Following an ethics review, a special committee appointed by Miami-Dade Mayor Carlos Gimenez has recommended Los Angeles-based AECOM Corp. for an $80 million contract to oversee a $1.6 billion overhaul of the county’s sewer system.

Gimenez will make the final determination.

The rivalry between AECOM and the other finalist, Colorado-based CH2M Hill Inc., was fierce.

AECOM asked the county Ethics Commission to consider whether the so-called “cone of silence” on bidding or any other ethic rules were violated when CH2M delivered 400 pages of supplemental documents to the project selection committee two days before a second-tier decision was made.

The Ethics Commission concluded CH2M did not break any rules or procedures but its actions raised doubts about the integrity of the bidding process. The county said it plans to make changes as a result.

“It was an open, fair, transparent process, and we were able to demonstrate we were the most qualified firm,” said AECOM attorney Miguel de Grandy of Holland & Knight in Miami. “There were two strong competitors, and I think AECOM was able to demonstrate it was the largest engineering firm in the world, it was highly qualified and it ranks superior.”

The county is working under a consent decree with the federal government to replace its deteriorating sewer pipes.

AECOM accused CH2M of “grossly misrepresenting” its experience to the committee.

AECOM “claimed they had 28 consent decrees in which they have worked as the prime consultant, but their submittals accurately reflected they had one or maybe two,” said CH2M attorney Al Dotson of Bilzin Sumberg Baena Price & Axelrod. “It looks like they won by grossly exaggerating their experience, and we plan to make sure the mayor and others are aware of what took place.”