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Deposition from United States v. SFWMD, et al., Case No. 88-1886-CIV-HOEVELER |
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834
1 UNITED STATES DISTRICT COURT
FOR THE
2 SOUTHERN DISTRICT OF FLORIDA
3
****************************
4 UNITED STATES OF AMERICA, *
Plaintiff *
5 * Case Number
VS. * 88-1886-CIV
6 * Hoeveler
SOUTH FLORIDA WATER *
7 MANAGEMENT DISTRICT, ET AL., *
Defendants *
8 *****************************
9
10 Deposition of WILLIAM W. WALKER, JR.,
11 taken on behalf of the defendants South Florida
12 Water Management District and John R. Wodraska
13 pursuant to the applicable rules of the Federal
14 Rules of Civil Procedure, before Linda Marie
15 MacDonald, Registered Professional Reporter and
16 Notary Public within and for the Commonwealth
17 of Massachusetts, at the offices of Skadden,
18 Arps, Slate, Meagher & Flom, One Beacon Street,
19 Boston, Massachusetts, on Tuesday, February 12,
20 1991, commencing at 9:08 a.m.
21
22
23 LINDA MARIE MacDONALD, RPR-CM
REGISTERED PROFESSIONAL REPORTER
24 60 LAWRENCE ROAD, PLYMOUTH, MA 02360
(508) 747-6615
835
1 A P P E A R A N C E S:
2 UNITED STATES ATTORNEY'S OFFICE
By A.U.S.A Richard Harrison
3 155 South Miami Avenue, Suite 600
Miami, FL 33130
4 for the United States of America.
5 SKADDEN, ARPS, SLATE, MEAGHER & FLOM
By Attorney Laura B. Ahearn
6 1440 New York Ave., N.W.
Washington, D.C. 20005
7 for South Florida Water Management
District and John R. Wodraska.
8
PEEPLES, EARL & BLANK
9 By Attorney Rick J. Burgess
One Biscayne Tower, Suite 3636
10 Miami, FL 33131
for the cities of Belle Glade and
11 Clewiston, defendant intervenors.
12 STATE OF FLORIDA OFFICE OF GENERAL COUNSEL
By Asst. Gen. Counsel David A. Crowley
13 Department of Environmental Regulation
Twin Towers Office Building
14 2600 Blair Stone Road
Tallahassee, FL 332301
15 for the Florida Department of
Environmental Regulation.
16
17 A L S O P R E S E N T:
18 Douglas Robson, Consultant, SFWMD
John Davis, Consultant, Belle Glade and
19 Clewiston
Peter Ghavami, Legal Assistant, Skadden
20 Arps
21
22
23
24
DEPOSITION OF WILLIAM W. WALKER, JR.
836
1 I N D E X
Witnesses Examination
2
WILLIAM W. WALKER, JR., resumed
3 (By Ms. Ahearn) 838
4 E X H I B I T S
5 Number For ID
DX 38 Total Phosphorus Trend Analysis, 841
6 Shark Slough
7 DX 39 S12 Composite, Shark River Slough, 909
Taylor Slough, Coastal Basin
8
DX 40 Yearly Total P Concs & Loads, 923
9 ENP Inflows, with attachments
10 DX 41 Total P Times Series - ENP Inflows 923
Excluding Outliers, Flow > 0,
11 with attachments
12 DX 42 WQ Summary - ENP Inflows 923
Not Flow-Weighted
13
DX 43 ENP Flow-Weighted Mean Concs 923
14
DX 44 WQ Summary - ENP Marsh Stations 923
15 Not Flow-Weighted
16 DX 45 ENP Marsh Data - Trend Analysis, 923
All Results by Station
17
DX 46 ENP Marsh Data - Trend Analysis, 923
18 All Results for Variable = DO,
TNTP and TP
19
DX 47 Station P35 Total P/Stage Graph 923
20
DX 48 Station P36 Total P/Stage Graph 923
21
DX 49 Memo to Garver from Walker 923
22 11/14/90; Re: Data Needs to
Support Research
23
DX 50 Document dated 1/7/91 923
24 Data Needs: Supplement to 11/9/91
Memo to G. Garver
DEPOSITION OF WILLIAM W. WALKER, JR.
837
1 E X H I B I T S
2 Number For ID
3 DX 51 Letter to Scheidt from Higer 923
dated 6/29/89, with attachments
4
DX 52 Memo to Clint Leaks from Walker 923
5 WATSTORE Retrieval Request
6 DX 53 Document entitled "Meeting Agenda" 923
Subject: Access to Technical Data
7 Maintained on District Computers
8 DX 54 Letter to Scheidt from SFWMD 923
(Mary Lou Daniel), 12/13/89,
9 with attachments
10 DX 55 Document entitled "Trends at 923
Other WCA Stations"
11
DX 56 Simulation of Trend Detection 985
12 Procedures; Tests on Means and
Frequency, Clean and Messy Data
13
14
15
16
17
18
19
20
21
22
23
24
DEPOSITION OF WILLIAM W. WALKER, JR.
838
1 P R O C E E D I N G S
2 WILLIAM W. WALKER, JR.,
3 having been previously duly sworn, was deposed
4 and testified as follows:
5 CONTINUED DIRECT EXAMINATION
6 BY MS. AHEARN:
7 Q. Good morning, Dr. Walker.
8 A. Good morning.
9 Q. What is the Chi2 test for homogeneity of trend?
10 A. Are you asking that in reference to a
11 particular document?
12 Q. Well, I guess first I'd like a working
13 definition of this test.
14 MR. HARRISON: Object to form. No
15 foundation, no predicate laid to show that it's
16 a term of art. You may answer.
