Answers to the most common questions from field contractors.
Most EPC pile elevation tolerances are in the range of plus or minus 0.02 ft (approximately 1/4 inch) vertical at the pile cutoff elevation, and plus or minus 0.04 ft horizontal from the design pile center. However, tolerances vary significantly by racking manufacturer and EPC specification. Fixed-tilt systems often allow plus or minus 0.04 ft vertical. Tracker systems (single-axis) typically have tighter tolerances because the tracker drive assembly has less adjustment range. Always confirm the tolerance with the EPC specification document before beginning pile installation, as using the wrong tolerance can result in re-drives after verification.
RTK GPS rovers achieve plus or minus 0.05 ft vertical accuracy under good conditions, which is adequate for EPC tolerances of plus or minus 0.02 ft only with careful setup and verification. Most solar pile verification is done with total stations (plus or minus 0.01 ft) for this reason - the tighter accuracy provides more confidence. If using GPS, use network RTK with a PDOP below 3.0, collect a minimum of 5-second average on each shot, and verify against a known benchmark before and after each session.
A pile outside EPC elevation tolerance requires either re-driving or a formal EPC waiver. Re-drives are documented with three data points: (1) original as-driven elevation and deviation, (2) re-drive action (who authorized, what method), (3) post-re-drive verification elevation. If a re-drive is not practical (concrete is set, adjacent piles would be disturbed), the EPC may issue a waiver for minor deviations if racking adjustment can compensate. Never assume a waiver will be granted - document the failure and request direction from the EPC before proceeding.
A complete EPC as-built package for pile elevation verification includes: pile-by-pile elevation data (pile ID, design elevation, as-driven elevation, deviation, pass/fail), block-by-block conformance summary, tracker row conformance data (if single-axis), re-drive log (pile ID, original deviation, corrective action, post-re-drive elevation), GPS coordinates for each pile, instrument calibration records for the survey equipment used, and field crew certification. Most EPCs also require a summary table showing total piles verified, piles within tolerance, piles requiring re-drives, and final acceptance statement.
Yes. Total stations are widely used for pile elevation verification and are preferred by many EPCs because of their higher accuracy (plus or minus 0.01 ft vs plus or minus 0.05 ft for RTK GPS). The tradeoff is speed - a total station crew can verify 200-400 piles per day compared to 400-800 per day with GPS. For utility-scale solar sites with 50,000+ piles, GPS is usually more practical. For smaller projects or in areas with GPS obstruction (tree lines, ridge topography), a total station is the right choice.
With RTK GPS, a single operator can verify 400-800 piles per day on open flat terrain. With a total station (2-person crew), expect 200-400 piles per day. Terrain and site organization affect productivity significantly - sites where piles are installed in organized grids are faster than sites with irregular layouts. The verification pace must match the installation pace: if the pile driver crew installs 1,000 piles per day, you need GPS verification to keep up and avoid creating a large unverified backlog.
Sitemark exports pile elevation data as PDF (pile-by-pile report, block conformance summary) and CSV (for importing into AutoCAD, Civil 3D, or custom EPC reporting systems). The PDF report format is designed to be attached directly to the EPC as-built submittal package. The CSV export includes all field columns: pile ID, northing, easting, design elevation, as-driven elevation, deviation, pass/fail, and verification date.
Remote solar sites often lack coverage from regional RTK networks (CORS, VRS). Options: (1) VRS network - check if your site is within range of a state or commercial network (most cover rural areas). (2) Single-base RTK - set your own base station over a known control point, broadcast to rover via radio or cellular modem. Typical range 5-15 km. (3) Satellite-based corrections (SBAS, StarFire) - slower convergence time and lower accuracy than network RTK, but no base station required. (4) Cellular modem with IP-based network connection if cellular coverage exists.
A mid-project tolerance change must be documented immediately. Request the updated specification in writing from the EPC. Re-verify any piles that were borderline passing under the old tolerance but would fail under the new tolerance. Document the specification change date and pile IDs affected. Do not assume previously verified piles are still acceptable - EPCs can reject blocks where verification was done under superseded specifications if documentation does not clearly reference the correct version.
Beyond pile elevation, single-axis tracker installations require tracker row conformance verification - confirming that the assembled torque tubes and tracker rows are within acceptable limits for tracker drive alignment. Sitemark logs row-by-row conformance data and generates a block conformance summary showing which rows are within tolerance and which require adjustment before the EPC will approve racking installation to proceed.
EPC-ready as-built packages, real-time pass/fail tracking, and block conformance summaries built for utility-scale solar.
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