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 13th, 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 – Fe2+ oxidized to Fe3+

• 4Fe2+ + O2 + 4H+ 4Fe3+ + 2H20

• Iron Hydrolysis: Iron Precipitation

• Fe3+ + 3H20 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/m2/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 400-700 L\min annually

• Influent pH = 5.95 ±0.06

• Net Alkaline (Alkalinity 393 ± 13 mg\L CaCO3)

• Average iron removal rate = 22 g/m2/day

Iron Zinc Lead Cadmium

Average Influent 192±10 mg\L 11.0±0.7 mg/L 60±13 µg/L 17±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– 0.250 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 Protocol

FF 15 min 30 min 1 hour 2 hour 3 hour 4 hour

24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

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 HNO3

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 C1Out1o Oxidation Pond (RImax = 0.31cm/hour)

High Intensity Storm C1out1o Oxidation Pond (RImax = 1.47 cm/hour)

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

Low Intensity Storms C2Out 2o SF Wetland: (RImax = 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

Sampling Support• CREW

• University of Oklahoma

• Advisory Committee

• Julie LaBar (ICP)

• Dr. R. Nairn

• Sarah Yepez

• Thomas Bisinar

• Brendan Furneaux

Acknowledgements