HomeMy WebLinkAboutItem 5.16- j
TOWN OF LOS ALTOS HILLS June 28, 2007
Staff Report to the Planning Commission
SUBJECT: DISCUSSION TO CONSIDER AMENDING THE DEVELOPMENT AREA
POLICY
FROM: Nicole Horvitz, Assistant Planner ��
APPROVED BY: Debbie Pedro, AICP, Planning Director -D?
RECOMMENDATION That the Planning Commission:
Review and discuss the Development Area Policy with regard to credit for the use of semi
permeable materials and direct staff to prepare text amendments to the policy as determined to be
necessary.
At their May 24, 2007 meeting, the City Council directed staff to research and prepare proposed
amendments to the Town's Development Area Policy to allow additional development area for
constrained properties with maximurn development area (MDA) of 7,500 sq. ft. or less. The
Council suggested that semi-pemeable materials used in landscape or hardscape improvements
could receive partial credit for development area coverage because it will not result in an
increase of runoff from the property. (Attachment 2)
Staff is seeking Planning comments and additional suggestions on revisions to the Development
Area Policy to allow credit for certain surface materials.
DISCUSSION
The Town's Development Area Policy provides guidelines that limit development area on a
property in order to protect the natural features and rural character of the Town and minimize ran
off and erosion related to construction on slopes. The current policy (Attachment 1) does not
give credit for the use of semi-penmeable materials on my of the following:
• Tennis or sports courts
• Driveways
• Required parking areas
• Turnarounds
• Above ground decks
Planning Courommion
Development Area Policy Amendment
June 28, 2007
Page 2 of 5
Given the advancements in technology, building techniques, and building materials on sloped
lots, it is recommended that the Planning Condunission review and consider allowing a
development area credit for certain semi -permeable materials.
Artificial Turf
The appearance of artificial turf has continued to improve and many manufacturers have
products that look like real grass. According to manufacturer Back Nine Greens, maintenance to
the artificial turf is minimal. An occasional brooming is recommended but not necessary. This
will stand the fibers up and even out the infill materials. Debris like leaves and twigs can be
easily removed with a leaf blower.
The long term effect of the sun does not baron the wificial turf lawnscape or make it fade. The
fibers have a UV protection coating and can withstand the damaging affects of sum, heat, wind,
snow, and ice. The drainage in the turf is very similar to natural grass. The turf backing has
many perforated holes allowing for water to drain vertically. (Source; Back Nine Greens,
Attachment 3)
Because of the natural appearance and permeability of artificial turf, staff recommends a 90%
credit for this material. The artificial turf should be installed in the rear or side yard of the
property to minimize its visibility to neighboring properties and may encroach within the
property line setbacks.
Grasserete Pavers
Grasscrete is a cast -in-place, monolithic, pervious concrete pavement that is continuously
reinforced to provide superior structural integrity. After the concrete is sufficiently hardened, the
voids are filled with topsoil and grass providing a free draining "pavement" with the structural
capacity to handle most heavy vehicle loads.
Planning Commission
Development Area Policy Amendment
June 28, 2007
Page 3 of 5
Grasscrete can be an excellent alternative to plain concrete surfaces for puking lots, driveways,
and access roads for vehicles or fire trucks. Grasscrete can also be used for erosion control.
Grasscrete drains at about the same rate as would an ordinary lawn in the same location. The
presence of concrete has little effect on the drainage; the soil and the slope are the controlling
factors.
The surface area of Grasscrete is 47% concrete and 53% open (to be filled with Grass). Grass
usually covers much of the concrete in areas not subject to regular vehicle traffic. Holes may be
filled and covered with crushed stone, seashells, etc. to provide drainage in cases where grass is
not desired. (Source; Concrete Network, Attachment 4)
Staff recommends a 50% credit for grasscrete. Because it is an artificially emplaced building
material, grasscrele should be installed outside property line setbacks except for fire truck
turnarounds and driveway backup areas.
Permeable Concrete
Permeable concrete is a special structural concrete with the fine particles removed. This creates
15 to 20 percent voids so the concrete looks like a giant rice cake. The pavement will support
traffic and allow water to pass through to a gravel layer underneath. The strength of pervious
concrete is about 85 percent of conventional concrete, making it suitable for sidewalks,
driveways, alleys, puking lots and residential streets.
Permeable concrete is much more porous than underlying soils. Typical infiltration rates are 250
to 300 inches per hour; typical installations require soils with percolation rates of more than 1/2 -
inch per hour. A gravel bed placed underneath the concrete stores water before it moves into the
soil or can provide a channel for movement of water to stonat water channels. A 4 -inch bed of
rock or aggregate 3/4 inches or larger with 30 percent voids will store 1.2 inches of water. In
addition to its water quantity benefits, pervious paving can remove some pollutants through
absorption, straining and microbial decomposition. (Source; Puget Sound Online, Attachment 5)
Plinning Commission
Development Area Policy Amendment
Jum, 28, 2007
Pope 4 of 5
Staff recommends a 50% development area credit for permeable concrete. Although permeable
concrete has some benefits for drainage and water run-offs, due to its appearance as a solid,
hardscape surface, the permeable concrete should qualify for development area credit only when
used for required fire truck turnaround, puking, and driveway.
Permeable Pavers
Permeable pavers replicate natural stomi water infiltration, provide treatment and eliminate the
need for conventional detention/ treatment systems. It is an alternative paving materials that can
be used to locally infiltrate rainwater and reduce the mnoff leaving a site.
The use of these materials can also eliminate problems with standing water, provide for
groundwater recharge, control erosion of streambeds and riverbanks, facilitate pollutant removal,
and provide for a more aesthetically pleasing site. The effective imperviousness of my given
project is reduced while land use is maximized. Alternative pavers can even eliminate the
requirement for underground sewer pipes and conventional storm water retention / detention
systems. The drainage of paved areas and traffic surfaces by means of permeable systems is an
important building block within an overall low impact development scheme that seeks to achieve
a storim water management system close to natural conditions. (Source; Low Impact
Development Center, Inc, Attachment 6)
Staff recommends a 10% credit for permeable pavers. Permeable pavers must be installed
outside the required setbacks except for fire truck turnarounds and driveway backup areas.
Planning Commission
Development Area Polic) Amendment
June 28, 2007
Page 5 of 5
CEQA STATUS
The project is categorically exempt under Section 15306 of the State CEQA Guidelines
ATTACHMENTS
I . Development Area Policy
2. Minutes From the May 24, 2007 City Council Meeting
3. Artificial Turf- Back Nine Greens, www.backninegreens.com
4. Grasscrete Pavers -Concrete Network, �.concretenetwork.com[bom�ite/preen.htm
5. Permeable Concrete- Puget Sound Online, www.psat.wa.go
6. Permeable Pavers- Low Impact Development Center, Inc, www.lid-stormwater.net
LOSALTOS HILLS
WAWIOW^�
CALIFORNIA
ATTACHMENT j
Policy Re: Development Area and Tennis/Sports Courts, Driveways, and
Pervious Surfaces
Code Sections:
Section 10-1.502(b) of the Zoning Code defines "development area7 to include
floor area as well as other coverage, including parking areas, patios, decks,
walkways, swimming pools, and tennis courts, and other surfaces comprised of
artificially emplaced building materials (paving, roofing, masonry, stone or wood).
Intent:
The purposes of limiting development area on a site are twofold: 1) to protect the
natural features and rural character of the Town; and 2) to minimize runoff and
erosion concerns related to construction on slopes. The City Council finds that
tennis/sports courts, driveways and parking areas appear as development
regardless of the surface used, and generally require considerable land alteration to
be accommodated on a site.
Policy:
No development credit will be granted for the use of semi -permeable
material(s) on any of the following:
a. Tennis or sports courts
b. Driveways
C. Required parking areas
d. Turnarounds
e. Above -ground decks
2. In other development areas, partial credit for the use of semi -permeable
material(s) may be granted depending on the permeability and appearance of
the surface. Make an appointment with the Planning Department, at (650)
941-7222, to discuss material selections with a Planner.
26379 Fremont Road
Los Altos Hills
California 94022
6 5 0 / 9 4 1 - 7 2 2 2
Fax 650/941-3160
Approved by City Council June 21,1995
ATTACHMENT 2
1117 Develop Comprehensive Plan for Expanded Recreational Facility Access and Begin
Implementation of Acquisitions—Report of the Ad Hoc Committee on Recreational
Facilities (To be Distributed at the Meeting) (Mayor Pro -Tem Jones)
Mayor Pro Tern Jones reported that the Ad Hoc committee had met prior to the Council
meeting (May 24, 2007) and were currently reviewing the alternatives for recreation.
Jones surnmarized the featured article in the June Newsletter that had outlined the
Committee's activities. They included: 1) review of current recreation facilities; 2)
responsiveness to recreation survey that showed a strong interest in a community park
and possibly a sports field; and, 3) investigation of partnerships with private clubs and/or
possible joint ventures for recreation opportunities.
Jones reported that there were a series of projects at the Little League fields that were
being assessed that could potentially enhance safety and improve the drainage problems
at the site. This should reflect in a reduction of maintenance costs. To appropriately
evaluate the drainage problems and move forward on any additional projects at the fields,
the City Manager had authorized a topographical survey of the site at a cost of $8,000.
Jones advised that the Committee would be developing a priority list of projects and
budgets. The needs of the Westwind Bana Committee would be integrated into the
overall recreation "master plan" with a projected multi-year capital improvement budget.
COUNCIL MEETING RECESSED: 9:40 P.M.
COUNCIL RECONVENED TO OPEN SESSION: 10:00 P.M.
12. 2007 Community Survey on Site Development and Zoning Standards
Planning Director Debbie Pedro introduced this item to Council. The City Council at
their February 8, 2007 meeting authorized the Town to conduct a community survey to
gauge resident opinions on current site development and zoning standards. Godbe
Research, a professional survey firm, was hired to conduct the telephone survey in April
2007. The survey consisted of sixteen questions with several culled from the 2001 mail -
in Community Survey.
Pedro proceeded with a PowerPoint Presentation that included: a comparison of
responses of 2001 and 2007 survey on questions regarding allowable maximum
development area and maximum floor area (MDA/MFA); estate homes; development
review process; and, open space easements. The presentation also included a list of
Planning Commission Comments and Recommendations from their May 3, 2007 review
of the survey findings.
Pedro noted that one of the key findings from the telephone survey was that the majority
of residents polled were satisfied with the development regulations and believed that the
status quo should be maintained. In comparing the results of the two surveys, there did
not appear to be my major shift in opinion, There was a trend however that more people
found the regulations too restrictive in 2007, particularly newer, younger residents. The
survey findings indicated an increase in "newer residents" with 1-10 years residency in
Town.
Reguln City Meeting Minutes
May 24,2007
Only a slight majority of responders believed that a cap or absolute maximum should be
set on the size of a home (Estate Homes). However, a majority of residents did concur
that setbacks should be increased for homes of 10,000 + square feet.
With regards to open space (conservation) easements, a majority clearly favored the
policy of requiring the dedication of open spare. However, the majority of residents were
not in favor of imposing more restrictive fence regulations and they were evenly divided
on the issue of allowing taller deer fencing.
