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New Total Dissolved Solids Requirements for Publicly Owned Treatment Works

by | Jun 1, 2016 | Bruder Jr, Paul J, Environmental Law, Industry News

New Total Dissolved Solids Requirements For Publicly Owned Treatment Works

DEP’s revised Chapter 95 regulations were published as final on August 21, 2010. These regulations address the acceptance of high-TDS wastes, particularly Marcellus Shale gas drilling wastes (frac fluids and other wastes) received by POTWs. The regulations were complex and DEP developed a Guidance Document to guide NPDES permit writers. A Draft Guidance Document was made available for public comment in early 2011, and comments were submitted by the EPWPCOA. The Final Guidance Document was published on November 12, 20111. The concerns expressed by the EPWPCOA were addressed in the final document.

The Guidance Document is rather complex, and includes different permitting strategies for discharges from POTWs and industrial facilities under a variety of circumstances. To keep this article to a manageable size, the discussion is limited to POTWs and to POTWs that were not accepting “frac” water wastes as of August 21, 2010 (the date of the regulations and a “grandfather” date for these facilities). “Grandfathered” POTWs and industrial direct dischargers of treated frac waters are not discussed in this review.

When Do the Rules Apply?

The regulatory requirements only apply to “New or Expanded Discharges.” This means that POTWs that continue to treat and discharge wastes as they have in the past will not be affected by the new regulations. However, there is an exception. DEP defines “existing” TDS discharges as those for which a permit application provided TDS data which were considered in the development of the NPDES permit. There is also a requirement in Chapter 92a to report substantial changes in influent that are different than the information provided in the most recent permit application. Hence, if the treatment plant currently discharges higher levels of TDS than were reported in the latest permit application due to unreported recent changes in the incoming sewage, DEP could decide that the current discharge is not an existing permitted discharge and would consider the plant not to be exempt. Therefore, a POTW that is contemplating accepting high-TDS wastes, whether from an industrial user or a fracking operation, should review its last NPDES permit application and, if necessary, update its “existing TDS” data by conducting additional effluent sampling prior to accepting the wastes.2


The following are considered not to be “new or expanded” discharges and the TDS permitting rules do not apply:

Existing discharges. The DEP Guidance Document clarifies that POTW discharges are deemed to be permitted to discharge TDS at historical levels even though no TDS limit actually appears in the Permit. That is, most POTWs provided some TDS sampling data as part of their NPDES Permit renewals, so DEP considers those levels of TDS to be allowed by the permits, even though there is no explicit permit limit. The “permitted” discharge mass load is determined as both an annual average using the annual average design flow and average reported concentration, and as the daily maximum, using the maximum daily reported concentration and the daily maximum design flow (both the annual average and daily maximum design flow ratings are shown on the WQM (Part II) permit). This “permitted” TDS limit is also used in evaluating whether an expansion is minor, as discussed next.

§ 95.10(a)(7). Minor expansion. If a new or expanded discharge generates less than 5,000 pounds per day of additional TDS discharged as an annual average, the rules do not apply. For expansions, the increase is measured only with respect to the “new” portion of the discharge. That is, as long as the amount of the increased discharge is less than 5,000 ppd the exemption applies, even if the total discharged TDS (old plus new) exceeds that amount.3

Remember, however, that any change in the incoming waste would still have to be reported to DEP for consideration for possible NPDES permit revisions. It is also important to understand that the exemption applies to the POTW permitting requirements, but not to the requirement discussed below-—that all frac water wastes, regardless of quantity, must be treated by a Centralized Waste Treatment (CWT) facility before being discharged to a POTW. Thus, POTWs accepting even small quantities of these wastes must still ensure that they were properly treated at a CWT and will likely be in violation of the regulations if the waste is not properly pretreated.

