The proposed rulemaking is related directly to an effort to consolidate and codify several long-standing GMPs, under which thousands of gravelless drainfield systems have been installed since VDH first began allowing chamber system installations in 1987.  Moving gravelless system management from policy to regulation meets the intent of 12 VAC 5-610-448.(A), which addresses codification of technologies that have been granted general approval under a VDH-issued policy.  In addition to broadening the single option Virginians have historically had for constructing a drainfield under the regulations, the effort also opens the door to future innovation, allowing VDH to adopt new gravelless technologies under a flexible rule structure.

Benefits of Regulatory Change:  The proposed rulemaking will consolidate requirements from GMP 127 and GMP 135 and move parameters such as a maximum 25% reduction into regulation.  Infiltrator Systems supports the use a uniform 25% reduction for all soil percolation rates.  Industry does not support what is referred to as double dipping, or taking a reduction as allowed for gravelless technology on top of a reduction associated with advanced treatment.  In addition to consolidating GMPs, the maximum 50% reduction is eliminated from Virginia sizing options with the withdrawal of GPM 116.  Industry believes that these collective changes represent a net improvement to the Commonwealth’s onsite wastewater treatment system regulatory framework.  In addition, establishing a single method for sizing gravelless systems simplifies the use of gravelless products while adding a safety factor to designs.

Ubiquity of Gravelless Technologies:  Proprietary gravelless drainfield products are approved in all 50 states and 10 Canadian provinces, with over 3 million systems installed over the past 25 years.  Approximately 50% of the septic systems installed in North America each year are constructed at reduced sizing compared to stone and pipe systems using gravelless drainfield products.  Proprietary gravelless drainfield products make up over 75% of all systems installed in 9 states.  In 16 other states, proprietary products make up between 50 and 75% of all drainfields installed.  The International Association of Plumbing and Mechanical Officials (IAPMO), allows a 30% sizing efficiency for gravelless technologies.

Third-Party Performance Studies:  The use of a sizing reduction for gravelless products compared to the size of a stone and pipe drainfield is a proven method that is supported by independent research.  Numerous statistically valid studies have been conducted on this subject, including the world’s largest onsite system field performance study conducted in North Carolina (see below).  Large-scale field performance assessments on installed, real-life gravelless drainfield products offer the advantage of a large sample population, differing physiographic and climactic conditions, and a wide spectrum of wastewater flows from the dwelling.  Taken as a whole, the weight of scientific evidence from these studies shows that the performance of reduced-size gravelless systems is consistent with that of “conventional” stone and pipe.

Hydraulics Research:  The North Carolina Department of Environment and Natural Resources (NC DENR) conducted a field performance study on 900 systems in total, including 303 stone and pipe, 303 chamber, and 306 expanded polystyrene systems in 2005.  Study systems ranged in age from 2 to 12 years, gravelless systems were installed at a 25% trench length reduction compared to the length of a stone and pipe system, and all were distributed uniformly within the coastal, Piedmont, and mountain physiographic regions.  At a 95% upper confidence level, the NC DENR found no statistical difference in malfunction rates between stone and pipe and gravelless systems.

The North Carolina study is important relative to Virginia’s gravelless sizing policy because North Carolina’s trench bottom area is consistently smaller than Virginia’s, due to daily flow and loading rate policy.  With similar coastal, Piedmont, and mountain soil textures between the neighboring states, sizing proven to function satisfactorily in North Carolina will function at least as well in Virginia.  For instance, for a 3-bedroom home in a 50 mpi soil, the minimum 3-ft-wide gravelless trench length in North Carolina would be 180 ft, while it would be over 50% longer in Virginia at 284 ft.  The additional length required in Virginia provides substantially more bottom area and sidewall for wastewater infiltration.

Longevity Research:  Other studies have been conducted to examine gravelless system longevity and treatment capability.  The University of Maine conducted a study on chamber systems at least 20, and up to 30 years in age. Regulatory agency records showed that, at a 95% upper confidence level, gravelless systems at a 50% sizing reduction compared to the sizing of a stone and pipe system outperformed stone and pipe relative to number of required repairs.

Treatment Research:  The Colorado School of Mines conducted a treatment efficacy study on operating gravel and chamber systems aged up to 11 years.  Percolate samples were analyzed from 1 ft beneath infiltrative surface for treatment performance, and effluent ponding was monitored in the chamber and gravel trenches. No significant difference was observed in hydraulic or treatment performance between the gravel and 50% reduced length chamber systems. 

Numerous additional third-party studies have been conducted on gravelless technologies and are available upon request from Infiltrator Systems.  If interested in reviewing these studies, please do not hesitate to contact me at 800-221-4436, and I can provide them to you.