Log Assignment
LCA Assignment

Inventory and Implications

In order to estimate how much water, paper, and electricity an individual uses, and what that means in terms of environmental impact and management costs, keep a daily inventory of your water, paper, and electricity use.


1. Water

Make a table of your different types of water use in a typical day, and estimate the number of gallons in each use. Note briefly in your report how you estimated the amount of water.

2. Paper

Make a table, noting the following quantities of paper in units of 8.5” X 11” (note book) sheets you discard, per day (or week) under the following categories:

  • Recyclable paper
  • Amount of recyclable paper that you actually discard in a recycling bin
  • Non-recyclable paper (excluding newspaper)
  • Newspaper

We assume here that all the other paper you have or get will be stored by you somehow and will not reach the waste stream. Note in your report what errors this assumption introduces in your accounting.

3. Electricity

Make a list of appliances and other electricity use, estimation of their wattage and the duration (in number of hours) of use, and the total kilowatt-hours used per week.


  • Current in ampere (A or amp) X voltage in volts = power in watts
  • Using 1 watt over one hour, you use 1 watt-hour.
  • 1 kilowatt-hour = 1000 watts X 1 hour
  • (energy) = (power) X (time)


  • Population of Pittsburgh = 1.4 million
  • Electricity by Duquesne Light Company = 8% nuclear, all the rest coal. (Note: this was written when Duquesne Light supplied the electricity for all of Pittsburgh. This is no longer true. But, make this assumption any way.)
  • Approximate fraction of paper in solid waste = 37%
  • Paper: 1 ream = 5 lbs (14 - 17 trees used per ton of paper)
  • For coal-generated electricity:
    • 10,000 BTU/kWhe 1Kwhe requires 3 kWh th
    • 65 lb C / 100 lb fuel 1 lb fuel / 1200 BTU
    • 44 lb CO2 / 12 lb Carbon


Hand in a report that contains the following data and summarizes your findings, along with all assumptions made and sources of inaccuracies. This is still a good measure of a part of the direct impact each of us has on the environment.

Each report should contain:

  • Brief Introduction: Methods you used, any other introductory observations
  • Data tables: Provide clear tables of your daily use inventory.

Hand in Summary Tables of your use -- don't hand in rough work, and make clear the sources of your numbers. Design the tables and keep them in an accessible place so it is easy for you to fill them in regularly.

Set up calculations.

Section 1: Usage in Pittsburgh and Impacts

Calculate the paper, electricity, and water usage for Pittsburgh, assuming that you are a typical resident. What are the main sources of error in this assumption? Does each answer you get over-estimate or under-estimate the actual usage?

Tables for Section 1:
Paper, Electricity, and Water Usage in Pittsburgh

per person per day
(in lbs)

Total for city
for one year

Solid Waste (deduced from paper)

Table 1: Paper for Pittsburgh
(Note this ends up as part of the solid waste stream)




All other paper      

Table 2: Tree use for paper for Pittsburgh



Quantity/year for Pittsburgh


Table 3: Water use for Pittsburgh


  kWh/day/person kWh/city/year CO2 released
(tons per year)

Table 4: Electricity use and carbon dioxide release for Pittsburgh

Section 2: Environmental Burdens Posed by a "Student Life Cycle"

Based on your inventory, answer the following questions. You may do the following in groups of no more than three people, by combining results after you keep individual logs:

I. For a four-year stay at the University:

  • Approximately how many trees are used to generate the paper to support the education of one student?
  • Approximately how many tons of CO2 is released into the atmosphere by the student’s electricity use?
  • How many gallons of water had to be handled by the sewage system?

II. A. What are the sources of inaccuracies in your data? (For example, note that these data were kept only for a limited time; was your use during this time typical (truly representative) of your long-term use? You made several approximations and assumptions. Note these and say what type of inaccuracies this would introduce. )

B. Would you say your numbers are an overestimate or underestimate? Explain your answer.

III. What did this exercise clarify for you? (Think in terms of behavior, resource consumption, waste production, impacts, and possibilities for change.) Any surprises?

  ©Copyright 2003 Carnegie Mellon University
This material is based upon work supported by the National Science Foundation under Grant Number 9653194. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.