Portions of a storm water retention pond located on Jackson Drive and Main Street in Berryville have been roped off behind police lines because residents discovered a deep hole Tuesday morning. The area is often used by children as a sleigh riding hill so when the hole was discovered police were notified of the safety hazard. Berryville Police arrived at the scene and contacted the Town Public Works and a safe zone was established around the hole with orange snow fence. Police remained on scene until the area was secured and added police lines to prevent the curious from crossing into the fenced area.
The small hole is approximately 12-18 inches across. However witnesses reported the hole was very deep and said they could not see the bottom. Town officials referred to this type of collapsed hole as a subsidence. Clarke County’s karst topology is prone to these types of sinkholes, both large and small. The Berryville Area Development Authority studied sinkhole and karst areas with geotechnical consultants in 2005 and included language in the Subdivision Ordinance concerning these features and their remediation.
Town Manager Keith Dalton said, “The party responsible for maintaining the pond has been provided with a VDOT Instructional Informational Memorandum which provides guidance on abating such problem areas. Essentially the memorandum calls for excavation of the area of subsidence and installation of an inverted filter.”
Since this event has occurred in a storm water retention pond it may need to be treated in a slightly different manner. Dalton added, “Town Planner Christy Dunkle has indicated that, given the fact that the area serves as a storm water management area, a cap of some sort (most likely clay) will need to be used in this instance.”
Ms. Dunkle has been spearheading the Town’s response to the incident and said, “That storm water facility is currently maintained by a business association. Mr. Echols (the developer of the subdivision the storm water pond serves) has contacted an excavator and it is my understanding that he will have someone on site in the next few days.”
Other residents in the subdivision have seen similar holes open up in the past. When asked what residents should do if they see this type of subsidence Ms. Dunkle said, “If someone in the Town of Berryville does see subsidence such as this in their yard, they should contact the Town of Berryville immediately. We will then advise the property owner on appropriate action to take. Because the subsurface area of these karst features is unknown, residents should not stand close to the opening.”
The inverted filter abatement involves a process whereby the sinkhole is excavated, filter cloth may be added, and the area is filled with large stone at the bottom with gradually smaller stone towards the top, followed by top soil and grass. This allows for ground water to continue through the stone and does not divert it elsewhere which may cause additional problems.
The area around the incident is being monitored. The Town has asked that a plan of action be submitted for this subsidence by 24 January.