Pedro reviewed the Planning Commissions comments and reconunendations that
included: 1) majority of residents felt the status quo should be maintained regarding site
development issues; 2) high percentage of residents would like to see increased setback
requirements for estate homes and recommended that staff return the Estate Home
Ordinance (proposed) for review; 3) continued strong support for the open space
easement policy; and, 4) in general, younger and newer residents (less than 15 years) were
more likely to feel that development standards were too restrictive compared to the more
established residents. The Commission recommended that staff develop a "Property
Improvement Inforination Booklet" to be included in the Town's welcome packet.
Council thanked Pedro for her presentation.
Mayor Pro Tern Jones concurred that the survey's findings had strongly endorsed the
status quo "on balance". Jones commented that he had several issues that he wanted to
address. He was in concurrence with the Planning Commission's recommendation to
revisit the Estate Homes with regards to setback and possible restriction of 20,000 square
feet. Second, with regards to fencing, he believed that the survey language may have been
confusing but there was an indication that there was support for deer fencing taller than 6
feet. Third, was development on sloped property and the LUF penalty. Jones suggested
that it appeared that people believed it was too restrictive. The final issue he proposed for
discussion was the feasibility of an incentive for people to construct energy efficient
homes. Jones added that the Council had previously requested this and he would like to
have the issue revisited. Jones noted these were the issues/topics he would like to discuss
and queried what the appropriate next step in the process would be.
Couricilmember Mordo commented on the suggested discussion topics. He noted that
historically, there have been very few homes approved in the estate home classification of
20,000 square feet and did not believe it was necessary to set a maximum for house size.
However, he did concur with a review of setback requirements for estate homes. Mordo
agreed that deer fencing would be a more attractive, aesthetically pleasing fence option
that would lend itself to a feeling of open space compared to a solid 6 foot fence and he
would be open to discussion. He expressed his concern with opening discussions on
MDA/MFA because it was an arbitrary number and preferred reviewing each special case
individually and granting variances where warranted. Mordo suggested that the Council
consider reviewing the calculations for petmeable and semi permeable materials.
Pedro offered that there was a currently a Council development policy adopted in 1999
that calls for discount in development area for the use of certain materials. Additional
materials could be added. Mordo suggested that the table be reviewed.
Regulw City Meeting Minutes
May 24, 2007
Jones concurred and requested that direction be given to the Planning Commission to
investigate ways to make it easier for people to develop their yards with methods and
materials that would not substantially increase the amount of run off from their
properties. One suggestion was the exploration of second story homes on sloped lots.
Councilmember Ken supported relief for building on slope lots including credit for
permeable driveways but believed that the current development allotment for flat lots was
appropriate. He also supported the use of taller deer fencing especially to protect gardens
and vineyards but did not want to see properties completely fenced.
Councilmember O'Malley noted that he was comfortable with forwarding the topics to
the Planning Commission for discussion. However, be was concerned with MDA being
increased on sloped lots. O'Malley explained that the velocity of runoff from the lot
potentially hurt the person residing below the property and could cause erosion but he
was open to listening to proposals.
Mayor Warshawsky thanked staff for the report. He believed that it was a good survey
and he had gamered several key points from his review of the findings. Warshawsky
noted the trend that new residents and younger residents believed the Town's
development policies were too restrictive. There also was a clear indication that the long
term resident population was decreasing. Warshawsky suggested that the new/younger
residents might be more supportive of the Town's long term capital improvement
projects.
In review of the discussion items proposed by Mayor Pro Tem Jones, Warshawsky's
comments included: no support for changes in the fence ordinance; support for green
energy incentives as long as they were "carrots not sticks"; review of setback
requirements for estate homes but no limit to the size of homes; and, he would support
discussion of MDA/MFA requirements.
City Attorney Steve Mattas advised the Council that they could refer the matters where
there had been Council consensus back to the Planning Commission for further
evaluation. He suggested that it would be preferable for the Council to give clear
direction on rather they wanted the Commission to consider and refer recommendations
to Council or consider, take action and then refer the matter to Council.
Mayor Pro Tem Jones suggested that he would be interested in the Planning
Commission's input on the issues being forwarded to Council for further Council
consideration. He acknowledged that there was no clear consensus on the topics but
Council had indicated they would like further discussion on the matters. He suggested
the topics be referred to the Planning Commission for study, analysis and
recommendations. The topics included:
1) Fencing: fence amendment to allow replacing 6 foot fences with 8 foot fences (open
deer fencing only).
2) Slope properties: analysis of a set of recommendations of what development might be
allowable given the advancements in technology, building techniques, and materials for
10 Regular City Meeting Minutes
May 24, 2007
projects on sloped lots. This would include review of materials that did not result in an
increase of runoff from the property and could be discounted on development
calculations. An additional option to be considered was calculations for a second floor
not being counted as development on a very steep slope.
3) Estate Homes: Review of setbacks for larger homes but no further study of maxim=
house size.
4) Definition of incentives for high- energy construction. Review to be forwanled to both
the Planning Commission and Environmental Initiatives Committee.
MOTION SECONDED AND CARRIED: Moved by Jones, seconded by Mordo and
passed unanimously to refer the items identified to the Planning Commission and
Environmental Initiatives Committee as; appropriate.
13. Consideration of Sergeamt William Signs Memorial
City Manager Cahill reported that at the direction of the Mayor, staff and Community
Relations Committee representative Duffy Price had reviewed options for an appropriate
tribute for Sgt. William Sigua of Los Altos Hills who was killed in combat operations
while serving in Iraq. Before Council was a proposal for their consideration to name one
of the Town's Little League playing fields on Purissima Road in his honor. David Rock,
Little League President, had advised the Board of the proposal.
Council consensus was to move forward with the memorial.
Staff was directed to work with the fmily and coordinate the dedication.
NEW BUSINESS
14. Discussion of City Council Summer Meeting Schedule
Following Council discussion, the June 28 and August 23, 2007 regular City Council
meetings were cancelled.
