A Jacksonville Electric Authority work crew takes GPS readings on a water main as it is being installed. By gathering data immediately, as-builts are more accurate. Photos: Reynolds, Smith and Hills Inc.
Internet driving directions are great—when they're right. Much like a mapping program that gives you the wrong driving directions, the privately owned Jacksonville (Fla.) Electric Authority was finding that many of its electric, water, and sewer services were incorrectly mapped.
The authority's Engineering, Construction, and Services (EC&S) department, which manages projects from conception to completion, couldn't close out projects because of delays in preparing as-built plans, leaving a lot of money on the table that could have been used on other projects. As-built plan accuracy was often questionable, and when crews excavated based on these plans, they often ended up digging in the wrong place.
The EC&S department now gathers as-built data during construction, so the authority can update its geographic information system (GIS) frequently and release much-needed funds for projects.The Plan
In January 2006, the authority, together with facilities and infrastructure consulting firm Reynolds, Smith and Hills Inc. (RS&H), crafted a plan to gather data 20 times faster and release money more quickly to the next phase of a project. Many of these projects involve millions of dollars, but unused money from one phase can't be released to the next phase until the as-builts are complete and the project is closed.
In the past, as-built drawings were delivered late, preventing project close-out. Typical close-out periods ran from six to 12 months after the completion of construction. Now, the as-built information is available two to three weeks after construction is complete.
Old as-built drawings also had inaccurate attribute and spatial (horizontal and vertical) data. Construction changes made in the field were often inaccurately reflected on the as-built plans because they were prepared after the utilities were already covered. These inaccuracies weren't discovered until work crews went into the field to make repairs. Crews might excavate a location and hit other utilities or features that were not shown on the as-built plan.
This project spans a 900-square-mile service area, covering more than 80% of all water and sewer customers within Duval County and portions of three surrounding counties. Jacksonville Electric Authority services more than 240,000 water customers with close to 3500 miles of water pipes, and 184,000 sewer customers with 2500 miles of collection pipe.
With the help of RS&H, the authority now collects better as-built data using global positioning systems (GPS) without ever interrupting its employees' regular tasks. A team uses a Trimble GeoXH handheld unit coupled with a Trimble Zephyr antenna to acquire subfoot horizontal accuracy. Data collectors use a digital level to establish the upstream and downstream invert elevations of the storm drainage, sewer mains, and elevation of water mains.Collecting Data
Since the outset of this new process, contractors have been required to install PVC stand pipe markers every 100 feet along the buried water and sewer lines to ensure that the GPS data represents their actual locations. The data collector gathers information on all the mains, valves, fittings, stand pipes, manholes, hydrants, services, and benchmarks. To get accurate information, the data collector stands in each spot for a minimum of 30 seconds at a logging interval of one second. These 30 positions are then averaged for the location of the feature.
In heavy tree canopy or areas with many buildings, the data collector occupies a position longer to ensure accuracy. The data are brought back to the office and post-processed against the National Geodetic Survey's Continuously Operating Reference Stations base data. The GPS data are then exported to GIS shapefiles, where it's checked. Points not meeting the required accuracy are collected again.