Health Risks Assessment from Cured-in-Place Pipe Lining Fugitive Styrene Emissions in Laterals

A mock sewer network was designed and constructed to represent a sanitary sewer with lateral connections. This network consisted of a 200-mm clay pipe with 21 100-mm PVC laterals with P-traps at the end of each lateral. P-traps on Laterals 1 to 11 were water-filled, while P-traps on laterals 12 to 21 were dry (air filled). Fig. 1 shows the field study layout.

The sewer main was constructed using 22 clay pipe sections that were 200-mm in diameter and 910-mm long. The clay pipe sections were laid at 1% grade to represent a typical sewer with laterals. At the end of each pipe length, a $100\times 610\text{-}\mathrm{mm}$ long clay-T section was installed. The main sewer pipe was designed to be below the ground surface, so all laterals were fully buried.

Figs. 1 and 2 show that the laterals were spaced at an interval of 1.52 m along the main pipe and at an interval of 3.05 m on either side of the main. In a typical sewer network, laterals have only one lateral on a property and a spacing that is much greater than 1.52 m. Thus, this mock layout is not deemed to represent typical industry practice. The short spacing of laterals was used to validate styrene concentrations using different measurement methods and to assess measurement variability along the CIPP lined main. Each lateral was created by connecting a 1.52-m long and 100-mm diameter PVC pipe segment to the clay-T. Additional 100-mm diameter PVC pipe segments were added to create a lateral length of 10.06 m. This lateral length was deemed to be typical construction practice. PVC pipe risers of 100-mm diameter were added to create surface styrene and VOC sampling locations at 4.57 and 7.62 m from the clay main. These locations are labeled as A and B, respectively, in Fig. 2. At the end of each lateral, a 100-mm diameter PVC P-trap with a PVC riser was added. The P-trap riser is labeled C in Fig. 2. P-traps were labeled as PTW to indicate water-filled and PTD to indicate a dry P-trap. All PVC pipe sampling points were extended 906 mm above the ground surface and capped with removable PVC caps. OATEY Heavy Duty Clear Cement, purchased at a local hardware store, was used to glue all PVC joints.

For styrene emissions monitoring, two approaches were used: (1) onsite direct read PIDs; and (2) laboratory analysis of passive air samples collected using the 3M Organic Vapor Monitor (OVM) and the WMS.

Fig. 3 shows sampler locations during the CIPP installation and steam-curing. PIDs were placed in Laterals 4, 9, and 15, OVMs in Laterals 14, 18, and 19, and WMS in laterals 1, 2, 5, 6, 10, 11, 12, 13, 16, 17, 20, and 21.

Construction of the mock network occurred during the week of May 27, 2019, in an open field west of Cepi Drive in Chesterfield, Missouri, which is northeast of Aegion corporate head office (see Fig. 4). The CIPP liner was installed on June 5, 2019, and field site monitoring performed from June 4 to 6, 2019. Fig. 5 shows the CIPP installation and termination locations. The weather on June 5 was mostly cloudy with temperature low of 21°C and high of 32°C, and wind speeds that ranged from 14 to $42\mathrm{km}/\mathrm{h}$. Around 6:00 p.m., a thunderstorm occurred that had wind gusts as high as $46\mathrm{km}/\mathrm{h}$. The weather on June 6, 2019, was similar to that of June 5, but the wind speed ranged only from 0 to $11\mathrm{km}/\mathrm{h}$.

The CIPP liner was composed of a felt tube and polyester resin. The felt tube was constructed of two needled polyester fiber felt layers with a thin thermoplastic coating on the outside. Tube dimensions were 200-mm in diameter by a nominal 6-mm thickness, with a total length of 53.3 m. The tube was vacuum impregnated (wet-out) with resin in Indianapolis and shipped to Chesterfield in a refrigerated truck. The resin was a filled, isophthalic polyester resin specially formulated for use with CIPP. No excess resin was added to the tube.

The wet-out tube (liner) was installed by the inversion process using a flow-through air inversion device. Air pressure during the installation was held at or slightly above Insituform’s recommended installation pressure. Steam was used to cure the liner followed by a cool-down period. Liner pressure during cure was held at or slightly above recommended pressure, with the termination end interface and internal air/steam temperatures reaching 82°C and 115.5°C maximum, respectively. The cured liner (CIPP) was cooled to an external interface temperature of 37.2°C and the ends of the CIPP terminations were cut and trimmed. A blower was then installed at the liner installation end, to blow VOCs and styrene out of CIPP-lined pipe and the termination pit. Laterals 2, 6, 9, 11, 13, 17, 20, and 21 were robotically cut open within 60 min of cutting the liner open. During lateral opening, uncured resin was noted in laterals 6, 9, 11, and 17.

