HomeMy WebLinkAbout1999-04-21 Engineer Review SPR � J
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February 25, 1999
C/o William Scott
Conservation Commission
Town Hall Annex
27 Charles Street
North Andover,MA 01$45
RE: Engineering Review
King Air Airplane Hangar
Notice of Intent
Dear Mr. Scott.
In response to your request, Coler& Colantonio, Inc. has reviewed the submittal package
for the above referenced site, Our efforts included a comparison of information submitted
with respect to the requirements of the Wetlands Protection Bylaw and Wetlands
Regulations. We visited the site on February 24, 1999 to observe existing site conditions.
We also compared the design assumptions and calculations with the Stormwater
Management Policy. The submittal package included the following information:
Plans Entitled
® "Airplane Hangar Pxoject Plans-Lawrence Municipal Airport", located in
North Andover, Mass."consisting of five sheets dated 2/9/99, Prepared by H-
Star Engineering Services. Received February 16, 1999.
o "Conservation Commission Issues" —dated February 9, 1999. Prepared by H-
Star Engineering Services. Received February 16, 1999.
o "Notice of Intent Filing including Hydrology Report", dated January 8, 1999,
and Prepared by If-Star Engineering Services. Received February 16, 1999.
We offer the following comments:
1. Section I11.)A,)4,)a.) The proposed water main extension is located in the 25'-no
distmbaa;ce zone, within the Umits of the existing roadway. It is unclear if the 2010 sf
restored in the buffer zone was wetland replication associated with a previous project.
101 Accord Park Drive 781-982-5400
Norwell, MA02061-1685 Fax, 781-982-5490
Section IV.)B.) State Storrnwater Standards:
Standard 1
Satisfactory subject to other coments,
Standard
The proposed detention basin should be modeled for 1 and 10 year storm events. The
entire system should be modeled for the 1-year storm event, approximately 2.6 'inches,
It is unclear why the entire post development flows from subcatchment areas 3,4,5 and 10
were routed through a the 530 foot reach. These flows do not all enter the reach at the
same point or peak at the same time interval. In addition the sub area plans do not include
contours which should be included to allow us to verify catchment area boundaries and
tithes of concentration. Catchment area plans should be at a specified and suitable scale.
Stand
Recharge calculations should be done.
Test pits performed by a licensed soil evaluator and witnessed by an agent of the town
should be done to demonstrate proper soil conditions for the assumed exftltratiozz from
the proposed basin.
The wetland report indicates a high water table and poorly drained soils. If these
conditions are verified by the soil evaluations, then it is not likely that the proposed
detention basins would properly drain. Note that the system includes a sump of 2.5-feet,
which has no outlet other than to infiltrate. We question the suitability of this system.
Standard 4
It was assumed that the proposed extended detention basin would have a.removal rate of
85%, however the DEP Stormwater Management removal limit for such a basin is only
70%. The two ponds are actually a detention basin with a forebay.
The overflow for the floor drain should not be directed into the proposed detention basin,
it should flow to an additional holding tank or a sanitary sewer line, We.recommend the
plumbing inspector review this aspect of the design.
Standard 5
The Water Quality Volume should be calculated and treated as required by the
regulations.
Standard 6
Not Applicable
Standard
Not applicable.
Sods 8 &9
These standards are typically reviewed by town staff,
Note that the haybales and silt fence should encompass the entire limit of work. Erosion
control is indicated through the building. The existing haybales and silt fence should be
replaced before construction.
Minimum Submittal Requirements!
2. Section IV.)B.)1.)b.jest. pits performed by a licensed soil evaluator were not
submitted. Existing and proposed flow paths were not indicated.
3. Section IV.)C.)l.) The existing and proposed 100-year floodplain elevation for the
wetland to the east of the site should be indicated. The ultimate discharge point of the
drainage ditch and wetland to the south of the site should be indicated one the.plans.
4. Section IV.)C.)2.) The 100-year flood elevations should also be dote for streams
crossing the site, The existing 12" RCP culvert to the south of the site, should be
modeled for the 100 year storm.
5. Section.IV.)C.)3.)Please refer to Stormwater Management comments,
6. Section 1V.)C.)5.)The lag method for the calculation of tirn,es of concentration is not
recommended. We have discussed the use of the lag method with the Natural
Resources Conservation Service. They developed the TR 55 and TR-20 models and
no longer recommends use of the lag method.
7. Section 1V.)C.)6,)d.) Test pits performed by a. licensed soil evaluator should be
included to determine the high groundwater separation from the bottom of the
proposed basin.
8. Section VI.)B.)4.)e.) The plans do not indicate existing septic systems, if any, on the
plans.
9. Section VI.)B.)4.)h.) Wetland flags across the access road and to the south of the site
are not indicated on the plans.
10. Section VI.)B.)4,)i.) The existing and proposed 100-year flood elevations should be
determined and indicated on the plans.
11. Section VI.)C.)4.)j.) Hydrologic calculations showing the full flow capacity and
velocity of all watercourses onto and out of the property should be submitted. The
existing 12" RCP culvert to the south of the site, should be modeled for the 100 year
storm.
12. Section VI,)B.)5.)a.)The limit of work is not clearly delineated.
13. Section VI.)C.)5.)b.) It is unclear where, if any, the subsurface sewage disposal
system will be located.
14. Section VI.)C.)5.)d,) The design and location of the proposed roof drain, system
should be submitted. Pipe calculations should be submitted,
General Comments:
15. The plans are very difficult to follow.
16. The proposed catch basin doesn't appear to capture much, if any, runoff, based on
spot grades and rim elevation.
17. The existing drainage ditch has not been analyzed or modeled under any conditions.
18. The drainage area maps are not at a noted scale and are difficult to follow.
19.It is unclear what is being modeled by the 60" pipe analyzed under the proposed
dummy reach,
We appreciate the opportunity to assist the Conservation Commission on this project and
hope that this information is sufficient for your needs, We would be pleased to meet with
the Board or the design engineer to discuss this project at your convenience. If you have
any questions please do not hesitate to contact us.
Very truly yours,
OLER&COLANTONIO, INC.
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J hn C, Chessia, P.E.
xe H-Star Engineering
Jim Rand