Prior to July 1, 2014, County development standards considered projects that discharged to an existing SWM facility (or that were included in an approved overall SWM plan) to be grandfathered for SWM purposes, as long as the SWM design included a water quality component, and the project design was consistent with the assumed SWM design parameters.
However, under the current VA SWM Regulations, all regulated land disturbing activities must be conducted in compliance with the water quality and quantity technical criteria in either Part IIB or Part IIC, determined as noted above. (Note: While there are some differences, Part IIC is generally consistent with the 1999 VA SWM Handbook, which was adopted by Loudoun County in November 2002). As a result, a project cannot utilize an existing SWM facility to satisfy its stormwater requirements without verification that it complies with the applicable criteria for the project. Importantly, the County cannot issue a land disturbance permit without this verification, even if there is an approved site plan for the project, meaning that a plan revision may be necessary to bring the SWM plan into compliance.
In the case of older facilities that were designed using other technical criteria, it may be possible to demonstrate compliance by performing a comparative analysis of the approved design to the Part IIC (or IIB) technical criteria (e.g., design volumes, features, calculations, etc.). If such an analysis is unsuccessful, the project must be designed to comply with Part IIB, either by providing SWM measures on-site, or by retrofitting the existing facility.