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<br /> ProJect Name: Navarre Kingdom Hall Client: City of Orono
<br /> To: Tom Kellogg File No: 139-05=000
<br /> From: Earth Evans Date: 5.5.05
<br /> Re: Stormwater Review
<br /> Development: Navarre Kingdom Hall
<br /> Engineer: Pioneer Development . ,
<br /> Submittal: Dra'vnage Calculations,Drainage and Grading Plans,Wetland Delineation Report
<br /> Date of Plans: 4.18.05
<br /> Summary of Recommendations .
<br /> Based on the stormwater review of Navarre Kingdom Hall,we offer the following comments. Details for each
<br /> recommendation follow.
<br /> 1. Off-site drainage should be included in calculations and shown on plans.
<br /> 2. Adequate water quality treatment has been provided.
<br /> 3. Proposed discharge rates are slightly higher then pre-development rates for the 1, 10 and 100-year evens.,
<br /> Off-site Drainase .
<br /> Based on USGS mapping it appears that the entire site eventually outlets via the 12"culvert under Togo Road to a l�zrge
<br /> existing wetland. All off-site drainage rnust be included in the calculations and plan.set in order to ensure that the pond
<br /> and low point south of Togo Road function as designed for water quality and quantity purposes. Off-site drainage to the
<br /> low point was included in the developer's engineers HydroCad modeling,but not for the south pond and adjacent wetland.
<br /> The low point storage shown on the plan doesn't correspond with the Hydrocad modeling. This should be confirmed
<br /> considering its proximity to the entry drive.
<br /> Water Ouantitv and Ouality
<br /> The�majority of the impervious on-site is routed south to the proposed pond. Adequate wet volume has been provided in
<br /> the pond to treat the 2.5-inch event. We recommend routing the entirety of the proposed building south to the pond via
<br /> roof drains since no water quality treatment is provided in the low spot south of Togo.
<br /> We recommend providing a 10-foot aquatic bench at 10:1 below the NWL of the proposed pond.
<br /> Since there is minimal proposed impervious for the north side of the site, no exisring and proposed discharge comparison
<br /> was made. The priinary change from pre-development condition discharge rates is due to the additional impervious on the
<br /> south side of the site. The following table lists lhe existing and proposed discharge rates from the south side of the site.
<br /> Scenario 2-year Discharge 10-year Discharge 100-year Discharge
<br /> cfs cfs cfs
<br /> Existin 0.1 1.7 4.2
<br /> Pro osed 0.4 2.5 5.3
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