All laterals were numbered and labeled using the labeling scheme shown in Fig. 6.

In this study, Hoenywell MiniRae 30000 and ToxiRae Pro handheld PIDs were used to take measurements and record data. PIDs are industry recognized and established broadband sensors that respond to a large variety of VOCs. VOCs are measured with PIDs provided that the ionization potential of a compound is lower than the UV lamp energy. The VOC-measurable concentrations are typically in the range of 0.01–10,000, while being most accurate in the lower end of that range up to about 2,000 ppm (Rae 2013). The response time of PID instruments (typically a few to several seconds) is usually determined by the rate at which the sample is pumped across the photoionization chamber and out of the device. Isobutylene is commonly used to calibrate PIDs because its response factor is about the midpoint in the range of sensitivity of the PIDs. PIDs can also be calibrated using a specific gas, but this is rarely done. The Rae manual states, “The monitor should be calibrated every time it does not pass a bump test, but no less frequently than every six months, depending on use and exposure to gas and contamination, and its operational mode.” In this study, all PIDs were calibrated using isobutylene gas before use.

PID isobutylene VOC readings can be converted to another gas by multiplying the PID reading by the appropriate unit manufacturer-determined correction factor(s). According to Honeywell Technical Note TN-106 (Honeywell Technical Note 2016), all Rae PIDs with a 10.8-eV lamp have a styrene correction factor of 0.43. Thus, a PID VOC isobutylene reading of 100 ppm would have a styrene reading of 43 ppm (100 ppm * 0.43) if calibrated using styrene gas. Rae (2013) provides guidance on the PID readings when the gas being measured contains several different gases.

Sendesi et al. (2017) reported that, during the CIPP lining process, VOC emissions can contain approximately 30% to 50% styrene, with equal parts heptane and ether. Using correction factors of 0.43 for styrene, 4.3 for heptane, and 1.0 for ether, a PID VOC isobutylene reading of 100 ppm would correspond to an actual styrene reading of only 25 to 33 ppm. In this study, the actual composition of VOC chemicals released during the CIPP installation and steam cure was not known. Thus, for this study, a conservative correction factor of 0.43 was applied to the PID VOC isobutylene readings to estimate the maximum possible styrene concentration in the air emissions.

PID readings were obtained continuously before, during, and after the CIPP liner was installed and steam-cured. Each PID was connected to a Teflon tube that had a filter placed near the bottom of a lateral riser. All lateral risers were capped and sealed to ensure that no air flowed up the riser during the PID monitoring process.

Here, we will only discuss the WMS measurement method and results. No OVM results will be presented.

The WMS is a patented permeation passive sampler developed at the University of Waterloo and commercially available from SiREM (Guelph, ON, Canada). Fig. 7 shows the WMS components.

Unlike all other sorbent samplers on the market, the WMS has a well-defined uptake rate that is not sensitive to the presence of water vapor. The sampler is activated by removing it from the packaging vial and exposing it upside-down to allow the sorbent to meet the polydimethylsiloxane (PDMS) membrane. After a defined period, the sampler is moved into a sealed glass vial and then packaged in a sealed foil packet containing activated carbon adsorbent to prevent cross-contamination. Standardized procedures are developed to desorb the contaminants for gas chromatographic (GC) analysis, which can be completed by any standard laboratory. The WMS provides time-weighted average (TWA) concentrations of all chemicals adsorbed during the exposure time. By capping the WMS at different time intervals (i.e., 1, 2, 6, 8 h, etc.), the public and worker styrene air concentration, in $\mathrm{mg}/{\mathrm{m}}^3$, can be determined using the following equation:

The WMS styrene air concentrations can be converted to ppm using the following equation:where 104.15 = styrene molar mass ($\mathrm{g}/\mathrm{mole}$); and 24.45 = molar gas volume ($\mathrm{L}/\mathrm{mole}$) for an air fraction at 25°C. Salim et al. (2017, 2019a, b) and Salim and Górecki (2019) provided details on the dynamic process of sampling using permeation passive samplers that utilize adsorbents as receiving phases and validate the sampler using test data and a mathematical model.

The WMS was calibrated and validated by exposing it to known concentrations of styrene for specific periods under controlled laboratory conditions. This calibration was performed at temperatures between 60°C and 78°C, which was the estimated lateral temperature range during the CIPP lining cure process. This calibration determined a constant styrene uptake rate of 2.9 $\mathrm{mL}/\min$.

PIDs were installed within the laterals, before the installation of the CIPP liner on June 5, 2019, so that background VOC and styrene levels could be determined. WMS were installed 24 h before the lining started. All WMS, along with a series of control blanks, were shipped back to the University of Waterloo for styrene analysis. WMS background and control blanks revealed less than 0.05 ppm of styrene.