17 A. As I have applied that test in the trend
18 analysis as described in Exhibit 17, it is a
19 test to determine the likelihood that there are
20 significant differences in the trend magnitude
21 from one season to another.
22 Q. Is the Chi2 test for homogeneity of trend a
23 special term in the field of science of
24 statistics?
DEPOSITION OF WILLIAM W. WALKER, JR.
839
1 A. I have used the term and the equations as they
2 are defined in a book by Gilbert that is
3 referenced in Exhibit 17.
4 Q. Could you, please, point me to that reference,
5 if you could identify for me where in
6 Exhibit 17 we'll see reflected your Chi2 test
7 for homogeneity of trend?
8 MR. HARRISON: Do you want the second
9 one first, Counsel, or the reference? It's
10 compound.
11 Q. Are those two different things, your reference
12 to Gilbert and where in the -- let's start all
13 over.
14 Direct me to the reference to Gilbert,
15 please.
16 A. The reference to Gilbert is on page 45 of
17 Exhibit 17. It's a book entitled "Statistical
18 Methods for Environmental Pollution
19 Monitoring."
20 MS. AHEARN: And I would like the record
21 to reflect that we have numbered each page on
22 the original Exhibit 17 here to which
23 Dr. Walker is referring to make sure that there
24 is a legible page number on each page in the
DEPOSITION OF WILLIAM W. WALKER, JR.
840
1 exhibit.
2 Q. Okay. That was in the list of references,
3 correct?
4 A. Correct.
5 Q. Could you point to me the textual discussion of
6 this Gilbert method?
7 A. I don't recall actually discussing that in the
8 report. This test for homogeneity of trend was
9 something that is included in the computer
10 program that I wrote for the purpose of
11 conducting these tests.
12 But the results -- as I recall, the
13 results of that trend did not indicate that
14 there were significant differences from one
15 season to another with respect to trend
16 magnitude, so there was no reason to discuss
17 those results in the context of the report.
18 Q. Just so it's clear, on reviewing Exhibit 17, I
19 found no mention of the Chi2 test.
20 A. That's right. That's probably correct. I do
21 not recall actually describing it in the text,
22 but it is a test that I applied.
23 Q. Do you recall if you discussed the Chi2 test in
24 any prior drafts of Exhibit 17?
DEPOSITION OF WILLIAM W. WALKER, JR.
841
1 A. I do not believe I did.
2 Q. When in the sequential process of your trend
3 analysis did you perform the Chi2 test?
4 A. I don't recall when I added that particular
5 algorithm to the computer program that I was
6 working with.
7 (Exhibit No. 38 marked for
8 identification)
9 Q. Dr. Walker, I'll ask the court reporter to hand
10 you Exhibit 38. Can you identify that?
11 A. This is two pages of graphs and statistics
12 entitled Total Phosphorus Trend Analysis for
13 Shark slough as described on the first page.
14 And I believe the second page describes --
15 summarizes a similar analysis for Station S332
16 -- that is Taylor slough -- and Station S18C,
17 which is the Coastal station.
18 Q. I see at the bottom of each page here a
19 reference to your Chi2 test.
20 A. That's correct.
21 Q. Let me first ask you, You generated both pages
22 of Exhibit 38?
23 A. Yes, I did.
24 Q. And this was on your personal computer?
DEPOSITION OF WILLIAM W. WALKER, JR.
842
1 A. Yes.
2 Q. I asked because it looks to be a somewhat
3 different format than other things I have seen
4 you produce.
5 Does this Exhibit 38 illustrate how you
6 performed the Chi2 test?
7 A. No. This Exhibit 38 merely states the results
8 of the Chi2 test.
9 Q. Do you recall if you produced any other
10 documents or computer files that illustrate how
11 the Chi2 test was performed?
12 A. The methods that were used to calculate the
13 Chi2 test are reflected in the FORTRAN computer
14 software that I turned over with my other
15 computer files.
16 Q. Those are the files reflected in Exhibit 18,
17 the printout of the directories?
18 A. That's correct.
19 Q. Can you, please, identify by page number and
20 name the directory where I'll find the program
21 that incorporates the Chi2 test algorithms?
22 A. Okay. We're referring now to Exhibit No. 18.
23 The program that contains the Chi2 test for
24 homogeneity of trend would be included in the
DEPOSITION OF WILLIAM W. WALKER, JR.
843
1 directory listed on -- starting on page 14, the
2 directory G:\LIB\FOR.
3 Q. Can you identify a particular file or files
4 that contains the Chi2 test?
5 A. I believe that a portion of the test is
6 contained in the file on page 18 called
7 SKEND.FOR. That's the sixth file from the top
8 on page 18. Other subroutines may be used in
9 calculating that test, as well.
10 Q. I note that there is one labeled CHISQP.FOR.
11 It sounds like a likely candidate.
12 A. Yes. That routine may be used as well in
13 calculating that test result. That's located
14 on page 14.
15 Q. Are each of the trend programs which we have
16 discussed before on page 13 of Exhibit 18, are
17 each of those trends programs designed to call
18 up the Chi2 subroutine from the FORTRAN
19 directory?
20 A. Yes.
21 Q. While we're here on Exhibit 18, I want to ask
22 you a couple more questions I'm not clear on.
23 You identified your G:\DBASE directory as
24 containing the surface water quality data that
DEPOSITION OF WILLIAM W. WALKER, JR.
844
1 you used with the KTEST program for producing
2 Exhibit 17?
3 MR. HARRISON: Counsel, are you on a
4 particular page on Exhibit 18?
5 MS. AHEARN: The DBASE is on page 24.
6 Q. I believe when I had asked you about this
7 before, I only spoke in terms of the surface
8 water quality data.
