Current through Register 1531, September 27, 2024
(1) For
each oil and/or hazardous material in each medium at each Exposure Point, an
Exposure Point Concentration shall be identified and documented.
(2) Exposure Point Concentrations shall be
determined or estimated in a manner consistent with the type and method of Risk
Characterization which is being performed and shall be based on a
representative data set that adequately characterizes site conditions at the
Exposure Point as described in 310 CNR 40.0924.
(3) Except as provided in
310
CMR 40.0926(4), analytical
data from the Exposure Point, as described in
310
CMR 40.0924, shall be the primary line of
evidence for the determination of Exposure Point Concentrations.
(4) Except as otherwise specified at
310
CMR 40.0926(9), fate and
transport models may be used in conjunction with other site information and
data or in cases where direct sampling of a medium of concern is not possible
or appropriate. Such models shall be clearly documented and supported by
evidence demonstrating the model's predictive performance, and shall
incorporate input parameters to provide a conservative estimate of the Exposure
Point Concentration.
(5) In
estimating Exposure Point Concentrations, the objective shall be to identify a
conservative estimate of the mean concentration contacted by a receptor at each
Exposure Point over the relevant exposure period.
(6) Maximum concentrations shall be used to
estimate an Exposure Point Concentration under the following conditions:
(a) evaluations of acute exposures;
(b) screening assessments that evaluate
maximum exposure potential to streamline the assessment process; or
(c) as otherwise provided in
310
CMR 40.0900.
(7)
Groundwater Exposure Point
Concentrations.
(a) Groundwater
Exposure Point Concentrations shall be determined for each Exposure Point in
the groundwater identified pursuant to
310
CMR 40.0924(6).
(b) A groundwater Exposure Point
Concentration shall be a conservative estimate of the temporal mean for the
exposure period of concern and shall consider temporal trends.
(c) Current groundwater contaminant
concentrations and site hydrogeologic conditions may be used to estimate future
groundwater Exposure Point Concentrations.
(d) Where appropriate, current soil
concentrations and site-specific factors such as infiltration, rate of
precipitation, and soil characteristics shall be used to estimate future
groundwater concentrations due to the leaching potential of soil
contaminants.
(e) For those sites
described at
310
CMR 40.0924(6)(c), no
exposure potential for petroleum hydrocarbons exists (the Exposure Point
Concentration for petroleum hydrocarbons may be set equal to zero) if the
following conditions are met and documented based on data collected at the
disposal site:
1. demonstration of source
elimination or control at the disposal site as described in
310
CMR 40.1003(5)(a) and
(b);
2. demonstration of diminishing contaminant
concentrations throughout the horizontal and vertical extent of the
plume;
3. demonstration that
contaminant concentrations are not detected at or above analytical limits
appropriate for a GW-1 area at the downgradient edge of the plume, at least
1,000 feet from the Public Water Supply well; and
4. the demonstrations pursuant to
310
CMR 40.0926(7)(e) are
confirmed by a minimum of two years of quarterly groundwater monitoring
conducted after:
a. the termination of any
Active Remedial System or Active Remedial Monitoring Program; and
b. the achievement of such contaminant
concentrations.
(8)
Soil Exposure Point
Concentrations.
(a) Soil Exposure
Point Concentrations shall be determined for each Exposure Point in soil
identified pursuant to
310
CMR 40.0924(7) according to
the following requirements:
1. For Exposure
Points where judgmental sampling has been implemented in accordance with
310
CMR 40.0904(4), the
arithmetic mean of data from the Exposure Point may be used as an Exposure
Point Concentration, provided that 75% of the data points used in the averaging
procedure are equal to or less than the applicable standard or risk-based
concentration limit, and no data point used in the averaging is ten times
greater than the applicable standard or risk-based concentration limit;
Otherwise,
a. the maximum concentration from
the Exposure Point may be used as the Exposure Point Concentration; or
b. the arithmetic mean may be used
to determine the Exposure Point Concentration, supported by a technical
justification that considers the size of the data set, density and potential
biases of the sampling, and other relevant factors.
