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City studies effects of underground structures on groundwater

Wednesday, June 2, 2010 by Mark Richardson

The city has paid a great deal of attention to its water quality over the years, but most of the attention has focused on surface water, found in its rivers and creeks. Recently city officials have begun taking a look at improving and preserving the quality of groundwater within the urban core.

 

City staff has developed reports and other information, requested by the Council, on what the city’s current policies are regarding underground water sources and how they are affected by excavations for structures such as underground parking structures and similar buildings.

 

In a presentation to the Environmental Board, Jose Guerrero, a consulting engineer with the Watershed Protection Department, reviewed a report titled “Groundwater Characteristics and Challenges for Subsurface Structures in Austin’s Urban Core.”

 

“In 2008, the City Council approved an amendment that clarified an exception to the impervious cover amendment associated with underground structures,” Guerrero said. “There were concerns raised to the impacts on groundwater, and this report is the response to those concerns.”

 

Guerrero said the city had encountered several situations where construction in the central business district has encountered pockets of groundwater that were polluted or disturbed. Part of the city’s response has been to create a GIS database of potentially contaminated groundwater in the urban core, using information provided by the Texas Commission on Environmental Quality and city departments. The project has mapped some 400 locations for polluted groundwater as well as 800 potential locations of underground storage tanks.

 

Guerrero pointed out some examples of how this has been useful, including a situation where an underground tank from an old dry cleaners that spilled PCEs, a toxic substance, into an underground stream in the downtown area. City officials were able to use maps to trace underground flows and prevent the spread of the toxins. 

 

He also pointed to a situation where a city-assisted project with the Tarrytown Methodist Church installed a collection system in a parking facility to save groundwater and reuse it for landscaping.

 

In August 2009, Council requested that the city manager process the necessary code amendments to implement the report’s recommendations. Following a report in March 2010, Council issued a number of additional recommendations for the city staff, including:

 

  • Ensure that the city’s “one stop shop” is performing a groundwater discharge review to provide more scrutiny of discharges from subsurface structures and to ensure that those buildings comply with drainage requirements;
  • Develop criteria requiring properties along stream corridors to recharge the base flow of the streams by means of linear French drains or infiltration trenches;
  • Evaluate the feasibility of allowing groundwater infiltration as an alternative to discharges to storm sewers;
  • Continue to encourage water reuse and evaluate and make recommendations on additional incentives and assistance that would encourage reuse of groundwater discharges; and
  • Consider and make recommendations on the implementation of a drainage infrastructure impact fee that can prevent increases in taxes and encourage smart growth.

The recommendations also included looking at Public Improvement Districts, or PIDs, and other methods of alternative funding and cost-sharing to facilitate storm sewer improvements ahead of redevelopment and densification of urban areas.

 

City staff said it would be bringing a number of the items requested by Council back to them in the next few weeks and months in the form of ordinances for their consideration.

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