WALNUT CREEK -- The high-stakes battle over a coveted $500 million garbage franchise in central Contra Costa County is growing more intense as the two chief competitors jockey for position leading up to a scheduled vote.

Republic Services is in the lead after securing last month the Contra Costa Solid Waste Authority staff's recommendation as the preferred and less-expensive provider. And the company is confident it will refute recent allegations that it illegally dumps food waste into landfills and fails to compost yard clippings.

Representatives of Mt. Diablo Recology, a new partnership between Garaventa Enterprises and a San Francisco recycling company, are fighting back with repeat public appearances before the five city councils and the Contra Costa Board of Supervisors. The franchise encompasses portions of the county and the cities of Danville, Walnut Creek, Orinda, Moraga and Lafayette.

"This isn't sour grapes," Mt. Diablo Recology spokesman Jim Nejedly said. "We don't feel our proposal received an apples-to-apples comparison."

The authority's 12-member governing board is set to take up the franchise discussion Thursday. The board is scheduled to meet from 8 a.m. to noon at Oak Hill Park Community Center in Danville.

The board will also hear findings of an independent consultant hired to investigate the California Compost Coalition's allegations that Republic Services is improperly managing the Keller Canyon landfill in Pittsburg.

The coalition cited as evidence of improprieties numerical discrepancies in annual reports that detail how much waste is collected, how much is recycled and how much goes into landfills.

If true, it could jeopardize Republic Services' lead heading into the vote.

Republic Services General Manager Tim Argenti vehemently denies the assertions.

"We have provided the staff and the independent investigator records that clearly show we compost and that we absolutely do not put food waste in the landfill," Argenti said. "For some unknown reason, these tonnages were omitted from the reports, and it opened the door to these false allegations."

State and local inspection records support Argenti.

Regulators have reported one instance since 2007 in which Keller Canyon operators improperly used yard waste, according to CalRecycle's database.

Republic was also dinged in 2009 for failing to adequately control litter. Six violations in 2011 involved excessive methane emissions associated with the installation of a new gas-recovery system. There have been no warnings or violations reported since July 2011.

Overall, inspectors recorded eight violations and 46 warnings at the Pittsburg landfill during 83 on-site visits in the past seven years.

For comparison, the Potrero Hills landfill in Solano County, where Mt. Diablo Recology proposes to haul the trash, received 17 violations and 31 warnings during 93 inspections in the same time frame.

In the January 2007 violation recorded at Keller Canyon, an inspector found unprocessed yard waste in the heavy layer used to cover the landfill nightly as a vermin and odor deterrent.

Green waste is allowed, but it must be ground into pieces of 6 inches or less, regulators say.

Like many operators, Keller Canyon uses processed yard waste in its nightly cover material. But it also composts green waste at its Newby Island facility in Milpitas.

The new franchise agreement -- no matter which provider prevails -- will require 100 percent composting of green waste as the authority moves to meet a state goal of diverting from landfills 75 percent of trash by 2020, said authority director Paul Morsen.

Experts commissioned to analyze the franchise bids concluded that while both companies are qualified and capable, Republic Services' service costs, paired with Pacific Rim Recycling of Benicia, is $38.2 million a year, $1.2 million a year cheaper than that of Mt. Diablo Recology.

The bottom line matters because garbage rates are based largely on the operator's costs.

Nejedly, with Mt. Diablo Recology, argues that those same experts failed to properly factor all the dollar differences between the proposals.

For example, he said his company will purchase an all-new compressed natural gas fleet while Republic proposed a phased garbage truck purchase plan in response to the authority's request for reduced costs.

Nejedly also contends that its state-of-the-art Pittsburg transfer facility -- where recyclables are separated from waste -- is superior to the competitor's, and the jobs would stay in the county.

In addition, the company says Republic is intentionally keeping out competition by charging other haulers higher Keller Canyon fees.

Mt. Diablo Recology's bid calls for hauling trash to Potrero Hills landfill in Solano County because it is cheaper, Nejedly said.

"In the final analysis, we believe our proposal is actually less expensive than Republic's," Nejedly said.

The experts fully examined the competing proposals and concluded otherwise, countered Republic's Argenti.

The allegations and arguments are "last-minute, desperate attempts by the competition to try and blow up the process," Argenti said.

if you go
What: Central Contra Costa Solid Waste Authority will meet and possibly choose a provider for a 10-year, $500 million trash hauling and recycling franchise agreement.
When: 8 a.m.-noon, Thursday
Where: Oak Hill Park Community Center, 3005 Stone Valley Road, Danville
Agenda and additional information: www.wastediversion.org