WRC Completeness Comments Generous, Bob
From: Strong, Vanessa
Sent: Tuesday, June 26, 2018 8:36 AM
To: Generous, Bob; Bender, George
Subject: FW: RPBCWD Permit 2018-043: Control Concepts - Initial Completeness Review
Comments
FYI
From: Scott Sobiech <SSobiech@barr.com>
Sent: Tuesday, June 26, 2018 8:25 AM
To: 'tgruys@loucksinc.com' <tgruys@loucksinc.com>
Cc: Terry Jeffery<tjeffery@rpbcwd.org>; Strong, Vanessa <VStrong@ci.chanhassen.mn.us>; Scott Sobiech
<SSobiech@barr.com>
Subject: RPBCWD Permit 2018-043: Control Concepts- Initial Completeness Review Comments
Trevor,
The RPBCWD received your application and supporting information for the proposed Control Concepts
Development in Chanhassen on June 19, 2018. The application has been assigned permit number 2018-043.
However, the application is considered incomplete. A review of the submitted information has generated the
following questions or comments. These are only preliminary comments and do not constitute an exhaustive
review of the submitted materials. Additional comments will be generated with complete submittal. Many of the
items listed below will need to be addressed before a recommendation can be made to the RPBCWD Board of
Managers.
The application will be considered incomplete until the following information is received:
101. Because the land disturbing activities is upgradient from regulated wetlands, the proposed
development will trigger Rule D —Wetland and Creek Buffers. The applicant must submit information
as stipulated in Rule D, subsection 7 and demonstrate conformance with all the criteria in subsection
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IC2. The District requires that the native electronic models be provided with the submittal. The existing and
proposed electronic HydroCAD and proposed condition MIDS models must be provided for review.
The model inputs must match design and plan information.
IC3. Section 2.1 of Rule A requires the application be signed by the owner(s) of the property. The
application indicates the property is owned by Zion Investments LLC which does not align with the
information on the Caver County Property website. The website indicates the property is owned by
CHASKA GATEWAY PARTNERS. Provide documentation confirming Zion Investments LLC is the
property owner or they must either sign the application or provide documentation that they are aware
of, and approve of Zion Investments LLC. applying on their behalf.
Because the project will involve 4 acres of land-disturbing activity, the project must conform to the
requirements in the RPBCWD Erosion and Sediment Control rule (Rule C, Subsection 2.1). To conform to the
RPBCWD Rule C the following revisions are needed:
C1.Redundant perimeter protection (e.g., double rows of silt fence) is needed between the land disturbing
activities and the wetlands on-site (i.e., wetland in NW corner of site).
C2.The inspection requirements on sheet C3.3 do not align with RPBCWD requirements. The inspection
frequency during construction must be revised to meet the RPBCWD rules as follows: The permittee
must, at a minimum, inspect, maintain and repair all disturbed surfaces and all erosion and sediment
control facilities and soil stabilization measures every day work is performed on the site and at least
weekly until land-disturbing activity has ceased. Thereafter, the permittee must perform these
responsibilities at least weekly until vegetative cover is established.
C3.Note 3 on sheet C3.1 indicates four (4) inches of topsoil. Final site stabilization measures must specify
that at least six (6) inches of topsoil or organic matter be spread and incorporated into the underlying
soil during final site treatment wherever topsoil has been removed. Please revise so that a minimum of
6 inches of top soil is required.
C4.The name and contact information of the general contractor responsible for the site must be provided
(this information does not need to be provided prior to making a recommendation to the RPBCWD
Board).
Because the proposed work triggers RPBCWD's Stormwater Management Rules (Rule J) and the regulated
wetland in the NW corner of the site is downgradient of the activities, Rule D, Subsections 2.1a and 3.1 require
buffer around these wetlands. To conform to the RPBCWD Rule D the following revisions are needed:
D1.The applicant must submit information as stipulated in Rule D, subsection 7
D2.The wetland function and values assessment using MnRAM is needed for the downgradient wetlands
to determine the value of the buffer according to Appendix D1 of Rule D, the buffer location and the
required average/minimum widths. Without the MnRAM information the wetlands on the parcel could be
assumed to be exceptional value and an 80 foot average, 40 foot minimum buffer width could be
provided.
D3.The buffer area and signage location must be clearly shown on the plans. The buffer must be indicated
by permanent, free-standing markers at the buffer's upland edge. A marker must be placed along each
lot line, with additional markers at an interval of no more than 200 feet or where the buffer changes
direction..
D4.Before any work subject to District permit requirements commences, buffer areas and maintenance
requirements must be documented in a maintenance declaration recorded with the County. A draft
declaration template is available for download from the RPBCWD website (www.rpbcwd.org/permits).
The draft must be submitted to the District for review and approval prior to recording.
Because the project will involve 4 acres of land-disturbing activity, the project must conform to RPBCWDs
stormwater management rule as described in Rule J, Subsection 2. To conform to the RPBCWD Rule J the
following revisions are needed:
J1. Please provide the native electronic HydroCAD and water quality models for review.
