Combined sewer overflow: CITY OF CHELSEA, Oct 11, 2026

Ended (as reported) · CITY OF CHELSEA (MassDEP sewage notification portal)

Source: CITY OF CHELSEA (MassDEP sewage notification portal) via MassDEP CSO API behind the portal (eeaonline.eea.state.ma.us/dep/CSOAPI/api/), record 335f9ae5-d8af-48b7-94ef-ffa733ff03fe, published Oct 20, 2026, 6:43 PM EDT, retrieved 2026-11-02 11:54 UTC · notice

Colours no water as of Nov 2, 2026, 6:56 AM EST: the windows on the methods page have passed, or the record has no time to count from.

A report is not a test of the water. See how statuses are worked out.

1. The reported outfall

Outfall reported by CITY OF CHELSEA (MA0101877 outfall CHE008): “NORTHERN EDGE OF GULF BULK OIL STORAGE”. Location: 42.39471, -71.01915, from the state's or EPA's outfall layer.

2. Waters named in the notice

The notice names: “CHELSEA RIVER”. Not placed on a tracked water.

3. Modeled downstream reach

Not modeled: the reach model runs on rivers above the head of tide only.

Source: water outlines from OpenBoatLaunch and OpenStreetMap contributors (ODbL); outfalls from EPA ECHO and the state outfall layers; modeled reaches computed by DirtyWaterWatch from USGS NLDI, NHDPlus and the nearest USGS gauge (Jobson 1996); basemap OpenFreeMap and OpenMapTiles.

Open on the main map

When: three different times

The time of the event, the time the source reported, published or updated it, and the time we fetched it are kept apart. Times are shown in New England time; the record keeps the original offsets.

Started: Oct 11, 2026, 9:30 PM EDT
Ended: Oct 11, 2026, 10:15 PM EDT
Precision: Known to the minute
Reported to the source: not given
Published: Oct 20, 2026, 6:43 PM EDT
Source last updated: not given
We fetched it: 2026-11-02 11:54 UTC

What and how much

Type: Combined sewer overflow
Status in the record: Ended (as reported)
Material: “CSO – UnTreated”
Volume: 48,091 gal (not stated whether estimated or measured)
Volume in the source's words: “48091”

Advice

“Avoid contact with these water bodies for 48 hours after the discharge or overflow ceases due to increased health risks from bacteria and other pollutants. See website for more information on whether specific resource areas, such as bathing beaches, are affected.”
CITY OF CHELSEA (MassDEP sewage notification portal) · 314 CMR 16.04(10)(g)

Advice window: 48 hours
Basis: 314 CMR 16.04(10)(g)

Source and revisions

Source: MassDEP CSO API behind the portal (eeaonline.eea.state.ma.us/dep/CSOAPI/api/)
Record id at the source: 335f9ae5-d8af-48b7-94ef-ffa733ff03fe
Original notice: https://eeaonline.eea.state.ma.us/portal/dep/cso-data-portal/detail…
Revision of: ma-massdep:2c3325e2-e087-4e98-910a-b0f60386e174
Revised by: no later revision

Every field of the record

All fields of event ma-massdep:335f9ae5-d8af-48b7-94ef-ffa733ff03fe
`event_id`	ma-massdep:335f9ae5-d8af-48b7-94ef-ffa733ff03fe
`source_id`	ma-massdep
`source_record_id`	335f9ae5-d8af-48b7-94ef-ffa733ff03fe
`parent_event_id`	ma-massdep:2c3325e2-e087-4e98-910a-b0f60386e174
`event_type`	cso
`status`	ended
`discharger_id`	ma-chelsea
`discharger_name`	CITY OF CHELSEA
`npdes_permit`	MA0101877
`outfall_id`	CHE008
`outfall_name`	NORTHERN EDGE OF GULF BULK OIL STORAGE
`waterbody_text`	CHELSEA RIVER
`water_slugs`	[]
`water_match`	none
`lat`	42.39471
`lon`	-71.019155
`coord_source`	outfall_layer
`coord_precision_m`	null
`started_at`	2026-10-11T21:30:00-04:00
`ended_at`	2026-10-11T22:15:00-04:00
`time_precision`	minute
`reported_at`	null
`published_at`	2026-10-20T18:43:51-04:00
`source_updated_at`	null
`fetched_at`	2026-11-02T11:54:49Z
`material`	CSO – UnTreated
`volume_gal`	48091
`volume_text`	48091
`estimate_flag`	unknown
`authority`	CITY OF CHELSEA (MassDEP sewage notification portal)
`advice_text`	Avoid contact with these water bodies for 48 hours after the discharge or overflow ceases due to increased health risks from bacteria and other pollutants. See website for more information on whether specific resource areas, such as bathing beaches, are affected.
`advice_window_hours`	48
`advice_window_basis`	314 CMR 16.04(10)(g)
`source_url`	https://eeaonline.eea.state.ma.us/portal/dep/cso-data-portal/details/335f9ae5-d8af-48b7-94ef-ffa733ff03fe
`parse_error`	null
`fixture`	false
`file`	events/ma-massdep~3A335f9ae5-d8af-48b7-94ef-ffa733ff03fe.json
`duplicate_of`	null
`placement_note`	null
`unplaced_reason`	null
`set_aside`	null
`superseded`	null
`reach`	null
`reach_band`	null

The source's record (raw)

{
  "incidentId": "335f9ae5-d8af-48b7-94ef-ffa733ff03fe",
  "incidentNumber": "26017868",
  "incidentDate": "2026-10-11T00:00:00",
  "incidentTime": "21:30",
  "amPm": null,
  "reporterClass": "Verified Data Report",
  "eventType": "CSO – UnTreated",
  "permiteeClass": "CSO",
  "permiteeName": "CITY OF CHELSEA",
  "permiteeId": "MA0101877",
  "outfallId": "CHE008",
  "municipality": "CHELSEA",
  "reportingType": null,
  "location": "NORTHERN EDGE OF GULF BULK OIL STORAGE",
  "latitude": null,
  "longitude": null,
  "waterBody": "CHELSEA RIVER",
  "waterBodyDescription": null,
  "volumnOfEvent": "48091",
  "rainfallData": "1.72",
  "hours": "0",
  "minutes": "45",
  "month": null,
  "year": null,
  "additionalInformation": "It was discovered that the activations on 10/11 were in fact just two separate discharges. Work has been done to change the way that the system alerts to better account for conditions like those that caused the confusion in the future.",
  "submittedDate": "2026-10-20T18:43:51.087",
  "parentIncidentId": null,
  "_report_class": "Verified Data Report",
  "_tz_assumed": "America/New_York (portal gives local clock time without zone)",
  "_ended_at_basis": "computed: started_at + verified duration 0 h 45 min (Verified Data Report)",
  "_coords": "MassDEP CSOs layer DEP_OUTFL_ CHE008 (locations are estimates)",
  "_water": {
    "no_slug": [
      "CHELSEA RIVER (Chelsea Creek - no slug)",
      "CHELSEA RIVER (Chelsea Creek - no slug)"
    ]
  },
  "_volume_note": "verified by permittee, reported to MassDEP (metered or modelled not stated)",
  "_advice_source": "required wording of 314 CMR 16.04(10)(g); the permittee's own advisory is only in an attachment the portal will not serve",
  "_link_basis": "same permittee and outfall as notice 26017812; start times 25 min apart"
}

Personal fields (names, emails, phone numbers of staff) are removed from raw records before they are stored.