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Below is a list of frequently asked questions regarding the Otter Creek TMDL Project. As the project progresses, some answers may be refined and new questions may be added. If you have a question that is not answered on this page, please contact Christina Staten at (406) 444-2836 or cstaten@mt.gov.
Frequently Asked Questions
What is a TMDL & Why Does DEQ Write Them?
TMDL stands for total maximum daily load, and is the maximum amount of a pollutant that a stream can receive and still meet water quality standards. The federal Clean Water Act established in 1972 (33 USC 1313 decribes TMDL requirements) and Montana’s Water Quality Act (75-5-703, MCA) require TMDLs to be written for waterbodies impaired by a pollutant. As of June 2013, more than 1,000 TMDLs have been written in Montana and subsequently approved by the U.S. EPA. Many TMDLs are also currently under development in Montana (see links in the right-hand sidebar and DEQ’s TMDL Project Status webpage).
Otter Creek is impaired by two pollutants, each of which requires a TMDL: iron and salinity. During this process, DEQ will determine significant sources of these pollutants in the Otter Creek watershed and how much reduction is needed from each of these sources in order for Otter Creek to meet Montana’s water quality standards. See the What is a TMDL page for a more detailed explanation of the TMDL process.
Why is DEQ Writing TMDLs for Otter Creek Now?
For more than 12 years, DEQ has done varying levels of TMDL development work in the Tongue and Powder River watersheds. This includes development of salinity standards (see “What is the Status of Montana’s EC and SAR Standards” question below) to protect agricultural uses in the region. Recently, DEQ has been working on improvements to an existing source assessment model for the Tongue River watershed, which includes Otter Creek.
Coalbed methane development was a primary reason for DEQ’s focus in the Tongue River watershed. Otter Creek has become a high priority because of the potential for new coal development, as well as proposed coalbed methane energy development in the Otter Creek watershed. The goal is to help ensure protection of Otter Creek’s water quality as well as downstream water quality in the Tongue River. The assessment and modeling work already completed will significantly help with Otter Creek TMDL development.
Isn’t it More Important to Write TMDLs for the Tongue River First?
DEQ prioritized the Otter Creek TMDLs over the entire Tongue River watershed in order to address potential new industrial development, but will take protection of the Tongue River into consideration when developing TMDLs for Otter Creek.
Are the Otter Creek TMDLs Only Being Written Because of the Mine?
Only the prioritization of these TMDLs has changed due to the proposed coal mine and related water quality concerns. Otter Creek was determined to be impaired for iron, salinity, and sediment* in 1996, and each of these impairments requires DEQ to write a TMDL (see Question 1 above). These TMDLs are required regardless of the proposed coal mine and other potential energy development.
*In 2013, DEQ determined that Otter Creek is not impaired for sediment, and therefore a sediment TMDL is no longer required.
How Long will the TMDL Project Take?
This project began in 2013. An iron TMDL has been written, and the "Otter Creek Iron Total Maximum Daily Load - Draft" document was available for public comment from October 1, 2015 through October 30, 2015. DEQ is currently in the process of responding to public comments and making related document edits. Once the public comment phase is complete, the document will be submitted to the U.S. EPA for approval, and the EPA must approve the document before it is considered final.
DEQ does not currently have an estimated timeframe for completion of site-specific salinity standards for Otter Creek (see Will DEQ Also Write a SAR TMDL?)
Do These TMDLs Have to be Complete before the Proposed Coal Mine can be Permitted?
The proposed coal mine will require multiple permits from DEQ, including a Montana Pollutant Discharge Elimination System (MPDES) permit for any proposed surface water discharges. Although the iron TMDL is scheduled for completion prior to the anticipated MPDES or other mine permitting actions by DEQ, these permitting actions can move forward without completion of the iron TMDL, or any other TMDLs. For additional details on the permitting process, please see DEQ’s Otter Creek Project Website.
What are the Implications of the TMDLs for the Proposed Coal Mine?
At a minimum, the iron TMDL will require development of loading limits that must be incorporated into any Montana Pollutant Discharge Elimination System (MPDES) - permitted surface water discharge.
What are the Implications of the TMDLs for Ranchers and Landowners in the Otter Creek Watershed?
The TMDL document will identify the significant sources of iron, sediment, and salinity in the Otter Creek watershed and will also provide recommendations for land management practices that can reduce the amount of these pollutants reaching the stream. The TMDLs will not impose legal requirements on landowners whose activities are not regulated by a permit. Therefore, potential water quality improvements linked to agricultural practices, if identified, would be voluntary consistent with Montana Law (75-5-703, MCA). The TMDL document will emphasize that any recommended land management changes are voluntary.
For landowners interested in implementing some of the recommended practices, the TMDL document will include information about potential funding sources and DEQ staff will be available to provide technical advice. In the meantime, DEQ's Nonpoint Source Program webpage may provide helpful information.
What are EC and SAR?
Electrical conductivity (EC) and sodium adsorption ratio (SAR) are measurements of water quality that can help determine the suitability of water for irrigation and other purposes. EC is a measure of how well a substance conducts electricity. It is one way to measure the amount of salt in the water because dissolved solids (ions) conduct electricity through the water. All untreated water is naturally saline with conductivity levels ranging from nearly zero to upwards of 200,000 microsiemens per centimeter (µS/cm). In general, water with lower conductivity levels (i.e., lower dissolved salt loads) are more suitable for irrigation.
Sodium adsorption ratio (SAR) is a measure of the suitability of water for irrigation. It measures the ratio of sodium in the water to other major cations (calcium and magnesium). Water with high levels of sodium can be damaging to soils and a high SAR indicates the water is less suitable for irrigation.
What is the Status of Montana’s EC and SAR Standards?
