Hazardous Waste Auditing

B.Sc. Course(Second Semester)
University of Babylon-College of Engineering
Environmental Engineering Department

Hazardous Waste Auditing:
H.W audit :
The tracking of hazardous wastes within an industry , a waste transfer station or after excavation from a contaminated site.
The basic for H.W audit is a source material balance, which is the same as reactor balance.

Example:
If 20-208L (55gal) drums are generated per month that contain 800 mg/L trichloroethylene (TCE), the mass of TCE in the drums is:
20×208L=4160L
800 mg/L×4160L=330000mg
TCE=3.33kg TCE

One of the goals of pollution preventation programs is the optimization of process condition (reactor temperature and pressure), to improve yields of the products while decreasing the volume of side streams that contain unreacted materials and waste products.



Output Input

Losses [Intcorporation into products,volatization,spillage]

Figure8: Procedure for performing a materials balance to serve as a basis for waste audits.

For industrial synthesis processes (e.g., the production of pesticides, dyes, etc. from chlorobenzenes, chlorophenols, and anilines), most of the source material is converted to the products. One of the goals of pollution prevention programs is the optimization of process conditions (e.g., reactor temperature and pressure) to improve yields of the products while decreasing the volume of side streams that contain unreacted materials and waste products.
The primary routes by which unreactive wastes leave an industrial facility are :
1-industrial wastewater discharges,
2-RCRA-related waste management activities,
3-volatilization(e.g., fugitive emissions), and
4-spillage and other unaccounted losses.

Such unreactive wastes include solvents, paint removers, and other chemicals that are not consumed in chemical reactions. Chlorophenols, hexachlorocyclopentadiene, and other industrial intermediates are usually consumed in chemical reactions during industrial synthesis processes, and their output is usually minimal. In fact, the goal in the chemical processing of reactive materials is to incorporate these intermediates into products. They are the building blocks of the products of synthesis, and the presence of an unreacted intermediate results in extra cost. The use of a hazardous waste audit for tracking wastes in industrial facilities is demonstrated in below example.



Example : Hazardous Waste Audit of a Waste Transfer Facility
The state regulatory agency has accused your company, a waste transfer facility, of massive spillage due to improper housekeeping practices over the past year. The agency alleges that the upper 5 cm of the soils on your property (approximately 140000kg of soil) are contaminated with polychlorinated biphenyls (PCBs) above the regulatory action level of 50ppm. You can sample your property and analyze the soils for PCBs to refute the agency s claims, but the cost is estimated at $60000. As an alternative, perform a waste audit on the transformer oils that were exchanged at the waste transfer facility over the past year. Based on your company s records given here, can you show that PCBs were not spilled on the property at a level greater than 50 ppm? Because PCBs are characterized by low volatility and water solubility, you can assume that volatilization and leaching losses were negligible.



Solution:
Determine the incoming mass of PCBs to the waste transfer facility.


Determine the mass leaving the facility.
Wastewater:
1890000 L?day×365 d×0.002 mg?L=1.38 kg



Because the total mass unaccounted for in waste disposal practices is less than the regulatory action level, a case could be presented to the state regulatory agency that the losses do not provide sufficient PCB concentrations in the soil to exceed the regulatory action level.

Hazardous Waste Site Assessments
Abandoned landfill, surface impoundments, and other hazardous waste sites must be assessed to determine the extent of contamination before cleanup is initiated. Unlike municipal wastewater or industrial waste streams, hazardous wastes disposed of improperly at waste sites are not usually evident to the naked eye because most of the contamination lies below the soil surface. Therefore, a series of site assessment procedures must be conducted, ranging from record searches to detailed subsurface sampling.
Site assessments follow a common procedure that is divided into three phases, each of which is increasingly complex. Site assessments are initiated whenever the existence of a hazardous waste site is suspected, which may include a leaking underground storage tank (UST), the discovery of hazardous chemicals in a drinking water supply, a high incidence of localized illness, or a routine property transfer. The pattern is much the same for small sites as for large ones. In fact, the Preliminary Assessment and Remedial Investigation/Feasibility Study (RI/FS) programs of CERCLA follow the same format as the general site assessment phases described below.
The three site assessment phases are appropriately named Phase I, Phase II, and Phase III, and each builds upon the previous phase with more extensive information. A Phase I assessment, which may also be called a Level1 assessment, preliminary assessment, or initial assessment study, is begun in an attempt to confirm the suspicions of the presence of hazardous waste. The procedure focuses on "soft" or non.

The primary routs by which unreactive wastes leave an industrial facility are:
1-Industrial waste water discharge.
2-Volatilization.
3-Spillage and other uncounted losses.

