Barron Park Wastewater (Sanitary) Sewer Replacement, 2009

By Doug Moran

Notes from meeting with City Utilities staff on this project (April 2009) augmented with additional information.

Simple questions

Why not replace just the worse lines, especially on streets that are still in decent shape? It is much cheaper to do the work in one area all at the same time, rather than bounce from one problem area to another. Expected life of sewer lines is 50 years.

When will the rest of Barron Park have this work done? As soon as the current project is done, they will (budget permitting) move on to the section roughly between La Para and Maybell (I haven't seen the map). The City's projections were for a start in late Fall or early Winter, but the contractor is moving well ahead of schedule.

When will they repave the streets? Repaving/rebuilding streets is the responsibility of the Public Works Department (The Utilities Department has funding separate from the rest of the City Departments). Public Works is well aware of this project (I personally confirmed this) and has plans to do street repairs, although I couldn't get details (which streets, much less when). The basic process is that the Utilities' contractor puts in a temporary (cold) patch, and then after the backfill has had a chance to settle, they come back and do a more permanent (hot) patch. Whether or not a more substantial resurfacing occurs depends on the condition of the street and a variety of other factors that Public Works uses to prioritize repairs.

Why isn't Utilities work better coordinated with street repaving? The current policy of Public Works and Utilities is to try to avoid any major work on a street for 5 years after resurfacing/repaving. There seems to be better coordination than in the past (when there was none): When I talked to Utilities staff about this project, they were already aware of the ages of the streets.

Is the work schedule coordinated with the school schedule? The route from across El Camino--along Matadero to Josina and then to BP Elementary--as well as Barron Avenue itself are part of this project. I alerted Utilities staff to this problem and they were going to make sure the contractor was aware of this. However, there may be some time when students need to detour around the Matadero/Josina segment, using Kendall to get to Barron.

Main Pipe Replacement Detail

Rather than trenching the length of the street and pulling out the old pipe, the technique being used is pipe-bursting (you may be able to get more info via a web search). Briefly, a device, called a pig, is inserted into the existing pipe and pulled slowly down its length. As the pig moves, it pulverizes the existing clay pipe with pneumatic "hammers" in its sides (this is the incessant pounding that you hear). The replacement pipe is modestly flexible plastic (high density polyethylene) and is attached to the back of the pig, so that, as the old pipe is pulverized, the new pipe is immediately slid into place.

Most of the main sewer lines in Barron Park have a 6-inch diameter, and current standard is 8-inches. So as the pig moves down the existing sewer line, it is not only pulverizing the existing pipe but compressing the surrounding soil to allow the larger pipe to slide in.

The work is done in segments between the manhole covers (actually the utility vaults under those covers).

An alternative to this approach would be to install a liner in the existing pipe. However, because many of the existing pipes are in such poor condition, it would provide much less bang-for-the-buck in terms of extending the life of the current pipes. The pipes being inserted has a rated lifetime of 100 years, but the City's current assumptions (for budget) are "only" 50 years.

Disruption of Sewer Service

For people not living on the segment being replaced, there is no disruption: Sewage can be pumped around that segment using a hose running down the street.

For people living on the segment, you need to minimize what you put down the drains. Especially avoiding using your washing machine. The critical portions of replacing a segment takes about 2 days, about a half day to replace the main pipe and the remainder to attach all the lines—the "laterals"—from houses in that segment. Until your lateral is connected to the new pipe, anything you put down the drain either stays in the lateral or leaks into the ground. For most circumstances, this presents no problem. Part of the reason for this delay is that the pipe may have stretched while being pulled and needs a little time to "relax". This movement could break the joint to the lateral if it was done too soon.

Disruption of Water and Gas Service

There is no need for the City to turn off water or gas service. However, if a water or gas line to a residence passes too close to the sewer line, dragging the new pipe into place could also drag one of those lines, breaking it. The City Utilities is aware of such possibilities and monitors for it. If there is a break, the City will shut off that service until it can repair that line.

Construction standards call for the various lines to be spaced far enough apart, both horizontally and vertically, so that this should not happen. However, in Barron Park, there are many non-standard items, from before we became part of Palo Alto.

Lateral Pipe Replacement

The laterals are the pipes connecting your house to the main sewer line. The City has responsibility--for both maintenance and cleaning--for the section up to your property line, you are responsible for the line from there to your house.

The City Utilities is replacing all the laterals as part of this project because it is much cheaper to replace them in a batch rather than piecemeal: The equipment is already on-site and set up. Plus the laterals won't need maintenance or replacement for 50 to 100 years, eliminating the need to cut through and then patch the street. Also, be aware that many of the laterals are as old as the main pipe and have deteriorated badly and would likely need replacing soon (next decade or so, which is "soon" in terms of these projects).

For the laterals, they will use a lesser pipe-bursting technique. Because the replacement line is smaller and runs only a short distance, the "pig" used does not have air-hammers, but bursts the pipes simply with the force it exerts while being pulled through the existing pipe.

Important: Many houses in Barron Park do not have clean-outs at the property line. In this case, the replacement of the lateral will include installing a clean-out at the property line. This allows the City to clean-out their portion of the line without the hassle and delay of contact the resident to get permission.

The new clean-out include a pressure relief feature (a rubber plug that can pop out) to reduce the chance of a backup on the main line from coming into your house. There were episodes of "exploding toilets" that occurred on Chimalus when the City Utilities was trying to clear a clogged line. Note that this is a simple friction fit, not a more sophisticated (and expense) valve.
Aside: If you have a clean-out near your house, it may also good to have a pressure-relief feature there—rubber caps are the simplest— especially if there is a nearby tree whose roots have penetrated the pipe.

Driveway Access

Project work is roughly 8am to 4pm. If you are likely to need to go out during the time your segment is being worked on, I would strongly encourage you to park your car outside of the work area. You might want to leave a note on the dashboard with contact information (in case there is a problem). People who have extra space in driveways just outside the project area might want to offer it to those affected.

The contractor is required to provide access to your driveway during the project. However, when work is being done on your segment, getting in and out can require a major disruption and corresponding delay. This is worse when the main line is being replaced (first day) and not that much of a problem during the remainder (when laterals are being replaced). Those near a manhole will experience the most serious difficulties: The hole is quite large and there need to be several trucks parked near it. And they will be obstructed when the pipe is being pulled down into the hole and then again when the pipe is being pulled toward that hole.

People on one side of the street in the segment just up from the segment where the pipe is being pulled will also be obstructed. The pipe is continuous and needs to be laid out on one side of the street. Naturally, the number of driveways affected decreases as the day progresses. They seem to aim to having the replacement done by about 2pm.


This work is being done as part of the City's Master Plan for Sewer Capacity established in 1988 (yes, 20 years ago). This work got way behind schedule because the City decided to defer maintenance on infrastructure (in 2000, former City Manager Frank Benest was brought in to address these problems). In 2006, the City Utilities assessed the condition of all 200 miles of waste-water sewers using video (rather than extrapolating from repair and maintenance records). The Chimalus line was in desperate need of replacement, with Matadero not far behind. But many of the sewer lines in Barron Park were also over the threshold of needing replacement.

Additional Resources

City's web pages overviewing such projects: