Environmental impact of cured-in-place pipe renewal on an asbestos cement water main

Asbestos cement (AC) pipe accounts for approximately 15% of the total length of pipe networks for water distribution systems in North America (US Environmental Protection Agency (USEPA) 2007). Renewal activities are needed to maintain these pipes as they deteriorate, however, concerns over the environmental impact of AC pipe renewal technologies and the associated regulations are an area of confusion for water utility managers (Griffin 2009).

The Water Research Foundation (WRF) commissioned project #4093, Long-Term Performance of AC Pipe, which included a study of renewal approaches (Hu et al. 2013). This study identified a need for environmental assessments of various renewal approaches. After the project, the industry was still struggling with regulations and practices for renewing AC pipes, and required help establishing reasonable regulations based on actual data (Salvo et al. 2012).

The concerns are primarily related to the release of asbestos fibers in the debris or at the site created from the renewal process. This led WRF to commission a second project to examine the concerns associated with the current renewal practices. The first phase of the project examined the kinds of renewal practices that are commonly allowed and the data required to determine the safety of a renewal practice (Matthews & Stowe 2015).

Subsequently, the second phase of the project focused on demonstrating and evaluating two renewal methods (namely, pipe bursting and cured-in-place pipe (CIPP)). The observations from the CIPP renewal project are laid out in the following sections. The CIPP technique was applied to a 940-m (3,100-ft) section of a 50-year-old 400-mm (16-in) AC water main. In order to evaluate the impact to the environment, air, soil, and water, samples were collected from the site during and after the CIPP demonstration and were analyzed by a certified laboratory for asbestos fiber content.

A glass-fiber reinforced CIPP liner product designed for use on pressurized water mains was chosen by the utility for the renewal of the 400-mm (16-in) AC water main. The liner is an American Water Works Association (AWWA) Class IV fully structural liner (AWWA 2014) that is National Sanitation Foundation 61 approved for potable water systems. The liner can be manufactured in lengths up to 300-m (1,000-ft) and can be applied to pipes ranging from 150 to 1,200-mm (6–48-in) in diameter. In the lining process, the glass-fiber reinforced liner is installed by inverting it through the host pipe and expanding it in place with the aid of pressurized air and steam. The internal pressure ensures the liner is pressed against the host pipe, and the steam cures the liner that is impregnated with thermosetting epoxy resin. The thickness of the liner ranges from 5.5 to 20-mm (0.22–0.79-in) based upon the number of felt and glass-fiber reinforcement layers, and the needed design strength. The design strength is calculated such that the pipe liner has self-supporting properties and is able to withstand all internal and external loads independent of the host pipe (i.e. AWWA Class IV). The liner design selected for this project consisted of two layers of glass-fiber reinforcement and one layer of felt. The final installed thickness of the liner was 7.3-mm (0.29-in) with a nominal operating pressure rating of 1.31 MPa (190 psi).

To gain access to the main, 20 pits were excavated. A 250-mm (10-in), high-density polyethylene (HDPE) bypass was installed that had 31 service connections and 14 fire hydrant connections. Following the installation of the bypass, the host pipe was drained and the sections of pipe exposed in the pits were removed using a wet-cutting technique to prevent the release of asbestos fibers.

To begin installation, the pressure vessel was filled with air to maintain a pressure of 69 kPa (10 psi), which led the liner to invert through the opening. The liner exposed the impregnated resin to make contact with the internal host pipe wall. The inverting rate of the liner was regulated using a rope connected to the spool. Regulating the speed of liner travel helps to preventing unnecessary liner stretching. The liner was fully inserted once a nylon rope is exposed at the exiting end (Station B) of the host pipe.

Following the installation of the end seals, each lined section of pipe was pressure tested to ensure that no leaks were present in the liner or seals. Water from a tanker truck was pumped into each segment at approximately 350 kPa (50 psi). An electric pump connected to the pipe supplied the deficient water to bring the pressure to 1 MPa (150 psi). Then the electric pump was turned off and the pressure was monitored for 1 hour. If no loss in pressure was observed after 1 hour, the liner was deemed leak free.

A major focus of this demonstration project was to evaluate the environmental impact the project had on the air, soil, and water, where possible. The following subsections describe the sampling and testing results for the air, soil, and water.

Nine air samples were collected on three separate days, including three field blanks, by placing air pumps on workers inside and around the access pit locations for 4-hour periods during CIPP lining preparation and lining activities. This is the only area where the AC pipe was exposed and therefore the only reasonable place where asbestos may be measured in the air. Due to an inadequate volume of air sampled on the first day, only six samples, including two field blanks, were analyzed. Air samples were collected using a personal air sampling pump with an approximate flow rate of 2 liters per minute (LPM). The pumps were calibrated in the field prior to sample collection using a flow calibrator. Table 1 summarizes the readings of air samples collected.

The air samples were analyzed using transmission electron microscopy (TEM) following the International Organization for Standardization (ISO) method 10312 (1995). As shown in the air sample analyses (Table 2), the asbestos concentration of all but one sample (i.e. Sample 5) was below the analytical sensitivity for the 8-hr time-weighted average (TWA)-permissible exposure limit (PEL) of 0.1 s/cc set by the Occupation Safety and Health Administration (OSHA). The asbestos concentration of sample 5 (i.e. 0.0048 s/cc) was measurable, but also below the OSHA TWA-PEL.

The air sample results are representative of all activities that occurred on site on the specific day of sampling, except for pit excavation and removal of AC pipe sections. While air samples during cutting of the AC were not collected, this is not expected to cause a negative impact when proper wet cutting practices are used, as were in this case (Matthews et al. 2015). Wet cutting is an AWWA- and OSHA-approved practice for working with AC pipe. The air samples were collected on the surface at the edge of the pits, due to space restrictions and worker safety air sampling personnel were not allowed inside the pit. During the lining operation, the air sampling personnel traveled between the insertion pit (Station A) and the end pit (Station B) in an attempt to collect representative samples. These results are comparable with another air sampling study conducted on an AC pipe renewal project (Jonsson 2011), which also used wet cutting.

Six pre-lining soil samples were collected from three different excavation pits over 2 days. Each soil sample was collected from the pit walls at two locations around the host pipe (i.e. one near the pipe crown and one near to the pavement surface). Post-renewal soil samples could not be collected due to the paving of access pits after lining, but a change in the soil asbestos content would not be expected since the host pipe is not disturbed during lining. Samples were analyzed using polarized light microscopy in accordance with USEPA Method 600/R-93/116 (USEPA 1993). Samples 1, 2, and 3 also underwent a 400-point count (soil sample analyses in Table 3).

No asbestos was detected in soil samples 4, 5, and 6. Samples 1, 2, and 3 each contained trace amounts of Chrysotile and the point count further narrowed the trace amount of Chrysotile as being less than 0.25% visual estimate. The results essentially suggest that asbestos has not leached from the pipe to the surrounding soil since its installation nearly 50 years ago. These results are comparable with the soil sampling from the other demonstration site that used the pipe bursting method (Matthews et al. 2015).

Baseline water samples were collected from services immediately downstream of the lining operation also connected to AC mains. Both samples were collected from backflow preventers located above ground in 1-liter HDPE bottles. The samples were analyzed using TEM following USEPA method 100.2 (USEPA 1994) and the results are presented in Table 4. Both samples were found to be non-detected (i.e. asbestos concentration was below analytical sensitivity of 0.03 million structures per liter). The USEPA maximum contaminate level for asbestos in drinking water is 7 million structures per liter.

Following the completion of the lining project and reinstatement of the main, two additional water samples were collected from the sample locations (Table 5). Both post-renewal water samples were also found to be non-detected. These results are comparable with the water sampling from the other demonstration site that used the pipe bursting method (Matthews et al. 2015).

This project resulted in the successful installation and evaluation of a glass fiber reinforced CIPP liner used to rehabilitate a 50-year-old AC transmission main. From the air, soil, and water sampling and test results, it may be concluded that no negative impacts to the environment were observed that could be directly attributed to the lining technology. The air and water sampling and testing showed no negative impact on the surrounding environment. The soil sampling and testing indicated only trace amounts of asbestos in the soil surrounding the pipe, with no increase in asbestos following the completion of the renewal activities.

It should be noted that this is the only known CIPP lining project of an AC pipe where environmental impact data has been collected and published. While that means this is a unique project, it also is a limitation of the study and the authors recommend similar data be collected on future AC CIPP projects. It should also be noted that data from multiple pipe bursting projects (e.g. a technology that is expected to be more disruptive than CIPP) has been collected and show no negative impacts (Matthews et al. 2015). It is recommended that more environmental impact studies be conducted to validate these two results.

This research was carried out in part with support from the Water Research Foundation (WRF) Project No. 4465, which was co-funded through the Innovation and Research for Water Infrastructure for the 21st Century US Environmental Protection Agency (USEPA) research program.