Site-specific water quality standards

Water quality standards (WQS) are frequently adopted statewide for a particular beneficial use or by ecoregion. These standards can include large areas with different types of water; for example, those with different depth, watershed area, biological communities and natural water chemistry. Sometimes it is more appropriate and information is available to derive standards based on information specific to a water body. This is done through development of site-specific standards. Site-specific standards must maintain and protect the beneficial use.

If considering a site-specific standard for nutrients (eutrophication) in a lake, shallow lake, or reservoir, consult Minn. R. 7050.0222. An ecoregion standard may be modified on a site-specific basis to account for unique characteristics. These include temperature, variations in hydraulic residence time, watershed size, and distance from neighboring ecoregion.

Other site-specific standards can be considered using Minn. R. 7050.0220, Subp. 7 (Site-specific Modification of Standards) and in the Lake Superior Basin using Minn. R. 7052.0270 (Site-specific water quality standards or criteria).

Information supporting a site-specific standard can be provided by MPCA or by any person outside the agency. MPCA will evaluate all data in support of a modified standard and determine whether a change is justified. All site-specific standards must be approved by EPA before being considered final. Communication with EPA starts early to help facilitate the process.

Then MPCA and other parties involved will do the following:

  • Evaluate all data and determine whether the change is justified.
  • If justified, document the reasoning.
  • Public notice the site-specific standard for 30-days along with an option for the public to request an informational public meeting.
  • Prepare a Findings of Fact with Commissioner’s signature and receive Attorney Certification.
  • Submit justification to EPA Region 5 for final approval.

Site-specific standards awaiting final EPA approval, those approved, and those being developed are listed below. Click on the tab for a full description of what water body or location within the water body where the site-specific standard applies.

Please consult Minnesota Rules for specifics on what standards apply and where. In some cases, site-specific standards have been adopted through rule. For example, portions of the Mississippi River, such as the Navigation Pools and Lake Pepin, have site-specific standards for phosphorus and chlorophyll-a listed in rule (Minn. R. 7050.0220, Supbp. 3b).

NOTE: Site-specific standards differ from site-specific criteria. Minnesota distinguishes between “standard” and “criteria” primarily to emphasize the fact that the EPA’s national criteria lack regulatory applicability until adopted as WQS in state rules.

In addition, site-specific criteria may be developed using the methods in Minn. R. 7050.0217, 7050.0218 and 7052.0110. When a toxic pollutant lacking a numeric standard in Minn. R. 7050.0220, 7050.0222, 7050.0227 or 7052.0100 is found in surface waters, MPCA is authorized to develop numeric “site-specific criteria.” Site specific criteria are applied in permits and remediation site following the procedures in Minn. R. 7050.0218, Subp. 2. In contrast, site-specific standards require approval by EPA, apply to pollutants with existing standards, and are not limited to toxic pollutants.

Public notice

Water: Lake Zumbro (55-0004-00)
Parameter: Eutrophication
Rule: 7050.0222 subp. 4 Eutrophication standards
Water Quality Standard: 65 µg/L total phosphorus, 22 µg/L chlorophyll-a, 0.9 m Secchi depth transparency.
Site-Specific Standard being considered: Segment 2: 105 µg/L total phosphorus, 48 µg/L chlorophyll-a, 1.1 m Secchi depth transparency; Segment 3: 75 µg/L total phosphorus, 40 µg/L chlorophyll-a, 1.4 m Secchi depth transparency. Note: These values apply over a range of flows up to ~960 cfs (~85th percentile) as measured or modeled at the outlet of Lake Zumbro.
Justification: Lake Zumbro is a run-of-the-river reservoir located on the Zumbro River. Lake Zumbro has large watershed-to-lake surface area with low water residence times and is located in the Driftless Area ecoregion which makes it a candidate for a site-specific standard. Given the unique characteristics of this waterbody, it is appropriate to propose site-specific eutrophication standards to protect aquatic life, swimming, and boating uses (Class 2). The lake is influenced by discharge level and sections of the lake respond differently to nutrient inputs. As a result the draft site-specific standard was adjusted to account for longitudinal differences in the lake and to address variable algal responses at different discharges. The site-specific standard for Lake Zumbro focuses on maintaining good clarity and minimizing the frequency and intensity of algal blooms so that aquatic life and recreational uses are protected.
Reference: PDF icon Technical justification for draft Lake Zumbro (55-0004-00) site-specific eutrophication standard (wq-iw9-21n)
Public notice: Open for public comment December 11, 2017 – February 1, 2018 (4:30 p.m.)

