The Hidden Risk Beneath Every Project: Why Subsurface Utility Engineering Matters More Than Ever
By Rusty Steel
As civil infrastructure ages and urban corridors become increasingly congested, the importance of accurately identifying and documenting buried utilities has never been greater. Subsurface Utility Engineering (SUE) has emerged as a structured, data-driven process for reducing conflicts, improving design quality, and preventing costly construction delays. Guided by the ASCE 38-22 Standard, SUE provides a framework for evaluating the reliability of utility information and clearly communicating confidence levels to designers, owners, and contractors. This article outlines the four SUE Quality Levels, explains the technology and methods behind SUE investigations, and highlights cost-benefit findings and real-world lessons learned.
ASCE 38-22 and the Purpose of SUE
ASCE 38-22 is the Standard Guideline for Investigating and Documenting Existing Utilities, as published by the American Society of Civil Engineers. In it, SUE is defined as the investigation, analysis, and documentation of existing utility networks to support responsible design. The standard evolved in response to decades of unpredictable construction risks caused by inaccurate or incomplete utility records. By establishing consistent terminology, data acquisition methods, and deliverable expectations, ASCE 38-22 helps project teams make informed decisions and reduce uncertainty. At its core, SUE focuses on risk: understanding what is known, what is unknown, and where further investigation is warranted.
SUE Quality Levels
Quality Level D — Utility Records Research
Quality Level D is the most basic form of subsurface utility information. It is derived entirely from existing utility records, as-builts, and historical documentation. QL-D provides designers with a preliminary understanding of utility congestion and possible conflicts but carries the highest degree of uncertainty. Records may be outdated, incomplete, or inaccurate. While QL-D is valuable for early route selection and concept planning, reliance on this information alone exposes projects to significant risk later in design and construction.
Quality Level C — Surface Feature Survey and Correlation
Quality Level C supplements records research with a field survey of surface-evident utility features such as manholes, valve boxes, fire hydrants, and pedestals. Correlating visible features to utility records helps identify inconsistencies that may require further investigation. Although QL-C improves confidence compared to record-only data, it provides no confirmed subsurface location information. It serves as a necessary bridge between paper records and geophysical investigation.
Quality Level B — Utility Designation, Surveying, and Mapping
Quality Level B is the most frequently requested SUE level for design projects. It involves non-destructive geophysical methods to determine the horizontal alignment of buried utilities so they can be accurately surveyed and mapped. Electromagnetic (EM) locating is the primary method, supplemented by ground-penetrating radar (GPR) where applicable. QL-B helps designers make informed decisions early, reducing the likelihood of conflicts, redesign, and construction delays. Although approximate depths may be inferred, vertical accuracy is still limited without exposure.
QL-B Methods and Limitations
Electromagnetic locating detects conductive or tracer-wire-equipped utilities, providing fast and reliable alignment data in suitable conditions. Ground-penetrating radar proves useful for non-conductive utilities but is highly dependent on soil conditions. Many regions—including large portions of the south-central U.S.—have moderate to low GPR suitability, reducing its effectiveness.
GPR Challenges in our regions-NRCS GPR Suitability Map
Image Credit: Sensors and Software Inc.
QL-B is not without limitations. Water lines often lack tracer wires, and even when installed, wires may be broken or deteriorated. Complex utility corridors, pavement reinforcement, or heavy surface congestion may also obscure signals. Nevertheless, QL-B remains a critical step for improving utility mapping confidence.
Quality Level A — Test Hole Excavation
Quality Level A provides the highest level of accuracy through vacuum-assisted excavation to physically expose utilities. This method confirms both horizontal and vertical position and documents material type, size, condition, and orientation. QL-A removes virtually all positional uncertainty and is typically used at critical crossings, conflict points, or high-risk areas. Although more costly than geophysics, targeted test holes often save orders of magnitude more in avoided delays and redesign.
The Cost of “Good Enough” Data
Field lessons echo the same theme. A local underground utility locator identified marks which missed an active bypass line near a proposed sign foundation until a dedicated SUE sweep uncovered it, avoiding a potentially severe hazard. In another case, three different underground utility locators placed a gas line in three different locations; a single test hole confirmed the true location. Private utility networks around gas stations–storage tanks, product lines, monitoring cables, abandoned or redundant lines–often aren’t marked by local underground utility locators at all, demanding disciplined SUE methods with cautious excavation and specialized investigation.
The Proven ROI
Multiple studies across North America have calculated the return on investment for SUE:
- Purdue/FHWA (1999): 5:1 savings per dollar spent
- University of Toronto (2005): 3.41:1 savings
- PennDOT (2012): 11.39:1 savings across 22 projects
- Louisiana DOTD (2021): 2.73:1 savings
Even the lowest documented value represents a compelling case for integrating SUE early in project development. Beyond direct cost savings, SUE enables safer work environments, fewer emergency shutdowns, and improved relationships with utility owners and contractors.
What different stakeholders should do—now
Private developers & architects. Engage SUE early—well before 30% design—and budget for targeted QL‑A at critical crossings or where record data conflicts with field observations. Integrate SUE outputs directly into your survey base and preliminary models so designers aren’t working from legacy or unverified layers. The goal is to eliminate “version chaos” and ensure that every decision reflects the most reliable underground reality available.
Municipalities. Require ASCE 38‑22 deliverables and quality levels in your scopes. Pair SUE with mobile mapping and GIS so you’re not just solving today’s project, but also building a reusable, authoritative utility dataset for asset management and future work orders. This mindset turns each capital project into a data‑collection opportunity that compounds value citywide.
State DOTs. Standardize SUE expectations across contracts and districts, and align SUE milestones with corridor mapping, right‑of‑way, and constructability reviews. QL‑B across the corridor with targeted QL‑A at interchanges, crossings, and complex utility clusters is a practical playbook that repeatedly delivers measurable savings.
Looking Forward
The future of SUE mirrors trends across the geospatial and civil engineering fields. Emerging developments include:
- Integration with BIM and Digital Twins: Accurate utility data is essential for reliable 3D digital models. QL-B and QL-A data feed directly into digital twins, enabling predictive analytics, lifecycle management, and improved asset planning.
- Improved Geophysics: Advancements in radar processing, AI-driven interpretation, and multisensor fusion will improve detectability in challenging soils.
- Autonomous and Mobile Utility Mapping: As with mobile lidar, mobile utility mapping may incorporate autonomy, allowing rapid corridor scanning and hybrid datasets combining lidar with utility locating inputs.
- Expanding Adoption of ASCE 38-22: Public agencies increasingly require SUE adherence in design contracts. Standardized expectations reduce ambiguity and improve coordination between designers, owners, and contractors.
With proven cost-benefit ratios and a growing emphasis on risk-based design, SUE has become an essential component of modern infrastructure development. Incorporating ASCE 38-22 methodologies early in the project lifecycle leads to better decisions, fewer surprises, and more predictable outcomes. For developers, architects, municipalities, and DOT’s, the most cost-effective move isn’t to react to surprises–its to prevent them early with correct SUE investigation and analysis.