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San Ysidro Family Housing

San Diego, California


San Ysidro CIC 


Hunsaker & Associates


Emmerson Construction, Inc. 


October 2018

Technical Description:

147' of 120" Aluminized Steel Type 2

With the rising cost of housing across California, it’s been a struggle for many families to find affordable housing, especially in Southern California. The San Ysidro Family Housing project is a low-income housing development of approximately 150 units in the city of San Diego. The project is considered infill development - developing vacant or under-used parcels within existing urban areas that are already largely developed. 

The consulting engineer initially specified a concrete vault for stormwater storage. During the late stages of the design, the contractor requested the engineering team to value engineer the system because it was too expensive. Using Contech’s Design Your Own Detention System online tool, Contech engineers were able to present a preliminary drawing and cost estimate of a corrugated metal pipe (CMP) solution to the engineer about a day after they requested it. The material and installation costs were half the cost of the concrete solution. 

There was some resistance from the City to allow the CMP solution. Cities in San Diego County have been replacing galvanized CMP culverts that have corroded due to corrosive soils and heavy abrasion. This has led to some resistance to use CMP in stormwater detention applications. Contech supported the engineer by providing documentation showing how the Aluminized CMP (also known as ALT2) met the minimum required lifespan. Aluminized CMP is very different from galvanized CMP and it has a much longer lifespan. Aluminized CMP is fabricated from steel that has been hot-dipped in commercially pure aluminum. Also, detention systems are not subject to the same abrasion levels as culverts. The National Corrugated Steel Pipe Association (NCSPA) provides a service life guidance for CMP of 75+ years for certain materials in recommended environments. Contech provided supporting documentation to address the service life issue, and the CMP solution was approved.

The system is made from 147' of 120” diameter, 12 gauge, aluminized, perforated corrugated metal pipe with a 30” internal flow control riser. The system provides 15,067 cf of storage, 11,545 cf of storage from the pipe, and 3,522 cf of storage from the stone backfill. The 120” CMP was used because it maximized storage volume. All of the stormwater drained to the back corner of the property away from where the utility hook-ups were. An easement was needed to run sewer, stormwater, and fire hydrant lines under the parking lot of the adjacent property.

Contech engineers provided drawings and a cost estimate and also provided guidance and language to help gain approval from the City of San Diego to allow the CMP solution.  Proposal drawings, including detailed drawings of the internal flow control tee, were also provided. The engineer and contractor were happy with the savings Contech provided with the CMP solution, as well as the quick turn-around times and assistance in getting the system approved by the City of San Diego.

Technical Description:

147' of 120" Aluminized Steel Type 2

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