(1) Streamflow
criteria are established by the categories described at 310 CMR
36.14(1)(a)
through (c), which describe the modeled 2000-2004 existing conditions at the
subbasin scale across a gradient of alteration from least to most altered for
five bioperiods: early summer (May-June), late summer (July through September),
fall (October and November), winter (December through February) and spring
(March and April). The streamflow criterion for each category is the upper
limit of the ranges shown at 310 CMR
36.14(1)(a) through (c). Withdrawals that
contribute to a subbasin changing to a more altered category do not meet
streamflow criteria and will only be permitted if the permittee demonstrates
that there is no feasible alternative available to meet demonstrated water
needs, and the permittee undertakes mitigation commensurate with the impacts of
the withdrawal to the greatest extent feasible.
(a)
Biological
Category for each subbasin is based on the simulated 2000-2004
existing condition of aquatic habitat using fluvial fish community
characteristics as the surrogate indicator variable. Each biological category
represents the percent alteration within the range of these fluvial fish
community characteristics as a function of the following subbasin parameters:
1. impervious cover;
2. cumulative groundwater withdrawal as a
portion of the unimpacted August median flow;
3. stream channel slope; and
4. percent wetland within the stream buffer
area.
Simulated Alteration of Fluvial Fish Community
Characteristics.
|
Biological Category 1:
|
0% to 5%
|
|
Biological Category 2:
|
>5% to 15%
|
|
Biological Category 3:
|
>15% to 35%
|
|
Biological Category 4:
|
>35% to 65%
|
|
Biological Category 5:
|
>65%
|
(b)
Groundwater Withdrawal
Category for each subbasin is based on the ratio of the 2000-2004
groundwater withdrawal volume to the unimpacted median monthly flow for August
and represents conditions during the late summer bioperiod (July through
September). Each groundwater withdrawal category represents the range of this
ratio that would result in the biological category of the same number under
conditions of low (1%) impervious cover.
Simulated Groundwater Withdrawal Ratio for the Late
Summer Bioperiod.
|
Groundwater Withdrawal Category 1:
|
0% to 3%
|
|
Groundwater Withdrawal Category 2:
|
>3% to 10%
|
|
Groundwater Withdrawal Category 3:
|
>10% to 25%
|
|
Groundwater Withdrawal Category 4:
|
>25% to 55%
|
|
Groundwater Withdrawal Category 5:
|
>55%
|
(c)
Seasonal Groundwater Withdrawal Categories for each
subbasin are based on the ratio of the 2000-2004 groundwater withdrawal volume
to the unimpacted median monthly flow for the four other bioperiods below.
Seasonal Groundwater Withdrawal Ratios for
Additional Bioperiods
|
Fall (Oct-Nov)
|
Winter (Dec-Feb)
|
Spring (March-April)
|
Early Summer (May-June)
|
|
Seasonal Category 1:
|
0% to 3%
|
0% to 3%
|
0% to 3%
|
0% to 3%
|
|
Seasonal Category 2:
|
>3% to 5%
|
0% to 3%
|
0% to 3%
|
>3% to 5%
|
|
Seasonal Category 3:
|
>5% to 15%
|
>3% to 10%
|
>3% to 10%
|
>5% to 15%
|
|
Seasonal Category 4:
|
feasible mitigation and improvement/no numeric
criteria
|
|
Seasonal Category 5:
|
feasible mitigation and improvement/no numeric
criteria
|
(2) Streamflow criteria have not been
established for groundwater-driven water sources (the southern portion of South
Coastal, Cape Cod, Islands, and portions of Buzzards Bay).