PID VOC readings obtained on June 5, 2019, before the CIPP liner installation, are shown in Fig. 8. This figure also shows the OSHA limit of 200 ppm, along with AEGL-1 20-ppm and AEGL-2 160-ppm exposure limits. In Fig. 8, time zero is the time when the CIPP liner was installed. PIDs located at risers 15A and 15C recorded background VOC readings as high as 162 and 34.8 ppm, while PIDs at risers 9A and P-trap 15-PTD recorded VOC readings as high as 16 ppm. The PID readings at P-trap 9-PTW were less than 2 ppm. If a PID styrene correction factor of 0.43 is applied to the PID VOC readings, styrene emission at the PID locations would be as high as 70 and 18 ppm at 15A and 15C respectively, 8.6 ppm at 15-PTD and 9A, and less than 1 ppm at 9-PTW. The styrene emission of 70 ppm exceeds AEGL-1 exposure limit of 20 ppm, but is lower than the AEGL-2 exposure limit of 160 ppm. All other PID styrene readings were below the AEGL-1 limit.

Because the WMSs recorded no styrene in the laterals, the PID background VOC readings were deemed to be from the glue used to join the PVC pipes, not from styrene in the laterals. This demonstrates the challenge in using PIDs to determine the styrene concentration at a CIPP site, especially where PID readings vary significantly at the construction site and the composition of the emissions is not known. It should be noted that the previous CIPP emission studies (Sendesi et al. 2017, 2020; Ra et al. 2019; Mathews 2020) report PID signal readings only and provide little information with respect to the PID gas calibration or correction factors used to determine the styrene concentration. This is despite the warning to use the appropriate PID styrene correction factor noted in the 2017 California Public Health CIPP Safety Bulletin (CDPH 2017). Thus, these studies could significantly overestimate the actual site styrene concentrations. These studies also do not discuss or report background PID readings prior to the installation of the CIPP liner. The large variation in the PID instruments background VOC readings demonstrate the difficulty in using PIDs to determine gas specific (i.e., styrene) concentrations accurately and confidently at a CIPP manufacturing site.

A PID and a WMS were installed in the CIPP termination pit to determine VOC and styrene concentrations during the CIPP liner curing and cool-down process. Fig. 9 shows the PID styrene estimated instantaneous air concentrations, in ppm, at 1-min intervals after the installation of the CIPP liner (time zero). It also contains styrene PID STEL and TWA values. PID styrene concentrations were determined using a PID correction factor of 0.43. This conversion factor assumes that all PID-measured VOCs are 100% styrene. Thus, this conversion factor was deemed to be the highest possible styrene concentration. Fig. 9 shows that PID styrene emissions at the termination pit increased quickly after the start of the liner steam cure, reached a maximum styrene concentration of 121 ppm in 3 min, and then decreased to less than 20 ppm after 9 min. The styrene levels then decreased to less than 2 ppm at 20 min. Thus, the PID data show that the CIPP styrene release occurred within 20 min and was below the AEGL-1 20-ppm limit after 9 min. The maximum styrene value of 121 ppm was lower than the OSHA limit of 200-ppm and AEGL-2 160-ppm exposure limit for a 10- to 30-min exposure.

Fig. 9 also shows that the 15-min STEL reached a maximum value of 30 ppm, then decreased rapidly to zero by 35 min. Fifteen min of PID readings are required to determine the first STEL value, and this is the reason for the shift of the STEL curve in Fig. 9. The 8-h TWA reading reached a maximum and constant value of 1.1 ppm at 20 min. The TWA value remained constant because no additional styrene was released from the CIPP liner. In this study, the maximum TWA value of 1.1 ppm was well below the OSHA 8-h styrene exposure limit of 100 ppm.

This study finding, that the termination pit styrene emissions were above the AEGL-1 20-ppm exposure limit, was consistent with other reported CIPP studies (Sendesi et al. 2017, 2020; Ra et al. 2019; Mathews 2020). However, the maximum styrene CIPP emissions in this study were found to be much lower than the above published studies and to only exceed the AEGL-1 values during the first 8 min of the CIPP liner steam cure.

The fugitive emission model assumes that the building has a basement with a well-mixed volume $V$, in which the air in the basement is replaced at a rate $f$. It is also assumed that the styrene vapor is present at concentration, $C_{\mathrm{lat}}$, in a lateral pipe of diameter $d$, and is transported by airflow of average velocity $v_{\mathrm{air}}$. Laterals are installed for the flow of wastewater from the building to the sewer main. This wastewater flow will result in airflow within the lateral to be away from the building (Lowe 2016). Airflow toward the building has also been observed due to intermittent pumping (Matos et al. 2019).

