestic wastewater in the state, review the fact sheet titled Who Regulates Wastewater in Missouri (PUB 1296). As described within that publication, either the Missouri Department of Health and Senior Services or the local on-site wastewater administrative authority has jurisdiction for facilities generating 3,000 gallons per day or less of domestic wastewater and dispersing effluent into a subsurface soil absorption system.
Subsurface soil dispersal systems should be included among alternatives evaluated when faced with new or more stringent effluent limitations. Facilities with flows 3,000 gpd or less proposing to change to a subsurface soil dispersal system will be reviewed on a case-by-case basis to determine if a change in jurisdiction is appropriate.
As defined in 10 CSR 20-2.010(26), domestic wastewater is “…wastewater (i.e., human sewage) originating primarily from the sanitary conveniences of residences, commercial buildings, factories, and institutions, including any water which may have infiltrated the sewers. Domestic wastewater excludes stormwater, animal waste, process waste, and other similar waste.” For the purpose of this publication “wastewater” or “domestic wastewater” shall be defined the same as “sewage” or “domestic sewage.” For the purpose of this publication, the term “septic” will only be used as a component of a system. (For example: septic tank or anaerobic treatment).
Facilities utilizing discharging lagoons generating a maximum daily flow of 3,000 gpd or less of domestic wastewater and propose to convert to a no-discharge lagoon, followed by either on-site surface land application, subsurface soil dispersal or is pumped and hauled to a permitted facility, should contact the Missouri Department of Natural Resources for assistance. All single-family lagoons serving only a single-family residence are the jurisdictional responsibility of the Department of Health and Senior Services or the local on-site wastewater administrative authority. All other lagoons are the department’s jurisdiction.
What is Subsurface Soil Dispersal?
Subsurface soil dispersal is the method of distributing effluent uniformly into an unsaturated (vadose) zone within the soil. This method effectively treats and controls bacteria and nutrients, and allows local reuse of the treated water.
Soil Treatment Area Requirements
In Missouri, the minimum soil treatment area required for a subsurface soil dispersal system is based upon the soil and site conditions, and their ability to effectively treat and hydrologically control the effluent. This is determined only after a thorough systematic investigation of the soil properties and landscapes of the primary and reserve soil treatment areas.
The minimum square footage for a soil treatment area is calculated by dividing the daily wastewater flow by the soil application (loading) rate assigned by a registered on-site soil evaluator. Example: 3,000 gpd of domestic wastewater divided by an application rate of 0.20 gpd/sq. ft. equals 15,000 sq. ft. of soil treatment area.
Note: This calculation is for general discussion purposes only. The calculated area does not include area for the septic tanks, secondary treatment, pump tanks, trench separation, reserve area, set back distances or other components of the wastewater collection and treatment system.
Operation and Maintenance
The primary challenge associated with any wastewater treatment system is that they are not always managed by individuals trained for a specific technology. Long-term operation and maintenance by qualified individuals is imperative to ensure all of the components, including the subsurface soil dispersal system functions optimally for the expected lifespan. System operation and maintenance must be addressed as part of the initial planning process.
Basic Documentation Needed for Review
The attached checklist is designed to be a guide to compiling the minimum documentation needed for review. More documentation may be required, depending upon the type of facility, soils, available area, geology and how the system is used. The majority of the information on the checklist should be on file with the continuing authority as part of their records. To help keep this review cost effective, neither the department nor the Department of Health and Senior Services asks for a preliminary engineering report or a site specific design of the new system at this time.
Once the appropriate documentation is compiled, copies should be sent to DHSS or the local on-site wastewater administrative authority for initial review and determination. If the use of a subsurface soil dispersal system is determined to be a feasible option and the change in jurisdictional authority is appropriate, the facility can begin working with the appropriate permitting authority.
The requirements of the residential housing development rule, 10 CSR 20-6.030(1)(C) 6, shall be considered met, provided that all other requirements of the Missouri Clean Water Law and regulations can be satisfied, including that continuing authority is established in accordance with 10 CSR 20-6.010. If those requirements are met, the facility would be exempt from the residential housing development rule, 10 CSR 20-6.030.
Facility construction may proceed once it receives the appropriate approvals and permits from the appropriate on-site wastewater administrative authority. After construction of the subsurface soil dispersal system and any other improvements to the wastewater treatment system are completed, the following shall be submitted to the department to complete the transition of jurisdiction:
- A copy of the approved construction final inspection form from the appropriate authority stating all design and construction activities are in compliance with 19 CSR 20-3.060 “Minimum Construction Standards for On-Site Sewage Disposal Systems” or any local ordinances.
- Request for Termination of Operating Permit
- A Class V Well Inventory Form for each active or new underground injection well (subsurface soil dispersal system), shall be submitted to the Missouri Department of Natural Resources, Geological Survey Program, P.O. Box 250, Rolla, MO 65402.
