HomeMy WebLinkAboutWPO201800093 Certified Engineer's Report 2022-02-08Drape
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Surveying • Environmental Services
Memorandum
To: Albemarle County — Office of Stormwater Management
From: E. Campbell Bolton, P.E.
Date: February 8, 2022
Project Name: Sunrise Senior Living — The Colonnades Expansion
Project Number: DAA: 18060111-020301
Subject: Construction Record Drawings for Bioretention
The Colonnades Sunrise Senior Living Expansion included the installation of a Level 1
bioretention, which was designed to meet water quantity and water quality requirements for the
project. Water quantity calculations followed Part II.B regulations (9VAC25-870-66) and water
quality calculations were based on the Virginia Runoff Reduction Method — Spreadsheet Version
3.0. Refer to the final permit document plans titled 'Sunrise Senior Living —The Colonnades
Expansion Project' with a seal date of 10/15/19 and the 'Erosion & Sediment Control Narrative
and Stormwater Management Report —The Colonnades Expansion Project' dated 9/11/19 for
approved design plan and calculations.
The design of the bioretention followed the 2013 version of Specification #9 of the Virginia
Stormwater BMP Clearinghouse for a Level 1 bioretention. The bioretention was designed to
have a storage stone base layer, followed by a layer of choker stone, bioretention soil media, and
shredded hardwood mulch.
The bioretention was designed with a perforated underdrain, an outlet control structure, an
observation well, and a gravel diaphragm. These design elements were installed generally per the
approved documents; exact elevations and volumes were within construction tolerances. Survey
shots were taken at the subgrade of the basin to verify the volume prior to placement of any
stone or media as well as the final surface conditions. Refer to Attachment A for the as -built
surveys of the bioretention (subgrade and final grade) titled 'As -Built Survey Bioretention Basin'
sealed 6/18/21. Given the construction was in general compliance with the approved plans and
no significant deviations were observed, no updates to the approved calculations were required.
The basin was installed at the location proposed on the plans; the coordinates are N3909879
El1478732. The as -built drainage area to the basin was also verified to be in general accordance
with the approved documents. Note: A revised drainage area map was submitted to the County
during construction on April 8, 2020 and approved by Mr. John Anderson; refer to Attachment B.
Photos were taken during construction to document the installation of the bioretention. A
selection of these pictures is included as Attachment C. These photos confirm the stone base, the
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Sunrise Colonnades
Bioretention Certification
choker stone, installation of the underdrain, the bio soil media, the landscaping, the outlet
control structure, the observation well, and the inlet from the roof drain. The bioretention mix
used on the project was'RainScape Biofilter Media DEQv2.0' from Luck Stone. This is an
approved bioretention media mix, and was indicated as acceptable with the County's Inspector,
Mr. John Yerby, via email on May 26, 2021; included in Attachment D. The delivery tickets
showing the quantity of stone and biofilter media that were delivered for the basin are also
included in Attachment D. They show 22.6 tons of VDOT #57 stone, 9.8 tons of VDOT #8 stone,
and 60.6 tons of RainScape Biofilter Media were delivered. This is consistent with the overall
amount of stone and bio-media anticipated for the basin.
The stormwater access and maintenance easement were obtained and recorded prior to
construction. The plat and deed documents have been included as Attachment E for reference.
Based on the above information, to the best of Draper Aden Associates knowledge, the installed
bioretention meets the design intent and the stormwater management requirements and
regulations.
Stormwater Management Facilities Certification
Pursuant to 9VAC25-870-55, I hereby certify that to the best of my knowledge and belief, the
stormwater management facilities shown on these record drawings have been constructed in
accordance with the approved plans and specifications.
E. Campbell Bolton, P.E.
Name
E "eo4
Signature
051495 February 8, 2022
Virginia License Date
"Certify" means to state or declare a professional opinion based on sufficient and appropriate
onsite inspections, material tests, as -built survey data, and information provided by other
professionals and the contractor, conducted during or after construction.
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