Methodology and Assumptions

Solid Waste

Recycling:

Calculating Recycling Quantity:
Calculations require the following:
Size of the container & frequency of collection or change (∆) in the size of the container and/or frequency of collection post-outreach.

One of the following density factors is used:

1.       Paper = 300 lbs/cy

2.       Paper, plastic, metal =  220 lbs/cy

3.       Plastic, metal = 150 lbs/cy

4.       Glass = 600 lbs/cy

Calculating Carbon Emissions:
We use an emissions factor of -2.14 tonsCO₂e per ton (U.S.) of mixed recycling.  This is equal to - 1.94 metric[1] tonsCO­₂­e reduction in emissions per ton of recycling[2].  

Composting:

Calculating Compost Quantity:

We calculate quantity of organic material diverted from the disposed (waste) stream using a density factor of 300 lbs/cy, which is applied to the size of the container and the frequency of collection. 

Calculating Carbon Emissions:

We use an emissions factor of -0.93 metric tonsCO₂e per ton of organic material composted[2]. 

The following assumptions were made to calculate the emissions factors for recycling and composting:

1. The marginal energy source in the Pacific Northwest is assumed to be natural gas, which is important if captured methane displaced the use of natural gas for electricity generation. 
2. A 75% collection of landfill gases is assumed and this gas is used to produce electricity (e.g. Allied Waste's Roosevelt landfill).
3. The "mix" of recycling is equivalent to the current composition estimate for the city's curbside recycling program[3].
4. Recycling has upstream pollution prevention benefits.  These are the emissions reductions that result when recycled materials are used in place of virgin feedstock to produce new products. 
5. Composting has upstream and use-phase benefits where the use of the compost replaces or reduces use of pesticides and synthetic/petroleum-based fertilizers (the production and transport of which have their own upstream effects). 
6. Emissions are produced in the collection, transfer and landfill disposal of recyclable and compostable materials as well as from collection, and composting or recycling of those materials.

Calculating Cost Savings:

We use the City of Seattle’s solid waste rates for 2009 ($135.00/ton)[4] to calculate the savings accruing to businesses as material is diverted from the waste stream.

 Water:

Calculating Water Savings:

 The Resource Venture database allows staff to target businesses with the highest modeled[5] water usage.  A team of Resource Venture technical experts visits these and other businesses requesting water conservation assistance and identifies conservation opportunities.  These include water savings by switching to more efficient fixtures and appliances and upgrading heating and cooling systems.  Additionally, we assist businesses in upgrading water fixtures (e.g. toilets and aerators) and based on use, estimate the water savings from the upgrades.

 Calculating Carbon Emissions:

 Carbon emissions are associated with the energy required to treat and pump water for the public water supply system as well as to treat wastewater at the wastewater plant.  We assume it takes 1.16 kilowatt[6] hour (kWh) to treat and pump 748[7] gallons of water into the public supply system and 1.15 kWh/748 gallons to treat it at the wastewater plant.  The emissions factor for this electricity is 0.00001 metric tons CO₂e.

Calculating Cost Savings:

We use the City of Seattle’s water ($3.78/748 gallons)[8] and sewer rates ($8.89/748 gallons)[9] for 2009 to calculate the savings accruing to businesses as water is conserved.  It is assumed that 73% of water that is supplied to the customer leaves the facility as wastewater[10].