REPORTS FROM COMMITTEES, SUB -COMMITTEES, AND
COUNCILMEMBERS ON OUTSIDE AGENCIES
15. Loan to the Friends of Westwind for the repair of the lower riding arcria surface at
Westwind Barn
Councilmember Mordo introduced this itern to Council. He summarized the recent
successes of the Westwind Community Bam Committee (WCBC) that included: the new
operating agreement between the Friends of Westwind and the Towri; and, the Friends of
Westwind's adoption of revised Bylaws. The Committee was now moving forward on
renovation plans for the Bam. They would be submitting an agreement for architectural
services and the development of a feasibility study to Council in the near future. The
estimated project costs were between $500,000 and $1 million with funding to be divided
Regular City Meeting Minutes
May24,2007
Back Nine Grei I Synthetic Ttirf Lawtis I Artificial Grass Field Turf I Athletic PlayArfAcTiMeNT 3
SYNTHETIC TURF LAWNS I GRASS
We use only the hlgre�t CUB[ ty Tree.alb Bva �able; it's not I like any synthetic or
anificial lawn or grass you have ever seem or folz before, Tno,igh it loolur, facie
and days so moci, I ke real lawn, 11 e incred blv durable and requires very little
"ailthena,ce,
Mairselance to tie synthetic turf is i-irrimal. An occasional broomng is
recommended but not necessary, This will Ssaid �he fibers tip sod even out the
johil nneteriale. :oore I ke leaves and twigs ca! be amady removed .,in a aef
WD-wer. As long as tine leaf blower �czz a �s isit placed �oo close to the turf, the
sal and rubber will at,, in Clare 10, too d�-, S is pays, way.
Tie long term effiect, C' -,J-e sun does not term -,fe synthetic tuff laverapOins Or
make it face, -tre liters have F UV U,U�etiln �Catirg and can withstard the
damaging affeets of su,t, neut, , md sno, o1c ce,
-is synthetic turf comes w!h a I , LeC 3 Y -B, ,,entY; actual life exPwch,1CY is
15-25 vea�.
7ne drainage in the turf o very sm 121 !0 ltltdca! gia5s� The turf backlog has many
rxerfa,aTed holes licing for water :0 zr,,li cull
Pets canrot fa on the tun. The turf s also instal ed smfly for dog runs. Jim-te is
i a problem as it abscribs, rho rhe said sod rLithther and cvertially evapol
You may Ban so-ary the soded area ,if a hose.
7 a cost romoaro,, to h.stallin. synthetic Awn, 0191... versus Iterating a
sibrurkler system, too Sol, and the price of sod, �Crnlbireql with water ol mowino,
weeping, and fact hz,g, �t can pay for f— f v a few years.
Synthetic bunions I Syncoho Putting, Greens I About 1 Pooling Gallery
T, SackwineGreens 2006. All Rights Rmm,m, Web Site Development cy Digital Assate
Ansioal Lieve Synthetle Timf Lwra, 'I Slae�
http://�.backninegreens.�m/la�s�pe/index.php 6/21/2007
GrVscrete by Bornanite: A Functional Green Paving Solution - The Concrete Network Page I of 2
ATrACHMENT ij
Ism ConcreteNetwork.com
UP
Grasscrete by Bomanite:
A Functional "Green" Paving Solution
Blending architecture and landscape is sometimes a complicated task when functionality, aesthete appeal and
eco -friendly criterion have to be considered. Grasscrete by Bomanite provides a variety of landscape solutions
while maintaining a sustainable "green" product design.
Grasscrete is a cast -in-place, monolithic, pervious concrete pavement that is continuously reinforced to provide
superior structural integrity. After the concrete is sufficiently hardened, the voids am filled with topsoil and grass,
thus providing a free draining "pavement" with the structural capacity to handle most heavy vehicle loads.
Grasscrete is great for emergency access lanes, delivery access routes, overflow parking areas, and for
intermittent drainage channels to help prevent erosion.
Available in a range of systems sp�ific to the required use, Grasscrete is essentially a cellular reinforced concrete
slab, the cells being voids created in the patented casting process which are subsequently filled with soil and
seeded with grass or other appropriate ground cover. The Grasscrete system selected can either be purely
functional or be a concealed product that is both purposeful and pleasing in appearance. Gresscrete offers the
end-user the ability to provide year round access for a variety of applications without compromising the aesthetics
of their exterior landscaping and having to utilize traditional hard pavements, eliminating the need to control storm
"ter runoff.
http://�.wncretenetwork.wm/bomanite/grem.htm 6/21/2007
Pegneable Paving Information - The Concrete Network Page I of I
COConcreteNetworkcom,
Grasscrete: A Permeable Paving option
Find a Grasscrete Contractor
Grasscrete can be an excellent afternative to plain concrete surfaces for parking lots, ddveways, and access roads
for vehicles or fire trucks. Grasscrete can also be used for erosion control.
Grasscrete drains at about the same rate as would an ordinary lawn in the same location. The presence of
concrete has little effect on the drainage; the soil and the slope are the controlling factors.
The surface area of Grasscrete is 47% concrete and 53% hole (to be filled with Grass). Grass usually covers much
of the concrete in areas not subject to regular vehicle traffic. Holes may be filled and covered with crushed stone,
seashells, etc. to provide drainage in cases where grass is not desired.
