As sump pumps in the water-logged Amber Meadows neighborhood continue to suck water from basements, the Great Bend City Council Monday night learned that any remedial steps to permanently solve the subdivision’s aquifer flooding would be costly.

“Our job was to formulate a high-level water management plan,” said Josh Golka with the city’s on-call engineering firm Professional Engineering Consultants of Wichita. He was giving a report on the groundwater study of the subdivision.

The up-front capital costs (wells, permits, piping, controls and design) are estimated at $1,088,000. Annual costs (electrical, monthly inspections, permit reporting and repairs) are estimated at $65,125 to keep it going.

In May, vocal Amber Meadows residents complained about the basement flooding caused by heavy rains this spring, calling for the city to respond. A split council approved contracting with PEC for the $25,000 multi-phase study. The first phase included examining data from existing monitoring wells to paint a historical picture of the aquifer, as well as a map of it.

Now, SCS Engineers, groundwater specialists out of Wichita, have completed phase 2 of the study which includes a summary of the fieldwork and the conceptual dewatering plan. PEC brought in SCS to perform the analysis.  

“There were no surprises in the data,” said Kevin Hopkins with SCS.

The second phase proposal suggested five wells to draw down the aquifer and keep it down below the level of area basements. The water would be pumped via subterranean pipes into Veterans Memorial Lake.

The proposal

As documented in phase one, groundwater elevations in the Great Bend area have been increasing over the past several years. Record precipitation in late 2018 and the first half of 2019 further increased groundwater elevations, resulting in basement flooding throughout the subdivision, the phase one report notes.

“The second phase consisted of data collection efforts on the aquifer’s characteristics, and establishing a geological and hydraulic model of the neighborhood,” Hopkins said. Lastly, concept costs were developed for the installation of the dewatering system.

SCS engaged Environmental Priority Service based in Salina to conduct the aquifer testing. EPS mobilized in early July and completed five borings, Hopkins said.

These determined soil composition, soil permeability and gradient of the water flow. Findings aligned with the regional groundwater model for Groundwater Management District Number Five and other previous testing.

Once the aquifer’s properties were defined, Hopkins said they constructed an groundwater model to forecast well locations and flow rates.

The idea is to establish a groundwater elevation of 1,847 feet above mean sea level. This represents an elevation approximately 2 feet below basement level.

To accomplish this, the five groundwater extraction wells are required at a depth of 40 to 45 feet below grade. Each well would be pumped at approximately 650 gallons per minute to draw the groundwater level down. Well diameters are projected at 36 inches.

Pumps, equipped with variable speed drives, are anticipated to have a 15 horsepower rating. The cost estimate was for running the pumps four months out of the year, but that number could go down in a dry year.

The discharge is routed via subsurface piping to Veterans Memorial Lake.

Questions

Some on the council questioned pumping the water into Vets Lake. They wondered if the lake would continually put pressure on the groundwater, exacerbating the problem, or by depositing more water there would diminish the park’s usability. 

There is a chance of recirculating the water, Golka said. But, most of the trouble faced by homeowners comes from beyond the city limits, not the lake.

And, Golka said, this was a very preliminary proposal. Other possibilities and downstream impacts would be studied prior to moving forward.

But, he said this is a baseline cost, meaning the Veterans Lake idea is the least expensive option. Other possibilities, such as pumping the water to the Arkansas River, would be much more expensive.

Golka also noted that this covers only the Amber Meadows addition. Although the cost gives some idea of what the costs would be elsewhere in Great Bend, soil conditions vary so much it is hard to make a comparison.