This section includes the standards for non-biological treatment ponds or ponds that accept commercial/industrial waste or wastewater that is primarily non-biological in nature and does not utilize biological organisms for treatment. Radiological effects considered by the Nuclear Regulatory Commission (NRC) from non-surface discharging treatment works within a NRC licensed permit boundary are exempt from this section.
(a) Location. - (i) Extraneous surface water and groundwater shall be excluded from entering the wastewater pond or entering the wastewater flow into the pond.
- (ii) Ponds shall not be located within the ordinary high water mark of perennial rivers, streams, or creeks. Ponds not containing hazardous or toxic wastes may be located within the ordinary high water mark of intermit tent rivers, streams, creeks, draws, coulees, or other natural drainages provided a by-pass ditch is installed capable of passing the 24-hour - 100-year precipitation event. All other ponds shall be protected from structural damage during the 100-year flood event.
(b) Basis of design. - (ii) In addition to the above, non-surface water discharging ponds shall be designed on the basis of a water balance that considers net evaporation and seepage. Non-discharging ponds shall be designed to provide sufficient storage to retain all wastewater and rainfall during the wettest occurring year of a ten year period.
(c) Pond layout. - (i) Discharging treatment systems and ponds that require liners to protect groundwater shall consist of a minimum of two cells. The largest cell shall not contain more than 55 percent of the total waste volume at the design capacity.
- (ii) Inlet and intracell structures for discharging treatment systems shall prevent short circuiting, and shall not erode or disturb the liner, seal or dike.
- (iii) Outlet structures from a discharging treatment system shall have an overflow device, prevent short circuiting, prevent floating debris from discharging, and keep outlet velocities to a minimum so as not to erode or disturb the receiving channel. Erosion control material shall be designed based on flow velocities and quantities. Ice formation shall neither stop the overflow nor damage the outlet structure.
- (iv) All pipe protruding through a dike or embankment shall have adequate seepage controls. Capabilities shall exist to drain the ponds for maintenance purposes.
- (v) A manhole or vented cleanout wye shall be installed prior to the entrance of the influent pipe into the primary pond(s) and shall be located as close to the dike as topography permits. The influent pipe invert should be at least six (6) inches above the maximum operating level of the pond.
- (vi) The maximum and minimum water depth shall be determined on a case-by-case basis. However, the design engineer must demonstrate that ponds with less than two (2) feet water depth will not have vegetation problems.
- (vii) Free board shall be provided to protect embankments and dikes from overtopping from wave action, and shall be a minimum of three (3) feet above the high water level. For ponds less than two (2) acres, two (2) feet of freeboard may be acceptable.
(d) Pond construction. - (i) Soils used in constructing the pond bottom and dike cores (not including the liner) shall be relatively incompressible, have a low permeability, and be free from organic material or trash. The soil shall be compacted at a water content that will insure structural stability, minimize hydraulic seepage, and minimize settling. The soil shall provide an adequate foundation for the liner, if used.
- (ii) On ponds that are not specified to receive an artificial liner, no rocks larger than six (6) inches in length shall be permitted in any of the designated embankment.
On ponds that are specified to be lined with an artificial liner, rocks larger than six (6) inches in length shall not be placed within five (5) feet of the interior slope surface of any pond embankment. Material containing by volume less than 25 percent of rock larger than six (6) inches and less than twelve (12) inches in length may be placed in the remainder of the embankment.
- (iv) The minimum top dike width shall be eight (8) feet to permit access of maintenance vehicles. Top dikes wider than eight (8) feet shall be required when necessary to ensure structural stability.
(e) Dike protection. - (i) Interior embankments shall be protected from wave action with riprap, paving, or other erosion resistant material. The following conditions may be exempted from the riprap requirements:
- (A) Ponds of one (1) surface acre or less:
- (B) Ponds with an artificial liner;
- (C) Embankments cut into natural slopes where a soil liner is not provided; or
- (D) Ponds that are sheltered from wind or where winds are slow enough that significant erosion will not occur.
- (ii) Exterior of dikes, top of dikes, and all interior dike surfaces where riprap or a seal is not provided shall be covered with topsoil and seeded with suitable dryland grasses to prevent erosion. A uniform coarse graded gravel may be substituted for the vegetation requirement.
(f) Liners. - (i) Seepage limits. The seepage through the pond bottom and side walls shall not cause, a violation of the groundwater standards as described in Chapter 8 (Quality Standards for Wyoming Groundwaters) of the Wyoming Department of Environmental Quality, Water Quality Rules and Regulations. Liners shall be required if the wastewater characteristics or site conditions will not insure the protection of the groundwater for which it is classified.
If the applicant cannot document that the facility poses no threat to groundwater and elects not to perform a subsurface study in accordance with Chapter 3, Section 15(a) and (b), then the groundwater shall be protected from contamination by the wastewater with a liner equivalent to three (3) feet of soil having a permeability of 10-7 cm/sec or less. When an applicant performs a subsurface study, the requirement for the liner shall be determined based on the results of the study and the groundwater protection required. In no instance shall the maximum seepage rate exceed 1/8 inch per day in the primary pond(s).
- (ii) Soil and bentonite liners. The specifications for a soil or bentonite liner shall be based upon the results of a preliminary testing program and shall contain at a minimum the type of material, optimum and acceptable range in water content, acceptable range for compaction, and maximum allowable particle size.
Soil or bentonite liners used to protect groundwater quality shall meet the following criteria. Written certification that the soil liner was constructed in accordance with specifications shall be provided by a Wyoming registered professional engineer or an independent soils laboratory. Tests for water content and density shall be taken during application of each lift. Additionally, either permeability testing of undisturbed core samples from the in-place seal, or detailed tests such as particle size distribution and Atterburg limits confirming that the soil used in the liner construction was the same soil initially tested, shall be provided. In all cases, at least one test shall be provided per acre per lift, except for core sampling of the in-place liner, where one core of the completed liner shall be tested per acre.
- (iii) Synthetic liners. The thickness requirements for synthetic liners shall be determined on a case-by-case basis but shall not be less than 30 mils. The type of liner shall be compatible with the wastewater characteristics. The synthetic liner shall have a permeability equivalent to that of Section 30(f)(i).
Synthetic liners shall be anchored to prevent movement, slippage, and flotation. The synthetic liner shall be protected from degradation by ultraviolet light, ice damage and settling of underdrain trenches. An air venting system may be required beneath the synthetic liner to expel gases trapped during installation, produced by decomposing organic material, or produced by a fluctuating water table.
- (iv) Prefilling. For soil or bentonite liners, a method of maintaining the seal at or above optimum moisture conditions is required.
- (v) Exfiltration evaluation. All ponds designated with a maximum exfiltration rate shall be tested for exfiltration. A maximum exfiltration rate not in excess of the design rate shall be deemed acceptable. If the exfiltration rate is deemed excessive, the seal shall be repaired and the test procedure repeated. This procedure shall be repeated until the maximum exfiltration rate criteria is met. Results of all testing shall be submitted to the Department of Environmental Quality.
(g) Miscellaneous. A permanent flow measuring device shall be installed at the outfall of discharging pond sites and shall measure the effluent under all climatic conditions. The accuracy of the flow measuring device must be within ten percent of the actual flow. Ponds with a maximum daily discharge of less than 50,000 gallons per day may be exempted from installing a permanent flow measuring device.
020-11 Wyo. Code R. § 11-30