Methodology and data sources for wastewater treatment plant compliance

Where the data comes from

Every figure on this site is loaded from U.S. EPA ECHO / ICIS-NPDES public downloads: facility and permit records, permit limits, discharge monitoring reports (DMRs) and effluent violations. Values are reproduced exactly as EPA published them. Nothing is modelled, estimated, or generated.

Which plants are included

The map shows municipal/public wastewater treatment facilities that hold an individual NPDES permit (NPD) and have current or recent EPA ICIS-NPDES monitoring data. For California, a facility is included when either:

EPA identifies it as a POTW; or
EPA does not flag it POTW, but the EPA data itself shows strong treatment-plant evidence: a sewerage industry code (SIC 4952, 4911 or 4959) together with usable permit limits, reported discharge monitoring results, at least one permitted outfall and a reported design flow.

The current map excludes:

terminated or retired permits with no monitoring reported in the last five years;
administrative and sewer-bypass-only records with no design flow, no limits and no reported monitoring;
records that are not wastewater treatment (for example industrial dischargers).

The rule is deterministic and versioned: it is applied from the EPA data on every refresh, not hand-curated plant by plant. Historical permit records remain in the underlying source data even when they are not shown on the current statewide map; a direct link to such a record opens it labelled as a historical / inactive permit record and it is excluded from current counts and statewide figures. A small number of borderline facilities remain flagged for review internally and are not published.

Texas coverage is built from the same EPA sources using EPA's own POTW identification.

How compliance status is derived

In California, status describes the physical wastewater treatment plant: it is derived only from violation records on monitoring points attributed to that plant. Records on a shared or common regional outfall are shown on the plant page for context and are never counted as any single plant's violations. In Texas, status still describes the NPDES-permitted facility.

Status is based only on the presence of EPA effluent violation records inside the selected period:

Violation reported — EPA holds at least one effluent violation record.
No violation identified — DMRs exist for the period and EPA identified no effluent violation. This is not a clean bill of health.
Insufficient data — no DMRs in the period, so no statement is made.

Violations are never inferred from reported values. If EPA did not flag it, this site does not call it a violation.

How reported values are compared with limits

DMR values and permit limits are compared only inside a single measurement series: the same outfall, monitoring location, statistical base (for example monthly average versus instantaneous maximum), EPA standard unit, and limit-value type. Series are never merged, because a monthly average in mg/L and a daily maximum mass loading are different quantities.

Percent of limit is shown only where both values exist in the same standard unit and the limit is an upper bound. ICIS minimum limits (limit value type C1/Q1) are excluded from percent-of-limit, since exceeding a minimum is compliant.

Missing values and no-data indicators

Where EPA holds a monitoring period with no numeric result, the reason is shown as reported (a no-data indicator, for example "no discharge" or "below detection limit"). Blank fields are labelled "Not reported" and never rendered as zero.

Map placement and periods

California markers are physical wastewater treatment plants: one marker per plant, however many NPDES permits or shared regional outfalls it discharges through. Permit limits, discharge monitoring reports and effluent violations remain EPA records held against the NPDES permits underneath, and each plant page lists those discharge relationships and the monitoring points attributed to the plant, to a shared outfall, or to an influent / internal point. Plants are published only where the identity record has been confirmed; plant coordinates are used, and a plant with no reliable plant-specific coordinate is listed below the map instead of being placed at a regional outfall. Marker colour shows EPA-reported status and marker size shows the plant's design capacity. Texas is published at the NPDES facility grain.

Markers use EPA-reported facility coordinates, falling back to a permitted-feature (outfall) coordinate where the facility coordinate is missing; the source of each coordinate is stated on the plant page. Plants with neither are listed below the map and remain fully searchable.

Periods are anchored on the latest complete monitoring month in the loaded data, so a partially reported current month does not make plants look unmonitored.

Statewide Infrastructure Intelligence

Every statewide figure counts EPA-reported records for the plants currently selected by the filters, over the selected period. Nothing is scored, graded, weighted or ranked against a standard we invented.

Monitoring and reporting frequency differs from permit to permit, so a plant with more reported violation records is not necessarily performing worse than a plant with fewer. Lists ordered by record count are ordered by that count alone, and shares always show their denominator (for example, 6 of 24 plants).

“Recurring parameter patterns” means EPA recorded three or more effluent violations for the same parameter at the same plant within the selected period. It describes the records only and does not identify a cause.

Permit-limit proximity bands use only comparable pairs: the reported value and the applicable limit must share the same outfall, monitoring location, statistical basis and EPA standard unit. Minimum limits (limit value types C1 and Q1) and records with a no-data indicator are excluded. A measurement at 90–100% of an upper limit stayed within the permitted value, and a measurement at or above a limit is only shown as a violation when EPA recorded one.

Effluent violation records are published on a lag, so recent months can show fewer violations simply because EPA has not yet posted them.

What this site is not

This is an independent analysis of public records, not affiliated with or endorsed by the U.S. EPA, the State Water Resources Control Board, or any permittee. It is not a regulatory compliance determination and should not be used as one. For the authoritative record, follow the EPA ECHO links on each plant page.

Back to the California wastewater treatment plant compliance map