9 Are all of the files for flow, rainfall
10 and stage data which the KTEST program
11 retrieved for purposes of doing the analysis
12 reflected in Exhibit 17, are all of those data
13 files also included in this G:\DBASE?
14 A. To the best of my recollection, yes.
15 Q. And in G:\DBASE we also see a number of files
16 for various variables that appear to relate to
17 marsh stations; is that correct? For example,
18 entries for P33, those files would denote data
19 concerning a marsh station within Everglades
20 National Park?
21 A. That's correct.
22 Q. In the preliminary analysis that you have
23 performed of Everglades marsh data, am I
24 correct you used a program called MULTI?
DEPOSITION OF WILLIAM W. WALKER, JR.
845
1 A. That's correct.
2 Q. All of the data files set up to be retrieved by
3 the MULTI program, are all of those data files
4 contained in directory G:\DBASE?
5 A. I believe I testified previously regarding the
6 procedures that one would use to execute these
7 programs. Basically the procedure involves
8 editing the file, in this case MULTI.DAT, which
9 contains essentially the instructions of the
10 program to access certain data files, so in
11 that file MULTI.DAT should be the directory and
12 the specific file names that would be used in a
13 particular analysis or run of the program.
14 Q. Would you need to actually look at that entry
15 in the program to ascertain where all of the
16 data files for use in that program are located?
17 A. That's correct. In the listing of that
18 MULTI.DAT input file should be an indication of
19 where the files are located and what their
20 names are.
21 Q. Is the same true for the RMED program? You
22 would need to look at the .DAT file in order to
23 tell us exactly in which directories the
24 appropriate data files were stored?
DEPOSITION OF WILLIAM W. WALKER, JR.
846
1 A. Yes.
2 Q. Just trying to see if I can cut some corners.
3 Dr. Walker, when you edited Exhibit 17
4 for submission to the Water Resources Bulletin,
5 did you look for statements that were more
6 likely to draw questions or criticisms from the
7 peer reviewers? Was that a consideration in
8 deciding which statements to take out of the
9 text?
10 MR. HARRISON: I object to the
11 characterization. I think we had a round on
12 that, whether it was editing or what it was. I
13 think there is a separate exhibit in here,
14 Counsel, that went to the Water Resources
15 Bulletin if you want to refer to that.
16 A. I believe I testified previously that my
17 objective in editing Exhibit 17 for submission
18 to Water Resources Bulletin was to shorten it
19 to provide an acceptable length for
20 publication.
21 Q. And you explained to us why you omitted the
22 section on the loading analysis. Did you omit
23 other parts of the text?
24 A. I may have omitted certain sentences or certain
DEPOSITION OF WILLIAM W. WALKER, JR.
847
1 paragraphs in the effort of -- in the interest
2 of shortening the overall text.
3 Q. In Exhibit 17, would you turn to page 3,
4 please? The last sentence in the first
5 paragraph, is there any reason why you deleted
6 that sentence from the draft submitted to the
7 Water Resources Bulletin?
8 A. I don't recall whether specifically I did
9 delete that sentence.
10 Q. If you would like to refer to Exhibit 12 to
11 verify that, it would be page 2 of Exhibit 12.
12 MR. BURGESS: Exhibit what? I'm sorry?
13 MS. AHEARN: Exhibit 12.
14 A. Well, as I stated, my primary emphasis in
15 editing this for submission was to shorten the
16 document. That was a sentence that I thought
17 was not essential to the rest of the document,
18 and it was rather long and it was an
19 opportunity to shorten the document.
20 I believe that the concept expressed in
21 that sentence is something that is generally
22 accepted in the water quality management field
23 and is not something that is essential for the
24 purposes of understanding this technical
DEPOSITION OF WILLIAM W. WALKER, JR.
848
1 document and understanding the analysis which I
2 performed.
3 Q. Do you feel that you would be able to defend
4 this sentence, the last sentence in the first
5 paragraph of page 3, Exhibit 17, before the
6 peer reviewers of the Water Resources Bulletin?
7 A. Yes.
8 Q. Let me see if I can shorten this up.
9 Recognizing the need to shorten the
10 document, can you tell me what other criteria
11 guided your exercise of judgment in deciding
12 which statements to extract from Exhibit 17?
13 MR. HARRISON: Object. Asked and
14 answered. Also, no foundation for your
15 characterization that there were other
16 criteria.
17 Q. Were there other criteria other than there was
18 a page limitation?
19 MR. HARRISON: Asked and answered.
20 MS. AHEARN: Excuse me. You just told
21 me --
22 A. No.
23 Q. There were no other criteria that guided your
24 judgment?
DEPOSITION OF WILLIAM W. WALKER, JR.
849
1 A. My objective was to shorten the document. And
2 in the process of selecting which particular
3 pieces I would remove for the purpose of
4 shortening the document, I removed those pieces
5 which I felt were not necessary to communicate
6 the essential components of the work and those
7 parts which were separable in a sense as I
8 described earlier.
9 I believe the analysis on the loading is
10 a separate piece that could very well
11 constitute a separate paper, a separate journal
12 article, and I may very well submit that for
13 publication separately. Those are the kinds of
14 considerations that I had, but my overall
15 objective was to shorten the article to make it
16 more acceptable for publication in a journal.
17 Q. Thank you. We had proceeded through page 5 of
18 Exhibit 17 yesterday. Would you turn to
19 page 6? On the first line there you refer to
20 fixed minimum delivery schedules. What do you
21 mean by that phrase?
22 A. I mean that there were certain volumes of water
23 that were scheduled to be released through
24 Structures S332 and S18C. And as distinct from
DEPOSITION OF WILLIAM W. WALKER, JR.
