Monitoring Considerations and Costs Stormwater BMP Selection, Design, and Monitoring Florida Stormwater Association September 9, 2016 Harvey H. Harper, Ph.D., P.E. Environmental Research & Design, Inc.
Objectives of BMP Monitoring Internal Objectives Just to satisfy contract requirements or to learn about BMP Evaluate the load reduction effectiveness of the BMP as constructed How much mass went in and how much left Most BMPs include both hydrologic/hydraulic and water quality components Evaluate hydrologic/hydraulic performance Wet ponds/wetlands Conduct complete hydrologic budget to include precipitation, inflows, evaporation, GW inputs/losses Evaluate water quality changes Monitor inflow/outflow quality Calculate BMP efficiency Calculate and compare pre vs. post loadings
Quality Assurance Project Plans Quality Assurance Project Plans (QAPP) QAPP provides details of proposed field and lab activities and QA procedures Sampling and analyses must conform to Requirements outlined in Chapter 62-160 F.A.C. Provides basic requirements for approved field methods, record keeping, lab certification, lab methods, holding times, sample preservation, audits Requirements for Field and Analytical Work performed for the Department of Environmental Protection under Contract (DEP-QA- 002/02), February 2002 Describes quality objectives, field and lab activities, documentation, record keeping, and QC requirements Methodologies for field monitoring are outlined in the FDEP document titled Standard Operating Procedures for Field Activities (DEP-SOP-001/01) dated March 1, 2014
FDEP Monitoring Requirements No. of Events Standard FDEP monitoring protocol specifies pre/post monitoring for a minimum of 7 10 events Only appropriate for BMPs where the performance is not impacted by previous runoff Inappropriate for wet ponds, wetlands, rain gardens, gross pollutant separators May be appropriate for infiltration devices and alum treatment Lab Analyses All labs doing analyses for DEP funded grant monitoring must be NELAC certified Not all labs are created equal Be sure to specify detection limits Do not use wastewater labs
Flow Monitoring The most common challenge in conducting stormwater monitoring is flow measurement at low flow conditions Flow meters with area/velocity (AV) autosamplers generally have a low end velocity measurement of 0.2 fps Data below this range are generally unreliable A velocity of 0.2 fps in a full 48 pipe is 2.5 cfs Some sites have a continuous baseflow that substantially exceeds the runoff volume on an annual basis This baseflow must be captured when conducting efficiency studies, especially for pond systems The flow monitoring challenge can be overcome by: Changing the flow measurement to a more accurate primary device such as a weir Pressure transducer probes on a primary device are much more accurate than AV probes Conduct periodic field measurements of discharge using an accurate device such as a SonTek Accoustic Doppler flowmeter Develop flow patterns for baseflow
Sample and Data Collection Discrete or Composite Discrete Individual samples collected during runoff hydrograph and then combined together Composite multiple samples collected at timed or flowweighted basis Number of Samples Collect flow-weighted samples over a wide range of rainfall conditions Commonly conduct hydrologic and water quality sampling for an annual period Sampling needs to include baseflow, if present Hydrologic Data Include flow meters, rain gauges, water level recorders, evaporimeter, staff gauges, monitoring wells
Monitoring Multiple Locations Basic approach is to monitor all significant inflows to a BMP that is being evaluated Characteristics of lesser inflows can be estimated using characteristics from nearby sites Runoff inflow volumes can be estimated using hydrologic modeling
