How to write a baseline monitoring report under 40 CFR 403.12(b)

Who reads a baseline monitoring report, and what do they decide?

A baseline monitoring report is read by the Control Authority, which is the POTW (publicly owned treatment works) if its pretreatment program has been approved, or the Approval Authority if it has not (40 CFR 403.3(f)). The Approval Authority is the state Director in a state with an approved pretreatment program, otherwise the EPA Regional Administrator (40 CFR 403.3(c)).

The reviewer decides three things from the baseline monitoring report. The first is whether the categorical pretreatment standards are being met on a consistent basis and, if not, whether additional operation and maintenance or pretreatment is required; that is the statement the report must certify (40 CFR 403.12(b)(6)). The second is which limits apply at which sampling point, including any alternative limit from the combined wastestream formula where regulated and other wastewaters mix before treatment (40 CFR 403.6(e)). The third is what the facility's monitoring and control mechanism will require afterwards (inference).

US EPA describes the report as "a one-time report, unless changes in the federal categorical standards require submission of a new or updated BMR" (US EPA, 2011). EPA's 1985 manual on production-based standards says production and flow data in the baseline report should be verified by the Control Authority soon after receipt (US EPA, 1985). Write each number so that a reviewer can trace it to an attachment without calling the plant (inference).

Who must submit a baseline monitoring report and when?

A baseline monitoring report must be submitted by every existing industrial user subject to a categorical pretreatment standard that discharges, or is scheduled to discharge, to a POTW, within 180 days after the standard's effective date (40 CFR 403.12(b), eCFR 2026). If the user asked for a category determination under 40 CFR 403.6(a)(4), the clock runs from the final administrative decision instead, whichever date is later (40 CFR 403.12(b)).

New sources, and sources that become industrial users after a categorical standard is promulgated, file at least 90 days before discharge begins (40 CFR 403.12(b)). Their report contains items (b)(1) to (b)(5) only; a new source also describes the pretreatment method it intends to use and gives estimates for the flow and pollutant items (40 CFR 403.12(b)). EPA explains that compliance from the first day of discharge is expected (US EPA, 2011).

Where the POTW performs the required sampling and analysis in lieu of the user, the user does not submit the compliance certification, and where the POTW collects all the information for the report, including flow data, the user does not submit the report (40 CFR 403.12(g)(1)).

Late filing has a defined consequence. Failure to provide a required report such as a baseline monitoring report within 45 days after the due date is one criterion of significant noncompliance (40 CFR 403.8(f)(2)(viii)). EPA notes that many POTWs kept the earlier 30-day threshold (US EPA, 2011), so check the local ordinance.

What goes in each section of a baseline monitoring report?

Each section of a baseline monitoring report answers one numbered paragraph of 40 CFR 403.12(b), and local forms such as the City of Gilroy form keep the same seven parts and paragraph references (City of Gilroy, 2024). The table below is the check to run on a baseline monitoring report before filing: what each paragraph requires and what to attach so the reviewer can verify it.

The flow and pollutant rows carry most of the work, because every later limit check depends on them, and a reviewer who cannot rebuild a flow or a result from the attachments will ask for it again (inference). Information already given in a permit application that is still current need not be resubmitted (US EPA, 2011). The regulation still asks for the Standard Industrial Classification code, while EPA's 2011 introduction lists North American Industry Classification System (NAICS) codes (US EPA, 2011); give both if the form allows. A schedule completion date may not be later than the compliance date of the standard (40 CFR 403.12(b)(7)).

What sampling does a baseline monitoring report need?

A baseline monitoring report needs at least one representative sample from each regulated process, analyzed by 40 CFR part 136 methods, with both daily maximum and average concentrations reported (40 CFR 403.12(b)(5)).

Sample type follows the pollutant. Grab samples must be used for pH, cyanide, total phenols, oil and grease, sulfide and volatile organic compounds, and a facility without historical sampling data must take a minimum of four grab samples for these parameters for the baseline report (40 CFR 403.12(g)(4)). All other pollutants need 24-hour flow-proportional composite samples unless the Control Authority authorizes time-proportional composite or grab sampling, and that authorization must be documented in the user's file (40 CFR 403.12(g)(3)). EPA adds that these grab-sample parameters need no monitoring when the categorical standard does not regulate them (US EPA, 2011).

Samples should be taken immediately downstream from pretreatment facilities if they exist, or immediately downstream from the regulated process if they do not; if other wastewaters mix with the regulated stream before pretreatment, measure the flows and concentrations needed for the combined wastestream formula (40 CFR 403.12(b)(5)(iv)). The report states the time, date and place of sampling and the analytical methods, and certifies that the results represent normal work cycles (40 CFR 403.12(b)(5)(vii)). Historical data are accepted only if the Control Authority allows them and they suffice to decide whether pretreatment is needed (40 CFR 403.12(b)(5)(vi)). Keep all sampling records for at least 3 years (40 CFR 403.12(o)(2)).

What does a baseline monitoring report look like for a metal finisher (illustrative)?

A baseline monitoring report for a metal finisher that mixes cooling water into its plating wastewater before treatment reports both flows and compares results with limits adjusted by the combined wastestream formula. The plant below is illustrative: an existing source that is not a job shop or independent printed circuit board manufacturer, under the metal finishing pretreatment standards for existing sources, 40 CFR 433.15(a), with 40,000 gallons per day (illustrative) of regulated process wastewater and 10,000 gallons per day (illustrative) of non-contact cooling water entering the treatment system.

