CIPP Pre-Lining Survey: What It Is and How to Document It Right

Before a cured-in-place pipe (CIPP) liner goes into the ground, a pre-lining survey must document the existing pipe conditions. This isn't paperwork for paperwork's sake — it's the baseline record that protects you from disputes, satisfies municipal specs, and proves the pipe was in the documented condition before your crew touched it. Get it wrong, and you're looking at a re-survey demand or a failed inspection sign-off.

What Is CIPP and Why Does the Pre-Lining Survey Matter

Cured-in-place pipe rehabilitation is a trenchless method for repairing deteriorated sewer and drain pipes. A resin-saturated felt tube is inverted or pulled into the existing pipe, then cured (via hot water, steam, or UV light) to form a structurally independent liner inside the host pipe. The result is essentially a new pipe inside the old one — without excavation.

The pre-lining survey is the documented inspection of the host pipe before any rehabilitation work begins. It captures existing conditions — invert elevations, grade, diameter, manhole depths, and observable defects — so the owner, engineer, and inspector can verify the pipe was properly characterized before lining.

Most municipal sewer rehabilitation contracts require a pre-lining survey report as a submittal before work can begin. Skipping it or submitting an incomplete one gets your work order put on hold.

Before any field work begins, use the Pipe Grade Calculator to confirm that the design grade for each pipe segment meets minimum slope requirements. If the design shows a segment at 0.4% on an 8-inch main, that's right at the code minimum — and you'll need precise invert data to confirm the installed pipe can still meet it after lining reduces the effective diameter slightly.

What to Measure on a CIPP Pre-Lining Survey

A complete pre-lining survey captures the following at each manhole and along the pipe run:

Pipe diameter and material. Confirm diameter matches the contract documents. If you're lining what the plans say is an 8-inch VCP main and you find a 10-inch RCP, that needs to go on the record before the liner order is placed.

Upstream and downstream invert elevations. Measure the invert (inside bottom of pipe) at each manhole with a rod and level or laser. These are the reference elevations for calculating grade and verifying the liner is installed at the correct invert.

Grade percentage. Calculated from the invert elevation difference divided by the horizontal run length. Most inspectors want to see this expressed as a percentage and confirmed against the design drawings.

Total fall. The vertical drop from upstream invert to downstream invert across the full pipe segment. Required field in nearly every municipal submittal format.

Manhole conditions. Document manhole frame and cover condition, structure integrity, step condition, inflow and infiltration indicators, and any observable defects at the pipe connections. Photograph each manhole before lining.

Pipe condition notes. Root intrusion, offset joints, cracks, broken sections, or debris blockages — all of these need to be noted. A CIPP liner installed over an unrepaired root ball or a broken lateral connection is a callback waiting to happen.

Common Documentation Failures That Fail Inspection

The most common reason pre-lining survey submittals get kicked back:

Missing invert data. Listing the manhole rim elevation without the invert elevation. Inspectors need the invert — the rim is irrelevant to grade verification.

No benchmark reference. If your elevation data isn't tied to a known benchmark, it's unverifiable. Every set of invert elevations should reference a USGS benchmark or a project-established control point with a published elevation.

Incomplete manhole-to-manhole segment coverage. A survey that covers only the upstream manhole and ignores the intermediate manholes on a multi-segment run will be rejected on most city contracts.

Informal formatting. Handwritten notes or informal tables submitted as PDFs don't match what inspectors are looking for. The submittal should include segment ID, manhole IDs (as-labeled in the field), pipe diameter, pipe material, invert elevations, grade percentage, total fall, date of survey, and field technician name. Every line, labeled.

Missing signature or certification. Many municipal specs require a licensed contractor or supervisor signature on the pre-lining survey document. An unsigned submittal isn't complete.

Field Setup: Shooting Invert Elevations

Accurate invert elevation data is the backbone of the pre-lining survey. Here's the field procedure that produces defensible numbers.

Step 1: Establish a benchmark. Every set of invert elevations should be tied to a recognized benchmark — a USGS monument, a city-established control point, or a project-established temporary benchmark (TBM) with a documented relationship to a published datum. If your elevations aren't tied to a datum, they can't be independently verified.

Step 2: Set up your level and shoot the first manhole. Using a rotating laser or optical level, establish height of instrument (HI) from the benchmark. Then shoot the invert of the upstream manhole. The invert is the inside bottom of the pipe opening — not the manhole rim, not the manhole floor. Measure carefully; rim-to-invert depth can be calculated from the rim elevation minus the depth to invert.

