HomeMy WebLinkAboutUrology Associates SW Second Peer Review 2022-01-19 DCE Answers markup 2-17-22DCE is confident the selected Curve Numbers adequately model the drainage areas,
a 0.32 coefficient is appropriate for the lawn/landscape and wooded areas, which represent
all areas of the site not paved or roofed.
The coefficient is straight from the TR55 manual for Woods/grass comb.
with the soils and conditions appropriate for this area.
GREEN FONT: Responses by Daniel A. Ojala PE, PLS down cape
engineering, inc. dated 2-17-2022
Calculations are attached for 100 yr. storm.
The general sequence is per the SCPPESCP, exact timing is highly dependent on contractor selected and is TBD,
will supplement once contractor selected.
Concur review not required due to containment
of entire 100 yr. storm event onsite.
The site is already mostly developed, and means and methods TBD.
Provided.
This is acceptable, supplemental calculations provided.
Secondary deep sump hooded basins/manholes in an "offline" configuration
provide precisely the 44% TSS removal required, "offline" simply means they are not inline with any other drains
with new flow which would re-suspend the solids. See attached diagram.
I have concurrence of independent PE's on this point.
Note added.
Will be owner.
A dedicated deep sump manhole receiving only the same flow as the credited
catch basin is properly considered "off-line". In-line means flow from others too.
The second deep sump in series handles the exact same flow as the first, and is dedicated, so off-line. see sketch.
Agree with condition, buyer UACC will be owner soon, current owner should
not sign the documents.
1ST 100 x 0.75 = 0.75 , 2ND - 0.75 x .75 = 0.56 remaining = 44% TSS removal per worksheet. OK.
The primary and secondary off line deep sump hooded structures
provide precisely the required TSS removal prior to infiltration.
This is a simple site, the Site Plans reflect all BMP's and areas to access them.
The plan can/will be printed separately, the Site Plan set shows all BMP's and was included
as an attachment to the Stormwater Report.
Confirmed- owner will be responsible.
See provided TSS removal worksheet, first basin 25%, second 25% of remaining 75%.
Provided anyway.
The calculations indicate a conservative safe design and the design was approved by SPR. No changes needed.
The quarter acre per basin flow is attached, no grate accepts more than a quarter acre.
All areas under 1/4 acre, see attached chart.
100 year for the corrected area is attached, system infiltrates this design storm safely.
Was same size as DA1 but higher elevation, revised sheet attached. Infiltration rate utilized is
consistent with current local subdivision regulations. Rawls rate is too conservative for the
onsite materials. Much smaller drainage currently has been functioning at the site
for over 30 years. Field design so not significant storage, but large fields, so represents
a safe design meeting the stringent local requirements.
See attached rational method calculations which indicate safe design, support the HydroCAD analysis.
OK, see attached chart.
Cape sands percolate much faster than Rawls rate, see sand example
falling head test which was 152 in./hr for example. (divide by 2 =76 in/hr)
A Limit of Disturbance is shown on the Site Utilities Plan to supplement
the silt fences and regrading lines previously indicated.
The structures setback to the septic leaching field and foundation are
all adequate, graphically shown to scale.
Edited graphic for clarity.
Responses after each comment, see attached calculations/charts and amended
DA2 HydroCAD report.