CHRISTIANSBURG -- While the town continues its investigation of a sewage backup that cost Cameo Court residents thousands to clean up, the neighbors have recruited an engineer to conduct an investigation of their own.

The verdict: An improperly constructed sewage invert proves the town is at fault, the neighbors say.

The invert is a channel at the bottom of the manhole on Cameo Court that sewage travels through to the main line at Independence Boulevard.

Jennifer Whittemore and Bill Cockey, whose basements filled with sewer water during a storm last month, addressed the Christiansburg Town Council at its meeting Tuesday night and shared video, pictures from the aftermath and concerns that the sewer draining system on their street needs to be fixed.

Whittemore said she wasn't satisfied with the inspections made by both the town's insurance adjuster and the independent engineer because they looked at the damage but gave little attention to analyzing the sewer system itself. She said both indicated that heavy rainwater was the sole cause of the flooding.

"I understand that there was a large amount of rain, but this was a system error," Whittemore said.

According to her presentation, the manhole invert in front of one of the affected houses is not built to handle the flow of sewage it receives because of its shape.

Whittemore said her engineer said the "T"-shaped invert should be curved, like an elbow, to drain properly. The video showed footage taken Tuesday afternoon of water collecting in one spot while the rest flowed through the circuit. It was drizzling at the time the video was made.

Whittemore said the "T" invert causes the sewage rushing from under Cameo Court to form a wall. That, she said, creates a "whirlpool effect" and, when the amount of stormwater received May 15 is added, can wreak havoc on residents. The consultant also told the neighbors that because of the improper construction of the invert, if multiple neighbors were to use their showers, washing machines or toilets simultaneously, sewage backup comparable to last month's can occur again, she said.

Following the presentation, Mayor Richard Ballengee asked Town Manager Lance Terpenny about the status of the investigation. Terpenny said that since May 15, town officials have been investigating every report in the area affected. Ballengee expressed his empathy for the Cameo Court residents, and said the town and insurance company would continue to look into the matter.

Wayne Nelson, the town's director of engineering and public works, said his staff is conducting its investigation of the neighborhood sewer system. That report will be given to the insurance company, which will then have an independent third party review it.

Residents will have the opportunity to review the report, Nelson said.

Cockey said he e-mailed Nelson asking whether the video shown at the meeting could be given to the insurance company as a supplement to the investigation. The video "is the smoking gun that proves the town negligent," he said Wednesday afternoon.

Whittemore said she and her neighbors have $15,000 in cleanup and repair bills that the town should be responsible for.

Cockey said no matter the outcome of the investigations, he and his neighbors want to make sure the town corrects the invert.

"We want to know how quickly this situation can be corrected regardless of liability, because we don't want it happening again," he said.