Construction Details
Construction Process
Additional Data (Maintenance, Drainage, Load Test Report, Slope Paving, Etc)
Section Sponsor
Find a Grasscrete Contractor
http://�.coneretenetwork.com/grmserete/ 6/21/2007
Gra�sscTetc by Bomanite: A Functional Green Paving Solution - The Concrete Network Page2 of2
Grasscrete can also be employed as a stabilization product for areas that experience seasonal mnoff, that require
max1imum water capacity to handle an adjacent hard surface or that require a structural base material prior to
application. Grasscrete can be customized to suit a wide variety of applications where the elimination of retention
ponds, males or other storm water management devices is desired. Grasscrete does not contribute to the heat
island effect like other hard surfaces such as asphalt, does not allow contaminants to mnoff during "first flush"
rainfall into potentially fragile eco -systems and allows for tree plantings in close proximity. Grasscrete is a very
sustainable product that can employ a large recycled material content both in the form of aggregate and binder
such as fly ash or slag- its Iffespan is indefinite and can be recycled itself to to= the aggregates for future
Grasscrete applications.
The plastic former utilized to create the void structure is designed to have a limitless number of re -uses, the
strength to accept live concrete loads, and capable to being removed during the concrete plastic state to create the
voids. Stmetural analysis of the finished concrete section is based upon the bending moment of the mesh
reinforcement contained within the slab, relatively to slab depth, contact area with base and an assumed allowable
ground bearing of 45kN/m2 for its base. By using combinations of depth and different mesh types, the system can
be tailored to provide the most economical solution.
http://�.wneretmetwork.com/bomanite/green.htm 6/21/2007
Perineable pavernent
ATTkA�9�T IS"
.................... ........
VVh.W. jBkje
Natural Appmaches to Starmwafer Management
Hatutial ADDrsiachg5
Permeable Pavement
to Stormwater
Manammen
Home Page
Country Lanes
Country Lanes, :1
Vancouver, B. C.
Vancouver. British
Columbia
Background
Alleys or back lanes in Vancouver, B.C.
Pervious Paving
provide access to garages and am used
Parking Lots
for public services such as garbage
Modification Puriect.
pickup. Consequently, both passenger
M
The Evergreen State
vehicles and heavy trucks frequently
QQlLgee. Olympia
we these Lanes. The city of Vancouver
developed! an environmentally
r Rarlsing Lot
sustainable -Country Lam" design that set� A. m W,�
m �rid
Pprformance Area.
rnakes back Lanes greener and mom
Preparing st�turat
Whdbev Island and
attractive. This alternative to paving Bran.
Bellineham
asphalt lanes to full width is a
I
response to the city's goal to reduce
Pervious Concrete,
environmental impacts and to create a
more Livable community. The city also
MUltiDLe LQU!JQD5 1 I
hopes to increase public awareness of
stomwater issues.
Pervious Concrete
Alj�, kilifigham
Diascription
Country Lanes feature two narrow
Pervious Driveway.
Strips of concrete that provide a Vancouver Country Lane
Beltineham
smooth driving surface. A plastic grid is completed.
placed between and beside these
commte strips and covered with
topsoji and grass. This stmctuml grass can support vehicles and prevents
the grass rodits from being compacted and creating nuts in the soil. The
mad base is a mixture of aggregate, which provicles stinicturat stability,
and a sand/wit mixture that allows for drainage and provides the wit
components required for grass growth.
Results
Country Lanes provide several berefits:
• Controlling stormwater at the source mears, less change to stream
hydrology.
• Surface water infiltration recharges groundwater.
• Topsoil fifters pollutants naturally.
• Adding green space improves air quality.
• Replacing asphalt with grass reduces the 'heat island effect,"
where warmer temperatures occur due to pavemant.
http://�.psat.wa.gov/Publications/LID—studies/P=eable_pavement.htm 6/21/2007
Penpeable pavernent
Vancouver is building three of these Lanes as a demonstration project.
With the success of these demonstration projects, this design will
become available as a standard local improvement lane project.
Costs
The costs are approximately 50 percent higher than conventional lane
paving. However, as builders and regulators gain more experience vdth
this approach, they wilL be able to refine the design and construction
process and costs should drop.
Contact
Pervious Paying Parking Lots Modification Project
The Evergreen State College, Olympia
Background
New building construction at The
Evergreen State College requires
additional parking capacity. The
philosophy of Evergreen is to reduce the
impact of the campus on the
envirownent Mich every maintenance or
redevelopment project, vherever
practical. In addition to reducing the
environmental impact, -soft" drainage
systems will provide monitoring and
teaching opportunities for students in
the college's envirorummui studies
program. Based on a Zeno Impact'
Feasibility Study (see page 27), the
college decided to intensify its use of
existing parking areas rather than
clearing more forest.
Description
The Parking Lots Modification Project
MLL provide additional parking in lots B
and C on either side of the main
entrance to the campus. Runoff from the
parking Lots currently discharges to the
East Fork of Houston Creek without
treatment or detention. The innovative
design adds new parking by removing and
reshaping planting islands and
reorganizing Lanes. Pervious paving
system will replace approximately
34,000 square feet of existing
landscaping for new parking stalls. The
combination of adding nev, Pervious
paving and converting existing paving to
pervious surfaces wIL result in a net
reduction of runoff to Houston Creek -
The paving bid package includes three
alternative paving systems, including
EcoStoneO by UniGnoup, Gravel Pave 2�,
and a system of crushed nock with
cellular confinement. The design for the
pavement includes infiltration to the
subgrade and storage in rock ballast
under the pavement. The objective is to
-Zer� Impact is a project
that adheres to the 65/0
(65 percent forest cover
preserved/wro effective
Impervious surface)
development standard
and is constrained by
characteristics of a
healthy watershed as
described in the Salmon
in the City Conference
Abstracts.
Approximately 9,ODO
square feet of
impervious Parking area
at The Evergreen State
College will be
moverted to
bioretention areas
(numbered In plan at
right).
