Fairfax County s Stormwater Learning Experiences Green Stormwater Facilities - Cheap and Simple Loved by All? Department of Public Works and Environmental Services Working for You! A Fairfax County, VA, publication 5/12/2017 Program Overview Fairfax County Size: 400 sq. miles 1.1 Million Residents Stormwater System MS4 since 1997 42,000 Storm Drainage Inlets 4,200 Private Stormwater Facilities 1,900 Public Stormwater Facilities 1,300 Miles of Pipe 850 Miles of Perennial Streams FY18 STW Budget $70M Department of Public Works and Environmental Services 2 1
Facility Counts as of August 2016 Type Indiv Lot Private Residential Subdivision Outlot/Common Area Total Private Res Public Private Non Res Maintenance and Stormwater Management Division TOTAL Infiltration Practices (TR) 711 66 777 47 381 1,205 Bioretention (BR+TF) 320 137 457 252 256 965 Vegetated Swales 20 3 23 45 3 71 Filtering Practice (SF) 0 7 7 6 216 229 Constructed Wetland 0 1 1 0 1 2 Wet Pond 12 151 163 23 141 327 Dry Pond 0 15 15 1,357 516 1,888 Manufactured (Proprietary) BMP 0 7 7 12 169 188 Other Types(Underground, Rooftop, Porous Pavement, etc.) 3 13 16 194 1,037 1,247 TOTAL 1,066 400 1,466 1,936 2,720 6,122 3 Stormwater Management Branch Inventory Growth 7,000 Fairfax County Stormwater Management Facility Inventory 6,000 5,000 4,894 5,139 5,399 5,722 6,091 6,210 NO. OF FACILITIES 4,000 3,000 2,000 3,508 3,308 1,586 1,631 3,876 3,655 1,744 1,846 4,136 4,241 1,955 1,969 1,000 - FY2012 FY2013 FY2014 FY2015 FY2016 FY2017 (as of 4-7-2017) YEAR Total Private Public Linear (Total) MSMD/DPWES 4 2
6/5/2017 Stringfellow Park and Ride 5 Wastewater Collections - Fred Oaks 6 3
George Marshall High School 7 George C. Marshall High School Rainwater Harvesting Project Pump and Treatment System Installation Pump & Disinfection System Pre Treatment System Maintenance and Stormwater Management Division/DPWES 8 4
Newington Bus Terminal Rainwater Harvesting Roof runoff collected in cisterns Water used to wash vehicles Porous Pavers Bioretention 9 Springhill and South Run 10 5
Stormwater Management Branch Maintenance MSMD/DPWES 11 Stormwater Management Branch Programmatic Gaps or Challenges LOE/SOP needs to be established: Invasive Species / Weeds How far do we go? Algae When do we act? MSMD/DPWES 12 6
Private Infiltration & Bio Retention 2010-2012 6Months after Completion 13 Stormwater Management Branch Private Inspections and Enforcement Improvements Revised NOI Cover Letter language Maintenance and Inspections web page Maintenance Contractor Awareness Training Private residential outreach packet MSMD/DPWES 14 7
Metrics Maintenance Unit Costs Facility Type Inspection Cost Routine Maintenance Cost Annualized Replacement Cost Annualized Insp, Maint, and Replacement Total Average Treated Area (acres) Cost to Maintain per Acre Treated ($/acre) Infiltration $304 $0 $300 $604 0.38 $1,600.00 Bioretention $200 1750 $4,200 $6,150 0.63 $9,800.00 Vegetated Swale $200 $1,750 $667 $2,617 2.12 $1,250.00 Filtering Practice $304 $0 $5,800 $6,104 1.35 $4,500.00 Constructed Wetland $304 $0 $4,500 $4,804 11.86 $405.00 Wet Pond $303 $4,500 $4,500 $9,303 50.57 $185.00 Dry Pond $303 $4,500 $4,500 $9,303 18.45 $505.00 Manufacture d BMP $304 $0 $210 $514 1.62 $320.00 15 Completed Facilities FY09-16 Practices Stream Restoration Pond Retrofits Dry Swales Infiltration Swales & Trenches Bioretention (Rain Gardens) Pervious Pavement Number Capital Cost ($/lb) Installed TN TP TSS 30 $ 2,100 $ 17,800 $ 53 55 $ 5,000 $ 92,200 $ 48 14 $ 8,280 $ 92,300 $ 135 7 $ 10,000 $ 93,000 $ 124 33 $ 24,700 $ 203,000 $ 268 14 $ 50,600 $ 437,000 $ 569 16 8
Evaluation of Fairfax County s Publicly Maintained Porous Pavers Fairfax County Porous Pavement Overview 33 Number of Assets Evaluated 4 Porous Concrete Porous Asphalt Porous Pavers Other Age Range (months) Porous Concrete 12 Porous Asphalt 12 Porous Pavers 3 33-36 13-84 * At the time of evaluation, October 2016 24 publicly maintained County facilities contain porous pavement 68 individual assets included on these 24 properties 61 assets evaluated as part of this study Are widely used as stormwaterbmps covering locations with light to heavy traffic load MSMD/NVSWCD 17 Evaluation of Fairfax County s Publicly Maintained Porous Pavers Evaluation Process Field Evaluation Criteria i. Surface Clogging ii. Depression iii. Rutting iv. Faulting v. Damaged pavers vi. Edge restraint damage vii. Excessive joint width viii. Joint filler loss ix. Horizontal creep x. Additional minor distresses David K. Hein Maintenance Guidelines for Permeable Interlocking Concrete Pavement System xi. Severity of drainage area instability xii. Severity of inadequate drainage area connectivity MSMD/NVSWCD 18 9
