2. StormwaterCity of Kalispell Public Works Department
Past Office Box 1997, Kalispell, Montana 59903-1997 - Telephone (406)?58-7i20, Fax (4�fs1i53-7831
James H. Patrick, City Manager
FROM: James C. Hansz, *E. Director of Public Works City Engi
SUBJECT: Storm Water Problems
DATE: 1 2006
At the request of the City Council, PWD staff has prepared the attached report
concerning the Sunnys de Subdivision and Leasure Heights Subdivision. The Following
additional information may also be helpful.
Both subdivisions, and most subdivisions currently under construction, were approved
several years ago. The City standards in place when these subdivisions were reviewed were the
old standards that lacked. the improving changes made with the revisions approved in June 2005.
Current standards would, in most cases, prevent the placement of a drainage retention
pond in a location. such as at Leisure Heights. Our current standards require placement at least
200 Feet from any place where children can congregate. I . addition, and as noted in the staff
report, we are currently requiring engineers to provide documentary tar evidence that proposed
infiltration structures are located on soils suitable for the purpose. However, it is -unlikely that
even this approach, had it been a requirement i. 2004 when Sunnyide was designed, would
have prevented problems resulting from rising ground water. As noted in the staff report, during
construction in 2004 no excess ground water was observed. This was most likely the result of
drought conditions which have since been relieved.
When this set of problems became evident staff began working with individual
homeowners to help them deal with their individual ground -water problems. We have identified
reasonable solution for the Sunn side problem. The design engineer has been directed to
implement a solution without further delay. If this is not done, PWD is planing to install our
solution and bill the engineer For the time and materials. We believe this can be done fairly
quickly. We have only one utility conflict to remedy so that construction can be done.
Leisure Heights presents a somewhat more difficult problem. We believe the engmeer
has identified a reasonable solution. He is working with the State to implement the solution as
soon as possible. However, the State has control over the roadside drainage that .s important t
this solution.. We have very little leverage to accelerate the resolution ofthis matter.
However, we are confident this can be resolved satisfactorily because both developments
are still under bond and covered by the construction warranty.
Please pass this on to the City Council for their information so they are able to ra..se other
questions for us to answer during the work session this Monday.
CITY OF
KALISPELL
Memo
Jiro Hansz, Public Works Director/City Engineer
From: Frank Castles, Assistant City Engineer
Date: April 14, 2006
Re: St rmwater Report for Sunnyside Subdivision and Leisure Heights
Subdivision
Background
The construction plans, specifications, and engineering report for every
subdivision constructed in the City rust be approved by the Public Works
Department prior to construction. As part of the review process, the
engineering report is examined to ensure that the design of the storm water
system conforms to City Standards and follows ordinary engineering
standards of care. Strrrwater detention/retention systems are designed for
a 1 -gear 6-Hour storm event. This is a commonly accepted design storm
gent.
S nnyside Subdivision
Sunnyside Subdivision was constructed with a storm water system that
included infiltration trenches located north of the intersection of Santa Fe
Street and Boise Avenue. These trenches were to percolate the excess
surface storm water (the difference between pre -development runoff a n d
post -development runoff) from an area north of Santa Fe Street along Ashley
Drive to Sunnyside Drive. The engineering report stated that the infiltration
trenches veld percolate the water into the surrounding soil. An
examination of the N CS soils raps and accompanying data indicates that
the infiltration trenches would be located in well drained soils with a
moderately high transmissibility index (9 mm per second — 21 inches per
minute).
Ashley Drive was constructed during the Summer of 2004. Construction of
the water and sever utility trenches was observed and little moisture was
observed at that time. By May of 2005, the backfill in the utility trenches in
Ashley Drive north of Santa Fe had failed to such an extent that the street
paving section was rebuilt. During the reconstruction of the street the utility
trenches contained free water in the trenches. The Water Department
determined that this was not a leaking water main, but groundwater.
In September, the engineer was notified that the infiltration trenches installed
for sunnyside, Phase 2, were not performing as designed and that remedial
action was expected. Due to the potential for the shutdown of asphalt plants
the following month, the decision was made to delay the installation of piping
from the infiltration trenches east along Santa Fe to a road ditch along
Denver. Santa Fe would have been torn up and not repaved until the start
up of asphalt plants this spring.
