Screening & Comparison Engine

The screening engine compares every analytical result in your imported dataset against one or more selected standard sets. For each analyte result, it finds the applicable standard from your selected standard set(s), compares the result value against the standard value, and classifies the outcome into one of five categories: Exceedance (result exceeds the standard), Compliant (result is at or below the standard), Non-Detect Compliant (result is non-detect and the reporting limit is below the standard), Non-Detect — Cannot Determine (result is non-detect but the reporting limit exceeds the standard), or No Standard Available (no applicable standard exists in the selected set for this analyte).

This five-category classification captures the full reality of environmental data — including the critical 'third state' where a non-detect reporting limit exceeds the standard and compliance cannot be determined. Excel workflows routinely miss this condition, which can result in false compliance conclusions in submitted reports.

Environmental analytical data uses qualifier flags that fundamentally change how a result should be interpreted. LimnaFlow handles each qualifier correctly during screening. U-flagged results (non-detect) are compared by their reporting limit against the standard — if the RL is below the standard, the result is Non-Detect Compliant; if the RL exceeds the standard, it is flagged as a detection limit inadequacy. J-flagged results (estimated, detected but with greater uncertainty) are compared against the standard and classified as 'Estimated Exceedance' if above — distinct from a firm exceedance, with the J qualifier preserved in all output.

R-flagged results (rejected data) are excluded from screening entirely and flagged as 'Rejected — Not Evaluated,' with an alert that rejected data creates a data gap requiring professional judgment. UJ-flagged results (non-detect with estimated detection limit) follow the same logic as U flags with an additional notation about detection limit uncertainty. B-flagged results (blank contamination) are flagged for professional review but not auto-excluded, since blank contamination does not necessarily invalidate the result.

Accurate screening depends on matching the right result to the right standard. LimnaFlow uses CAS number as the primary matching key because it is unambiguous — CAS 79-01-6 is trichloroethylene regardless of how the lab or the standard names it. When CAS numbers are present in both the EDD and the standard database, matching is automatic and exact.

When CAS numbers are missing, secondary matching uses analyte name with fuzzy matching for common name variants. The system recognizes that 'Trichloroethylene,' 'TCE,' and 'Trichloroethene' are the same compound, and that '1,1-Dichloroethylene' and '1,1-DCE' and 'Vinylidene chloride' refer to the same analyte. When name matching is ambiguous — for example, 'Chromium' could mean total chromium or hexavalent chromium — the system flags the match and requires user confirmation before proceeding.

Detection limit adequacy is one of the most commonly overlooked issues in compliance reporting. When a sample is non-detect (U-flagged), it means the analyte was not detected above the laboratory's reporting limit. But if that reporting limit is higher than the applicable standard, you cannot conclude compliance — the analyte could be present at a concentration between zero and the RL, which might exceed the standard.

LimnaFlow flags every instance of detection limit inadequacy with a distinct visual treatment — it is not an exceedance, not compliant, but a third state requiring attention. The engine generates a separate Detection Limit Adequacy summary table listing all analyte/location combinations where compliance cannot be determined, with columns showing the location, analyte, reporting limit, standard value, and the gap between them. This table is a deliverable many project managers require but that Excel workflows rarely produce systematically.

Environmental projects frequently require screening against multiple standard sets simultaneously. A New Jersey groundwater project might need to compare results against NJ GWQS, EPA MCLs, and EPA RSLs. LimnaFlow applies all selected standard sets in parallel and shows every applicable standard for each analyte, highlighting which is most stringent. You see the full regulatory picture in one view instead of running separate comparisons.

The engine automatically converts between units when the result unit differs from the standard unit. Supported conversions include ug/L to mg/L, ppt (ng/L) to ppb (ug/L), ppb to ppm, and pCi/L for radionuclides. When a conversion cannot be performed automatically — for example, between fundamentally different measurement types — the system flags the mismatch and requires manual resolution. Matrix-aware screening ensures the correct standard is applied based on sample matrix: a groundwater sample at a cleanup site uses different standards than a drinking water sample at a public water system.