20100251 Ver 1_Staff Comments_20100920

10-0251 - Harnett Health Hospitals, Harnett Co. - RETURN
AML Comments
September 20, 2010
RETURN OF APPLICATION
Under Brightwater Biotechnology and Medical Center:
1. Item 3 stated: "Please provide a table of elevations, areas, incremental volumes
and accumulated volumes for the ponds and forebays. This must include rows for
key elevations (bottom, sediment cleanout, permanent pool, temporary pool,
etc.)."
The Pond Volume Calculation Sheets provided for each of the four proposed
ponds are incorrect. The accumulated volume at the bottom of the pond should
be zero and increase with decreasing water depth. Also, the table did not extend
to the temporary pool, which is needed to check whether the stated water quality
volumes will be treated.
2. Item 4 requested a number of items to be shown on the pond profile.
Most of the requested items were provided, however, the temporary pond
elevation was not included. Also, in the future, please call out the pond
elevations on the pond profile rather than using a table for ease of reference.
3. Item 5 stated: "The average depths provided are less than the required minimum
of 3 feet. This depth cannot include the V of sediment storage. Please revise the
ponds to provide the minimum depth or more. Please correct the errors in the
calculation of average depth in your resubmittal."
The DWQ has checked the calculation of average depths using the Method 2
formula found on page 10-13 of the BMP Manual. The average depths given
on the Supplement Forms appear to be incorrect.
4. Item 7 stated: "Planting plans for the ponds must be provided on the plans as per
10.3.7 of the BMP manual."
The planting plan should show the actual locations of plant species - random
placement of eight different types of species on the shallow water and the
shallow land portions of the shelf will be difficult. Specifications for watering
should have been provided as well.
5. Item 8 stated: "Please provide the drawdown calculations for each pond."
These were not found by DWQ. It seems unlikely the each pond draws down in
exactly 2.00 days.
6. Item 9 stated: "Please provide a soils test based on in-field borings conducted in
the footprint of the proposed wet detention ponds to document the SHWT
elevation. Liners may be required if it is well below the permanent pool
elevations. See also 10.3.2 of the BMP manual."
The note on the plan to provide a liner pending SHWT testing is not sufficient.
This information needs to be provided as part of a submittal. In addition to
checking if the SHWT is too low to maintain a permanent pool, the DWQ also
needs to ensure that the ponds will not dewater any adjacent wetlands.
7. Item 10 stated: "Please show details of all the pond outlets and associated energy
dissipation devices."
The DWQ did not find this information on the BMP plan sheets SW 4.1
through 4.4. The DWQ will not approve plans without a clear depiction of the
outlets.
8. Item 11 stated: "Per the BMP Manual, the emergency spillway must be hardened
with concrete, rip rap or other appropriate material."
Root reinforcement matting is insufficient.
Under Harnett Health Hospitals:
Item 2(f) stated: "Please provide the SHWT elevations. A liner may be required
if it is well below the permanent pool elevation."
The information provided shows the water table elevations observed on the day
of exploration, but does not estimate the SHWT. Please provide an estimate of
the SHWT. If the SHWT of Pond I is more than 0.5 feet below the permanent
pool, then please provide a liner. Pond 2 appears to have a different issue: a
SHWT that is significantly above the permanent pool. This could result in
dewatering of the groundwater table. Please explore the possibility of raising
the elevation of the permanent pool to avoid this problem.
NOTE: In the new application, the stormwater plan for Harnett Health Hospitals may
include only the new information requested in Item (1) above. A complete resubmittal of
the entire stormwater plan for Harnett Health Hospitals will not be required.