850
1 the schedule for Shark slough, where the
2 volumes were based upon rainfall, these
3 deliveries at S332 and S18C were not based upon
4 antecedent rainfall.
5 Q. I just want to make sure that we're clear here.
6 By "schedules," are we talking about hydrologic
7 ranges as opposed to a calendar schedule?
8 A. What do you mean by "hydrologic ranges"?
9 Q. By "delivery schedule," are you referring to a
10 preset time period for water deliveries? Is it
11 a schedule in that sense like scheduled for
12 every Monday or it's already established on a
13 calendar that deliveries occur on X day?
14 MR. HARRISON: Object to form.
15 Q. Is that what we mean here by "schedules"?
16 MR. HARRISON: Object to form. It might
17 be easier just to ask him when he -- what his
18 understanding of the schedules are.
19 A. To my recollection, the flows through S332 and
20 S18C are operated to provide a certain
21 guaranteed minimum amount of flow. I'm
22 uncertain as to whether that is an annual flow
23 or whether that flow is broken out on a
24 seasonal basis. And then on top of that
DEPOSITION OF WILLIAM W. WALKER, JR.
851
1 minimum guaranteed amount would be any flows
2 that would occur as a result of excess runoff
3 or drainage from the basin following storm
4 events.
5 Q. Are water deliveries scheduled to be made at
6 any specific time?
7 A. I believe that there is a seasonality to the
8 delivery schedule.
9 Q. Are you knowledgeable of the currently
10 effective operating criteria for water
11 deliveries to Everglades National Park?
12 MR. HARRISON: Object to form. There's
13 different delivery points to the Park.
14 A. Which -- which basin are you referring to?
15 Q. Are you familiar with the operating criteria
16 for all three basins?
17 A. I am generally familiar with the operating
18 criteria as they are discussed in Exhibit 17.
19 Q. Are you aware of any changes in operating
20 criteria since the time period which ends 1989
21 that's discussed in Exhibit 17?
22 A. I'm not aware of any such changes.
23 MR. HARRISON: Was that December '89,
24 Counsel?
DEPOSITION OF WILLIAM W. WALKER, JR.
852
1 MS. AHEARN: The text says 1989,
2 Mr. Harrison.
3 MR. HARRISON: But without a month.
4 Q. In the second full paragraph on page 6, the
5 second sentence, you state that:
6 Values reported to be below the
7 detection limit are set equal to the
8 detection limit minus a small
9 concentration increment.
10 At what point in your trend analysis
11 work did you set these below-detection-limit
12 values minus a small concentration increment?
13 A. What do you mean by "point"?
14 Q. Did you do trend analyses with the detection
15 limits without deducting the small
16 concentration increment?
17 A. I believe that the first draft of the work did
18 not perform that task. In other words, the
19 first set of trend analyses that I performed
20 that's described in the July 1990 draft I did
21 not make that adjustment in detection limit.
22 Q. Is there a reason why that wasn't attempted for
23 the first draft?
24 A. To perform that task, it involved a substantial
DEPOSITION OF WILLIAM W. WALKER, JR.
853
1 amount of work. I had to go through and
2 essentially edit the data files, the source
3 data files, to make that adjustment. And I
4 felt in the first draft that since the overall
5 percentage of total phosphorus values below
6 detection limits was on the order of 7 percent
7 or less, it was unlikely that that adjustment
8 would make a significant difference in the
9 results of the trend analysis. Therefore, I
10 did not undertake that adjustment in the first
11 draft.
12 Q. Why did you feel it was worthwhile to do that
13 substantial work after the first draft?
14 A. Because I was given more time -- as I testified
15 earlier, I was under some commitment to
16 complete the first draft by July of 1990, and I
17 had additional time between July and September.
18 And it was also -- a comment regarding this
19 topic was made by one of the reviewers. So
20 those were the reasons why this adjustment was
21 made in the second or in the final version of
22 the trend analysis.
23 Q. Did you have this in mind independent of the
24 comment of the reviewer?
DEPOSITION OF WILLIAM W. WALKER, JR.
854
1 A. I had it in mind as something that might be
2 done as part of the analysis.
3 Q. Did you perform sensitivity analyses to see the
4 effect of setting below-detection-limit values
5 at other levels?
6 A. As the text on page 6 describes, the trend test
7 is based upon ranks of the data and, as such,
8 the results for the trend analyses would not be
9 sensitive to the particular magnitude selected
10 for this adjustment.
11 Q. Could you set it at zero and not have any
12 impact on the trend analysis?
13 A. Setting it at zero would be problematical for
14 the Series C analyses because the Series C
15 analyses involved taking logarithms -- in fact,
16 all of them involve taking logarithms of the
17 data prior to the trend analysis. So now that
18 I think about it, zero could not have been used
19 in the way I performed this test.
20 Q. Does the selection of the level at which to set
21 below-detection-limit values affect the
22 calculation of the Kendall slope?
23 A. Possibly.
24 Q. Did you do any sensitivity analyses of that?
DEPOSITION OF WILLIAM W. WALKER, JR.
855
1 A. Only insofar as the draft -- the July draft did
2 not make any of this sort of adjustment and the
3 final draft did make this adjustment.
4 Q. So you tested between no adjustment and an
5 adjustment of .0001 milligram per liter?
6 A. Correct.
7 Q. What is the difference between those two
8 scenarios?
9 A. Well, it's difficult to generalize about the
10 difference between those scenarios for all
11 variables and all stations. But, for example,
12 if we take what I identified as Series A at
13 Station S12T, the Kendall slope estimated in
14 the July draft when I did not make that
15 adjustment for detection limits was 7.1 percent
16 per year; that is, the median rate of increase
17 in phosphorus concentration at the S12s was
18 7.1 percent per year.
