presents an AT YOUR DESK LIVE Webinar:
A Tiered Approach to Corrective Action
Speaker Alan G. Stone, PG
February 26, 2015
THIS EVENT IS NOW CLOSED
Comparison of TACO Equation R26 With
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.
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.
February 26, 2015 (noon - 1:00pm CT)
Event will last 1 hour, includes Q&A
Participants will receive a
certificate for 1.0 Professional
Call in Information will be emailed to you 24
hours prior to the event, once payment has been processed.