4.12 Groundwater

Goal 12 - Groundwater

Protect and maintain existing groundwater flow, promote groundwater recharge and improve groundwater quality and aquifer protection.

Discussion

Maintenance of groundwater recharge is important in the Langdon Lake subwatershed to maintain base flows and recharge aquifers that supply public and private water wells.  Development, with the associated creation of new impervious surface, increases the volume of stormwater runoff and reduces the amount of stormwater that naturally percolates into the soil to recharge groundwater. 

Increased infiltration in the Langdon Lake subwatershed is desirable for two primary reasons: to reduce the amount of pollutant loading into Langdon Lake, and to protect the hydrology of the large discharge (groundwater-fed) wetlands in the subwatershed.  Many of those wetlands are key resources with high ecological values that are dependant on groundwater to maintain those functions and values.  Much of the subwatershed has at least moderate infiltration potential.  Requiring new development and redevelopment to infiltrate some of the new stormwater generated would reduce new volumes downstream and help reduce future erosion in streams and channels; minimize new pollutant loading that would have been conveyed by that stormwater; and help maintain groundwater levels, preserving wetlands. 

Some parts of the subwatershed are areas of aquifer sensitivity or are drinking water wellhead protection areas, where care should be taken when infiltrating stormwater.  Proper design of infiltration practices is necessary to avoid groundwater contamination.  Other land use practices such as the use of private water wells or individual sewage treatment systems, or agricultural practices such as the use of chemicals and handling of animal waste should be monitored to prevent contamination of groundwater resources.

Groundwater management in the Langdon Lake subwatershed will focus on increasing the amount of infiltration in the subwatershed, and minimizing opportunity for groundwater contamination from land use practices.

Desired Outcomes: Maintain function of existing groundwater flow, assist in the protection of drinking water supply, no degradation in surficial groundwater quantity or quality.

 Metrics:

  • Acre-feet volume abstraction
  • Surficial groundwater levels and parameters

Goal 12.1 - Langdon Lake

Protect and maintain groundwater recharge and groundwater quality.

Actions

  1. Amend existing or establish new District rules requiring abstraction of the first one inch of rainfall on new permitted development and redevelopment. 
  2. Establish new District rule requiring an additional level of analysis and review of permitted development and redevelopment where there is a potential to adversely impact groundwater connected to a surface water feature.
  3. Require pretreatment of stormwater discharged to wetlands or infiltration areas in the in the areas of high aquifer sensitivity.
  4. Coordinate stormwater and groundwater management within identified drinking water management areas and wellhead protection areas with city and private wellhead protection plans.
  5. Develop infiltration strategies appropriate to wellhead protection areas and areas of groundwater sensitivity.
    1. Work cooperatively with Hennepin County, the Minnesota Department of Health, and other agencies charged with managing individual sewage treatment systems and private and public groundwater wells to assess the potential impacts of surface water management practices on groundwater quality.
    2. Provide assistance to LGUs and developers to foster low impact development and redevelopment that minimizes new impervious surface and provides for increased infiltration.
  6. Develop and distribute model ordinances and design standards that incorporate low impact design principles.
  7. Sponsor educational opportunities for LGU staff, developers, elected and appointed officials and other interested parties to provide practical information and opportunities for sharing experiences.
  8. Require developers to identify existing drain tile lines on property proposed for development.
  9. Identify a network of surficial aquifer monitoring wells across the entire Minnehaha Creek watershed, monitor groundwater levels and groundwater quality, and if change is detected identify strategies for addressing that change.