19 Q. Dr. Walker, are you referring to a particular
20 page or table in Exhibit 7?
21 A. Yes. I'm referring to Exhibit 7, Table 5.
22 Q. Thank you.
23 A. And in that Exhibit 7, Table 5, as I just
24 mentioned, the trend for S12T was 7.1 percent
DEPOSITION OF WILLIAM W. WALKER, JR.
856
1 per year. And in the final version, Table 5,
2 Exhibit 17, the trend for the same station and
3 variable was 7.0 percent per year.
4 Q. Is the change from 7.1 to 7.0 not significant?
5 MR. HARRISON: Object to form.
6 A. The change from 7.1 to 7.0 is a change from 7.1
7 to 7.0. I don't know what you mean by
8 "significant."
9 Q. Do you have the sense of what the slope would
10 have been if you had set below-detection-limit
11 values at .002?
12 A. I did not test that directly. But as I stated
13 earlier, since on the order of 7 percent of the
14 observations were below detection limits and
15 since the slope is calculated as the median of
16 all the slopes calculated within each season,
17 it is unlikely that a change in this adjustment
18 factor would have influenced the calculated
19 slope. And in no case would an adjustment of
20 this factor for detection limits influence the
21 calculated P level or the significance level
22 upon which we base -- we estimate the
23 likelihood of a trend.
24 Q. Thank you. I understand that distinction
DEPOSITION OF WILLIAM W. WALKER, JR.
857
1 there. In the middle of the middle paragraph
2 on page 6, Exhibit 17, you state:
3 The detection limit for total and
4 ortho phosphorus increased from .002 to
5 .004 milligram per liter in 1981.
6 What was the cause of that change?
7 A. I do not know.
8 Q. Do you know if there were any changes in lab
9 technique at this time?
10 A. Not to my knowledge.
11 Q. Are you aware of any changes in the detection
12 limits of other constituents?
13 A. The database that was supplied by the District
14 included measurements of trace metal
15 concentrations, heavy metals. And in reviewing
16 the listing of that data, it was apparent that
17 there were some fluctuations in the detection
18 limit in those cases. I did not conduct a
19 trend analysis on that information.
20 Q. Are you aware of any changes in detection
21 limits among any of the water quality
22 constituents you did analyze?
23 MR. HARRISON: Other than total
24 phosphorus?
DEPOSITION OF WILLIAM W. WALKER, JR.
858
1 MS. AHEARN: Yes.
2 Q. Other than the ortho and total phosphorus in
3 '81.
4 A. Of the constituents which I analyzed, the other
5 species for which I recall the presence of
6 values below detection limits would include
7 ammonia nitrogen and nitrate and nitrite
8 nitrogen. The remaining species to my
9 recollection were generally reported at values
10 -- at quantifiable values above the detection
11 limit, so there would be no way of knowing
12 precisely what the detection limit was for
13 those constituents because the concentrations
14 were always above the detection limits.
15 In the case of ammonia nitrogen and
16 nitrite nitrogen, I don't recall a systematic
17 change or a shift in the detection limit in a
18 particular time period.
19 Q. You said that those other constituents were
20 reported at levels. Do you know what the lab
21 detection limit for those constituents were?
22 A. Which constituents?
23 Q. Well, you told us that for ammonia -- I'm
24 afraid I forget the other you pointed out --
DEPOSITION OF WILLIAM W. WALKER, JR.
859
1 you recalled reports below detection limit --
2 A. Right.
3 Q. -- for those two constituents. And all the
4 others you see as being reported at
5 quantifiable values.
6 A. Correct.
7 Q. Do you know at what level the lab felt they
8 could detect those values for those other
9 constituents?
10 A. I'm still unclear as to what you mean by "other
11 constituents."
12 Q. Among the 20 listed in Table 1 that you
13 analyzed in Exhibit 17. I guess my point is
14 quite simple, Dr. Walker. I asked you if you
15 were aware of changes in detection limits among
16 the constituents other than total and ortho
17 phosphorus, and what you have told me is that
18 you saw these other constituents reported above
19 detection.
20 The fact that they are reported above
21 doesn't tell us what the detection limits were,
22 does it?
23 A. That's correct.
24 Q. Okay. It doesn't tell us whether there were
DEPOSITION OF WILLIAM W. WALKER, JR.
860
1 changes of detection limit?
2 A. It tells us if there were detection limits,
3 they were not such that they would be greater
4 than the -- that the new detection limits would
5 not be greater than any value which is reported
6 as quantified in the database.
7 Q. Prior to 1981 were there any values for total
8 or ortho phosphorus reported between .002 and
9 .004?
10 A. There may have been. I don't recall.
11 Q. What was the accurate detection limit for total
12 and ortho phosphorus prior to 1981?
13 MR. HARRISON: Object to form. There's
14 been no predicate laid.
15 A. I don't know what you mean by "accurate."
16 Q. If in 1979 a value for total phosphorus, the
17 .003, was reported, was that value below
18 detection limit?
19 A. If it was reported in the database as a numeric
20 value without a -- an accompanying indicator
21 that would indicate that it was below detection
22 limits such as the less-than sign or K symbol
23 -- I don't recall what the symbol was that the
24 District used in their data sets. But if it
DEPOSITION OF WILLIAM W. WALKER, JR.
861
1 was reported as a numeric value, then it was
2 assumed to be above the -- above or equal to
3 the detection limit that was present in the
4 laboratory at that particular time.
5 Q. With the instrumentation available in 1979,
6 what was the lowest detection limit possible
7 for total phosphorus?
