To: The Dewey-Humboldt Planning and Zoning Commission
Date: 8/20/06
Re: Agua Fria Center Development and errors in the concept of permeable asphalt use


Dear Members of the Dewey-Humboldt Planning and Zoning Commission,

  I have been somewhat intrigued by the idea that one could use something so simple as permeable asphalt to filter unwanted chemicals from water. This I learned from Dennis Roberts as he outlined his plans for a rainwater harvesting system to use at the Agua Fria Center and talked of the ability of permeable pavement to actually filter automotive oil drippings from rainwater.

  For some time now I've been looking for a way to filter discharge water from my washing machine so that I can use it to water my lawn, so you can imagine my delight upon learning that a filtration solution might be found in the secrets of permeable pavement. So I went to the Internet and did a Google searches for "permeable pavement" and "porous asphalt" and learned far more than I thought I knew.

  Permeable pavement has use as a method for collecting rainwater and retaining it for a time while it percolates through the underlying soil and eventually into the groundwater. This is useful for reducing the necessary size of storm drainage systems and reducing storm surge in existing drainage systems. To describe it in a simplified fashion, a typical system is constructed by digging down about 4 feet and then laying in a deep bed of very coarse gravel (rocks, perhaps 3" in diameter). The porous asphalt (or permeable block or tile arrangements) are then built on top of that. Water seeps easily through the porous top layer and collects in the gravel bed below which can hold quite a lot of water while it slowly percolates through the soil underneath. It is a simple and impressive system, but it suffers from some deficiencies.

  Technically, porous asphalt has no filtration capabilities beyond rudimentary sediment retention. The claims of porous pavement itself being able to filter automotive oil are patently false. What does the actual filtering is the soil underneath the gravel bed and this is no more miraculous than the method employed by Mother Nature in your back yard. Further disadvantages include low weight and traffic tolerance and the need to vacuum the pavement periodically as dust can clog it.

  Beyond my disappointment that my lawn will remain dry for lack of a simple filtration system, I have realized that Mr. Roberts never really did understand permeable pavement enough to know that using it would be either very expensive or simply not feasible. First, a substantial bed of soil that will allow water to percolate through it is necessary, not just for filtration characteristics, but simply as a means of disposing of excess water. However, as we already know from Mr. Roberts' reference to his hillside as "one big rock," the proposed site does not perc. Frankly, I'd be surprised if there is even 4 feet of soil over any significant portion of the land. This means that even with permeable pavement in place, collected water has no means of escape from the gravel substrate and would remain unfiltered in any way. Of course it may be possible to install a drain to a filtration system but that would raise costs significantly.

  Furthermore, porous asphalt is structurally challenged. The permeability is achieved by removing the finer particles as it is made, leaving a coarse, less tightly bound material, which happens to pass water. As such it is not rated for heavy loads and frequent use shortens its life. It is not recommended to use permeable pavement in commercial parking lots and it cannot withstand the weight of delivery trucks for long. This idea does work well in employee parking lots, long-term airport parking and the like. It should be clear that most of the parking at the Agua Fria Center is not of this type.

  Finally, dust is a problem for porous asphalt as it can clog the pavement and render it useless. Periodic vacuuming is recommended in average climates but in dustier and windier areas as we find here, there is no doubt that strong preventative measures would have to be taken. This is important, as clogged pavement would then require replacement or the presence of a secondary drainage system.

  I encourage you to go and do some research on the Internet to verify that what I say is true. To get you started I have included a six page fact sheet from the EPA that will reveal further reasons why permeable pavement is not advised on Robert's land.

  While it may be easy for Dennis Roberts to simply drop permeable pavement as a feature of the Agua Fria Center plan, I find a deeper implication at hand. Mr. Roberts has portrayed himself as knowledgeable and experienced in matters of development yet his lack of understanding of a feature that he touts suggests otherwise. At the last Planning and Zoning meeting I had indicated my belief that the Agua Fria Center is not a plan for a commercial complex, but a plan to profit from land brokering by fooling the town into granting a zoning change. This finding on the significant disadvantages of using permeable pavement in this particular scenario only bolsters my belief.

  It would seem to me that if a person really intended to build such a complex as the Agua Fria Center, he would have at least learned something about the feasibility of features that would be employed. As it stands, I look at the Agua Fria Center and see merely collection of selling points.


Len Marinaccio
Humboldt, AZ