Loading...
HomeMy WebLinkAboutWallace_Dr Rubin Report_20171126Interim Wallace Farm Operations Assessment By A. R. Rubin, Professor Emeritus, NCSU - BAE Background: The Wallace Farm operations in North Carolina have grown from the initial site near Mecklenburg County to a second facility in Davie County. The expansion was driven in part by public pressure exerted by an expanding neighbor base opposing operations at the initial site. In response management at Wallace Farm assessed the potential for expanding the service base into near-by areas and simultaneously expanding business opportunities. Following a lengthy search for suitable sites, the management at Wallace Farm in cooperation with local economic development staff identified a site in Davie County deemed suitable to the production of high quality compost from societal by- products. A site investigation indicated the site met the criteria established in the NCDEQ DWM Compost Rules (15 A NCAC 13B .0201). This site-specific information was included in a permit application for a compost system operation permit submitted to DWM. Included in this application were: compost system design plans and a compost site operations and maintenance plan, planning and zoning statements regarding operation of facilities in the area, wetland surveys, flood-plain maps and other materials required for permitting. Following appropriate administrative procedures (permit review and public announcement) a compost site permit was issued to Wallace Farm (Permit Number: 3004-Compost-2014). This current permit is due to expire on 17 November 2019. The facility was constructed in accordance with the plans submitted and the Wallace Farm Davie County operation began receiving compostable materials in the fall of 2014. In 2017 HB 244 (Public Participation/Composting Facilities) was introduced in the general Assembly and this bill appeared to put compost operations under some additional levels of regulatory and administrative review. Objectives: in 2017 Mr. Eric Wallace requested an independent assessment of the compost operation in Davie County. There were several stated objectives to the request including: 1. Review feedstocks and assessment of each for compatibility with the operation 2. Review procedures for receiving incoming feedstocks 3. Review mixing and blending operations 4. Review procedures and practices associated with windrow construction 5. Assess practices associated with windrow management 6. Assess off site impacts detectable during site visits 7. Report findings and provide recommendations Findings garnered from the three (3) separate site assessments are summarized below. 1. Feedstocks: Allowable feedstocks are listed in the Operations and Maintenance Manual initially submitted with the initial application and as condition listed in Attachment 3, item 8 of the NCDWM issued Permit to Construct and Operate as a Type 3 facility (24 November 2015). Allowable feedstocks include: animal manure, woody waste, yard waste, cotton crop material, meat, food waste, grease trap residuals, U. S. domestic tobacco crop residues, cardboard, bleaching clay, animal fats, virgin gypsum board, lime and starch water. These feedstocks are ideal as either a source of organic matter and nutrients required in a compost operation or as a bulking material that adds porosity to the mass of material composted. The operations and maintenance manual prepared for Wallace Farm provided some guidance on the ratios of these feedstock materials to optimize the compost operations. The most problematic of the feedstock materials are those that vary in actual quality; for example, food waste is highly variable. The actual quality of food waste may contain high levels of leafy and high moisture vegetables one day and the following day contain a high level of dry material such as baked goods, potatoes, and spent hot bar food. This variability renders mixing and blending as a challenge. The mix-blend operations ongoing in the mix pit did appear to render these incoming feedstocks well suited for subsequent compost operations in the windrows. The most critical of the assessments for the feedstock materials is the carbon, nitrogen and phosphorus level. The C:N and C:P ratios are important in operation of compost systems. Review of the feedstock quality and the quality of the finish product suggest the C:N and C:P ratios are suited to generate high quality compost. Optimum C:N ratio for compost is between 20:1 and 40:1. Ratios below the 20:1 often generate adverse odor. C:N ratios over 40:1 may slow the composting process. The feedstock blends should be monitored periodically to insure the C:N ratios remain within this optimum range. The list of feedstocks did not include wood ash and inspection of the facility did indicate a significant volume of wood ash on site. The permit to operate the compost system must be amended to allow for continued acceptance of this material. The addition of the wood ash to the compost feedstock list will allow acceptance of a porous, carbon based material that has exhibited good potential to contain odor generated during the compost production. The feedstocks permitted for the operation are all well suited to composting. All of the organic materials are high in