Storm Event-Driven Metal Transport Dynamics in the Initial Oxidation Cells of a Passive Treatment System Center for Restoration of Ecosystems and Watersheds, Civil Engineering and Environmental Science, University of Oklahoma, Norman OK June 13 th, 2012 L.R. Oxenford and R.W. Nairn

Presentation Overview Introduction and Objectives Methods and Materials Results and Future Work

Understanding Iron Chemistry Remediation of AMD impacted waters rely on a two step process for iron removal: Iron Oxidation – Fe 2+ oxidized to Fe 3+ 4Fe 2+ + O 2 + 4H + 4Fe H 2 0 Iron Hydrolysis: Iron Precipitation Fe H 2 0 Fe(OH) 3(s) + 3H + Understanding Iron Chemistry

Influent water quality and loading rates – Metals species and concentrations – Flow rates (hydroperiod) Removal efficiency (rate) – Overall and per surface area unit (kg/m 2 /year) – System sizing and transport state (aqueous vs. solid) Settling and storage – Rate of settling – Pond depth for solids accumulation Understanding the System

Objective and Purpose To investigate storm induced transport of metals within the oxidative cells of a passive treatment system. To determine the optimal settings for autosampler sample collection maximizing transport profile resolution. Objective and Purpose

The Mayer Ranch Passive Treatment System (MRPTS) was designed to treat net-alkaline, ferruginous lead-zinc mine drainage at the Tar Creek Superfund Site, Commerce OK. Location

MRPTS Layout MRPTS Layout and Design

AMD Characteristics Q varies between L\min annually Influent pH = 5.95 ±0.06 Net Alkaline (Alkalinity 393 ± 13 mg\L CaCO 3 ) Average iron removal rate = 22 g/m 2 /day Iron ZincLeadCadmium Average Influent 192±10 mg\L11.0±0.7 mg/L60±13 µg/L17±4 µg/L AMD Characteristics

Sample Locations C1 Out C2N Out C2S Out AMD Sources Equipment and Setup

Storm Frequency

Location and Storm Activity Storm Intensity

Sampling Regieme Rainfall intensity threshold sampling trigger – cm/hour, measurements every 15 minutes 24 HDPE sample bottles fill based on pre-set program time intervals. Immediate vs Delayed Transport Sampling program Sampling ProtocolF15 min30 min1 hour2 hour3 hour4 hour

Lab Sample Analysis Collection Only total metals analysis possible. (dissolved + ppt) Timely collection in less than a week after the 39 hour sampling period. Acidification in sample bottles with HNO 3 Analysis EPA Methods 3050 and 6010 – Microwave digestion – ICP-OES Analysis Plot total metals concentration vs time and include storm intensity (cm rainfall / hour) Lab Sample Analysis

Low Intensity Storms C1Out 1 o Oxidation Pond (RI max = 0.31cm/hour)

High Intensity Storm C1out 1 o Oxidation Pond (RI max = 1.47 cm/hour )

Low Intensity Storms C2Out 2 o SF Wetland: (RI max = 0.34 cm/hour)

Low Intensity Storms C2Out 2 o SF Wetland: (RI max = 1.47 cm/hour)

Transported iron likely from disruption of settling rather than resuspension. Source of Transported Iron?

Discussion Iron transport between the preliminary oxidation cells occurs due to storm events, but not as expected. Transport likely due to settling disruption, but theoretical calculations and laboratory experiments will be used to verify. Immediate and delayed transport events must both be considered. Discussion

Future Work Refine storm triggered sampling increments Iron oxide floc settling rates (Stokes Law – placid and disturbed) Accumulated iron oxide re-suspension Secondary metals transport via Fe sorption Future Work

Acknowledgements SamplingSupport CREW University of Oklahoma Advisory Committee Julie LaBar (ICP) Dr. R. Nairn Sarah Yepez Thomas Bisinar Brendan Furneaux Acknowledgements