Fall
2011
Water Security Manual
Part II, Section 6: Water Security Risk Scoring Tool
Draft for Comment
ABSTRACT
This section of the water security manual outlines the steps involved to apply the water security
risk scoring tool and describes an application to a setting relevant to aggregate mining. Land use
activities within a watershed, including anthropogenic infrastructure and anthropogenic changes
to the natural infrastructure, such as aggregate pits and quarries, may increase susceptibility of
an aquifer by modifying contaminant migration pathways. The tool can be used as a screening
tool for identifying the importance of changes to the natural infrastructure in a rural or urban
setting.
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WATER SECURITY MANUAL
PART II, SECTION 6- DRAFT
TABLE OF CONTENTS
TABLE OF CONTENTS ................................................................................................... 2
Background: Key Issues and Context ........................................................................... 3
Purpose of the Tool ..................................................................................................... 3
Intended Users ........................................................................................................... 3
Description of Tool...................................................................................................... 4
A Step-by-Step Guide to Applying the Tool .................................................................. 5
Step 1 – Define the Scope and Scale of Assessment....................................................................................5
Step 2 – Prepare the Required Data ..................................................................................................................6
Step 3 –Transmission and Likelihood of Release ........................................................................................6
Step 4 –Contaminant Source Characteristics ................................................................................................6
Step 5 – Targets .........................................................................................................................................................7
Step 6 – Assess the Potential Consequences of the Risk Score ..............................................................8
Example/Application of the Tool ................................................................................. 9
Recommendations and Further Areas for Research ................................................... 13
Bibliography ............................................................................................................. 14
Authors: Cassandra Banting and Ed McBean
(University of Guelph, School of Engineering)
Note: This tool is based on the thesis entitled “Development and application of a risk
scoring tool for aggregate mining extraction sites within the Grand River Watershed”, by
Cassandra Banting, School of Engineering, University of Guelph (in progress)
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Background: Key Issues and Context
Calculating water quality and quantity risk to groundwater and surface water represents
a useful means to prioritize municipal water issues. The purpose of this risk scoring tool
is to assess the impacts of degradation of natural infrastructure or the use of
anthropogenic infrastructure changes which may influence pathways of a contaminant
source to impact the water supply system. The basis of the methodology follows the
hazard ranking system (HRS), an approach used by the Environmental Protection Agency
(EPA) to evaluate contaminated sites and the threat posed to people and/or sensitive
environments.
The risk scoring tool approach uses three components to identify a risk score: the source
characteristics, the pathway and transmission and the target groups. It also looks at
three pathways: groundwater, surface water flooding and groundwater to surface
water. The groundwater migration pathway is described by the potential movement of
contaminants within the groundwater to nearby wells. The surface water flood pathway
is described by the potential movement of contaminants on the surface or near the
surface which can travel on the ground surface to nearby bodies of water. The
groundwater to surface water pathways may include any potential migration of a source
from the groundwater into surface water, which occurs when aggregate material is
extracted and the removal of surface materials creates a flow of groundwater to the
area.
Purpose of the Tool
This tool is intended to be used as an additional form of decision-making at all levels of
government, particularly at the watershed and municipal scale. It can be used to assist
communities in decision-making on projects that may alter the natural landscape. The
application of this tool can be adapted for other uses and purposes, not restricted to
evaluation for an aggregate pit; however, since this is a highly contentious issue within
the Grand River Watershed, the case study demonstrates the principles in application to
aggregate mining.
Intended Users
This tool is intended for community water groups, aggregate mining industry officials,
water managers, municipal water policy and decision-makers, source water protection
groups, provincial water planners and watershed groups.
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WATER SECURITY MANUAL
PART II, SECTION 6- DRAFT
Description of Tool
The risk scoring tool uses three pathways: groundwater migration, surface water flood
migration, and groundwater to surface water migration. Each of these pathways is
scored in three categories: likelihood or release or the transmission pathway,
characteristics of the sources, and targets (people or sensitive environments), which
may be impacted by a release. The tool uses a bin methodology where data falls into
relevant categories and then is scored accordingly. This bin methodology allows rapid
assessments to be accomplished. The calculated score is completed using addition and
multiplication of the combining factors.
The likelihood or release or transmission score is calculated using factors such as
containment type, and depth to groundwater. The source characteristic component
requires information about the types of chemicals present, and the associated toxicity
and chemical quantity values. The target component is based on the population using
nearby wells for drinking water or other uses, or using surface water as drinking water.
