HomeMy WebLinkAbout2016-07-27 Response Re 07-21-16 MnDot Letter Kimley>>>Horn
July 27, 2016
Camilla Correll, PE
EOR
651 Hale Avenue North
Oakdale, MN 55128
RE: Brown's Creek Watershed District Permit Application Review Comment Response:
Proposed by The Driessen Group
Oak Park Heights-Permit 16-08 Brackey 4th Addition
To whom it may concern,
Kimley-Horn received the Watershed Permit Application review comments via email on July 20, 2016 for the
proposed development located at the intersection of 60th Street North and Krueger Lane in Oak Park Heights, MN.
All of the Review Findings from the Report have been copied below and Kimley-Horn offers the corresponding
responses in red. Please review and let me know if there are any questions in regards to the responses offered.
1. I am noting a discrepancy between the drainage boundaries provided in the drainage report and the
stormsewer information provided on the Drainage and Grading Plan. DA-2 looks like it should be pulled
back to STM MH-5 and it also looks like it should be made smaller to account for STM MH-9. I could be
reading the figures incorrectly so if you could confirm the drainage boundaries that would be great.
The drainage map in the report was discussed with EOR,and the discrepancy was clarified by phone on
July 25,2016
2. I think the approach to providing volume control using the ET calculations is great. Overall,I agree with
the approach. It looks like the details/information for the tree trenches is missing from the plan
set. Need to see the following:
a. According to MPCA documentation for calculating credits for tree trenches and tree boxes(the
site where the formula you used for the site comes from)the minimum recommended volume
for each tree is equal to 2 cubic feet of rootable soil per square foot of mature tree
canopy. There is no documentation supporting that this minimum volume of material provided
for the trees.
We agree with this comment;we feel the native soils on this site provide the adequate additional
rootable soil volume needed for the mature tree canopy, as outlined by the MPCA. We are
providing the amended soils to provide the plants an area to establish themselves early in the
growth process,but the sandy silt,sandy loam,and sandy soils that existing on the site provide
for an acceptable environment for the plant material to mature. The buried topsoil layer is an
effort to decrease the amount of infiltration on the site, but will also provide an acceptable
environment for the plant material to mature. Please see the attached soil boring logs for the
site.
b. Grading plans do not show depressional storage at the tree locations. As the MPCA
documentation states"ET results when water is held in storage and allowed to be taken up by
roots and released through leaves". It is difficult to see how the water is being delivered to and
stored at the base of the trees included in the ET calculations.
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The grading plan for Phase 1 and Phase 2 on the respective sheet C4.0s have been updeated to
provide for depressional storage in the tree areas. Also see the detail sheet C4.1 for further
detail related to planting material,trench depth,and draintile invert information.
3. A couple of comments regarding the water quality calculations are as follows:
a. The approach taken to establish how much WC/treatment needed is incorrect. See the following
calculations based on P8 model submitted.
Annual phosphorus load cannot increase when compared with pre-development conditions:
Target removal efficiency=84%(Appendix 2.2)
Post-development load=7.31 lb/yr
Target load removal:(84%*7.31)=6.14 lb/yr
Filtration load removal=3.65 lb/yr
Menards Pond load removal:(36%*3.65)=1.31 lb/yr
Total load removal:(3.65+1.31)=4.96 lb/yr(67.9%)
Additional treatment needed:(6.14-4.96)=1.18 lb/yr
The water quality calculations were discussed with EOR on July 27,2016,and it was
determined that sufficient water quality is provided on site.
b. There is an inconsistency in the amount of impervious coverage assumed in the P8 model and
the HydroCAD model(85%in P8 and 74.4%in HydroCAD). Which is the correct amount? It
appears the P8 model is overestimating the amount of impervious coverage under post-
development conditions.
The p8 impervious percentages have been updated to reflect the correct impervious
calculations for the site.
c. Have you considered using the tree trenches/tree boxes to demonstrate the water quality
requirement is being met?
The water quality calculations were discussed with EOR on July 27,2016,and it was
determined that sufficient water quality is provided on site.
The below comments were received at a later time on July 20,2016
1) Add the BCWD's contact information to the table on page SWPPP-1. The contact information is
Karen Kill, District Administrator, (651)330-8220 ext. 26.
The SWPPP has been updated with the above information.
2) Add a note to the Sequence of Maior Construction Activities to comply with Rule 3.3.1 which states
"All erosion and sediment control measures shall be installed, and the District shall be given three
business days'notice in writing. before land disturbance commences".
The above note has been added to the SWPPP.
3) Sequence of Major Construction Activities in the SWPPP(SWPPP-3)change step 8 to 'Construct
filtration area"and add more detail indicating how 'Filtration basin will be kept offline until site is
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fully stabilized and all impervious areas are complete"as noted in the Filtration Basin Construction
Notes on sheet C4.1 of the construction plans.
The above note has been modified/added.
4) Sequence of Major Construction Activities in the SWPPP (SWPPP-3) — Identify when the tree
trenches/tree boxes will be constructed.
The Sequence of Major Construction Activities has been modified in the SWPPP to identify the
construction of the tree trenches.