8 A. The detection limit reported by the District
9 which reflected the instrumentation that they
10 had at that particular time in their laboratory
11 proceedures was .002 milligrams per liter.
12 Q. Are you familiar with the instrumentation that
13 was generally available for water quality
14 analyses in 1979?
15 MR. HARRISON: Object to form.
16 A. I am aware that there was instrumentation
17 available that was capable of analyzing total
18 phosphorus concentrations to within a detection
19 limit of .002 to .004 milligrams per liter.
20 But in terms of the specific hardware, I
21 couldn't give you any details on that.
22 Q. How about with respect to instrumentation
23 available presently for total phosphorus
24 analysis?
DEPOSITION OF WILLIAM W. WALKER, JR.
862
1 A. There may have been some improvements in the
2 instrumentation over time that might have made
3 it possible to detect total phosphorus to lower
4 values, but again I cannot give you the details
5 on the specific hardware involved or the
6 technology.
7 Q. In the other constituents where you said you
8 did see values reported below detection, did
9 you employ the same procedure with regard to
10 those constituents of setting the values equal
11 to detection limit minus a small concentration
12 increment?
13 A. To my recollection, yes, I did.
14 Q. What specific detection limits did you use for
15 these other constituents?
16 A. I don't recall.
17 Q. Do you recall the source of the detection limit
18 which you did use?
19 A. It would have been derived by reviewing the
20 data file and essentially identifying the
21 largest numeric value that was reported as less
22 than the detection limit.
23 Q. You adopted that as the lab detection limit?
24 A. For the purpose of adjusting the data to
DEPOSITION OF WILLIAM W. WALKER, JR.
863
1 account for values below detection limit, yes.
2 Q. Just to make sure I'm clear, that's not the
3 source of the .002 and .004 detection limit
4 used for total and ortho phosphorus, correct?
5 A. Yes, it was the same procedure that I used for
6 total and ortho phosphorus.
7 Q. You just derived that by reviewing the data?
8 A. Correct.
9 Q. From that review of the data, you were able to
10 determine that the detection limit changed in
11 1981?
12 A. Yes.
13 Q. Did you have any other source of information on
14 that?
15 A. Well, it may have been discussed in the ONRW
16 meetings. I don't recall for sure.
17 Q. Are there alternative methods for adjusting
18 values reported below detection limits for use
19 in the Seasonal Kendall test other than the
20 method you used here, setting it equal to a
21 detection limit minus a small concentration
22 increment?
23 MR. HARRISON: Did you just say,
24 Counsel, are there other methods or --
DEPOSITION OF WILLIAM W. WALKER, JR.
864
1 MS. AHEARN: Are there alternatives --
2 A. One could conceive of other procedures. A
3 procedure that I have used is the procedure
4 that was recommended in one or more of the
5 papers by Hirsch and Slack on the Seasonal
6 Kendall test.
7 Q. If I could direct your attention a little
8 farther down in this middle paragraph on
9 page 6, Exhibit 17, there is a sentence that
10 starts "Phosphorus time series have been
11 adjusted..." Could you read that sentence and
12 tell me if it is accurate?
13 A. Phosphorus time series have been
14 adjusted to a uniform detection limit of
15 .004 mg/liter by setting each value
16 equal to the minimum of the reported
17 value and .004 mg/liter.
18 I believe there is an error in that
19 equation -- in that sentence. The term
20 "minimum" should be replaced by the term
21 "maximum." That was a grammatical error on my
22 part.
23 Q. If the trend you see in phosphorus
24 concentrations in Park inflows is attributable
DEPOSITION OF WILLIAM W. WALKER, JR.
865
1 to the discharge of agricultural waters, what
2 trends would you expect to see in other
3 constituents that you have analyzed in
4 Exhibit 17?
5 MR. HARRISON: I'm going to object to
6 form. Counsel, does your question assume that
7 the trends are solely due to the discharge of
8 agricultural water without any of these other
9 variables? If that is your assumption, I will
10 object to the assumption since the assumption
11 has no basis in evidence in this deposition.
12 But I want the hypothetical cleared up.
13 A. I believe yesterday I testified to my
14 preliminary conclusions regarding possible
15 causes of these apparent trends, and increases
16 in loadings from the watershed -- watersheds of
17 the Water Conservation Areas was indicated as
18 being one of the likely causes, among others.
19 Other -- if one were to take your
20 hypothetical and if it is based on the
21 assumption that it is agriculture runoff that
22 is the causal factor or contributing to these
23 loads, one might be concerned about potential
24 trends in other substances that are also found
DEPOSITION OF WILLIAM W. WALKER, JR.
866
1 in agricultural runoff.
2 Q. Which would be those substances?
3 A. Well, agricultural runoff would contain a wide
4 range of substances, including nutrients,
5 inorganic species, pesticides, heavy metals.
6 Q. If a trend in phosphorus was attributable to
7 agricultural runoff, would you expect to see
8 corollary trends in other conservative
9 constituents such as chlorides?
10 A. Not necessarily.
11 Q. Are there any constituents other than ortho
12 phosphorus and the nitrogen species in which
13 you would expect to see corollary trends if the
14 trend in total phosphorus concentrations was
15 caused by agricultural runoff?
16 A. Well, I would be concerned about things such as
17 pesticides.
18 Q. And you have not conducted a trend analysis on
19 pesticides, correct?
20 A. To my knowledge, there's not an adequate
21 database to perform such an analysis.
22 Q. Okay. Any other constituents?
23 (The witness gave no response.)
24 Q. How about ions and cations?
DEPOSITION OF WILLIAM W. WALKER, JR.
867
1 A. Well, ions and cations are part of the natural
2 system. They are contained in rainfall, and
3 they are contained in natural drainage. They
4 wouldn't necessarily be exclusively earmarks
5 for agricultural runoff.
