Sustainable Replacement of Aging Drinking Water Lines Using Horizontal Directional Drilling Technology

Background: Due to deterioration from aging, the City of Yuma, Arizona undertook the replacement of approximately 5800 L.F. (1767 m) of existing aging and undersized asbestos cement water lines in the vicinity of the downtown core to reduce maintenance and repairs and improve water service levels. Installed between 1938 and 1940, six line segments of existing 2-inch (50 mm) to 6-inch (150 mm) asbestos cement water lines were replaced by 6-inch (150 mm) diameter PVC pipe. Methods: To study advantages and disadvantages of traditional open-cut construction compared to Horizontal Directional Drilling (HDD), the City separated the project into approximately 2000 L.F. (609 m) of HDD and 3800 L.F. (1158 m) of open-cut. Analyzing the same project provided an opportunity to study a true head-to-head comparison of the two methods. PVC C900 DR18 was installed using open-cut, while Fusible PVC (FPVC) DR18 was installed by HDD. Data was collected in the field over a twomonth period with factors analyzed including comparison of: (1) environmental impacts; (2) traffic impacts; and (3) productivity. Results: The results found HDD to have inherent advantages in all three areas when compared to traditional open-cut. The HDD option emitted approximately 23% of airborne emissions compared to open cut. Traffic was restricted in the sections involving open-cut construction, while the HDD sections had continuous traffic flow due to the closure of only one lane. HDD achieved an average productivity of 1.91 L.F./min (0.58 m/min) compared to traditional open-cut, which achieved an average productivity of 0.43 L.F./min (0.13 m/min). This translates to HDD achieving a production rate greater than four times that of open-cut. Conclusions: The adoption of trenchless technologies such as HDD will continue to increase as municipalities turn to sustainable solutions for replacing and/or rehabilitating their existing water pipe line infrastructure. HDD has proven to be superior to open-cut construction in environmental, traffic control and productivity. Open Access Received: 31 October 2019 Accepted: 29 May 2020 Published: 04 June 2020 Copyright © 2020 by the author(s). Licensee Hapres, London, United Kingdom. This is an open access article distributed under the terms and conditions of Creative Commons Attribution 4.0 International License. Journal of Sustainability Research 2 of 14 J Sustain Res. 2020;2(3):e200028. https://doi.org/10.20900/jsr20200028

presents information on the specific equipment used on each of the three open-cut sections. The Case 590 Super L excavator used in the project is shown in Figure 2.  involves an initial pilot bore that follows the prescribed design alignment as shown in Figure 3(a). This is followed by a backreaming/pipe installation process in which a reamer is used to enlarge the initial pilot J Sustain Res. 2020;2(3):e200028. https://doi.org/10.20900/jsr20200028 bore to a size of 1.5 times the outside diameter of the product pipe being installed as shown in Figure 3(b). A bentonite-based drilling fluid mixture composed of approximately 97% water is used to facilitate product installation. Installations with surface access are generally installed using a walkover locating systems to track the progress of the drill bit during the pilot bore installation via an electromagnetic signal. For installations beneath waterbodies or with limited surface access, a wireline system such as employed in petroleum exploration is used for locating the drill head. Further information on the state-of-the-art in HDD can be found in [1]. Table 3 presents the information on the equipment used on each of the three sections. The Vermeer D24 × 40A rig used in the project is shown in

Environmental Calculations of Airborne Emissions
An emission calculator tool was developed in MS Excel using Visual Basic coding. E-Calc TM estimates emissions (i.e., hydrocarbons (HC); carbon monoxide (CO); nitrogen oxide (NOx); particulate matter (PM); carbon dioxide (CO2); and sulfur oxide (SOx)) from underground utility projects based on EPA-approved methodology [2]. A comprehensive description of E-Calc TM can be found in [3]. Required input data can be obtained from daily progress reports or productivity estimates, while equipment-specific information should be acquired from the contractor. As with any software tool, the accuracy of output information depends on the accuracy of the input data. The calculator is a proven tool intended for contractors, engineers, and owners to obtain an estimate of the environmental impact of their proposed underground utility project [4,5].
The tool provides a comparison of emissions generated from two possible installation methods with default information available for four typical utility construction methods: (1) horizontal directional drilling; (2) trenchless pipe replacement; (3) trenching; and (4) traditional open-cut. It should be noted that the tool is portable and can be applied to any construction process that incorporates machinery and equipment such as water main replacement technologies studied in this research. This software tool has been used for evaluating numerous trenchless technology options [3][4][5].  The activity rate is a function of the specific activity under consideration. The activity rate determination is based on the emission factor, which was calculated based on the test data ratings. If the emission factor is expressed as the weight of pollutant released for a volume of fuel consumed by the activity, the activity rate should be the measurement of the volume of fuel consumed by that activity [5].
In the case of emission factors expressed in terms of g/hp-hr, the activity needs to be measured in terms of power (hp) consumed and duration (hr.) of the activity that emits the pollutants. If the emission factor is expressed in terms of g/gal, then the activity rate should be the measure of gallons of fuel burned. An example of the summary screen from eCalc TM is shown in Figure 6.

Traffic Impacts
Numerous researchers have cited reduction in traffic impacts as a major benefit of adopting trenchless technologies such as HDD [7][8][9]. Being in a residential neighborhood near the downtown core, it was important to minimize traffic impacts and inconvenience to the local residents. The   In the case of open-cut, this included compaction of the backfill material.
As previously stated, HDD was able to achieve more than four times the productivity rate as traditional open-cut. This may be attributed to the ability of HDD to navigate horizontally once the drill rod is inserted into the ground. Improved accuracy of the tracking equipment and tooling enables for more accurate installation, thereby reducing the likelihood of striking an existing buried utility. Furthermore, the HDD contractor was required to pothole and confirm the depth of all existing utilities that crossed the path of the PVC pipe installation.

DATA AVAILABILITY
The dataset of the study is available from the authors upon reasonable request.

AUTHOR CONTRIBUTIONS
SA and NG designed the study. NG designed/engineered the project. SA performed and oversaw the field data collection and analysis. SA and NG wrote the paper.