Virginia Administrative Code › Title 9 - ENVIRONMENT › Agency 25 - STATE WATER CONTROL BOARD › Chapter 790 - VIRGINIA POLLUTANT DISCHARGE ELIMINATION SYSTEM (VPDES) PERMIT REGULATION › Part III - Manual of Practice for Sewerage Systems and Treatment Works › Article 3 - Sewage Treatment Works › Section 9VAC25-790-460 - Standards

Current through Register Vol. 40, No. 24, July 15, 2024
A. The
					 minimum degree of treatment to be provided shall be adequate in design to
					 produce an effluent in accordance with this chapter, that will comply with the
					 provisions of the State Water Control Law and federal law, and any water
					 quality standards adopted by the State Water Control Board or effluent
					 limitations adopted by the State Water Control Board or Department of
					 Environmental Quality or orders issued by the Department of Environmental
					 Quality. The expected performance levels of conventional treatment processes
					 are described in subsection F of this section.
B. Industrial flows. Treatment works
					 receiving industrial wastewater flows at a rate or volume exceeding 90% of the
					 combined average daily influent flow can be designed and operated through the
					 applicable requirements imposed by the State Water Control Board or Department
					 of Environmental Quality, provided that public health and welfare protection
					 issues are resolved. Otherwise, consideration shall be given to the character
					 of industrial wastes in the design of the treatment works. In such cases, the
					 treatability characteristics of the combined (sewage and industrial) wastewater
					 shall be provided and addressed in the treatment process design. Pilot-scale
					 testing as described in this chapter may be required to predict the full-scale
					 treatment works operations.
C.
					 Design loadings. Design loading refers to the established capacity of a unit
					 operation or treatment process to reliably achieve a target performance level
					 under projected operating conditions. Component parts and unit operations of
					 the treatment works shall be arranged for greatest operating convenience,
					 flexibility, economy, and to facilitate installation of future units.
1. Treatment works to serve existing sewerage
					 systems shall be designed on the basis of established average sewage
					 characteristics with sufficient capacity to process peak loadings. Excessive
					 inflow/infiltration is an indication of deficiencies in the sewerage system and
					 the design engineer shall provide an acceptable plan for eliminating or
					 handling these excessive flows so that there will be no discharge of
					 inadequately treated wastewaters or impairment of the treatment
					 process.
2. A new treatment works
					 must be designed in accordance with anticipated loadings. Table 3, found in
					 this section, presents generally accepted minimum design flows and loadings.
					 Deviations from Table 3 shall be based on sound engineering knowledge,
					 experience and acceptable data substantiated in the design consultant's report.
					 Numbers of persons per dwelling shall be based upon planning projections
					 derived from an official source.
3.
					 The design of treatment process unit operations or equipment shall be based on
					 the average rate of sewage flow per 24 hours except where significant deviation
					 from the normal daily or diurnal flow pattern is noted. The design flow for
					 industrial wastewater flow contributions shall be determined from the observed
					 rate of flow during periods of significant discharge or, in the case of
					 proposed or new contributions, the industrial owner shall provide flow
					 projections based on existing facilities of a similar nature. The following
					 factors shall be included in determining design flows:
a. Peak rates of flow delivered through
					 conduits as influent to the treatment process unit operations.
b. Data from similar municipalities, if
					 applicable.
c. Wet weather
					 flows.
4. The design
					 organic loading should be based on the results of acceptable analytical testing
					 of the wastewater or similar wastewater and shall be computed in the same
					 manner used in determining design flow.
5. All piping and channels shall be designed
					 to carry the maximum expected flow. If possible, the influent interceptor or
					 sewer shall be designed for open channel flow at atmospheric pressure. If a
					 force main is used to transmit the influent to the treatment works, a surge or
					 equalization basin should be provided upstream of biological unit operations to
					 provide a more uniform loading. Bottom corners of flow channels shall be filled
					 and any recessed areas or corners where solids can accumulate shall be
					 eliminated. Suitable gates and valves shall be placed in channels to seal off
					 unused sections which might accumulate solids and to provide for
					 maintenance.