Supporting guide to calculate the design sewage flow for subsurface sewage works subject to section 53 Ontario Water Resources Act

Ontario is proposing a guide intended to replace the ministry’s “Interim Fact Sheet on Design Sewage Flow Rates for Seasonal Trailer Parks and Park Model Units, 2015” and will incorporate an updated version of “Table 5-3 Common Sewage Flow Rates for Commercial and Institutional Uses” from the ministry’s Design Guidelines for Sewage Works, 2008. The guide, if approved, will support applicants seeking ECAs for large subsurface sewage disposal works to prepare high-quality ECA applications, promote options for optimizing these sewage works and help protect human health and the environment.

Overview of the proposed Design Sewage Flow Guide

Generally, the owners of large subsurface sewage disposal works (LSSDS) with a design capacity over 10,000L/day are required to obtain an environmental compliance approval (ECA) from the ministry under section 53 of the Ontario Water Resources Act (OWRA) and Part II.1 of the Environmental Protection Act (EPA). These works are often used in recreational trailer parks and campgrounds, as well as residential developments.

To help provide greater clarity and reduce burden on ECA applicants, the ministry has developed the proposed draft Supporting Guide to Calculate the Design Sewage Flow for Subsurface Sewage Works Subject to s. 53 OWRA (DSF Guide). The proposed DSF Guide is primarily intended for use in seasonal campgrounds or similar settings where significant surges in water use or sewage flows may occur.

Key elements of the DSF Guide

The proposed DSF Guide outlines criteria for calculating daily design sewage flows for subsurface sewage works when applying for an ECA. For existing systems, it sets out how to use historical metered flow data to support design flow calculations for replacement or expansion projects. This approach promotes consistency for owners who have monitoring data, rather than relying solely on prescribed design flow values. Optimizing design using historical flow data may result in lower design flow estimates, potentially reducing capital, operational, and maintenance costs.

In addition, the proposed DSF Guide will:

• provide design options such as modular systems, flow equalization, and reserve areas to enhance system longevity and flexibility
• clarify the information required to prepare high-quality ECA applications for these types of works
• support reduced design flow values for new systems serving seasonal occupancy sites
• specify design flow values for larger seasonal occupancy sites and mobile home parks
• include alternative design approaches to manage flow exceedances during surge events
• encourage innovation by allowing for alternative designs supported by third-party performance data
• reduce the required monitoring period to rerate systems from three years to two years
• extend the definition of “seasonal” use sites from six months to ten months
• provide direction on developing management plans for ongoing operation, maintenance and operation
• clarify terminology and definitions to align with current industry practices

The proposed DSF Guide does not change the regulatory process and is intended to:

• replace the ministry’s “Interim Fact Sheet on Design Sewage Flow Rates for Seasonal Trailer Parks and Park Model Units, 2015”
• replace “Table 5-3 Common Sewage Flow Rates for Commercial and Institutional Uses” of the Ministry’s Design Guidelines for Sewage Works, 2008 with Table 1 in the DSF Guid

In the absence of historical monitored flow data, the ministry is proposing that ECA applicants use the common sewage flow rates in the updated Table 1.

Cutting red tape

Ontario is committed to building smarter processes and cutting unnecessary red tape that adds to the high cost of doing business, while ensuring strong environmental protections. The DSF Guide will reduce burden on the regulated community by:

• allowing owners of existing sites to optimize the size of their proposed sewage works, thus reducing the project’s capital, operation and maintenance costs
• saving them time and planning costs when preparing their ECA applications by clarifying the ministry’s requirements for a high-quality ECA application
• reducing the ministry’s review time through the submission of complete ECA applications thereby avoiding delays in the implementation of projects

This draft Design Sewage Flow (DSF) Guide was developed with a significant input from the camping and tourism stakeholders.

Public consultation opportunities

This proposal has been posted for a 60-day public review and comment period. We encourage interested parties to make comments on this proposal.

This ministry is also consulting on a proposal to replace Table 5-3 of the Ministry’s Design Guidelines for Sewage Works, 2008 with Table 1 of the proposed DSF Guide under ERO number 026-0643.

We encourage interested parties to review and submit comments on both postings.

Comments made on both proposals will be considered prior to making a decision on the proposed DSF Guide and the replacement of table 5-3.