NEW YORK, Sept 10 (Reuters) - Michigan's environmental

agency on Tuesday issued a new air permit to Marathon Petroleum ( MPC )

covering emissions from its Detroit refinery, which will

allow the refiner to boost crude throughput at the plant.

In March, Marathon filed an application with the Michigan

Department of Environment, Great Lakes, and Energy to run its

refinery continuously by removing monthly and annual throughput

limits.

The refinery's permit had capped its capacity at 140,000

barrels per day on an annual average, but the new permit removes

limits on how much crude it can put through the plant.

The facility, which produces gasoline, fuel oils, asphalt,

propane, and propylene, had relied on periods of shutdown or

reduced production to meet the annual average limit.

A Marathon spokesperson said the new air permit conditions

include a reduction in emissions limits, voluntary emissions

reduction projects and a six-year enhanced air monitoring

program. "We did not propose any changes to our existing

footprint," the spokesperson said.

However, local environmental groups worry the facility could

add more pollutants to the air by processing more crude oil.

The approval highlights the need for local lawmakers and

regulators to implement rules that account for the overall

health effects on fence-line communities, rather than evaluating

pollution on a pollutant-by-pollutant basis, said Bryan

Smigielski, Michigan campaign organizer for the Sierra Club.

"The absence of cumulative impact regulations means this

permit was approved without thorough review of the combined

impact on already vulnerable neighborhoods," Smigielski said.

The Marathon refinery is located in Southwest Detroit, an

area with one of the highest levels of air pollution in the

state due to significant industry presence.