Why did the flooding occur?

SANDUSKY — On Wednesday and Thursday, a record amount of rainfall drenched and drowned many places — homes, basements, lawns, businesses, streets, shelters and more — across the region. But, heading into the weekend, hundreds, if not thousands, of locals continue to reel from the unprecedented storm. Many still don't have power, and calamities from downed trees to upended utility lines, often resulting in flooding, have created many hardships. Sandusky officials, along with other crews working for public agencies and private businesses, are still working around the clock to remedy what they can. This would include city public works director Aaron Klein, who took some time to address a few pressing questions — which include "Why did the flooding occur?" — many residents want answered: Q: With the severe rain across the Sandusky region Wednesday into Thursday and Thursday into Friday, how is it that so many areas, streets, lawns, homes and basements were flooded? Does the city's pipes and plants not have the capacity to handle that much water? AK: The rain event occurred from 10:45 p.m. to 3:30 a.m. and again from 8 a.m. to 9 a.m. on Aug. 23-24. During that time, 6 inches of rain was measured by the rain loggers. Of that total, 2.8 inches was received between 10:45 p.m. and midnight, meaning that this was a very severe portion of the storm. I am still trying to gather hour-by-hour information to determine when this intense surge that occurred over the first couple of hours began to dwindle. When the intensity is so severe, at the onset of the storm, the sewers receive more water more quickly, which reduces their available capacity for the duration of the storm. This is also true of the wastewater pollution control/wastewater treatment plant. Storm sewer systems in Ohio are generally designed, per typical engineering principles and various standards, to a 10-year, 24-hour rain event, which is considered the typical design-year event. These standards also are based on a dedicated storm sewer, not a combined storm/sanitary sewer, which were common prior to current engineering design standards. And, as we all know, normal weather patterns really don't exist anymore, even though the sewers that were installed under those standards and even prior to those standards have. The full event that occurred from 10:45 p.m. to 9 a.m. would be assigned a 500-year event, meaning that its probability of occurrence would be once every 500 years based on historical information of all recorded rainfalls with normal weather patterns. If we eliminate the 8-9 a.m. time period, the first 5.25 hours of the storm may have been larger than a 500-year event and possibly closer to a 1,000-year event. Many variables exist within each neighborhood throughout every city, such as engineering standards used when the infrastructure was installed; building and architectural standards used when the houses were built; housing density; impervious surface in the sewer shed; vegetation; greenspace; maintenance of public and private infrastructure; separate-versus-combined sewers; retention/detention; proximity to a stream or ditch; depth to bedrock, etc. So to answer the last portion of the question: Some sewers kept up, but some did not. In many areas, the soil conditions didn't keep up and flooding was surficial. Q: What about the basements? What recourse do residents have to address this issue? AK: We continue to encourage residents to call (419-627-5829 7 a.m. to 3 p.m. Mondays through Fridays or 419-627-5761 anytime after this time frame) and let us know if they have had a backup so we can continue to track and prioritize locations as we continue to implement sewer separation, lift station improvement, sewer lining and other projects throughout the neighborhoods. Additionally, we can discuss with the property owner other options that exist to help reduce the possibility of basement backups. Q: What about the city sewer plant? With this record rainfall, is it overflowing sewage directly into the bay because it might not be able to handle so much in so little time? AK: The water pollution control overflow listed in our permit was activated as a result of this rain event. Editor's note: This means overflow sewage from the combined sewers went into the water. I would guess that an overflow event would have occurred in most if not all communities that have permitted combined sewer overflows if they had received this sort of event. As stated earlier, engineering principles many decades ago were different than today. They installed small combined sewers and added overflows that would activate at a much more regular basis. The city has gone to great lengths since the early 2000s to reduce overflow volumes to the point where well over 90% is captured and treated at the wastewater treatment plant. Editor's note: Many pipes in Erie County, such as in Sandusky and Perkins Township, ultimately lead to the city's wastewater/sewer treatment plant on Harrison Street. Q: Has an overflow situation like this occurred before? AK: In 2022, there were 13 overflow events that occurred. Details of each are provided to Ohio EPA and are updated on the City's website once information is gathered. Q: Right now, the city is moving forward with a $33.5 million project to make Sandusky more environmentally friendly, which does involve reducing how often overflows happen in homes and Lake Erie. When complete, which should occur in spring 2025, will this eliminate sewer overflows? AK: The 16-million-gallon-per-day high-rate treatment that is being added to the existing water pollution control/wastewater treatment plant (on Harrison Street) will not eliminate overflows entirely but is designed to capture and treat additional water that enters the plant. It will not be designed to eliminate overflows but to minimize future overflows. It is important to emphasize that this addition to the plant will treat water entering the facility, not necessarily transport more water to the plant. This is the reason we have been doing so many projects over the past 10 years. For example, we have: • Improved every lift station in the city since 2013 through repairs, replacement, additions and/or upgrades in capacity • Added a new stormwater lift station on the west end bringing our total number to 17, five are dedicated storm • Lined miles of sewers in the neighborhoods where inflow and infiltration was known • Cleaned the interceptor and various other sewers • Eliminated roots in older neighborhoods • Separated sewers on Shoreline Drive, Meigs Street and, soon, Warren Street • Installed backflow devices, where the bay backed into the system, during high lake levels • Expanded the grit tanks at the water pollution control plant • Eliminated flooding on Foxborough Circle • Constructed small connections like at Decatur and Monroe streets through Central Park • Dverted flows where capacities would allow • Developed a green infrastructure program • Increased our routine televising, cleaning, and maintenance throughout the city • Investigated and eliminated significant volumes of inflow and infiltration in public sewers We also have several other future projects in the capital plan, like three sewer separation projects on Monroe Street between Central Park and Cold Creek, that will provide more available capacity within existing sewers in those neighborhoods. I actually had one employee say that they couldn't believe how bad it would have been in certain neighborhoods throughout the city if we hadn't done all of the work we had. Q: What else is the city doing to help residents with flooded basements? AK: Additionally, we have created the utility health and safety grant program that provides an opportunity for residents to improve their private laterals, which are the connections on private property from the house to the sewer main. Depending on many factors, such as age and material of those laterals as well as vegetation in the yard, a large portion of those laterals are leaking groundwater into the public sewer system overwhelming them and reducing their available capacity to handle the needed rain surcharge. Since repairing all of the laterals in a given sewer shed would create a huge impact on the sewer system, the city has created a program to pay a large amount of the repair/replacement of that infrastructure. This is a successful great program that many residents have taken advantage of and I'm not sure if it exists anywhere else.