This page provides information and guidance for MS4 (Municipal Separate Storm Sewer System) permittees who have total maximum daily load (TMDLs) wasteload allocations (WLAs) for dissolved oxygen or oxygen demand.
The amount of dissolved oxygen (DO) an aquatic organism needs depends upon species, water temperature, and other factors such as the life stage of an organism. For most Class 2B waters, the DO standard is 5 mg/L as a daily average and 4 mg/L as a daily minimum. Oxygen demand is a measure of the oxygen used by microorganisms to decompose organic matter. Oxygen demand is expressed either as biochemical oxygen demand (BOD), chemical oxygen demand (COD), or nitrogenous oxygen demand (NOD).
Waters that have adequate DO under natural conditions but that are impaired for DO typically have one or more anthropogenic sources of organic matter that create an oxygen demand. For urban stormwater, examples of organic matter sources include leaves and other yard wastes, pet and animal wastes, fertilizer, sediment containing organic matter (e.g. topsoil), and hydrocarbons (e.g. oil). A median value for BOD in stormwater runoff in urban settings is about 8 mg/L, while a median value for COD is about 22 mg/L. These BOD levels are greater than Class 2B water quality standards, which range from 1.5 to 3.5 depending on geographic location.
Currently there are three approved total maximum daily load (TMDLs) - for Hardwood Creek (Waterbody ID: 07010206-596), Trott Brook (Waterbody ID: 07010207-680), and Buffalo Creek (Waterbody ID: 07010205-638 (formerly 07010205-501)) - that include MS4 (Municipal Separate Storm Sewer System) wasteload allocations (WLAs) for oxygen demand that are not assigned a zero percent reduction. Hardwood Creek is impaired for aquatic life (fish) due to low dissolved oxygen and Trott Brook and Buffalo Creek are impaired for aquatic life (fish and aquatic macroinvertebrates) due to low dissolved oxygen.
MS4s with applicable dissolved oxygen/oxygen demand WLAs
Link to this table
|TMDL Project||MS4 with a WLA for oxygen demand|
|Hardwood Creek Impaired Biota and Dissolved Oxygen TMDL||Anoka County|
|Lino Lakes City|
|MNDOT Metro District|
|Rice Creek Watershed District|
|Trott Brook (Rum River Watershed TMDL)||Elk River City|
|Saint Francis City|
|Buffalo Creek (South Fork Crow River Watershed TMDL)||Glencoe City|
|A compliance schedule is a a schedule of compliance leading to compliance with Clean Water Act regulations. Compliance schedules must meet the following.
Sections 12.8 and 22.2 of the MS4 permit provides the requirements for permittees who have a TMDL WLA for dissolved oxygen or oxygen demand.
Section 12.8: The applicant must submit a compliance schedule for each applicable Waste Load Allocation (WLA) not being met for oxygen demand, nitrate, total suspended solids (TSS), and total phosphorus (TP). The applicant may develop a compliance schedule to include multiple WLAs. The applicant's compliance schedule must include the following information:
a. proposed BMPs or progress toward implementation of BMPs to be achieved during the permit term;
b. the year each BMP is expected to be implemented;
c. a target year the applicable WLA(s) will be achieved
Section 22.2: If the permittee has an applicable WLA not being met for dissolved oxygen or oxygen demand, nitrate, TSS, or TP, the permittee must provide a summary of the permittee's progress toward achieving those applicable WLAs with the annual report. The summary must include the following information:
a. a list of all BMPs applied towards achieving applicable WLAs for oxygen demand, nitrate, TSS, and TP;
b. the implementation status of BMPs included in the compliance schedule at the time of final application submittal;.
The following discussion provides guidance for the condition where a permittee claims to meet an oxygen demand WLA and the condition where the WLA is not met at the time of application.
The MS4 permit does not specifically describe requirements for permittees claiming to meet a WLA for oxygen demand. Because there may be multiple sources of oxygen demand, it is not possible to directly calculate reductions in oxygen demand associated with implementation of specific BMPs. Consequently, permittees can claim to meet an oxygen demand using one of two methods.
MPCA does not currently provide pollutant reduction credits for organic carbon (organic matter) and specific BMPs. These credits could potentially be developed upon request.
The MS4 permit does not require permittees to quantify pollutant loading for oxygen demand. Consequently, MPCA recommends including BMPs/activities in your MS4’s compliance schedule that reduce organic matter and carbon (e.g. leaf litter), since these BMPs/activities will also reduce oxygen-demanding substances in the streams (see table below). Most BMPs that reduce organic matter (e.g. street sweeping), will also reduce phosphorus, sediment and/or bacteria (Escherichia (E.) coli, fecal coliform) loading to waterbodies. Additionally, if BMPs/activities are implemented across the entire jurisdictional area of your MS4, some activities may be used to demonstrate progress towards additional applicable phosphorus, total suspended solids (TSS), and/or bacteria (E. coli, fecal coliform) WLAs.
Other sources of oxygen demand in urban stormwater runoff include animal and food waste, trash, gasoline and motor oil, heavy metals, fertilizers, and pesticides. The following table lists some stormwater practices that may be effective in reducing oxygen demand in stormwater runoff. The list is not comprehensive and any practice that removes phosphorus or TSS will also likely reduce oxygen demand. If BMPs are targeted toward oxygen demand, practices that reduce organic matter will be most effective.
Permittees have two permit requirements for oxygen demand WLAs not being met.
Potential sources of organic matter and carbon and BMPs/Activities that could be included in your compliance schedule to address dissolved oxygen/oxygen demand applicable WLAs
Link to this table
|MS4 Infrastructure||Decaying plant matter, litter, and sediment in the storm drain system||Enhance street sweeping program|
|Remove leaf litter and soil in street and gutters (e.g. implement an Adopt-a-storm drain program). Educate property owners on proper yard waste management|
|Stormwater runoff from impervious surfaces||Implement source, rate, volume controls (i.e. adopt minimal impact design standards (MIDS) for new, redevelopment, and linear projects)|
|Minimize impervious surfaces|
|Implement filtration practices, infiltration practices, and sedimentation practices|
|Domestic pets||Dogs, cats, dog parks, walking trails, residential yard and sidewalk runoff (spring runoff after winter accumulation)||Install pet waste disposal stations along trails, in dog parks, etc|
|Pass and enforce pet waste ordinances and educate pet owners about them|
|Add infiltration BMPs downstream of parks/residential areas and upstream of stormwater pipes (i.e., somewhere between the park/residential area and the stormwater outfall to intercept and infiltrate some or all of the flow from these areas)|
|Residential sources||See this section|
|Industrial and commercial practices||See this section|
Additional information on potential BMPs/activities to address the Hardwood Creek, Trott Brook Creek, and Buffalo Creek dissolved oxygen impairments may also be available in the following:
The following references provide information on oxygen demand.
Additional information and guidance related to TMDLs may be found at this link.