MAJOR RETROFITS – REDUCING POLLUTANT LOADING TO

COMFORT LAKE USING IRON FILINGS

DAVID FILIPIAK & JEREMY NIELSEN, SRF

PRESENTATION OUTLINE

• PROJECT OVERVIEW

• DESIGN GOALS/CONSIDERATIONS

• CONSTRUCTION/TECHNIQUES

• MONITORING RESULTS

• CONCLUSIONS/LESSONS LEARNED

PROJECT OVERVIEW

PROJECT OVERVIEWSITE PARAMETERS

64.9 ACRES OF EXISTING COMMERCIAL/RESIDENTIAL DRAINAGE AREA (60% IMPERVIOUS SURFACE)

36.5 ACRES OF PROJECT AREA (50% IMPERVIOUS SURFACE)

DESIGN GOALS/CONSIDERATIONS

DESIGN GOALS/CONSTRAINTS

GOALSo MATCH PRE-DEVELOPMENT DISCHARGE RATESo NO NET INCREASE IN RUNOFF VOLUME (FROM PRE-DEVELOPMENT

CONDITIONS) FOR A 2-YEAR 24-HOUR STORMo NO NET INCREASE IN TOTAL PHOSPHOROUS LOADING

CONSTRAINTSo HIGH GROUND WATERo SHALLOW STORM SEWERo FLAT TOPOGRAPHY

IRON FILING SAND ENHANCEMENT

ENHANCED DESIGN

ADDED IRON FILINGS SAND INTO THE FILTRATION BASIN DESIGN BIOENGINEERED SOIL PRIMARY FILTER MECHANISM/IRON FILING

SAND SECONDARY FILTER MECHANISM INCREASE THE DEPTH OF WATER THAT WILL PERMEATE THROUGH THE

FILTER MATERIAL BY 50%

DESIGN

DESIGN GOALS/CONSIDERATIONS

ENHANCED DESIGN CONSIDERATIONS

o STANDING WATER IN UPSTREAM PIPES – ADDED MECHANICAL VALVE TO DRAIN DOWN POND IN FALL

o VEGETATED BASIN DRAWN DOWN – MODIFIED SOIL TO HIGHER SAND CONTENT TO ASSIST DRAINAGE GIVEN ADDED WATER

o IRON FILING CONTENT – USED MECHANICAL MIXING FOR CONSISTENT MIX

DESIGN GOALS/EXPECTATIONS

EXPECTED PERFORMANCE

DescriptionTotal Drainage Area/ Project

Area ac

% Total Impervious/

(Project Impervious)

TP Loadinglbs/yr

TP Removedlbs/yr TP Reduction, %

Existing Conditions 64.9 (36.5) 53.7% (40%) 54 5.2 9.6%

Proposed Conditions 64.9 (36.5) 59.8% (50%) 59.6 41.5 69.6%

Enhanced Conditions 64.9 (36.5) 59.8% (50%) 59.6 46.7 78.4%

CONSTRUCTION/TECHNIQUES

CHALLENGING SUBGRADE SOILS

CONSTRUCTION/TECHNIQUES

BURIED CONSTRUCTION DEBRIS

CONSTRUCTION/TECHNIQUES

FINE FILTER AGGREGATE

CONSTRUCTION/TECHNIQUESMIXING OF IRON ENHANCED SAND

CONSTRUCTION/TECHNIQUESMIXING OF IRON ENHANCED SAND

CONSTRUCTION/TECHNIQUES

PLACEMENT OF TILE/FILTER AGGREGATE

CONSTRUCTION/TECHNIQUES

PLACEMENT OF IRON ENHANCED SAND

FINAL PRODUCT – 1 YEAR LATER

PRETREATMENT BASINFILTRATION BASIN

MONITORING/RESULTS

MONITORING LOCATIONS• INLET

• CONNECTION BETWEEN THE POND/FILTRATION BASIN

• TILE OUTFALL

• FIRST YEAR OF A 3 YEAR PROGRAM

MONITORING/RESULTS

FIRST YEAR RESULTS • INCREASE ON CONCENTRATIONS AND LOADS OF TP, SRP AND TSS FROM THE

INLET OF THE IRON-ENHANCED INFILTRATION BASIN TO ITS OUTLET

• THE POND OPERATES WITHIN EXPECTED REMOVAL RATES

• SOME ORANGE WATER HAS BEEN DETECTED PERIODICALLY AT THE OUTLET, INDICATING POTENTIAL FERRIC HYDROXIDE COMING OUT FROM THE IRON FILLINGS

• INCREASES IN LOADING DECREASED WITH SIMILAR STORM EVENTS OVER THE COURSE OF THE YEAR

• ANY 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

CONCLUSIONS/LESSONS LEARNED

• IRON SYSTEMS NEED TO DRY OUT – CHALLENGING IN WET CONDITIONS OR IN POOR SOILS

• TAILWATER CONDITIONS FOR OUTLET COULD IMPACT PERFORMANCE

• DRYING OUT IRON MAY IMPACT VEGETATION OVER THE TILE SYSTEM (MAY IMPACT LONG-TERM VIABILITY OF VEGETATION)

• IT TAKES TIME TO SEE RESULTS WITH VEGETATED FACILITIES

PROJECT PARTNERS

QUESTIONS?

• DAVID FILIPIAK – DFILIPIAK@SRFCONSULTING.COM

• JEREMY NIELSEN – JNIELSEN@SRFCONSULTING.COM