Water Management
Who is responsible for monitoring water discharge at Oak Knoll?
All water runoff control at Oak Knoll during construction is being managed on an ongoing basis by our storm water and erosion control specialists, Emerald Site Services, Inc., to conform with the State Water Resources Control Board Construction General Permit Order and San Francisco Bay Regional Water Quality Control Board’s discharge permit regulations. This is a state-licensed firm that is an industry leader in erosion and sediment control.
What agency do they report to?
Multiple public agencies have authority over water discharge at Oak Knoll and Rifle Range Creek. They are the Environmental Protection Agency, San Francisco Bay Regional Water Quality Control Board, the California Department of Fish and Wildlife, and the City of Oakland. These agencies previously reviewed and approved Oak Knoll’s Erosion and Sediment Control Plan under the California General Permit for Construction.
Who’s monitoring the monitors?
Oak Knoll’s construction managers work with the water specialists to monitor and maintain the water control measures and make adjustments as needed. But beyond this, officials from the Regional Water Quality Control Board and the City have inspected Oak Knoll. In addition, the California Department of Fish and Wildlife has conducted unannounced inspections.
What measures are being employed to manage the rain runoff?
A variety of methods are being used to control sediment and erosion on the site, including but not limited to: erosion control straw wattles on slopes; a combination of silt fencing and wattle along Rifle Range Creek to retain sediment; geotextile fabric installations; sediment silt sifter bags around drain inlets to minimize silt/debris infiltration; drain inlet filter bags to catch sediment; a check-dam system to slow water flows; and ponded sediment traps. This program is being managed on an ongoing basis by our water specialists in conformance with the San Francisco Bay Regional Water Quality Control Board’s discharge permit regulations, and our specialists actively work to mitigate any issues that may arise. This team also samples the water turbidity (water cloudiness) at various locations to comply with water quality regulations.
What are the ponds of water that are visible on the property?
These low areas along Mountain Boulevard are defined as a ponded sediment trap area the Erosion and Sediment Control Plan. They accumulate water and sediment during rainstorms. They have been seeded, but remain dirt areas as they cannot grow vegetation due to being covered with water during rain events.
Are the ponds permanent features?
No, they are temporary as the land here will eventually be raised with fill dirt after grading work resumes in the spring. Further, a system of buried storm drains will be installed throughout the property to support the new development, as specified in the master plan.
Do these ponds hold contaminated water?
No, the water in the ponds is not contaminated with any toxins or chemicals; it is only rainwater that holds some sediment.
How is water discharged from these ponds?
The ponds’ purpose is to slow runoff from the property, allow the particles to settle and trap sediment. If the water is within permit discharge allowance limits for clarity, it is allowed to discharge from these ponds to Rifle Range Creek. If water requires more settling time, it is pumped to trucks and dispersed on upper vegetated areas of the property for further filtration before reaching the creek.
When pumping water out of the ponds, what is the acceptable procedure?
The ponds are dewatered via multiple methods that are in compliance with the California General Permit for Construction. The primary method is to pump the ponds to an uphill location, use a filter bag and allow vegetation to filter the sediment before a comingled discharge. The entirety of the Oak Knoll site runs off to Rifle Range Creek and the site is well stabilized.
Why have water tanker trucks been used to remove water from the holding basin?
These trucks help carry out the dewatering of the ponds and this is an accepted industry practice. They carry the water to an uphill location on the property and empty the tank, using a filter bag and allowing vegetation to filter sediment before a comingled discharge takes place farther down on the property.
Is the water leaving the property clean?
Yes, it is. Some turbidity or water cloudiness in rain runoff naturally occurs as water flows across soil, despite mitigation measures that are in place, but testing has shown that the turbidity is below the permitted discharge limit.
What is the industry standard for testing water turbidity, which is more simply described as water cloudiness?
The official system of measuring the turbidity or cloudiness of water is Nephelometric Turbidity Units (NTU) which measures the visible suspended particulates. This is a key test of water quality. The instrument used for measuring turbidity is called a nephelometer or turbidimeter, which measures the intensity of light scattered at 90 degrees as a beam of light passes through a water sample.
Is some turbidity of runoff water acceptable during construction?
Measures are in place to trap and filter sediment before it reaches Rifle Range Creek, but some limited rainstorm turbidity in discharge water, up to 250 NTU (Nephelometric Turbidity Units), is permitted during a project’s construction period.
What levels are acceptable?
If the property discharges rainwater at the corner of Sequoia and Mountain when the ponds are full, our water specialists have repeatedly sampled this water with similar results: it is below the 250 NTU discharge limit of the California General Permit for Construction; NTU is a standard measure of turbidity or visible suspended particulates in water.
Are the filter bags at drain inlets being maintained?
Yes, the sediment filter bags at the drain inlets are monitored and cleaned as necessary on a continuing basis to ensure they are doing their job of catching sediment from the water that goes into the drains.
What will the future situation be for Rifle Range Creek?
The Navy paved over much of the creek, but Oak Knoll’s development will see it restored to a natural condition. After the paved areas are removed, the waterway will be planted with native vegetation typical of such creeks, and rocks and boulders will be placed along the creek bed. This restoration will be carried out in conformance with the plans that were reviewed and approved by various public agencies.
