Whenever a sewer rehabilitation project is undertaken, the primary consideration is usually the cost factor. There are two options available for undertaking a repair and rehabilitation project: open trenching and trenchless rehabilitation. Undertaking a sewer system evaluation survey (SSES) will give an idea of the initial cost of construction and benefits that each method provides. The method that projects the lowest cost with the greatest benefits is preferably selected unless site conditions call for the other alternative.
The cost also varies based on where the rehabilitation is undertaken. Highly populated areas and urban cities will have a higher project cost than that in a rural area or for individual homes. However, small jobs, as those required for homes, will have a higher cost per linear foot compared to those undertaken for municipalities because of the scale of the project. Populated cities also have to bear the socio-economic cost at a higher rate than that required for rural areas, especially when the open trenching method is used.
Costs Associated with Sewer Repair
Urban cities have more population per square foot when compared to rural cities. This means that the cost per square foot for conveniences and infrastructure is also higher. The cost factor comprises three categories, namely: direct, indirect and social inconvenience costs. Often municipalities base their estimate only on the direct cost component. However, it is necessary for municipalities to base their cost considerations on all factors affecting everyone involved directly and indirectly in the project.
This is paid by the municipality and includes planning and bidding costs, contractor cost and project management and consultant cost.
This is also borne by the municipality and includes compensation for customer claims and damage to property such as roads and driveways.
Social Inconvenience Cost
This cost is borne by the public and is a result of the execution of a project. It is estimated to be twice the sum of the direct and indirect cost that the municipality pays. These costs include traffic delay, business loss, vehicle operating cost and accident costs, damage caused to vehicles due to uneven road surface, damage to the environment and pollution arising from dust and noise.
Open Trenching or Trenchless
About 70 percent of the cost associated with open cut replacement is taken up by excavation and replacement of the dug-up ground. Trenchless technology compared to open cut in populated areas and urban cities is definitely a better option because cost of rehabilitation is higher per foot, especially with greater depths requiring shoring and extensive excavation resources. (For another comparison, see The Essential Pros and Cons of Trenchless Sewer Rehabilitation.)
Cost for Trenchless Repair
For undertaking a trenchless cured-in-place pipe (CIPP) replacement approach for repairing city sewers, the average cost will range from $80 to $100 per linear foot (LF) compared to $100 to $150 per LF for the open cut method. Trenchless methods can reduce costs by 50 to 75 percent when compared with open cut methods and reduce rehabilitation time by 60 percent. Trenchless methods also significantly reduce – and sometimes eliminate – the social inconvenience cost related to the project.
Rehabilitation Cost in Suburban Towns
For a relining project of 10,000 feet or more in a typical suburban town, and depending on the condition of the sewer pipe and pipe diameter, an estimated cost of pipe rehabilitation can be made at $25 per foot. For coating a manhole 4 feet in diameter with a depth of 4 feet is $1,500 and a depth of 6 feet is $2,500. Sealing lateral connections at a main will cost about $1,400. Sealing laterals from a main sewer to a home will cost about $2,000.
A suburban town of approximately 20,000 people may have about 500,000 feet of main sanitary sewers. For 1,000 feet of main sewer, there may be 10 to 20 services and 4 manholes. On an average, 2 manholes and 3 to 5 services may need sealing and lining, giving an average cost of $35 per foot. (For more on trenchless construction in suburban areas, see 4 Common Reasons for Trenchless Construction and Rehabilitation In Your Neighborhood.)
Cost of Trenchless Repair for Homeowners
When it comes to rehabilitating pipes at home, the cost per linear foot may be more than that for a large scale municipality repair, since repairing longer stretches at once is always cheaper. Since the open cut method requires excavating a long and deep trench to dig up and replace old pipes, the cost can vary from $50 to $250 per foot depending on the depth of the existing pipe and the length of installation, ease of access and the current rates in the locality. An average sewer line from a house to the public sewer system may cost anywhere from $3,000 to $6,000, and if the main sewer happens to be in the middle of the road, the cost can jump up to $25,000 or more in some cases.
The trenchless method requires minimal digging by using methods such as pipe bursting, CIPP and sliplining. The cost can vary from $60 to $200 per foot or $3,000 to $20,000 for an average sewer pipe running from the home to the main sewer.
Cost Saving with Trenchless Technology
Below is a table of comparison for pipe replacement in a city per linear meter using open cut and trenchless methods:
|Pipe size (mm)||Open trench ($/LM)||Trenchless ($/LM)||Average Trenchless ($/LM)||% Savings|
* The above cost estimates are approximate and do not indicate the final price.
It is clear that trenchless technology offers cost-effective alternative for rehabilitating buried sewer infrastructure. There is an estimated 20 percent reduction in direct and indirect costs when appropriate trenchless methods specific to prevalent site conditions are used in place of open trenching.
A study was carried out in 2007 by Jung and Sinha considering 8 sewer renewal projects for open trench and trenchless pipe bursting. The traffic delay costs for a renewal project for buried pipe in a high-traffic-volume area over a 55-day period was about 80 times the direct cost when open trench construction was used. The same project was 10 times the direct cost when pipe bursting trenchless repair was used. Another study estimated that it was possible to achieve 300 percent reduction in traffic delay costs and greenhouse gas emissions when trenchless methods were used. Considering the value of time, significant reduction in social inconvenience cost and overall cost when trenchless rehabilitation techniques are used, the scale tips in favor of trenchless technology in nearly every case.