Too Hot. Too Cold. Just Right?

As part of the Virginia Stormwater Management Program MS4 Phase I Permit, the City of Virginia Beach (City) implements an Enhanced Dry Weather Screening Program.  The goals of dry weather screening and sampling is to identify and locate illicit discharges, cross-connections, and/or dumping into the City’s stormwater system.  Because many outfalls discharge directly to surface waters without treatment, it’s important to screen outfalls periodically  during dry weather conditions for discharges and to screen any discharges for  pollutants.

Dry weather screening activities are to be performed after a  period of at least 72 hours with no more than 0.10 inch of precipitation accumulationto safeguard against flows from a rainfall event being sampled.  The purpose of sampling is to identify the source of the discharge and any potential illicit discharges.

While dry weather screening is required to be completed annually, the time of year the screening is performed is not regulated.  Seasonal variations can impact many aspects of dry weather screening, including sampling results, types of dry weather flows observed, and even equipment performance and personnel health and safety. Analyzing data, challenges, and lessons learned from the City’s previous six years of dry weather screening efforts, is there a “just right” time period for dry weather screening?