From: "Sweiss, Fuad" <email@example.com>
Date: February 8, 2005 8:46:26 PM PST
To: 'Chiye Azuma' <firstname.lastname@example.org>, "'email@example.com'" <firstname.lastname@example.org>
Cc: "Brooks, Desley" <DBrooks@oaklandnet.com>, "Quan, Jean" <JQuan@oaklandnet.com>, "Nadel, Nancy" <NNadel@oaklandnet.com>, "Godinez II, Raul" <email@example.com>, "'firstname.lastname@example.org'" <email@example.com>, "Lau, David W" <firstname.lastname@example.org>, "Neary, Mike" <email@example.com>, "'firstname.lastname@example.org'" <email@example.com>, "Ward, Ron (PWA)" <firstname.lastname@example.org>, "Uzegbu, Marcel" <MUzegbu@oaklandnet.com>, "Osalbo, Faustino Jun" <email@example.com>, "Cappio, Claudia" <CCappio@oaklandnet.com>, "Madison, William" <firstname.lastname@example.org>, "'email@example.com'" <firstname.lastname@example.org>
Subject: RE: detention ponds spill again
Dear Ms Azuma and Mr.. Brest van Kempen,
In early January you sent an email to our inspector Jun Osalbo questioning the functionality of the Leona Project detention pond. The attached word document explains in detail the purpose and functionality of the pond and hopefully addresses your concerns regarding this subject.
Thank you for your patience while we responded to your concerns.
Fuad Sweiss, PE
Interim Engineering Division Manager
Engineering Design & ROW Management
City of Oakland Public Works Agency
Tel (510) 238-3437
Cell (510) 385-9217
Fax (510) 238-7227
LEONA DETENTION POND
Edwards Avenue has had a history of flooding on a yearly basis. This year with all the record rain that we have experienced, only one incident of minor flooding has occurred in which water flowed onto Edwards Avenue, early in the Leona Quarry grading operations. This occurred after an unexpected storm prior to the October 15th (start of the rainy season) and was a result of a failure of a temporary sedimentation pond intended to remove silt from the water during construction.
Since the initiation of grading work at the site of the Leona Quarry, there have been complaints about runoff from the site, and some statements from residents along Chimes Creek have implied that the flows coming off the site have greatly exceeded typical winter flows.
Specifically, in some emails, Ms. Chiye Azuma questioned whether the detention pond is functioning as designed and intended and questioned the impact of the introduction of baker tanks and temporary filtration pond on the outflow from the Leona site. In another correspondence, Mr. Mark Van Brest Kempen claimed that “the developer can’t control run off on their site”, “the creek has been roaring, full of silt and eroding the banks”, and that “all the measures introduced by the contractor were not called for in the original SWPPP and have failed”.
In many of the emails and discussions concerning storm water flows from the Leona Quarry, the issues of water quality and water quantity have been discussed interchangeably. To accurately address recent storm water runoff concerns I would like to focus on two main aspects of the “surface runoff” from the Leona Development, “Quantity” and “Quality”.
The following description of runoff conditions is to mainly clarify whether there has been an increase or decrease in volume in Chimes Creek since the beginning of the project.
In the most basic sense, the amount of surface runoff (Quantity) in a given watershed is directly related to the area or size of the watershed, how much rain falls in a given amount of time, and how much of that rain will infiltrate into the ground before it has a chance to leave the site. The amount of rainfall that can infiltrate into the ground is primarily a function of the drainage area, land use, soil type, and ground slope.
The accumulation of the surface runoff from the Leona site increases during a rainfall event up to a “peak flow” at which time the surface runoff will begin to decline. The peak flow during a rainfall event is typically observed in our creeks during the highest water surface elevation. Peak flow may be controlled by use of detention facilities, which are designed to allow stormwater runoff to be stored temporarily and released gradually.. The hydrologic modeling conducted for the Leona project determined that the restoration of the quarry site would reduce peak discharge and total runoff from the site even with the construction of the residential units.
The City and Alameda County and Flood Control and Water Conservation District (ACFC) insisted on requiring a detention basin at the Leona site mainly to control the amount of flow entering the existing 39” SD pipe under I-580. ACFC also required that the development at Leona would not adversely impact downstream property by increasing the flood hazard.
Currently all surface runoff from the Leona site drainsto the new detention pond. The pond is sized to capture the 100-year storm runoff volume. The pond outfall structure has one 18” orifice at the base that will restrict the amount of water leaving the pond and flowing through the 39” SD pipe under I-580. The outfall structure also regulates the peak discharge to the 39” culvert up to the 100-year event. The effect of the detention basin is to hold the surface runoff from the developed site and discharge the volume over an extended period of time without exceeding the historic runoff conditions prior to development.
In Chimes Creek, according to Mr. Kempen, water in the creek typically overflowed to his porch. This has not happened this year. This has demonstrated that the detention pond has been effective at attenuating the peak volume of runoff during these recent storms.
Because the project is still under construction, the slopes are not completely vegetated, and the storm drainage system is not completely done, the project’s Storm Water Pollution Prevention Plan (SWPPP) was modified to utilize the detention pond as a retention basin to allow sediments to settle and storm water to be filtered/treated before being discharged into the City’s Storm Drain system. A retention basin is used to store water for a longer period of time to allow sediments to drop out before allowing the stormwater to enter into the downstream pipes and creek.
The retention basin was used for adaptive management to improve the quality of water leaving the site. In order to achieve this, the 18” orifice at the base was temporarily plugged for the duration of the grading operations and the 3 feet square opening in the vertical concrete structure was covered with a board to act as a weir to increase the capacity of the basin. The weir was raised twice in late December based on observations at the site as to the most effective weir level to achieve the maximum desired retention. At the built out condition, it is anticipated that the detention pond will receive surface runoff with less suspended sediments from the fully developed and re-vegetated basin.
With regard to runoff quality during construction, the SWPPP in effect for the Leona Quarry project requires the contractor to construct best management practices (BMPs) to prevent erosion and discharge of sediment laden waters from the site. The contractor is also required to keep turbidity of discharge waters below a target level set by the State. A caveat to these requirements is that measures taken are limited to an effort by the contractor that is considered the "maximum extent practicable" (MEP). MEP is generally accepted to mean the highest level of effort and technology that is economically feasible and is typically utilized to control erosion in projects of this size in areas of similar rainfall amounts.
So if the turbidity standards are exceeded in the discharge water, the contractor is first required to identify the cause of the high turbidity. If further BMPs are identified as an effective way to reduce the turbidity, the contractor is then responsible for implementing those BMPs. The baker tanks, temporary upper bowl and filtration system were introduced as additional measures to minimize the turbidity of the water before it is discharged into the storm drain system.
The level of effort that went into designing the detention facilities has shown to be effective at reducing the potential flood hazards at Chimes Creek and to properties downstream. Efforts to improve the quality of runoff have exceeded the contractor’s initial requirements under SWPPP. There has been extensive ongoing monitoring of the site related to hydrology, geology, noise, dust and water quality. These reports are available for anyone to examine.