A large amount of "granite-like rock" is again raising costs for finishing a boardwalk along the South Chickamauga Creek Greenway at the Faith Road trailhead off Youngstown Road.
There was a $187,254 cost overrun last March.
Officials said the new change order is for $192,170.
That brings the total cost of the project to $434,521.
Officials said, "The South Chickamauga Greenway – Youngstown has taken significantly longer that expected due to an unexpected large quantity of granite like rock. As you may be aware, per the specifications of the Engineer of Record for the boardwalk, each pile is to be driven to refusal at a minimum of a 10-foot depth. In rock, where encountered near the surface, a minimum of 4 feet of drilling into the rock is desired.
"According to the geotechnical report provide by S&ME, rock was expected to be found at STA 32+50 to STA 34+50. However, rock was not expected to be at STA 31+00 to STA 32+50.
"This section has rock relatively close to the ground and is also the highest section of boardwalk requiring the tallest piles. Boring to a four foot depth in the rock is critical in this section.
"Because of the extra time it has taken to drill into the rock, the cost has exceeded the proposed budget for both Nature Bridges and Arcadis. With less than 100 feet to boardwalk to be built, the city of Chattanooga is willing to pay 100 percent of the overage for both Nature Bridges and Arcadis."