MAJOR RETROFITS – REDUCING POLLUTANT LOADING TO COMFORT LAKE USING IRON FILINGS D AVID F ILIPIAK & J EREMY N IELSEN, SRF

S ITE P ARAMETERS 64.9 ACRES OF EXISTING COMMERCIAL / RESIDENTIAL DRAINAGE AREA (60% I MPERVIOUS S URFACE ) 36.5 ACRES OF PROJECT AREA (50% I MPERVIOUS S URFACE )

D ESIGN G OALS /C ONSTRAINTS G OALS o o M ATCH P RE - DEVELOPMENT DISCHARGE RATES o o N O NET INCREASE IN RUNOFF VOLUME ( FROM P RE - DEVELOPMENT CONDITIONS ) FOR A 2- YEAR 24- HOUR STORM o o N O NET INCREASE IN T OTAL P HOSPHOROUS LOADING C ONSTRAINTS o o H IGH GROUND WATER o o S HALLOW STORM SEWER o o F LAT TOPOGRAPHY

E NHANCED D ESIGN A DDED IRON FILINGS SAND INTO THE FILTRATION BASIN DESIGN B IOENGINEERED SOIL PRIMARY FILTER MECHANISM / IRON FILING SAND SECONDARY FILTER MECHANISM I NCREASE THE DEPTH OF WATER THAT WILL PERMEATE THROUGH THE FILTER MATERIAL BY 50%

E NHANCED D ESIGN CONSIDERATIONS o o S TANDING WATER IN UPSTREAM PIPES – ADDED MECHANICAL VALVE TO DRAIN DOWN POND IN FALL o o V EGETATED BASIN DRAWN DOWN – MODIFIED SOIL TO HIGHER SAND CONTENT TO ASSIST DRAINAGE GIVEN ADDED WATER o o I RON FILING CONTENT – USED MECHANICAL MIXING FOR CONSISTENT MIX

Description Total Drainage Area/ Project Area ac % Total Impervious/ (Project Impervious) TP Loading lbs/yr TP Removed lbs/yr TP Reduction, % Existing Conditions 64.9 (36.5)53.7% (40%) % Proposed Conditions 64.9 (36.5)59.8% (50%) % Enhanced Conditions 64.9 (36.5)59.8% (50%) %

M ONITORING L OCATIONS I NLET C ONNECTION BETWEEN THE POND / FILTRATION BASIN T ILE OUTFALL F IRST YEAR OF A 3 YEAR PROGRAM

F IRST YEAR RESULTS INCREASE ON CONCENTRATIONS AND LOADS OF TP, SRP AND TSS FROM THE INLET OF THE IRON - ENHANCED INFILTRATION BASIN TO ITS OUTLET T HE POND OPERATES WITHIN EXPECTED REMOVAL RATES S OME ORANGE WATER HAS BEEN DETECTED PERIODICALLY AT THE OUTLET, INDICATING POTENTIAL F ERRIC HYDROXIDE COMING OUT FROM THE IRON FILLINGS I NCREASES IN LOADING DECREASED WITH SIMILAR STORM EVENTS OVER THE COURSE OF THE YEAR A NY FINAL CONCLUSIONS ABOUT THE EFFECTIVENESS OF THE FILTRATION BASIN BASED ON THE FIRST YEAR MONITORING IS PREMATURE SINCE THESE SYSTEMS TYPICALLY REQUIRE AT LEAST A YEAR TO STABILIZE ( VEGETATION / SOILS SETTLING ) AND REACH STEADY STATE OPERATION