Rating System

LEED BD+C: New Construction

Rating System Version

v2 - LEED 2.2

Inquiry

When construction is completed in January 2007, the Dell Children's Medical Center of Central Texas (DCMCCT) will consist of a 470,300 square foot full service hospital. The existing 32.2 acre site is part of an abandoned airport facility (RMMA). The hospital project is the first building to be constructed within what is designated as Phase 1A of a 708-acre Planned Unit Development (PUD) less than three miles from downtown Austin, Texas. The Phase 1A development site totals 82.2 acres. The intent of SS Credit 6.1 is for the site to have no increase in the rate and quantity of storm water runoff due to the proposed development. The storm water management system for the RMMA PUD Phase 1A development, which promotes a wide variety of sustainable practices, is designed with a sedimentation pond and dual extended detention ponds to create a system that minimizes run-off, increases infiltration, reduces the potential for downstream flooding and erosion and reduces contaminant loads into the watershed in order to fully comply with the City of Austiníªs and the Lower Colorado River Authorityíªs ordinances for storm water management for all new building sites and developments. The City of Austin encourages regional water quality and detention ponds for developments, preferring fewer larger ponds rather than many small ponds on each separate property in order to achieve better management and maintenance of the ponds. The DCMCCT project will help directly fund the capital and maintenance costs for the new RMMA PUD storm water management system infrastructure of ponds and greenspaces. The RMMA PUD is within what is designated as the Tannehill Branch Watershed. The outfall from the detention ponds connects to an existing Texas Department of Transportation (TxDOT) drainage system. TxDOT requirements for the RMMA PUD Phase 1A development are that storm water flow rates from the extended detention ponds to the point of connection at the TxDOT drainage system be maintained at equal to or less than the existing storm flow rate which is equivalent to 9.2 cfs for a 1.5 year storm. The Zoning Regulations for the RMMA PUD allow development of 80% impervious cover. The proposed DCMCCT site impervious cover as designed is 72%. Several methods have been utilized to minimize the imperviousness of the site including íºGrasspaveí¿ pervious pavers, green roof and interior courtyard areas, a 3 acre íºHealing Gardení¿ and grass vegetative strips and numerous tree islands throughout the surface parking areas and around the perimeter of the site. The existing DCMCCT site impervious cover is 35% consisting of asphalt airport runways. The remaining pervious cover on the site consists of turf grass and weeds surrounding the runways. The 1.5 year storm event runoff for the RMMA Phase 1A development site with existing conditions equates to 96 cubic feet per second (cfs). The contribution of the DCMCCT site to this total is 52.8 cfs. With Phase 1A of the RMMA PUD fully developed (including CMCCT) the proposed 1.5 year release to the TxDOT drainage system from the sedimentation pond and dual extended detention ponds is 7.7 cfs. This exceeds the LEED requirement for no net increase in storm water rate and quantity on the post-development site. The design team would like to confirm that the intent of the requirements for SS Credit 6.1 are met for this project. The combination of the measures designed for the DCMCCT site and the 82 acre RMMA PUD Phase 1A site mentioned above will far exceed the LEED Credit requirements for the DCMCCT project.