MCM 5 - POST CONSTRUCTION STORM WATER MANAGEMENT

Transcription

1 MCM 5 - POST CONSTRUCTION STORM WATER MANAGEMENT

2 POST CONSTRUCTION STORM WATER MANAGEMENT Minimum Control Measure INTRODUCTION Riverdale City has committed to Joint Permit with Weber County to meet the requirements of Post Construction Storm Water Management. The City will take the major role for responsibility for this Measure as a condition of the joint permit with Weber County This section is similar to MCM 6 - Pollution Prevention/Good Housekeeping, except that this section applies mor to Redevelopment and long term Operation and Maintenance. MCM 6 applies more to preventing pollution in areas other than construction. 5.2 POLLUTANTS OF CONCERN Because of the many different types of residential, commercial and construction activities, there can be a wide variety of pollutants that make it into stormwater runoff. Even different facilities of the same industry may need different approaches to reducing pollutant discharges to stormwater. Therefore, it is imperative that the owner/operator of each facility understand the potential pollutants and impacts from their individual processes. This chapter will only discuss the most typical pollutants found in industrial stormwater runoff. Solids, nutrients, metals, oxygen demanding substances, bacteria and viruses, and oil and grease are the pollutants most frequently associated with stormwater runoff. These pollutants are discussed in the following subsection. Solids Solids (often referred to as total or suspended solids) can cause many receiving water problems. First, it can cause direct toxicity to aquatic organisms, through such mechanisms as fouling of gills, suffocation, etc. Second, high solids concentrations can reduce water clarity. Third, solids act as a vehicle to transport other pollutants. Excessive solids are often the result of poor construction practices at the industrial site. Nutrients Excessive nutrients such as nitrogen and phosphorus in the receiving water can cause problems by stimulating the growth of algae or rooted aquatic plants. Excessive plant growth can cause dissolved oxygen problems, reduce biologic diversity, worsen aesthetics, or impair use for water supply. Some industrial activities typically associated with nutrients include fertilizer/pesticide manufacturing and distribution, waste treatment, and food processing. Metals Metals, especially heavy metals can be toxic at very low concentrations. Metals can also bioaccumulate in fish and other species and be passed on to higher levels of the food chain, including humans. Certain metals including cadmium, copper, lead, silver, and zinc are the most common metals which contaminate waterways. Industrial activities which commonly deal with metals include mining, electroplating, cement, battery production, and metal recycling. 5.1 JONES & ASSOCIATES CONSULTING ENGINEERS

3 Oxygen-Demanding Substances Oxygen-demanding substances tend to deplete the dissolved oxygen levels in streams and lakes. The depleted oxygen supply can result in loss of aquatic life. Oxygen demanding substances are commonly found in food processing industries and chemical manufacturing plants. Bacteria and Viruses Bacteria and viruses are the most common microorganisms found in surface water runoff. Bacteria and viruses often carry diseases which can be transferred to animal life and to humans. Food processing and medical wastes are often associated with microbiological contamination. Oil and grease Oil and grease contain a wide array of hydrocarbon compounds, some of which are toxic to aquatic organisms at low concentrations. Industrial sources of oil and grease are generally associated with automobile related industries such as: repair shops, body and paint shops, retail distribution, and dismantlers/recyclers. Floatables Trash and litter from industrial sites may contain amounts of pollutants which will effect stormwater quality. Floatables in waterways and drainage systems pose both aesthetic and maintenance problems. Other Toxic Materials (Priority Pollutants) Facilities may contribute other toxic materials to storm water in low concentrations. Pesticides, phenols and polynuclear or polycyclic aromatic hydrocarbons (PAHs) are most frequently found in stormwater discharges associated with industrial operations. 5.3 MEASURABLE GOALS AND FISCAL ABILITY The following table summarizes the BMPs, Measurable Goals, Implementation Schedule and Fiscal ability of the City s for each BMP. MCM 5 - POST CONSTRUCTION STORM WATER MANAGEMENT Name BMP Measurable Goal Implementation Schedule Fiscal Ability legal Establish Ordinances penalizing Illicit discharges Establish an ordinance Dec 2004 See MCM 3 basin Detention Basin Require detention basin for all sites > 1 acre Dec 2004 Cost to Developer study Storm Drain Study requirements Require all storm drain studies to conform to County Standards (ie HEC-HMS) Immediate Training to be provided by Weber County at no cost to the City 5.2 JONES & ASSOCIATES CONSULTING ENGINEERS

