Project Plans

CALABASAS LAKE AERATION SYSTEM REPLACEMENT PPROJECT

SPECIFICATION NO. 2026-13

IN THE CITY OF CALABASAS, CALIFORNIA

The City of Calabasas Public Works Department is soliciting bid proposals from qualified Lake Maintenance contractors for replacement costs of the five (5) aeration systems at Lake Calabasas. The aeration system was originally installed thirty-six (36) years ago in late 1990 by Marine Biochemists. Various components have been replaced or repaired over that time, primarily thought to be compressors, compressor vanes, exhaust fans, sump pumps, and other minor parts that fail.

The current aeration system consists of five (5) below ground vaults in various locations around the lake consisting of one (1) cabinet per vault with two (2) one (1) horsepower compressors with a variety of additional support components. Each vault supplies air through eight (8) self-sinking tubing lines of various lengths to eight (8) air stations (bubblers) placed on the lake bottom. Two (2) aeration systems are controlled by remote valve boxes labeled Remote Valve Box -1 and Remote Valve Box-2 on the map below. Vaults are fitted with exhaust fans/pipes to support venting hot air out of the vault created by compressors in the cabinet and vault space.

Provided below is a schematic that shows the location of vaults, aeration tubing, and air stations.

Each of the five (5) aeration systems will be addressed separately since each are made up of different lengths of aeration tubing line, valves and conduit configurations, and have unique characteristics.

The aeration vaults are numbered one (1) through five (5) in clockwise order beginning with Vault 1 at the end of Park Mirasol, south of the beach/Calabasas Tennis & Swim Center.

CALABASAS LAKE AERATION SYSTEM OVERVIEW MAP

Vault 1 Aeration System

Vault 1 supplies air to eight (8) air stations and is a hybrid system fitted with a remote valve box located in the shoreline walkway at Park Jacaranda. The remote valve box has a single hose originating from one compressor which then distributes compressed air to four (4) air stations through a four (4) valve manifold (see below picture at below right).

Four (4) valves within the vault supply air to the other four (4) air stations. It is thought that conduit buried underground extends from the vault under the sidewalk to the lake through which five (5) aeration tubing lines emerge. A cap of cement that blends with the shoreline hardscape has been placed over the tubing lines as it emerges from under the sidewalk to improve aesthetics. Images are provided below of the vault next to the lake, the open vault and aeration cabinet, and open remote valve box. An aeration schematic for Vault 1 is provided.

Vault 1 next to lake Vault 1 open aeration cabinet Vault 1 – remote valve box

Vault 2 Aeration System

Vault 2 supplies air to eight (8) air stations through a remote valve box located between the shoreline walkway and the lake (see below picture at right for remote valve box).

Two (2) aeration tubing lines pass through probable conduit from the vault, then under the fence and walkway to the remote valve box containing the two (2) x four (4) valve manifolds. Images are provided below of the vault location in the common area outside the fence, the open vault and aeration cabinet, and open remote valve box. An aeration schematic for Vault 2 is provided.

Vault 2 in common area outside fence

Vault 2 open aeration

Vault 2 – Remote valve box

Vault 3 Aeration System

Vault 3 and vault 4 aeration systems are located adjacent to each other surrounded by rose bushes (see image below at left). Vault 3 is designed to supply air to eight (8) air stations though all air stations are not operational. Eight (8) aeration tubing lines are each connected to a valve inside the aeration vault which then passes under the sidewalk. This seems to be a hybrid system which connects air tubing lines to eight (8) galvanized pipes that pass under the sidewalk which then connects to aeration tubing lines that run to the air stations.

The galvanized pipe carries air and does not act as a conduit for tubing lines. A cap of cement that blends with the shoreline hardscape has been placed over the tubing line as it emerges from under the sidewalk to improve aesthetics. Air is escaping from either connections or from the galvanized pipe but due to limited space caused by the cement cap it is not possible to determine required repairs without breaking the cap.

