BLD2023-1530+EOR-CYA Letter+11.4.2024_8.02.39_AM+4598981O M EGA 2707 Wetmore Avenue
Everett, WA 98201
ENGINEERING, INC. t 425_387_3820
f 425_259_1958
October 31, 2024
Landsverk Quality Homes, Inc
Attn: Duane Landsverk
Via email: duane _Igh-inc.com
RE: Modified Permeable Pavement Design for Maplewood Lot A, B & C SFRs.
Dear Duane,
This letter is being prepared to provide engineering verification that the proposed modified
permeable pavement design will meet the code requirements for these projects. This analysis
is based on my site visit to inspect the driveways, walks and patios along with our conversation
for the modified design components proposed.
The approved plans for these projects called for permeable pavement to be used for driveway,
walks and uncovered patios. A standard permeable pavement section was provided on the
approved plans.
The proposed modified permeable pavement design will still provide the subsurface gravel
layers the system utilizes as a reservoir course to store collected rain water and allow adequate
time for the rainwater to infiltrate into the native soil. The proposed modifications to the design
will only affect the surface improvements which are detailed below. Therefore, the bottom area
for the pervious pavement areas will not change and the function of the systems will be as
expected.
The changes to the permeable pavement design is to provide a standard concrete pavement
around the perimeter of the permeable pavement to provide a more durable boundary. In
addition, this will aid in long-term maintenance since adjacent landscaping materials will not be
located immediately adjacent to the permeable surfaces so it will be easier for the home owners
to clean up these areas of the driveway without any impacts to the function of the permeable
surfaces.
Next, instead of pervious concrete or asphalt, the driveway within the standard concrete border
will consist of pavers with a '/2" gap between blocks filled with clean crushed rock. These gaps
will make up a significant portion of the internal paver area so any rainwater that falls on the
standard concrete perimeter or on the pavers will have ample gaps to migrate into the
subsurface reservoir course. The percentage of the internal paver area that consists of gaps is
approximately 20%. This is more than adequate to provide the surface area necessary to
collect the rainfall over the entire driveway area.
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ENGINEERING, INC.
•;
It should also be noted that the areas of the driveways, walks and uncovered patios on all the
lots are flat. As a result any water that is collected in the paver gaps will migrate easily into the
reservoir course and then spread out evenly over the native ground beneath the gravel layer.
This will ensure that the entire area of rock beneath the driveways, walks and patios will be
utilized for infiltration and the runoff will not collect in a low area of the facility.
Is summary, the proposed modification to the permeable pavement surfacing will function as
expected to mee the approved design requirements for this project, and the system will be
easier to maintain both in the short-term and long-term. Thank you for taking the time to review
this letter. Please feel free to contact me with any questions you may have.
Sincerely,
Smeby, P.E.
rofessional Engineer