California’s stormwater discharge regulations, have changed significantly over the last couple of years. Often referred to as “C.3”, these regulations have required new projects with over 10,000 square feet of new or improved impervious surfaces to clarify the stormwater runoff prior to leaving the site. Hydro modification requirements, however, are fairly new, with the definition of sites that require it only recently being determined.

Hydro modification is now required on sites that create or replace over 1 acre of impervious surfaces and drain to a natural channel. Hydro modification regulations require that much of the stormwater runoff be stored on the site with only limited releases to offsite drainage facilities.

U&R recently completed the design of one of the first projects in Alameda County to require Hydro modification. The Fremont Times Square retail center project on Warms Springs Blvd. in Fremont is an urban in-fill project where space is at a premium. It was calculated to require over 20,000 cubic feet of stormwater storage.

In order to accommodate the unique space and drainage requirements of this project, U&R designed three separate below ground storage ponds using a StormTech Chamber System. The chambers are open on the bottom allowing the retained water to percolate into the ground, while a weir located in a downstream manhole controls the discharge. These ponds are located underneath the parking lots thus not interfering with everyday operation of the retail center. Fremont Times Square is currently under construction with plans to open for business in summer of 2009.