The Environment and Sustainability Department evaluated the lot for opportunities to add shade trees and provided two (2) initial options for the June 21 PSNQLC meeting. The first option is to add medium to large canopy trees. The second option is to add smaller trees on the eastern
side of Royal Palm Avenue to improve the pedestrian experience and increase tree canopy.

Option 1 – Canopy Trees

 
The Environment and Sustainability Department worked with the Office of Capital Improvement
Projects to develop a planning level project scope and estimate. Due to the current lot
configuration, lot changes would be necessary to create planting space to add canopy trees to
provide substantial shade and thrive. A suspended pavement system would be needed to
provide adequate uncompacted soil volume for the trees to flourish.

Optimal Tree Planting Locations

 
The P-63 surface parking lot is an existing asphalt paved parking lot, consisting of 4 aisles of
parking divided by three raised concrete medians (Attachment B). The lot has an existing drainage system, connected to the City's public right-of-way drainage, and existing parking lot lighting. In an attempt to minimize the impact to parking spaces and reduce project costs, staff considered limiting tree planting to occur within the concrete medians. Tree planting would need to be coordinated with existing lighting to avoid the creation of dark spots as the trees mature.
Restricting planting to occur within the medians would also avoid any potential grading and drainage upgrades or alterations.

Permitting and Underground Infrastructure Requirements

 
The proposed project, occurring within the limits of a Government Use District property, would require a full permit review and issuance by the City's building department, as the project would include relocation of existing underground electrical infrastructure as well as new asphalt,
concrete and landscape irrigation, in addition to the new trees.

Considering the existing conditions, the project would include work to remove the compacted limerock, concrete and asphalt which, if not removed, would impede root growth and
establishment. To ensure the longevity of the trees, provide sufficient area for root growth, and
encourage larger tree growth, the sub-surface soils would have to be replaced with a nutrient rich, non-compacted material, while simultaneously providing the structural bearing capacity to
withstand vehicular loads. This "suspended pavement" system (Attachment C) includes a
structural grid, infilled with a mix of favorable planting materials, fostering root growth while providing a durable paving surface and eliminating future root damage to the asphalt. In order to
provide proper root area, the suspended pavement system should include an area generally equivalent to the spread of the tree canopy. In this case, the system would cover an area of 20'x
20' (400 sf) for each tree, with a depth of approximately 36".

Cost Estimate

 
Staff developed a conceptual plan (Attachment D) for the parking lot which also identifies the
limits and quantities of the anticipated work. With this conceptual plan, an order of magnitude
estimate was derived, utilizing historical cost data for other City projects, including a variable for
cost escalations over time. At this time, the cost estimate to install twenty-four (24) trees within the P-63 surface parking lot, with a minimum overall height of 18', inclusive of related suspended pavement, irrigation, electrical work, design, permitting and other soft costs is approximately $1,655,000. This estimate also includes milling and resurfacing the parking lot.

While performing the analysis and cost exercise, City staff did identify an opportunity to further reduce project costs, depending on the timing and availability of Tranche 2 of the 2018 General
Obligation Bond. As tranche 2 would include funding for Citywide reforestation, the costs of the
trees could be funded through the GO Bond, potentially reducing the necessary funding by as
much as $100,000. It is worth noting that there is considerable uncertainty in the estimated costs for trees due to current volatility and extreme market variability.

Option 2 – Smaller Trees on Lot Perimeter

The second option is to add smaller trees in available planting spaces surrounding the lot to
improve the pedestrian experience and increase tree canopy. Smaller trees would need to be utilized to avoid safety issues posed by the existing overhead power lines. This would provide some shade for the pedestrians and improve lot aesthetics. Twenty (20) small to medium trees
could be planted, which would cost approximately $40,000 dollars. However, based on current and prior projects, the estimated costs for trees is highly variable.