MCP Category GW-1 Standards (310 CMR 40.0974(2)) apply to groundwater that is considered either a current or a future source of drinking water. The regulatory criteria used to determine the applicability of the GW-1 standards are described at 310 CMR 40.0932(4). This section of the MCP references definitions of "Current Drinking Water Source Area" and "Potential Drinking Water Source Area" that are found in 310 CMR 40.0006.
Drinking water standards are the most common type of environmental standard, and there are existing state and federal regulatory programs that regulate contaminant concentrations in public water supplies. In order to build upon the existing body of drinking water standards and guidelines, and to promote inter-agency consistency, the Bureau of Waste Site Cleanup has decided to adopt existing values whenever possible:
- Existing drinking water standards (Massachusetts Maximum Contaminant Limits, or MMCLs) promulgated in 310 CMR 22.00 file size 1MB have been adopted as MCP GW-1 standards. There are 48 such standards on the MCP GW-1 list.
- Existing drinking water guidelines developed by the MA DEP Office of Research and Standards (ORS) for the MA DEP Water Supply Program have been adopted as MCP GW-1 standards. There are 18 such standards on the MCP GW-1 list.
- MCP GW-1 standards are calculated de novo only for those chemicals for which MMCLs or ORS Guidelines have not been established.
The sequential approach taken to develop the MCP GW-1 standards is as follows:
1. Adopt an existing drinking water standard or guideline when one exists (Workbook: MCP GW.xls, sheet: GW-1, columns: B and C). If no such standard or guideline exists, follow steps 2 through 8
2. Standard toxicity information, risk assessment methodologies and odor thresholds (when available) are used to identify concentrations in water associated with:
- 20% of an allowable intake based on non-cancer health effects (Workbook: MCP GW.xls, sheet: GW-1, column: G)
- an excess lifetime cancer risk equal to one-in-one million (10-6) (Workbook: MCP GW.xls, sheet: GW-1, column: K), and
- a 50% odor recognition threshold (Workbook: MCP Toxicity.xls, sheet: Toxicity, column: AH).
3. The lowest of these three values is carried through the process.
4. A ceiling concentration of 0.005% (50,000 Âµg/L) is noted (Workbook: MCP Toxicity.xls, sheet: Toxicity, column: BP).
5. The lower of the concentrations identified in steps 3 and 4 is carried through the process.
6. A Practical Quantitation Limit (PQL) for an appropriately sensitive analytical method is identified (Workbook: MCP Toxicity.xls, sheet: Toxicity, column: AO).
7. A background concentration is identified, if available (Workbook: MCP Toxicity.xls, sheet: Toxicity, column: AD).
8. The highest of the three values identified in steps 5, 6 and 7 is chosen.
9. The value identified in step 8 is rounded to one significant figure. This value is adopted as the MCP GW-1 standard.
This process is diagramed:
The GW-1 standards are based on the assumed long-term use of groundwater for drinking, cooking and bathing.
|Body Weight (BW)|
|1-8||16.8||Kg||This value is the arithmetic average of the median (50th %-tile) body weights for each year in this age group (females).|
|Drinking Water Intake (VI)|
|1-8||1||Liters/day||Standard USEPA default assumptions, between the mean and 90 th percentile values (EPA, 1997)|
|Showers per day (n)|
|Shower Duration (Ds)|
|1-8||45.7||minutes||95 th percentile value (EPA, 1997)|
|Time in Shower Room (Dt)|
Ds + Time spent in room after shower,
95th percentile value (EPA, 1997)
|Skin Surface Area (SA)|
|1-8||7130||cm2||50th percentile value, female, entire body (EPA, 1997)|
|Duration of Dermal Contact with Water (tevent)|
|1-8||0.76||Hours||Same as Ds, expressed as hours|
|Exposure Frequency (EF)|
Ingestion & Inhalation
|Daily use of water for drinking is assumed. 24% of respondents reported taking more than 1 bath/shower per day. (USEPA, 1997, table 15-24)|
|Exposure Period (EP)|
|1-8||7||Years||30 years is approximately the 90 th percentile value for residence time. (USEPA, 1997)|
|Averaging Period (AP)|
|1-8||7||Years||Equal to EP for noncancer risk, a lifetime for cancer risk.|