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Unformatted text preview: CEE 3104 (Mm) Exam 2 2007.11.01 HONOR CODE
I have neither given nor received unauthorized assistance on this exam.
Name Signature last, ﬁrst Potentially useful equations _ @552 = [41:95! E? = 4“
co/_c(BW AT] R1sk (CDI)(SF) Rm dt kC =>C(t) Coe 1
'1 4 =  — k 1/2 = (T20)
Cout=Coe°+Cin[1'e°i CM C°eXpi (19* it] 19:39" kr kzoe
H3/2 BOD, = M P = vs/Vtot L, = Loe'k’ L0 = BOD, + L, BOD, = L0 (1 — e'k’)
= M (e—kdt _ e—krt )+ Duek» ,c = 1 1n{_lgr_[l _ Da(kr — m}
[6,  kd k, — kd kd dea
Physical constants
Molecular masses H = 1.01 g mol'1 C = 12.0 g mol'1 N = 14.0 g mol'1
0 = 16.0 g mol'1 F = 19.0 g mol'1 C1 = 35.5 g mol"
Water density pm = 1000 kg m'3 = 1 kg L'1 = 1000 g L'1 = 1 g ml" = 1 g cm’3
Conversion factors
Length 1m=3.281 ft 1km=0.6214mi
Volume 1 m3 = 1000 L 1 113 = 0.02832 m3 1 gal (US) = 3.785 L
Mass 1 lbm = 0.4536 kg
Temperature K = °c + 273.15 °C = 5/9 * (°F — 32)
Normality l meq L'1 = 50 mg L'1 as CaCOs
Pressure 1 atrn = 101,325 Pa lof8 WWW' w—Wmﬁ.__w, r, , SHOW YOUR WORK! You do not have to answer in complete sentences. 1) In the movie A Civil Action, residents of Woburn, Massachusetts sued a chemical company
for contaminating the water with trichloroethene (also known as trichloroethylene) and
causing high rates of childhood leukemia. The EPA has withdrawn its cancer potency slope
for oral exposure to TCE due to insufﬁcient evidence, but it reports a cancer potency slope of
0.006 kg day mg'1 for inhalation exposure. a) (8 points) Determine whether exposure to TCE during bathing might have been
'   or the cancers. Measurements in well water found TCE concentrations of
' which according to Henry’s Law, would produce a concentration of
air if the water temperature were 100 °F. The child takes a bath every day
for 15 min. Other exposure parameters are provided in the table above. What is the
child’s CDI of TCE due to inhalation and dermal exposure during bathing? lawman = C3” : C = M ’5 “33/0! [5 min m3>( ) min) : 0: \ _.————~ OOOL
.. me 0000 "1 '0.ng "1413“) '79)) 19%
CD! (0.2 L) 0 (I‘m mm 3of8 b) (6 points) What risk does the child incur due to inhalation exposure to TCE in air during
bathing? Is this value of concern? (/hch aposwe risk: CPI '5’: = (0,7,2 ﬁdxaoao ﬁ):lz.7xmzl We. Vaﬁm rs 9NWW W, £19,415 Mere/me,
of" 1x10", 50 yes, I7 15 of Cancun. c) (6 points) Arsenic has also been found in wells in the area at concentrations of 70 pg L'1
s us If the oral cancer potency slope for arsenic is 1.5 kg day mg“, what is the chi] ’
from exposure to drinking water? (70 % (re/MM N iii—43> mm} 2% (ar er “W k
TCE “5 1‘
dgﬁoims) Naine one slte “in risk assessment. @ ex W S Um a 5 355 W @‘WXICAU (ddsevPegmgg)~fesﬁry @ risk Warm/zafm e) (4 points) Is mutagenesis considered an acute or chronic effect?
