Door No. 3: A Simple Common Sense Approach to Lateral Lining
Rehabilitating lateral services is quickly becoming a hot button issue for many municipalities and sewer system managers. Trying to reduce inflow and infiltration (I/I) and service problems while simultaneously avoiding the political, legal and financial pitfalls inherent to the sewer network that connects private property to the public system often leads to indecision or worse, inaction.
In this discussion, we will highlight the challenges contractors and municipalities face in lining laterals and offer a common sense solution that will aid in fulfilling the mandates of lateral lining while reducing the budget stresses often associated with such work.
Why Line Laterals?
As infrastructure grows to accommodate increasing population needs, a larger emphasis is being placed on our current trunk sewer system and its ability to meet the expected flows. Therefore, reducing I/I has become a primary focus of wastewater departments everywhere and lateral services are the next logical place to concentrate. As well as an important reduction in I/I, service interruptions in laterals can be more costly than mainline sewers due to their reduced size and fewer access points for trenchless equipment; so reducing the frequency and severity of service interruptions in lateral services is another reason why lateral lining is gaining in popularity.
The Legal Surveyed Property Line (LSPL) vs Operational Property Line (OPL)
O Property Line – Where Art Thou? In almost every tender regarding lateral lining in municipalities where there is a shared ownership between the public and private property owners, the legal wording having bearing on the lining mandate can be ambiguous and leave the municipality open to future liability. (see schematic diagram below) This ambiguity stems from the term “property line.” It may seem straightforward — but it’s not. It most cases, contracts for lining the public portion of the sewer say that it is the contractor’s responsibility to line to the property line. While the actual property line (LSPL) can be surveyed exactly aboveground, it is not easily transferred to what is in the ground. How does one stop or even know where the LSPL is within the lateral? In the absence of a cleanout, it simply cannot be done with any legal certainly. So, in many municipalities, the junction AREA where the public portion of the sewer meets the private portion of sewer is often considered the “defacto” (OPL) property line regardless of where that transition may be located above ground in relation to the actual LSPL.
The Truth about Lateral Lining
The very nature of lateral lining does not permit liners to stop on a dime or be precisely measured due to fabric stretch, bends and the wide variety of insitu pipe conditions. Thus, contractors are forced with choosing one of two available options, stop short by a margin (usually within 1 to 2 ft) or extend the liner past the desired end-point by a satisfactory amount (again 1 to 2 ft). Because most property line transitions (OPL) are accompanied by a 6- to 4-in. or 5- to 4-in. size transition, it is difficult to ensure the liner will properly invert through this transition and so it is generally accepted as a higher risk practice without the use or availability of an existing cleanout to monitor the inversion or allow for an access should the liner need to be touched up after curing.
Some contractors discourage the practice of installing cleanouts for precisely these reasons. If there is no cleanout, it is impossible for the municipality to determine whether the installed liner reaches the LSPL and therefore contractors will use the OPL as the property line and stop their liners short to avoid potential problems with inverting a liner through a transition while at the same time avoiding the costs associated with installing cleanouts.
The practice of stopping liners short of the OPL is widely accepted and we would argue does not go far enough to cover the public portion to reduce future liability if the transition piece (generally accepted as the public’s responsibility) is not addressed. For a municipality to meet its legal mandate it must ensure the contractor is lining to the LSPL and not stopping short. The only way this can be ensured is to make the installation of lateral cleanouts mandatory so the LSPL can be transferred to the sewer pipe below the ground.
Why Line The Transition?
A recurring problem area is the size transition/test tee, commonly found on or near the property line. There are multiple reasons why this section of pipe produces problems. As the town lays its public portion before individual builders lay their private portions, there is typically little to no quality control when the pipes are joined and extremely expensive to fix after the fact. Often there are two different materials of pipe being connected at this junction, and in many cases different sizes, as well. Typically, you find the public portion to be 6 in. transitioning into 4 in. As is well known, each separate connection point poses a possible threat where roots or water could potentially infiltrate and the nature of the size transition connection/test tee is a prime spot for this type of service issue or I/I. It is for these reasons, that the section of pipe usually found at or around the property line is very often the source of headaches for municipal owners due to the precarious location of said problems at the property line for reasons noted above.
Why Not Line the Whole Lateral?
Other municipalities have employed an all or nothing platform wherein liners extend all the way from the main sewer line to the building foundation. This method definitely ensures a reduction in I/I and service issues but how financially feasible is it to employ this program on a grand scale and how can managers handle the political pressures associated with providing this service to some property owners and not others?
In more than 20 years of inspecting and rehabilitating lateral services, D.M. Robichaud Associates Ltd. has encountered the gambit of lateral service problems. The public section of the sewer lateral is deeper near the main gradually sloping up as it reaches the property line. It is that difference in depth that typically results in a higher probability of groundwater infiltration on the public portion of the pipe due to the higher pressure of groundwater found there. Although each lateral service offers its own unique challenges, the most typical and numerous problems adding to water infiltration and service issues are found on the public portion or at the weak point on or near the property line.
In a perfect world with unlimited resources, lining all the way to the building foundation on every lateral would be ideal. However, budget limitations prevent municipalities from being able to broadly implement full lateral lining to the point of making a substantial enough impact to effectively reduce I/I. By carefully investigating via CCTV lateral inspections and identifying recurring problem areas and targeting those specific spots, municipalities can reduce I/I on a larger scale and see a bigger return on their investment. As an added bonus, the municipality avoids the legal and political issues that accompany installing public works infrastructure on private property by not extending the liner all the way to the building foundation.
Door No. 3 — The Common Sense Approach
In those few situations where trenchless technology cannot be utilized to fix problems at the transition/property line, open pit digging and replacement is the only option. When this occurs, municipalities and property owners alike agree that encroachment on to the private property is necessary to fix the problem and is accepted without recourse. The town pays for the burden of the repair and the property owner is secure and content knowing that the issue will be permanently repaired.
Why not apply this same necessary encroachment principle when thinking about trenchless repairs? By using a transition liner that extends through the transition and into the private portion of the pipe by a small amount, the encroachment is minimal, the cost is covered by the municipality, and the property owner does not have to sustain the various landscaping frustrations and costs associated with an open pit dig.
The financial benefits of the transition liner vs. full lateral lining for municipalities is overwhelming when you take into consideration the substantial return on investment accompanied with the ability to fix most of the I/I and service issues on a much larger scale. Effectively managers are able to double or triple the scope of areas designated for rehabilitation due to the reduced cost of the transition liner over traditional full-length lateral lining. In addition, the transition liner is designed to solve problems at the transition where other lining problems stop just short thereby leaving a weak point for infiltration exposed for future works. For the minimal extra cost of lining an extra few feet, municipalities are able to stop a major source of infiltration and service issues in one fell swoop.
The transition liner offers a simple, common sense approach to the issues surrounding rehabilitating lateral services. By fixing the most prevalent and numerous instances of I/I and service issues located on the public side and extending through the size transition/ test tee connection, municipalities can expect a more substantial reduction in I/I and service problems. In using the necessary encroachment line of reasoning (Door No. 3) for the transition liner trenchless repair, the various legal issues associated with encroachment on to private property and the need to perform a legal survey to locate the property line dissipate altogether.
And lastly, the minimal cost increase for the extra transition piece provides a bigger return on investment than other lateral lining programs currently being implemented or considered. Maintaining lateral infrastructure is an important part of reducing I/I and municipalities can no longer afford to be timid or indecisive about the methods for rehabilitating this vast sewer network.
Randy Kowal is an engineering technologist and vice president and Lisa Pike is a technology specialist of DM Robichaud Associates Ltd.