5) Erosion Control Plan Notes on sheets'C2.1 and C2.2—Add locations of tree trenches/tree boxes
and identify the erosion and sediment control measures that will be used to protect these practices
during construction.
Erosion Control Plan on sheet C2.2 has been updated in Phase I to include the locations of the tree
trenches.Erosion control measures have been indicated to protect the tree trenches.
6) Erosion Control Plan Notes on sheets'C2.1 and C2.2 need more information detailing how
"Filtration basin will be kept offline until site is fully stabilized and all impervious areas am complete"
as noted in the Filtration Basin Construction Notes on sheet C4.1 of the construction plans.
Note 12 has been added to the Erosion Control Plan C2.1 and C2.2 in Phase I to address this comment.
7) Erosion Control Plan Notes on sheets'C2.1 and C2.2. note 8 should be revised to indicate that
erosion control measures will remain in place until the site is fully stabilized and all impervious
areas are complete.
Note 8 on Erosion Control Plan on sheets C2.1 and C2.2 has been updated in both phases.
8) Provide more detail explaining how note 11 under Filtration Basin Construction Notes(sheet C4.1)
will be met. There is no temporary ponding provided on the erosion control plan.
A diversion ditch and sediment trap have been added to the Erosion Control Plans in Phase I of the project
to address this.
9) Provide more detail for the hydraulic soil stabilizer:what type of hydraulic soil stabilizer and where
is it proposed to be located on site.
In consulting with our Landscape Architects, the soil stabilizer for this site is not needed and has been
removed from the details on sheet C4.1. Soil stabilization will occur with the planting and the mulch
blanket being added to each basin at the end of the construction of each basin.
10) Orange construction silt fence noted in the Filtration Basin Construction Notes not included in the
Erosion Control Plan(sheets C2.1 and C2.2).
Orange construction fence has been added to The Erosion Control Plans on sheets C2.1 and C2.2 in Phase
I.
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I have also revised the comments I provided on the Volume Control requirement as follows:
- The approach to providing volume control using the ET calculations is great and the calculations
using tools and guidance from the MPCA appear to meet the District's volume control
requirement. The following information needs to be submitted to demonstrate that the tree trenches
and/or tree boxes needed to achieve the evapotranspiration numbers calculated are designed
correctly:
o Provide details for tree trenches and/or tree boxes.
See updated grading plan for Phase I and Phase 2 on the respective sheet C4.0s for
depressional grading detail. Also see the detail sheet C4.1 for further detail related to planting
material,trench depth,and draintile invert information.
o According to MPCA documentation for calculating credits for tree trenches and tree boxes
(the site where the formula you used for the site comes from)the minimum recommended
storage volume(planting medium) for each tree is equal to 2 cubic feet of rootable soil per
square foot of mature tree canopy. There is no documentation supporting that this
minimum volume of material provided for the trees.
We agree with this comment;we feel the native soils on this site provide the adequate additional
rootable soil volume needed for the mature tree canopy, as outlined by the MPCA. We are
providing the amended soils to provide the plants an area to establish themselves early in the
growth process,but the sandy silt,sandy loam,and sandy soils that existing on the site provide
for an acceptable environment for the plant material to mature. The buried topsoil layer is an
effort to decrease the amount of infiltration on the site, but will also provide an acceptable
environment for the plant material to mature. Please see the attached soil boring logs for the
site.
o Provide specifications for the soil medium being proposed for the tree trenches/tree boxes.
The amended soil is called out on the tree trench detail on sheet C4.1
o Clarify how water is being delivered to the free trenches/tree boxes. Grading plans do not
show depressional storage at the tree locations, nor do they show curb cuts allowing water
from the parking lots to get into the tree trenches/tree boxes.
See updated grading plan for Phase 1 and Phase 2 on the respective sheet C4.0s for
depressional grading detail.
- Comments on the landscaping plan(Sheet L1.0)include:
o Short 5 trees(1 of each of the following trees:ABS, FFM, SWO, BHS, and TAV)
Quantities on all plant materials have been checked and are accurate between Landscape
Plans (L1.0-L1.2 for both Phase 1 and Phase 2), and the Planting Schedule (on sheet L1.2 for
both Phase 1 and Phase 2).
o Provide a planting plan (layout) for the shrubs and perennial plant material that identifies
species and density.
Sheets L1.1 and L1.2 for both Phase 1 and Phase 2 illustrate detailed planting areas that identify
shrub and perennial species and planting density.
o Landscape Note 14 states that"All plant material quantities shown are approximate..." If
the tree and shrub material being included in the ET calculations, they cannot be
approximate.
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The note stating"All plant materials and quantities shown are approximate..."on sheet L1.0 has
been removed on both Phase 1 and Phase 2 plans.
Please contact me at(651)643-0428 or mike.brandt@kimlev-horn.com should you have any questions or
comments.
Sincerely,
/19,A;47_
Michael Brandt,PE
kimley-horn.com 2550 University Avenue West, Suite 238N, St. Paul, MN 55114 651 645 4197