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PPI TR-53

Life Cycle Assessment of North American Stormwater Pipe Systems

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Organization: PPI
Publication Date: 1 January 2021
Status: active
Page Count: 20
scope:

Goal and scope definition

During this phase of the LCA, a number of important decisions are made related to the goal and scope of the project. In defining the goal of the study, the following items are established related to the research:

o the intended application and audience,

o the reasons for conducting it, and

o whether the results will be used for comparative assertions.

The goal of the PPI study is to develop baseline data for North American corrugated HDPE pipe used as municipal stormwater drainage pipe. The HDPE pipe systems are compared to alternative material piping systems used for the same applications. The intended use of this study is to inform PPI and its member companies about the environmental profiles of HDPE and alternative stormwater pipe systems.

In the full LCA report, the results are presented by life-cycle stage (for example, pipe production, installation, use, end of life management). However, in this technical note, the results are presented in aggregated form for the full life cycle. The LCA has been conducted following internationally accepted (ISO) standards for LCI methodology. Since PPI is using this report as the basis for public comparative assertions about HDPE pipe systems and alternative pipe systems, a panel peer review of the study is required for conformance with ISO LCA standards.

The scope phase of the LCA establishes such things as the product system studied, the function of the product systems, the functional unit, the system boundary, the allocation procedures, and any assumptions, among other ISO- 14044 requirements. For the current LCA, a functional unit of 1000 ft of 24-in.- diameter piping is used with an assumed 100 year length of service.

The following functionally equivalent pipe systems were chosen to be studied in the LCA. Each system is made of a different material, but overall measurements and expected performance are unchanged.

o 24-in. corrugated high-density polyethylene (HDPE) double-wall pipe made with virgin HDPE and having bell and spigot joints with gasket

o 24-in. corrugated HDPE pipe made with 50% post-consumer recycled content, and having bell and spigot joints with gasket

o 24-in. corrugated polyvinyl chloride (PVC) double-wall pipe with PVC bell and spigot joints with gasket

o 24-in. Class III reinforced concrete pipe (RCP) with concrete bell and spigot joints with gasket

o 24-in. aluminum coated type 2 spiral-wound corrugated steel pipe with gasket

Although LCA studies can be performed with a more-limited scope or time scale, the most representative accounting of a product's environmental impact includes all environmental flows over the full life of the product. Thus the full life cycle of the pipe systems-from extracting raw materials from nature, any transformation or manufacturing of these raw materials into a product, the product use, to end-of-life scenarios-was included in this study, which is also called a cradle-to-grave LCA.

Three different end-of-life scenarios were considered: leave-in-place, recycle, and landfill. Only the results of the leave-in-place scenario are presented, which assumes that once the pipes are done with 100 years of service without complications, they will be left in the ground. Results from all three end-of-life scenarios are included in the full LCA, but only the leave-in-place scenario is included in this technical note. There is considerable uncertainty with how products will be handled at the end of their service lives so far in the future. This level of uncertainty is one reason why many manufacturers have avoided full cradle-to-grave LCA studies. The leave-in-place scenario has the fewest assumptions and the least uncertainty given that future technology related to recycling or landfilling is unknown. Thus, because of the significant uncertainty related to circumstances 100 years in the future, the leave-in-place scenario is conservative when estimating the end-of-life impacts for all pipe systems.

Allocation procedures

When raw materials and emissions associated with the manufacturing process cannot be easily attributed to several product outputs from a system, these LCI data must be allocated to the various co-products. There are several methods available to allocate co-products, and in this LCA, mass and enthalpy allocation are used.

Co-product allocations were needed in this LCA due to the multiple useful outputs from some of the "upstream" chemical processes involved in producing the resins used to manufacture plastic pipes and fittings. In this LCA, environmental impacts were assigned to any useful process output that is produced and sold. All scrap co-product was allocated on a mass basis.

For heat or steam co-products or a co-product sold for use as a fuel, the energy amount (Btu or J) of the heat, steam, or fuel was allocated as recovered energy that reduced the net process energy assigned to the resin.

Assumptions

There are a number of assumptions made for any LCA study, which must be presented to put the results in the correct context. It's worth noting that, for comparative assertions, ISO 14044 requires that assumptions related to non-represented industries be conservative. Because this study is a comparative assertion and non-HDPE industries were not involved in the decision-making process for assumptions, the ISO standard requires that the non-represented industries be given the benefit of a decision.

Many of the conservative assumptions made during this study are described in the following:

Companies operate in compliance with emissions standards. If actual industry emissions data are not available, published emissions standards are used as the basis for determining environmental emissions. In reality, exceptions to compliance may occur.

Energy and emissions for production of imported crude oil is assumed to be the same as that for U.S. crude oil. This assumption is followed even though standards and regulations for foreign production can vary significantly from those of the United States.

Space-conditioning energy in manufacturing facilities is much less than process energy. The fuels and power consumed to heat, cool, and light manufacturing establishments are omitted from the calculations. Energy consumed for space conditioning is usually less than one percent of the total energy consumption for the manufacturing process.

• Energy and waste associated with research and development, sales, and administrative personnel or related activities are also small and have been omitted from this study.

• The energy and emissions associated with production of capital equipment, facilities, and infrastructure are not included.

• Miscellaneous materials and additives (catalysts, pigments, or other additives) that total less than one percent by weight of the net process inputs are typically not included. No low-level use of resource-intensive or high-toxicity chemicals or additives was identified for any of the pipe systems; therefore, they are not expected to significantly affect the results.

• Inputs and outputs reported in the data sources used account for any input materials that are converting scrap.

• Transportation to construction site by tractor-trailer for all pipe types.

Pipes did not develop cracks that may cause leakage and water contamination. This analysis did not attempt to quantify rates of cracks and leakage from the stormwater pipe systems evaluated, nor does the analysis address potential human or ecosystem health issues that could result from contamination issues associated with stormwater pipe cracks and leakage.

Pipes did not require replacement during the 100-year service life. While some pipe systems have proven service lives of 100 years, other systems are known to be more susceptible to corrosion or deleterious contaminants.

• The need for high-quality backfill soil was identical for HDPE, PVC, and steel pipe systems, and reinforced concrete pipe used more native soil. This is a conservative assumption, especially for installations beneath pavement or inside the public right-of-way.

Comparative assertion

The LCA study was conducted "as the basis for public comparative assertions about PE pipe systems and alternative pipe systems." ISO 14044 requires an additional level of technical rigor for these types of studies, especially if representatives of the alternative-pipe-system industries are not involved in the development or review process, which was the case in this project.

Peer-review

The full LCA report was reviewed by an external peer-review panel "to ensure the study has been conducted in a manner consistent with ISO 14044 standards, including goal and scope, data acquisition and compilation, key assumptions, and interpretation of results." The peer-review panel adequately fulfilled its duty to perform an unbiased external peer review that was in conformance with the ISO 14044 standard. In addition, the LCA practitioner appropriately responded to the external peer-review comments.

Document History

PPI TR-53
January 1, 2021
Life Cycle Assessment of North American Stormwater Pipe Systems
Goal and scope definition During this phase of the LCA, a number of important decisions are made related to the goal and scope of the project. In defining the goal of the study, the following items...
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