Vandals in Oroville, Calif., stole manhole covers for their recyclable value and dumped everything from furniture and rocks to bushes and debris down the structures. Of the six occurrences, three caused minor sanitary sewer overflows.

"Fortunately, alert citizens called us and we quickly removed the blockages," says senior civil engineer Rick Walls, P.E. "But that was three too many SSOs and we were fed up."

Walls and Public Works director Art Da Rosa, P.E., searched the Internet for solutions and found the locking cover security system from SewerLock. Oroville became the first city in the nation to install a major number of units.

Loose cannon

The city has 436 36-inch concrete manholes outside public right-of-ways. They access 6- to 8-inch clay sewers running through undeveloped land or in backyards of older subdivisions. "The secluded structures pose a greater risk for vandalism and unauthorized entry," says Walls. Many manholes belong to sewer lines installed in the early 1900s.

The first product the city selected was a plastic composite manhole cover and frame. Installation was estimated at $850 per manhole because workers would have to remove the old frame and cover, break out and clean up the mortar, lay fresh mortar on the barrel, and set the replacements. The city would bid the installation to free crews for more important work.

"I about fell out of my chair when I realized we were looking at $600,000 to secure these manholes," says Walls. "Then there was the unknown of how much collateral damage they would suffer and the cost of those repairs. The prospect was scary."

Likely candidate

Walls returned to the Internet and found a manhole locking cover that installs below the cover. The cover is adjustable to release overflow, or it can be fitted with compression springs and a neoprene seal to control odor and pressure problems. Stainless steel units include a 10-gauge insert with two eyebolts, four 1/4-inch anchor bolts, and a 14-gauge cover with 12-gauge handle.

"SewerLock is a new company selling one product, so I had a long talk with owner Dave Ross," says Walls. "The cover is a simple design, easy to install, and guaranteed to work."

The city bought 64 units at a price similar to the composite product. R.J. Heuton Construction in Chico won the bid to install them for less than $100 each. A worker completed the project in five days.

Besides the six vandalized manholes, Walls selected structures in the most remote areas with the highest potential for trouble, yet grouped close enough together to minimize travel time. All were at-grade and accessible by truck.

No moving part

A technician from R.J. Heuton cleaned the surface of the mounting area to remove deposits that would prevent the caulking agent from bonding. He positioned the insert slightly below grade inside the manhole cover frame, then drilled into it using the 12, 3, 6 and 9 o'clock pilot holes in the insert's 1 1/8-inch skirt.

After boring with a roto-hammer drill powered by a portable generator, the worker inserted anchor bolts in the holes, then sealed the insert's perimeter with Liquid Nails. "The installation is very robust and not going anywhere," says Walls. "The cover is strong enough to support a person standing on it."

While the adhesive dried in 15 to 20 minutes, the technician installed another insert, then returned to slip the cover over the eyebolts in the rim at 3 and 9 o'clock. He lined up the matching notches in the cover, slid them over the eyebolts, and attached padlocks through the eyes to secure the cover. The entire installation took about 30 minutes.

"We looked at spending big bucks on locks, but figured anyone wanting to access a manhole badly enough would bring bolt cutters," says Walls. "That's also why we didn't purchase the anti-theft chain that attaches from the insert to the underside of the cover." The city ordered laminated, commercial Master Lock padlocks that opened with the same key.

The City of Oroville does not endorse any product or service, but Walls said they were "very happy with the product and intend to expand the program."