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6.2. SR 11-19-2007`rt °` REQUEST FOR ACTION ..,.~. River To Item Number Ma ox & Ci Council 6.2 Agenda Section Meeting Date Prepared by Communi Develo ment November 19, 2007 Rebecca Hau Environmental Admin Item Description Reviewed by Approval of Loading Assessment, Nondegradation Report and Outstanding Resource Value Water Reports Reviewed by Action Requested Staff is recommending the Council approve the ciry's Loading Assessment, Nondegradation and Outstanding Resource Value Water Report completed by Bonestroo as required by the Minnesota Pollution Control Agency (MPCA). Background/Discussion In August 2007, the city council authorized Bonestroo to complete the city's Loading Assessment, Nondegradation and Outstanding Resource Value Water (ORV W) Report as required by the MPCA as part of the ciry's National Pollutant Discharge Elimination System (NPDES) permit. This report is due on December 1, 2007. The MPCA will consider the pemrittee to be in compliance with the nondegradation Hiles if 19881oading levels of storm water volume and pollutants can be achieved, either through existing facilities, programs and policies, or through proposed modifications. The report detemuned that current practices will not meet the 19881oading levels for Average annual flow volume, Total suspended solids, and phosphorus levels. In order for us to achieve compliance, the report includes Best Management Practices (BMP) that will need to be developed. These new BMPS focus on new development, thus mitigating the impacts of future growth. They also focus on redevelopment through the creation of a redevelopment ordinance that seeks water quality retrofits on a sliding scale. The BMPs also include modifications to water quality treatment requirements and implementation of water quality treatment ordinance, implementation of a dtywide infiltration ordinance and implementation of BMPS with public projects. The MPCA will be reviewing the report and will let the city know if the report is adequate to meet the 1988 loading levels for Average annual flow volume, Total suspended solids, and phosphorus levels. The City Council should expect staff to be developing ordinances to achieve these requirements and bringing them forth fox approval in the next year. Attachments • Summary of Nondegradation report Action Motion by Second by _ Vote Follow Up cHy a ....- 'ver NONDEGRADATION REVIEW Nondegradation Report Elk River, MN October 2007 Project Number: 1482-07-001 INTRODUCTION Since 2003, the MPCA has required municipalities with a population hetween 10,000 and 100,000 to secure a Minnesota Pollution Control Agency (MPCA) permit authorizing discharge of storm water from their municipal storm drainage system to waters of the state. This authorization occurs under the National Pollutant Discharge Elimination System (NPDES) program. These municipal systems are known as Municipal Separate Storm Sewer Systems or MS4s. In 2003, the MPCA was sued by the Minnesota Center for Environmental Advocacy aver the State's alleged noncompliance with its nondegradation rules. As part of the court action, the Minnesota Court of Appeals ruled specifically that the permit issued by MPCA to conditionally authorize storm water discharge from an M54 system under the NPDES program had to address nondegradation requirements in the rules. To comply with the court action, the MPCA revised the NPDES permit program in 2006 to require 30 municipalities across the state, whose storm water discharges are permitted through the M54 program, to complete additional work called a "Nondegradation Review" that will enable the state agency to determine if nondegradation rules are being met. MPCA selected these 30 MS4s based on their assessment of those communities most likely to have expanded storm water discharges to surface waters as reflected hy: 1. population changes since 1990, 2. current population, and 3. projected population growth to 2020. Elk River is one of the 30 permitted M54s to which this Nondegradation Review requirement applies, MS4s must complete a Nondegradation Report when their Loading Assessment indicates they have significant new and expanded discharges. Elk River's loading Assessment calculates new and expanded discharges of pollutants to certain water bodies. In some cases these new and expanded discharges are clearly significant. For this reason the City of Elk River includes this Nondegradation Report with its Loading Assessment. The Nondegradation Report must propose BMPs that address nondegradation far inclusion in Elk River's Storm Water Pollution Prevention Program or SWPPP. As a par[ of minimum control measure 5 in the City's existing SWPPP several BMP summary sheets were developed dealing with stormwater management for new development and redevelopment. Elk River's Nondegradation Report includes a discussion of potential BMPs to attain 1988 levels for total phosphorus (TP), total suspended solids (TSS), and water volume. Elk River has also developed new BMP summary sheets for inclusion in its SWPPP and these are attached to this Nondegradation Report. These