Letters

BioCycle July 2009, Vol. 50, No. 7, p. 20

Green Roof Media Standards
Laurel Valley Soils and Skyland USA was included in your recent article about green roofs and use of compost in producing specialized growing media for them (“Green Roofs Take Compost To New Heights,” May 2009). After reading the article, I would like to address the comments from Mr. Buist on green roof media standards.

As a producer of some 3,500 cubic yards/week of compost, Laurel Valley Soils would be ecstatic to see these specialized green roof growing media contain the highest percentage of compost possible. We know few things work as well to replenish weak soil profiles or aid in plant growth as compost. So why don’t we use more compost in green roof media? Used in excess, compost presents negative issues such as nutrient overloading, spongy soils, and in container situations (a green roof would be considered a very large container) volume reductions and potential rotting.

Mr. Buist suggests that the FLL Guidelines for Green Roof installations are a “loose” standard. These Guidelines, which recommend high mineral-based green roof media versus high organic media, have been refined and amended by the German green roof community after countless trials, successes, failures, and testing in the academic world as well as in the practical world of application. They are based on experience and data from green roof installations that include a very wide range of climatic conditions.

The green roof industry is always looking towards improvement. Mr. Buist mentions that “performance” is what we should be using as the standard. With over 30 years of international experience and research behind it, the FLL Guidelines are based on standards that perform.

Joe DiNorscia
Skyland USA LLC
Avondale, Pennsylvania

Sub-Committee Response
The standards being developed by the Green Roofs for Healthy Cities’ Growing Medium Sub-Committee are performance-based, rather than prescriptive-based like the FLL standards noted in Mr. DiNorscia’s letter. The Subcommittee, comprised of 10 industry experts from both the aggregate and compost worlds, determined that by creating performance-based standards (while still incorporating the benefits of the FLL prescriptive standards), we would be providing an opportunity for all players in the industry to create growing medium so long as it performed certain criteria related to the specified benefits of the green roof. This will ensure that no company is disqualified from providing the product because they don’t meet the pre-set standards determined by the German FLL standards. Rather, if their growing medium performs as required by the standards, then their product is acceptable for use.

The FLL standards were created in Germany for the German market and prescribe a certain percentage for aggregates and organics for both intensive and extensive green roofs. The determination of this percentage was based upon their available compost, which differs from the North American market, and was designed to minimize the amount of leaching of harmful materials into the stormwater runoff. As we have different types of compost in North America, the rationale to limit the organic content does not apply in the same way. The standards being created by the Growing Medium Subcommittee will be completed by early December and will be distributed to the corporate members for input and comments.

Rick Buist, Chair
GRHC Growing Medium
Sub-Committee
BioRoof Systems, Inc.
Hornby, Ontario

Shortage Of Composting Data
The April issue included an article titled “Composting Trials Evaluate VOC Emissions Control,” by C.E. Schmidt, T.R. Card and B. Kiehl. The authors do not present any data on oxygen and very little data on temperature. Any data on emissions, whether odors or VOCs, should provide information on oxygen and temperature. Oxygen levels must be above 5 percent and preferably 10 percent or higher.

I have seen several instances where limited porous fabrics constrain oxygen resulting in anaerobic conditions in several locations of a pile. Temperature data are also important as the temperature greatly affects volatilization. Under mesophilic conditions there is a lower volatilization rate than under thermophilic conditions. In a proper aerated static pile system, thermophilic conditions occur during the initial period of 10 days. I have published numerous data showing that under proper aerated static pile composting, odors and VOCs are greatly reduced during the first 14 days. The authors indicate that they were measuring emissions under very cold conditions and that normal pile operating temperature was not achieved until 10 days. Therefore, it would have been to be expected that the volatilization rate would be very low during that period.

Eliot Epstein
Epstein Environmental Consultants
North Easton, Massachusetts

AUTHORS’ RESPONSE
The authors appreciate Dr. Epstein’s comments and agree with his observation that the reported data do not allow a full appreciation of the study. A significant amount of data was generated under regular composting conditions scientifically validating the reported findings. For Site 2 a total of 47 samples on 7 monitoring days dispersed over the composting cycle were taken. Not all these data are contractually available for publication and concurrently too voluminous to publish in this article. However, we welcome open discussion and are available to discuss the data and findings from the testing in person.

C.E. Schmidt, T.R. Card and B. Kiehl
CE Schmidt Consulting, Environmental Management Consulting and
W.L. Gore & Associates Inc.
(respectively)

BioCycle welcomes your Letters to the Editor about recent articles and news coverage. Please send your letters via email to biocycle@jgpress.com. Article authors or individuals interviewed for articles will have an opportunity to respond.

Copyright 2009, The JG Press, Inc.