The surface water to flood, and groundwater to surface water pathways also evaluate
the risk to human food chain threats if applicable, and sensitive environments or
protected wetlands. Table 1 indicates the required parameters for each pathway and
component of the risk scoring tool.
Table 1: Variables Required for Risk Scoring Tool
Contaminant
Transmission
Source Type
-toxicity
-containment factor
-mobility
-net precipitation
-chemical quantity -depth to aquifer
Groundwater
-travel time (based on
conductivity and
thickness of hydraulic
layer)
-persistence
-drainage area
-toxicity
-surface soil group
-chemical quantity -rainfall/runoff value
Surface Water -bioaccumulation
-distance to surface
Flood
-ecotoxicity
water
-potential for flooding
(design/construction)
-flood frequency
Ground Water -toxicity
-containment
to Surface
-mobility
-net precipitation
Water
-persistence
-depth to aquifer
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Targets/Receptor
-nearest well
-water used for
resource purposes
-wellhead protection
zone
-nearest water intake
-resources
-surface water intake
-water used for
resources
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WATER SECURITY MANUAL
PART II, SECTION 6- DRAFT
-ecotoxicity
-bioaccumulation
-chemical quantity
-travel time factor
-sensitive
environment
-human food chain
The risk scoring tool uses a structured analysis approach for scoring sites by assigning
values to factors that relate to risk, based on the conditions at the site. This tool can be
used as a screening tool to evaluate how changing the natural infrastructure may alter
the relative threat posed by a contaminant to certain pathways.
A Step-by-Step Guide to Applying the Tool
Table 2: Summary table outlining the fundamental steps
Step
1
Define the Scope and Scale of Assessment
2
Prepare the Required Data
3
Transmission and Liklihood of Release
4
Contaminant Source Charactersitics
5
Targets
6
Assess the Potential Consequences of the Risk Score
Step 1 – Define the Scope and Scale of Assessment
The risk scoring tool can be used for a range of environmental issues which accounts for
changes to the natural landscape. The first step of applying the tool is to specify the
study area.
Using a matrix, shown in Table 3, the contaminant pathways warranting attention can
be identified.
Table 3: Applicable Contaminant Pathways
Groundwater
Transmission
Surface Water Flood Pathway
Drinking Human Environmental
Water
Food
Threat
Threat
Chain
Threat
Groundwater to Surface Water
Drinking
Human Environmental
Water
Food
Threat
Threat
Chain
Threat
Chemical
X
Chemical
Y
Chemical
Y
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WATER SECURITY MANUAL
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Step 2 – Prepare the Required Data
Different source, transmission and receptor group data will be required for each
pathway as it applies to the application of the model. Table 1 outlines the factors that
make up each component of the site score to indicate the type of data required.
Within the original HRS framework, EPA has supplied a chemical data matrix that
provides much of the contaminant data, such as toxicity, mobility, persistence, and
bioaccumulation. These values may also be calculated using first principles.
The geographic data are commonly found in public geographic spatial data resources,
such as GIS layers. Depth to aquifer, travel times, well locations, and distances can
usually be found within GIS layers. GIS maps are often provided to the public by the local
municipality, the conservation authority, provincial levels of government or other
special interest groups. In Ontario, Source Water Protection documents provide many
applicable data values. For contaminant specifics, site studies may need to be conducted
to determine the location and types of potential hazards nearby.
Step 3 –Transmission and Likelihood of Release
The likelihood of a chemical being released to a pathway is an essential part of
calculating the risk score. If there is minimal chance of transmission of the chemical then
the overall risk score will be low. Table 4 summarizes the components for calculating the
transmission portion of the risk score for the groundwater pathway, as an example.
Table 4: Transmission Component for Groundwater Pathway
Transmission:
Based on:
Observed Release
Containment
Net Precipitation
Depth to Aquifer
Travel Time
0 if no release
10 for confined and well protected
net precipitation - net evaporation for area
depth to aquifer used for drinking water
based on conductivity and layer thickness
Reclassified to:
0 or 550
0-10
0-10
1-5
1-35
Potential to release= [containment x (net precipitation + depth to aquifer + travel time)]
Likelihood of release: higher of observed release or Potential to Release
Step 4 –Contaminant Source Characteristics
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WATER SECURITY MANUAL
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The next step is for each source to be quantified based on the characteristics as outlined
in Table 5 below. As above, the groundwater pathway is used as an example. EPA has a
superfund chemical data matrix (SCDM) which provides the known toxicity, mobility,
persistence, bioaccumulation and ecotoxicity values required for the various pathways
which are used for assessing the potential risk of each of source (EPA, 2004). For
example, benzene has a cancer slope factor between 0.05 and 0.5 mg/kg-day-1, and
therefore is classified to a toxicity factor of 1000 (EPA, 2004).
