Subject: RE: detention ponds spill again
Dear Mr. Brest Van Kempen,
The Leona Quarry detention pond is functioning as designed and intended:
water will discharged at a level where the concrete opening will allow. The size of the opening was designed to prevent any excess runoff to leave the development site. Excess runoff was defined as any runoff that is more than what the 39" Storm Drain pipe under I580 can handle which is also equivalent to the runoff leaving the site prior to the development. The original 3' by 3' concrete structure opening in the pond was raised 18" to allow more storage capacity in the pond last December 10th. And as of today, due to more forecast of rain and discharge at existing elevation, the contractor
implemented another measure to prevent more discharge: the opening has been raised to another foot for more capacity. These weirs will reduce the amount of runoff leaving the site by more than half and increase the detention
capacity of the pond. Since the water is still detained at the large detention pond, this means that the "roaring" thru the creek as you described it is normal and not more than what occurred in previous years. Creek banks have been observed to be eroding over many years prior to the start of construction at Leona.
In case of the small pond, the implemented BMP's at this location will filter the overflow before going into the storm inlet at Mountain Blvd. There are two pumps utilized at the small pond and one standby pump. The contractor has been on the site everyday to monitor all erosion and sediment control at the site.
The detention pond NTU reading today was 298 NTU. At Chimes Creek, the reading was 77 NTU. And at discharge from the existing filter system, the reading was 64 NTU. The turbidity is better and an improvement from the incoming runoff from Ridgemont which is 101 NTU.
We appreciate your concerns and the City will continue to monitor the Leona Quarry runoff flowing into Chimes Creek.