Wednesday, August 14, 2013
Sarah Ferdico, Communications
Getting water to cities has undergone a massive design shift since water collection began in the first part of the 20th century. Early methods consisted of constructing vertical wells to collect water and pumping it to water treatment plants for residents’ uses.
Today, Olsson engineers are working with improved technology and design techniques to construct horizontal wells, which can collect water over a larger area during dry summer months. The Olsson team is currently applying this design with the Lincoln Water System (LWS) by constructing as many as two new horizontal collector wells to meet Lincoln’s water demands.
The City of Lincoln’s water supply system currently consists of 40 vertical wells and two horizontal collector wells that are situated along the Platte River. A horizontal collector well consists of a large-diameter caisson, which is a watertight, vertical retaining structure. At the bottom of the caisson, horizontal laterals are extended out into the aquifer. The laterals include sections of slotted screened pipe that allow water to transfer to the caisson. Large, vertical turbine pumps situated in the bottom of the caisson pump the water into a raw water transmission main where it is conveyed to the water treatment plant in Ashland, Nebraska.
LWS’ vertical wells date back to the 1930s. The horizontal collector wells were constructed in the early 1990s when Olsson teamed with Black and Veatch to study and design two horizontal collector wells, some of the first in the region.
LWS’ water supply relies on the Platte River to recharge the aquifer as groundwater is drawn out. During normal flows in the Platte River, the current well field can provide adequate capacity to meet peak day customer demands. However, in dry conditions and summer months when the river flow is low and the system experiences peak customer demands, the aquifer can struggle to satisfy demand. This results in short-term, reduced groundwater levels.
As a result of the drought in 2012 and conditions that drew down the aquifer near the vertical wells, LWS determined it was necessary to move forward with designing and constructing new horizontal collector wells. The proposed new horizontal collector wells will be situated downstream of the current vertical wells and horizontal collector wells. They will allow the water system to draw from a larger area within the aquifer, resulting in less drawdown of the aquifer in dry months and during peak demands and creating a more reliable system.
Olsson and Black & Veatch have teamed again to design the new collector wells.
Due to the urgent need for the additional supply, the project timeline has been substantially expedited. The major hurdle to move the horizontal wells to construction is obtaining all of the necessary permits. For this project, Olsson has provided environmental permitting, coordinated with the Nebraska Department of Health and Human Services for approval of the well sites, and designed the temporary and permanent access roads and water transmission mains that range in size from 30 inches in diameter to 54 inches in diameter. Olsson also provided the instrumentation and controls design and will provide on-site observation during construction.
Work commenced in March 2013, and the project has been designed in segments. The caisson construction was bid in June, and construction is currently under way. The well house, access roads, and water transmission mains have been designed, and bids will open the first week of September. The intent is for the first well will be in service by June 2014. Over the course of the summer, the city will decide if it will construct the second well, which would be available for use in 2015.