REGULATION OF LARGE GROUNDWATER WITHDRAWALS: SETTING AND ENFORCING STANDARDS FOR RESOURCE PROTECTION

Maintenance of minimum streamflows and minimum water levels in lakes and wetlands is necessary to protect aquatic resources and maintain water quality standards. These flows and water levels can be altered by individual large groundwater withdrawal projects, by the cumulative impact of other alterations and developments within the watershed, or by a combination of large and small projects. Projects with large groundwater demands may have adverse effects on nearby sensitive natural resources, such as wetlands, vernal pools, and small headwater streams, even if the total groundwater withdrawal is only a small fraction of flow through the larger watershed. These isolated projects and localized impacts can be managed within a regulatory framework that establishes minimum flows and water levels and defines reporting criteria and remedial actions. However, regulatory programs that use only the footprint or total area of the development as jurisdictional criteria may not capture many projects with significant groundwater withdrawal; alternative criteria should include the volume and rate of withdrawal and the distance to a protected resource.

Criteria for minimum flows and water levels must address the natural variability of these parameters in order to maintain, to the greatest possible extent, the physical and biological functions of the pre-development resource. Necessary streamflow and water level characteristics include maintenance of the depth, volume, and velocity necessary to provide habitat conditions for all life stages of indigenous aquatic organisms, provide water exchange and aeration, substrate scouring and sorting, temperature moderation, wetland replenishment, sediment erosion and deposition, and channel formation, ingress and egress to habitats, wetland maintenance, and pathways for migration, drift, insect emergence, organic matter and nutrient cycling. If adequate flow records are available from the watershed of concern, these parameters may be relatively easy to define, but this is generally not the case. Models adjusting measured flows to the relevant drainage area may be used, but are less accurate for smaller watersheds, particularly in the outwash deposits in which large extraction wells are generally located; surface topography in these deposits frequently underestimates the source area for baseflow to smaller streams.