Non-contact cooling water counts as a dilute stream in the formula (40 CFR 403.6(e)). The total flow through the treatment system includes the regulated, dilute and any unregulated streams, and the flows are averages of at least 30 days (40 CFR 403.6(e)). With one regulated stream, the alternative limit is the categorical limit multiplied by the total flow minus the dilute flow, divided by the total flow (US EPA, 1985). Here that fraction is 40,000 divided by 50,000, or 0.8 (illustrative).

The table below checks the illustrative plant against its adjusted nickel and zinc limits.

The key row is the alternative average: the illustrative nickel average of 1.7 mg/L passes the adjusted 1.90 mg/L. Comparing the diluted sample with the unadjusted 2.38 mg/L would overstate the margin, which is the dilution the formula removes (inference). The flow section lists both streams with average daily and maximum daily flow in gallons per day (40 CFR 403.12(b)(4)), and the pollutant section attaches the calculation and supporting data (40 CFR 403.12(b)(5)(iv)).

Why do POTWs reject baseline monitoring reports?

POTWs reject baseline monitoring reports when an item required by 40 CFR 403.12(b) is missing or cannot be verified from the attachments. No public dataset ranks rejection reasons; each gap below breaks a specific clause, and the selection is our judgment (inference).

• One total flow instead of average daily and maximum daily flow per stream, or no flows for the other streams the combined wastestream formula needs (40 CFR 403.12(b)(4)).

• A grab sample for metals without the Control Authority's documented authorization, or fewer than four grab samples for pH, cyanide, oil and grease or volatile organics without historical data (40 CFR 403.12(g)(3) and (g)(4)).

• Samples taken upstream of pretreatment, or after other flows join without a combined wastestream formula limit (40 CFR 403.12(b)(5)(iv), 403.6(e)(4)); for metal finishers, cyanide self-monitoring belongs after cyanide treatment and before dilution with other streams, unless the final effluent is sampled against limits adjusted for the dilution ratio (40 CFR 433.12(c)).

• Only a daily maximum or only an average, or no sampling time, place or method (40 CFR 403.12(b)(5)).

• An alternative limit derived by the user without supporting data or without the Control Authority's written concurrence (40 CFR 403.6(e)).

• A toxic organic management plan offered instead of total toxic organics sampling, which EPA says cannot replace baseline monitoring (US EPA, 2011).

• A compliance schedule with increments over 9 months or a completion date after the standard's compliance date (40 CFR 403.12(c)(2)).

Local programs add conditions. The City of Gilroy requires an inspector to witness the first sampling event of a new or modified permit (City of Gilroy, 2024), and San Diego's form (revised 2001, still posted in 2024) warns that reports more than 30 days late lead to significant noncompliance and publication (City of San Diego, 2001).

Who must sign a baseline monitoring report?

A baseline monitoring report must be signed under 40 CFR 403.12(l) by a responsible corporate officer for a corporation, by a general partner or proprietor for a partnership or sole proprietorship, or by a duly authorized representative of one of them, and must carry the certification statement in 40 CFR 403.6(a)(2)(ii).

A responsible corporate officer is a president, secretary, treasurer or vice-president in charge of a principal business function, or a facility manager with authority over the regulated facility as defined in the rule (40 CFR 403.12(l)(1)). A duly authorized representative qualifies only if all three conditions are met: the officer or partner authorizes in writing, the authorization names an individual or position with overall responsibility for the facility or for environmental matters, and it has been submitted to the Control Authority (40 CFR 403.12(l)(3)). A change of person or position needs a new authorization before or with the next signed report (40 CFR 403.12(l)(4)).

The section 6 compliance statement adds a second role: an authorized representative reviews it and a qualified professional certifies it (40 CFR 403.12(b)(6)); the Gilroy form has separate signature blocks for both (City of Gilroy, 2024). The signed certification opens: "I certify under penalty of law that this document and all attachments were prepared under my direction or supervision in accordance with a system designed to assure that qualified personnel properly gather and evaluate the information submitted." (40 CFR 403.6(a)(2)(ii)). False statements in these reports fall under 18 U.S.C. 1001 (40 CFR 403.12(n)).

Baseline monitoring report checklist

Run this baseline monitoring report checklist on the draft before it goes to the Control Authority.

1. The filing date is within 180 days of the standard's effective date, or at least 90 days before discharge for a new source.

2. Facility, operator and owners are named with addresses, and every environmental control permit is listed with agency, type and number.

3. Operations, average production rate and industry classification code are given, with a schematic marking each regulated discharge point.

4. Average daily and maximum daily flows are given per stream in gallons per day, measured, or estimated only where the Control Authority allows verifiable estimates.

5. The applicable categorical standard and subpart are named for each regulated process.

6. Grab and composite sample types match the pollutant list, and the grab count meets the minimum where no historical data exist.

7. Sample points sit downstream of pretreatment, and any formula streams are measured.

8. Results show daily maximum and average, with time, date, place and part 136 method.

9. Any alternative limit shows the calculation, the 30-day flow basis and the Control Authority's concurrence.

10. A qualified professional certifies the compliance statement and an authorized representative has reviewed it.

11. The signatory is a responsible officer, partner or proprietor, or a representative whose written authorization is on file.

12. Any compliance schedule has dated increments of 9 months or less and ends by the compliance date.

Lubinpla can organize a report like this from a facility's own laboratory reports, flow records and permits, with each value cited, as a draft for the user's review.