I have a pond of water that has a pH of 4 due to sulphuric acid coming
from the sulphur in the clay. How many pounds of calcium hydroxide per
gallon (or lb.) of water do I need to neutralize the water? I need the
answer in increments of pH from 3.0 to 6.0.

Here is the calculation you need to complete in order to figure out
how much calcium hydroxide you need for a given pH:

The pH equals the negative logarithm of the concentration of hydrogen
ions in moles per liter.  Therefore, for a pH of three, the
concentration of hydrogen ions is 10^-3 moles/liter.  Sulfuric acid
has a molecular weight of 98.1 g/mole which means there are 0.0981 g
of sulfuric acid per liter of water.

0.76 g of calcium hydroxide are required to neutralize each gram of
sulfuric acid.  This means that for a pH of 3, 0.0746 g of calcium
hydroxide are required per liter of water.  This equates to 0.0006213
pounds of calcium hydroxide per gallon.

Therefore, for a pH of 3, you will need approximately 6.22 pounds of
calcium hydroxide for every 10,000 gallons to be treated.  Each
increase in pH by 1 results in 10 times less calcium hydroxide being
required.  So, for a pH of 4, 6.22 pounds of calcium hydroxide will
treat 100,000 gallons of water.  For a pH of 5, 6.22 pounds of calcium
hydroxide will treat 1,000,000 gallons of water.  For a pH of 6, 6.22
pounds of calcium hydroxide will treat 10,000,000 gallons of water.

Alternatively, you can divide the pounds of calcium hydroxide per
gallon calculated for a pH of 3 by 10, 100, or 1000 and multiply by
the quantity of water to be treated in gallons to determine the number
of pounds of calcium hydroxide required in the case of a pH of 4, 5,
or 6.

"Hydrated lime (calcium hydroxide) is the most commonly used reagent
and reacts with AMD as shown by the following equation:

H2SO4 + Ca(OH)2 Þ Ca2+ + SO42- + 2H2O

Hydrated lime can be introduced dry or as an aqueous solution. One lb
of sulfuric acid needs 0.76 lb of calcium hydroxide for
neutralization, or equivalently, 1.00 kg of sulfuric acid needs 0.76
kg of calcium hydroxide for neutralization. Skousen (1989) reports
that when neutralizing large amounts of AMD with high acidity levels
for long periods of time (greater than 3 years), the more capital
intensive but cheaper hydrated lime reagent is generally used.
Hydrated lime treatment systems require a power source for mechanical
mixing of the lime with the water and pH meters to control the
application rate."

"Chapter 6 - Mine Drainage Treatment Facilities"
http://www.dep.state.pa.us/dep/deputate/minres/districts/Eng_Manual/chapter6.html

Additional source: "Chemical Principles" Fourth Edition By Dickerson,
Gray, Darensbourg, and Darensbourg, The Benjamin/Cummings Publishing
Company, Inc. (1984) Pages 56 and 165

Sincerely,

Wonko

Great answer, full of detail and confirmable calculations. Thanks for
the very quick reply. This allows me to fix my problem today.