Wyoming Administrative Code
Agency 020 - Environmental Quality, Dept. of
Sub-Agency 0011 - Water Quality
Chapter 23 - MINIMUM STANDARDS FOR SUBDIVISION APPLICATIONS
Section 23-7 - Standards for Sewage Systems

Universal Citation: WY Code of Rules 23-7

Current through September 21, 2024

(a) All applications shall contain the following information:

(i) Identification of the type of sewage system to serve the subdivision and identification of the entity or entities responsible for the design, construction, operation and maintenance of the proposed facility;

(ii) An assessment of the adequacy of the proposed sewage system in relation to the proposed population density of the subdivision and any other existing or proposed land and water uses in the vicinity of the subdivision that may affect the adequacy of the system; and

(iii) Demonstration that the proposed sewage system will meet all county, state and federal standards.

The demonstration shall include, but not be limited to addressing the relationship of the development to any local or state approved water quality management plans established pursuant to Section 201 of the federal Clean Water Act, 33 U.S.C. Section 1281 and demonstrate no conflict exists with any state approved local wellhead protection plan or local source water protection plan.

(b) In addition to the information required in part (a) of this section, applications proposing the use of a new central sewage system shall contain the following:

(i) An estimate of the average and maximum number of gallons per day of sewage generated by the proposed subdivision;

(ii) A demonstration that technical requirements and design standards of the department of environmental quality applicable to central sewage systems can and will be met. The demonstration shall include, but not be limited to the information contained within Chapter 11, Section 6 of Wyoming Water Quality Rules and Regulations;

(iii) An estimated schedule for the development and occupancy of the proposed subdivision; and

(iv) A detailed demonstration that the proposed sewage system for the subdivision is compatible with the proposed water supply system for the subdivision. The demonstration must determine that the operation of the sewage system will not affect the suitability or safety of the proposed water supply system and include a determination of the potential impacts of downgradient use of groundwater. The demonstration shall include:
(A) Documentation that the facility poses no threat of discharge to groundwater; or

(B) A subsurface study and a contaminant fate and transport analysis demonstrating that groundwater standards contained within Chapter 8, Wyoming Water Quality Rules and Regulations will not be exceeded.

(v) Confirmation that the owner of the subdivision collection system will provide for certified operators pursuant to Chapter 5, Wyoming Water Quality Rules and Regulations.

(c) In addition to the information required in part (a) of this section, applications proposing to connect to an existing central sewage system shall contain:

(i) Certification by the owner of the wastewater collection and treatment facilities that the system can and will provide adequate service to the proposed subdivision. This certification should address the willingness and a commitment of the owner to provide service as well as the ability of all downstream sewers, lift stations and treatment facilities to handle the hydraulic and organic loading from the proposed subdivision.
(A) The certification shall clearly identify the point of connection if the connection is not within the boundaries of the proposed subdivision.

(B) It is the responsibility of the owner to consider the capacity and ability of the system to provide sewer service to the proposed subdivision in accordance with existing laws, regulations and permit requirements.

(ii) The information required by Section 6, Chapter 11, Wyoming Water Quality Rules and Regulations shall be provided by a registered professional engineer. If the necessary information is not already available, the owner of the sewage system has the discretion to require the subdivider to provide the required information.

(iii) The party responsible for operation and maintenance of the subdivision collection system will provide for certified operators pursuant to Chapter 5, Wyoming Water Quality Rules and Regulations.

(d) In addition to the information required in part (a) (i) of this section, applications proposing the use of on-lot sewage systems shall contain information to document the following:

(i) Separation of the drainfield relative to groundwater and impervious soils will meet or exceed the minimum standards established in Chapter 25 of Wyoming Water Quality Rules and Regulations.

(ii) Soil percolation rates will meet or exceed the minimum standard established in Chapter 25 of Wyoming Water Quality Rules and Regulations.
(A) Percolation tests must be performed according to the procedure described in Chapter 25, Appendix A, of Wyoming Water Quality Rules and Regulations or other procedures approved by the department.