Montana adopted electrical conductivity and sodium adsorption ratio (EC and SAR) criteria in 2006. For additional information, see DEQ’s A Review of the Rationale for EC and SAR Standards published August 5, 2011. The standards were approved for implementation within Montana, however they have not been approved by EPA.
What are Site-Specific Standards and How Will They be Developed for Otter Creek?
Montana’s water quality standards can be refined to more accurately represent or reflect natural and attainable conditions for a specific waterbody or defined geographic area. These are identified as site-specific standards, and are developed by DEQ using sound science and site-specific evidence and data. Site-specific standards must fully protect the designated and existing water quality beneficial uses of the waterbody. If adopted, they replace the standards that normally apply to the waterbody.
DEQ is developing site-specific electrical conductivity and sodium adsorption ratio (EC and SAR) standards for Otter Creek. As part of the TMDL project, DEQ developed a salinity model to determine the existing EC and SAR in Otter Creek, and the simulated results show that EC and SAR under pre-Columbian (or pre-European) Era conditions exceed (i.e., do not meet) Montana’s standards for Tongue River tributaries over 99% of the time. As a result, the modeling information is being used to develop Otter Creek-specific EC and SAR standards, which will result in higher numeric EC and SAR values than the current Tongue River tributary standards of 3 SAR during the growing-season and 500 µS/cm for EC.
This process will require rule-making and the new standards will have to be adopted by Montana’s Board of Environmental Review (BER). This process includes opportunities for public comment. Once adopted by the BER, the standards become effective, but also must be approved by the U.S. EPA. Contact Amy Steinmentz (406-444-0371) in DEQ's Water Quality Standards Section for additional information about the status of the standards.
How is DEQ Applying Salinity Standards for Otter Creek?
Assuming approval of site-specific EC and SAR standards for Otter Creek (see question above), the new standards will become the salinity TMDL target values. There is a possibility however, that it may be determined that Otter Creek is not impaired for salinity, and therefore a TMDL will not be required. DEQ is currently drafting an implementation procedure for the site-specific standards that will address how salinity water quality assessment decisions are made for Otter Creek. See “How Will DEQ Address Naturally High Levels of Salinity, Iron, and Sediment?” below for details on how a salinity TMDL will be developed.
Is DEQ Collecting Additional Water Quality Data for TMDL Development?
Iron data was collected throughout the watershed in 2013, which added to a significant amount of existing iron data from a sampling site near the mouth of Otter Creek, as well as sampling sites further upstream for the purpose of mine baseline characterization. There is a substantial amount of existing salinity (EC and SAR) data for Otter Creek, and additional data was also collected at several locations during 2013. The iron and salinity (electrical conductivity collected in the form of specific conductance) data collected in 2013 is available on the Otter Creek TMDL Documents page. DEQ will be collecting EC data again in 2014 from March through October, as well as other water quality parameters, in partnership with the Bureau of Land Management and the U.S. Geological Survey. Additional sediment data was not collected during this project since there was adequate existing data and information.
How Will DEQ Address Naturally High Levels of Salinity, Iron and Sediment?
Salinity:
DEQ developed a salinity model to determine the existing electrical conductivity (EC) and sodium adsorption ratio (SAR) in Otter Creek, and was used to run a scenario to determine the condition of Otter Creek with and without current agricultural practices or urban environments (i.e., post and pre-Columbian Era, or European Era). The simulated results show that EC and SAR under pre-Columbian Era conditions exceed (i.e., do not meet) Montana’s Tongue River tributary standards 99% of the time. The modeled results are being used to develop EC and SAR standards specific for Otter Creek (see "What are Site-Specific Standards and How Will They be Developed for Otter Creek" above), which will address the naturally high levels of salinity in Otter Creek.
Iron:
Iron samples collected at various locations along Otter Creek and some of its tributaries have been used to determine the current amounts of iron in Otter Creek. The "Otter Creek Iron Total Maximum Daily Load - Draft" document provides a discussion of this data, and a draft iron TMDL and allocations. The document discusses the significant sources of iron in the Otter Creek watershed, including an evaluation of natural sources and the natural background load of iron in Otter Creek. The document was available for public comment from October 1, 2015 through October 30, 2015. DEQ is currently in the process of responding to public comments and making related document edits. Once the public comment phase is complete, the document will be submitted to the U.S. EPA for approval, and the EPA must approve the document before it is considered final.
Sediment:
DEQ determined that Otter Creek is not impaired for sediment and has removed this impairment from Montana's list of impaired waters. A weight-of-evidence approach examining suspended sediment concentrations and discharge (flow) relationships was used, and a “Sediment Beneficial Use Support Assessment for Otter Creek” that examines and details this approach is available on the Otter Creek TMDL Documents page.
Will DEQ Also Write a SAR TMDL?
The salinity impairment for Otter Creek equates to both EC and SAR concerns, therefore TMDL development for salinity incorporates both EC and SAR. Sodium adsorption ratio (SAR) could be treated as a separate TMDL, along with electrical conductivity (EC), to address any salinity impairment. DEQ has developed a water quality model that addresses both EC and SAR, and the model results are being used to inform the development of site-specific standards for Otter Creek. If site-specific salinity standards are adopted for Otter Creek, a new salinity water quality assessment will be conducted for Otter Creek. It is possible that this may result in a determination that Otter Creek is not impaired for salinity, and therefore neither an EC or SAR TMDL would be required (see "How is DEQ Applying Salinity Standards for Otter Creek" above). However, if a salinity TMDL is still required for Otter Creek, the final TMDL document may include both EC and SAR TMDLs. It is important to note that protection of EC values also helps protect against potential related issues from sulfates, chlorides, and other major ions in the water.
Page Released: June 5, 2013
Last Updated: February 26, 2016 (repaired links to DEQ webpages only)
