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Home My WebLink About2C, Storm Water Ponds Maintenance Program_TL AI�EN HILLS Request for Council Review Prepared By: Terry Maurer, Public Works Director Matt Woodruff, Civil Engineer Worksession Date: November 15, 2010 c Storm Water Pond Maintenance Program Discussion Topic: Please refer to the attached memorandum. Supportin! Documents: 1. Memorandum dated November 15, 2010 from Matt Woodruff. 2. MPCA "Managing Dredged Materials" (summary). 3. Indian Oaks Court Location Maps. DATE: November 15, 2010 TO: Honorable Mayor and City Council Members Patrick Klaers, City Administrator FROM: Terry Maurer, Public Works Director Matt Woodruff, Civil Engineer SUBJECT: Storm Water Pond Maintenance Program Background A1WFI HILLS MEMORANDUM The City's storm water collection system contains numerous catch basins, manholes, sewer pipes, ditches, and ponds that receive runoff from rainfall events. Storm water runoff becomes polluted with sediments, road salts, metals, fertilizers, pesticides, and many other contaminants. Within Arden Hills, a portion of this runoff is directed to storm water ponds which treat and improve water quality by removing the pollutants before the runoff reaches a surface water body. A surface water body includes lakes, rivers, and streams. The City of Arden Hills has numerous ponds and wetland areas that receive storm water either through the storm sewer system or by overland runoff. Many of these ponds were either constructed as part of a neighborhood development or were an existing lowland /wetland area that had storm water runoff directed to them. In either case, the constructed ponds or existing wetlands have received storm water runoff (containing the pollutants previously discussed) for many years and it is important that they be considered for maintenance. Mainly, pond maintenance includes dredging of sediment deposits, as well as addressing erosion problems and cleaning out storm sewer pipes that enter /exit the ponds. In order for storm water ponds to be an effective means of water quality improvement, they must have adequate storage volumes such that sediments and other pollutants can settle -out from the storm water before reaching the surface waters. According to City records, the City's storm water ponds have not been dredged and have received little maintenance. In accordance with the City's Municipal Separate Storm Sewer System (MS4) permit with the Minnesota Pollution Control Agency (MPCA), the City is required to inspect 20 percent of the City's storm water ponds on an annual basis. MS4 permits are administered by the MPCA to regulate the amount of sediments and pollutants that enter surface waters through a City Council Meeting P:\Admin\Council\Agendas Packet Information\2010 \1 1 -15 -10 Worksession\Packet Information\2C 11- 15- lOMemo Pond- Maintenance.doc Page 1 of 3 municipality's storm water system. Based on the need to start inspections and the history of little maintenance performed, City staff is recommending that dredging and other associated maintenance be programmed into the Capital Improvement Plan (CIP) on an annual basis. The 2010 CIP contains a $50,000 line item for pond maintenance. Since storm water runoff contains many pollutants, it is likely that the City's ponds have sediment build -ups that are polluted with metals and other contaminants. If a pond were proposed to have sediments dredged, the City should perform this maintenance in accordance with the MPCA's "Managing Dredged Materials" guidelines, dated June 2009. A brief summary of the MPCA's guidelines are attached for reference. In accordance with the guidelines, the City would have to determine the level of contamination within the pond sediments. The MPCA has three levels of contamination which are: Level 1 Level 2 Level 3 To determine the level of contamination within pond sediments, the City would hire a consultant to take samples from the bottom of a pond and have them analyzed. As recommended by the MPCA, the number of samples that should be taken depends on the amount of sediment material anticipated to be dredged from a pond. Once the appropriate level of contamination is known, the City can solicit bids from contractors to perform the work. The cost of sediment removal is directly related to its level of contamination. Since pond maintenance would be a new capital expenditure for the City, it is proposed that maintenance be started on the Indian Oaks Court pond because it is small in size, it has easy access to the road, the neighborhood has expressed concerns about pond maintenance, and the Ramsey Conservation District (RCD) has grant money available for the pond's shoreline restoration. The following timeline could be anticipated if the Indian Oaks Court pond were scheduled for maintenance: December 2010 February 2011 May 2011 May /June 2011 Unrestricted reuse of sediments: can be reused in residential areas Restricted reuse of sediments: can be reused in industrial zoned areas Significant contamination: material to be placed in a landfill Receive contractor bids Pond Dredging Restoration and Landscaping Outlet pipe replacement The following estimated costs and financing could be anticipated for the project. Estimated costs include contingencies and engineering. Pond Dredging $32,200 100% City funds Restoration (RCD) $22,000 50% City funds, 50% RCD grant Outlet Pipe 4,800 100% City funds Total Cost $59,000 City Council Meeting P:\Admin \Council\Agendas Packet Information\2010\ 11 -15 -10 Worksession\Packet Information\2C 11-15-10Memo_Pond- Maintenance.doc Page 2 of 3 Please note that the restoration estimate was provided by the RCD. From the total estimated project cost, the City's obligation would be $48,000 while the RCD grant would cover $11,000. City staff is seeking direction from the City Council to proceed with the Indian Oaks Court pond maintenance. The City must indicate to the RCD by the end of November, its commitment to proceed with the project such that the RCD can earmark the proposed shoreline restoration grant money. City Council Meeting P:\Admin \Council\Agendas Packet Information\2010\ 11 -15 -10 Worksession\Packet Information\2C 1 1 -15- l OMemo Pond Maintenance.doc Page 3 of 3 Environmental Risk Assessment Overview In determining the most appropriate management method for dredged material, an evaluation of the reasonable Likelihood for a given pollutant to be present in the material must be made. A determination as to whether a pollutant has `reasonable likelihood' is done through a combination of empirical and technical evaluation of the sediment to be dredged, which may include sampling and analysis. The following methods are used in preparing a risk assessment for the proposed dredging material: grain size analysis past industrial activities /sources of pollutants sampling and analysis of pollutants likely to be present Together, these methods characterize the dredged material. In addition to characterizing dredged material, any non exempt discharge from a project and /or management unit requires complete characterization. Characterization of effluent from the dredge project site and/or management unit(s), if proposed, are described in Chapter 4 of this document. Exempt discharges are described in Chapter 5 of this document. An evaluation of the reasonable likelihood for a given pollutant to be present in the material must be made, so that the proper management method for the material can be determined. Grain size analysis Begin the dredge site risk assessment by determining whether the material to be dredged is predominantly sand, gravel or pebble, or is comprised of other materials. Dredge material that is predominantly sand, gravel or pebble is unlikely to be contaminated, as pollutants do not generally adhere to these types of particles, and are therefore not incorporated into the sediment. Dredge materials that are primarily sand are unlikely to be contaminated and do not require additional chemical evaluation, and can proceed to permitting. To demonstrate that dredged material from a given project or site is predominantly sand, 93 percent of the dredged material must be coarser than silt; i.e. only seven percent of the dredged material can be silty materials that are finer than sand. To make this determination, the following procedure must be used: a. Conduct a sieve grain size analysis using ASTM Method C -136 for the gradation analysis and ASTM Method D -2487 for classification. b. Determine the minimum number of samples required using Table 6, based on the total amount of material to be dredged. c. Conduct the analysis using the following US Standard sieves: 1", 3/8 #4, #10, #100, and #200. d. Report the results for each of the discrete sample locations as a mass percentage of retained sediments. If 93 percent or more of the dredged material is retained on a #200 sieve, that is, the material is coarser than silt, the dredged material is unlikely to be contaminated, and does not require additional evaluation. Dredged material not excluded from additional analysis, as determined using the grain size analysis described above, must be more thoroughly characterized by evaluation of past industrial activities and analysis of dredged material for any pollutant has a reasonable likelihood to be present in the dredged material. Continue the evaluation as described by the following sections. Analysis of base -line and additional sediment parameters are described in the following chapter. 10 In projects where more than 93 percent of the dredged material is coarser than sand, additional evaluation is not required. Managing Dredged Materials in the Minnesota Pollution Control Agency State of Minnesota June 2009 For example, in the Great Lakes Basin, especially in the large tributaries and harbors, a more extensive list of parameters is required to properly characterize sediment. It is known that many of these tributaries have concentrations of polycyclic aromatic hydrocarbons (PAIL) from former coal gasification plants, urban run- off, oil spills, and vehicle and smoke stack particulate emissions that are deposited on the watershed. For projects involving sediment in urban areas associated with inland waters and Great Lakes tributaries, PAH analysis is required. Two contaminants that bioconcentrate up aquatic food chains are highly bioaccumulative in upper trophic level organisms like game fish are PCBs (polychlorinated biphenyls) and mercury. In the risk assessment phase, fish consumption advisories issued by the MDNR should be reviewed to determine if the project area is in a water body included in the advisory. For projects involving sediment from water bodies included