Code of Massachusetts Regulations
310 CMR - DEPARTMENT OF ENVIRONMENTAL PROTECTION
Title 310 CMR 40.0000 - Massachusetts Contingency Plan
Subpart I - RISK CHARACTERIZATION
Section 40.0924 - Identification of Exposure Points

Universal Citation: 310 CMR 40.0000 MA Code of Regs 40.0924

Current through Register 1531, September 27, 2024

(1) All potential Exposure Points shall be identified and described in the documentation of the Risk Characterization after considering the site and receptor information described in 310 CMR 40.0904 through 310 CMR 40.0923.

(2) The identification of an Exposure Point shall be consistent with the type and method of Risk Characterization which is being performed.

(3) The Exposure Point(s) in all environmental media shall be identified for all current and reasonably foreseeable Site Activities and Uses.

(4) For comparisons to Applicable or Suitably Analogous Standards in Method 3, the Exposure Point shall be identified in a manner consistent with the applicable regulations.

(5) Consideration shall be given to the identification of Exposure Points which may be located at a distance from the original source of the release, particularly when the migration of oil and/or hazardous material may result in Exposure Points in addition to those identified under current site conditions.

(6) Groundwater Exposure Points.

(a) In Methods 1 and 2 Risk Characterizations, the Exposure Point(s), for all groundwater categories, shall be the groundwater resource itself, as measured at each wellhead and/or nearest tap of a well screened within the horizontal and vertical distribution of the oil and/or hazardous material in the groundwater. Existing water supply wells and monitoring wells shall be used to represent current or potential groundwater Exposure Points.

(b) In Method 3 Risk Characterizations:
1. For comparisons to Applicable or Suitably Analogous Standards as described in 310 CMR 40.0993(3), the Exposure Point shall be identified in a manner consistent with the applicable regulations;

2. Except as provided in 310 CMR 40.0924(6)(c), in GW-1 groundwater areas, for the comparison to drinking water standards listed in 310 CMR 22.00: Drinking Water and for the calculation of current and/or potential exposure to the groundwater, the Exposure Point(s) shall be the groundwater resource itself, as measured at each wellhead and/or nearest tap of a well screened within the horizontal and vertical distribution of the oil and/or hazardous material in the groundwater. Existing water supply wells and monitoring wells shall be used to represent current or potential groundwater Exposure Points;

3. In areas where the groundwater is categorized as GW-3 only, groundwater Exposure Points shall be determined based on site-specific conditions, and potential current and future exposures.

(c) In GW-1 areas that are designated GW-1 solely on the basis of being located within a Zone II or an Aquifer Protection District that overlays or is contiguous with a Zone II and where the relevant disposal site meets the criteria specified at 310 CMR 40.0924(6)(c)3 through 8, the Exposure Point shall be the existing Public Water Supply well(s) for the evaluation of current and future drinking water exposures to petroleum hydrocarbons at or from the disposal site and the Exposure Point Concentration shall be identified pursuant to 310 CMR 40.0926(7)(e).
1. For the purposes of this provision, the term "petroleum hydrocarbons" shall mean the petroleum-derived constituents of crude or fuel oil, such as those constituents defined by the analytical methods for Total Petroleum Hydrocarbons, Volatile Petroleum Hydrocarbons, Extractable Petroleum Hydrocarbons, Benzene, Toluene, Ethylbenzene and Xylenes, but not including additives;

2. This Exposure Point is only applicable to petroleum hydrocarbons at or from the disposal site and shall be used in combination with Exposure Points identified for the evaluation of any other contaminants at or from the disposal site, including but not limited to additives;

3. A Phase II Report for the disposal site pursuant to 310 CMR 40.0830 has been submitted;

4. The disposal site is located at a distance greater than 1,000 feet from a Public Water Supply well;

5. It has been demonstrated that the requirements at 310 CMR 40.1003(5)(a) and (b) and 310 CMR 40.1003(7)(a) have been met to address any NAPL present;

6. It has been demonstrated through adequate characterization of horizontal migration that groundwater petroleum hydrocarbon concentrations are:
a. 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(s); and

b. decreasing within the boundaries of the plume; demonstration of diminishing contaminant concentrations within the plume shall consider both the spatial and temporal distribution of the contamination and other measures indicative of biodegradation of the contaminants;

7. It has been demonstrated through adequate characterization of vertical migration that contamination has not entered bedrock, including through the submittal of a profile sectional map showing the following information:
a. known or inferred depth to bedrock;

b. depths to the top and bottom of the plume throughout the length of the plume; and

c. existing well screen depths in comparison to the plume.

8. It has been demonstrated that there is no potential Exposure Point Concentration in accordance with the criteria specified at 310 CMR 40.0926(7)(e).

(7) Soil Exposure Points.

(a) For Methods 1 and 2 Risk Characterization, the Exposure Point(s) shall be defined by the horizontal and vertical extent and distribution of the contamination in combination with the soil category(ies) determined to be applicable.
1. For a contiguous volume of contaminated soil comprised of one or more soil categories as defined in 310 CMR 40.0933, a separate and distinct Exposure Point shall be represented by the soil in each category.

2. The top three feet of surface soil shall also represent a separate Exposure Point for current use scenarios.

(b) For Method 3 Risk Characterization for current or potential soil exposures, the following depths shall be considered with any applicable site-specific information when determining Exposure Points:
1. zero to three feet for exposures associated with surficial activity;

2. zero to six feet for exposures associated with utility installation and repair; and

3. zero to 15 feet for exposures associated with excavation scenarios and building construction.

(c) For Imminent Hazard Evaluations, the top foot of soil shall be the Exposure Point.

(8) Indoor Air Exposure Points.

(a) Indoor air Exposure Points are locations within a building where exposure occurs or could occur.

(b) Indoor air Exposure Points shall be identified considering the nature, duration and likely frequency of exposure.

(c) Areas of the building where exposure is likely to be different shall be identified as distinct Exposure Points.

(9) Sediment Exposure Points.

(a) Sediment Exposure Points shall be identified for human and ecological receptors separately.

(b) Sediment exposure Points shall be identified considering the life history of potential ecological receptors, potential human activities and uses, the timing of the exposure and the potential for short-term effects from the contaminants of concern.

(10) Surface Water Exposure Points.

(a) Surface water Exposure Points shall be identified for human and ecological receptors separately.

(b) Surface Water Exposure Points shall be identified considering the life history of potential ecological receptors, potential human activities and uses, the timing of the exposure and the potential for short-term effects from the contaminants of concern.

(11) Each of the following shall be considered distinct Exposure Points:

(a) Hot Spots; and

(b) Visible coal tar deposits.

(12) Examples of typical Exposure Points for disposal sites shall include, without limitation:

(a) an existing public or private water supply;

(b) a future drinking water supply;

(c) a Hot Spot of contamination in a neighborhood playground;

(d) a volume of subsurface soil at a potential construction site; and

(e) a distant shellfish bed.

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