Pennsylvania DEP
Pennsylvania environmental lab accreditation, DEP and Chapter 252.
Who needs DEP accreditation, how the state and NELAP pathways differ, how out-of-state labs qualify, and the initial calibration criteria written into Pennsylvania’s code.
At a glance
How environmental lab accreditation works in Pennsylvania.
The Pennsylvania Department of Environmental Protection’s Bureau of Laboratories accredits labs under the Environmental Laboratory Accreditation Act. DEP is a NELAP accreditation body, and it also runs a state pathway under the same chapter of the code.
NELAP accreditation body
- Program
- Laboratory Accreditation Program, Bureau of Laboratories, Pennsylvania Department of Environmental Protection
- Legal basis
- Environmental Laboratory Accreditation Act, 27 Pa.C.S. Chapter 41; 25 Pa. Code Chapter 252, Environmental Laboratory Accreditation
- Two pathways
- State accreditation under Chapter 252, or NELAP accreditation, where applicants must also meet the current NELAC or TNI standard (25 Pa. Code 252.5). TNI’s directory lists DEP as accrediting to the 2016 TNI standard.
- Who needs it
- Labs testing drinking water, non-potable water, or solid and chemical materials for compliance with Pennsylvania environmental statutes, including the Clean Streams Law, the Safe Drinking Water Act, the Solid Waste Management Act and Act 2 Land Recycling
- Exclusions and by-rule
- Some storage tank testing, and testing of landfill cover soils and liners, is excluded (252.3). Certain simple tests, such as pH, dissolved oxygen, turbidity and residual disinfectant, can be accredited by rule for registered water, wastewater and industrial labs (252.6).
- Fields
- Drinking water, non-potable water, and solid and chemical materials, across chemistry, toxicity, microbiology and radiochemistry
- Out-of-state labs
- Primary or secondary accreditation (252.205). Secondary accreditation is based on a primary NELAP accreditation, or on a substantially equivalent program in the lab’s home state.
The accreditation cycle
The Pennsylvania accreditation cycle.
The steps below summarize 25 Pa. Code Chapter 252. NELAP labs also follow the TNI standard’s requirements for assessment and PT.
-
Apply by field
Apply for the fields of accreditation your lab reports, under the state or NELAP pathway.
-
Annual renewal
Renewal applications are due every year, at least 60 days before the certificate expires (252.203).
-
Proficiency testing
At least one PT study per accredited field every 12 months, from a DEP-approved provider, with results reported directly to DEP (252.501).
-
On-site assessment
Required before primary accreditation, and DEP may conduct announced or unannounced assessments to verify compliance (252.601).
Initial calibration
What auditors check in your initial calibrations.
Pennsylvania writes initial calibration acceptance criteria directly into its code. Where your method does not set its own, these are the numbers a DEP assessor will hold you to.
A range that brackets what you report
The lowest standard should sit at or below your reporting limit and the highest at or above the top concentration you report. Results outside the calibrated range need to be qualified.
Error at the low end, not r² alone
A correlation coefficient of 0.999 can still hide a low standard that back-calculates 30 percent off. Auditors look at relative error, especially at the lowest levels.
Records that rebuild the curve
Raw responses, the model and weighting used, any excluded points with the reason, and the verification that followed. An auditor should be able to reconstruct every initial calibration from the record.
Second source, and criteria in the code
25 Pa. Code 252.402 requires that “initial calibrations shall be verified with a standard obtained from a second manufacturer,” and sets RSD, r² and minimum standard criteria for each curve type.
Source: 25 Pa. Code 252.402
252.402 sets less than 20 percent RSD for average response factors, r² of 0.99 for linear curves, and 0.999 for nonlinear curves with at least six standards. It also requires a calibration verification standard at the beginning and end of each analysis day, except that internal standard methods need no end-of-day standard unless the method requires one.
Self-check
Are your initial calibrations ready for a Pennsylvania assessment?
Tick what your lab could show an auditor today. Nothing you select is saved or sent anywhere.