J2. The project must limit peak runoff flow rates to that from existing conditions for the two-, 10- and 100-
year frequency storm events using a nested 24-hour rainfall distribution, and a 100-year frequency,
10-day snowmelt event for all points where stormwater discharge leaves the site. According to Table
1.1 there will be a significant increase in site discharge to Century Boulevard under proposed
conditions which does not meet the requirement of Rule J, subsection 3.1a. In addition, altering the
hydrology of the wetland by reducing the discharge volume has the potential to adversely impact the
existing wetland. The proposed design should be revised to provide rate control at all point where
discharge leaves the site.
J3. The project appears to provide no runoff abstraction based on the narrative and plan sheets. The
proposed stormwater management facility must be reconfigured to provided abstraction in accordance
with Rule J, subsection 3.1b.
a. The presence of Hydrologic Soil Group (HSG) D soils onsite does not automatically qualify an
applicant as having a restricted site. Previous permit applicants, also having sites with HSG D
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soils and clay identified in boring, have been able to provide the required abstraction volume of
1.1- of runoff using a design infiltration rate of 0.06 in/hr (MN Stormwater Manual). While the
geotechnical report demonstrates the clay soils present in the upper soil horizon has a
significantly lower infiltration rate than those published in the MN Stormwater Manual, the
geotechnical report does not provide testing for the poorly graded sand or silty sand
encountered in boring ST-4. These types of soils are conducive to infiltration, thus the site does
not appear to be a restricted site .
b. Infiltration appears feasible at soil boring ST-4 where poorly graded sand or silty sand was
encountered at an elevation above the bottom of the proposed underground detention
system. This suggests that an underground infiltration/detention chamber is feasible and the
stormwater management facilities can to be reconfigured to utilize infiltration at ST-4.
c. In addition, the landscaping plans indicate that an irrigation system will be installed. The
proposed irrigation system could take advantage of the proposed stormwater management
facility and reuse the runoff, thus providing additional abstraction. It appears feasibly to irrigate
the lawn and areas planted with native vegetation to maximize abstraction on the site.
J4. Without the native HydroCAD model it is unclear if runoff is calculated separately from impervious
and pervious areas. Runoff should be calculated separately from pervious and impervious surfaces in
the HydroCAD model.
J5. Several of the times of concentration for proposed conditions are direct entry of 7 minutes. Please
provide supporting documentation supporting those times of concentration.
J6. The printout from HydroCAD suggest a two stage outlet from the underground detention system but I
was unable to locate a detail of the outlet in the plan set. Please provide a detail of the outlet on the
construction drawings.
J7. The printout from HydroCAD suggests an 18" pipe downstream of the underground detention system
but the plans indicate a 12-inch HDPE. Please review, clarify, and revise as needed.
J8. Please clarify if the plan view footprint of the proposed retaining walls is included in the impervious
area calculations. Based on permits issued by the RPBCWD Board of Managers, retaining walls are
considered impervious surface and stormwater treatment must be provided for any new or
reconstructed retaining walls.
J9. Based on the construction plans, it appears the project will involve land disturbing activities on
Century Boulevard.
a. All disturbed impervious surface areas must be accounted for in the stormwater calculations and
the applicant must demonstrate conformance with criteria in Rule J.
J10.The pollutant removals estimated by the MIDS model appear to only reflect the proposed Jellyfish
BMP. The proposed Jellyfish is a proprietary device. It is my understanding that the manufacturer
provided removal estimates assume no upstream treatment. By routing runoff from the upstream
BMPs to the Jellyfish in MIDS the model will removal TSS and TP (at whatever percentage entered)
regardless of the inflow composition, thus over estimating the removal potential. Also, RPBCWD has
allowed the Jellyfish BMP to be installed at one other location in the District and required the
applicant monitor performance for two years to confirm the manufacturer removals. The first year of
monitoring data indicated the jellyfish is underperforming for TSS (13%-96%) and significantly
underperforming for TP (-64%-45%). After seeing those results it will be difficult to approve the same
device at another location. To avoid the potential pollutant removal shortfall, I suggest revising the
design to exclude the Jellyfish.
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J11.The water quality information provided indicates the required 90% TSS and 60% TP removals are not
being achieved by the proposed design. The design must be modified to achieve the pollutant
removals required in Rule J subsection 3.1c.
J12.The MIDS modeling does not appear to account for the treatment capacity of the underground
detention system. The modeling must be update to account for all proposed BMPs. You might
consider using the P8 model to better estimate the removal in the underground detention system.
J13. Permit applicant must provide a maintenance and inspection plan. The plan must be documented in a
form acceptable to the District. A draft maintenance agreement is available on the permits page of
the RPBCWD website. (http://www.rpbcwd.orq/permits/)
Review of the additional materials will result in additional comments that will need to be addressed prior to
issuing a permit. We will do everything we can to ensure that we move you through the permitting process as
quickly as possible. Please contact me or Terry Jeffery (cc'd on this e-mail, 952-807-6885) with any questions
or concerns.
Thank you,
Scott Sobiech, CFM, PE
Vice President
Senior Water Resources Engineer
Minneapolis, MN office: 952.832.2755
ssobiech s barr.com
www.barr.com
resourceful. naturally.
BARR
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