The infiltration trenches designed for Sunnyside, Phase 2, contain a gross
volume of 5,900 cubic feet. The perception of the residents along Santa Fe
is that the infiltration trenches are the sole reason for high groundwater
problems in that area. The lets fronting on Santa Fe cover an area of
approximately 109,000 square feet (2.51 acres). Water tends to seek its
own level over a broad area. 5,900 cubic feet of water spread out over an
area of 109,000 square feet increases the elevation of the eater by 5/8 on
April 13, a vacuum excavation was performed at the intersection of Santa Fe
and Boise to locate an underground utility. Upon excavation, a large volume
of water was observed entering the pit immediately under the pavement from
the east. This water stabilized at an elevation at the pavement/subbase
interface* The infiltration trenches are approximately twenty feet vest and
forty feet north of the excavation. It is interesting to note that there has not
been any significant rainfall in that area in over a week.
Notice has been provided to the developer and engineer that the City is
expecting construction to begin on the installation of the pipe network within
two creeks. A meeting will be scheduled this week with the developer and
engineer to initiate the construction. As construction proceeds on the pipe,
storm surer taps will be provided for the homeowners to install sump pump
discharges from their basements and crawl spaces. As groundwater is
encountered in the trench, perforated pipe will be installed to relieve
groundwater. The engineer and/or developer will be installing the pipe,
manholes, and repaving at no oast to the City. The City will be paying for the
storm suer taps and perforated pipe.
Page
Leisure Heights subdivision
Leisure Heights subdivision was designed with a storm grater detention pond
located at the southwest corner of the development adjacent to Willow Glen
Drive. This pond was designed to contain the excess runoff from the
subdivision. An examination of the N CS soils maps and accompanying
data indicates that the detention pond would be located in well drained soil
with moderately high transmissibility index mm per second s 21 inches per
minute).
n June, 2005, during a heavy rain event, it became evident that the
detention pond was not performing as designed} rainfall for June, 2005,
exceeded the thirty-year average by over 200%. Water was standing in the
rear yard of the adjacent property owner, Ms Judy Ferry. The engineer was
immediately notified of the detention pond failure. since that time, during
every rain event, water stands in Ms rr's back yard. Pumping of the pond
is performed by the contractor to provide temporary relief during storm
events.
The engineer is proposing to install berms along the north and west property
line of Ms Judy Perry)s lot (Lot No. 11 , The Willows, Unit No. , and to
slightly re -grade part of the existing road ditch along Willow Glen to allow the
pre -development storm grater to flow to the east entrance to the Willows at
Kelly road. The storm water would then utilize the existing storm water
system in the willows to direct the runoff to the existing detention basin along
the south edge of the Willows.
The Montana Department of Transportation is responsible for Willow Glen
Drive. The engineer has submitted a request to MDT to re -grade the road
ditch and install berms to direct the pre -development storm grater to the Kelly
Road entrance to the Willows. Steve Herzog, Kalispell Area Maintenance
Engineer for Montana Departrnnt of Transportation, was contacted on April
6. He indicated that the permission to perform the grading and berm
construction wouId be issued with conditions early in the week of April 10.
This correspondence has not been received. A request from the engineer to
MDT was submitted on January 23, and a similar request was submitted
from the Public Works Department to MDT on February 24. No construction
work was considered during the printer months due to the frozen ground.
PWD Operational Changes
As a result of the infiltration trench and detention pond failures to perform as
designed, the Pubic Works Department is now requiring designers to
perform on -site percolation tests to determine actual percolation rates for the
soil conditions existing on site.
Page 3
t is unknown at this time how to address the high groundwater conditions.
The elevation of groundwater is directly influenced by the rainfall on an area.
This area of Montana has been under a drought condition for the past fear
years. June} 25 rainfall exceeded the thirty year average by
approximately 200%, September, 2005 rainfall exceeded the thirty year
average by approximately 10 %, and January, 2005 rainfall exceeded the
thirty year average by approximately 0%.
With this in mind, it may be prudent to consider some type of restriction o
basement construction that limits basements to areas where historical
ground water elevations are well known to be below the proposed basement
floor level. Alternatively, basements could be prohibited in certain areas,
such as those currently known to have problems. This could require the
development and maintenance of a significant database f factual data t
support the prohibition.
Fags