Spatial Distribution of Arsenic in Ohio Soils Nate Wanner, CPG Cox-Colvin & Associates, Inc. Ohio Brownfield Conference 2016 Columbus, Ohio April 6, 2016

Introduction Arsenic occurs naturally in soils and groundwater Can also be associated with historical site activities This complicates site assessment and remediation, particularly in Ohio: –High natural concentrations –Industrial history –Relatively populous USGS:

Arsenic in Soil and the VAP 1.Do maximum As concentrations exceed standards? 2.Can another representative concentration be used, such as 95 th UCL? 3.Do concentrations exceed background levels? –Ohio EPA county studies –Site-specific studies Contact PathwayVAP Standard Residential12 mg/kg Commercial/Industrial77 mg/kg Construction/Excavation690 mg/kg

Goals of the Study When is a site-specific study worthwhile? Should something other than per-county studies be considered? Potential considerations: –Surficial geology –Bedrock geology and glaciation –Soil types Are there subsets that show statistically significant distributions? –Normal, lognormal, etc.

Previous Studies Venteris, et al (2014) – Ohio State and ODNR –Used USGS National Geochemical Survey data and Gaussian simulation to compare arsenic concentrations to bedrock geology. Brief mention of glacial geology. AECOM (2010) – analysis of arsenic concentrations and bedrock geology in Ohio and 6 other states. –Spatial analysis by simple overlay, no evaluation of glacial geology –Data not readily available Venteris Shallow SoilVenteris SubsoilAECOM Bedrock

Sources of Geologic Data Bedrock Geology from USGS ODNR Quaternary Geology ODNR Glacial Drift Thickness

Sources of Arsenic Data Ohio EPA background studies in 6 counties –High quality data, but limited number of sampling locations –Used laboratory data. Did not use XRF screening data Cox-Colvin Evaluation of Background Metal Concentrations in Ohio Soils (1996) –Data compiled from various background studies conducted near CERCLA/RCRA sites –Not VAP-Certified USGS National Geochemical Survey Database –Compiled from various mineral exploration studies over the years. –Soil and stream data available – only soil data was used –Not VAP-Certified –Both atomic absorption data (AA) and inductively coupled plasma (ICP) mass spectrometry data were collected at each point. –Used AA data because there was only a single non-detect.

Arsenic Data Points Combined datasets included data from over 2000 analyses of arsenic in soil.

Interpolation Kriging Mathematical method to interpolate values in mapping Originally developed for gold exploration in Africa Accounts for spatial variability by attempting to fit data to a smoothed mathematical function Based on changes over distance, and optionally direction Predictive or Probability Evaluating possible functions to model a semivariogram. From Geographic Information Analysis 2 nd Edition (O’Sullivan and Unwin ), Figure 10.9

Predicted Arsenic Concentrations

Standard Error Map

Probability of Exceeding 5.7 ppm 5.7 mg/kg (ppm) is the U.S. EPA ecological screening level.

Probability of Exceeding 12 ppm 12 mg/kg (ppm) is the VAP Residential Direct Contact Standard.

Sulfide Minerals in Shale? Evaluation of Venteris et al hypotheses that arsenic concentrations in Franklin County (Columbus) are associated with sulfide minerals in Devonian shales.

Glacial Drift Thickness? Evaluation of whether there may be a correlation between glacial drift thickness and predicted arsenic concentrations.

Age of Glaciation? Evaluation of whether there may be a correlation between the age of glaciation and predicted arsenic concentrations.

Lake Deposits? Evaluation of whether there may be a correlation between lake deposits and predicted arsenic concentrations.

Unglaciated Areas? Evaluation of whether there may be a correlation between unglaciated areas and predicted arsenic concentrations.

Proposed Regions Proposed regions of similarity in background arsenic concentrations in soil.

Summary of Arsenic in Ohio Soils Concentrations in mg/kg (ppm) UTL = Upper Tolerance Limit All DataUnglaciatedLake InfluenceIllinoian GlaciationFranklin County Samples Minimum Maximum Standard Deviation Mean Distribution-Lognormal-Gamma- 95% Upper Confidence Limit (UCL) of Mean % Upper Prediction Limit (UPL) CuyahogaFranklinHamiltonLucasMontgomery Summit Ohio EPA Representative Background ( ≤ 50% sand) 2.42 (>50% sand) Method UPL UTL Mean + 2*SD UTL Mean + 2*SD

Spatial Distribution of Arsenic in Ohio Soils Nate Wanner, CPG Questions?