energy value and are well suited for the operation. The nitrogen and phosphorus rich materials (tobacco and cotton waste, food processing waste and food waste) are all well suited for the operation. The list of feedstocks suggest the materials currently permitted at the facility are high in organic carbon, additional nutrient rich (N, P, and K) materials would improve the quality of the end product and the management at Wallace might examine additional N and P sources. Recommendation 1: Send request to NCDWM to add the wood ash to the list of permitted feedstocks. Recommendation 2: Seek additional feedstock materials high in N and P. 2. Receiving Procedures – There are two phases to the receipt of materials. All materials received pass through the weigh station and the material is logged into the facility. Inert materials such as noncommercial yard and leaf waste, landscape waste and other typically residential wastes are diverted to a receiving area specified for these landscape wastes. Individual homeowners typically deliver to this area. In addition, Wallace Farm employees collect ground, chipped or shredded yard waste from facilities throughout the service area and these inert woody wastes are diverted to a staging area for use as bulking material/carbon sources in the compost operation. A third category of incoming vegetative waste consists of dry agribusiness residues such as cotton waste or tobacco processing residues. Each of these dry sources is ultimately used in the compost operation and these materials pose no significant aesthetic concerns when used in a timely manner. The second phase of the receiving operation involves the dispersal of the commercial potentially putrescible materials into the operation. These materials are directed from the incoming weigh station directly to the mix pit. The individual vehicle operators discharge these materials directly into the pit along the proximal portion of the pit against the concrete push wall. These materials typically consist of food waste, FOG waste, and food processing residuals. Vehicle operators do wash the tank and trailer beds prior to leaving the facility; these wash-down products are introduced into the mix-pit. The mix-pit barrier wall is open along portions of the structure to allow wash-down materials that may have fallen on the receiving pad to wash into the pit. Vehicle operators are responsible for cleaning the pad if necessary. The procedures to track incoming materials appear well conceived and well executed. No commercial material enters the facility without passing through the scale house. 3. Mixing and Blending: Mix Pit operations are now well developed and incorporation of these potentially putrescible materials into the leafy organics and woody waste is routine. These practices have been refined to minimize adverse aesthetic consequences. The policies and procedures for receiving incoming materials are well choreographed. FOG waste and food waste, each of which exhibits significant potential to generate odor, are incorporated into a large mass of organic waste typically within an hour of receipt. The mix-pit operator places a large mass of leaf waste, against the proximal wall of the pit and as the potentially odiferous materials are added to the pit, the operator covers the incoming feedstock with this mass of organics. This procedure helps to control odor in the facility. The operator has a well-developed lift and drop procedure to assure the incoming material is thoroughly mixed and blended with the leafy organic material. This assures the material will compost well and controls odor. In addition to this procedure for incorporating the materials, the operator incorporates wood ash into the mix and the organic carbon acts as activated charcoal to hold and trap odor. Mix pit operations were observed (figures attached) on three different days (27 April, 30 June, 10 July). The procedure was consistent during all site visits, including the un-announced visit to confirm the practices were routine and not staged. The mix pit operator is skilled at mixing and blending incoming materials to minimize potentially adverse conditions. During each of these visits, operators were cognizant of wind speed and direction and operations were tailored to address these conditions. During each visit the materials received in the mix pit were processed (thoroughly mixed and blended) and removed by late morning. The pit was empty by the lunch break and again at the end of the workday. The mix operation and the delivery of the blended feedstock to the individual windrows is accomplished by dump bed vehicles. The mix/blend/load operations are well coordinated by staff; each of the various vehicle operators coordinates activities into a near seamless operation. During the initial announced site visit, there was a vehicle mishap that resulted in a deflated tire, but could have been much more serious. As a result of this mishap, vehicle ingress into the mixing area and egress from the pit is better controlled. Conversation with staff indicates this procedure has reduced the time required in the process and improved safety on the site. Mixed and blended materials are transported continuously from the pit to the compost area until the various