BMP summary sheets are not for the actual landscape BMPs that attain 1988 pollutant loads. Rather these BMP summary sheets describe the development of official controls that lead to these landscape BMPs and build on the BMP summary sheets Sa-1, 5b-1 and 5c-1 already developed. These new official controls focus on new development, thus mitigating the impacts of future growth. These official controls also focus on redevelopment through the creation of a redevelopment ordinance that seeks water quality retrofits on a sliding scale. The city intends that the new development strategy apply uniformly throughout the city but that the retrofit strategy will be focused in areas where new and expanded discharges have occurred. E!k River 1482-0 70 0 1 Nondegradation Report page 1 A discussion of Elk River's proposed mitigation steps and why these alternatives are both reasonable and practical follows. REVISIONS TO THE CITY'S WATER QUALITY TREATMENT REQUIREMENT AND IMPLEMENTATION OF WATER QUALITY TREATMENT ORDINANCE The Loading Assessment shows that for Elk River's urban land uses (urban and high density residential, commercial/industrial, Old Town, Mixed Use and public/semi-public) additional water quality treatment is necessary to meet Baseline loading rates. It also shows that a conversion from agricultural land use to rural residential land use is a slight improvement on the Baseline pollutant loads. The City's current Section 2500 Design Standards require sedimentation basins and wet extended detention ponds designed in accordance with the Minnesota Stormwater Manual. This is currently only a design standard and not an adopted ordinance. Options far increasing the water quality treatment required for urban land uses were considered. For comparison, a requirement of 60% total phosphorus removal from urban developments was analyzed to determine whether itwould be adequate to meet mitigate increased loadings. Using an accepted relationship between TP and TSS shown in Figure 1, removal of 60% of TP generally correlates to 93% TSS removal. figure 7 -Stormwater Pollutant Removal Efficiencies Related to Pond Detention Time. (Adapted from OWML,198.y) 100 90 80 o ~o 60 a 50 40 ~ 30 C 20 ° 10 0 0 5 10 15 20 25 30 35 40 45 50 Detention Time (hrs) Subwatershed ER04 is primarily urban for 2020'conditions, versus large tracts of agriculture for 1988 conditions. As an example, the 60% TP removal requirement was applied to all urban land uses within ER04 for 2020 conditions to determine if it is adequate to meet the nondegradation goals. Table 1 presents a comparison of loading rates with and without the 60% TP removal requirement. _ .~ -- __ . . -- -- ~_ T~ I ~ 1 __ - ~! -F TP _ - -~ - T55 1 Elk River 1482-0 700 1 Nondegradation Report Page 3 TABLE 1 SUMMARY OF MODELED LOADINGS GENEUATED IN ER04 TP Load (Ibs/yr) `TSS Load (Ibs/ r) Runoff VoWme <: (ac-fU r) Baseline Condition 1,230 440,600 1,050 Present Condition 1,920 678,600 1,740 2020 Condition w/o 60% TP removal 2,230 772,700 2,000 2020 Condition w/60% TP removal 890 54,100 2,000 As shown in Table 1, there is a significant improvement in the 2020 loading rates far TP and T55 to less than the Baseline condition with the 60% TP removal requirement in place. This implies same retrofit of water quality treatment for areas already developed. Conservatively, it was assumed that there would be no effect on runoff volumes based on this water quality treatment requirement. An infiltration requirement is necessary to mitigate the increase in runoff volumes. It should be noted that the 60% TP removal requirement was applied as a general standard to all urban land uses without specific guidance or analysis on how it would he achieved. Typically standard National Urban Runoff Program (NURP) designed ponds provide adequate water quality treatment to achieve the 60% TP removal. Ultimately the City will be required to apply a water quality treatment requirement that meets nondegradation goals. Structural and non-structural BMPs developed as a part of BMP summary sheet Sa-1 should be designed to meet the water quality treatment requirement. To address revisions to the city's water quality requirements, the City of Elk River proposes aBMP Se-1 modification to the citywide water quality treatment standard and adoption of a water quality treatment ordinance as modification to its current SWPPP. OF AN INFILTRATION REQUIREMENT As discussed above, application of a water quality treatment requirement was not assumed to provide a reduction in runoff volume. Therefore an additional infiltration requirement is needed to mitigate the increase in runoff volumes for urban land uses. Based on the Soil Survey, the City is dominated by hydrologic soil group A and B soils and therefore a good candidate for infiltration best management practices. At present, the Minnesota Pollution Control Agency National Pollution Discharge Elimination System (MPCA NPDES) General Construction Permit sets an infiltration guideline such that the runoff generated by the 0.5-inch rainfall over the impervious surfaces of a development is infiltrated/filtrated. Continuous simulation