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Environmental
Science and Planning
Site
Assessment, Remediation and
Earth Sciences
Biology
and Wetland Resources
GIS and Graphics Resources
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The objective
of a Phase II Environmental Site Assessment is to evaluate
the nature and extent of contamination and to assess the significance
of the contamination relative to established threshold levels
or some other risk-based criteria. Assessment is typically
conducted in phases, which may include a preliminary site
assessment, and one or more subsequent phases of assessment.
The assessment involves working within established regulatory
agency guidelines for sampling and reporting. Typical
components of the assessment program include:
- Preliminary
Site Assessment
- Preparation
of Site Safety Plans and Workplans
- Site
Assessment
- Periodic
Monitoring
- Risk
Assessment and Evaluation of Risk-Based Cleanup Levels
Our approach
to environmental assessment is to tailor the sampling program
to the specific project. Samples can be obtained using
a variety of methods, including:
- surface
grab sample
- shallow
hand auger sample
- backhoe
sampling
- soil
gas sampling
- direct
push sampling (i.e., Geoprobe or CPT)
- hollow-stem
auger or air rotary drilling and sampling
The appropriate
sampling methodology is dependent on the following:
- suspected
source of contamination (point source versus non-point
source)
- suspected
type of contaminant (volatile or non-volatile)
- media
affected (soil only or soil and groundwater)
- anticipated
depth of contamination
- soil/geologic
conditions at the site
- depth
to groundwater
If groundwater
sampling is required, this can be conducted in conjunction
with direct push soil sampling or conventional drilling.
Sampling can include one-time sampling conducted during
the soil sampling event, or installation of wells to allow
periodic monitoring. If three or more wells are installed,
depth to water can be referenced to established survey points,
and groundwater flow direction and gradient can be established.
Soil
or groundwater samples are tested for suspected contaminants
using appropriate EPA or State methodology in laboratories
certified by the State to conduct such tests. The
testing program is tailored to the suspected contaminants.
For example, if a site involves a tank that was used to
store gasoline, the soil samples would be tested for total
petroleum hydrocarbons - modified for gasoline and volatile
aromatics (benzene, toluene, ethylbenzene, and total xylenes).
The testing may also include lead, if the tank was used
to store unleaded gasoline, and gasoline additives, such
as MTBE, based on the period of operation.
The
levels of contamination detected are initially compared
to published threshold action levels. If the levels
of contaminants can be demonstrated to be below these general
cleanup standards, remediation might not be required.
If the levels are above the general cleanup levels or there
are no listed standards for a specific contaminant, then
risk-based analysis can be conducted to further evaluate
the significance of the contamination levels. CAL-EPA
and US-EPA have developed a number of risk based methodologies
to evaluate human health and environmental risk. Risk-based
cleanup levels can be applied to a site that incorporates
site specific conditions (nature of contamination, proximity
to receptors, exposure pathways, etc.) and establishes cleanup
objectives. In our experience, it is critical to
establish cleanup objectives (in concurrence with regulatory
oversight agencies) early on in an assessment program.
This avoids unnecessary assessment in areas that may have
levels of contaminants below significant thresholds.
Back
to Phase I Environmental Site Assessments
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