# Other Questions

- pH of Organic Liquids
- Total Organic Carbon Methods for Soil
- Equation for Surface Area in Method 1110

#### pH of Organic Liquids

**Question: **Is Method 9045C (pH of solids) applicable to organic
liquid waste matrices?

**Answer:** Section 1.1 of Method 9045C states that the pH of non-aqueous
liquids can be determined by the procedure. Water should be added to the
non-aqueous liquid and mixed, because pH cannot be determined without
the presence of water. The non-aqueous liquid should be separated from
the water [aqueous phase] and the water analyzed. The water will contain
compounds that leached out of the non-aqueous liquid waste so that the
waste is not directly measured. Liquid organic wastes, such as oily wastes,
may damage the pH electrode if the electrode is exposed directly to the
oil.

**Note:** This does *not* mean that you must use Method 9045C
to evaluate non-aqueous liquids to see if they exhibit the RCRA characteristic
of corrosivity (40 CFR 261.22).

#### Total Organic Carbon Method for Soils

**Question:** Where in SW-846 can I find a method for total organic
carbon (TOC) in soil and other solid matrices?

**Answer:** There is no SW-846 method for TOC in soils. EPA does not
have any regulatory requirements that govern the total organic carbon
content of soils or solid matrices. Therefore, without a regulatory driver,
there is no need for a method for TOC in soil in SW-846. Soil scientists
have developed a variety of methods for TOC over the years. Some of them
are based on titration of "easily oxidizable organic carbon,"
while others involve the high temperature combustion of any organic carbon
in the soil and measurement of the resulting carbon dioxide. If you need
a method for TOC in soil, you should either consult the open soil science
literature or check with the environmental regulatory agency in your state
to see if they have a method of choice.

#### Equation for Surface Area in Method 1110

**Question:** The equation for the surface area of the stainless steel
coupon in Method 1110 is not clear to us. We have received widely differing
answers from different laboratories for the analysis of the same waste
and we believe it is because they calculated the area differently.

**Answer:** The apparent cause of the confusion is due, in part, to
the age of Method 1110, for corrosivity towards steel. It was written
at a time when word processing programs did not have the ability to display
equations as clearly as they do at present. However, going back to first
principles, the equation is used to determine the surface area of the
coupon. The area of a circle is determined from the familiar product of
the radius of the circle, squared, and the constant Pi. Since the radius
(r) is half of the diameter (d) of the circle, the area can expressed
in the three ways shown below.

**Area = II (r) ^{2} = II (d/2) ^{2}
= II (d ^{2}/4)**

The total surface area of the coupon is the sum of the areas of the two faces of the coupon, plus the area around the outside edge, plus the area around the edge of the hole in the center of the coupon. Sec. 4.5 of Method 1110 contains an equation that illustrates adding these areas together to determine the total surface area.

Some laboratories are apparently misreading the equation in Sec. 4.5 of Method 1110 and placing the two diameters in the first term of the expression in the denominator of the equation, not the numerator. Using the mathematical rules for the order of precedence of the operations of addition, subtraction, multiplication, and division, the equation shown in the method is correct. However, it is shown below in a format that is less subject to misunderstanding:

**A = [3.14 (D ^{ 2} - d ^{2})]/2
+ (t)(3.14)(D) + (t)(3.14)(d)**

where:

t = thickness

D = diameter of the coupon

d = diameter of the mounting hole

and 3.14 is a simple approximation of the constant Pi.