New/expanded Discharge

Assuming that the plant is not exempt under the above criteria, a “new or expanded” discharge of TDS-containing wastewater (i.e., the POTW begins accepting high-TDS wastes into the treatment system) must meet the regulatory requirements and will have NPDES requirements which differ depending on the source of the waste being accepted. Frac water wastes are treated differently than other industrial wastes. In particular, all frac wastes must be treated at a Centralized Waste Treatment (“CWT”) facility before being discharged to the POTW. As noted above, this requirement applies to any quantity of waste, even if it results in less than 5,000 pounds per day of TDS discharged. Since the rules are different depending on the source of the wastewater, the discussion below is divided into two parts-—new Industrial waste and new Fracking wastes.

Accepting High TDS wastes other than Frac wastes

If the POTW is not exempt and proposes to accept industrial wastes with high TDS concentrations, the permit requirements depend on the expected effluent concentration resulting from accepting the new wastes. DEP has established two classifications for POTWs accepting high-TDS industrial wastes.

Unaffected. If the increased discharge loading will be greater than 5,000 ppd but will not produce effluent TDS concentrations exceeding 2,000 mg/L, the permit will normally contain no provisions related to TDS. If the data are not clear, but it is generally believed that the effluent will not exceed 2,000 mg/L then the permit writer may include monitoring and reporting requirements for TDS to generate data for the next permit. If there is doubt that the effluent will reliably remain below 2,000 mg/L the permit writer may choose to classify the discharge as Conditionally Non-Exempt (Other) (See below.). The Guidance discusses the use of effluent data to make this determination; however, since the determination must be made before the new wastes are accepted, that approach will be unworkable in most cases and the POTW and DEP will have to make educated guesses. In some cases, pilot testing may be beneficial to show whether or not new incoming TDS is likely to pass through the treatment process. For instance, a food manufacturer may have a high TDS loading of degradable materials (e.g., sugars) that will be removed by the treatment process, so that the POTW effluent will not see an effluent TDS increase proportionate to the new influent loading.

Conditionally Non-Exempt (Other). This classification is for all POTWs (and other dischargers) that have an existing permitted discharge of TDS, wish to increase the TDS discharge by more than 5,000 pounds per day on an annual average basis by accepting industrial wastes other than frac water wastes, and have a “reasonable potential” to exceed 2,000 mg/L, so that the “Unaffected” classification discussed above does not apply. These facilities will receive a mass-balanced effluent limit. The existing permitted discharge TDS loading (calculated using the existing concentrations and flows–—see discussion at the first bullet under “Exemptions” above) is retained and the additional mass load is subject to a 2,000 mg/L average, 4,000 mg/L daily maximum at the increased flow. It is not clear from the guidance whether the final permit limits will be expressed as concentration, mass, or both, but the general practice within the Department is to include both measures as effluent limits. Since both mass and concentration are at issue, the expected maximum flow rate from the new industrial source is a critical bit of information and should be confirmed with the industry as part of the application process (and probably “locked in” via a permit issued to the industrial user).

POTWs Accepting Frac wastes

All frac wastes, regardless of volume, must be treated at a Centralized Waste Treatment (“CWT”) facility before being discharged to the POTW. If the wastewater delivered to the POTW contains frac fluids and results in a TDS discharge from the POTW in excess of 5,000 pounds per day, the POTW is denominated a “Non-Exempt (Natural Gas)” facility in the Guidance Document. However, as discussed below, all of the requirements for acceptance of frac waters apply to the incoming wastes; no special effluent limits are required to be imposed on the POTW.

The CWT (pretreatment) facility could be a part of the POTW, but because it is subject to separate EPA standards, would normally be constructed and operated separately, with the treated discharge then delivered to the POTW for final treatment and discharge. (A “direct discharge” from a CWT facility to a receiving water is also permitted by the rules, but is not discussed in this summary.)

