BioCycle May 2006, Vol. 47, No. 5, p. 22
A social marketing-based survey of compost bin users in northern Oregon yields a high response rate and demonstrates an air quality benefit of home composting.
LOCATED in rural northeastern Oregon, the community of La Grande (population 12,500) has worked for years to reduce air pollution that is easily trapped in the scenic Grande Ronde Valley. The burning of yard trimmings and other debris has long been implicated as a significant contributor to air pollution in this area.
In 2001, La Grande began a yard debris composting program to give residents an alternative to burning yard debris. The city’s franchised garbage hauler, City Garbage Service, opened a yard trimmings drop-off site and composting operation, called “Waste Pro”. To further reduce the burning of yard debris, the city applied for and was awarded a solid waste reduction grant from the Oregon Department of Environmental Quality (DEQ) to purchase home compost bins. The bins cost roughly $50 each but were sold to households at a low price ($10 each). A total of 311 bins were sold to 303 households.
Home compost programs are more challenging to evaluate than curbside collection or yard debris dropoff programs because participation and waste diversion occurs largely out of sight of program sponsors. In order to evaluate the effectiveness of the compost bin program at increasing landfill diversion and reducing the burning of yard debris, the city and Oregon DEQ surveyed compost bin program participants more than a year after the bins were sold. The survey yielded an exceptionally high response rate (89 percent) and demonstrated a clear connection between home composting and reduced outdoor burning.
SURVEY DESIGN AND IMPLEMENTATION
A mail-back survey of bin purchasers was sent to all 303 households that purchased a bin. Prior experience suggested that most mail-back surveys only yield a 20-40 percent response rate. Low response rates introduce significant potential for nonresponse bias (respondents aren’t representative of the sample population). Several techniques from the field of community-based social marketing were applied to increase the response rate. Specifically:
Commitments: People that make a formal commitment to engage in a specific behavior are more likely to follow through. When residents first purchased their bins, they signed a simple contract with the city agreeing to leave the bin on-site if they moved out of La Grande and also to respond to a participation survey a year later. The cover letter sent with the survey reminded participants of their commitment.
Community norms: The cover letter was signed by the city manager, a community leader.
Incentives: Survey recipients were offered a free Natural Gardening booklet (provided by DEQ) if they responded to the survey form. They were also offered the opportunity to be entered into a prize drawing for two cubic yards of finished yard trimmings compost, donated by City Garbage Service. Sixty-nine percent asked for the booklet and 75 percent asked to be entered into the drawing.
Prompts: Three weeks after mailing the original survey, the city mailed a follow-up letter with another copy of the survey to nonrespondents. Four weeks later, a phone call was made to households that still hadn’t responded.
Almost 200 (198) of the 303 households responded to the first letter – yielding a 65 percent response rate without any prompting. The second letter brought the cumulative response rate to 83 percent, with only 52 households not responding. Telephone reminders to these 52 households brought in another 20 surveys, for a total response rate of 89 percent. By utilizing social marketing techniques, an exceptionally high response rate was obtained, thereby minimizing the potential for nonresponse bias. Of course, the fact that the survey population was self-selected (people who had already purchased a compost bin) also contributed to the high response rate.
More than a year after receiving their city-sponsored bin, 89 percent of respondents reported that they were composting some yard trimmings, and 82 percent reported that they were using the city-sponsored bin. Home composting rates for different materials are shown in Table 1. Although the survey did not ask specifically about composting food scraps, fully 55 percent of respondents reported that they were composting kitchen wastes as well, following bin distribution.
Among the 48 households not using their bins, 17 said that they tried but experienced problems with the bin itself, and another 14 reported not composting due to unrelated circumstances (moved, became too ill to garden, etc.).
NEW VS. SHIFTED DIVERSION
Both before and after bin distribution, residents had a variety of methods available to manage yard debris. Besides on-site composting, options included grasscycling, on-site chipping, hauling off-site for composting, disposing yard debris with garbage, and burning (both outdoors and indoors). Some households who purchased a bin were already composting at home. Further, the bin distribution program had the potential to shift tonnage away from the Waste Pro composting site and into people’s backyards, with no net reduction in disposal.
DEQ attempted to evaluate these dynamics by asking residents to describe how they managed each of four substreams (grass, leaves, green prunings, and woody prunings) both before and after they received their bins. The analysis was complicated due to the fact that many households use more than one method for each substream at any one time. For example, significant numbers of households (46 percent) report grasscycling (leaving grass clippings on the lawn), even as 76 percent report composting their grass clippings at home – clearly, some are doing both.
Among households responding to the survey, 130 (48 percent) were already composting some yard debris before they received their bin from the City. All but five of these households continued to compost at home, and reported an increase, on average, in the variety of materials composted.
Among the 141 respondents who weren’t composting at home before bin distribution, 118 (or 44 percent of all survey respondents) started composting after receiving their bin. Thus, bin recipients who reported composting at the time of the survey were roughly evenly divided between “former” and “new” composters, but even residents who had already been composting demonstrated benefits from receiving a bin.
Table 2 explores the relationship between the bin distribution program and deliveries of yard debris to Waste Pro, and demonstrates that most of the yard debris put into compost bins resulting from the city’s distribution program was not material that previously had been sent to Waste Pro.
Survey respondents – 27 percent – reported that they previously burned at least some of their yard debris outdoors. This finding was very consistent with results from a larger air quality survey of all La Grande residents undertaken about the same time, suggesting that households choosing to buy bins had started out as similar to other residents – at least as far as outdoor burning behavior was concerned. However, after receiving their bins, almost half of these households stopped burning altogether, dropping the practice of outdoor burning to 14 percent. Bin recipients, although relatively small in number, are now much less likely than other households to be burning yard debris. Details are shown in Table 3.
Even households who continued to burn yard debris reported burning fewer sub-types, on average. Further, the majority of households who eliminated or reduced outdoor burning did so by taking advantage of one or more of the nondisposal alternatives, such as home composting or Waste Pro, as opposed to sending yard debris to the landfill. The abandonment of outdoor burning by some households was also reflected in a 39 percent decrease in requests for open burning permits in the year that Waste Pro opened and bins were distributed.
The survey also evaluated the need for additional bins, benefits and problems associated with home composting, level of satisfaction with the city-provided bins and educational materials, use of finished compost, and interest in additional information and services. DEQ attempted to estimate the tonnage of material managed in the home compost bins – both total material as well as “new” diversion from disposal. This proved to be challenging given lack of information on per-household yard debris generation, volumetric estimations, volume-to-weight conversion factors of material “in the bin”, and the significant overlap between different waste management options. Full results including all data and the survey form itself are contained in an evaluation report that can be viewed on-line at www.deq.state.or.us/wmc/solwaste/data/LGReport.htm. The evaluation conducted by DEQ and La Grande demonstrated both a very high survey response rate as well as meaningful increases in home composting and reductions in open burning.
David Allaway is in the Solid Waste Policy & Program Development office of the Oregon Department of Environmental Quality based in Portland. E-mail: Allaway.David@deq.state.or.us.
May 24, 2006 | General
Surveying Residential Yard Trimmings Practices
BioCycle May 2006, Vol. 47, No. 5, p. 22