CR 91-84 Ramsgate Apartments - Sanitary Sewer Improvements
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March 28, 1991 Council Report: 91-84
RAMSGATE APARTMENTS - SANITARY SEWER IMPROVEMENTS
ProDosed Action.
Staff recommends the following motion: Move that Council adopt
Resolution 91-42. Resolution Acceptinq Preliminary Report and Ordering
Sanitary Sewer Improvements at Ramsqate Apartments.
This action will continue a sanitary sewer improvement project at the
Ramsgate Apartment site. Plans and specifications will be developed
for Council approval.
Overview.
Recent development plans for a parcel east of the Ramsgate Apartments,
bounded by Hiawatha Avenue on the east and Cambridge Street on the
north, precipitated a closer examination of sanitary sewer main
capacity in Hiawatha Avenue. Preliminary findings showed sewer
backups and an undersized main in Hiawatha. Council at its March 5
meeting authorized a feasibility study to evaluate alternative
solutions to the problem.
primary Issues to Consider.
0 Should the Council accept the feasibility report?
0 What are the engineer's conclusions and recommendations?
0 What is the cost and how will the project be funded?
0 Should the project be ordered?
SUDDortinq Information.
0 Letter from RCM 3/5/91
0 Feasibility report
0 Resolution 91-42
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James Gessele
Engineering Superintendent
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CR: 91-84
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Analysis.
o Should the Council accept the feasibility report?
staff finds the report to be complete with all viable options explored
and recommends its acceptance.
o What are the engineer's conclusions and recommendations?
The engineer concludes that the existing sanitary sewer in Hiawatha
Avenue is inadequate in capacity and that either replacing the pipe or
rerouting a portion of the existing contributing flow would
significantly reduce the risk of backups into homes in the
neighborhood. A preferred solution to the problem would be to reroute
flow from the Ramsgate apartments to a new connection to the
interceptor sewer in Lake street Northeast. Such rerouting would best
be accomplished by placing a new sewer main from the apartment complex
through its parking lot southward to Lake' Street Northeast. Such a
plan would require necessary easements from the apartment owners and
necessitate some restoration costs.
The engineer finds replacement of sewer in Hiawatha Avenue and
replacement of pavement to be a cost prohibitive alternative.
o What is the cost and how will the project be funded?
The engineer's recommended alternative is estimated to cost $47,060.
Funding for the project is slated to come from sanitary sewer utility
funds. .
o Should the project be ordered?
In light of the city assuming considerable liability from sewer
backups in homes, staff recommends the project be ordered.
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. March 5, 1991
Mr. Jim Gessele, Engineering Supervisor
City of Hopkins
1010 First St. S.
Hopkins, MN 55343
RE: Ramsgate Townhouses
Letter #2
Storm Water Management, Sanitary Sewer
RCM Project No. 14000.08
Dear Mr. Gessele:
We have gathered more information since we sent our first letter, dated
February 25, 1991. We have met with: Ivan Nohner (Highland Villa
Builders), Duane Temple (Temple Associates), Nancy Anderson (City
Planning Department), and you.
~rnTI We have also reviewed the sanitary sewer capacity along Hiawatha Avenue in
addition to storm water concerns.
rieke Storm Water Management
t!rrOIl We do not believe that reduced low area and pond volume as proposed is
uller
ssociates, inc. acceptable since downstream residents would experience slightly increased
en~neers water levels. We recommend that the developer should increase the proposed
arc itects pond as described in our first letter.
land surveyors
equal opportunity The development, since its land area is very small compared to the drainage
employer area of Minnehaha Creek, will only have a small effect on the creek
elevation. During a 100-year flood event, the development should not
increase the creek elevation by more than one inch.
One house along Hiawatha Avenue appears to be lower than the 100-year
flood elevation. Another house reportedly is affected by the 100-year flood
in the creek.
...
Sanitary Sewer
We also reviewed concerns about sanitary sewer backups along Hiawatha
Avenue. The sewer accepts wastewater from Ramsgate Apartments, Creek
Point Apartments, Hiawatha Court Apartments, 13 houses, and Lift Station
#3. It discharges into a lift station owned by the Metropolitan Waste Control
Commission (MWCC). The proposed townhouses would also contribute
wastewater to this sanitary sewer.
