TAMPA — The contractor building an $8.8 million section of Tampa's Riverwalk will pay $10,000 in fines for dumping concrete waste into the Hillsborough River.Johnson Bros. Corp. of Lithia also agreed to cover the investigative costs of the Florida Department of Environmental Protection and Hillsborough County Environmental Protection Commission, which each imposed a $5,000 fine.Together, those costs bring the total that Johnson Bros. will pay to slightly more than $11,000.The fines result from two days when Johnson Bros. workers washed concrete-laden water from its construction barge into the river, according to a seven-page agreement between the company and environmental regulators.One of those washouts, on Aug. 12, was captured on video by downtown worker Matthew Von Dohre, who saw a similar dump the day before.Tampa Mayor Bob Buckhorn called the washout reckless and stupid, but said it appeared to be the act of one employee and expected that the river, which has seen worse, did not sustain permanent harm."We don't believe that there's any lasting effects," said Andy Schipfer, the county EPC's assistant director of waste management.In the days after the video became public, Johnson Bros. told City Hall that it had fired at least one worker, disciplined others and retrained its crews on proper procedures. It also moved where it does its washouts to dry land, not on its barge on the river.In a written statement released Thursday, Johnson Bros. said it "has a long history of environmental stewardship building construction projects through environmentally sensitive areas," including cypress swamps and state-protected "Outstanding Florida Waters.""This was an isolated incident and immediate and decisive corrective actions were taken," the company said. "Procedures are in place to prevent future occurrences."Von Dohre said he wasn't necessarily glad the company got fined, but, "I am happy they've taken corrective measures to no longer dump in the river.""They're doing things right," said Von Dohre, 36, whose office is near the job site.In addition to the state and county environmental regulators, the U.S. Army Corps of Engineers is "reviewing the situation," corps spokeswoman Nikki Nobles said, but "no determination has been made at this time."Johnson Bros. is building the over-the-water walkway under the Kennedy Boulevard Bridge north to Curtis Hixon Waterfront Park.The company, which also built the Riverwalk under the Brorein Street Bridge, was the lowest of six bidders for the job. A federal transportation grant is paying for the work.The 1,460-foot-long section is expected to be completed in late December or January.Once it opens, the city will have a continuous 1.8-mile waterfront trail from the Channel District around the Tampa Convention Center and north to the David A. Straz Jr. Center for the Performing Arts.After that, the city plans to build one more section from the Straz north to Water Works Park.