Approved

Water: Spring Lake (70-0054-00)
Parameter: Eutrophication
Rule: 7050.0222 subp.4 Eutrophication standards
Water Quality Standard: 40 ug/L TP, Chl-a 14 ug/L, Secchi 1.4 m
Site-Specific Standard: 60 ug/L TP, Chl-a 20 ug/L, Secchi 1.4 m
EPA approved: July 19, 2016

Justification: A paleoecology study was conducted to determine the TP levels in a natural background condition. Using radioisotorpic techniques, individual sediment layers were dated and the remains of various types of algae, including diatoms, were analyzed. The study concludes that Spring Lake had a pre-European settlement (prior to 1850) TP range of 60 ± 5 μg/L. MPCA proposes a Chl-a standard of 20 μg/L using the statewide-based regression equation.

Water: Lake Winona (21-0081-00)
Parameter: Eutrophication
Rule: 7050.0222 subp.4 Eutrophication standards
Water Quality Standard: TP 60 ug/L, Chl-a 20 ug/L, Secchi 1.0 m
Site-Specific Standard: TP 75 ug/L, Chl-a 20 ug/L, Secchi 1.0 m
EPA approved: July 12, 2014
Justification: Lake Winona is located in the City of Alexandria, is 185 acres in size, and has a mean depth of 4.5 feet. Given the lakes very small watershed, relative shallowness, short water residence time and proximity within the City of Alexandria, the focus for site-specific standard for Winona is on reducing the frequency and severity of nuisance algal blooms and improving transparency such that rooted macrophytes can become established. The site-specific standard establishes a Total Phosphorus standard needed for the response variables of chlorophyll-a and Secchi to meet the shallow lake eutrophication standard in the North Central Hardwoods Forest ecoregion.

Water: Lake Nokomis (27-0019-00)
Parameter: Eutrophication
Rule: 7050.0222 subp.4 Eutrophication standards
Water Quality Standard: TP 40 ug/L, Chl-a 14 ug/L, Secchi 1.4 m
Site-Specific Standard: TP < 50 ug/L, Chl-a < 20 ug/L, Secchi 1.4 m
Date approved: August 29, 2013
Justification: Lake Nokomis is located within the Minnehaha Creek Watershed District jurisdiction in the Twin Cities Metropolitan area. Lake Nokomis has a surface are of 200 acres. Sixty-six percent of the lake is less than 15 feet deep, and a large part is only minimally deeper (84% is 16 feet or less). The site-specific standard is based on a hybrid of the existing standard and the shallow lake standard, as the lake displays characteristics of both. The MPCA’s review of in-lake water quality data indicates that achieving a TP concentration of 50 ug/L will result in a chlorophyll-a level of 20 ug/L. Achieving chlorophyll-a and Secchi disk depth standards translates to producing minimal nuisance algal blooms and exhibiting desirable water clarity, which further translates to meeting desired beneficial aquatic recreational uses of the lake.

Water: Lake Hiawatha (27-0018-00)
Parameter: Eutrophication
Rule: 7050.0222 subp.4 Eutrophication standards
Water Quality Standard: TP 40 ug/L, Chl-a 14 ug/L, Secchi 1.4 m
Site-Specific Standard: TP < 50 ug/L, Chl-a 14 ug/L, Secchi 1.4 m
Date approved: July 24, 2013
Justification: Lake Hiawatha and its watershed are located within the Minnehaha Creek Watershed District jurisdiction in the Twin Cities Metropolitan area. MPCA based the site-specific standard on a detailed analysis of the lake’s hydraulic residence time, the long-term response to phosphorus loading and other factors. The MPCA’s review of in-lake water quality data indicates that due to the lake’s relatively short residence time, the lake need only meet 50 µg/L in order to achieve chlorophyll-a and Secchi disk depth standards. Achieving chlorophyll-a and Secchi disk depth standards translates to producing minimal nuisance algal blooms and exhibiting desirable water clarity, which further translates to meeting desired beneficial aquatic recreational uses of the lake.