(B) Percolation tests are required for every third lot, or for each soil type as mapped by the Natural Resource Conservation Service (NRCS), whichever requires the least number of percolation tests.
(I) A copy of the NRCS county soil map must be submitted if soil types and distributions were used to establish the number of percolation tests required.

(II) Percolation test data and results from existing permitted on-lot sewage systems on properties adjoining the proposed subdivision may be substituted for new tests when the existing test results were obtained from the same type of soils as those that exist within the proposed subdivision.

(C) Percolation test data, results, and map illustrating test locations shall be submitted in the application.

(iii) Topographic slope, or grade, for sufficient area within each lot within the proposed subdivision will meet or exceed the applicable minimum standards established in Chapter 25 of Water Quality Rules and Regulations, and will not result in a direct or indirect discharge of pollution at the surface, into a surface water body, or into a wetland.

(iv) A 1:24,000 scale U.S.G.S. topographic map illustrating and identifying watersheds located on, or draining into, under, or over the proposed subdivision, including all ephemeral, intermittent, and perennial streams, surface waters, wetlands, and watershed boundaries within one-quarter (1/4) mile of the proposed subdivision shall be included in the application.

(v) Each lot contains sufficient area for a replacement leach field.

(vi) The proposed population density of the subdivision, determined from the proposed type of use (e.g., residential, commercial, industrial, multiple use) of the subdivision.
(A) Applications for subdivisions proposing non-domestic use, or domestic use that exceeds 2000 gallons of wastewater per day on one or more lots of the subdivision must identify:
(I) The type(s), strength, and chemical composition of non-domestic wastes most likely to be disposed of, including the average and maximum daily flows;

(II) Specific lots within the subdivision where the disposal of non-domestic wastewater could occur; and

(III) Design(s) and treatment capabilities of the type(s) of on-lot sewage systems proposed to treat such wastes.

(vii) Groundwater and surface water use is protected, as documented by:
(A) Characterization of the geologic setting from well logs, soil borings, and/or published geologic maps and reports, including documentation of:
(I) Thickness, lithology, and extent of surficial materials;

(II) Stratigraphy, lithology, thickness, and extent of underlying geologic formations; and

(III) Faults, fractures, and karst features.

(B) Characterization of the hydrogeologic setting from well logs, soil borings, test pits, and/or published geologic maps and reports, including documentation of:
(I) Depth to groundwater, including seasonal fluctuations;

(II) Degree of groundwater hydraulic confinement;

(III) Vadose zone thickness, stratigraphy, and lithology; and

(IV) Degree of hydraulic connection and interaction between groundwater and surface water, where applicable.

(C) Classification of groundwater that is unconfined or semi-confined, according to the standards established within Chapter 8 of Wyoming Water Quality Rules and Regulations must be established according to the following:
(I) A survey of the existing wells permitted by the State Engineers Office and completed within the unconfined or semi-confined aquifer within one (1) mile of the proposed subdivision must be included and contain:
(1.) A map illustrating well names and locations relative to the proposed subdivision;

(2.) State Engineers Office permitted use for each well; and

(3.) State Engineers Office appropriated production volume for each well.

(II) If there are no permitted wells within one (1) mile of the proposed subdivision a field survey shall be performed to identify and record all potential locations where unpermitted water users may be located and potential water use.

(III) If the well surveys in subsections (I) and (II) of this part do not reveal any existing wells used for domestic purposes, ambient groundwater quality of the unconfined or semi-confined aquifer must be established, either from existing representative sample results or by collection of new representative samples. At a minimum, analytical laboratory results must be provided for:
(1.) Total Dissolved Solids (TDS)

(2.) Nitrate + Nitrite as N

(3.) Total Coliform

(4.) Sulfates

(5.) Chloride

(6.) Zinc

(7.) Lead

(8.) Copper

(9.) Arsenic

(10.) pH

(11.) Selenium

(12.) Additional constituents as may be deemed necessary by the department to classify the groundwater.