Pervious paving
Page 2 of 7
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Per�peable paverrient
infiltrate the 100 -year, 24-hour slorm
materials vary according
without surface runoff. A sand filter
to the Intensity of use
providing water quality treatment is
in parking lots. In the
located directly below the paving
above diagram, a
system.
cellular confine-ment
system stabili� a
Approximately 9,000 square feet of
parking surface of
parking lot access Lanes will be
crushed rock.
convened to tioretention facilities. The
design provides for soil restoration to a
depth of two feet. The objective is to provide bioretention areas with
sufficient surface and subsurface storage volume to infiltrate runoff
from all events up to the 100 -year, 24�hour SUDM.
Evergreen may also build a motorcycle parking structure with a
vegetated roof that will be a study focus for students in it*
environmental studies program. The motorcycle port will have
approximately 6 inches of soil on the roof with plants selected for their
tolerance to extreme wet and dry conditions.
Challenges
One complication of the project was old fill material found under the
existing pavement. Because it is unsuitable for pavers or bloretention
facilities, contractors had to remove and dispose of it. This cost would
not have occurred with the asphalt paving alternative.
costs
The cost of the zero discharge parking retrofits is the same as, or lower
than, traditional alternatives using new treatment and detention
systems. Costs for green mfing will be higher, but the increased life of
the mof will help offset these costs. An important factor in chming the
pervious paving systems is that this approach negates the need to clear
and grade surrounding forest areas for detention ponds.
Contacts
Michel George
Thomas W. Holz
Grass Parking Lot and Performance Area
Whidbey Island and City of Bellingham
Background
A farmers' market and community
hall at Bayvlevv Corner on Whidbey
Island needed weekend parking. 2020
Engineering designed a reinforced
gram pavement system that makes
the area took like open space when
not used for parking.
In Bellingham, the owner of the
Boundary Bay Brewery wanted to
expand the winter parking area and to
Grass parking lot design
meets standards for
traditional traffic Loads and
resembles open space when
not used for parking.
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http://�.psat.wa.gov/Publications/LID—studies/l)�eable pavemenathtm 6/21/2007
Permeable pavement
provide a summer beer garden and
performance area.
Description
The grass parking tons use an
interlocking plastic grid (GeoBLock'
at Bayview Comer and Grassy Pavers -
at Boundary Bay Bre�ry). The grid
was fitted with a mixture of sand and
chicken compost and planted with
grass.
Result,
The parking tot designs meet
standards for traditional traffic
Loading. The grass parking repticates
natural conditions for slowing and
infiltrating stononwater rumfif and
eliminates the need for conventional
detention/ treatment systems.
costs
The cost for both lots was $3 to $4
per square foot, installed.
Contact
2020 Engineering, Inc.
(360) 671-2020
Website: www.2020ensamaering,com
Pervious Concrete
Multiple Locations
Background
Builders
have
used
pervious
Concrete
nationally
for
MOM
than
zo
years.
In the
1980s,
several
Projects
used
pervious
concrete
in the
Puget
Sound
basin,
including
at
Husky
Stadium
and at
�1. pr�x. " 0- J. f.",
Pervious c.ncreve
infiltrates water
extremely well—
typically 250 to 300
inches per hour.
Sayview comer, Whidbey
Island. Top photo: after
construction. Lower photo:
during construction.
Boundary Bay Brewery,
Bellingham. Top photo:
during construction. Lower
photo: after cons-truction.
Page 4 of 7
http://�.psat.wa.gov/Publicatiom/LID—studies/Permeable_pavement.htm 6121/2007
Perracable payment
I
a park in Redmond. In recent years, builders have used pervious
concrete in several new projects and more are planned.
Description
Pervious concrete is a special structural concrete with the fire Particles
removed. This creates 15 to 20 percent voids so the comcnem Looks like
a giant rice cake. The pavement will support traffic and allow water to
pass through to a gravel Layer underneath. The strength of pervious
Concrete is about 85 percent of conventional concrete, making it
suitable far sidewaEks, driveways, alleys, parking LOU and residential
streets. Designers and installers need special training to ensure
structuraL integrity and ixmasity. Post -placement testing is important.
Pervious Concrete is much mom porous than underlying soils. Typical
infiltration rates am 250 to 300 inches per hour; typical installations
require soils with percolation rates Of More than 1/2 -inch Per hour. A
gravel bed placed underneath the Concrete stores water before it moves
into the soft or can provide a channel for movement of water to
stomwater channets. A 4-hich bed of nock or aggregate 3/4 inches or
larger with 30 percent voids will store 1.2 Inches of water. In addition to
in water quantity benefits, pervious paving can remove some pollutants
through absorption, stratnirg and microbial decomposition.
Following am same of the locations of recent pervious concrete
installations around Puget Sound:
• Four blacks of sidewalks on N. 145th Street, Seattle.
• 400 feet of sidewalks at 1 00th A�e., Marysville.
• Six parking Lots at Fort Lewis.
• Sidewalk on North Street in Olympia.
• Plaza at GneenwDod Park, Seattle.
• Alley in Bellingham.
• Parking lot for the Washington Aggregates B Concrete Association
office, Des Moines.
• Nine parking spaces at Bayvim Corner, Whidbey [stand.
Planning is currently underway for a residential subdivision to
demonstrate the usefulness of permeable comnete for residential
somets, driveways and sidewalks.
costs
The cost for pervious concrete is typically $6 to 9 per square foot. This
is comparable to conventional comcnete.
Contacts
Bruce Chattin
Washington Aggregates it Concrete Association
(206) 878-1622
Itchattin0washingtonconcrete."r
Greg McKinnon
Stoneway Concrete
Office Phone: (425) 226-1000 ext. 3313
Mobile Phone: (2D6) 255-2647
grickinnomIX,stonewayconcrete.com
Pervious Concrete Alley
City of Bellingham
Background
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http://�.psat.wa.gov/Publications/LID studies/petTricablepavernent.litan 6/21/2007
Penneable pavmmt
A residential homebuiLder was interested
in sustainable construction and decided
to try pervious paving in an alley that
provides access to homes. This was the
first application of a pervious concrete
roadway in a Whatcom County right-of-
way.
