Odour Control - More than Sewage when Installing Cured-In-Place Sewer Pipe Liners

NASTT No-Dig, March 2004
By Gerry Bauer, P.Eng. & David McCartney, P.Eng, City of Ottawa

The City of Ottawa, Canada, is a major urban community of 785,000 people covering an area of 276,000 hectares (682,008 acres). Some infrastructure dates back to the 1800's, with city pipes reflecting the array of materials and installation methods that have come and gone over the past 100 years. Over this period, infrastructure has been installed to meet the demands of growing populations. All infrastructure deteriorates over time and eventually requires rehabilitation and/or replacement. As with most North American cities, the City of Ottawa must deal with deteriorating infrastructure and is proactive in conducting condition assessments and developing programs to ensure the infrastructure's life is maximized.

During an infrastructure needs assessment study on a large sanitary sewer collector, it was determined that parts of the sewer required rehabilitation. The sewer was located in an old residential area with narrow streets and numerous homes. Structural and hydraulic deficiencies existed throughout the sewer. The evaluation identified that the preferred solution was a combination of spot repairs and linings. Of the locations selected for lining, five sections were identified for a cured-in-place method. The contract was tendered and rehabilitation began. The procedure proposed by the successful contractor consisted of pulling the felt liner, impregnated with resin into the section to be lined and then using an inversion tube to expand the felt liner with water until the tube was tight against the host pipe. The liner was then to be cured to a solid state.

During lining of the initial sections, numerous complaints were received from the public regarding an unpleasant odour in their homes. The pipe being lined was a 165 m (541 feet) long, 1520 mm (60 inch) diameter concrete pipe with an inset brick invert, serving an area of about 800 hectares (1977 acres). The pipe was originally installed in the 1950's as a combined sewer with a total of about 50 services connected to it. The lining program was put on hold until the odour issue was resolved. Investigations revealed that the odour complaints occurred as a result of a resin compound identified as "Styrene".

During the investigation it was determined that many residences had faulty plumbing such as broken pipes, caps missing, no goosenecks, etc. Odour was able to travel into the residences and was subsequently detected by the public. The following figure illustrates the location of the lined sections in the discussion and the surrounding area.

Figure 1. Site Map (City of Ottawa - Cave Creek Collector Sewer)

The complaints initiated a series of public meetings where elected officials, senior municipal staff and consultant staff expended a considerable amount of time interacting, one on one, with residents to hear their concerns. Based on discussions with the public, the contractor, and investigations of the CIPP process, the installation program was revised to better control the odour. On the subsequent section linings no complaints were received regarding odour.

The installation process was modified whereas exhaust fans were installed in downstream access structures. The purpose of which was to develop a small negative pressure in the pipe and create a positive air flow from the building service to the main pipe (see figures 2 and 3 for typical exhaust fans used). In addition, flow through plugs were installed at the larger connections to prevent odour from entering adjacent sewers (see figure 4). Visual monitoring of the sewers was carried out at regular intervals to ensure that surcharging and other problems were not occurring.

Air testing was conducted in homes with known faulty plumbing; all results indicated styrene levels well less than recommended levels for a 15 minute interval. The highest level recorded in homes was 2.5 ppm which can easily be detected by humans. Figure 5 shows a typical air sampling instrument used to determine styrene levels. If necessary, fans of the type illustrated in Figure 6 were available to vent homes.

BACKGROUND - Styrene

It is estimated that about 95 percent of all CIPP liners being installed consist of polyester resins. These resins are comprised of about 45 to 48 percent, by weight, styrene with the rest being Alkyd. Styrene is considered a reactive diluent, a compound that lowers the viscosity of the base material. The base material is a solid at room temperature but when combined with styrene through a special manufacturing process the combined product, a polyester resin, is liquid at room temperature.