Table 5: Source Characteristics Component for Groundwater Pathway
Toxicity
Mobility
Chemical Quantity:
Chemical Threat:
Based on:
HRS SCDM hazardous substance factor values(EPA,
2004)*
HRS SCDM hazardous substance factor values (EPA,
2004)*
based on the volume, or weight of contaminant
source
Reclassified to:
0-10000
0-10000
0-1000000
Chemical Characteristics: (toxicity x mobility x chemical quantity)
Reclassified to Values between: 0 to 1000
*SCDM can be found online:
http://www.epa.gov/superfund/sites/npl/hrsres/tools/scdm.htm
Step 5 – Targets
The target component of the site score is based on the receptor groups of the potential
contamination, such as municipal drinking water wells, private drinking water wells, and
water used for resources such as irrigation. Table 6 indicates the components needed to
calculate the target group part of the risk score for the groundwater pathway as an
example.
Table 6: Target Component for Groundwater Pathway
Targets:
Nearest Well
Population
Resources
Based on:
distance of source to well – over 6.5 kilometers away
will be assigned a value of 0
based on the distance to well and population drinking
from that well. The shorter the distance to well and the
larger the population drinking from the well then the
larger the number. Tables given in HRS manual may be
used for assigning values.
if water is used for irrigation, livestock, recreation use
then a value of 5 will be assigned
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Reclassified
to:
0-50
0-5200000
0 or 5
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WATER SECURITY MANUAL
PART II, SECTION 6- DRAFT
Wellhead Protection
Zone
source within or near wellhead protection zone will be
assigned a higher value
0-20
Targets= (nearest well + population + resources + wellhead protection zone)
Step 6 – Assess the Potential Consequences of the Risk Score
Calculating the final score is accomplished by combining the three components using
Equation 1.
Groundwater Pathway Score:
= [(Likelihood of Release x Chemical Characteristics x Targets)/82500]
[1]
Equation 1 is used to calculate a score for each pathway and then the root mean square
equation in Equation 2 is used to determine the overall score which ranges from 0 to
100.
Score= [(GW +SW + GWSW)/3]0.5
[2]
Where,
GW= Groundwater score
SW= Surface water flood score
GWSW= Groundwater to surface water score
Each score is capped to a maximum of 100
Since the risk score as determined using this model, is a screening tool as opposed to a
comprehensive risk analysis, the scored values which are higher than 28.5 may be a
strategy for priority, and warranting further investigation, according to the HRS
methodology. However, more than likely, this tool will be used as a comparative
framework between two scores to determine how changing a migration pathway may
lower or increase risk. If the site score has changed dramatically, then the following
options may be recommended:




Removal of the source of contamination, or perhaps better containment structure
for the possible sources of contamination
Removal of nearby wells (especially private wells) which may not follow the same
testing as municipal drinking water wells
Demonstrate that the land use change will cause too much of an increase to risk and
the change should be altered before the construction phase
Further investigation, sampling or site follow-ups should be done
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WATER SECURITY MANUAL
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Example/Application of the Tool
This is a general tool, which can be used on a variety of natural infrastructure and
contamination issues; however, for this case study, the tool will be applied to an
aggregate extraction site example to indicate how changing the landuse may change
pathways.
Although the model employs a general methodology, the case study will be specific to a
natural infrastructure issue common within the Grand River Watershed: aggregate
mining. Aggregate resources are governed by the Aggregate Resources Act in Ontario
which is implemented and enforced through the Ministry of Natural Resources (MNR).
The Province of Ontario has made aggregate extraction a provincial interest. Local and
upper-tier municipal governments must be consistent with the Provincial Policy
Statement, in which they must include provincial policies in their Official Plans related to
mineral aggregate resources. Other existing provincial policy affecting aggregate mining
includes the Greenbelt Plan which consists of the Niagara Escarpment Plan and the Oak
Ridges Moraine Plan. The most significant non-renewable resource in the Greenbelt
Study Area is aggregates, including limestone, sand, gravel, clay, shale and sandstone.
