Methodology and data sources
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 first release covers California only, and only wastewater treatment plants operating under individual NPDES permits. A plant is included when the latest version of its permit is an individual permit (NPD) and EPA classifies the facility as a POTW. Facilities that are not flagged POTW but carry primary SIC 4952 (sewerage systems) are captured as candidates and marked for review; they appear publicly only once reviewed. The rule is deliberately conservative: a plant EPA does not clearly identify as municipal wastewater treatment is left out rather than guessed in.
How compliance status is derived
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
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.