Elder Rd. Monitoring Locations for the Elder Creek Site 18 RCP from Elder Rd. Not Monitored Site 3 Elder Ditch/Elder Rd. Inflow 48 RCP Staff Gauge Water Level Recorder Broad-Crested Concrete Weir 18 RCP from Elder Rd. Not Monitored Rain Gauge Evaporimeter Shallow Planted Area Site 2 Elder Ditch Inflow 34 x53 ERCP Site 4 Pond Outflow Compound Weir Narcissus Rd. Site 1 Elder Creek Inflow 58 x91 ERCP
Powering Monitoring Equipment Use 120 VAC power when available Especially useful when refrigerated samplers are being used For long term projects, a power pole and meter is set at the project site Possible hook up to public utility sites (lift stations, etc.) or private individuals Also use 12 VDC batteries to power equipment using solar panels for recharging the batteries Sites are visited at least once each week to review battery status and replace if necessary
Dry Detention and Underdrain Monitoring Sites Field Monitoring - Conducted for 12 months - 17 Isco Avlanche autosamplers - 17 Isco flowmeters - 17 insulated equipment shelters - 4 Isco Model 674 rainfall recorders - 4 Bulk precipitation collectors - 10 Global Water digital water level recorders - 4 Class A pan evaporimeters - 10 shallow monitoring wells - 1 SonTek Acoustic Doppler flow meter - 1 Hydrolab Datasonde 4a water quality monitor Orlando Underdrain Site Bonita Springs Dry Detention Site Naples Dry Detention Site Pembroke Pines Dry Detention Site
Bonita Springs Dry Detention Pond Site Dry Detention Pond Dry Detention Pond Conservation Area Dry Detention Pond Wiggins Pass Rd.
Bonita Springs Stormwater System 42 36 Parameter Units Value Pond 2 (0.45 ac.) Basin = 2.92 ac. 42 Pond 1 (0.09 ac.) Basin = 2.92 ac. Project Area acres 22.11 Impervious Area acres 16.68 DCIA % 75.4 Conservation Area Commercial Retail Store 15 Stormwater System Pervious CN Value acres 1.57 % of area 7.1-63.1 15 42 42 36 Water Quality Vol. Treatment Depth Year Constructed ac-ft 1.54 Inches over basin 0.84-2006 Pond 3 (1.11 ac.) Basin = 16.27 ac. Outfall Structure 24 54 15 15 15 15
Pembroke Pines Dry Detention Ponds Pond 1 Inflow from Parking Area Inflow from Pond 1 Inflow from Parking Area a. Inflow to Pond 1 from parking lot b. Inflows to Pond 2 Outfall Structures c. Dual outfall structures in Pond 2 d. Pond 2 under flooded conditions
Schematic of aluminum V-notch structure used to measure pond inflows Fabricated V-notch Weir
Naples Monitoring Sites 1 & 2 Fabricated V-notch Weir Fabricated V-notch Weir Site 1 Parking Lot Inflow monitoring site Site 1 Parking Lot Inflow equipment Fabricated V-notch Weir Site 2 Parking Lot Inflow Site Conduit for Tubing and Cables Site 2 Parking Lot Inflow equipment
Naples Monitoring Sites 3 & 4 Fabricated V-notch Weir Fabricated V-notch Weir Monitoring Well Site 3 Rear Store Area Inflow Site Site 3 Monitoring Equipment Site 3 Equipment Shelter Outfall Structure Conduit for Tubing and Cables Skimmer Site 4 System Outfall Site 4 Monitoring equipment at outfall structure
Pembroke Pines Monitoring Site 1 Fabricated V-notch Weir Fabricated V-notch Weir Site 1 North pond monitoring equipment Site 1 Storm event conditions
Monitoring Open Channels Ditch Inflow From S.R. 46 Inflow from Lake Gem Inflow to Club II Pond
Monitoring Open Channels con t. a. Weir structure formed and poured with concrete b. Completed weir structure used to provide constant control section for flow measurement
Monitoring Open Channels con t. Equipment Shelter Pond 1 Weir Weir a. Inflow channel with weir structure b. Inflow channel upstream of weir structure Water Level Recorder c. Horizontal weir
Monitoring Costs A typical 12-month monitoring program for a wet detention based BMP is ~ 80 100K Typical 12-month monitoring for an infiltration BMP is ~ 75K
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