“When the quantity and quality of the gas declined as a result of site remediation, co-generation was no longer commercially viable, so today we flare the methane,” said Butler.
To meet Colorado's monitoring requirements, WMC monitors the landfill gas probes at the former landfill property boundary quarterly. In response to the Douglas County Sheriff Department's concern for public safety, South Suburban began monitoring after the athletic fields were opened to determine if any adjustments were required to the gas collection system. WMC also monitors the vacuum pressure at the wellheads to confirm that operating conditions are within required standards.
After installing the methane collection system, WMC compacted a 2-foot clay soil cap over the landfill. That cap challenged ACC in both design and construction. ACC covered the clay cap with a $250,000,30-mm linear low-density polyethylene liner topped by aggregate to drain off any rainwater or snow-melt soaking through the fields and the common areas. McLaughlin Water Engineers of Denver designed the offsite detention pond to hold that water until it could be routed into the storm sewers.
In a usual construction project, the contractor would cut and fill the 5% graded topography to achieve a 1% slope for the playing fields. “In this instance with the clay cap, cutting wasn't permitted, so we brought in 60,000 cubic yards of select fill to level the area for the fields and parking,” said Wesley W. Homer, ACC project manager. “We didn't accept just any fill: we needed a Class A2 non-expansive soil so the fields above the cap wouldn't move,” said Woodcock.
The clay cap also affected the design of the baseball backstop. In order not to penetrate the cap, the supports for this 30- foot high structure are 2-foot deep concrete outriggers. Another design change to the backstop addresses the five nearby radio towers. Fiberglass poles and nylon netting were used above a 10-foot elevation to eliminate metal at a height that could reflect the radio waves.
ACC built the park without water or sewer lines so no water can ever leak from utility pipes into the landfill. But this means there are no permanent concession stands or restrooms, only portable chemical toilets. Also to protect the synthetic turf no pets, chewing gum, or smoking is permitted in the park. “I refer to this as a totally sustainable park,” said Woodcock of the “no-water” and “no utilities” features. The only phone is a solar-powered emergency phone connection, and, with the methane collection system still in operation, prominent signs warn, “No smoking!”TRASH TO TREASURE
In following the “trash to treasure” master plan, the park design relies extensively on recycled materials. Although most of the settlement occurred in the first 10 years after closure, the site may experience some residual settlement, said Butler. This makes paving the parking lot infeasible, so ACC treated the soil and installed compacted asphalt millings. The parking blocks are recycled rubber. The Prestige synthetic turf system is based on an infill made from 3 pounds per square foot of 0.5 to 1.5 mm scrap rubber tire aggregate (the Prestige System is marketed in the United States by Kiefer Specialty Flooring, www.kieferfloors.com). The walk-ways and roadway consist of compacted crusher fines, a byproduct of stone crushing operations. “Staplestone,” concrete blocks from the demolished Stapleton Airport runways, form the retaining wall of the practice field. WMC is funding an educational kiosk to be built at the site out-lining its history from the County Line Landfill in the mid 1960s to January 1987 and its subsequent transformation from “trash to treasure.”
At roughly S1 million per field— including the site preparation and synthetic turf—South Suburban has made a major investment, but with the savings in maintenance, Woodcock expects payback in 15 years. By comparison, a tournament size 2½-acre, natural-grass playing field costs the district $300,000 to construct and $4000 a year to maintain with the mowing, fertilizing, irrigating, weeding, and replacing sod in worn areas. Also, natural bluegrass fields need to be taken out of play periodically so the grass can recover.
Maintenance for the artificial turf includes a weekly brushing and, on an as-needed basis, decompaction of the system and additional rubber, said Mike McGraw, representative for the Prestige System. Woodcock adds that the district also regularly sanitizes the fields with a spray to remove blood, sweat, and tears. Since the fields are multi-use, only the sideline stripes are permanent. With the synthetic turf, stripes can be applied for soccer, lacrosse, rugby, or football and then washed off.
Lorenz cites a number of intangibles of the synthetic turf. In Colorado, particularly with the recent drought, water is a valuable commodity, so the district is environmentally conscious by building fields that don't require watering. Then because the synthetic turf is more durable than grass, players can start practicing in January while other parks don't open until mid-March. The district sometimes limits play on other fields to protect the grass while the synthetic fields can support unlimited play.