Newsletter: The Future of Water for the City of Columbus

The city of Columbus public water system provides drinking water to Columbus, Ohio, and 22 communities in the metropolitan region from its three water treatment plants, which have a combined capacity of 240 million gallons per day (mgd). The distribution system, which consists of more than 3,600 miles of waterlines, numerous booster stations and storage tanks, serves approximately 1.1 million people.

In recent years, severe droughts have occurred in many parts of the United States, resulting in the drastic curtail-ment of nonessential water uses and, in some instances, water rationing. Rationing occurred in central Ohio during a severe drought in the Midwest in 1987-88 when Columbus’s largest reservoir (Hoover) was within 50 days of depletion. City leaders realized that additional water supplies were needed, and in 1989 initiated a study called Water Beyond 2000.

The study evaluated several options to supply the additional water needed to meet central Ohio’s growing demands, including on-stream reservoirs, upground reservoirs, quarries and groundwater. Public input was gathered during evaluation of the options. Completed in 1998, the study recommended developing additional groundwater wells for the Parsons Avenue Water Plant, and to construct three upground reservoirs within the Scioto River water-shed to augment the existing O’Shaughnessy and Griggs reservoirs. They serve as the raw water supply for the Dublin Road Water Plant located some 30 miles down-stream. More than 2,500 acres of land in northwest Delaware County needed for the three reservoirs was purchased during the next several years.

In 2005, the city of Columbus selected ms consultants to conduct detailed investigations and prepare a preliminary design report outlining an implementation plan for all three reservoirs, as well as the associated pumping and raw water transmission facilities. ms developed a long-range, multiple-phase strategy to provide an adequate and dependable raw water supply to the city’s Dublin Road Water Plant for current and future use, as completion of all three reservoirs will provide an additional safe yield of at least 53 mgd during a 50-year drought condition.

So what is an “upground” reservoir? It is an engineered water basin, separate, or off-stream of its water source. These reservoirs are typically comprised of earthen embankment walls and a clay-lined bottom, and are classified as a dam by regulators.

Unlike on-stream reservoirs which receive runoff from an upstream watershed, water must be pumped from a nearby river and directed to an upground reservoir. Water stored in the reservoir is then released for use during drought or prolonged dry periods.

When sizing the reservoirs for Columbus, the safe yield of the existing water supplies had to be evaluated.  The city has developed its water supplies using the concept that the 1:50 safe yield, or the available water from water sources during a 50 year drought, be adequate to meet or exceed projected potable water demands.

A major benefit of this project is that it will assist another major water utility north of Columbus. During a prior settlement agreement regarding the issue of water boundaries, it was decided that the upground reservoirs would also support the Del-Co Water Company, Inc., which supplies water to much of Delaware County. Under this settlement, Del-Co is participating in the cost of construction and operations.

Construction began on the first reservoir (known as R-2) in May 2011. R-2 has a footprint of 850 acres and will impound more than 9.3 billion gallons of water at the normal pool. When all three reservoirs are completed they will hold approximately 18.3 billion gallons.

The embankment that forms R-2 is about five miles in length and ranges in height from 35-45 feet. When filled with water, its size and unique design will make it the largest single upground reservoir Ohio, and the largest synthetically lined reservoir in the United States.

Due to the presence of shallow sand and gravel deposits overlying karst limestone geology and high groundwater in the area, the reservoir bottom was constructed using 37 million square feet of a polypropylene geomembrane overlying 18 inches of Compacted Clay Liner, and protected with geotextile and 18 inches of cover soil. This composite bottom liner design will result in negligible seepage of stored water into the underlying karst limestone beneath the reservoir, which minimizes the potential for formation of sinkholes or cavities in this type of geology.

It was anticipated that dewatering activities required during the liner installation would lower groundwater levels for extended periods well beyond the project work limits, and such conditions could adversely affect nearby residential and agricultural water supplies. The project team identified and assisted in the execution of a multi-step, proactive program to address this issue.

