From: "Ward, Ron (PWA)" <>
To: "Nadel, Nancy" <>, "Osalbo, Faustino Jun"

Cc: "Brooks, Desley" <>, "Uzegbu, Marcel" <>, "Estes, Lesley" <>, "Schwarz, Alison" <>, "''" <>, "''" <>, "''" <>, "Neary, Mike" <>, Office of the Mayor <>, "''" <>, "''" <>, "Lau, David W" <>, "''" <>, "''" <>, 'Barbara Sutherland ' <>, "''" <>, "Mirsaeidi, Emad" <>, 'nancy peterson' <>, "Movassaghi, Maziar" <>, "Cappio, Claudia" <>, "'McGill, Phillip'" <>, 'Mark Brest van Kempen' <>, "''" <>, "''" <>, 'Kent Peyton' <>

Subject: RE: Chimes Creek turbidity and pumping
Date: Thu, 29 Dec 2005 14:32:22 -0800


Prior to the first significant rainfall this season, the developer installed
even more of the erosion prevention measures than were successfully used
last year, including more than 33 acres of erosion control fabric, more
extensive use of straw waddles and miles of concrete ditches, with paved
streets and a functioning storm drain system.  In fact, the Regional Water
Quality Control Board described the Leona Quarry site as "well planned and
well-installed ... erosion and sediment control" in early December, 2005.
Things could be much worse.

The detention pond is sized for a fully developed and vegetated site.
Extensive hydrologic modeling has been used to determine the necessary
storage volume of the pond to prevent flooding.  An as-built field survey
has been completed that confirms the pond was built according to plan.

During this first rainy season after completion of the site grading, one of
the Best Management Practices implemented by the developer is to block the
orifice at the bottom of the detention pond.  This allows the developer
additional retention time to settle the stormwater and to filter and
discharge it.  In the fully developed and vegetated state, stormwater will
be allowed to drain continuously out of the pond, through an orifice in the
bottom of the pond.  Again hydrologic modeling was performed to analyze the
effect of beginning a storm with the orifice at the bottom of the pond
blocked and stored water to the level of the discharge structure opening.
The modeling indicates that the pond will function very similarly with
respect to peak flow controls in this scenario versus the permanent
configuration, i.e., containment of a 100-year design storm.

I hope this answers your questions,

Ronald Ward, P.E.
Supervising Civil Engineer
PWA Project Delivery Division
(510) 238-6606
(510) 238-6633 (FAX)