4 Name BMP Measurable Goal Implementation Schedule Fiscal Ability CW Constructed Wetlands Study with the Storm Drain Master Plan update Dec 2004 Included in MCM 6 EDB Extended Detention Basins Study with the Storm Drain Master Plan update Dec 2004 Included in MCM 6 OWS Oil/Water Separators and Water Quality Inlets Require in suspected development such as commercial Dec 2004 Cost to developer SB Sediment Basin Study with Storm Drain Master Plan update Dec 2004 Included in MCM 6 SPR Site Plan Review and Inspection Require erosion control plan for all sites >1 Ac Immediate Cost to Developer inspect Site Inspection Have procedure form for Inspector Dec 2004 $0 Estimated Annual Cost for Implementation $0 Estimate One-Time cost within next 5 years $0 5.4 BEST MANAGEMENT PRACTICES (BMP) The following pages consist of the BMP s for the City. Each page represents a separate BMP with details given. The intent of this section is to provide a variety of practices that could be related to Post Construction Storm Water Management. The format is similar to other communities on the Wasatch Front, having been originally obtained from Salt Lake County s Storm Water Management Plan. 5.5 REFERENCES Salt Lake County Engineering Division. September Guidance Document for Stormwater Management. State of California. March California Storm Water Best Management Practice Handbooks. 5.3 JONES & ASSOCIATES CONSULTING ENGINEERS

5 BMP: Constructed Wetlands CW CONSIDERATIONS : Soils : Area Required : Slope : Water Availability : Aesthetics 9 Hydraulic Head : Environmental Side Effects DESCRIPTION: Constructed wetlands have a significant percentage of the facility covered by wetland vegetation. APPLICATION: < Need to achieve high level of particulate and some dissolved contaminant removal. < Ideal for large, regional tributary areas. < Multiple benefits of passive recreation and wildlife. INSTALLATION/APPLICATION CRITERIA: < Suitable soils for wetland vegetation are required. < Surface area equal to at least 1% and preferably 2% of the tributary watershed. < Include a forebay for extra storage and to trap incoming sediment. < Involve qualified wetland ecologist to design and install wetland vegetation. < Establishing wetland vegetation may be difficult. LIMITATIONS: < Concern for mosquitoes. < Cannot be placed on steep unstable slopes. < Need base flow to maintain water level. < Not feasible in densely developed areas. < Nutrient release may occur during winter. < Overgrowth can lead to reduced hydraulic capacity. < Regulatory agencies may limit water quality to constructed wetlands. MAINTENANCE: < Remove foreign debris and sediment build-up. < Areas of bank erosion should be repaired. < Remove nuisance species. < Control mosquitoes South Weber River Drive Riverdale City, UT (801) TARGETED POLLUTANTS # Sediment # Nutrients # Heavy Metals # Toxic Materials # Oxygen Demanding Substances # Oil & Grease # Floatable Materials : Bacteria & Viruses # High Impact : Medium Impact 9 Low or Unknown Impact IMPLEMENTATION REQUIREMENTS # Capital Costs : O&M Costs : Maintenance 9 Training Post Construction Storm Water Management 2004

6 BMP: Extended Detention Basins EDB CONSIDERATIONS 9 Soils : Area Required 9 Slope 9 Water Availability 9 Aesthetics : Hydraulic Head 9 Environmental Side Effects DESCRIPTIONS: Extended detention basins are dry between storms. During a storm the basin fills. A bottom outlet releases the stormwater slowly to provide time for sediments to settle. APPLICATION: < Objective is to remove only particulate pollutants. < Use where lack of water prevents the use of wet ponds, wetlands or biofilters. < Use where wet ponds or wetlands would cause unacceptable mosquito conditions. INSTALLATION/APPLICATION CRITERIA: < Basin volume is sized to capture a particular fraction of the runoff. < Drawdown time of 24 to 40 hours is required. < A shallow basin with large surface area performs better than a deep basin with the same volume. < Place energy dissipators at the entrance to minimize bottom erosion and resuspension. < Vegetate side slopes and bottom to the maximum extent practical. < If side erosion is particularly severe, consider paving or soil stabilization. < If floatables are a problem, protect outlet with a trash rack or other device. < Provide bypass or pass through capabilities for 100-year storm. LIMITATIONS: < May be less reliable than other treatment control BMPs. Inability to vegetate banks and bottom may result in erosion and resuspension. < Limitation of the orifice diameter may preclude use in small watersheds. < Requires differential elevation between inlet and outlet. MAINTENANCE: < Check outlet regularly for clogging. < Check banks and bottom of basin for erosion and correct as necessary. < Remove sediment when accumulation reaches 6-inches, or if resuspension is observed South Weber River Drive Riverdale City, UT (801) TARGETED POLLUTANTS # Sediment : Nutrients : Heavy Metals : Toxic Materials : Oxygen Demanding Substances : Oil & Grease : Floatable Materials 9 Bacteria & Viruses # High Impact : Medium Impact 9 Low or Unknown Impact IMPLEMENTATION REQUIREMENTS # Capital Costs : O&M Costs : Maintenance 9 Training Post Construction Storm Water Management 2004