2. For Exposure Points where systematic
sampling has been implemented in accordance with
310
CMR 40.0904(4), the
90th percentile Chebyshev non-parametric upper
confidence limit on the mean of the concentrations within the Exposure Point
may be used as the Exposure Point Concentration.
a. If the 90th
percentile Chebyshev non-parametric upper confidence limit on the mean is
determined not to provide a suitable estimate of the Exposure Point
Concentration, an alternative conservative estimate of the arithmetic mean may
be used to determine the Exposure Point Concentration, supported by technical
justification. Such technical justification shall document the determination
that the 90th percentile Chebyshev non-parametric
upper confidence limit on the mean is not suitable, and the suitability of the
alternative approach, considering the size of the data set, density and
potential biases of the sampling, applicable statistical analyses of the data,
and other relevant factors.
3. For Exposure Points where direct contact
with a visible coal tar waste deposit is possible, the Exposure Point
Concentration shall be based on the OHM concentration known or estimated to be
present in the coal tar itself.
(b) For assessing wildlife exposure to
contaminants in soil in an Environmental Risk Characterization, the arithmetic
mean concentration of OHM within the Exposure Point for each receptor of
concern is acceptable.
(9)
Indoor Air Exposure Point
Concentrations.
(a) A
conservative estimate of the OHM concentration contacted by a receptor over the
exposure period of concern, based on concentrations measured in indoor air,
shall be used for the Exposure Point Concentration.
1. Except where multiple rounds of data have
been obtained in a manner that adequately establishes spatial and temporal
variations as specified in 310 CMR 40.0926(9)(a)2., maximum concentration
values shall be used as the Exposure Point Concentration for each contaminant
of concern.
2. When sufficient data
are available to characterize the spatial and temporal variability at the
Exposure Point, a conservative estimate of the mean for the exposure period of
concern that considers temporal trends may be used. In such cases, a valid
justification must be provided that indicates that the sample mean is unlikely
to underestimate the true mean.
(b) A sub-slab soil vapor dataset and/or
conditions may be used to:
1. estimate or aid
in the estimation of Exposure Point Concentrations in the event that it is not
possible to distinguish disposal site-related contamination at the Exposure
Point from interior sources at ongoing commercial and/or industrial operations
or interior building materials contaminated by past commercial or industrial
operations; and
2. where
appropriate, to rule out an indoor air Exposure Pathway.
(c) Fate and transport models shall not be
used to estimate future indoor air Exposure Point Concentrations in the indoor
air of buildings that have not been constructed.
(10)
Sediment Exposure Point
Concentrations.
(a) For assessing
human direct contact exposure, the Exposure Point Concentration shall be the
arithmetic mean concentration within each Exposure Point.
(b) For assessing exposure to aquatic and
semi-aquatic organisms, the Exposure Point Concentration shall be the
arithmetic mean concentration within each Exposure Point.
(11)
Surface Water Exposure Point
Concentrations.
(a) For assessing
human direct contact exposure, the Exposure Point concentration shall be the
arithmetic mean concentration within the Exposure Point over the relevant time
period.
(b) For assessing exposure
to aquatic and semi-aquatic organisms, the Exposure Point Concentration shall
be the arithmetic mean concentration within each Exposure Point.
(12)
Hot Spot Exposure
Point Concentrations in Soil or Sediment.
(a) Where a Hot Spot is likely to be present
based upon the Conceptual Site Model and visual, olfactory, and/or analytical
data, discrete samples shall be taken to delineate the boundaries of the Hot
Spot.
(b) The Exposure Point
Concentration to evaluate risk from a Hot Spot shall be the arithmetic mean
concentration within the Hot Spot.
(13)
Method 3 Ceiling Limits
Comparison Concentrations. The concentrations to compare to Method
3 Ceiling Limits shall be the arithmetic mean concentrations within the site,
and within any identified Hot Spots.
