The city Board of Estimates stepped deeper into the world of sewer consulting yesterday, approving another $1.1 million to a global infrastructure firm to help design and engineer the city’s “outfall sewershed system.”

That’s a fancy phrase for the subterranean network of sewers, stormwater outfalls, storage tanks and manholes that constitute the region’s wastewater system operated by the city’s bureau of water and wastewater.

Gannett Fleming Inc. will prepare designs and specifications over five years for the rehabilitation of 18 miles of sewers, nearly 2,000 manholes and the cleaning of other wastewater infrastructure.

Gannet Fleming describes itself as a “global infrastructure firm” whose mission is to “amaze our clients with our responsiveness and innovation.” Baltimore County will contribute another $931,000 for the consulting work.

The action follows the board’s approval last week of a $1.7 million contract with two consultants to prepare and oversee improvements to the Gwynns Falls sewer system and $1.6 million in December for consultants to review 14,000 manholes and manhole covers.

The city is under a consent decree with state and federal regulators to stop sewage overflows or face stiff penalties.

In other action yesterday, the board headed by City Council President Bernard C. “Jack” Young and Mayor Stephanie Rawlings-Blake, approved the following:

• $1,385,650 to AIDS Interfaith Residential Services (AIRS) to oversee permanent housing for 39 newly released prisoners with HIV/AIDS over three years. Other services to be provided by AIRS include “housing readiness training, job skills training and job search assistance” between now and February 2015, according to the board’s agenda.

• $1 million to Abacus Corp. and Watkins Security to provide uniformed security guards for city agencies between April 1 and June 30, 2012.

• $745,371 of federal funds to Johns Hopkins University for outpatient and outreach services and patient counseling for HIV/AIDS patients. The programs are funded by Ryan White Part A and Part D services.

• $600,000 to Correlli Inc. for parts and repair services of city-owned Caterpillar construction equipment.

• $373,522 to Rummel, Klepper & Kahn for “on-call” consulting on the demolition of two downtown pedestrian bridges: the Gay Street Bridge located over Pratt St. and the Charles Street Bridge located over Pratt and Charles streets.

• $367,885 to Baltimore Medical System Inc. to help administer school-based health centers at Collington Square Elementary/Middle School, Maritime Industries Academy High and Friendship Academy of Science and Technology.

The board also approved a $146,836 extra work order (EWO) to T.Y Lin International for the design of a rebuilt Annapolis Road Bridge over the Baltimore-Washington Parkway.

Jamie Kendrick, deputy director of the Department of Transportation, said the EWO “is related to the city’s upgraded stormwater management requirements, improvement of the terrain model, coordination with the selected artist (1% for art requirement) and working to package this project with the Waterview Avenue bridge project.”

This is the project’s third EWO, which has boosted its cost from $998,821 to $1,613,413.

The board also approved a $155,583 increase to a $10.5 million contract to Associated Black Charities (ABC) to act as administrative fiscal agent for the city Health Department for HIV emergency relief project grants.