Description stixt pixxo to A� in uir,nn
The alley provides access to two Pervious concrete alley,
residentiat properties while minimWng Bellingham.
environmental impacts. Porous concrete
allows for the inflitra tion of stormwater
nunoff while providing the same structural capacity as conventional
concrete. Engineers determined! the depth of the crushed rock base
material—used to support the cowrete—based upon the type of
underlying soil conditions and amount of water storage area needed W
accommodate storm events. No fine materials were mad.
Since this project was the first of its kind, the city of Bellingham wanted
to know about durability, Load, treatment and maintenance
requirements.
Ptesults
Stormwater treatment occurs as water flows through the pervious
concrete mad section and underlying wits. Other characteristics, such
asi maintenance issues, are comparable to conventional pavement
systems. The engineer used the Departmerit of Ecology's Smormwater
Management Manual for Western Washington as one of the gundes to
document the stormwater infiltration benefits of the project,
Costs
Materials cast approximately $1.50 per square fact. Installation costs
were similar to conventional paying.
Pervious Driveway
City of Bellingham
Background
Stormwater runoff causes pollution in
the Lake Whatcorn watershed In
Bellingham, as it does in many other
developed areas. Because Lake Whatcom
is if* sole source of drinking water for
the city of Bellingham, this can have
serious consequences for the city's
drinking water supply. A homeowner in
sel. Pnot. A. in t.W
the watershed wanted to demonstrate
.1t,
Pervious driveway,
alternative sustainable building practices
Bellingham.
and decided to replace the existing
impervious asphalt driveway with a
pervious one.
Description
The homeowner installed a pervious
paving system composed of individual
intedmking paving blacks pieced on a
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http://�.psat.wa.gov/Publications/LID stuadies/permeablepaveromt.hLin 6/21/2007
I Per;peable pavernent
Page 7 of 7
bed of fine gravel. The configuration of
the pavement blocks provides a series of
voids to allow stormwater to infiltrate.
Results
The new driveway has better structural
properties than the replaced asphat
surfaced driveway. The pervious paver
system replicates naturaL conditions for
stm-mwater infiltration, provides
treatment, and eliminates the need for
conventional cletention/treatment
systems. The homeowner reports a
significant reduction in the volume of
stormwater flowing down the driveway
and into the Lake.
The pervious paver
system replicates
.tural stormwater
infiltration, provides
treatment and
eliminates the nee,d for
conventional detention/
treatment systems.
Costs
The cost was approodonavaLy $5 per square foot installed.
Contact
2020 Engineering, Inc.
(360) 671-2020
Website: www.2020eneineerme.conn
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PRIVACY NOTICE
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http://�.psat.wa.gov/Publi�tions/LID studies/p=eablepavernent.litm 6/21/2007
. Watprshed Benefits of Permeable Pavers
HO�e I LID 8,,k,,o,-d I Dgaign I Sit, Map I D�dave
MN
"�—= T.- Watershed Benefits of Permeable Pavers
Typical scenario..
Page I of 5
ATTACHMENT
Most of thepaving over'm developed areas is due to common roads and parking lots, which play a
major role in transporting increased stormwater ranoff and contaminant loads to receiving waters.
Alternative paving materials can be used to locally infiltrate rainwater and reduce the nmoff leaving a
site. This can help to decrease downstream flooding, the frequency of combined sewer overflow (CSO)
events, and the thermal pollution of sensitive waters. Use of these materials can also eliminate problems
with standing water, provide for groundwater recharge, control erosion of streambeds and riverbanks,
facilitate pollutant removal, and provide for a more aesthetically pleasing site. The effective
imperviousness of my given project is reduced while land me is maximized. Alternative pavers can
even eliminate the requirentent for underground sewer pipes and conventional stormwater retention /
detention systems. The drainage of paved areas and traffic surfaces by means of permeable systems is
an important building block within an overall Low Impact Development scheme that seeks to achieve a
stomwater management system close to natural conditions.
... nithpermeablepaver$!
Water Quality
Some current studies on the effectiveness of permeable pavers for reducing Total Suspended Solid
(TSS), nutrient, metal arid thermal loadings are being conducted in Florida, Toronto, and Washington
State.
The parking lot of the Florida Aqum
Tampa, which serves 700,000 visitor=ually,
has been innovatively designed as a research
http://�.lid-stomwater.netip=eable_pavers/p=pavers—benefits.htm 6121/2007
. Wawrshed Benefits of Permeable Pavers
and demonstration project for the use of
permeable pavers as part of a treatment train
approach, comparing three paving surfaces in
conjunction with swales.1 First-year results
found that load removal efficiencies for metals
(copper, iron, lead, manganese and zinc) ranged
from 23 to 59% for asphalt pavement with a
swale; 62 to 84% for cement pavement with a
gwale; and 75 to 92% for porous concrete with a
swale. In general, metals were measured at
much higher concentrations in the basins paved
with asphalt than those paved with cement
products. The porous system with a swale also
achieved 91% removal efficiency for total
suspended solids, higher than the other two
paving systems.
Studies at the University of Guelph in Canada
have also observed greater pollutant loads from
asphalt surfaces than from concrete or
permeable pavers. There, a research team led by
Professor William James has been performing
field and laboratory tests since 1993 on the
influence of permeable pavers on runoff
pollutant levels and thermal characteristics.
They have found that a permeable paver made
up of interlocking concrete blocks can
significantly reduce the surface runoff loads of
such contaminants as nitrite, nitrate, phosphate,
phosphorus, metals, BOD, and ammonium.2 In
addition, during a lab simulation, the permeable
pavers were found to reduce surface ruroff
temperatures by 2 to 4 degrees Celsius
compared to the runoff from asphalt paving.