Discharge Requirements

The TDS regulations do not impose any effluent limits on POTWs accepting wastewater from a Centralized Waste Treatment Facility treating high-TDS wastes. This was a concern with the Draft Guidance Document, which imposed the same discharge limits on POTWs as on the CWT itself (see shaded areas on the table below). The Final Guidance Document more accurately reflects the provisions of the regulations, which do not require any limits on POTWs since the wastes are being adequately pre-treated by the CWT. However, DEP permit writers might choose to include additional monitoring requirements or effluent limits in the NPDES permit on a case by case basis and this should be discussed with them at the time the permit is being prepared.

The frac water waste received by the POTW from the CWT must meet quality requirements, expressed as numerical monthly average limits for TDS, total chlorides, barium and strontium plus the Pretreatment Standards for New Sources at 40 CFR § 437.47(b) (combined wastes from A, B and C type facilities). All of these limits are shown in the table below.

The regulations do not establish a monitoring frequency for the delivered wastes. It is possible, however, that the NPDES permit issued to the POTW could include a monitoring frequency for the incoming waste. If none is provided, the POTW may determine its own frequency, with the understanding that the EPA Industrial Pretreatment Program regulations (40 CFR Part 403) require self-monitoring and reporting by Categorical Industrial Users in June and December (unless required more frequently by the POTW). See 40 CFR § 403.12(e)(1).

If the POTW has an EPA-approved industrial pretreatment program, the list of required sampling parameters may be shortened and the self-monitoring can be replaced by POTW sampling, as provided by the federal regulations. If the POTW does not have an EPA-approved pretreatment program, the CWT facility will report directly to EPA, which is the “control authority” in such a case, with a copy of the reports sent to the POTW. Note that the limits for TDS, chlorides, Ba and Sr are not federal Categorical standards and the CWT will need to be notified to include these additional tests in its monitoring so that compliance with the DEP regulation can be assessed.



Maximum daily (mg/L)

Max. Monthly Average (mg/L)

Total Dissolved Solids



Total Chlorides



















































Bis (2-ethyl hexyl) phthalate





















2,4,6 Trichlorophenol



Shaded cells are DEP-only requirements; all others are EPA Categorical Standards (also called Effluent Limits Guidelines—ELGs) as found at 40 CFR § 437.47(b).

Additional Reporting Requirements

In addition to monitoring requirements, the CWT must complete and submit to the POTW an Initial Certification described at 40 CFR § 437.41(a) and an Annual Certification of continuing treatment operation as described in 40 CFR § 437.41(b). Since this is a regulatory requirement, the POTW should ensure that the CWT facility submits this Certification each year. (The Certification is submitted to the POTW regardless of whether or not the POTW has an EPA-approved pretreatment program.)

Since the Chapter 95 regulations and the NPDES permit regulate the POTW, not the CWT, if the CWT does not meet the above standards it is a violation by the POTW to discharge effluent resulting from acceptance of the non-conforming wastes. This is not only part of the Guidance Document, it is a requirement in all NPDES permits. See, e.g., Section B.I.C.5.e of most permits, which requires the Permittee to ensure that industrial users comply with all applicable pretreatment standards.4 Hence, POTWs should be careful to ensure that the wastes they receive from CWTs meet the standards at all times and that the annual Certification Statement is received. A contract with the CWT’s owner providing that it will reimburse the POTW for any penalties resulting from the CWT’s violation of its requirements would be worth considering in addition to any discharge permit that the POTW might issue to the CWT facility.

Water quality-based Effluent limits

It should always be kept in mind that the Chapter 95 TDS regulations are primarily technology-based and intended to set a uniform “floor” for all TDS discharges. If water quality is impacted by TDS or other constituents of a discharge, however, permit limits to preserve the quality of the receiving stream are always possible. Hence, TDS discharges in any amount could be subject to permit limits if they threaten to impact the receiving water, regardless of the standards established by Chapter 95. Thus, all discussions about permitting must consider that site-specific water quality-based TDS limits established outside of the technology-based Chapter 95 regulations may be a possibility.