Evaluation of Fairfax County s Publicly Maintained Porous Pavers Findings: Porous Pavers Porous pavers: Infiltration Rate Measurements / Age Permeable Pavers (40 measurements) Design Infiltration Rate * VA Clearinghouse (1.0 in/hr) ICPI (10.0 in/hr) Infiltration Rate (in/hr) % of measurements below design rate 5% 48% * Design Infiltration Rate: Long term equilibrium infiltration rate reached under "good maintenance" condition ICPI: Interlocking Concrete Pavement Institute Age (Month) Design I Rate (10.0 in/hr), ICPI Design I Rate (1.0 in/hr), VA DEQ BMP Clearinghouse Guidelines MSMD/NVSWCD 19 Evaluation of Fairfax County s Publicly Maintained Porous Pavers Findings: Porous Asphalt Porous Asphalt: Infiltration Rate/Age Infiltration Rate (in/hr) Permeable Asphalt (16 measurements) Design Infiltration Rate * VA Clearinghouse (3.0 in/hr) The Industry % of measurements 88%? below design rate * Design Infiltration Rate: Equilibrium infiltration rate reached under "good maintenance" conditions Age (month) Design I Rate (3.0 in/hr), VA DEQ BMP Clearinghouse Guidelines 20 10
Evaluation of Fairfax County s Publicly Maintained Porous Pavers Findings: Porous Concrete 1,000.0 Porous Concrete: Infiltration Rate/Age 306.8 313.6 302.3 294 212.66 Infiltration Rate (in/hr) 100.0 10.0 3.58 21.12 3.42 17.72 Permeable Concrete (10 measurements) Design Infiltration Rate * VA Clearinghouse (5.0 in/hr) The Industry (200.0 in/hr) % of measurements 20% 40% below design rate * Design Infiltration Rate: Equilibrium infiltration rate reached under "good maintenance" conditions 1.0 0 5 10 15 20 25 Age (month) Design I Rate (5 in/hr), VA DEQ BMP Clearinghouse Guidelines Design I Rate (approx. 200 in/hr), Industry 21 Libraries and Schools 22 11
Porous Pavement Challenges Deteriorated Porous Concrete Replaced with Porous Concrete Slabs Sealed Porous Asphalt 23 Evaluation of Fairfax County s Publicly Maintained Porous Pavers Porous Pavement Conclusions Porous pavement is not a low maintenance BMP! Ensure surrounding drainage area is stabilized Install signs directing that no winter maintenance should occur Construction oversight-bmp inspection checklists MSMD/NVSWCD 24 12
Bio Retention Learnings Evaluated 90 Publicly Maintained Facilities 67% of bioretention facilities evaluated did not comply with the original design ponding depth 59% of bioretention facilities evaluated did not comply with design soil media depth. 32% of bioretention facilities did not comply with the original design surface area. No clogging or decline in flow movement due to filter fabric between planting soil media and the gravel layer was observed. Seepage or continuous base flow into bioretention facility might develop localized wetlands. Only 1 of 66 tested for infiltration rates was less than 8 /hr. 2007 Study 9 of 20 were less than 8 /hr. 25 Review of Plants Survey Procedures for each facility Annotate missing plants/existing plants on the planting plan List weeds that have a significant presence including: location sun/shade approximately how many exist. List observations: are there invasive plants weeds dead or dying plants (typically those that were originally installed) wetland plants (i.e., cattails) need for pruning. Others (i.e. thoughts on why plants are failing or thriving) Fairfax County Stormwater Management Division 26 13
Findings Inconsistencies between field survey and original plans Identified Survival Rate by Species type We have a detailed list of this effort Weeds Mixed Thoughts Provide cover, protecting the facility from erosion Uptake nutrients From a maintenance and focal standpoint: to maintain gardens, frequent attention to weed eradication is necessary and expensive. Plants installed must be able to handle harsh conditions Dry sandy soils Very high infiltration rates Low organic content Occasional inundation from standing water Plant selection Avoid exotics Use of natives has the greatest success Compact planting is encouraged to outcompete other vegetation 27 Recommendations Simplification of Plant Palette Simplification necessary for maintenance crews to identify between weeds and installed plants. Currently 30 Trees 18 Shrubs 52 Perennials Need 5 Trees 8-10 Shrubs 10 Perennials For easier maintenance, plant monocultures may be a good option Choose a plant palette that establishes quickly and outcompetes weeds Choose plants suited for sandy/beach environments Consider plants with seasonal interest for high visibility areas Recommendations 28 14
Maintenance Guidance Maintenance and Stormwater Management Division 29 Maintenance Guidance Contractor Training Held two training sessions for industry. Currently have 31 contractors on the list. Next training to be held Winter 2018 See http://www.fairfaxcounty.gov/dpwes/stormwater/maintenancetraining.htm for an attendance list Maintenance and Stormwater Management Division 30 15
s Maintenance Guidance Partnering with the National Green Infrastructure Certification Program (NGICP) National program targets green infrastructure maintenance personnel and sets maintenance standards and best practices for specialized facilities (bioretention gardens, infiltration trenches, etc.) Maintenance and Stormwater Management Division 31 Industry Still Learning 32 16
Additional Information 2/13 3/14 Randy Bartlett (703) 324-5732 Randy.Bartlett@Fairfaxcounty.gov 9/15 33 17