of urban residential development indicates that 0.5-inch off of impervious surface infiltration standard reduces by 80% the average annual runoff volume over the case where no infiltration is used. Though this assumption would have to be verified and subsequently redefined for other land uses, it becomes a useful benchmark in determining what can be done to eliminate new and expanded discharges. As a starting point, this standard was applied to subwatershed ER04 to determine its adequacy in meeting the Baseline loads. Table 2 presents a comparison of loading rates with and.without the infiltration requirement. E!k Rrver 1481-0 700 1 Nondegradation Report Page 4 TABLE 2 SUMMARY OF MODELED LOADINGS GENERATED IN EROS TP Load' (Ibs/yr) TSS Load i (Ibs/ r} ": Runoff Volume :! (ac-ft/ r} Baseline Condition 1,230 440,600 1,050 Present Condition 1,920 678,600 1,740 2020 Condition w/o infiltration 2,230 772,700 2,000 2020 Condition w/infiltration 450 54,100 400 The results presented in the table above are based on the assumption that 80% volume reduction implies 80% phosphorus reduction (though greater than 80% removal likely occurs) and 93% 755 reduction. Application of the 0.5-inch infiltration requirement is adequate to meet Baseline conditions far all three parameters based on this example. It is also possible to consider the decrease in load by a runoff depth comparison between agricultural land use and urban residential land use. 0.14 Rv Agriculture * 31.5 inches average annual precipitation = 4.4 inches/year 0.21 Rv Urban residential * 31.5 inches average annual precipitation = 6.6 inches/year 6.6 inches/year' 20%= 1.3 inches/year This simple calculation shows that the runoff depth for urban residential with implementation of the infiltration requirement is considerably less than the runoff depth generated with agricultural land use. City staff and the City Council will consider whether an adjustment is needed to the infiltration requirement to meet nondegradation requirements. Structural and non-structural BMPs developed as a part of BMP summary sheet 5a-1 should be designed to meet the infiltration requirement. To address the need for a citywide infiltration requirement, the City of Elk River proposes BMP 5d-1, implementation of the citywide infiltration ordinance. IMPLEMENTATION OF BEST MANAGEMENT PRACTICES WITH PUBLIC PROJECTS Another means of attaining nondegradation compliance is for the City to begin retrofitting BMPs to areas through routine and periodic public improvement projects such as street reconstruction, park and other public facilities projects. In the case of street reconstruction projects very often these are mill and overlay and not full reconstruction projects. Nonetheless, some opportunities might present themselves for retrofitting different BMPs depending on the specifics of each project. A potential annual load reduction would be speculative if offered now. Rather, the BMP summary sheet for this SWPPP modification emphasizes adaptive management through experience and reporting through the annual reporting required by the permit. To address the need for retrofitting BMPs, the City of Elk River proposes BMP Sf-1, implementation of BMPs with public projects. Elk River 1482-07001 Nondegradatlon Report Page 5 SUMMARY OF NONDEGRADATION REPORT Elk River's Nondegradation Review consisu of a Loading Assessment and this document which is considered Elk River's Nondegradation Report. According to the M54 General Permit, Elk River is required to complete the Nondegradation Report since its Loading Assessment showed that the city had new and expanded discharges. Elk River's Nondegradation Report focuses on mitigation through revisions to its official controls with an emphasis on controls over new development and redevelopment. The components of the revised official controls are contained in the revised BMPs that fallow. These new BMPs, or proposed SWPPP modifications, are summarized as follows: 1. Modifications to water quality treatment requirement and implementation of water quality treatment ordinance 2. Implementation of a citywide infiltration ordinance 3. Implementation of BMPs with puhlic projects f!k River 1482-07001 Nondegradation Report Page 6 BMP Summary Sheet M54 Name: City of Elk River Permit requirement addressed: Part X.C Nondegradation Report Unique BMP Identification Number: Sd-1 *BMP Title: Implementation of Citywide Infiltration Ordinance *BMP Description: This Best Management Practice includes the development of a new infiltration standard that strives to attain nondegradation, defined as maintenance of 1988 water volumes discharged to a receiving water. Structural and non-structural BMPs developed as a part of BMP 5a-1 will be designed and reviewed for compliance with its infiltration and stormwater standards. Reviews conducted subsequent to implementation of this ordinance revision will consider nondegradation compliance. Location(s) in SWPPP of detailed information relating to this BMP: BMP 5d-1 Implementation of a Citywide Infiltration Ordinance *Measurable Goals: • Adoption of ordinance • Number of developments reviewed under