The work that’s been done to include Rainwater Harvesting in the proposed Virginia Stormwater Management Regulations is very exciting, but the guidance could be even stronger.

By capturing rainwater and reusing it within a development, nutrients that would normally be discharged from the site are retained. This reduced environmental impact is achieved while offering a benefit to the developer though reduced water consumption and the associated savings. By acknowledging the nutrient removal benefits of cisterns (Reference: Table 1 – BMP Removal Efficiencies), Virginia will have a Market-Based solution to meet Water Quality requirements while offering a benefit – not a cost – to the developer.

Where the proposed changes could be improved upon is in the language regarding stormwater quantity discharges. Section 4VAC-50-60-74 Stormwater Harvesting says (on line 1212) “stormwater harvesting is encouraged.” While this is a step in the right direction, more guidance to the locality is needed to ensure consistent application across the state.

For example, most new developments include a pond or underground stormwater detention system that collects stormwater runoff, holds it temporarily and discharges it slowly to reduce the potential to erode natural waterways or prevent flooding of municipal storm sewers. It would be beneficial if the new regulations included guidance on how the detention volume could be converted to a harvesting system.

There are a number of methods for making this conversion. Two simple alternatives include:

1)      Identify a percentage of the detention volume that may be converted to harvesting. (Example: Up to 100% of the required detention volume may be diverted into a Cistern for reuse. Where the previous regulation required a 10,000 cubic foot pond, the new regulation allows the pond to be reduced to 7,500 cubic feet if a 2,500 cubic foot cistern is installed.)

2)      Identify a ratio at which detention volume may be converted to harvesting. (Example: 75% of the harvesting volume will be credited toward the detention requirements for the site. Where the previous regulation required a 10,000 cubic foot pond, the new regulation allows the pond to be reduced to 7,500 cubic feet if a 3,333 cubic foot cistern is installed, as 75% of 3,333 is 2,500 cubic feet.)

The primary benefit of inserting this language into the regulations would be to strengthen the Commonwealth’s stance on encouraging stormwater reuse and ensuring consistent application of the regulations throughout Virginia.

Care must be taken, however, to ensure that runoff stored in a cistern will be used on-site. Obviously if there is no use of the harvested water and the cistern remains full, all runoff directed to the cistern exits through the over-flow, and the expected benefits are lost. However, models are easily developed that balance the volume of water stored with the water demands of the site. Limits should be placed on the maximum allowable size of the cistern. Again, many options exist for creating these limits based on average daily demand, peak monthly demand, or the size of the collection area.

Market-based solutions are the best hope Virginia has for the restoration the Chesapeake Bay. By adopting the new regulations and strengthening the language on how cistern volumes are integrated into the design of a site’s detention system, we can help reduce nutrient loading on the Bay while both reducing the cost of development in Virginia and reducing demand on potable water supplies.