Research and BMP Installation Considerations at a Municipal Snow Dump Facility

James Houle, UNHSCDan Bourdeau, Geosyntec

Maine Stormwater Conferense11/17/2015

Special Thanks

City of Portsmouth, NH

• Brian Goetz

• Peter Britz

UNHSC

• Tim Puls

• Tom Ballestero

Geosyntec

GISCC Team

Water in the solid phase

Snowfall (in) SWE

1/27/2015 14.28 1.19

1/30/2015 2.52 0.21

2/2/2015 4.56 0.38

2/5/2015 2.04 0.17

Totals 23.4 1.95

Portsmouth Snow Dump

Snow LoadingAnnual Snow Loading Estimate:

• 59.9 inches of snow per year 1981-2011 (NCDC, 2015)

• 33 Acres of road surface

• 7.1M CF (164 AC FT) snow exported from the city streets

• 5.31 SWE gallons

Snow Loading

• TSS Load in Snow based on EMCs from a Alaskan DEC study (CH2M Hill, 2006).

• Limited DataRange TSS EMC (mg/L) TSS (lb/year)

Low estimate 30 13,400

High estimate 1398 622,600

Bioretention Design

Bioretention Design

Hydraulic and Pollutant Loading

– Pretreatment

– Static sizing due to unknown nature of a snow and pollutant load

– Meet NH DES design criteria for WQV (1 inch)

Bioretention Design

Pretreatment • Dual chambered pretreatment tank

• Concrete apron around inlet

• Accessible location during snow stockpile activities

Bioretention DesignBioretention Cell• Filter Area = 1280 SF• Media Depth = 1.25 FT• Salt tolerant vegetation• Site location to keep bioretention from snow stockpile

Bioretention Design

Maintenance Frequency– 260 cubic feet per year sediment loading

– 130 cubic feet of sediment pretreatment capacity

– Biannual cleaning

– Biweekly inspections during snow stockpiling activities

– Hooded outlets to trap floatables and debris

– Easy access during snow stockpiling activities

Results

Pile Volume (ft3) Water Equiv (gal)

Ave Annual Total 793,108 3,747,827

Project Totals (Ave Annual)

2014 Winter

2015 Winter

TSS Zn Cu TN TP Cl

Ave Annual Total 42,570 21 5 143 28 22,034

Total Remaining 36,044 17 4 116 23 16,709

Total Exported 6,526 4 1 27 5 16,709

Total Exported w/ BMP 848 1 0 11 2 16,709

Total Removed w/ BMP 5,678 4 1 16 3 0

Total Removed 41,722 20 4 132 26 5,324

%RE Snow Dump only 85% 80% 81% 81% 82% 24%

%RE Snow Dump w/ BMP 98% 97% 98% 92% 92% 24%

% Export Rate 15% 20% 19% 19% 18% 76%

*%RE = Percent Removal Efficiency; BMP = Best Management Practice (Bioretention System in this example)

Project Totals (Ave Annual) Kg

Conclusions

• Snow management in a urban area is a BMP!

• Simple runoff management strategies for snow dump areas can increase pollutant load reductions dramatically

• Chloride is the exception and needs consideration if snow dump activities are discharging in fresh water areas