Charm 6, f) (4 points) How is the RID related to the NOAEL? : Mama, sappny a? 4of8 2) You have been conducting a water quality study of Lake Nanhuatzin, which has a surface
area of ' = I ‘ X 105 m2. The average depth of the lake is so its volume is
The lake is fed by a stream having a ﬂow rate 0 Q = 1.02 m3 s'1 and a
p osp orous concentration of C, = 0.023 mg L". Runoff from the homes along the lake adds
phosphorous at an average annual rate of m, = 1.25 g s". (Hint: this is a mass ﬂow rate that is already in terms of Q,C,.) A river ﬂows from the lake at a ﬂow rate of Q0“, = 1.02 m3 s". The average phosphorous concentration in the lake is C = 13.2 pg L". The lake’s volume
remains constant over time. Phosphorous removal is caused by gravitational settling and can
be treated as a ﬁrstorder reaction where the settling rate is essentially the rate coeﬂicient, k, in units of inverse time. a) (4 points) Write the mass balance equation describing the rate of change of mass of
phosphorous in the lake using the terms in the problem statement above. Your equation
may also include t. 9159’): QSCsl' ’Y'lr’ QM C“ kCV
We b) (8 points) What is the'rate coefﬁcient that describes the loss of phosphorous? L  L
aha“: = [010% ‘ 010 3'
Ce m I’i? (1000/13): 0.0132 ’3
v: 8% (o6 m 3 (L339) = sax/0" L
((020 ‘75)(0023 tramso @ ~(zozo aroma LE?)
(0.0137 '."i*)( @0sz L) :[.1X(0‘/S(Kéioags)=/lro3 /0l c) (4 points) Why is phosphorous considered a pollutant? 1+ Is at mace WCML Cash/‘9‘“ *0 excessug Qﬁgan gramme. th’bphJCaZTan.) and
WW 0x on ld’oz‘r‘n. 50f8 k.— 3) According to a Washington Post article on 23 October 2007, raw sewage is ﬂowing into the
Anacostia River from a leak in a major sewer line that carries waste in Washington, DC. This
question examines a similar problem on a smaller scale. The saturation DO at 20 °C is 9.17 mg L'l. M
30135 at 20 °C m L'
m—
m— a) (8 points) What is the ultimate BOD of the wastewater? govt = L, U— 6'”) 30171: {28 "34 “(at =Wx5¢o = M4 "3L Lulu) : b) (6 points What is the ultimate BOD at the discharge point, just after mixing?
mass lo Meg, an Lo 6d discharg 6 Point": d( a  QwLWerLm‘f/Qa Lam
0H:
QwLalw‘r Qt L—OV Lo, 01. : “"ﬁ/J
a a (0W)
l .29 .213
j — 6of8 Wmmq—r .,_.,......w._,___ w...“ 7w” 7 m.” . .7 m, c) (6 points) What is the DC at the discharge point, just aﬁer mixing?
Mass \aaﬂaMce, srmZar +0 par'f“ Cb)’ Dﬂ : W DOW + gr D0;
K 62a.
z (0.25 @(I "13% (11%)(2 m.)
(‘2'; g3
= 71¢ [all d) (20 points) What is the critical DO? Space for this problem continues on the next page. Qu' ’2
(DEM kr: IO: Eme’li 3.9(0/1‘0) : 0'52 2,83"
@FM Da mammal:— 6117—719 = 20; MyL
 ___I, k ’ Dq(kr"l<d) i
@F’M’ ‘tc: {cfkr'kd IniﬁD [Wu];
J“ oi“ 1 0.5260Hlf/d In {0.44 ' (My (213) J
a ms 0, {1,H5[O.018é]} = 1.90 at m4 4%“ Jeri: 4ft
@Fmd Dc: Dsmk '6 +Q5 C .— ‘5' I
(034x273) (6‘(awwgéaszaaﬁoy+ 2‘0, 6 a 2W) I ’ (0.0%) .. 139.7(O.93§'o.365’)+ 0.790 : 482 "z @ fir/Ad D06; DQ:m'DC:9r/?~ q—Ww VWMW._W NV. V V, Tn ream}, "HM; D0 canmo+ be less
than 1w, qudaﬁm 1001416! S/aw (M133 e) (4 points) How far downstream does the critical DO occur, in km? m m = (m Maw aways); és 6&4 m :1 66 km f) (4 points) Draw the oxygen sag curve on the axes below. Label the axes and important
features. 'i: (a!) g) (4 points) What two processes contribute to determining the rate of change in oxygen deﬁcit?demygmm (blomﬂm Mal Namm 80f8 ...
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This note was uploaded on 03/31/2008 for the course CEE 3104 taught by Professor Lcmarr during the Spring '07 term at Virginia Tech.
 Spring '07
 LCMarr

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