6Checks to work through
Select each item your lab could show an auditor today.
A self-assessment to help you prepare, not a compliance determination.
Pennsylvania specifics
The criteria are in the code, so the evidence has to be too.
Many programs leave calibration acceptance entirely to the method. Pennsylvania’s chemistry QC section sets defaults of its own: an RSD limit for response factor calibrations, r² thresholds that tighten for nonlinear fits, a six standard minimum for nonlinear curves, verification with a standard from a second manufacturer, and daily verification standards.
Those criteria are a floor, not a finish line. A nonlinear curve can clear 0.999 and still miss the lowest standard badly, because an unweighted r² is dominated by the high end of the range. The record still has to show the curve is accurate where your low-level results sit.
DEP is proposing higher program fees through rulemaking 7-578. The Environmental Quality Board approved the proposed rule in September 2025, and it was published for comment on November 1, 2025. A final rule had not been submitted as of October 2026.
How WLTR helps
Calibration evidence ready for a DEP assessment.
WLTR independently reviews the calibration your instrument software produced. Your analyst still makes the final call. What changes is that the evidence is complete, consistent across analysts, and ready before the auditor asks for it.
- Each analyte reviewed one at a time in the instrument software.
- The model and weighting are whatever the batch was processed with.
- r² is the number most people look at, even though it does not measure error at the low end.
- QA signs off without an independent check on the curve.
- Every analyte and every candidate model side by side in the Calibration Intelligence dashboard.
- Diagnostics run automatically and the best fit curve is identified, with the reasons recorded.
- Relative error at every level, including the lowest standard, shown on one screen.
- A traceable record your QA manager can review, sign and hand to a DEP assessor.
See how your curves measure against Chapter 252 and against every candidate model, with the low end on the same screen.
Questions
Pennsylvania accreditation FAQs
Is Pennsylvania a NELAP state?
Yes. Pennsylvania DEP is a NELAP-recognized accreditation body. It also runs a state accreditation pathway under 25 Pa. Code Chapter 252.
What are Pennsylvania’s initial calibration criteria?
25 Pa. Code 252.402 sets less than 20 percent RSD for average response factors, r² of 0.99 for linear curves, and 0.999 for nonlinear curves with at least six standards, and requires the initial calibration to be verified with a standard from a second manufacturer.
How often must a Pennsylvania lab renew accreditation?
Every year. Renewal applications are due at least 60 days before the certificate expires, and labs analyze at least one PT study per accredited field every 12 months.
Can an out-of-state lab be accredited in Pennsylvania?
Yes. Out-of-state labs can apply for primary or secondary accreditation. Secondary accreditation is based on a primary NELAP accreditation or a substantially equivalent home-state program.
Which tests can be accredited by rule?
Certain simple tests, such as pH, dissolved oxygen, turbidity, residual disinfectant and conductivity, for public water supply, wastewater and industrial labs that register with DEP.
Sources
Primary sources for this page.
- Pennsylvania DEP, apply for laboratory accreditation (opens in a new tab)
- 25 Pa. Code Chapter 252 (opens in a new tab)
- IRRC, rulemaking 7-578 (laboratory accreditation fees) (opens in a new tab)
- 25 Pa. Code 252.402, chemistry quality control (opens in a new tab)
- 25 Pa. Code 252.205, out-of-state laboratories (opens in a new tab)
- TNI list of NELAP accreditation bodies (opens in a new tab)
This page summarizes public program information to help labs prepare. Requirements change, and the agency’s current rules and guidance always take precedence. WLTR is not affiliated with or endorsed by the Pennsylvania Department of Environmental Protection. Spot something out of date? Tell us at admin@wltr.tech.
Before your next assessment
See your Pennsylvania ICALs the way an assessor will.
Bring a recent initial calibration. We will walk you through every analyte and candidate model in the Calibration Intelligence dashboard, the best fit, and the record your QA manager would sign.
Request a demoHow the methodology works
Running environmental methods? See how WLTR works for environmental testing labs and water and wastewater utility labs.