The City Water and Sewer Utility Master Plan, prepared by RCM, noted a
"problem area" on this sewer downstream of the area of concern. However, no
sanitary sewer backup complaints were on file with the City from this area.
Water use estimations show that flow to the sewer during a maximum day
demand may exceed the capacity of the sewer by about 30 percent.
Infiltration, inflows, lift station #3 operation, and MWCC lift station
10901 red circle drive
box 130
minnetonka, minnesota 55343
612-935-6901
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i Mr. Jim Gessele
March 5, 1991
Page 2
operation may cause further 'sanitary sewer backups. Based on these
calcula tions, the existing sanitary sewer, with existing development, is
undersized. Any increased flow from new development would increase the
probability for sewer backups. The proposed Ramsgate Townhouses would
increase flows by about 3 percent.
Feasibility Study - Sanitary Sewer
Several alternatives could be implemented to control sanitary sewer backups
along Hiawatha Avenue. We propose the following feasibility study scope of
services to evaluate the alternatives.
The first part of the study will collect data necessary for the evaluations.
Basement elevations will be measured, and water level records in the MWCC
lift station will be obtained and reviewed. We would like the City to conduct
a survey of each home along the A ven ue. RCM will discuss topics of this
survey with City staff.
Alternative sanitary sewer modifications will be evaluated, considering cost,
land availability, and effectiveness. We will summarize our findings in a
report to the City, and recommend an alternative that appears most feasible
for construction.
. We will invoice the City for the feasibility study at our normal hourly rates
for the personnel working on the project up. to a maximum of $4,500.
Summary
Under existing conditions, some of the homes along Hiawatha Avenue are
subject to water damage due to backups from the sanitary sewer or due to
flooding in Minnehaha Creek. Any development along Hiawatha Avenue
could increase the probability of water damage from both sources. We
recommend that a feasibility study be conducted to identify sanitary sewer
capacity solutions prior to additional development, and that new development
in the area include recommended storm water management measures to
minimize downstream surface flooding.
Please call us with any Questions.
Sincerely,
~~L MULLER ASSOCIAT111i ~
Dale Folen, P.E. Peter J. Carlson, P.E.
Project Engineer Project Manager
DAF/jj
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FROM ReM MTKR.MH 3.27.1991 15:54 P. 2
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FEASIBILITY REPORT
SANIT ARY SEWER SERVICE
FOR
RAMSGATE TOWNHOUSES
HOPKINS, MINNESOTA
ReM PROJECT NO. 10112.03
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FROM RCt1 MTKi=!. MN 3.27.1991 15=54 P. 3
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March 22, 1991
Mr. Jim Gessele
City of Hopkins
1010 lst Street South
Hopkins, MN 55343
l RE: Feasibility Report for Providing
~DTIJ Sanitary Sewer Service to
Ramsgate Townhouses
Hopkins, Minnesota
ReM Project No. 10112.03
carroll Dear Jim:
muller'
associates, Inc. This report presents our findings, recommendations and a preliminary cost
en~neers
arc itects estimate for providing sanitary sewer service for the proposed Ramsgate
land surveyors Townhouses.
equal opportunity If you should have any questions regarding this report or require any further
employer
data, please call me at any time.
Sincerely,
Peter J. Carlson, P.E.
RIEKE CARROLL MULLER ASSOCIATES, INC.
PJC/jj
10901 red circle drive
box 130
minnetonka, minnesota 55343
612-935-6901
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FROM ReM MTKR. Mt~ 3.27.1991 15:55 P. 4
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. , ReM 10112.03
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INTRODUCTION
This feasibility report has been prepared and is submitted to the City of Hopkins in
accordance with our proposal of March 5, 1991. By this proposal we were to provide an
analysis of the sanitary sewer system in Hiawatha Avenue, and make recommendations for
modifications to the existing system to anow service to the proposed Ramsgate Townhouses.
A proposal has been brought forth for the construction of 12 townhomes on a parcel of land
lying in the southwest quadrant of the intersection of Hiawatha Avenue and Cambridge
Street. Currently, the average day sanitary sewer flows in the sanitary sewer that would
serve this site are approximately 88% of the capacity of the system and the introduction of
additional flows from the 12 townhouses would raise the percentage to 90%. Of a greater
concern, however, are the peak hour flows. Current peak hour flows are approximately 2.3
times the capacity of the existing system. With the additional 12 units, this factor would
approach 2.4 times.