Nevertheless, with the need for growth, as outlined in the Ontario Growth Plan and the
need for resources for an aging infrastructure and growing population, the aggregate
mining debate continues to be a complex issue. An expanding Greater Toronto Area
increases pressure for aggregate sources located nearby. For example, 18,000 tonnes of
aggregate are used per kilometer of a 2 lane highway in Southern Ontario (MHBC
Planning and Golder Associates, 2009). Since the province’s interest for aggregate
mining is focused on keeping market supplies close to point of use and protecting the
resource for long term use, then the Grand River Watershed is a prime location for
aggregate materials due its proximity to Toronto.
Increasing pressures from green space protection legislation, and source water
protection plans have aided in the resistance to future aggregate mining sites. The
Ontario Municipal Board courts often have the deciding ruling on whether the aggregate
extraction sites will be developed because of appeals made by various stakeholders. This
process is often a lengthy and expensive task, therefore suggesting that the current
process is not a stable approach. The current licensing process does not require a risk
assessment or cumulative impacts assessment on a site. Gravel pits are listed as a land
use activity in which cumulative effects may contribute to environmental degradation
(GRCA, 2009). The risk scoring tool can address both cumulative impacts and provide a
risk score for the site.
Within Ontario, aggregate mining is often carried out below the water table to reach the
most valuable aggregate. This may compromise the protective aquitard layer if not
effectively accounted for in the planning process and therefore the three pathways of
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concern may now be altered. The risk scoring tool can be adapted for use to either
evaluate cumulative impacts of multiple sources of contamination on a particular site, or
can be used to address multiple aggregate pits and quarries and the impact to risk when
adding another pit or quarry. Pits and quarries are often clustered together because of
the location of the aggregate materials and the current procedures do not account for
other extraction sites located nearby.
The aggregate site used for this case study is located within the Grand River watershed,
here approximately 82 percent of the population relies on groundwater for water supply
(GRCA, 2009). The Growth Plan for the Greater Golden Horseshoe, released by the
province in 2006, anticipates continued high rates of growth and intensification of use in
the watershed’s cities over the next 25 years (GRCA, 2009). With the recent economic
downturn and the ensuing emphasis on infrastructure renewal and development, there
may be an increase in demand for aggregate resources (GRCA, 2009).
The aggregate extraction site used in this case study is located on the City of Guelph and
Township or Eramosa border. The limestone quarry has been infringed by the city’s
growing population over the last few decades. A mix of land use types, such as
residential, roadways, and rural, all border the site. The City relies on 23 municipal
drinking water wells (Aqua Resources, 2010), in which 3 are within 5 kilometers of the
site. The quarry has recently broken through the aquitard and into the water supply
aquifer for the City. The quarry is currently dewatering 8000 m3/day of water from the
bedrock aquifer and has a significant influence on the groundwater (Aqua Resources,
2010). It is currently hydraulically controlled; however, once the quarry has exhausted
its resources the quarry will have altered the surface water and groundwater pathways
(Aqua Resources, 2010).
The scale of this project looks at a 6 kilometer radius surrounding the limestone quarry.
The use of this metric is to determine the wells located in this area. However, the
potential contaminants are characterized as either being on site, or within a 0.5
kilometer radius away from the site.
Data required to complete the assessment is best acquired using a GIS database. Public
GIS data sources can provide most of the data required for determining the score.
Hydrogeologic data can often be found in online GIS data, or printed maps from the
local watershed authority, municipality or provincial level government. Locating the
specific contaminants on and near the site can be done with the aid of Google mapping
or other satellite and ortho imagery, or reviewing source water protection documents
which outline various threats to source waters. Conducting a final site assessment may
be required to find any other sources of contamination. Specific containment data for
each source must be found by contacting the responsible party for the source, such as
containment characteristics for an underground gasoline storage tank.
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WATER SECURITY MANUAL
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Table 7 summarizes examples of the contaminants found near the site.
Table 7: Contaminant found near site and applicable pathways
Groundwater
Transmission
Gas station
with
underground
storage tank:
Benzene
Road Salt
Application:
Sodium
chloride
Water
Treatment
Plant:
Chlorine and
Sodium
Bisulphate
Surface Water Flood Pathway
Drinking Human Environmental
Water
Food
Threat
Threat
Chain
Threat
Groundwater to Surface Water
Drinking
Human Environmental
Water
Food
Threat
Threat
Chain
Threat
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Table 8 outlines the final scores for each pathway using the example of benzene which is
a chemical associated with underground gasoline storage tanks. The transmission
pathway was calculated using the likelihood of release since there have been no
observed releases of contamination at or around the site.
