Texas Administrative Code › Title 30 - ENVIRONMENTAL QUALITY › Part 1 - TEXAS COMMISSION ON ENVIRONMENTAL QUALITY › Chapter 317 - DESIGN CRITERIA PRIOR TO 2008 › Section 317.10 - Appendix B-Overland Flow Process

Current through Reg. 49, No. 28; July 12, 2024
The overland flow process is the application of wastewater
				  along the upper portion of uniformly sloped and grass-covered land and allowing
				  it to flow in a thin sheet over the vegetated surface to runoff collection
				  ditches. The primary objective of this process is treatment of wastewater.
				  Utilization of this process does result in a discharge and therefore a waste
				  discharge permit from the Texas Water Commission is required. This process is
				  best utilized on soils with low permeability. The performance of the overland
				  flow process is dependent on the detention time of the wastewater on the
				  vegetated sloped area. Therefore, in order to meet a specified effluent
				  criteria, the hydraulic loading rate, the application rate, and the
				  effectiveness of the distribution system are essential design considerations.
				  For detailed process design guidance, the latest edition of the Environmental
				  Protection Agency Technology Transfer Process Design Manual for Land Treatment
				  of Municipal Wastewater may be used.
(1) Hydraulic loading rate. The hydraulic
				loading rate and application rate can vary depending on levels of pretreatment,
				quality of effluent, temperature, and other climatic conditions. A hydraulic
				loading rate of 1.5 to 2.0 inches per day and an application rate of six to
				eight gallons per hour per foot of slope width are suggested as general guides.
				The design rates selected and their justification shall be submitted in the
				design report.
(2) Wastewater
				storage. Storage capacity for inclement weather conditions shall be provided.
				To minimize the impact of algae on the treatment performance, this storage
				shall be designed as an off-line basin, used only as needed and emptied as soon
				as possible by blending with other pretreated wastewater prior to application.
				To control odors, provisions for aeration in the storage basin should be
				considered.
(3) Soil testing. For
				the overland flow process, the soil profile evaluation should extend to a depth
				of at least three feet. The soil sampling and testing specified in subsection
				(b) of this section shall be representative of the soil to this
				depth.
(4) Other design
				considerations.
(A) The overland flow process
				treatment area shall be subject to the same buffer zone requirement as a
				treatment plant.
(B) The minimum
				slope length for the applied wastewater shall be 100 feet.
(C) The sloped areas to receive wastewater
				shall be uniformly graded to eliminate wastewater ponding and short circuiting
				for the length of the flow. Site grading procedures and tolerances shall be
				included in the specifications. Minimum slopes shall equal or exceed 2.0%;
				maximum slope shall not exceed 8.0%. The application site shall be protected
				from flooding.
(D) The application
				cycle should provide a maximum of 10 hours for dosing followed by a minimum
				period of 14 hours of resting.
(E)
				The method of application shall provide uniform coverage of the area.
(F) A vegetative cover shall be provided on
				the application site. The plant types selected shall be suitable for overland
				flow conditions and shall provide uniform coverage of soil to prevent short
				circuiting and channelization of the area.
(G) Wastewater quality and disinfection
				requirements for overland flow process discharges will be established by the
				discharge permit.
(H) An effluent
				sampling station shall be provided prior to discharge to surface waters. The
				sampling and reporting requirements will be established by the discharge
				permit.