Use the Elevation Calculator to compute your HI and each invert elevation from your rod shots. Enter your benchmark elevation and backsight rod reading to get HI, then compute each manhole invert from the foresight rod readings.

Step 3: Work downstream at standard intervals. For CIPP pre-lining surveys, shoot invert elevations at each manhole and, on accessible runs, at 25-foot intervals. Document:

• Station (distance from upstream manhole)
• Rod reading
• Computed invert elevation
• Cumulative fall from upstream invert
• Grade percentage for each segment

Step 4: Calculate grade per segment. Grade percentage = (upstream invert − downstream invert) ÷ run length × 100. On a 200-foot run with 1.0 foot of fall: 1.0 ÷ 200 × 100 = 0.5% grade. Flag any segment below the project minimum. On most 8-inch sewer rehabilitation contracts, the threshold is 0.40–0.50%.

Step 5: Flag anomalies. Any station where the measured invert is higher than the adjacent upstream station (reverse grade) or where the grade drops below the project minimum needs to be flagged in your report. These are the sections the engineer will scrutinize.

How Sitemark Streamlines Pre-Lining Survey Documentation

Sitemark's MH-to-MH Pipe Run Tool is purpose-built for this workflow. You enter the upstream and downstream manhole IDs and invert elevations, pipe diameter, design grade, and run length — and Sitemark automatically calculates grade percentage, total fall, and design invert at each intermediate station.

As your crew logs actual rod shots at each station, the tool compares as-built elevation to design grade in real time, flagging any deviation beyond your tolerance threshold (0.05 ft is standard for CIPP pre-lining surveys on most city contracts). You know before you leave the site whether the grade documentation is clean.

The pre-lining survey PDF export matches the format most municipal inspectors expect: segment ID, manhole IDs, upstream and downstream inverts, grade percentage, total fall, pipe material and diameter, field technician info, and a grade profile chart. It's generated directly from your field shots — no transcription, no reformatting in Excel Sunday night.

Use Sitemark's CIPP Pre-Lining Survey template — included in the Pro plan. Start your free 14-day trial at sitemark.ai/signup and have your first pre-lining survey report ready before you pull your equipment off site.

Grade Calculations for CIPP: What the Numbers Mean

Understanding the grade numbers in your pre-lining survey prevents costly misinterpretations when the engineer or inspector reviews your data.

Grade percentage is the primary metric. A 0.5% grade means the pipe drops 0.5 feet for every 100 feet of horizontal run, or 0.06 inches per foot. This sounds small, but it's enough for gravity flow in an 8-inch pipe if the pipe is clean and in good condition.

Total fall across the segment is how most engineers verify the overall grade. On a 300-foot segment at 0.5% grade, total fall = 300 × 0.005 = 1.5 feet. If your measured upstream and downstream inverts differ by less than 1.4 feet or more than 1.6 feet, your grade calculation is off — or the pipe has a problem.

Invert comparison to design. The pre-lining survey should compare measured inverts to the original design inverts from the as-built drawings (if available). Discrepancies greater than 0.10 feet indicate either measurement error or that the pipe was installed at a different elevation than designed. Both need to be documented.

For quick calculations in the field, the Pipe Grade Calculator converts between grade percentage, inches-per-foot, and total fall for any run length. Enter your measured invert elevations and run length and it gives you grade percentage instantly — no mental math, no transcription errors.

After the Survey: What a Complete Submittal Looks Like

A pre-lining survey package that passes inspector review on the first submission includes:

1. Cover page — project name, owner, contract number, date of survey, field technician name and signature
2. Benchmark documentation — benchmark ID, published elevation, and method used to establish HI
3. Manhole inventory table — manhole ID, rim elevation, invert elevation, pipe diameter and material at each connection, and observed condition notes
4. Invert elevation table — station, rod reading, computed elevation, design elevation (if available), and variance for each measured point
5. Grade summary table — segment ID, upstream MH, downstream MH, run length, total fall, grade percentage, minimum grade per project spec, and pass/fail for each segment
6. CCTV footage reference — footage file names indexed by segment, with timestamp references to key defects
7. Recommendations — clear list of any segments that require pre-lining repairs, with segment ID and reason

Submitting all of this in a single organized PDF — not a collection of separate files — speeds review significantly. Engineers and inspectors are reviewing multiple projects simultaneously; a well-organized submittal gets reviewed and approved faster than a disorganized one.