(D) When groundwater is unconfined or semi-confined and is Class I groundwater as defined in Chapter 8 of Wyoming Water Quality Rules and Regulations, the following additional documentation must be provided:
(I) Horizontal and vertical extent of the aquifer;

(II) Type of flow (i.e., diffuse, porous, or conduit) within the aquifer;

(III) Direction and degree of hydraulic gradient;

(IV) Hydraulic conductivity of the saturated zone; and

(V) Porosity of the saturated zone.

(viii) Separation distances to wells and property boundaries are adequate, according to the following:
(A) Except as provided for in sub-part (B) of this part, where unconfined groundwater is Class I as defined in Chapter 8 of Wyoming Water Quality Rules and Regulations, small wastewater systems designed in accordance with Chapter 25, requirements and these regulations may be used provided that:
(I) The analysis described in Appendix A is provided in the application and determines that nitrates from on-lot sewage systems will not exceed 10 mg/L at the downgradient property boundary;

(II) The minimum isolation distances between drainfields and wells (completed or proposed within the unconfined aquifer), property boundaries, or surface waters as determined by the analysis described in Appendix B and provided in the application will be achieved or exceeded on each lot; and

(III) The analysis described in Appendix C is provided in the application and determines that nitrates from on-lot sewage systems will not exceed 10 mg/L in existing or proposed on-site public water supply wells, or off-site public water supply wells (completed or proposed within the unconfined aquifer).

(B) Unless the application materials demonstrate through fate and transport analysis that leachate will not impair ground water and/or surface water quality or use, enhanced treatment systems capable of achieving, at a minimum, the enhanced treatment standard must be used where:
(I) Small wastewater systems overlying unconfined Class I groundwater as defined in Chapter 8 of Wyoming Water Quality Rules and Regulations and designed in accordance Chapter 25, Wyoming Water Quality Rules and Regulations fail to comply with one or more of the standards established in Section 7 (viii) (A) (I) through (III) of this section; or

(II) The geologic setting of the proposed subdivision indicates that sewage leachate may come into contact with faults, fractures, or karst features.

(C) Enhanced treatment systems must be capable of achieving, at a minimum, the following treatment standards prior to additional treatment or subsurface discharge:
(I) Fecal Coliform: 800 colonies/100 mL (Maximum 30 day geometric mean);

(II) Total Kjeldahl Nitrogen: 25 mg/L (Maximum 30 day average).

(D) Where an enhanced treatment system is used it must be constructed and operated in conjunction with a subsurface disposal system that meets or exceeds the requirements of Chapter 25, Wyoming Water Quality Rules and Regulations.

(E) Where enhanced treatment systems are proposed or required, applications must contain a system design, developed and certified by a Wyoming licensed engineer, documenting the system's ability to achieve the required treatment standards, and include:
(I) Plan view and cross-section view of a proto-type enhanced wastewater treatment system;

(II) Enhanced treatment system performance standards for the proposed system(s);

(III) Number of bedrooms or average daily volume of wastewater flow; and

(IV) Operation and maintenance (O&M) requirements necessary to ensure optimum system performance, which include:
(1.) Sampling points for effluent quality monitoring prior to discharge to the leach field shall be identified.

(2.) A conceptual schematic of how the system is constructed and how it is designed to work, including the flow paths of the waste, re-circulation pathways, detention or contact times, etc.

(3.) A complete set of the manufacturer's O&M recommendations and specifications for the system, including part names and identification numbers for each of the system components for replacement purposes.

(4.) A summary or overview of the O&M requirements for all aspects of the system, identifying by component the frequency of inspection or servicing required and type of service needed to be performed to maintain the proper performance of the system.

(ix) Identification of the nearest facility that can and will accept septage wastes, and any limits, or conditions, of acceptance.

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