Alternatives to Gravel Drainfields

1 SPRING 2005. Vol. 16, No. 2. Small Community Wastewater Issues Explained to the Public Alternatives to Gravel Drainfields ore than one-fourth The primary purpose of the Across the , engineers call for M of all American homes use some type of onsite wastewater treatment system, and thousands drainfield is to efficiently deliver effluent to the soil for absorption and subsequent treatment. Bacteria and viruses in the efflu- the use of aggregate (usually rock chips called Gravel , most often crushed limestone) in association with onsite wastewater systems in of new onsite permits are issued ent are removed by filtration and many capacities. Gravel is the each year. The most common sys- naturally occurring microscopic most common media used in soil tem involves a watertight septic organisms. Nutrients are absorption trenches. Gravel and tank followed by a conventional absorbed by soil particles or sand are the main elements in subsurface soil absorption system.

2 Taken up by plants. However, subsurface-flow constructed wet- Soil has a considerable capacity these processes only work in soil lands. There are many advan- to transform and recycle waste- that has air in it; the soil cannot tages to using rock chips in these water. Subsurface soil absorption be saturated with water. situations; it is generally avail- systems are reliable and the least able and reasonably priced. But Traditional Drainfields use Gravel expensive disposal option. there are regions of the country or crushed stone and perforated where Gravel is scarce, therefore Septic systems are wastewater pipes as a means to deliver the expensive, and existing supplies treatment systems that collect, wastewater to the soil. Gravel are being used up by the con- treat, and dispose of wastewater provides structural support for struction industry, thus the hunt generated by homes or business- the excavated trench, storage for alternative materials for use es.

3 Inadequate treatment of capacity during peak wastewater with onsite systems. sewage allows bacteria, viruses, discharges, and a home for the and other disease-causing growth of a bacteria layer where pathogens to enter surface and the treatment of the wastewater groundwater. occurs. 1. The conventional septic system consists of two main parts: a sep- Figure 1 A Typical Trench System tic tank and a soil absorption sys- 2. tem, also known as the 1 3. Inspection Port drainfield . The drainfield pro- vides the final step in the waste- water treatment process. A 2 Soil Backfill standard field is a series of 4. trenches or a bed lined with 3. crushed stone or Gravel and Barrier Material 5. buried one to three feet below the ground surface. Perforated pipes 4 Perforated Distribution Pipe or drain tiles run through the 6. trenches to distribute the waste- water onto the aggregate. See the 5 Gravel /Alternate Aggregate diagram at right.

4 6 Original Soil Alternatives to Gravel Properties of drainfield media Most natural aggregates are There are certain physical char- obtained by quarrying, which acteristics that an aggregate produces a number of environ- should have in order to be an mental problems. Quarrying cre- effective media in a wastewater ates large cavities in the distribution system. An aggregate landscape and the mining and used with onsite wastewater processing produces noise and treatment systems must be able dust pollution. At the same time to be crushed or chipped to meet the Gravel sources have become certain size specifications, yet not scarcer and more expensive, a contain too many fines tiny search has begun for the re-uses particles that can block flow of bulky products such as used between the larger pieces. The tires, glass, and concrete rubble, aggregate should be reasonably instead of sending them to a priced and handy to the location.

5 Landfill. These products have (The shipping cost for hauling potential as being excellent sub- Gravel over long distances is one of stitutes for common Gravel in the detriments to using that media onsite wastewater treatment sys- in some parts of the country.) tems. This issue of Pipeline will investigate the use of crushed Another required characteristic of glass, broken concrete, and rub- a good media is that the chips or ber tire chips to replace Gravel in pieces must remain separate areas where the supply is limited. from each other (in other words, Gravelless Drainfields systems as not pack down) to allow the flow optional effluent treatment are of water through the substrate. also presented. Effective media should not react chemically with the water or Shredded Tires degrade over time. Worn automobile tires have been accumulating at an alarming rate. A small percentage of these tires are recycled into other rub- ber-based uses; shredded or Problematic discarded chipped tires are being used for a Pipeline is published quarterly by the wide variety of products includ- tires can be turned into National Environmental Services Center at West Virginia University, ing playground covers and door- useful drainfield media.