Water: Lake Byllesby  (lower two-thirds of 19-0006-00, the combined transitional and near-dam segments)
Parameter: Eutrophication
Rule: 7050.0222 subp.4 Eutrophication standards
Water Quality Standard: Total Phosphorus (TP) 65 ug/L,  Chlorophyll-a (Chl-a) 22 ug/L,  Secchi not less than 0.9 m
Site-Specific Standard: TP less than or equal to 90 ug/L; Chl-a less than or equal to 30 ug/L; Secchi disk transparency greater than or equal to 0.8 m. The standards apply for flows that range from 180 cubic feet per second (for summer 122 day, one in ten year recurrence, 10th percentile flow) to 940 cubic feet per second (for 80th percentile flow) as measured at the combined transitional and near dam segments. The flow ranges correspond to a residence time of 8 to 10 days.
EPA approved: August 26, 2011
Justification: Lake Byllesby is a reservoir and drains more than one ecoregion. The best available bathymetry data suggest that 48 percent of the Byllesby Reservoir is less than 10 feet deep, and an approximation of the littoral area is 66 percent. That value is very close to the criterion put forth in the shallow lake definition: maximum depth of 15 feet or 80 percent or more littoral. The other criterion in the shallow lake definition is that it is uncommon for shallow lakes to thermally stratify in the summer. In terms of surface area, the majority of the Byllesby Reservoir meets that criterion as well, with the exception of the single deep hole in the near-dam portion of the reservoir. Absent this portion, the remainder of the transitional and near-dam bays remains well-mixed throughout the summer, with at most temporary stratification during very warm and calm periods. Given this relative shallowness, the very large watershed, short water residence time, and predominance of agriculture throughout the watershed, the focus for site-specific criteria for Byllesby is on reducing the frequency and severity of nuisance algal blooms. This is consistent with other shallow lakes in the Western Corn Belt Plains ecoregion.

Water: French River at SW003 (T.51N, R.12W, S.17, SW 1/4) station located between County Highway 61 and Lake Superior. Covers only the area near the mouth/ confluence with Lake Superior (located on 04010102-698).
Parameter: Temperature
Rule: 7050.0222 subp.2
Water Quality Standard: No material increase
Site-Specific Standard: For the months from November through April - not to exceed 50 deg F as a monthly average. For the months from May through October, not to exceed the monthly average temperature at SW001 (located 0.04 miles upstream from SW003 at T.51N, R.12W, S.17, SW 1/4)
EPA approved: July 8, 2004
Justification: The site-specific standard for this station on the French River has two components. The first is a temperature standard that applies during the winter months (November through April). During that time, the temperature at monitoring station SW003 cannot exceed 50 degrees F. The second component relates to the relationship of the temperature at monitoring station SW003 and the temperature at monitoring station SW001, which is upstream of SW003. During the warm weather months when the 50º F standard does not apply, the site-specific standard requires that the temperature at SW003 cannot exceed the temperature at SW001. For both standards, the temperature is based on a monthly average at each monitoring station.

Detailed information about this site-specific limit can be located in the MPCA’s documentation of the 2004 effluent limit review for MDNR French River Hatchery, Permit No. MN004413. In that documentation, the MPCA required that a new temperature monitoring station (SW003) should be established downstream of the discharge and at a point after complete mixing has occurred. A temperature that did not exceed 50º F as a monthly average at SW003 during the period November through April would assure adequate temperatures to protect the fish spawning cycle (10º C or 50º F optimum, and range 1-13º C ), and also be within acceptable boundaries for egg incubation (7-12 degrees C optimum, and range 5-15 degrees C ). During the warm weather months (May through October) the temperature at SW003 must not exceed temperatures at SW001, based on the monthly average temperature. This component of the site-specific standard ensures that the narrative temperature requirement in Ch. 7050.0222 Subp. 2 of “no material increase” is met during the time period when the 50º F standard is not applied.

Water: Red River of the North, from just downstream of 12th Ave N bridge in Fargo to the confluence with the Buffalo River (09020104-502 & 09020104-511)
Parameter: Total ammonia nitrogen
Rule: 7050.0222 subp.3
Water Quality Standard: 0.04 mg/L unionized ammonia
Site-Specific Standard: Ammonia, total  in mg N/L  Chronic Standard (CStox)
-Thirty Day Standard:  The concentration of total ammonia nitrogen, in mg N/L, in any thirty day period cannot exceed the applicable CStox values (as derived below), more than once every three years on average; AND
-Four Day Standard:  The average concentration of the four days of highest ammonia, in mg N/L concentrations within the 30 days applied to the equation must not exceed 2.5 times the value of the applicable CStox. The CStox varies depending on the applicable months for each equation and also on pH and temperature.
For March through September:
CStox =( 0.0577/(1+ 〖10〗^(7.688-pH) )+  2.487/(1+ 〖10〗^(pH-7.688) )  ) x MIN(2.85,1.45 x 〖10〗^0.028(25-T) )
Where: pH means ambient water pH; and MIN means multiply by the minimum value of either 2.85 or 1.45 x 〖10〗^(0.028(25-T)), where T means the ambient water Temperature in degrees Celsius (C). In this equation, 2.85 is used when T is less than or equal to 14° C.
For October through February
CStox =( 0.0577/(1+ 〖10〗^(7.688-pH) )+  2.487/(1+ 〖10〗^(pH-7.688) )  ) x MIN (4.63,1.45 x 〖10〗^0.028(25-T) )
Where: MIN means multiply by the minimum value of either 4.63 or 1.45 x 〖10〗^(0.028(25-T)). In this equation, 4.63 is used when T is less than or equal to 7° C. Other variables as previously defined.
EPA approved: June 20, 2000
Justification: The MPCA worked with the state of North Dakota to cooperatively develop this standard. North Dakota's regulations include specific formulas for the calculation of the chronic standard. This site-specific standard reflects MPCA’s intent to maintain consistency with the standard as it exists in North Dakota’s regulations. The site-specific standard for this stretch of the Red River of the North has two components, a thirty day standard and also a standard limiting the four highest days of ammonia concentration. The allowable levels of ammonia are calculated based on ambient water pH and water temperature.