feedstocks proposed for composting have been removed. Placing these materials into the windrows promptly reduces potential for odor and insects at the pit. 4. Windrow Construction: Compost feedstocks produced through the mixing and blending operation are transported to the windrow area via dump bed vehicles (figures attached). These dump bed vehicles are capable of transporting 10 to 12 of freshly blended feedstock cubic yards per trip. The vehicle operators place the feedstock at a designated location in the compost area and once windrow construction is initiated, the operators simply place additional materials in the windrow until the desired windrow length is achieved. Windrows measure approximately 5 feet in height and 16 to 20 feet in width. Windrow length will vary depending on the location in the windrow area. Once a windrow is established, woody material (sawdust, ash, wood chips) is spread over the windrow using a modified Knight Spreader. The spreader has been modified to gently place this odor scrubbing layer along the outer edge of the windrow rather than sling the material as is typical with a Knight Spreader. This practice is unique to Wallace Farm and reflects concern for neighbors. The windrows are typically formed as long, narrow windrows extending to a height of between 5 and 6 feet. The windrow is turned initially following construction typically within a few days to assure materials are thoroughly mixed and blended. These are standard practices in the operation of a windrow operation. Placement of the finished compost, sawdust or wood chip on the top and sides of the newly formed windrow as odor control is an exemplary practice and was developed by personnel al Wallace Farm. 5. Windrow operations: Windrows are left quiescent for several days until temperatures rise over the required 131 degrees F and the windrows are then turned using a self propelled Backhus drum turner or a smaller tractor towed drum turner. The time/temperature requirements imposed in Rule mandate a temperature in the windrow mass over 131 degrees F for a minimum of 15 days with a minimum of 5 turning events. These activities are practiced on the site. Windrow operations were observed throughout the assessment with the final assessment to address the operation of the large Backhus turner in September 2017. At no time during the assessment were significant adverse odors observed more that 50 feet from an active windrow turning as accomplished through this evaluation. Odor assessed was typically fishy suggesting ammonium and piercing as suggested by volatile fatty acids. These odor producing compounds were not detected in older, more mature windrows, but were in the windrows that were typically less than a month old. Temperatures are monitored in the windrows as required by Rule and as described in the Operations and Maintenance Manual (figure attached). Staff from the facility accomplishes the required temperature monitoring and this information is used to schedule windrow-turning operations. Windrows are turned as necessary to accomplish compliance with rule. The timing of windrow turning is critical in a compost operation. Ideally compost windrow turning should be performed early in the day and no later than 3 PM. This is critical since rising air currents can lift odors into the atmosphere where they dissipate. This is one of the strongest recommendations =to follow from this evaluation – turn windrows before 3 PM. Material that has been composted and meets the required time and temperature to establish rule compliance remains in windrows for several months before the compost is moved to storage piles. This within windrow curing time helps assure that the finish compost moved to storage is mature. No adverse odor was detected as windrows containing the mature compost were dismantled and the product was transported to the storage area. Other windrow area operational needs include removing water pooled or ponded at the base of windrows. Liquid does migrate downward through a windrow. The accumulation of liquid at the base of a windrow may be liquid that migrated through the windrow, rainwater that was diverted from a windrow to the adjacent soil, or a combination of both. Regardless, the liquid accumulating at the base of a windrow may generate odor. Typically the liquid does exhibit a significant Biochemical Oxygen Demand (BOD) and BOD does often generate odor. There is a natural transfer of air from the atmosphere to the land surface and these areas of saturation are exposed to air that will satisfy a small portion of that BOD, unfortunately the air supplied by natural processes is inadequate to satisfy all of the oxygen demand and odor is common. Operators at the facility did make attempts to minimize the liquid retained at the base of the windrows through grading and placement of wood chip. These are good site management practices and may be required on a more frequent timeframe than currently practiced. 