To carry out a tubing replacement at this site will require a section of sidewalk to be removed and then repaired along with the cement cap.

Images are provided below of the vault location in the green space of the common area, the open vault and aeration cabinet, open aeration cabinet vault, and hoses emerging from shoreline under walkway. An aeration schematic for Vault 3 is provided.

Vaults 3 & 4 behind rose bushes Vault 3 aeration cabinet without grate and lid Vault 3 open aeration cabinet

Overhead view of Vaults 3 and 4 aeration tubing lines emerging from under walkway including cement cap

Lake level view of Vaults 3 and 4 aeration tubing line emerging from under walkway including cement cap

Vault 4 Aeration System

Vault 3 and vault 4 aeration system are located adjacent to each other surrounded by rose bushes. Vault 4 is designed to supply air to eight (8) air stations though all air stations are not operational. Eight (8) aeration tubing lines are each connected to a valve inside the aeration vault which then passes under the sidewalk. This seems to be a hybrid system which connects all eight (8) air tubing lines to eight (8) galvanized pipes to pass under the walkway which then connects to aeration tubing lines that run to the air stations. The galvanized pipe carries air and does not act as a conduit for tubing lines. A cap of cement that blends with the shoreline hardscape has been placed over the tubing line as it emerges from under the walkway to improve aesthetics. Air is escaping from either connections or from the galvanized pipe (s) but due to limited space caused by the cement cap it is not possible to determine required repairs without breaking the cap. To carry out a tubing line replacement at this site will require a section of sidewalk to be removed and then repaired along with the cement cap.

Images are provided below of the vault location in the greenspace of the common area, the open vault and aeration cabinet, open aeration cabinet vault, and hoses emerging from shoreline under walkway. An aeration schematic for Vault 4 is provided.

Vaults 3 & 4 behind rose bushes

Vault 4 aeration cabinet without grate and lid

Vault 4 open aeration

Overhead view of Vaults 3 and 4 aeration tubing line emerging from under sidewalk including cement cap

Lake level view of Vaults 3 and 4 aeration tubing line lines emerging from under sidewalk including cement cap

Vault 5 Aeration System

Vault 5 is located at the western side of the lake, opposite the beach and spillway, close to the lake edge in a common area. A cap of cement that blends with the shoreline hardscape has been placed over the tubing lines as they emerge from under the sidewalk to improve aesthetics. To carry out a tubing line replacement at this site will require removal and repair of the cement cap.

Images are provided below of the vault location in the greenspace in the common area, the open vault and aeration cabinet, open aeration cabinet vault and cabinet. An aeration schematic for Vault 5 is provided.

Vaults 5 next to lake

Vault 4 aeration cabinet without grate and lid

Vault 4 open aeration

Replacement Costs

Many components, such as aeration tubing lines, air stations, and various connections are at or beyond their useful life and must be replaced. Given that the aeration system is over 35 years old, there are components that require replacement.

The aeration tubing, for instance, typically has a warranty of 15 years, and air stations diffuser heads five (5) years. It is understood that equipment will last longer than warranty periods, but continuous use (24/7/365) and wear and tear can cause sub-optimal performance over the longer term. We have found that aeration tubing lines have become hard with age, especially lines that emerge from the lake edge, as are aeration tubing lines found below the water surface. It also appears that the current air stations contain one single diffuser disk on a PVC pipe base (see picture below at left) compared to more modern air stations with multiple diffuser disks that create larger water circulation (see image at bottom right). Air station configuration, style, and size is based on water depth to achieve optimal water circulation.

Two diffuser head air station example – for shallow water Lake Calabasas air station – single diffuser head

Please estimate for replacement cost for each vault with the same or similar equipment.

Bids should include costs for breaking concrete and concrete caps, concrete disposal, and replacing concrete and concrete caps, as well as cost associated with removal and disposal of aeration tubing lines, air stations, and other related debris. It should also be estimated where sidewalks need to be broken to access system components, how many days of inconvenience along the walkway would be required while replacement or repairs were made.