6 Box 6064, Morgantown, WV 26506-6064 mats. But an estimated 250. Pipeline is funded through a grant from the million tires are discarded annu- Environmental Protection Agency ally in the United States. This Washington, The number of discarded tires equals about one tire per person Steve Hogye Project Officer used in onsite systems is signifi- Municipal Support Division per year. The disposal of these Office of Wastewater Management cant. For example, approximate- tires presents a difficult problem Rick Phalunas Interim Division Manager ly 30 percent of used tires in for solid waste authorities. Marilyn Noah Editor Oklahoma are now being used in Jennifer Hause Technical Advisor There are several drawbacks to Ed Winant PE Technical Advisor septic systems. John Fekete Senior Graphic Designer discarding used tires into land- Jamie Bouquot Graphic Designer Tires can be cut into small pieces fills: Whole tires sent to landfills by various techniques, and the Permission to quote from or reproduce articles in require a large amount of space, this publication is granted when due acknowledgement is given.

7 Physical characteristics of the tire Please send a copy of the publication in which information tires tend to float or rise in a was used to the Pipeline editor at the address above. chips, such as size, wire protru- landfill and come to the surface, an equal opportunity/affirmative action institution sion and fines can be controlled. and the void space provides Tire shreds are stable in composi- potential sites for rodents and tion, meaning they do not break mosquitoes. In response, a vari- ISSN 1060-0043 down into other elements and The contents of this newsletter do not necessarily reflect the views and policies of ety of innovative research proj- other elements do not leach from the Environmental Protection Agency, nor does the mention of trade names ects have attempted to find good or commercial products constitute endorsement or recommendation for use. them when exposed to the sun ways to use them.

8 Tire chips as a and water over time. There seems Printed on recycled paper substitute for stone aggregate in to be no difference in performance septic system Drainfields is one of between new and used tire chips. these possibilities. 2. PIPELINE Spring 2005; , National Environmental Services Center (800) 624-8301 or (304) 293-4191. Alternatives to Gravel Tire chips are three times lighter capacity by 30 percent because than stone aggregate ( , a the void space between the tire cubic yard of stone aggregate chips is greater than the void weighs 2,800 pounds compared space for Gravel (60 percent for to a cubic yard of tire chips that tire chips; 40 percent for stone). only weighs 800 pounds), mak- Several studies have shown that ing it much easier to work with. effluent showed similar values Tire chips are much cheaper for most of the important bio- than Gravel and have the added logical parameters used to benefit of not creating dust.

9 Measure effectiveness (such as (Dust is a nuisance and health biological oxygen demand, total concern associated with the pro- suspended solids, ammonia- duction and transport of Gravel ). nitrogen, nitrate, fecal coliforms, There is no significant com- and pH), were similar for the paction of the shreds; therefore, Gravel and the tire chips in the 12 inches of tire chips equals 12. trenches. Actually, these trials inches of Gravel . Porosity (the have been so successful that the desirable quality of large open demand for tire chips has grown spaces between the individual faster than the number of pieces) was found to be higher processors; in some areas, mak- with tire chips than stone. ing tire chips a scarce commodity. More than 17 states currently Using tire chips as an aggregate permit the use of tire chips or in onsite systems has gained shreds as a substitute media in favor in many states.

10 It would septic system Drainfields . The seem to be a win-win situation if major differences in state regula- a beneficial use could be found tions are in the percent of tire for a material that has been an chips meeting specifications environmental liability. While required and the oversight, tire chips are a proven alterna- inspection, and/or certification tive to Gravel , it will be up to of the tire chip specifications. approval from appropriate state Regulations in states where tire agencies to allow the market to chips are approved as a substi- Bottom layer of trench with six inches of expand to its fullest. tute for stone aggregate in onsite tire chips and four-inch pipe. systems require them to be of similar size as stone aggregate (approximately 2 inch pieces), with wire protrusions of one-half inches or less. Concerns for tire chip use include the handling of the chips with protruding wires.