Evolution with time of the styrene concentration, $C$, must satisfy the following styrene balance:

If no styrene is initially present in the lateral, the styrene concentration in the basement, as a function of time ($t$), is given by

Eq. (4) can be used to plot the time evolution of the average styrene concentration in a basement at risk from fugitive emissions due to a dry P-trap. This analysis assumes continuous airflow within the lateral from sewer to basement, and that the lateral styrene concentration is continuous and constant. These assumptions are deemed not to be typical for a properly functioning lateral, as the airflow will normally be from the basement to the main, and the persistent source of styrene at a high concentration is very unlikely because styrene will only be released at the start of the CIPP liner cure. For these reasons, the predictions from Eq. (4) are deemed to represent the worst-case scenarios of a nonfunctioning (dry) P-trap.

For a house, an air exchange rate of $f=3$ to $4{\mathrm{h}}^{-1}$ is recommended, and it is recognized that the effective air exchange rate can be a factor of two lower because of deviation from perfect mixing (ANSI/ASHRAE 2019). Matos et al. (2019) measured the greatest lateral air average velocity to be $0.6\mathrm{m}/\mathrm{s}$. Thus, this is deemed to be an upper limit for airflow in a lateral.

Fig. 12 was generated using these values as a guideline, along with a 200-mm diameter lateral, and a house basement with volume $V=283{\mathrm{m}}^3$. Thus, Fig. 12 estimates the basement styrene concentrations that would be expected over time due to fugitive emissions from a dry P-trap, like that in Fig. 11(b), and under the very conservative assumption of continuous airflow from the main to the basement. Fig. 12 also contains the acute exposure guideline levels, as well as the EPA styrene odor threshold of 0.32 ppm.

Fig. 12 shows that poor ventilation ($f=0.1{\mathrm{h}}^{-1}$) and a constant CIPP styrene source of 1,000 ppm will cause the odor threshold to be exceeded in less than 2 min and that the AEGL-1 exposure limit of 20 ppm will be exceeded in approximately 20 min. With poor ventilation, the styrene concentration in the basement will increase to a maximum value of around 800 ppm in 2,000 min. This styrene maximum value exceeds the 10–30 min AEGL-2 exposure limit of 130 ppm and the OSHA limit of 200 ppm. Again, it is noted that this will only occur in a dry trap, with airflow from the main toward the building, and at constant styrene concentration of 1,000 ppm at the source. All of these conditions are deemed to be not typical.

Under the condition of a normal air exchange ($f=3{\mathrm{h}}^{-1}$) and a constant styrene concentration of 1,000 ppm, the maximum basement styrene concentration will be 20 ppm, which is the AEGL-1 exposure limit. This AEGL-1 exposure limit will be reached in approximately 50 min. With a normal air exchange rate and a constant styrene concentration below 1,000 ppm, the AEGL-1 exposure limit will not be exceeded.

The fugitive emissions model demonstrates that a normal air change rate, will reduce high lateral styrene emissions, to basement concentrations that are lower than the AEGL-1 exposure limit.

Fig. 9 shows the CIPP styrene release to be less than 30 min. If the styrene release is assumed to be 90 min, Fig. 12 shows that a building with poor ventilation and a constant styrene lateral source at 1,000 ppm will have a basement styrene concentration of approximately 100 ppm. This styrene air concentration is below the 130-ppm AEGL-2 10–30 min exposure limit.

Fig. 12 also shows that a basement with poor ventilation and a constant styrene lateral source at 500 ppm would exceed the 130-ppm AEGL-2 exposure limit in about 6 h. If the constant styrene source is reduced to 100 ppm, the basement styrene air concentration will be below the 130-ppm AEGL-2 limit. When the air exchange rate is at the recommended level of $3{\mathrm{h}}^{-1}$, both the 500- and 100-ppm constant lateral source will create a basement styrene concentration that is below the 20-ppm AEGL-1 exposure limit. These basement styrene air concentrations will be above the EPA odor threshold of 0.32 ppm. Fig. 12 shows that a basement with normal ventilation and a constant 100-ppm styrene lateral source will exceed the basement odor threshold in about 4 min. While the odor threshold will normally be exceeded, normal ventilation will result in basement styrene concentrations that are below the 20-ppm AEGL-1 exposure limit. The fugitive emission modeling also shows that a styrene exposure risk could arise in basements that have very poor ventilation, dry P-traps, and high lateral styrene concentrations that remain constant over an extended period. These conditions will not occur with a properly maintained and functioning P-trap that is water-filled.