Horizontal Directional Drilling of a New 18-in Siphon Sewer under the Licking River

The purpose of this presentation will be to discuss how the design used an Electrical Resistivity Imaging survey to find a highly feasible bore path under a river for Horizontal Directional Drilling. A recently completed project will be use a case study as well as another project with very similar conditions, but different outcomes due to the different approaches to geotechnical exploration. To reduce annual overflow volume for the Sanitation District No. 1 of Northern Kentucky, a new 18-in gravity siphon sewer was needed to convey flow across (under) the Licking River in Wilder Kentucky. The Licking River is tributary to the Ohio River and located just south of Cincinnati. The width of the river where the new siphon sewer crossing is located is between 300 and 400 feet, depending on the river level. Horizontal Directional Drilling (HDD) was the selected method of construction selected for the new siphon sewer. Since the proposed Licking River Siphon is a gravity system and connects into upstream and downstream sewers, the bore elevations had to be within a rather tight tolerance. From prior experience and challenges with HDD not maintaining line and grade, specifically along a riverbank where cobbles and boulders can often be found, Hazen and Sawyer utilized Electrical Resistivity Imaging (ERI) to find an optimal bore path. Standard split-barrel soil borings and rock cores were also used to calibrate the ERI survey, but they were not solely relied upon to determine the best bore path. Cobble and boulder fields are very hard to identify with only standard soil bores. Another prior HDD project on a very similar river crossing will be discussed where the cobbles and boulders led to construction delays and overruns, until ERI surveying was implemented. This presentation will also discuss other lessons learned related to trenchless and open-cut construction, such as inadvertent returns (frac outs), high river water, HDD tracking systems, production rates in hard rock, bidding document interpretations, USACE permitting, and various other issues. Part of this sewer project was located in a railroad's property which added its own design and construction challenges. The project was successfully completed in 2022 with the HDD being very close to the specified line and grade.