Methodology & data sources

Agency: California State Water Resources Control Board

Report: Final 2026 California Integrated Report — Clean Water Act 303(d) List

Dataset: Appendix A — 2026 303(d) List of Impaired Waters

Coverage in this build: 1,679 listed waterbodies, 5,962 listing decisions, 1,669 with official geometry.

• • SMARTS — industrial stormwater permit coverage, monitoring, and reporting.
• • NPDES / CIWQS — permits, violations, and enforcement actions.
• • 303(d) Impaired Waters List — listed pollutants and TMDL status.
• • GIS watershed layers — watershed and receiving-water relationships.

• • Source: SMARTS "Download NOI Data By Regional Board" — TMDL dataset, retrieved per Regional Water Board. Records are keyed on WDID.
• • Every limit value, limit period, exceedance basis, due date, TMDL name, and receiving water name is reproduced exactly as stated by the Water Board. Nothing is restated, rounded, or converted.
• • Only Regions 4 (Los Angeles), 8 (Santa Ana), and 9 (San Diego) currently publish industrial TMDL requirements, so an absent requirement is not evidence that a facility discharges to an unimpaired water.
• • Records whose stated permit ID is blank (permit not yet issued) and lines malformed by an embedded tab are rejected at import and counted, never silently altered.
• • Derived: the parameter is matched to the 303(d) pollutant vocabulary, and the stated receiving-water name is linked to a 2026 303(d) waterbody only on an exact normalized name match. Most stated names are watershed- or reach-level descriptions that do not match a single 303(d) segment, and those are left unlinked rather than fuzzily matched.
• • No comparison is made between reported monitoring results and stated TMDL limits. The application makes no exceedance, violation, Level 1 / Level 2, or compliance determination.

• • Rulebook: the Numeric Action Levels of the Industrial General Permit are transcribed from the adopted Orders — Order 2014-0057-DWQ (effective 1 July 2015) and its 2018 amendment — and stored as versioned rules with effective dates, thresholds, units, averaging basis, exceedance basis, and the source section for each parameter. Order 97-03-DWQ, in effect before 1 July 2015, adopted no NALs and no comparison is made for reporting years it governed.
• • Reporting year: the permit reporting cycle of 1 July – 30 June. Each year is evaluated against the permit version in effect for that year.
• • Eligibility: only numeric analytical results from permitted discharge locations, in units convertible to the NAL units, and for parameters with an adopted NAL. Every excluded sample is counted and given a machine-readable reason (no NAL for the parameter, incompatible units, non-effluent sampling location, no numeric result) rather than being dropped silently.
• • Annual NALs are compared against the arithmetic average of eligible results for the reporting year, with non-detects treated as zero. Instantaneous maximum NALs (total suspended solids, oil and grease, pH) are exceeded when two or more eligible results in the reporting year fall outside the level; pH is a range (6.0 – 9.0), not a maximum.
• • Every calculated figure is published with its inputs: eligible sample count, excluded sample count, non-detects counted as zero, samples above the threshold, applicable threshold and units, calculation method, ruleset version and calculation version.
• • An NAL exceedance is a permit-defined condition that triggers Exceedance Response Actions. It is not a violation, an enforcement action, a Level 1 / Level 2 determination, or any Water Board compliance finding, and the application makes none of those claims.
• • Pollutant overlap between an NAL exceedance and a 303(d) listing for the same pollutant is informational co-occurrence over a derived spatial association. It is not evidence of causation or contribution.

• • Confirmed receiving water — the permit record names the receiving waterbody.
• • Hydrologically associated — the facility sits in the same watershed as the impaired segment.
• • Nearby — spatial proximity only; no established discharge pathway.

Data freshness: checking…

• • Monthly cadence. Each source system is re-checked about once a month. These are regulatory datasets that change on the order of weeks to years, so a faster cadence would add load to State systems without improving the record.
• • Incremental, never destructive. Refreshes merge on stable official identifiers — WDID for permits, monitoring and TMDL records, WBID for impaired segments. Unchanged records keep their original values and their first-seen date; records that disappear from a source are retired, not deleted. The full historical backfill is never repeated.
• • Published cycles stay fixed. The Final 2026 California Integrated Report is a published cycle. The monthly job checks whether the State Water Resources Control Board has published a newer cycle; when it has not, the 2026 import date correctly stays where it is.
• • Derived intelligence recalculates only what changed. New or corrected monitoring results are compared against the applicable versioned Industrial General Permit numeric action levels, and only the affected parameter/reporting-year summaries and pollutant overlaps are recomputed.
• • The site stays live during a refresh. The previously validated snapshot continues to serve every page until the new work passes its validation checks. If a refresh cannot complete, the dates above simply stop advancing — nothing is shown half-loaded.

Intelligence indicators summarize publicly available regulatory and geographic information and are not official Water Board compliance determinations.