6 Q. Could they be earmarks for agricultural runoff?
7 MR. HARRISON: Object to form.
8 A. I said they wouldn't necessarily be earmarks
9 for agricultural runoff.
10 Q. Have you looked for any earmarks for
11 agricultural runoff in the work you have done?
12 A. I have analyzed the data for 12 water quality
13 components for trends at the Park inflow
14 points.
15 Q. Twelve or twenty?
16 A. Excuse me. Twenty.
17 Q. Even apart from this trend analysis, has the
18 work you performed on South Florida water
19 quality issues included any investigation of
20 what constituents might be earmarks for
21 agricultural runoff?
22 A. No.
23 Q. Page 9. We're really moving.
24 For the purposes of the record,
DEPOSITION OF WILLIAM W. WALKER, JR.
868
1 Dr. Walker, could you, please, define the term
2 "robust" as you use it, for example, here in
3 the paragraph at the top of page 9, Exhibit 17?
4 A. I used the term "robust" in page 9 in reference
5 to the Seasonal Kendall slope. What I mean
6 when I say that the estimate of the Seasonal
7 Kendall slope is robust is that it is more
8 likely to reflect the underlying distribution
9 of the bulk of the data than to be -- than to
10 reflect a few data points at the extremes of
11 the data and it is less likely to be sensitive
12 to outliers or other unrepresentative samples.
13 Q. I'd like to refer you to page 3 in Exhibit 7,
14 which is your July 3 draft.
15 You can see in the mid paragraph there
16 under the heading "Methods," the last sentence
17 there in Exhibit 7 does not appear in the
18 comparable text in Exhibit 17. Can you explain
19 that difference?
20 A. You're referring essentially to the omission of
21 one sentence, is that --
22 Q. In Exhibit 17, page 3, middle paragraph,
23 there's a sentence.
24 MR. HARRISON: Exhibit 7, I think,
DEPOSITION OF WILLIAM W. WALKER, JR.
869
1 Counsel.
2 MS. AHEARN: Thank you.
3 Q. Exhibit 7, page 3, middle paragraph, the last
4 sentence starts, "Another advantage is that..."
5 That sentence largely does not appear in
6 Exhibit 17 and, if you can, can you explain why
7 this was changed?
8 A. I don't recall specifically. It may have been
9 in response to one of the reviewers' comments.
10 I don't view it as a particularly important
11 statement.
12 Q. The statement as it appears in Exhibit 7?
13 A. Right.
14 Q. Again with reference to Exhibit 7, page 3, the
15 bottom paragraph, midway in the body of that
16 paragraph is a sentence starting, "Loftis et
17 al..."
18 Is there a reason why that does not
19 appear in Exhibit 17?
20 A. Well, the statement that you're referring to, I
21 believe, is:
22 Loftis et al. (1989) cautioned
23 against using the second test because of
24 its relatively low power (ability to
DEPOSITION OF WILLIAM W. WALKER, JR.
870
1 detect trends); they felt that
2 "reduction in power was too high a
3 price to pay for insensitivity to serial
4 correlation."
5 That statement was derived from -- I
6 derived that statement from the report by
7 Loftis et al. And I believe one of the other
8 reviewers of my report, I think it was Helsel
9 -- Helsel and Slack who together put together a
10 review of my report, took issue with that
11 statement. They disagreed with that statement
12 and they felt it was Loftis' opinion and they
13 disagreed with it. So I decided that it was
14 not an essential statement as far as I was
15 concerned to the report, so I took it out at
16 the suggestion of the reviewers.
17 Q. Well, you included the statement from Loftis in
18 your draft. Do you agree with Loftis?
19 A. I agree in the sense that if you're using the
20 second version of the Seasonal Kendall test
21 which accounts for serial correlation, you are
22 paying a price in that you are being very
23 conservative; you are trying to account for
24 serial correlation, and you're running the risk
DEPOSITION OF WILLIAM W. WALKER, JR.
871
1 of not detecting trends. You are reducing the
2 power of the test. But on the other hand, you
3 are accounting for a real phenomenon -- that
4 is, serial correlation.
5 There are trade-offs involved here. And
6 essentially the decision that I have made in
7 conducting the analysis was in fact to use this
8 more conservative test that accounts for serial
9 correlation even though it may have a chance of
10 failing to detect trends, it may miss trends at
11 some frequency, because I'm trying to account
12 for serial correlation.
13 Q. With a database such that you're using in
14 Exhibit 17, do Helsel and Slack agree that this
15 second version of the Seasonal Kendall test has
16 a reduction in power?
17 (Pause)
18 Q. Do you feel you need to refer to the written
19 comments in order to answer that?
20 A. I'm just looking at one of the previous
21 exhibits for a second.
22 Q. And you're referring to which exhibit number?
23 A. I'm referring to Exhibit No. 37.
24 Q. Thank you.
DEPOSITION OF WILLIAM W. WALKER, JR.
872
1 A. Exhibit No. 37 is the paper by Hirsch and Slack
2 entitled "A Nonparametric Trend Test for
3 Seasonal Data With Serial Dependence."
4 Figure 2 of that paper on page 730 shows the
5 results of power tests that were done in order
6 to compare essentially the power of the test
7 when serial correlation was considered as
8 compared with the power of the test when it was
9 ignored.
10 And those results do show that for a
11 series of ten years' worth of data, that the
12 percent of the time that trends -- that a trend
13 was detected was indeed lower when the test
14 accounted for serial correlation. That's for
15 the ten-year time series.
