Evaluation of surface water supply impacts from permit exemptions: A comparison with climate change and demand growth

Many states in the Eastern U.S. have limited water withdrawal regulations, posing significant risks to water supply management during periods of low flows. While these states require water withdrawal permits, exemptions for grandfathered withdrawals that allow unregulated access to surface water are common. Such permit exemptions present a challenge to water supply management, as full utilization of allowable withdrawals by permit-exempt users could pose risks to maintaining adequate water supplies for current and projected demand. This study used reported permit exemption data in Virginia to understand the extent, volume, and potential impact of permit-exempt withdrawals on 30- and 90-day low flows. The permit-exempt withdrawal values used in this study were obtained from Virginia Department of Environmental Quality. Maximum permit-exempt withdrawal volumes were significantly higher than projected future demands in permitted users. The impacts of these withdrawals on drought flows were compared with the impacts presented by climate change and demand growth. Widespread reduction in flows was observed with the "dry" future climate change scenario, while impacts were more localized in the exempt users and the demand growth scenarios. The impacts of exempt users exceeded the impact of climate change and demand growth scenarios in many regions during low-flow periods. Therefore, more comprehensive water planning, policy and research is needed to address the impact of permit exemptions.