Hazardous Waste Site Assessment:
There are three site assessment phases each builds upon the previous phase:
1-PhaseI [level 1, preliminary, initial assessment] start with:
a-A search of historical documents including newspaper, reports of spills, official records of any safety violation that may have taken place.
b-Also focus on information from the past few decades.
c-On site inspection and personal interviews.
d-Awalk-through of the site can provide class of improper waste disposal.

2-Phase II
a-Confirm the presence of hazardous waste at the site[depending on phase I].
b-Finalizing any record searches that were not completed in phase I assessment.
c-A detailed evolution of pathways and potential receptors is begun, include analysis of surface to assess ground water flow directions and travel times of drinking water wells or other receptor.
d-Involve an increased sampling effort based on where the contamination is expected, if phase II studies show that the site is contaminated.

3-Phase III
Study is initiated.
Investigation is to detail the extent of contamination in terms of area , volume, and the contamination concentrations. [soil, subsurface and / or groundwater may be sampled extensively lead to provide sufficient information to assess the site hazard and provide criteria for the design of remedial processes.
Example:
A1890-L (500gal) tanker containing a 40% formulation of 2,4-D in acetone has spilled contaminating an area of soil approximately 200m2 and 50cm deep-if the soil bulk density is 1800 kg/m3 estimate 2,4-D concentration in the soil?
Sp.gr.(2,4-D) 1.416

Source Sampling:
Sampling of source materials, including contaminate soil, lagoons and drum contents is necessary to assess their degree of hazard and to comply with regulations.

Statistical Fundamental For Sampling:
Two fundamental statistical concepts that are important in developing sampling plans they are:
Accuracy: How close a measured values is to the true value.

Precision:
The measure of the variability between samples. Soils and sludge s are characteristically heterogeneous, and the concentration of hazardous chemical in each subsample is likely to be quite different as a result, hazardous waste samples are often characterized by low precision and high variability.

Statistical analysis are concerned with some aspects related to accuracy and precision:
1-The level of accuracy must be specified
?=error allowed
1-?=is the corresponding confidence level.

Example:
A specified error of 5% correspond to a 95% confidence that the sample value is an accurate estimate of the true value.

2-Precision required (D) is the deviation from the true value , in H.W management, this value represented by a regulatory standard such as TCLP [Toxicity Characteristic Leaching Procedure] value.

3-Population: represents the true value of the global data set for the system under consideration, may be thought of as the universe of data within the system boundaries, may be described by such parameters as a mean [?] with a variance [?^2 ] and standard deviation [?].

A sample is a data set regardless of size, collected from population. Sample variable include data point [x_i ] and the number of data points in the sample [n].
The sample mean [x ? ] is:
x ?=(??x_i )/n
variance?S^2=(??(x_i-x ? )^2 )/(n-1)
The sample standard deviation S=?(S^2 )
Degree of freedom [df]: a parameter used in several statistical distributions, is an integer equal to the sample size [n]-no. of population parameter being evaluated through analysis of the sample.
In most cases, one parameter used df=n-1

Probability Sampling: is based on the t-distribution. A probability density function that is used to evaluate sample means when the population variance [a^2 ] is not known but can be estimated by [S^2 ].
The t-distribution is defined as:
t=(x ?-?)/(S??n)………………………………………………………………………………….(1)
S??n is also called the standard deviation of the mean [Sx ? ]. Values of [t] listed in tables.
Rearranging the above equation gives:
n=(t^2 S^2)/D^2 ………………………………………………………………………………...(2)
Where:
t = Students two sided t with n-1 degrees of freedom for a confidence level of (1-?)%.
S^2= the sample variance for the initial data.
D= a specified limit relative to the sample mean.
The value of D is derived from the term [x ?-?]

Table1:Procedures for the Simple Randomized Sampling of RCRA Hazardous Waste Sources

A specific application of equation 1 is the strategy for sampling RCRA waste sources, that is, determining the number of samples that needs to be collected, a procedure that is outlined in table1. A more general application of a sampling design is demonstrated in below example.

Example: Source Sampling Design
A drying bed holding sludge from an electroplating process is to be sampled for cadmium content. The dimensions of the drying bed are 6m×8m, and the sample volume will require an area 40cm×40 cm. five preliminary samples were collected randomly with the following results: 25, 36, 49, 28, and 48 mg/kg Cd. Based on this information, develop a simple randomized sampling scheme. Determine:
1-The number of samples required for 95% confidence limits within 5 mg/kg of the sample mean and
2-The location of the samples in the sludge bed.