The only pathway having a final score above 0 is groundwater which is because the
surface water sources are not being used for drinking water purposes in Guelph, and
therefore no target groups exist.
Table 8: Pathway Score Sheet
129
Source
Characteristics
10
580.5
Pathway
Score
9.08
27
6
0
0
27
56
0
0
27
56
0
0
129
6
0
0
129
56
0
0
Transmission
Groundwater
Surface
water/flood
Groundwater
to Surface
Water
Drinking water
threat
Human Food
Chain Threat
Environmental
Threat
Drinking water
threat
Human Food
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Targets
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Chain Threat
Environmental
Threat
129
56
0
0
To calculate the final score, equation 2 is used. The value for the final score with the
quarry is 6.42 for benzene, and 2.2 for pre quarry conditions. Demonstrating this value
can be done in a variety of ways, but using colour coded bars may help to visually
represent the data.
Figure 1: Risk scores for two examples of sources of contamination: after aquitard removal
Figure 2: Risk scores for two examples of sources of contamination: before aquitard removal
The colour bars can quickly indicate that the risk scores for those contaminants are low
for the quarry site; however, the values are even lower when modeling conditions prior
to the aquitard removal. Visually, one can see the risk score was lower for each source
of contamination before the removal of the aquitard due to the quarry operations.
The final score can be used to prioritize decision-making. The risk score does not
demonstrate a comprehensive risk assessment to the site but may be used as an
indicator for further site investigation.
Local concerns regarding the environmental impacts for new and expanded pits are
strong and there is increasing pressure to find alternative sources of aggregate, such as
recycled and reused aggregates supplies. Since aggregate mining is considered an
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WATER SECURITY MANUAL
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interim use of land, it is required that aggregate pit approvals include rehabilitation
plans; however, in 2009 40% of pits and quarries had not yet initiated progressive
rehabilitation (Skelton Brumwell Associates and Savanta Inc., 2009). This illustrates the
need for examining the risk of pits after they are decommissioned because they may
used for dumping materials and since the aquitard has been compromised this could
also be a concern of risk for the public.
Recommendations and Further Areas for Research
Finding the best-suited risk assessment methodology for different environmental
problems is an important part of water security. Before a risk assessment is completed,
investigating the problem in terms of policy is an integrative approach in determining
the gaps in the current process. Looking at water in terms of pathways which are
affected by infrastructure helps to include a larger scope of problem investigation. Using
a screening tool such as the risk scoring tool can help to illustrate the difficulties in
capturing complex relationships between site characteristics. Cumulative risk involving
multiple sources and exposure pathways can be difficult to quantify. The risk scoring
tool can organize and analyze multiple threats and exposure pathways which can
eventually be combined to address potential adverse effects. Additional pits or quarries
can also be added into the risk scoring tool to assess the changes to the risk score if
additional sites are created. A systematic scoring tool may help to prioritize different
threats and concerns to the natural infrastructure and be an integral part of examining
water security.
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PART II, SECTION 6- DRAFT
Bibliography
Aqua Resources, (2010), City of Guelph Source Protection Project: Final Groundwater
and
Surface
Water
Vulnerability
Report.
(Available
at:
http://guelph.ca/uploads/ET_Group/waterworks/Source%20Protection/COG_Vulnerabil
ityReport_100319_Secure.pdf)
Environmental Protection Agency, (2004), Superfund Chemical Data Matrix. (available
at: http://www.epa.gov/superfund/sites/npl/hrsres/tools/scdm.htm)
Environmental Protection Agency (1990), Hazard Ranking System: Final Rule. (available
at: http://www.epa.gov/superfund/sites/npl/hrsres/index.htm)
Grand River Conservation Authority (2009), Cumulative Effects Assessment Best
Practices Paper for Below Water Table Aggregate Operations within the Grand River
Watershed.
(Available
at:
http://www.grandriver.ca/policyplanningregulations/Aggregatebestpractices_April2009.
pdf)
MHBC Planning and Golder Associates (2009), State of the Aggregate Resource in
Ontario Study Paper 1 –Aggregate Consumption and Demand. MNR Number 52654.
Queen’s Printer for Ontario.
Skelton Brumwell Associates and Savanta Inc. (2009), State of the Aggregate Resource
in Ontario Study Paper 6 – Rehabilitation. MNR Number 52659. Queen’s Printer for
Ontario.
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