Massachusetts Water Resources Authority

This is a Massachusetts State Auditor review of corrosion and odor problems at MWRA sewage treatment facilities, mainly Deer Island and Nut Island, covering November 1990 through December 1999.

“Our audit, which covered the period November 1990 through December 1999, was conducted in accordance with applicable generally accepted government auditing standards and included such audit tests and procedures as we considered necessary under the circumstances.”

Auditors looked at whether repair, replacement, and added protective coating costs tied to hydrogen sulfide and sulfuric acid were legal, reasonable, economical, and efficient.

“The objectives of our audit were to determine whether these activities complied with applicable laws and regulations, and whether they resulted in an effective, economical, and efficient utilization of resources.”

For residents and ratepayers, the issue is about protecting a major public sewer system that serves millions of people and avoiding expensive fixes that can affect public costs and service reliability.

“These responsibilities include providing water and sewer services to approximately 2.6 million people in 61 communities within the Commonwealth.”

The facilities were designed for hydrogen sulfide levels up to 25 ppm, but actual levels were far higher, so MWRA had to upgrade odor controls, add coatings, and pursue legal action over alleged design deficiencies.

“Both facilities were designed to handle H2S concentrations to a maximum level of 25 parts per million (ppm), whereas actual levels experienced were significantly higher, resulting in the odor and corrosion problems.”

The auditor said it would monitor MWRA’s lawsuit and urged MWRA to make sure future sewer projects are designed to avoid similar hydrogen sulfide problems.

“However, due to the costly nature of rectifying this problem, we recommend that the MWRA take the necessary actions to ensure that other ongoing and future sewerage projects are designed adequately to minimize similar H2S complications.”

The report shows a major public works project faced costly problems because expected sewer gas levels were too low, and it connects this issue to broader MWRA sewer odor and corrosion risks beyond Deer Island and Nut Island.

“In addition to the H2S problems encountered at Deer and Nut Islands, significant corrosion and odor problems have been observed in the Framingham Extension/Relief Sewers, the Wellesley Extension Sewer, and the West Roxbury Tunnel.”

Hydrogen sulfide is a smelly gas that can come from wastewater; when it mixes with water it can form sulfuric acid, which can corrode metals and concrete.

“When wastewater containing levels of dissolved sulfides is released to areas of normal atmospheric pressure, the dissolved sulfides are released from the liquid wastewater and form H2S gas odors, which, if combined with water, reacts to form sulfuric acid corrosion.”