preparing a site conceptual model. typical site management problems: site complexities complicated...
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Preparing a Site Conceptual Model
Typical Site Management Problems:
Site complexities Complicated hydrogeology Multiple contaminants of concern (COCs) Multiple receptors/pathways
Multiple phases of investigation and remediation Deliverables that are not stand-alone documents Changes in consultants Changes in regulatory oversight Case load
Common Outcome:
An abundance of dataLack of clarity concerning the major site
issues and how to move the site toward closure
Suggestion:
Direct the Responsible Party (RP) to complete a Site Conceptual Model
Site Conceptual Model (SCM):
EPA: A representation of site conditions developed using readily available (existing) data that illustrates the relationship between contaminants, retention/transport media, and receptors.
EPA. November 2000. Using the Conceptual Site Model to Select Performance Standards and Develop Data Quality Objectives in the CAS.
Purpose:
Organize information already known about the site
Help identify additional information that must be obtained
Suggest when site characterization is complete—i.e., if the SCM is not likely to significantly change upon collection of additional information, the existing data are adequate
SCM Presentation:
The SCM is generally documented by written descriptions and supported by maps, geological cross-sections, tables, diagrams and other illustrations.
EPA. November 2000. Using the Conceptual Site Model to Select Performance Standards and Develop Data Quality Objectives in the CAS.
SCM Support:
1) Local and regional plan view maps showing location of sources, extent of contamination (i.e., an interpretive drawing—not a plot of laboratory results), direction and rate of groundwater flow, and locations of receptors. “Receptors” include, but are not limited to, all supply wells within 2000 feet of the source area.
Arulanantham, R. December 2000. Assessment and Management of MtBE Impacted Sites.
SCM Support:
2) Cross-section maps showing subsurface geologic features, depth to groundwater, man-made conduits, monitoring well construction, and an interpretive drawing of the vertical extent of soil contamination (i.e., an interpretive drawing—not a plot of laboratory results)
Arulanantham, R. December 2000. Assessment and Management of MtBE Impacted Sites.
SCM Support:
3) Exposure evaluation flowchart (similar to Figure 2 in ASTM’s Standard Guide for Risk-Based Corrective Action Applied at Petroleum Release Sites)
Arulanantham, R. December 2000. Assessment and Management of MtBE Impacted Sites.
SCM Support:
4) Plots of chemical concentrations vs. time (e.g., if groundwater monitoring is being conducted, plots should be shown for each monitoring well which has had detectable levels of contaminants)
Arulanantham, R. December 2000. Assessment and Management of MtBE Impacted Sites.
MW-6 Chemical Concentrations versus Time
0
50000
100000
150000
200000
250000
2/18/99 5/26/99 8/13/99 12/3/99 3/20/00 5/25/00 7/31/00 10/27/00 2/2/01 4/12/01 9/18/01
Date
Ch
emic
al C
on
cen
trat
ion
s (p
pb
)
0
2
4
6
8
10
12
14G
rou
nd
water E
levation
(feet abo
ve MS
L)
TPHg
Benzene
Groundwater
SCM Support:
5) Plots of chemical concentrations vs. distance from the source
Arulanantham, R. December 2000. Assessment and Management of MtBE Impacted Sites.
TPHg Concentrations versus Distance
0
20000
40000
60000
80000
100000
120000
140000
160000
180000
0 20 40 60 80 100 120 140
Distance (feet)
TPH
g C
once
ntra
tion
(ppb
)
MW-1
RW-1MW-5
MW-7 MW-13
SCM Support:
6) Summary tables of chemical concentrations in different media
Arulanantham, R. December 2000. Assessment and Management of MtBE Impacted Sites.
SCM Support:
7) Boring and well logs (including construction/screening)
Arulanantham, R. December 2000. Assessment and Management of MtBE Impacted Sites.
Summary:
SCMs are a “big picture” look at a site contamination problem
SCMs may help you through some common site management problems and clarify major site issues