Cover Letter 2-18-20
February 18, 2020
Douglas McDonald
Stormwater Manager
Department of Public Works
125 Locust Street
Northampton, MA 01060
Re: Colvest/Northampton, LLC
Commercial Redevelopment
301 & 303 King Street
Dear Mr. McDonald,
Looking through the plans it is apparent that some of the conditions of approval were addressed after
10/10/19 which you may not have received. After reviewing the Stormwater Permit and Special Permit
conditions again, I also realized I had misunderstood some of what you were looking for when I
prepared the last revision. As a result, I have revised the site plan set and drainage report again with
what I hope will be the final revision before start of construction. The revised plan set is dated
2/17/20. The Drainage Report was also updated with the same date 2/17/20. As I promised, the
following is an explanation of how each of the conditions of approval have been met by past and
present revisions:
Stormwater Permit Conditions
1. You should find enclosed a revised Attachment A for the stormwater agreement which excludes
the pervious pavement and added the infiltration trenches. The infiltration basin maintenance
now notes the 72 hour drawdown requirement. The attachment also includes provisions for
maintenance of the WQU at 301 King Street. This document is also included as an Appendix in
the revised stormwater report.
2. I am in the process of completing the NOI and SWPPP and will forward that to you as soon as it
is completed later this week.
3. The plans are revised and attached. We do not typically prepare written specifications for
Colvest projects because the plans and details are deemed sufficient for the contractors they
work with.
4. The drainage report was revised as follows:
a. The 4” underdrains in the rain gardens were raised 2’ above the water table elevation of
144 so that the bottom of the underdrain is at elevation 146. This change was made in
the 10/10/19 revision.
b. I misunderstood the request for underdrain calculations. I thought you were asking
about groundwater contribution to the system but you want to know how much water
Re: Colvest/Northampton, LLC
Commercial Redevelopment
301 & 303 King Street
Page 2 of 3
the underdrains will direct back into the system to be sure it does not exceed the
system capacity. The calculations have been modified to model the 4” underdrains as a
low level orifice. This is conservative since most flow will infiltrate and bypass the
underdrain. The peak flows were adjusted accordingly and we are still not increasing
peak flow rates. Rain Garden #9 was enlarged to account for this change in infiltration
but the basin is still contained within the existing island. No changes were required for
the other rain gardens. Rain Garden #9 now has a static volume which exceeds the
WQV not accounting for infiltration.
c. The Rain Garden detail on sheet 10 was updated to clarify that the underdrain will only
be a 30”x4” stone trench with perforated pipe, 10’ long in two directions. The previous
detail seemed to suggest the stone would extend the entire area of the basin which is
not necessary. The range of depth of the soil media is specified as is the range of
elevation difference between the bottom of the gardens and the top of the overflow
structures.
d. The VortSentry detail on sheet 11 was updated to specify that it is a 36” diameter
structure with typical dimensions noted. A copy of the sizing calculations was also
included in the revised drainage report.
5. Infiltration BMP’s must be stabilized before receiving runoff. This was not phrased as a required
plan change but is a condition of the approval.
6. Development cannot increase runoff or pollution. If it is found to increase these, the owner
must correct. This also was not phrased as a required plan change but is a condition of
approval.
Special Permit Conditions
1. Traffic revisions were provided as follows:
a. Signal plans provided by VHB
b. Tactile panel and ramp upgrade was incorporated on the plans by noting Mass DOT
ramp at both the NW and SW corners of the driveway on the 10/21/19 revision. A
detail added to sheet 11 on this current revision.
2. Cross access easements are address by separate easement map exhibits prepared by our office
and easement documents prepared by Colvest’s attorney.
3. Utility easements were likewise addressed
4. Bike share easement was likewise addressed
5. Sidewalk easement was likewise addressed
6. Water and sewer connections in accordance with DPW. This appears to be a condition not a
plan revision.
7. Unused line shall be removed to the main. Notes for the two water services are added to the
Demolition Plan Sheet 2.
8. Lane widths are all 11’ wide with a 2’ shoulder. This change was made on the 10/10/19 revision.
9. Granite curb is noted to be removed for the new accessible ramps on King St. This note was
added to the Layout Sheet in the 10/10/19 revision.
10. The ramp type along King Street was changed to a Mass DOT standard. This note was included
on the Layout Sheet in the 10/21/19 revision. I have since added the specific Mass DOT detail to
sheet 11.
Re: Colvest/Northampton, LLC
Commercial Redevelopment
301 & 303 King Street
Page 3 of 3
11. The details for the 301 curb cut were coordinated with staff and included on the 10/21/19
revisions.
12. The pipe in King Street was replaced with RCP on the 10/10/19 revision.
13. A note to remove buried slabs was added to the Demolition Plan in the 10/10/19 revision.
14. The concrete walk detail on sheet 9 was updated on 10/10/19 to note the required 8” thickness
and WWF at the driveway crossings.
15. The concrete walk detail was updated to depict the WWF graphically and bold the note on an
11/8/19 revision.
16. A granite curb detail was added to sheet 11 in an 11/8/19 revision.
I trust you will find all conditions addressed to your satisfaction. If you have any questions,
please contact my office at 860-623-0569.
Sincerely,
Dana Steele, P.E.
Principal Engineer
J.R. Russo & Associates, LLC