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<p dir="ltr">The frequency and intensity of wildfires occurring at the wildland-urban interface is increasing, and public drinking water systems operating in these communities are at risk. Widespread volatile organic compound (VOC) and semi-VOC (SVOC) contaminations have been detected in water distribution systems, often at concentrations above regulatory limits. Uncertainty about the source and fate of these contaminants has hindered recovery efforts. It is hypothesized that one source of the contaminants is the thermal degradation of plastic components within water distribution systems. Plastics are commonly used for water conveyance due to their low cost and ease of installation. However, plastics are vulnerable to thermal degradation, and have been shown to release VOC/SVOCs into the air when thermally degraded. Further, certain plastics such as polyethylene, are vulnerable to organic compound permeation, which could result in the contamination of otherwise undamaged components. This dissertation is comprised of four studies aimed at evaluating if plastic components within water distribution systems may be a source of contamination post-wildfire.</p><p dir="ltr">First, the aqueous leaching from commercial drinking water pipes was evaluated following thermal degradation in air. In this work, eleven plastic drinking water pipes were exposed to elevated temperatures (200°C to 400°C), and subsequently submerged in water or in <i>n</i>-hexane to observe the extent of VOC leaching. Results indicated that thermally damaged drinking water pipes can be sources of VOC leaching, with ten of the eleven materials leaching benzene, a carcinogen, into water. As exposure temperature increased, there was an increase in VOC leaching from the polyethylene plastics. Conversely, in the vinyl plastics the significant mass loss associated with high exposure temperature was inversely proportional to the amount of leaching that was observed.</p><p dir="ltr">The second study determined how the direct contact of water during plastic thermal degradation impacts the formation and aqueous leaching. Experiments were carried out using a continuously stirred tank reactor (CSTR) to expose plastics to a range of temperature (100°C to 300°C) in the presence of water. Five polyethylene materials were tested, including three cross-linked polyethylene (PEX) pipes, one high-density polyethylene pipe (HDPE), and one HDPE resin. Following degradation, clean water was pumped through the reactor to evaluate the efficacy of flushing to remove contaminants from thermally damaged plastics. Again, material type and exposure temperature impacted the leaching profile. Flushing removed contaminants from the thermally damaged plastics, however the removal rate varied based on chemical properties. Exhumed materials from wildfire impacted water systems were extracted in water to assess similarities and leached up to twelve different compounds, seven of which were also detected in laboratory experiments.</p><p dir="ltr">The third study investigated the impact of polyethylene formulation on aqueous leaching following thermal degradation to further understand the underlaying phenomenon causing the formation and leaching of contaminants. The impact of resin density, antioxidant type (Irganox 1010^® or Irgafos 168^®), antioxidant dose (0 to 10 wt. %), and impact of carbon black (0 or 2 wt. %) was investigated by compounding 12 different composites and thermally degrading them in the CSTR reactor described previously. Results found that all variables tested impacted the observed leaching. The addition of antioxidants decreased the observed leaching of polyethylene degradation products but increased the leaching of a variety of antioxidant degradation products. Carbon black was found to interact with the antioxidants during compounding, leading their consumption, and as a result decreased their effectiveness in protecting the polymer chain.</p><p dir="ltr">Lastly, the susceptibility of plastic water supply connectors such as ice-maker lines, faucet connectors, and washing machines hoses was assessed. The vulnerability of rigid plastic materials within water systems has been well studied, however, water supply connectors tend to be made of flexible plastics such as plasticized PVC and low-density polyethylene, and limited data exists on the susceptibility of these materials to contamination. In this study, seven connectors were exposed to hydrocarbon contaminated water, and subsequently decontaminated by water flushing. Following an initial 24 h contamination period, water samples were collected at three consecutive periods of 72 h. Results found that all materials sorbed more than 90% hydrocarbon contaminants. All materials released contaminants into the water during decontamination, at times above health-based limits. The majority of sorbed mass remained in the plastics at the end of the decontamination periods.</p>

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The lifetime of plastic pipes for water supply and other applications is demanded to exceed at least 50 years. Such a long lifetime is difficult to prove by standard testing methods like the hydrostatic pres-sure test. However, it is possible to calculate an estimation of the lifetime, as the most frequently oc-curring mechanism of failure of plastic pipes is the creep crack propagation and subsequent failure. The method is based on describing the crack propagation by parameters of the linear-elastic fracture mechanics. An important part of this method is a finite element simulation of crack propagation in a pipe loaded by various types of loads. Residual stress, a side product of solidification after extrusion, is one of these loads. This thesis begins with an introductory part and literature review of the relevant topics – most of all the typical material properties of the pipe materials, mechanisms of failure, methods of residual stress determination suitable for plastic pipes and their results, methods of testing the materials and calculating lifetime. After the introduction, the problems to be solved are defined. The description of the residual stress state in the wall of various plastic pipes is the main topic. Both tangential (hoop) and axial residual stress in pipes of different dimensions and materials are determined using a combination of experiments and numerical simulations. Also, a simplified method of tangential residual stress is designed that can provide a sufficiently precise description of the tangential resid-ual stress state and is not difficult to carry out. A method to include the residual stress in the lifetime calculations and its influence on the lifetime is also dealt with. Apart from residual stress, the influence of soil loads in case of a buried pipe is studied. The residual stress can also influence the experimental determination of crack growth rate. If the CRB (cracked round bar) test is used to measure the crack growth rate, the crack can propagate asymmetrically due to the presence of residual stress in the specimens, which affects the results. Based on a finite element simulation of crack propagation in a CRB specimen, the severity of the influence is assessed.