7 BMP: Oil/Water Separators and Water Quality Inlets OWS CONSIDERATIONS 9 Soils : Area Required 9 Slope 9 Water Availability 9 Aesthetics 9 Hydraulic Head : Environmental Side Effects DESCRIPTION: Oil/Water separators are designed to remove a specific group of contaminants: petroleum compounds and grease. However, separators will also remove floatable debris and settleable solids. Two general types of oil/water separators are used: conventional gravity separator and the coalescing plate interceptor (CPI). APPLICATION: < Applicable to situations where the concentration of oil and grease related compounds is abnormally high and source control cannot provide effective control. The general types of businesses where this situation is likely are truck, car, and equipment maintenance and washing businesses, as well as businesses that perform maintenance on their own equipment and vehicles. < Public facilities where separators may be required include marine ports, airfields, fleet vehicle maintenance and washing, facilities, and mass transit park-and-ride lots. < Conventional separators are capable of removing oil droplets with diameters equal to or greater than 150 microns. < A CPI separator should be used if smaller droplets must be removed. INSTALLATION/APPLICATION CRITERIA: < Sizing relates to anticipated influent oil concentration, water temperature and velocity, and the effluent goal. < To maintain a reasonable separator size, it should be designed to bypass flows in excess of first flush. LIMITATIONS: < The lack of data on oil characteristics in stormwater leads to considerable uncertainty about performance. < An air quality permit may be required. MAINTENANCE: Clean frequently of accumulated oil, grease, and floating debris South Weber River Drive Riverdale City, UT (801) TARGETED POLLUTANTS : Sediment : Nutrients : Heavy Metals : Toxic Materials : Oxygen Demanding Substances # Oil & Grease # Floatable Materials 9 Bacteria & Viruses # High Impact : Medium Impact 9 Low or Unknown Impact IMPLEMENTATION REQUIREMENTS # Capital Costs : O&M Costs : Maintenance 9 Training Post Construction Storm Water Management 2004

8 BMP: Sediment Basin SB OBJECTIVES 9 Housekeeping Practices 9 Contain Waste 9 Minimize Disturbed Areas 9 Stabilize Disturbed Areas 9 Protect Slopes/Channels 9 Control Site Perimeter : Control Internal Erosion DESCRIPTION: A pond created by excavation or construction of an embankment, and designed to retain or detain runoff sufficiently to allow excessive sediment to settle. APPLICATION: < At the outlet of all disturbed watersheds 10 acres or larger. < At the outlet of smaller disturbed watersheds, as necessary. < Where post construction detention basins will be located. INSTALLATION/APPLICATION CRITERIA: < Design basin for site specific location, maintain effective flow length 2 times width. < Excavate basin or construct compacted berm containment, ensure no downgradient hazard if failure should occur. (Provide minimum of 67 cy. per acre of drainage area). < Construct dewatering and outfall structure and emergency spillway with apron. LIMITATIONS: < Should be sized based on anticipated runoff, sediment loading and drainage area size. < May require silt fence at outlet for entrapment of very fine silts and clays. < May require safety fencing to prevent public access. < Height restrictions for embankment regulated by Utah Division of Dam Safety. MAINTENANCE: < Inspect after each rainfall event and at a minimum of monthly. < Repair any damage to berm, spillway or sidewalls. < Remove accumulated sediment as it reaches 2/3 height of available storage. < Check outlet for sedimentation/erosion of downgradient area and remediate as necessary. Install silt fence if sedimentation apparent South Weber River Drive Riverdale City, UT (801) TARGETED POLLUTANTS # Sediment 9 Nutrients : Toxic Materials 9 Oil & Grease : Floatable Materials 9 Other Waste # High Impact : Medium Impact 9 Low or Unknown Impact IMPLEMENTATION REQUIREMENTS # Capital Costs : O&M Costs : Maintenance 9 Training Post Construction Storm Water Management 2004