IAEP presents an AT YOUR DESK LIVE Webinar:

A Tiered Approach to Corrective Action

Speaker Alan G. Stone, PG

February 26, 2015



Comparison of TACO Equation R26 With Alternative Models

Tiered Approach to Corrective Action Objectives (TACO) Tier 2 equations are currently used to model contaminant migration from impacted soil and groundwater at Leaking Underground Storage Tank (LUST) sites in Illinois.  Equations R15 and R26, from 35 IAC 742 Appendix C Table C,  are steady state equations used to calculate theoretical downgradient extents of groundwater impact from reported soil and groundwater contaminant concentrations.  These equations are relatively easy to use with a spreadsheet, but have some limitations.  They assume source area concentrations remain constant and do not decrease over time, which may overestimate the maximum downgradient extent of potential subsurface contaminant migration.  The Tier 2 modeled results may require institutional controls such as groundwater use restrictions for on- and off-site properties, including off-site properties that may never become impacted.  These equations also do not determine time required for the plume to reach its calculated maximum extent (steady state conditions).  

Tier 2 results are not always acceptable, especially when off-site property owners will not agree to ground water use restrictions for their properties.  In such cases, IEPA may consider Tier 3 analysis.  Tier 3 analysis in accordance with 35 IAC 742 is a flexible framework to develop remediation objectives outside of the requirements of Tiers 1 and 2.  Alternate methods of analysis can be used under Tier 3. 

Alternative equations such as those presented in ASTM E 1739-95 and the USAFCEE guidance document (1995) also calculate theoretical downgradient extents of groundwater contamination, and should be considered under Tier 3.  They are less restrictive, and less prone to overestimate the downgradient extent of groundwater impact.  That can lead to fewer offsite properties being listed as potentially impacted and needing groundwater use restrictions.

Groundwater analytical and site-specific hydrogeologic data from a site in Sheboygan, WI were entered into a spreadsheet model.  Theoretical downgradient extents were calculated using equation R26 and alternative equations.  Results from the alternative equations were compared with R26.  Equation R26 provided the largest theoretical downgradient extent.  The Domenico solution with source area degradation reported the smallest theoretical downgradient extent.

Mr. Stone received his B.S. in Water Resources Management (with geology and soil science minors) from UW-Stevens Point in 1991, M.S. in Earth Science from Western MI University in 1996 and an M.S. in Environmental Engineering from Milwaukee School of Engineering in 2005.   He is currently licensed as a professional geologist in Illinois.  His experience includes hydrogeologic site investigations, contaminant fate and transport calculations for soil and groundwater contaminants, wastewater and stormwater infiltration and environmental site assessments in Illinois, Wisconsin and Michigan. He is currently a hydrogeologist who does part-time and contract work with environmental consulting firms. His interests include hiking, fishing, church and time with wife, friends and family.


Thursday, February 26, 2015 (noon - 1:00pm CT)

Duration:  Event will last 1 hour, includes Q&A


IAEP Member:   $25              

Non-member:  $65 

Participants will receive a certificate for 1.0 Professional Development Hour

Call in Information will be emailed to you 24 hours prior to the event, once payment has been processed. 



1999 - 2015  IAEP. All Rights Reserved.

Home | About Us | Calendar Of Events | Join IAEP | Contact Us