HomeMy WebLinkAboutRevisions - - 1450 Osgood Street -
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ME,
Storm Conveyance
Stormwater Revisions to the model and calculations to ensure compliance with federal,
All Networks and Features Management Report state, and local code have been made.
Revisions to watershed area to both features and individual structures
CG100 Series, PRWS,
All Networks based on below revisions.
DACB
Conveyance Network B-1
Network B-1 CG105, CG108 Slopes, pipe sixes and configuration revised based on increases bottom of
pond elevation due to groundwater conflicts.
Networks to ponds A1.2 and A1.5 Combined to one network. Minor
Network A-10 CG106 structure location shifts and elimination of OCS A1.5. Revisions based on
high groundwater and raise parking lot grades.
Network to pond A1.4. By owner request, convert three structures to
double CB to lessen flooding potential.Addition of structure along curb line
CG106 due to reversed cross slope direction on roadway. Minor layout
adjustments.
Network C-1 CG104 Added additional 24 inch outlet pipe to basin C-1 connection to C-2.
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Revisions due to high groundwater and the addition of the driveway
interconnection to lots A and B. Because of reduced volumes and
infiltration area, an underground system was required.
Subdivided into three Networks, D-1.1, D-1.2 and D-1.3.
Network D-1 CG103, CG505 Addition of Underground infiltration system D-1.3 with Isolation rows to
provide pretreatment. Regulated flow discharged to system D-1.2.
System D-1.2 (with flows from D-1.3) discharge to Infiltration basin D-1.2
with an increased bottom of pond elevation from 40 to 40.5. Regulated
Flows discharge to Extended Dry Detention Basin D-1.1
System.
Underground infiltration system details sheet added.
Changes driven by revised grading. Minor revisions including increased pipe
slopes, improved crossings, modified drainage areas. CB-6 and CB-1 minor
Network A-1 location shift.
CG 107
FES-2 extended to sediment forebay instead of swale daylight.
All Structures CG200 series All conveyances systems revised. Meeting all previous requirements, 25
year storm with tail water condition, HGL below grade within system.
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Grading and Earthwork
Grades along Lot A, north unsignalized entrance remain relatively the
same.Slopes pitching to the north decreased to raise grade along northern
parking lot extent.
Raise top of pond elevation to 46.5.
Split previous D-1 into two above ground features due to addition of
interconnection to driveways and high groundwater.
North Parking Lot A CG103
D-1.1, bottom of extended dry detention pond is 42.5
D-1.2, Raised the bottom of the infiltration pond from 40 to 41.5 to avoid
high groundwater and maintain 4 foot separation. Note that the scour pad
allows for a lower outlet invert of 40.5.All volume below elevation 41.5 is
not accounted for in the model.A tail water condition based on the 25
year storm in the basin with a bottom elevation was used to model the
HGL to ensure free flowing conditions.
Preliminary MassDOT revised lanes, curb line, site access and addition of
Osgood Street Frontage CG103, CG106 multi-use trail graded in.
Raised the bottom of pond from 38 to 39 to avoid high groundwater and
maintain 4 foot separation. Note that the scour pad allows for a lower
Infiltration Basin C-2 CG104
outlet invert of 38.All volume below elevation 39 is not accounted for in
the model.A tail water condition based on the 25 year storm in the basin
with a bottom elevation was used to model the HGL to ensure free flowing
conditions.
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Revisions due to encountered high groundwater.
South west parking lot grades raised roughly 5 to 6 feet. Max slope onsite
does not exceed 4.5
Southern Parking Lot A CG106 South east parking lot grades adjusted to accommodate southern Lot A and
Lot B driveway interconnect.
Previous Ponds A-1.2 and A-1.5 combined, bottom of pond at 48.2.
Minor chiller units shift, pad remains, at a minimum, a 1 to 1 zone of
influence from outer extent of drainage line to remain to the south.
Parking lot grades raised several feet throughout the area to eliminate the
need for a retaining wall between lot A and Lot B parking lots.This
maintained required plantings, avoids wall placement on storm pipes. Max
4.5%grades within parking area.
South eastern Parking CG107 Grades raised serval feet in the south eastern most extent of the Lot B
parking field, reducing wall height.
Addition of a retaining wall to accommodate the secondary emergency
access guard house.
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High groundwater encountered in area of extended dry detention basin B-
1.
Bottom of pond raised from 30 to 31.
South western Lot B CG108 Reduced retaining wall length by 500 ft. Graded at max 3 to 1 slope into
revised extended detention basin B-1.
Additional capacity added to revised B-1 by following existing flood line
and expanding southern width of pond.
Minor Compensatory flood adjustments made. (mentioned below)
Minor revision due to expansion of extended dry detention pond B-1.
Over compensation between elv. 29-30 reduced by 2,000 sf.
Compensatory Flood Storage CG802
Over compensation between elv. 30-31 reduced by 2,000 sf.
Area being reduced is out of flood zone under existing conditions today.
Proposed design still over compensates at these elevations.
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