Use of styrene in CIPP liners provides the industry two main advantages. First from a chemical perspective, styrene makes the best polymer from a reactive point. This allows the installation of the liner to occur over a shorter period of time due to the reactivity of the products to cure (shorter curing time required). The second is cost. Styrene provides a more cost effective product to most other alternatives. Other products are available with different properties, costs and curing time.

Material Safety Data Sheets (MSDS) indicate a number of potential health effects to respiratory and other organs to the resin compounds over time. Styrene produces a pungent odour at only a few parts per million. Therefore, developing an effective odour management program during installation is a key to the overall success of a project using CIPP liners.

Various agencies have established threshold limit values such as Time Weighted Average (TWA) and Short-Term Exposure Limits (STEL) for styrene. The TWA is defined as the time weighted average concentration for a conventional 8-hour workday and 40 hour work week, to which nearly all workers may be repeatedly exposed, day after day, without adverse effect. The STEL is defined as the concentration to which workers can be exposed continuously for a short period of time without suffering from 1) irritation, 2) chronic or irreversible tissue damage, or 3) narcosis of sufficient degree to increase the likelihood of accidental injury, impair self-rescue or materially reduce work efficiency, and provided that the daily TWA is not exceeded. The STEL is defined as a 15 minute TWA exposure which should not be exceeded at any time during a workday even if the 8 hour TWA is within the TWA. For Styrene various agencies have identified limits, such as, the American Conference of Governmental Industrial Hygienists (2003) has set threshold limits for TWA at 20 ppm and for STEL at 40 ppm. In Canada the Ministry of Labour has listed the limits for TWA as 50 ppm and the STEL at 200 ppm.

Based on the experiences and knowledge gained from previous lining projects, a proactive program was recommended for implementation into a recent sewer lining program. A number of contractural requirements were established such as the preparation of an odour control program for implementation during the lining operation. The contractor was required to identify potential odour sources, proposed measures to be implemented, equipment to be used, and where it would be installed. A separate odour control strategy was required for each section to be lined that showed locations for venting, flow through plugs, or other equipment to be installed.

Establishing a program to handle odour during the installation was considered as only part of an overall strategy. As such, measuring the success of the program was considered as the second step. In order to determine the success of the odour control strategy, two mechanisms were used. First, an air monitoring program was carried out in conjunction with the installation of the lining and second, public complaints received and recorded.

Monitoring locations were determined in consultation with the testing agency. These were typically downstream of the lining installation as air movement and flows followed the downstream direction. Air monitoring was carried out using a Photoionization Air Monitor, PE Photovac Model 2020, as illustrated in Figure 5. For each section being lined the monitor was calibrated utilizing a two point calibration procedure, the low point being 0 ppm using medical air, and the high point using 101 ppm isobutylene. On occasion, the monitor was removed from the access structure to record street level values.

The following presents two case studies of lining sites.

CASE STUDY 1 Pinecrest Sewer PC04300 to PC04200

Figure 7 illustrates the general sewer configuration, surrounding area, monitoring location and venting location. The sewer was located in a busy commercial area on one side and an established residential area on the other. During the lining process the sewage was bypassed from just upstream of PC04400 shown on the drawing to PC04000 (gravity flow in the sewer follows the descending structure numbers). The sewer lined was a 762 mm (30 inch) diameter concrete sewer 77 m (253 feet) long with a cured-in-place (CIP) liner 29.5 mm (1.16 inches) thick. The CIP resin used was COR72-AA-451 which has the generic name Unsaturated Polyester Resin and shipping name Resin Solution (Styrene Monomer). The Technical Data sheet as supplied by the manufacturer describes COR72-AA-451 as thixotropic, rigid, corrosion resistant, unsaturated, polyester resin for use in the manufacture of liner pipe according to cured-in-place techniques.

The sewer was monitored for styrene levels by a qualified firm during the installation at structure PC04100. This was considered to be the best location for obtaining monitored results. A venting fan as illustrated in Figure 2 was installed at structure PC04100 to draw air out of the sewer.