Water: Crow River, South Fork at Hutchinson WWTP outfall T.116, R29W, s.7 NE1/4 (located on 07010205-510, NPDES permit MN0055832).
Parameter: Copper
Rule: 7050.0222 subp. 4
Water Quality Standard: 23.2 ug/L based on a hardness of 400 mg/L
Site-Specific Standard: Less than or equal to 67.3 ug/L, based on a hardness of 400 mg/L
EPA approved: January 8, 1996
Justification: Federal regulations at 40 CFR 122.44(d)(1) require that pollutants be evaluated for the potential to exceed water quality standards (“Reasonable Potential”) using acceptable technical procedures, accounting for variability in the effluent. Copper was calculated with and without the Water Effect Ratio (WER) to demonstrate the difference in calculation of preliminary effluent limits. The WER of 2.9 was determined in a 1993 study by the discharger. The WER was evaluated at 400 mg/l total hardness both in effluent and receiving water, since both are over 400 mg/l. The WER is the ratio of copper toxicity in discharge site ambient water versus that found in clean lab water.

Water: Unnamed wetland adjacent to Lake Winona (21-0081) at ALASD outfall T.128, R38W, S.25 NW1/4
Parameter: Copper
Rule: 7050.0222 subp.4
Water Quality Standard: 23.2 ug/L based on a hardness of 400 mg/L
Site-Specific Standard: Less than or equal to 111 ug/L, based on a hardness of 400 mg/L
EPA approved: April 19, 1994
Justification: Federal regulations at 40 CFR 122.44(d)(1) require that pollutants be evaluated for the potential to exceed water quality standards (“Reasonable Potential”) using acceptable technical procedures, accounting for variability in the effluent. A Water Effect Ration (WER) is a site-specific determination of toxicity of copper to live organisms in site water versus standard laboratory water to determine a ratio applicable to the numeric WQS. The copper WQS includes a WER (4.8) adjustment factor in the analysis. The WER was approved in 1993.

 

In development

Water: Sauk River Chain of Lakes - Flowage Lakes:  Zumwalde (73-0089-00), Great Northern (73-0083-00), Knaus (73-0086-00), Krays (73-0087-00), Horseshoe North (73-0157-00), Cedar Island Koetter (73-0133-03), and Bolfing (73-0088-00).
Non-Flowage Lakes: Cedar Island Main (73-0133-01), Horseshoe South (73-0157-00), and Horseshoe West (73-0157-00)
Parameter: Eutrophication
Rule: 7050.0222 subp. 4 Eutrophication standards
Water Quality Standard: Flowage Lakes: 40 ug/L total phosphorus, 14 ug/L chlorophyll-a, 1.4 m Secchi depth transparency. Non-flowage Lakes: 60 ug/L total phosphorus, 20 ug/L chlorophyll-a, 1.0 m Secchi depth transparency
Site Specific Standard being considered: Flowage Lakes: 90 ug/L total phosphorus, 45 ug/L chlorophyll-a, 0.8 m Secchi depth transparency. Non-flowage Lakes: 55 ug/L total phosphorus, 32 ug/L chlorophyll-a, 1.4 m Secchi depth transparency
Justification: The Sauk River Chain of Lakes is a reservoir system. Given the unique characteristics of this reservoir system, it is appropriate to propose and use site-specific eutrophication standards to protect swimming and boating uses. The flowage lakes are very shallow, with a large watershed to lake surface area, and water residence times are very low. The non-flowage lakes are influenced by their connection to the flowage lakes and were adjusted accordingly to utilize appropriate standards. The site-specific standards focus on reduction in the frequency and intensity of algal blooms so that aquatic recreational uses are protected for the majority of the summer.

Submitted to US EPA for approval on June 6, 2017.

Staff contact

Miranda Nichols - Water Quality Standards
520 Lafayette Road North
St. Paul, MN  55155-4194
651-757-2614
Miranda.Nichols@state.mn.us