Solution:
For the five preliminary samples:
x ?=(25+36+49+28+48)/5=37 mg/kg Cd
S^2=(??(X_i-X ? )^2 )/(n-1): (25-37)^2=144
? (36-37)?^2=1
(49-37)^2=144
(28-37)^2=81
(48-37)^2=121
(??(X_i-X ? ) =491) ?
S^2=491/4=123
S=?123=11
From the students t table , t_(95%)=2.776 (note:Use the ?=0.025 column,because 2×0.025=0.05[5%], which is the error level for the 95% confidence level). The number of subsequent samples (n) is
n=(t_(95%)^2 S^2)/D^2 =((2.776)^2 (123))/S^2 =37.9 samples;round up to 38 samples.

The number of sampling units in one direction is 8m/0.4m=20 units, the number in the other direction is 6m/0.4m=15 units. The 15×20=300 sampling units(Figure9) are numbered consecutively, and then 38 random numbers are selected from Appendix. Random number selection may be started at any point on the table: for this example, begin selection at line1, column5 and move down the columns. Three –digit numbers within the window 1 to 300 are taken from each group. During random number selection, only numbers within the range of 001 through 300 are selected (i.e., numbers outside of this range are disregarded). If a number comes up twice, it is ignored the second time, because it is assumed that the sampling unit does not contain sufficient medium to be sampled twice. Based on these procedures, the 38 locations of the random samples are

The locations of the sampling units are shaded in Figure9.
Stratified Random Sampling
The basis for stratified random sampling is dividing the site into layers, or strata, each of which is then sampled using randomized sampling techniques.


Figure9: Sampling grid developed for Example. The shaded sampling units have been selected using random numbers.


Volatilization:
The transfer of chemicals from solids or liquids to the gaseous phase.
Volatilization is function of contaminates, vapor pressure and Henrys Law constant
Vapor pressure of organic compounds ranges 10-10 mmHg to 760 mmHg at 20°C
Vapor pressure increased with temperature
Henrys Law States that the concentration of a compound in the aqueous phase is directly proportion to its partial pressure in the gaseous phase.
P=H.X
Where:
P=partial pressure (atm)
H= Henrys Law constant (atm. m3/mole)
X=Concentration of the compound in water (mole/m3)
Henrys Law constant is the best indicator of tendency of chemical to volatilize from water.

Volatilization Fluxes across liquid surfaces from an open container:
Hanna and Drivas provided a quantitative description of volatilization:
Q=?KA(V_P-P)/RT
Q= the evaporation rate (g/sec)
?=Contaminant molecular weight (g/mole)
K=A mass transfer coefficient per area A (m/sec)
R=The ideal gas constant (8.21×10-5 m3.atm/mole. k)
T=temperature (k)
VP=the saturation vapor pressure of the liquid (atm)
For most cases, P=0 because the container is open
Q=(?KAV_P)/RT
The ratio of two mass transfer coefficient may then be related to their gas diffusion coefficients:
K_1/K_2 =(D_1/D_2 )^(2?3)
Where:
K_1 ,K_2=mass transfer coefficients for compound 1,2
D_1 ,D_2=corresponding gas diffusion coefficients.
A well-documented method for estimating gas diffusion coefficients uses the following equation:
D_1/D_2 =?(?_2/?_1 )
Where:
?_1 ,?_2= corresponding molecular weights
Combining the above two equations
K_1=K_2 (?_2/?_1 )^(1?3)
Water is used as a mass transfer coefficient reference K=0.83 cm/sec.

Example: An open vat(1.25m ×0.75m ×0.3m deep) is used to store spent ?IBK prior to distilling it for reuse. The temperature is 20°C. estimate the rate of volatilization across the surface of the vat?

Volatilization Concentration in an Enclosed Area:
The calculation of the steady – state concentration resulting from volatilization is based on a mass balance on enclosed space below:





Contaminant Volatilization rate Qm(g/sec)

The rate of change of the hazardous compound in the system is:
(V d_c)/dt=Q_m-K Q_v C
Where:
C= the vapor , phase concentration of the compound (g/m3)
V=volume of the enclosed area (m3)
Qm=volatilization rate of the compound (g/sec)
Qv=ventilation rate for the enclosed area (m3/sec)
K=a factor that accounts for incomplete mixing.

Assuming steady-state
(V dc)/dt=0
Therefore, C=Q_m/?K Q?_v
Because C is more commonly expressed as ppm it may be converted using
C_ppm=C(RT/R?)×?10?^6
Combining the above equations
C_ppm=(Q_m RT)/(?K Q?_v P?)×?10?^6

Example:
A storage tank 1.5m in diameter containing waste toluene has been left open in a small RCRA 90-day drum storage area 220 m3 in volume. The temperature is 20°C and the atmospheric pressure is 1 atm. ventilation in the structure provides 12 changes of air per hour. Determine the steady –state toluene concentration in the structure. Assume k=0.2