The money that a tax on plastic bags was expected to generate for the District is bringing in about half of what analysts had predicted -- but those responsible for spending that revenue say it's a good thing.

"It's a trade-off," said Christophe A.G. Tolou, director of the D.C. Department of the Environment. "What we want to see ultimately is a very small revenue and very large numbers of [reusable] bags being used."

Tolou said that through August, the 5-cent fee per bag used at stores in the city had generated about $1.5 million in revenue through August. The tax went into effect Jan. 1.

Original estimates had the tax generating nearly $4 million during its first fiscal year, which ends Sept. 30.

"We're not going to get anywhere close to that," Tolou said.

The revenue shortfall is roughly in line with reports that disposable bag use has fallen by 50 percent -- and that's the point of the tax, its supporters say.

Elizabeth Campbell, deputy director of the Alice Ferguson Foundation, said the foundation's Hard Bargain Farm on the Potomac River 10 miles south of Washington, has had less garbage to clean up since the tax started.

She said after the spring's annual shoreline restoration, during which trash trappers such as fallen tree limbs and other plant debris are removed from the shore, something different happened.

"We fully expected that all the trash would wash back up on shore and it hasn't this year," she said.

In April, the annual Potomac River Watershed Cleanup collected roughly 21,600 plastic bags -- 50 percent fewer bags than the prior year's cleanup.

Tolou noted retailers are reporting they are buying half as many bags as they were a year ago.

For consumers, the drop-off was almost immediate. D.C. residents used about 3 million disposable bags in January -- down from the average 22.5 million bags per month. Tax revenue has been averaging about $200,000 per month.

Lou George, a downtown employee, said during the first few months of the tax he refused to get a bag when ordering takeaway food, opting to juggle his lunch items back to the office.

"Now I give in every once and a while," he said.

Tolou said the lower revenue, which is slated to help fund cleanup efforts and clean water education, won't hurt those causes.

"We have alternative funding sources to help deal with these problems -- [the tax] revenue is in addition to efforts already underway," he said.