Figure 7. Area Map, (City of Ottawa - Pinecrest Collector Sewer)

CASE STUDY 2 Stittsville Trunk ST03400 to ST03300

Figure 8 illustrates the general sewer configuration, surrounding area, monitoring location and venting location. Gravity flow in the sewer follows the descending structure numbers. The sewer lined was a 762 mm (30 inch) diameter concrete sewer 16 m (53 feet) long with a cured-in-place liner 34 mm (1.34 inches) thick. The CIP resin used was COR72-AA-451. During the lining sewage was bypassed from structure ST03500 to ST03100.

The venting fan was installed at structure ST03200. The sewer was monitored for styrene levels by a qualified firm during the installation of the liner at structure ST03200. In addition, a short duration test was carried out in the access structure located at the intersection of Carbury and Oakfern during the lining process to determine area styrene levels. Styrene levels were undetectable.

Figure 8. Area Map, (City of Ottawa - Stittsville Trunk Sewer)

The monitoring was carried out in order to assess the levels of styrene, how the levels varied over the installation period and whether or not the venting was effective.

CASE STUDY 1 Pinecrest Sewer PC04300 to PC04200

Figure 9 presents the styrene levels recorded during the installation of the liner in the Pinecrest Sewer.

Figure 9. Styrene Levels - Case Study 1

During the installation a number of key times/operations are of note. These are illustrated on Figure 9 with a corresponding number. The liner installation started late morning on November 1 but during the initial installation no monitoring or venting was occurring. This was the result of the following issues. First the monitors only have a limited battery life and the high styrene odour potential was believed to occur during the curing process. Thus the monitoring was started after installation to ensure this time would be captured. Secondly exact timing of the start of the installation and the length of time to install the liner could not be guaranteed due to many variables, and thirdly the availability of the monitoring staff could not be guaranteed. The inversion of the liner started at 1:15 pm.

• Point 1 on the graph - Monitoring started at 1:20 pm, during the first hour of monitoring levels in the sewer exceeded 100 ppm without venting.
• Point 2 on the graph - Inversion of the liner continued until 2:30 pm, the peak recorded level occurred about 3:00 pm and then started to fall, most likely due to reduced air movement with the liner completely blocking the pipe.
• Point 3 on the graph - Cooking of the liner started at 3:20 pm, the styrene levels started to climb and exceeded 60 ppm until the venting started.
• Point 4 on the graph - Fan started venting at structure PC04100 at 6:00 pm. The styrene levels were reduced to about 10 ppm during curing process with only minor fluctuations.
• Point 5 on the graph - Water in liner was heated from 3:20 pm to 10:43 pm where it reached a temperature of 80 ° c.
• Point 6 on the graph - Temperature was held at 80 ° c until 3:15 am on November 2.
• Point 7 on the graph - Cool down of liner started at 3:15 am and was complete at 6:10 am. During this time the styrene levels increased to about 40 ppm. This is most likely due to the water exchange and discharge occurring.
• Point 8 on the graph - At 8:10 am the liner in structure PC04200 was cut to allow the water to drain. The styrene levels increased to 60 ppm for about an hour then decrease to almost zero.
• At 11:30 am the liner was fully open in structure PC04200.
• Point 9 on the graph - At 11:35 am the fan was removed from structure PC04100. The styrene levels then rose to about 12 ppm for a short period of time and then decreased to almost zero.
• Point 10 on the graph - At 1:05 pm the liner in structure PC04300 was cut.
• At 3:50 pm the lined sewer was fully operational.
• At 4:00 pm monitoring stopped.

CASE 2 Stittsville Trunk ST03400 to ST03300

Figure 10 presents the styrene levels recorded during the installation of the liner in the Stittsville Trunk.

Figure 10. Styrene Levels - Case Study 2

During the installation a number of key times/operations are of note and are illustrated on Figure 10. Again monitoring of the styrene levels was set up after the start of the liner installation due to the reasons discussed in the previous case study. The liner installation started about 10:45 am on October 6.

