Michigan embraces predictive tools to develop a lead service line inventory

Tom Neltner, Chemicals Policy Director.

Earlier this year, the Michigan Department of Environment, Great Lakes, and Energy (EGLE) released ground breaking guidance to help utilities in the state develop their “Complete Distribution System Materials Inventory” (CDSMI) that is due in 2025. The guidance is important because it explicitly allows utilities to use predictive tools to prepare an accurate materials inventory that is essential to effective lead service line (LSL) replacement efforts. Because the Environmental Protection Agency’s (EPA) service line inventory in its revised Lead and Copper Rule (LCR) has many elements in common with Michigan’s inventory, we encourage EPA and other states to look closely at Michigan’s guidance as a model to help all utilities develop accurate service line inventories.

Michigan’s inventory requirement and guidance

Michigan’s version of the LCR requires utilities to fully replace all LSLs – the portion on both public and private property – at an average rate of 5% per year by 2040.[1] The key to compliance is an accurate CDSMI that must be submitted to EGLE and made public by January 1, 2025.

EGLE states that the CDSMI’s purpose “is to characterize, record, and maintain a comprehensive inventory of distribution system materials, including service line materials on both public and private property.” It supports effective asset management planning, LSL replacement efforts, and notification of those served by an LSL.

The CDSMI builds on a preliminary inventory that utilities submitted to EGLE by January 1, 2020.  In the EGLE’s December 2020 update to that inventory, it reported more than 138,000 known LSLs (including galvanized previously connected to lead) and more than 1.16 million unknowns out of a total of 2.6 million. Of the unknowns, more than 193,000 are likely lead, 314,000 are unknown with no information and 649,000 are unknown but likely not lead.

With the complete inventory due in 2025, unknowns must be resolved as either LSLs or not lead. This is an important difference from EPA’s revised LCR which allows service lines to be considered “Lead Status Unknown” as long as there are enough LSLs to conduct tap sampling.

EGLE’s March 2021 guidance describes a useful approach to developing the CDSMI as follows:

  1. Organize and review existing records (much of this should already have been done for the preliminary inventory);
  2. Evaluate existing and/or create an inventory tracking system and procedures;
  3. Conduct physical verification of service line materials (see below for method);
  4. Evaluate results of physical verification;
  5. Conduct additional verification of service line materials or other distribution system components, if needed; and
  6. Update and/or expand records to develop the CDSMI.

Physically verifying a “statistically sound subset” of service line materials using predictive tools

Physically inspecting every service line to determine if it is lead is unrealistic. Even assessing the 1.16 million unknowns in the preliminary inventory is a significant undertaking.

Fortunately, in its March 2021 guidance, EGLE makes clear that utilities “are not expected to physically verify every service line, but rather a statistically sound subset. To effectively evaluate the accuracy of service line records and/or predict service line materials, a representative, uniformly random number of service lines must be physically verified.” This information can be used by predictive tools to estimate the likelihood of a given line being lead or not.

EGLE also provides guidance on the minimum verification requirements and recommends that such verification should be completed by the end of 2022. The predictive tools are focused on unknowns so lines that are “known” – whether LSLs or not LSLs – are excluded. The only types of unknowns that may be excluded are those four or more includes in diameter.

Utilities must physically verify a minimum number of unknowns based on a statistical calculation. The minimum number ranges from 20% for those utilities with fewer than 1,500 unknowns with smaller percentages as the number of unknowns grows up to a maximum of 386. The physical verification is to include 18 inches of the public side at the curb stop, 18 inches of the private side at the curb stop, and the portion of the service line coming into the home.

To be considered “known,” and, therefore, excluded from the pool of sites from which a random sample will be drawn, a service line must either be:

  1. Physically verified after 1988 based on specific criteria and the records are demonstrated to be reliable; or
  2. Ordinances or other controls were in place at the time the service line was installed specifying the materials that must be used in service line construction.

In addition, the utilities must not have observed deviations from those conditions during operations and maintenance.

The results of the physical verification of the random selection of unknowns are to be compared to existing records to determine if the records are reliable and may prompt additional investigation. The results are used to develop a system-wide inventory that forms the basis of the CDSMI and can be used to notify residents whether they have an LSL.

A model for EPA and other states

Utilities need a clear mechanism to predict where LSLs are and where they are not. They also need a reasonable means to demonstrate that they do not have LSLs at all. EGLE provides that mechanism. EPA and other states should consider Michigan as model for their guidance for developing a service line materials inventory, especially when they need to reduce the number of unknowns.

[1] EGLE may approve an alternative schedule.

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