Page 12

INFRASTRUCTURE

Private side standards for sanitary and stormwater sewer infrastructure are woefully inadequate By Barbara Robinson

U

nacceptable amounts of inflow and infiltration (I/I) in new construction have been identified as a significant issue, particularly with the advent of more frequent and more intense rainfall events. As it can account for 50% of total I&I, proper construction of the sanitary sewer lateral on the private side (defined as the “sanitary building sewer” in Canadian building codes) is an important factor in this issue. The building code governs the construction of sewers on the private side. There are a few pressing areas in which the Ontario Building Code (OBC) is not sufficiently protective of I/I. Sources of I/I on the public side, however, are extensively studied and well understood, if still occurring. The collection of new subdivision flow monitoring data since 2015, and ongoing detailed surveys of municipal staff and stakeholders has allowed the identification of many significant contributing factors that need to be addressed in the development process. Hundreds of building inspectors, building plumbing inspectors and chief building officials have been consulted over the course of this work. A variety of new subdivision construction sites were visited and construction, inspection and testing procedures were observed first hand by shadowing building inspectors. An important part of this project was to share information with building departments and educate them on I/I issues.

Proper bedding and backfill of plastic pipe is essential to its integrity and lifespan. Pictured is an example of a stormwater lateral pipe not properly bedded.

Then, backfill continues to 300 mm above the crown of the pipe, again compacted to 95% dry density. The embedment material for flexible pipe must be Granular A,B, or unshrinkable fill. Proper bedding and backfill of plastic pipe is essential to the integrity and lifespan of sewers. Plastic pipe is now being used almost exclusively on both the public and private sides in new subdivisions. Unlike concrete pipe, plastic pipe gets its structural integrity from the soil around BEDDING AND BACKFILL OF PRIVATE SIDE LATERAL it (plastic pipe is embedded, not bedded). Installation of pipe is covered exten- As such, proper bedding and embedPOTENTIAL I/I SOURCES ON THE PRIVATE SIDE sively in Ontario’s Public Standards and ment procedures are vital for the success Of extreme importance is the fact that Specifications (OPSS and OPSD), which of plastic sewers. The OBC, by contrast, provides a sinthe Acceptable Solutions in the OBC are are used by 95% of municipalities. It is preceded by Objectives related to Health also referenced in Ontario Sewer Design gle sentence in the code with reference & Sanitation, and Functional Statements, Guidelines. As described in OPSS 401, to an Appendix. It is not prescriptive – “a which are more detailed and lay out the the embedment shall be placed as per the base that is firm and continuous” is vague. goals of the Code. Several of the Func- bedding and backfill. Bedding needs to There is some clarification provided in an tional Statements in the Code relate be placed in uniform lifts not more than Appendix, but Appendices are not legally directly to I/I, including the need to limit 300 mm in thickness and compacted to part of the Code. continued overleaf… excessive demand on downstream infra- 95% dry density. 12  |  August 2018

structure, and to minimize injury as a result of contact with sewage. There are many areas where Acceptable Solutions in the OBC differ markedly from public side requirements and are not protective against I/I, including bedding and backfill, jointing, and connection of the sewer at property line. Construction practices are also a factor in the success of private side pipe construction.

Environmental Science & Engineering Magazine

Environmental Science & Engineering Magazine (ESEMAG) | August 2018  

Environmental Science & Engineering Magazine’s August 2018 issue. Our August 2018 issue includes 15 articles covering drinking water, wastew...

Environmental Science & Engineering Magazine (ESEMAG) | August 2018  

Environmental Science & Engineering Magazine’s August 2018 issue. Our August 2018 issue includes 15 articles covering drinking water, wastew...