new ordinance *Timeline/Implementation Schedule: • Winter 2007/2008 -Develop technical basis for standard and ordinance language • Spring 2008 -Council adopts new ordinance • Summer 2008 -Begin review of developments under new ordinance • Annually after adoption -Document the number of development sites reviewed under new ordinance Specific Components and Notes: • Analysis of water volume discharge for commercial land use as allowed by Elk River • Comparison of water volume discharge to that of undeveloped land • Determination of infiltration standard • Draft ordinance for review • Council approval of ordinance • Implementation of ordinance *Responsible Party for this BMP: Name: Rebecca Haug Department: Environmental Division Phone: 763-635-1068 E-mail: rhaug@ci.elk-river.mn.us *Indicates a REQUIRED field. Failure to complete any required faeld will result in rejection of the application due to incompleteness. BMP Summary Sheet MS4 Name: City of Elk River Permit requirement addressed: Part X.C Nondegradation Report Unique BMP Identification Number: Se-I *BMP Title: Modification of Citywide Water Quality Standard and Implementation of Water Quality Ordinance *BMP Description: The current citywide water quality standard requires sedimentation basins and extended detention ponds designed in compliance with Minnesota Stormwater Manual guidelines for a development site. This standard is contained in the city's Section 2500 Design Standards. This Best Management Practice includes the modification of the water quality standard that strives to attain nondegradation, defined as maintenance of 1988 TP and TSS loads discharged to a receiving water. Structural and non-structural BMPs developed as a part of BMP Sa-1 will be designed and reviewed for compliance with its stormwater standards. Reviews conducted subsequent to implementation of this ordinance revision will consider nondegradation compliance. Location(s) in SWPPP of detailed information relating to this BMP: BMP 5e-1 Modification of the Citywide Water Quality Standard and Implementation of Water Quality Ordinance *Measurable Goals: • Modification of design standard • Adoption of Ordinance • Number of developments reviewed under new ordinance *Timeline/Implementafion Schedule: • Winter 2007/2008 -Develop technical basis for standard and ordinance language • Spring 2008 -Council adopts new ordinance • Summer 2008 -Begin review of developments under new ordinance • Annually after adoption -Document the number of development sites reviewed under new ordinance Specific Components and Notes: • Comparison of TP and TSS loads discharged to that of undeveloped land • Determination of water quality standard • Draft ordinance for review • Council approval of ordinance • Implementation of ordinance *Responsible Party for this BMP: Name: Rebecca Haug Department: Environmental Division Phone: 763-635-1068 E-mail: rhaug@ci.elk-river.mn.us *Indicates a REQUIRED field. Faidure to complete any required field will result in rejection of the application due to incompleteness. BMP Summary Sheet M54 Name: City of Elk River Permit requirement addressed: Part X.C Nondegradation Report Unique BMP Identification Number: Sf-1 *BMP Title: Implementation of Best Management Practices with Public Improvement Projects *BMP Description: This strategy considers implementation of BMPs on public lands within or downstream of street major maintenance projects or other development projects. Public lands could include those owned by schools, dhurches, and the city. The city might also utilize undeveloped lands to retrofit treatment. The BMPs constructed for the retrofit would be over and above those the future development would need to meet current city standards. This BMP will provide the city the information it needs to determine whether this model for retrofitting BMPs can be consistently implemented and be cost effective. The knowledge gained from this BMP will result in a more cost effective long-term implementation plan. The city will review its projects and report on these through its annual report. Location(s) in SWPPP of detailed information relating to this BMP: BMP 5f-1 Implementation of BMPs with Public Improvement Projects *Measurable Goals: • Number of infiltration areas installed and area over which treatment is retrofitted • The calculated load reduction obtained from these BMPs • The cost of this load reduction *Timeline/Implementation Schedule: • Winter 2007 -Begin considering how to retrofit BMPs into different types of proposed projects • Spring, Summer, Fall 2008 - BMPs implemented with projects • Spring 2009 -Review extent of implementation and other measurable goals, document in annual report Specific Components and Notes: • Cost/benefit will be considered in light of previous research by others • Maintenance costs and other life cycle costs will be considered *Responsible Party for this BMP: Name: Rebecca Haug Department: Environmental Division Phone: 763-635-1068 E-mail: rhaug@ci.elk-river.mn.us *Indicates a REQUIRED field. Failure to complete any regzrired field will result in rejection of the appdication due to incompleteness.