While there do not appear to be any significant problems in the system during times of
normal operation, this does appear to change at times of significant rainfalls (in excess of 1-
1/2 - 2 inches). There have been reports from owners of some of the lower properties in 'the
area, that during periods of appreciable rainfall serious backups ha~e occurred in the
sanitary sewer system which have resulted in basement damage to several of these low
residences. Due to the concerns of these residents, the City has chosen to review the inplace
system. The results of the review are presented in this report.
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FROM P.Ct1 tHKfl. MH 3.27.1991 15:56 P. 5
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ReM 10112.03
DESIGN
Improvement in the level of service of the sanitary sewer system in Hiawatha Avenue can
be accomplished with several solutions. Upon review it was determined that two (2)
potential solutions would be pursued as being the best alternatives. The first solution would
involve removing all of the current sanitary sewer flow from the Ramsgate Apartments
from the Hiawatha Avenue system. This would require 200 lineal feet of existing g-inch
sanitary sewer be relaid, an existing manhole be rebuilt and would require the installation
of 460 lineal feet of new 8-inch sanitary plus two additional manholes (see Figure 2). The
new segment of 8-inch sanitary sewer would connect to the existing 33-inch interceptor
sewer located in front of the Ramsgate Apartments in Lake Street N.E.' With the
installation of this system, 88 gpm on an average day basis and 353 gpm on a peak hour
basis would be eliminated from the Hiawatha Avenue system. These flows amount to 35%
of the flow on an average da y basis and 55% of the flow on a peak hour basis. With the
elimination of these flow,S from the Hiawatha Avenue system, the flow rates in the last two
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. segments of the system in Hiawatha Avenue, which are the flattest and most critical. would
reach a level compatible with the capacity of the system.
ExistinR S-inch yep Sanitarv Sewer at 0.30~
Capacity existing: 276 gpm
Existing flow; average day basis: 244 gpm
Post development flow; average day basis: 248 gpm
Existing flow; peak hour basis 638 gpm
Post development flow; peak hour basis 654 gpm
Should the Ramsgate Apartments be eliminated from the system, flow rates would be as
follows:
Capacity existing: 276 gpm
Existing flow; average day basis: 156 gpm
Post development flow; average day basis: 160 gpm
Existing flow; peak hour basis 285 gpm
. Post development flow; peak hour basis 30 I gpm
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FROI'1 RCt1IHKA.t1N 3.;:7.1991 15:57 P. 6
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RCM 10112.03 I
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With the elimination of the Ramsgate Apartment flows from the Hiawatha Avenue systemt
it can be seen that the opportunity for further incidents of backups would be greatly
reduced.
The second alternate would require the rebuilding of the Hiawatha Avenue system from its
beginning at Blake Road upstream to the drop manhole where the connection from the
Ramsgate Apartments is made (see Figure 3). This would require the replacement of 1455
lineal feet oC 8-inch clay sewer pipe with 850 feet of 8-inch PVC and 605 feet of to-inch
PVC sewer pipe as well as the replacement of approximately 1500 lineal feet of Hiawatha
Avenue pavement.
Caoacity Analvsis
Existing 605 LF sit VCP @ 0.30% Capacity 276 gpm
Proposed 605 LF 101t PVC @ 0.30% Capacity 700 gpm
Post Development Average Day Flow 248 gpm
Post Development Peak Hour Flow 654 gpm
Existing 850 LF 81t VCP @ 0.60% Capacity 390 gpm
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Proposed 850 LF 81t PVC @ 0.60% Capacity 546 gpm
Post Development Average Day Flow 209 gpm
Post Development Peak Hour Flow 498 gpm
By replacing the existing 8-inch clay sewer pipe with 8- and lO-inch PVCt the flow
characteristics will be greatly enhanced and the opportunity for backups in the sanitary
sewer system will be minimized.
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FROt'1 ReM MH:A.MN 3.27.1991 15:57 P. 7
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CONCLUSIONS AND RECOMMENDATIONS
1. The existing sanitary sewer. in particular the downstream 60S LF prior to its
connection at Blake Road. appears inadequate to handle both current and post-
development sewage flows.