The department, the Department of Health and Senior Services and local on-site wastewater administrative authorities recognize a subsurface soil dispersal system is a sustainable solution that is protective of the public health and the environment. Regardless of who has jurisdiction of a wastewater treatment facility, all wastewater shall be handled in such a manner that there is no violation of the Missouri Clean Water Law and its regulations. Please contact the department at 800-361-4827 or the Department of Health and Senior Services at 866-628-9891 for more information.
To help the appropriate wastewater administrative authority determine if converting a point-discharge domestic wastewater treatment system to one with subsurface soil dispersal is a sustainable solution and if a change in jurisdiction (permitting authority) is necessary, please provide the following information. Most of this information should be on file with the current owner and/or continuing authority. More information may be required, depending upon the complexity of the existing domestic wastewater treatment system, soils, landscape and geology.
Please provide the following:
- Current NPDES operating permit number and expiration date for the facility. If available, a copy of the current operating permit should be included.
- Name of the facility’s current owner and/or continuing authority and their mailing address
- Physical address, legal description and county where the facility is located
- Copies of the most recent Missouri Department of Natural Resources’ inspection report
- Copies of all discharge monitoring reports submitted to the department for the previous 12 months
- If the facility is currently in violation of the Missouri Clean Water Law and its regulations, describe the violation and attach any documentation received from the Department of Natural Resources.
- If the facility is in violation of the Missouri Clean Water Law, contact the department to learn the case’s status and if conversion to a subsurface soil dispersal systems is applicable.
Note: If written approval is required from the department, as described in 10 CSR 20-6.030, it shall be received before the developer can apply for any on-site wastewater treatment system approvals or permits under 19 CSR 20-3.060 or local ordinances.
Daily Design Flow
Please provide the following:
- The maximum daily design flow for domestic wastewater in gallons per day as stated in the NPDES permit.
- Calculate the estimated accumulated maximum daily domestic wastewater design flow in gallons per day for the entire facility using 19 CSR 20-3.060, Table 2A – Quantities of Domestic Sewage Flows.
- If available, provide the actual water use records for review. Monthly metered water-use records can be used, but daily verifiable water meter readings are preferred. The following should be considered the minimum supporting documentation:
- Minimum of one year for year-round-use facilities
- Minimum one full-season water-use records for seasonal establishments, such as recreational vehicle campgrounds, schools, outdoor theaters, church retreats, etc.
- Description of water-use patterns must be included:
- Days and hours open
- High and low business days
- Number of weeks per year or season
- What season(s) the facility is opened
- A multiplication factor of 2 to 6 may be used to help determine the maximum daily flows when using monthly averages
Please provide the following:
- Copies of the original engineering plans of the current wastewater treatment system, if available
- Brief description of the existing wastewater treatment systems components and design flow
- Copy of the operation and maintenance manual
- List of problems and noncompliance issues not previously discussed (attach documentation)
Please provide the following:
- If another domestic wastewater collection and treatment system is available, provide the following information: approximate distance to the collection line and who is the continuing authority.
- Owners' names, if changing
- For the purpose of this checklist, the owner is defined as the individual or entity responsible for the continued operation and maintenance activities required to ensure the dependable function and financial responsibility of the collection and treatment system.
- Any and all documentation related to expected growth or change in the nature of use that will affect the maximum daily flow or the type of wastewater being treated. (For example: increase in population for a school, expansion of a restaurant, expansion of residential housing units, change of business that would generate industrial process waste versus domestic wastewater).
- For the purpose of this checklist, industrial process waste is anything not defined as domestic wastewater.
- List of proposed pretreatment upgrades, modifications or replacement of existing components
- Documentation of ownership of proposed soil treatment area location
- Copy of the detailed soil and site evaluation. If a detailed soil and site evaluation has not been conducted, provide the date of scheduled evaluation.
- Amount of estimated soil treatment area needed as determined by the soil and site evaluation, if known.
- Description of the proposed soil treatment/dispersal system
- List of variances that might be needed from the appropriate wastewater administrative authority
- Copy of the soil map and legend from the U.S. Department of Agriculture-Natural Resources Conservation Service-County Soil Survey with the proposed soil treatment area boundary clearly delineated
- Copy of the U.S. Geological Survey Topography Map with the soil treatment area boundary clearly delineated
- Copies of any other pertinent information
Once the documentation is compiled, copies should be sent to the appropriate wastewater administrative authority for initial review and determination. If it is determined that the use of a subsurface soil dispersal system is a feasible option and a change in jurisdictional authority is appropriate, the facility can begin working with the appropriate permitting authority.
If the change in the method of wastewater treatment requires written approval from the department, to satisfy the residential housing development rule, it shall be received prior to applying for any approvals or permits under 19 CSR 20-3.060 (1)(B) Applicability.
Submitting the items on this checklist does not obligate any of the administrative authorities to approve the use of any subsurface soil dispersal system.