Since the permeable pavers also increase
infiltration, the total heat content of rLmoff
leaving a site is reduced substantially.3
Page 2 of 5
Finally, surface and subsurface nmoff samples we being collected by the Center for Urban Water
Resources Management in Washington State from a test parking area, which contains five different
surface materials.4 Constructed in 1996, the King County employee puking lot contains nine staHs, of
which one is traditional asphalt, and the others we few pairs of alternative permeable pavement
surfitces: gravel -filled interlocking concrete blocks, soil and grass -filled interlocking concrete blocks,
gravel -filled plastic cell networks, and soil and grass -filled plastic cell networks.
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. Waiershed Benefits of Permeable Pavers
Page 3 of 5
The projects primary goal is to determine the long-term water quality benefits of these systems under
real world usage. A system of pipes, gutters and gauges collect and enable the measurement of the
volume and chemistry of both the surface runoff and the subsurface infiltrate. A comprehensive water
quality analysis is being conducted over the winter of 2001/2002. Preliminary results indicate that the
subsurface runoff is consistently cleaner than the surface runoff statistical analyses and reports will be
produced in future months (Derek Booth, Feb. 2002, personal comnittnication).
For more specialized users, continuing research at Coventry University in England has been looking at
applying nutrients to permeable pavers in order to support a microbial population that can serve as an in-
situ bioreactor for oil degradation in highway and puking lot ranoff.5 Studies have demonstrated the
potential to maintain microbial activity for over 12 months ftom one application of a slow-release
fertilizer, with warnings given about ensuring the effective use of the nutrients so that high effluent
levels will not cause eutrophication in receiving waters.
Water Quantity
Most of the above studies have also examined the influence of permeable pavers on runoff volume,
tending to show a marked reduction in the surface runoff that leaves a permeable paver site due to
increased infiltration. In the University of Guelph experiments, field sites with permeable interlocking
concrete pavers demonstrated a 90% reduction in runoff volume.3 ne treatment train studies at the
Florida Aquarium showed that, in general, the use of swales reduced runoff volume but that paving type
also played a major role in runtiff reduction, with permeable pavers being the most effective. The figure
below demonstrates this fact as well as the caveat that the me of swal es and permeable pavers has the
most influence on runoff during small storrns.� For high intensity rainfalls or when soil conditions are
saturated, runoff is not reduced as substantially. Note the different scales on the two graphs; the first is
for a rain event that produced just over 0.5 inch of rain in about 75 minutes, while the second is for an
event producing almost 2.5 inches in under 2 hours and occurring less than 24 hours after four preceding
days with rain.
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. Watershed Benefits of Permeable Pavers
Page 4 of 5
The studies by the Center for Urban Water Resources Management in Washington State have looked for
similar differences in the hydrologic response of pavers based on storm intensity or if the storrin
followed a long dry period versus a period of abundant rain. To date, however, results show a general
absence of surface nmoff from the permeable pavers regardless of conditions: "it all just infiltrates, all
the time" (Derek Booth, personal communication). The figure below, representing a typical observation
during the study's first year, compares surface runoff produced from traditional (asphalt) and permeable
(Turfstone) pavements. 7 The Turfstone permeable paver is a 60% impervious surface made up of soil
and grass -filled interlocking concrete blocks. The measured surface runoff from the Turfstone is less
than I percent of the total rainfall and is probably a result of observed leaks in die� covering over the
collection system. All other permeable pavement systems showed equivalent results. The asphalt
paving, however, responds quickly to the rainfall, with most of the rain that hits the surface running
off.
Suffacenunoff]Fram lraffat�ne�s Asphalt
1—aatnz.
Tirn. in Min
It is likely that results are different from those in Florida due to differences in the two regions'rainfall
regimes. The Washington rain event had a maximurn rainfall intensity that was under 0.2 in/hr, this was
typical of the storms recorded. In comparison, the heavier rain event presented in the Florida graph had
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. N4ershed Benefits of Permeable Pavers
Page 5 of 5
a maximum rainfall intensity of 1.5 in/hr. Rain events in Washington State are generally of a lower
intensity and longer duration than those measured in Florida� where the rainfall, particularly in the
summer, is dominated by short and more intense convective events.
* all six photographs from LTNI Eco-Stone� Permeable Concrete Pavers PowerPoint presentations,
02000 LTNI-GROUP U.S-A. www.uni-uoupusa.org
1 Rushton, B.T., 200 1: Low -impact puking lot design reduces runoff and pollutant loads. Journal of
Water Resources Planning and Management, (May/June), 172-179.
2 junes, W., ed., 1997:Advances in Modeling the Management ofStomwater Impacts Volume 5.
Proceedings of the Stormwater and Water Quality Management Modeling Conference, Toronto,
Ontario, February 22-23, 1996, 520 pp.
3 James, W., 2002: Green roads: Research into Permeable Pavers. Stormwater, (Much/April), 48-50.
4 Booth, D.B., J. Leavitt and K_ Peterson, 1996: The University of Washington Permeable Pavement
Demonstration Project. Background and First -Year Results, available online at
hLtpi//dQ-t.w�hington.edu/ under Research.
5 Pratt, C.J., A.P. Newman and P.C. Bond, 1999: Mineral oil bio -degradation within a permeable
pavement: longterm observations. Wat. Sci. Tech., 39 (2), 103-109.
6 Southwest Florida Water Management District, 2001: Florida Aquarium Parking Lot - A Treatment
Train Approach to Stormwater Management, Final Report for FDEP Contract No. V'TM 662,
Brooksville, Florida, 220 pp.
7 Booth, D.B. and J. Leavitt, 1999: Field evaluation of permeable paver systems for improved
stormwater management. Journal ofthe American Planning Association, 65(3), 314-325.
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