First, a pre-construction assessment program was initiated during the design phase, with more than 260 residential and agricul-tural wells surveyed to determine the condition, quantity and quality of the water in those wells before construction dewatering began. Local residents were provided with a city representative to contact should they experience operational problems with their well during construction. Once contacted by a homeowner, the representative conducted a site visit to investigate current well condition and water levels in relation to the pre-construction assessment information. When data indicated that the dewatering activities caused operational problems or a well to go dry, the city directed the construction contractor to remedy the impact by providing temporary, potable water to the affected residence, modifying the existing well or drilling a new well.

A drainage system utilizing two-stage ditches with underlying storm sewers was installed around the perim-eter of the reservoir to intercept numerous agricultural field tiles and direct surface runoff around the reservoir embankments. The perimeter ditch system not only preserved existing surface and subsurface drainage patterns, but also qualified as a post-construction stormwater best management practice, since it will act as a vegetated filter – reducing the amount of total suspended solids carried by the stormwater flow and ultimately discharged to the Scioto River.

The need to relocate Ottawa Creek was eliminated by adjusting the configuration of the northern embankment. Some wetlands present on the site could not be avoided and the city was obligated to mitigate for those wetlands.

Although nearby state routes were designed to accommodate them, the significant number of vehicles carrying heavy loads needed for construction had a high probability of damaging most county or township roads in the project area. So, a limited number of these roadways were established as dedicated haul routes for use by construction vehicles – not only for the reservoir, but also for the new pump station on the Scioto River nearly four miles away and a 72–inch raw water transmission main linking them. The existing pavement was strengthened through pavement reclamation or reconstruction before construction vehicles began using them, and will receive new asphalt at the conclusion of the project. Contractors were penalized when drivers delivering products or materials to/from the project work sites were observed traveling on roadways not authorized as dedicated haul routes.

The second component of the initial project was construction of a new intake and pump station adjacent to the Scioto River to divert water from the river to R-2 and the other reservoirs when they are constructed. The pump station is equipped with four vertical turbine style pumps that can each deliver 40 million gallons of water per day to fill the reservoirs. To build up a pool of water in the Scioto River, intake and wet well to provide adequate pump submergence, a 152-foot inflatable weir was designed and constructed in the Scioto River. The weir will be inflated during times of high flow so the pump station can be activated to fill the upground reservoir, and will remain deflated at other times and lay flat in the bottom of the river.

Federal and state regulators required that no construction occur within the Scioto River during spawning season – April 15 to June 30 – and that operation of the proposed inflatable weir be limited to two successive weeks during this period. Additionally, an upstream low-head dam on the river near Prospect, Ohio, was removed as a mitigation condition to facilitate construction of the new inflatable weir. The design solutions implemented in response to these regulatory requirements will not only improve in-stream water quality, but also minimize impacts to aquatic organisms and allow migration upstream to foster redevelopment of species in the upper reaches of the Scioto River.

Even though public access and recreational activities such as fishing and boating will not be permitted on R-2 because of the risk of potential damage to the liner system, recreational opportunities are included as part of the overall project. This includes construction of an adjacent park in conjunction with Preservation Parks of Delaware County that will provide passive recreational activities such as walking, running, biking, picnicking and a natural playground area for children. Additionally, a portage was built that can be used by canoeists when the inflatable weir is raised, and a new canoe access point was constructed downstream of the weir near the confluence of Ottawa Creek and the Scioto River.

Currently, local fire departments in the area must withdraw water from the Scioto River or nearby ponds to fill their tanker trucks during fire runs. The Thompson Township Trustees asked if the local fire departments could access stored water in the reservoirs to improve response time and refill tanker trucks.

In response, several non-potable hydrants with appropriate hose connections will be installed along the Phase 1 raw water pipeline that can be accessed by local fire departments.

The successful implementation of these initial projects has been a direct result of the collaboration with our partners and various governmental officials, regulators and affected/interested residents, which began at the inception of the project and have continued throughout the construction phase.

Key partners in this project include the adjacent counties of Union, Marion and Delaware, the Ohio Department of Natural Resources (ODNR) and the state legislature, which allowed this project to pilot new bonding requirements and inspection costs for large upground reservoirs. This reduced the cost of the project and provided inspection funds for ODNR.

At the conclusion of this project, Columbus and central Ohio will have a new water supply to satisfy the region’s thirst for drinking water for many decades to come.

You can read more about the ms team’s involvement in the project here.

For more information about this project, contact Ken Ricker at 614.898.7100 or by email.