2. Increased capacity by either replacing existing piping with new more efficient
piping or by rerouting a portion of the existing flow should significantly reduce the
risk of backups into the lower lying homes in the vicinity.
3. Disruption of service and cost of maintaining service to all residents would be
minimal with the rerouting of the flow from Ramsgate Apartments to a new
connection to the 33-inch interceptor sewer in Lake Street Northeast.
4. Total cost for replacement of sanitary sewer in Hiawatha Avenue and replacing the
street pavement. appears to be prohibitive in comparison to the cost of rerouting
flow from Ramsgate Apartments.
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FROM ReM tHKR. MN 3.27.19?1 15:58 P. 8
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COST ESTIMATE
This cost estimate is based upon a review and capacity analysis of the Hiawatha Avenue
_ sewer system and our recommended method of relieving pressure on the inplace system. By
rerouting the flows from the Ramsgate Apartments to the 33-inch interceptor sewer located
in Lake Street Northeast, it is anticipated that both the construction costs and the amount
of-disruption will be significantly less. Utility easement costs are not included in the cost
estimates below.
Reroutinsz Solution
Unit Unit
l1ul Ouantitv ~ :Iaal
1. 8" SDR 35 PVC Sewer Pipe 660 LF 18.00 $11.880.00
2. 4' Dia. Standard Manhole 3 EA 1,100.00 3,300.00
3. 8" Outside Drop 7.1 LF 125.00 887.50
4. Connect to Existing 33" Interceptor 1 LS 1,000.00 2,000.00
5. Bituminous Pavement 840 SY 8.00 6.720.00
6. Class S Aggregate Base for Pavement 280 TON 10.00 2.800.00
7. Replace Existing Curb 160 LF 7.00 1.120.00
8. Restoration (Sodding) 1650 S Y 2.25 3,712.50
9. Dewatering 1 LS 2,000.00 ' 2.000.00
10. Foundation Material 100 Ton 10.00 1.000.00
Subtotal 535,420.00
Contingency 3.J40.00
Subtotal 538.560.00
Engineering and Administrative 8.S00.00
TOTAL $47,060.00
ReDlacement Solution
Unit Unit
1.Wn Quantitv fcitt IsWU.
1. 8" SDR 3S pye Sewer Pipe 850 LF 18.00 $15.300.00
2. 10" SDR 35 PVC Sewer Pipe 60S LF 22.00 13,310.00
3. 4' Dia. Standard Manholes 4EA 1.100.00 4,400.00
4. Connect to Existing Manhole 2 EA 300.00 600.00
S. Service Wyes 17 EA 40.00 680.00
6. Service Pipe 425 LF 10.00 4,250.00
7. Bituminous Pavement 3850 SY 5.00 19.250.00
8. Class 5 Aggregate Base for Pavement 1270 TON 10.00 12,700.00
9. Restoration (Sodding) 2000 SY 2.25 4.500.QQ
Subtotal $74,990.00
Contingency 11.110.00
Subtotal $86,100.00
Engineering and Administrative 20.000.00
TOTAL $106,100.00
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. CITY OF HOPKINS
Hennepin County, Minnesota
RESOLUTION NO: 91-42
RESOLUTION ACCEPTING PRELIMINARY REPORT AND
ORDERING SANITARY SEWER IMPROVEMENTS AT RAMSGATE APARTMENTS
WHEREAS, a preliminary report has been prepared with respect to
the improvement of sanitary sewer main at the Ramsgate
Apartment site, and
WHEREAS, the engineer has advised this council that the
aforesaid improvement is feasible and should best be
made as proposed at an estimated cost of $47,060.00,
and ,
WHEREAS, the City Council deems it necessary and expedient that
the City of Hopkins construct the aforesaid improvement
in accordance with the report;
NOW THEREFORE BE IT RESOLVED BY THE CITY COUNCIL OF HOPKINS,
MINNESOTA:
1. Such preliminary report is hereby approved
and ordered placed on file in the office of
the city clerk.
2. Rieke Carroll Muller Associates, Inc. is
hereby designated as the engineer for this
improvement and shall prepare plans and
specifications for the making of such
improvement.
Adopted this 2nd day of April, 1991.
Nelson W. Berg, Mayor
ATTEST:
James A. Genellie, city Clerk
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