in a fish and/or wildlife consumption advisory, mercury and PCB analysis, as relevant, is required. Stormwater projects Stormwater project proposers should also review the "Modified Characterization and Permit Approach for Urban Stormwater Ponds" section below. Management levels Based on the results of completed sediment characterization, that is, the type and level of pollutants in the material in comparison to established SRVs, dredged material is categorized into one or more Management Levels. The Management Level of a dredged material dictates the appropriate disposition of the material. Dredged Material is categorized into three Management Levels: Level 1 Level 2 Level 3 Level 1 Dredged Material is suitable for use or reuse on properties with a residential or recreational use category. Level I Dredged Material is characterized as being at or below analyte concentrations for all of the SRVs listed in the Level 1 SRV column of Table 5. The SRVs incorporate the most common human exposure pathways (ingestion, dermal contact, and inhalation of contaminants volatilized from soil in outdoor air) using generic exposure assumptions. The Level 1 SRVs generally use a chronic residential exposure scenario, but are also protective of acute health effects in young children when acute toxicological data is available. For dredged materials, the Level 1 SRV limits in Table 5 are the most restrictive. Note: Exposure pathways in an agricultural land use setting have not been evaluated, and is therefore not an appropriate land use category for comparison to SRVs. Level 2 .dredged Material is suitable for use or reuse on properties with an industrial use category. Level 2 Dredged Material is characterized as being at or below analyte concentrations for all of the SRVs listed in the Level 2 SRV column of Table 5. The Level 2 SRVs use an industrial exposure scenario based on average working adults according to a typical industrial site use. Level 2 SRVs are less restrictive then the Level 1 SRVs. Level 3 Dredged Material is characterized as having significant contamination, as demonstrated by one or more analyte concentrations being greater than the Level 2 SRV column of Table 5. Sites that have potentially important exposure pathways or other conditions that are not incorporated into a residential or industrial risk characterization must be evaluated in the context of a fully site specific risk assessment for which site specific SRVs are calculated that account for all potentially significant exposure Managing Dredged Materials in the State of Minnesota June 2009 15 Dredged material is categorized into management levels, based on the level of contamination, Minnesota Pollution Control Agency Analysis of parameters beyond the baseline analytes may be indicated based on the evaluation of historical land uses and the reasonable likelihood for pollutants in sediment to be dredged. pathways and characteristics of the site. Level 3 Dredged Material is considered to be significantly contaminated and must be managed specifically for the contaminants present. In some cases a Level 3 Dredged Material may have levels of contaminants at levels subject to regulation under the Resource Conservation and Recovery Act (RCRA) and/or the Toxic Substances Control Act (TSCA), if PCB levels in sediment are 50 mg/kg or greater. In these cases, significant additional regulation applies, and disposal of the waste is strictly regulated. Contact 'CA staff for additional information on regulatory requirements for disposal of Level 3 Dredged Materials. Larger projects may produce dredge materials that can be segmented into areas with dredged materials that are distinctly different from each other. Subsets of dredged material may be able to be managed differently from each other, depending on the Management Level applicable to each discrete subset. If subsets of Management Levels exist within the project, dredged material may be managed separately by Levels, i.e. each subset of dredged material is managed at the relevant Management Level; managed at the most restrictive Management Level, if separation and management by subset is not feasible or desired; or, managed at the most restrictive Management Level if subsets from a given project or multiple project, such as at a use /reuse staging area, are co- mingled prior to disposal. Calculation of BAP equivalents Minnesota uses Potency Equivalency Factors (PEFs) to evaluate toxicity and to assess risks of carcinogenic PAHs. A PEF is a relative estimate of toxicity of chemical compared to a reference chemical. Benzo(a)pyrene (BaP) was chosen as a reference chemical for carcinogenic PAHs because its toxicity is well characterized. The BAP equivalent should be calculated in accordance with the MPCA document Polycyclic Aromatic Hydrocarbons, (p- eao2 -03), and the Soil Reference Value (SRV) spreadsheet at www.pca. state. mn. us/ publicatiionslrisk- tier2srv.xls. More information on Minnesota Soil Reference Values found can be found on the MPCA Web site at www.pca.state.mn.us/cleanup/riskbasedoc.html#pathway. Managing Dredged Materials in the Minnesota Pollution Control Agency State of Minnesota June 2009 16 NIUM NM filiffiEtann IMIAltig, a SW MEM MP 1:61110 &Nati ingt *WV* rff RE qcw ItIT' 11 1101 utigiliikal. oit IPA, 1E9 D iu I 4 46 i i, "s i fi b 4411IP if g NEMBINXIMNIVAVra Ets","'l