City of Twin Oaks, MO Design Requirements

[Ord. No. 23-11, 9-20-2023]

201.1 Design. The design of erosion and sediment controls required for land disturbance activities shall comply with the following minimum requirements:

Land disturbance, erosion and sediment control practices, and watercourse crossings shall be adequate to prevent transportation of sediment from the site.

Materials brought to any site or property under a permit issued under this Code, where said material is intended to be utilized as fill material at the site for land disturbance, erosion, or sediment control, shall consist of clean uncontaminated earth, soil, dirt, sand, rocks, gravel or masonry materials or other approved materials.

Cut and fill slopes shall be no greater than 3:1 except as approved by the Department of Public Works or the Department of Highways and Traffic to meet other community or environmental objectives.

Clearing and grading of natural resources, such as forests and wetlands, shall not be permitted, except when in compliance with all other County Ordinances.

Clearing techniques that retain existing vegetation to the maximum extent practicable shall be used and the time period for disturbed areas to be without vegetative cover shall be minimized to the extent practical.

Clearing, except that necessary to establish sediment control devices, shall not begin until all sediment control devices have been installed and have been stabilized.

Phasing shall be required on all sites disturbing greater than thirty (30) acres of land. The size of each phase will be established by the Department of Planning at the time of plan review for the issuance of a major land disturbance permit.

201.2 Erosion control design. Erosion control requirements shall include the following:

Permit holder shall install temporary stabilization when soil disturbing activities will cease on any portion of the site and are not planned to resume for a period exceeding fourteen (14) calendar days. Temporary stabilization must be initiated immediately upon knowing the duration is more than fourteen (14) days. Temporary stabilization must be completed within seven (7) calendar days. Final stabilization of disturbed areas must be initiated immediately and completed within seven (7) calendar days whenever any clearing, grading, excavating or other earth disturbing activities have permanently ceased on any portion of the site. County may grant allowances to the seven-day completion period for temporary and final stabilization due to weather or equipment malfunctions. The use of allowances shall be documented in the SWPPP.

If seeding or another vegetative erosion control method is used, it shall become established within two (2) weeks, or the site shall be re-seeded, or a non-vegetative option employed.

Techniques shall be employed to ensure stabilization on steep slopes and in drainage ways.

Soil and material stockpiles must be stabilized or covered at the end of each workday or perimeter controls must be in place to prevent silt from the stockpile from leaving the site.

The entire site must be stabilized, using a heavy mulch layer or another method that does not require germination to control erosion, at the close of the construction season.

Techniques shall be employed to prevent the blowing of dust or sediment from the site.

Techniques shall be employed to divert upland runoff past disturbed slopes.

201.3 Sediment control design. Sediment control requirements shall include:

Settling basins, sediment traps, or tanks and perimeter controls.

Settling basins shall be provided for each drainage area within ten (10) or more acres disturbed at one (1) time and shall be sized to contain one-half (0.5) inch of sediment from the drainage area and be able to contain a two-year, twenty-four-hour storm. If the provision of a basin of this size is impractical, other similarly effective best management practices (BMP), as evaluated and specified in the storm water pollution prevention plan (SWPPP), shall be provided.

Settling basins shall be designed in a manner that allows adaptation to provide long-term storm water management, as required by the County department(s) having enforcement authority and responsibilities described in Section 407.103 of this Code.

Settling basins shall have stabilized spillways to minimize the potential for erosion of the spillway or basin embankment.

Protection for adjacent properties by the use of a vegetated buffer strip in combination with perimeter controls.

201.4 Watercourse design. Watercourse protection requirements shall include:

Encroachment into or crossings of active water courses/riparian areas and wetlands shall be avoided to the maximum extent practicable. All City, County, State, and Federal permits, and approvals shall be obtained by a permit holder prior to beginning work authorized by a County land disturbance permit.

Stabilization of any watercourse channels before, during, and after any in-channel work.

If a defined watercourse is to be re-aligned or re-configured, clearing, and grubbing activities within fifty (50) feet of the watercourse shall not begin until all materials and equipment necessary to protect the watercourse and complete the work are on site. Once started, work shall be completed as soon as possible. Areas within fifty (50) feet of the watercourse shall be re-contoured and stabilized. Permit holder shall install temporary stabilization when soil disturbing activities will cease on any portion of the site and are not planned to resume for a period exceeding fourteen (14) calendar days. Temporary stabilization must be initiated immediately upon knowing the duration is more than fourteen (14) days. Temporary stabilization must be completed within seven (7) calendar days. Final stabilization of disturbed areas must be initiated immediately and completed within seven (7) calendar days whenever any clearing, grading, excavating or other earth disturbing activities have permanently ceased on any portion of the site. County may grant allowances to the seven-day completion period for temporary and final stabilization due to weather or equipment malfunctions. The use of allowances shall be documented in the SWPPP.

All storm water conveyances shall be designed according to the criteria of the City, County, and the St. Louis Metropolitan Sewer District (MSD) and the necessary permits obtained.

Stablization adequate to prevent erosion shall be provided at the outlets of all pipes and paved channels.

Except as otherwise permitted above, stream buffers along floodplain zoned streams and other natural waterways as required by City Code shall not be disturbed.

201.5 Construction site access design. Construction site access requirements for major land disturbance activities shall include:

A temporary construction access entrance, located to provide adequate sight distance, shall be provided at all land disturbance sites including a wash down area supporting all active sites.

The City or Department of Highways and Traffic may require other measures to ensure that construction vehicles do not track sediment onto public streets or roadways or be washed with wash effluent channeled directly into storm drains.

201.6 Control of construction materials and waste. Control requirements for construction materials, construction wastes and other wastes generated on site at the land disturbance site, including facilities that process and handle materials and waste such as temporary concrete or asphalt batch plants, temporary recycling or waste incineration facilities, and similar temporary construction material and waste handling facilities shall include provisions, satisfactory to the City or those County department(s) having enforcement authority and responsibilities described in Section 407.103 of this Code for:

Spill prevention and control facilities for materials such as paint, solvents, petroleum products, chemicals, toxic or hazardous substances, substances regulated under the Resource Conservation and Recovery Act (RCRA) or the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), and any wastes generated from the use of such materials and substances, including their containers. Any containment systems employed to meet this requirement shall be constructed of materials compatible with the substances contained and shall be adequate to protect both surface and ground water.

Collection and disposal of discarded building materials and other construction site wastes, including those listed in Subsection (F)(1) above.

Litter control.

Control of concrete truck washouts.

Assurance that on-site fueling facilities will adhere to applicable Federal and State regulations concerning storage and dispensers.

Provision of sufficient temporary toilet facilities to serve the number of workers on major land disturbance sites as directed by the Department of Health.

Assurance that on-site temporary construction materials or waste handling equipment and facilities including, but not limited to, batch plants, recycling or grinding facilities, and temporary incineration equipment also adhere to County Department of Health regulations.