• Point A on the graph - Monitoring started at 11:10 am, styrene levels continued to rise to over 17 ppm until the venting started.
• Point B on the graph - Fan started venting at structure ST03200 at 12:15 pm, at which time styrene levels gradually fell to about 1 ppm.
• Point C on the graph - Inversion was completed and heating started at 2:35 pm, the levels continued to drop to almost zero, most likely due to the liner blocking the entire sewer so that very little air movement downstream occurs.
• Point D on the graph - Between 3:00 pm and 3:40 pm monitor recorded street level concentration for verification. At 3:40 pm regular sewer monitoring resumed. Heating of liner continued with styrene levels increasing to almost 20 ppm at 4:00 pm - Point E on the Graph, then dropped quickly to about 1 ppm, then rebounded back to 13 ppm by 17:30. No explanation was established for this variation.
• Point F on the graph - At 6:00 pm water reached 80 ° c, after which styrene levels did not exceed 3 ppm.
• Point G on the graph - Temperature was held at 80 ° c until 11:00 pm.
• Cool down of liner started at 11:10 pm and was completed at 2:00 am on October 7.
• At 4:45 am (Point H on the graph) to 6:15 am liner in structure ST03300 was cut open.
• Between 6:50 am (Point I on the graph) and 7:15 am liner in structure ST03400 was cut open.
• Monitoring stopped at 9:30 am on October 7.

A total of four installations were monitored for styrene levels at a cost of $1100.00 each (all inclusive). This cost included equipment, staff, installation, removal, analysis, reporting and travel for a 24 hour period. During the initial monitoring, verification sampling was carried out as per the equipment requirements at a cost of $1200.00.

Rehabilitation of infrastructure has become an integral part of maintaining municipal assets, providing a cost effective solution to repair and extend their life expectancy in today's fiscal restraint. CIPP forms one of a number of important rehabilitations initiatives and will continue to do so. As with most trenchless technology methods, modifications will occur to improve it's performance and/or cost effectiveness.

The CIPP process used in the linings described in this paper used styrene as a major component in the resin. The odour produced during the lining installation was the result of varying levels of styrene. The monitored results indicate that precautions should be taken to protect the worker in all installations and where warranted, the public, typically in older areas with internal plumbing deficiencies.

The results indicate that styrene levels vary during the liner installation and with the amount of resin used. The liner installed on the Pinecrest Collector Sewer was four times longer than the liner installed on the Stittsville Trunk Sewer and resulted in much higher styrene levels. Venting is an effective method of reducing styrene levels but from the monitoring results, the venting should be in place and operational before the lining installation starts. Some of the highest levels recorded occurred during the initial stages of the installation.

Styrene levels will vary from site to site due to specific conditions. It is recommended that an investigation of the system be completed before installation in order to determine the potential for odour to enter buildings. If the potential exists, plan ahead by developing a flexible venting and monitoring program that can be changed quickly to react to changes as they occur. This can only be accomplished if proper investigations have occurred which produce accurate mapping of the sewer system. The monitoring program will identify levels of styrene in the system. This provides an effective tool to assist in addressing any queries by outside individuals and agencies, as well as for monitoring the levels of styrene staff may be subjected to.

In closing, the program developed as outlined in the case studies illustrates that a well prepared and implemented odour control strategy does reduce concentrations of styrene during the lining process.

• Agency for Toxic Sustances and Disease Registry - U.S. Department of Health and Human Services, CAS # 100-42-5.
• American Conference of Governmental Industrial Hygienists - 2003 TLVs and BEIs, Threshold Limit Values for Chemical Substances and Physical Agents, Biologicial Exposure Limits.
• Fraser, B. Jaques Whitford Limited, Personal discussions
• International Chemical Safety Cards, Styrene, ICSC: 0073
• Ministry of Labour - R.R.O. 1990 Reg 833, S.9(4)
• MSDS for COR72-AA-451
• Rahaim, K. Technical Representative, Interplastic Corporation
• Sewer Matic Drain Service, Personal discussions