Utility Mapping - Quality Level "A"... What is it?
What is Quality Level A (QLA)?
When working with existing subsurface utilities data, QLA provides the highest level of certainty. It is obtained by exposing, surveying, and recording the exact location of a specific subsurface utility, usually at a single point. In order to minimize the potential for utility damage, exposure is typically performed by digging test-holes using vacuum excavation equipment.
QLA is sometimes referred to erroneously by the subsurface utility engineering profession as "locating." Locating describes the act of excavating test holes and exposing a utility for subsequent data collection. QLA is the data derived from a located utility. It includes measuring, recording, depicting, and judging type, function, and other observable and measureable attributes, and correlating them to other available information. In other words, “locating” is the exposure of a utility; collecting and certifying information about that exposed utility leads to QLA data.
Excavation must comply with applicable utility damage prevention laws, permits, and specifications, and must be coordinated with utility and other inspectors, as required. Some municipalities only allow air/vacuum excavation or hand-digging as the exposure method. Water-jet excavation is often prohibited under roadways due to environmental and pavement restoration integrity concerns. The air-vacuum excavation system has been used as a leading method for QLA because of its minimally-intrusive and non-destructive nature.
QLA information may be obtained any time design or planning functions indicate a need for it. It may be more cost effective to perform some tasks leading to QLA attribution before or in parallel with tasks leading to QLD, QLC, or QLB attribution, based upon the project’s requirements and schedule. Sometimes a few early QLA data points during or immediately after QLB, QLC, or QLD mapping can be beneficial for timely decisions on structure placement or types. For example, there are many times very early in design when an early QLA attribute is vital to determine whether a true conflict exists for important structures (e.g., bridges, retaining walls, sound barriers, some storm structures, etc.), since the entire process forward is dependent upon those early decisions.
QLA information is highly accurate. Survey accuracies to obtain it are typically set at 15mm (1/2-inch) vertically, and to project survey standards horizontally (typically the same as for topographical features), although these accuracies and precisions are generally left to the owner to specify in a scope of work. The horizontal and vertical accuracies, if different than specified, should be stated in a Utility Report and on a drawing or map that depicts utility assets, or otherwise included within the documentation that accompanies electronic utility data. In addition to the applicable standard of care and any other additional standards imposed by commercial indemnity clauses, the accuracy of this data is also typically guaranteed by the provider.
Other data typically characterized in conjunction with test-hole excavation include material type, surface elevation, utility size/capacity, outside dimensions and configurations, soil type, and utility condition. QLA data are typically portrayed as a 3-D point location; whereas, QLB, QLC, or QLD horizontal data are line segments.
Differences between depicted QLA data and other quality levels should be resolved. This may require additional surface geophysical searches or depictions of adjacent or nearby data points at lower quality levels. It may require additional QLA data and/or that utilities already depicted at QLD, QLC, or QLB be re-depicted to coincide with the more accurate QLA data.
QLA data means that the professional certifying that data is certain that the data is correct: the owner is correct, the function is correct, the location is correct, the size is correct, the material type is correct; etc. etc.
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