30 ENVIRONMENTAL, ENGINEERING
a value on an unspoiled wilderness area? Unfortunately, qualitative judgments are
required to assess many impacts of any project.
PROBLEMS2.1 Develop and apply an interaction matrix for the following proposed actions
designed to clean municipal wastewater in your home town: (a) construct a large
activated wastewater treatment plant, (b) require septic tanks for households and
small-scale package treatment plants for industries, (c) construct decentralized, small-
scale treatment facilities across town, (d) adopt land application technology, and (e)
continue direct discharge of untreated wastewater into the river. Draw conclusions
from the matrix. Which alternatives appears to be superior? Which environmental
characteristics appear to be the most important? What should the town do?
2.2 What conclusions may be drawn about the abilities of the three towns to
finance a proposed water treatment facility:
Debt per capita as Debt per full propertyCity Current Projected Current Projected Current ProjectedA $946 $950 22.3 22.3 15.0 15.1
B $335 $337 9.1 9.1 7.8 7.9
C $6 $411 0.1 10.7 0.1 8.6
Debt per capita % per capita income valuationDiscuss the current financial picture of each town as well as the projected incremental
impact of this new proposed construction.
2.3 Discuss the advantages and disadvantages of a benefitkost ratio in deciding
whether a town should build a wastewater treatment facility. Focus on the valuation
problems associated with analyzing the impacts of such a project.
2.4 Determine the average residential sewer charge for the three cities listed
below. What is the incremental impact on these charges if the cost of sludge disposal
increases as noted?Annual ProjectedWastewater % Flow Wastewater Sludge disposal
flow (mgd) residential treatment budget increase
A 20.0 60 $5,100,000 $1,500,000
B 5.0 90 $3,600,000 $1,000,000
C 0.1 100 $50,000 $20,000Discuss your assumptions.