Conical Sink, Phelps County, Missouri

Mark Twain National Forest

Conical Sink is a 100-foot deep sinkhole located in Phelps County, Missouri. The sink is located adjacent to a county road. Prior to Forest Service acquisition approximately 30 years ago, the sinkhole was used as a dump. However, even after the dump was closed. it was still being utilized as an illegal dump site as recently as the spring of 2008.

The Meramec Regional Planning Commission (MRPC) received a grant from the Ozark Rivers Solid Waste Management District and Missouri Department of Natural Resources to pay for the expense of cleaning up Conical Sink. A 75-ton crane with a 202 foot long boom was rented on three days for a total cost of over $9,150. The grant funds also paid for transfer station disposal costs, safety equipment, fence installation, food and drinks for volunteers, some heavy-duty trash bags and other supplies.

Sinkhole Clean Up Begins

Clean-up work, which began in November 2007, was finally completed in November 2008 with the construction of a fence between the county road and Conical Sink. Due to numerous weather delays, the project took about one year to complete. Another reason the project took so long is that many pieces of trash had to be handled numerous times. First, the trash was bagged and then the trash bags were moved and stockpiled at the bottom of the sinkhole. During the three different crane days, volunteers loaded the trash bags by hand into cargo nets and the crane would lift the cargo nets out of the sinkhole. The cargo nets had to be unloaded by hand and transferred to waiting dump trucks or a backhoe bucket, which emptied the trash bags into the trucks.

Crane Lifts Trash from Conical Sink

The South Central Correctional Center (SCCC) in Licking, Missouri provided the vast majority of the labor for the project. Inmates and Correctional Officers contributed 177 workdays. Volunteers who worked a total of 33 days included Wal-Mart employees, students from Missouri University of Science and Technology, educators, cavers, Missouri Department of Conservation and Missouri Department of Natural Resources’ employees and other interested individuals.

Volunteer Labor and Donations

Wal-Mart Distribution Center 6069 donated $1,000 and the Missouri Cave & Karst Conservancy donated $500 to help with the overall expenses of this project. In addition, Wal-Mart supplied over 2,250 heavy-duty trash bags and numerous cases of bottled drinking water.

The Phelps County Highway Department (PCHD) also provided help for the project. PCHD employees hauled all the trash to the transfer station in Rolla, Missouri and all the metal to a metal recycling location. In addition, they hauled a truckload of tires from the sinkhole and provided over 1,000 trash bags. The PCHD also supplied the material and constructed a berm between the county road and Conical Sink. Approximately 59,000 pounds of trash was removed from Conical Sink, including 126 tires and 11,500 pounds of metal, which was recycled.

After Conical Sink was cleaned out, a berm was built between the county road and the sinkhole. A chain link fence was installed on top of the berm to discourage any future dumping.

Today, Chainlink Fence Prevents Dumping in Conical Sink

Slaughter Sink, one of the largest sinkholes in the State of Missouri, is located within one-fourth mile of Conical Sink off the same county road. The area is typical of the karst topography common in the Missouri Ozarks.

Both Conical and Slaughter Sinks are located approximately a half mile from the Onyx Cave and three-fourths of a mile from Boiling Spring, one of the larger springs that feed the Gasconade River.

About the author: Klaus Leidenfrost, member of the Missouri Caves and Karst Conservancy, is also a retired wildlife biologist from the Houston/Rolla/Cedar Creek Ranger District of the Mark Twain National Forest.