6. Offsite impact assessments: during each of the site visits and on several occasions when traveling westward on I 40 off site impacts were assessed. The assessment consisted simply of smelling the air along the interstate highway. The smell test was accomplished both by my wife and me. On one occasion (4 September), odor was detected by both of us. On one occasion (6 September) I was the only one detecting odor and it was very faint. On a third drive-by (17 September) no adverse odor was detected either in the morning or evening. The odor was detected before 9AM at the low area between Wallace and the Winery. No other off site impacts were noted during these off site assessments. Off-site impacts can be best managed by following the management practices outlined in the Operations and Maintenance Manual and by assuring windrows are not turned early in the morning when odor can be trapped in the area or after 3 PM when rising air currents begin to settle and retain air near the surface. A second practice is to continue to manage water accumulating at the base of windrows. Conclusions: The Wallace Farm operation in Davie County is an excellent example of an operation that transforms waste resources into valuable end product. The feedstocks used to produce these resources are by-products and waste materials generated by our patterns of consumption. These materials can generate odor as they decompose. The compost process is intended to be an aerobic process. Aerobic conditions tend to reduce odor and the operators maintain good aerobic conditions within the windrows as indicated by the high temperatures generated in the process. Mix pit operations are often associated with generation of adverse odor. The operation at the mix pit assures mixing of incoming feedstock with stable organic matter like wood chip, leaf waste, and organic material generated in leaf processing operations. Windrow construction can be a source of odor. The windrows are constructed within a few hours of receipt of materials on the site. The windrow construction is followed by placement of stable organic material over the mass of organic material in the windrow. The stable organics help control odor in the windrow area. In general, the compost operation is following practices that are intended to minimize adverse impacts. There is no method I am aware of that will reduce odor 100% of the time. The intent is to manage and reduce odor as much as possible and the manager and staff at the Davie County Wallace Farm operation are following good practices. Respectfully Submitted, A. R. Rubin Figure 1: Site overview Initial view of site is of a clean, well managed facility and this image follows through the entire operation. Figure 2: Mix pit - wet Mix pit operation addition of liquid waste into preformed receiving area facilitates drying of liquid waste and reduces potential for odor. Figure 3: Mix pit with commingled feedstock ready for transport to windrow: note material is dry and no leachate at base. The mix-pit operator prepares receiving area with thick layer of leaf waste and berms the area to reduce potential for liquid to migrate outside the preformed receiving area. The operator mixes material using a lift and drop procedure that facilitates good mixing. The mixing is necessary to achieve high quality compost; it assures well-mixed feedstocks and that minimizes potential for adverse conditions during the composting operation. This is the most critical of the operations at this or any compost operation. The mix pit operator is skilled. Figure 4: Windrow formation Windrow formation involves placing the freshly blended feedstocks into uniform windrows. The windrows are typically 5 to 6 feet in height and the length varies depending on the site where the windrow is formed. Once the windrow is fully formed, a layer of finished compost or sawdust/woodchip is placed over the entire newly formed windrow. This practice is unique to Wallace farm and is an excellent practice to control adverse impacts such as odor and vectors. The practice will not eliminate these conditions, but will minimize their impact on the overall aesthetic of the operation. Figure 5: Windrow turning – Larger turner: significant volume Windrow turning is necessary to comply with Rules established by NCDWM to control pathogens and reduce vector attraction. Records indicate that the turning is accomplished as required by rule. The large drum turner is capable of moving large volumes of composting material in a short time. The large turner effectively moves material from near the soil surface up into active compost zones in the windrow. Small Turner: limited volume Windrow turning is necessary to comply with Rules established by NCDWM to control pathogens and reduce vector attraction. Records indicate that the turning is accomplished as required by rule. The small turner is capable of moving material effectively from the base of the pile into active zones within the windrow, but may be limited in moving material close to the surface of the pad into the mass of composting materials. Figure 6: Windrow temperature must me monitored frequently to assure the material remains above 131 degrees F for the required 15 days as described in Rule. Temperature monitoring in the compost windrows demonstrate temperatures in all of the active windrows is well above the minimum required 131 degrees F. Mature windrows (those over 60 days in place) show high temperatures and this assures reduction of compounds that may be odiferous and of organisms that may cause disease.