The Guidance Document outlines permitting rules for all of the situations that a POTW is likely to encounter and provides clarity to the somewhat confusing regulatory requirements. The following situations of interest to most POTWs are covered (DEP designation is shown in parentheses):5

Existing permitted discharge (as of August 21, 2010) of TDS with no anticipated change–—no Permit changes are required. However, if the existing discharge is near 2,000 mg/L the DEP permit writer may decide to include additional monitoring conditions (but not effluent limits) in the permit on a case-by-case basis. (Not Regulated)

Existing permitted discharge of TDS proposing to discharge less than 5,000 ppd of added TDS from wastewater from an industrial source–—no Permit changes are required, although the DEP permit writer may decide to include additional monitoring conditions in the permit on a case-by-case basis. The proposed change in influent constituents must be reported to DEP for consideration for possible permit amendment. (“Exempt.”)

Existing discharge of TDS proposing to discharge more than 5,000 ppd of added TDS from wastewater from an industrial source, but effluent TDS is not likely to exceed 2,000 mg/L–—the proposed change in influent constituents must be reported to DEP for consideration for possible permit amendment. The Permit will not include discharge limits for TDS under Chapter 95, but may include monitoring requirements or site-specific water quality-based discharge limits. (“Unaffected.”)

Existing discharge of TDS proposing to discharge more than 5,000 ppd of added TDS from wastewater from an industrial source and there is a potential to exceed 2,000 mg/L–—the Permit will include discharge limits for TDS based on a mass balance analysis–—no diminution of the existing mass load, but the added TDS is limited to 2,000 mg/L monthly average and 4,000 mg/L daily maximum. (“Conditionally Non-exempt (Other).”)

Existing discharge of TDS proposing to discharge less than 5,000 ppd of new TDS from wastewater from a natural gas source (frac waters or other)–—no Permit changes are required, but the POTW must ensure that the source of the frac water being delivered is a Centralized Waste Treatment facility and that the CWT complies with all of the federal regulations, along with the state-imposed limits for TDS, chlorides, barium and strontium. No permit changes should occur but the Permittee can nevertheless be held responsible for ensuring compliance by the CWT. Also, DEP might impose monitoring requirements on a case-by-case basis. If the change in influent constituents is significant, the proposed change must be reported to DEP for possible permit amendment. (“Exempt.”)

Existing discharge of TDS proposing to discharge more than 5,000 ppd of new TDS wastewater from a natural gas source (frac waters or other)–—the Permit will require that the POTW must ensure that the source of the waste is a Centralized Waste Treatment facility and that the CWT complies with all of the federal regulations, along with the state-imposed limits for TDS, chlorides, barium and strontium. DEP might also impose monitoring requirements on a case-by-case basis. (“Non-exempt (Natural Gas).”)

The above discussion is an attempt to clarify and summarize a complex set of regulations and guidance and is not intended to replace the official documents. Since some of the rules and procedures remain ambiguous, the actual process followed by individual DEP permit writers may differ from the above. It is important that POTWs intending to accept additional high-TDS wastes read the regulations and Guidance Document carefully; acquire valid supporting data; and work cooperatively with the Department to obtain a permit that is both environmentally protective and compliant with the regulations.

1 The Guidance Document can be found on the DEP website at . Or use the “DEP Programs” link and click on TDS. (Do not use the “Search DEP” option.)

2 Since, as discussed below, accepting new wastes requires reporting the plan to DEP, this additional sampling should be a normal part of any plan to accept additional wastes.

3 There was some ambiguity in the Draft Guidance Document about where the 5,000 ppd criterion is applied. The Final Guidance Document clarifies that the value is measured as the effluent loading.

4 This requirement was in the prior Chapter 92 regulations (§ 92.53(c)) but was deleted when those regulations were revised and reissued as Chapter 92a in 2010. However, it has been a standard condition of all POTW permits for many years and is likely to continue to be included in future permits.

5 Other situations, such as a POTW that currently accepts frac waters and wishes to increase its discharge of these wastes, are subject to different requirements that are not discussed in this report.