Virginia Law

A. Reliability is a measure of the ability of a component or system to perform its designated function without failure or interruption of service. Overflow criteria, such as the allowable period of noncompliant discharge, are utilized solely for the establishment of reliability classification for design purposes and are not to be construed as authorization for, or defense of, an unpermitted discharge to state waters. The reliability classification shall be based on the water quality and public health and welfare consequences of a component or system failure.

B. Reliability Class I is required for dry ditch and intermittent stream discharges with 250 feet of easement available and wetland discharges with 100 feet of easement available.

1. For biological treatment processes, Reliability Class I shall be met by providing one of the following:

a. A passive, backup biological treatment system (e.g., an intermittent sand, peat, or media filter or a constructed wetlands);

b. A generator for the treatment system with automatic transfer switch;

c. A 24-hour holding tank for raw wastewater with telemetry system to immediately notify the operator of system failure; or

d. Any alternative means that limits the discharge of a noncompliant effluent to a maximum of 24 hours.

2. For disinfection, a Reliability Class I design shall ensure that the effluent is continually disinfected by providing electronic or mechanical means of monitoring the process such that failure of disinfection systems may be corrected within 24 hours.

C. Reliability Class II is required for dry ditch and intermittent stream discharges with 500 feet of easement available and wetland discharges with 250 feet of easement available. Reliability Class II is also required for the reduction of the distance between discharge points to 250 feet on an all weather stream.

1. For biological treatment processes, Reliability Class II shall be met by providing:

a. A fixed film biological treatment process such as an intermittent sand filter, recirculating media filter, or a peat filter;

b. A suspended growth biological system followed by post-filtration;

c. Telemetry to relay alarm conditions to the operator; or

d. Any alternative means that limits the discharge of a noncompliant effluent to a maximum of 36 hours.

2. For disinfection, a Reliability Class II design shall ensure that the effluent is continually disinfected by providing electronic or mechanical means of monitoring the process such that failure of disinfection systems may be corrected within 36 hours.

D. Reliability Class III is required for all weather stream discharges with a separation distance between discharge points of 500 feet or greater. For the purposes of this chapter, noncompliant discharges must be limited to a maximum of 48 hours.