Case Study: Evaluating Retrofit Urban Best Management Practice Performance and Lessons Learned Nick Muenks, Marc Leisenring, Mark Willobee – Geosyntec Consultants, Inc. Nicki Fuemmeler - Boone County, Missouri, Resource Management Jessie Fears – Knoxville, TN

Outline Project Background Project Objectives Project Design – Step Pool Project Design – Bioretention Field Sampling Results Lessons Learned

Background Hinkson Creek Impairment Reason TMDL (2011) On 303(d) List since 1998 Aquatic life impairment Impairment Reason Urban runoff sources Pollutants unknown TMDL (2011) Reduce stormwater runoff Help “No longer impaired” Hinkson Creek has been on Missouri 303(d) list due to aquatic life impairment from unknown toxicity. But the impairment was attributed to urban runoff sources. TMDL presumed that sufficient reduction in urban runoff will result in WQ improvements such that Hinkson Creek will no longer be impaired.

Characterize reduction of common urban stormwater pollutants Project Objectives Characterize reduction of common urban stormwater pollutants Quantify runoff volume reduction Implement BMPs and study their performance Pollutant load reductions Hydrologic response Variety of storm events over several years Because performance of current BMPs have not been field validated wrt runoff volume reduction and water quality improvement, Boone County wanted to determine efficiency of two BMPs, step pool and bioretention.

Owned and operated by the City Existing Conditions Grissum Building 10 acres Industrial operations No stormwater management Owned and operated by the City BMPs constructed in Sept. 2012 and step pool was monitored through Dec. 2014. Bioretention monitoring is ongoing. A total of 11 rain events captured through Feb. 2015.

Project Design Two BMPs implemented Bioretention cell Step pool system November 2012 – January 2015 11 rainfall events Step pool system September 2012 – December 2014 20 rainfall events The step pool BMP was designed to stabilize an eroded drainage ditch receiving continuous flows from the City of Columbia’s power plant (Power Plant) and storm flows from both the Power Plant and Grissum Building properties.

Project Design Step pool system Bioretention Treatment area – 2.2 acres With sand filters Bioretention Treatment area – 1.3 acres With underdrains

Project Design – Step Pool

Project Design – Step Pool

Project Design – Step Pool

Project Design – Bioretention

Project Design – Bioretention

Min. antecedent dry period Field Setup Auto Sampler Hach Sigma 900 max Installed at inlet and outlet H-flumes for flow Storm Event >0.2 inches rain in 24-hours Tipping bucket rain gauge Min. antecedent dry period 6 hours Bioretention – No ponded water for a valid sampling event. Each sampler was equipped with an ultrasonic sensor to measure depth of flow.

Field Setup Ultrasonic Sensor Records collected To measure depth of water At inlet and outlet For flow computations Records collected Water level Flow Precipitation Every 5 minutes One of the samplers at each of the BMPs was equipped with a tipping bucket rain gauge that loged precipitation event’s size and intensity.

Field Sampling Sampling methodology Flow-weighted composite samples Event mean pollutant concentrations Sample aliquots composited into a 2.5 gal bottle Constant flow volume/ variable time approach All samples were containerized, preserved and handled per QAPP and lab quality control manual. The target pollutants selected for the study were anticipated to be present given the urban/industrial land use of the Grissum Building.

Field Sampling Target pollutants

Field Sampling Laboratory analyses Standard analytical methods Methods for the Examination of Water and Wastewater 40 CFR 136

Baseline Sampling Results Two baseline events were sampled for background concentrations for the continuous flow generated by the power plant. Baseflow sample results indicate low total suspended solids (TSS) concentrations but total dissolved solids (TDS) results higher than most storm EMCs. Comparison of inlet and outlet EMCs show most parameters had reductions with the exception of total nitrogen. Total nitrogen (TN) concentrations were relatively high compared to storm sample EMC’s and show a slight increase from inlet to outlet. Metals concentrations were not detected or at relatively low compared to storm sample EMCs.

Precipitation and Flow Step pool storm monitoring occurred over a range of hydrologic conditions. Table presents the hydrologic factors (e.g. antecedent dry period, rainfall totals, rainfall intensity and storm duration) that affected collection of EMC samples. Antecedent dry periods ranged from 17 hours to over 19 days with the median dry period of about 6 days preceding a monitoring event. Rainfall totals ranged from 0.25 to 1.67 inches with a median of 0.63 inches. Ranging from 0.24 to 4.2 inches per hour maximum rainfall intensity affected a number of storm event samples by producing overland flows that entered the step pool between the inlet and outlet samplers. The duration of storm events ranged from 0.5 hour to 21 hours with the median storm lasting approximately 3 hours.

Step Pool Maturation July 2013 July 2014

Results – Step Pool

Results – Step Pool

Flow Reduction

Results – Bioretention

Results – Bioretention

Results – Bioretention

Results – Bioretention

Results – Bioretention

Results – Bioretention

Flow Reduction 0.83 inches of rain in 0.8 hours.

Annual Average Removals Monte Carlo simulation was used Predicted annual average pollutant reductions Grissum Building BMP TSS Load Reduction (tons/yr) TP Load (lbs/yr) TN Load Step pool 25 24 79 Bioretention 40 399 78

Lessons Learned Step Pool Conveyance System Bioretention Mature vegetation enhances pollutant removal efficiency Routine maintenance is key for gathering representative data (see images Bioretention Establish a robust maintenance program prior to implementation Proper outlet flow monitoring design is important – must consider accurately measuring the entire range of flows (infiltrated vs overflow)

Bioretention - Maintenance

Gravity Flow Media Filter Schematic (hydraulic failure mechanisms) Bioretention - Design Gravity Flow Media Filter Schematic (hydraulic failure mechanisms)

Bioretention – Enhanced Design 1) Empty Media Bed 2) Media Bed Filling