16 Other tests -- other simulations that
17 are described in this same paper show that the
18 power of the test and the Type 1 error is --
19 other simulations described in this paper show
20 that for time series less than ten years in
21 length, the procedure underestimates the -- the
22 procedure has a Type 1 error rate that is below
23 the nominal Type 1 error rate for time series
24 less than ten years in length.
DEPOSITION OF WILLIAM W. WALKER, JR.
873
1 Q. What about time series 12 years in length?
2 A. They consider the case of ten years in their
3 simulations and show that the test closely
4 approximates the nominal Type 1 error rate for
5 that condition.
6 Q. Have Hirsch and Slack or others addressed the
7 power of the test using a 12-year time series?
8 A. They considered five-, ten- and twenty-year
9 time series, and they recommend that the test
10 for periods of ten years or more, that the test
11 involving -- including serial correlation is
12 appropriate.
13 Q. In other words, it has adequate power to --
14 A. It may -- there may be some loss of power that
15 is associated with using this test which is a
16 more conservative test than the test that is --
17 that does not account for serial correlation,
18 but it has a more accurate representation of
19 the Type 1 error.
20 Q. When we talk about serial correlation here,
21 what does that mean?
22 A. We are talking about the tendency for the
23 values to be -- to occur not as random values
24 over time but to be correlated from one season
DEPOSITION OF WILLIAM W. WALKER, JR.
874
1 to the next.
2 Q. So that the serial correlation accounted for in
3 the modified Kendall test accounts for seasonal
4 serial correlation?
5 A. It accounts for serial correlation in the
6 values after the seasonal effects -- fixed
7 seasonal effects have been removed from the
8 data.
9 Q. Does it account for any serial correlation as
10 between years?
11 A. I believe that we discussed that previously.
12 The test does not account for serial
13 correlation from one year to the next.
14 Q. I apologize, but I'm learning. I want to make
15 sure I keep this straight.
16 What kind of correlation structure did
17 Hirsch and Slack use in simulating and testing
18 the power of their modified test?
19 MR. HARRISON: You mean in their own
20 report, Counsel, or in their review of
21 Dr. Walker's report?
22 Q. Has Hirsch prepared a review of your report,
23 Dr. Walker?
24 A. Dr. Slack has, yes.
DEPOSITION OF WILLIAM W. WALKER, JR.
875
1 Q. Has Dr. Hirsch?
2 A. Not to my knowledge.
3 Q. Okay. You told us about simulations performed
4 of the modified Kendall test for five-, ten-
5 and twenty-year time series --
6 A. Correct.
7 Q. -- by Hirsch and Slack?
8 A. Correct.
9 Q. What kind of correlation structures were they
10 using for those simulations?
11 A. They used a range of correlation structures
12 that are essentially defined as autoregressive
13 moving average models, ARMA models, and they
14 used a range of coefficients to reflect
15 different levels of autoregressive and moving
16 average dependence in the time series.
17 Q. By "models," does this mean that these are
18 artificially constructed correlation
19 structures?
20 A. These are correlation structures which have
21 been found to be representative of and typical
22 of water quality time series that have been
23 studied and analyzed with -- using these time
24 series techniques.
DEPOSITION OF WILLIAM W. WALKER, JR.
876
1 Q. Do you know how representative they are of the
2 correlation structure of the water quality
3 database utilized in Exhibit 17?
4 A. As described in 17, for example, on page 18 I
5 report values for what is called RA, which is
6 the first-order serial correlation coefficient
7 of the values.
8 Also, in Appendix A for each test result
9 I list the serial correlation coefficient for
10 each of the time series or each of the -- for
11 each set of tests that are documented in
12 Appendix A.
13 Q. Is the correlation structure of the water
14 quality data collected from the real world
15 utilized in Exhibit 17 accurately represented
16 by the correlation structures of the models
17 employed by Hirsch and Slack?
18 A. The cases considered by Hirsch and Slack were
19 designed to reflect a wide range of water
20 quality time series that they have examined in
21 their studies. I have not precisely fit these
22 types of time series models to the water
23 quality data that I analyzed for trend, but I
24 have characterized the serial correlation
DEPOSITION OF WILLIAM W. WALKER, JR.
877
1 structure as I mentioned with this term RA that
2 is documented in the report.
3 And the other factor that's important is
4 that -- the reason that we are concerned about
5 this serial correlation structure is because we
6 -- one limitation or one assumption of the test
7 is that there's no serial correlation in the
8 data from one year to the next other than
9 whatever serial correlation would be reflected
10 in a trend. And I have characterized that
11 possibility or evaluated that possibility by
12 calculating the serial correlation coefficients
13 from one year to the next within each season,
14 and these are documented on page 18, Table 2,
15 under -- again, under this column RA for each
16 month.
17 The magnitudes of those correlation
18 coefficients are generally low and not in a
19 range where I would be concerned about serial
20 correlation from one year to the next or in a
21 range where I would be concerned about the
22 applicability of the test.
23 Q. Your RA values are calculated based on years,
24 correct?
DEPOSITION OF WILLIAM W. WALKER, JR.
878
1 A. The RA value reported for a particular month
2 would be the serial correlation coefficient for
3 the values that are one year apart collected
4 within each month.
5 Q. And that would be a first order of correlation
6 structure?
7 A. That's correct.
8 Q. Did you look at any other correlation
9 structures in this database?
10 A. Since the first-order correlation structure for
11 the values one year apart are generally
12 insignificant, there would be no point in going
13 further in -- the difficulty that we have here
14 is that in order to quantify and define a
15 serial correlation structure from one year to
16 the next, it would be very hard to do with only
17 12 years' worth of data.
18 Q. Is it a limitation of the size of the database
19 that precludes looking at other correlation
20 structures in the database employed?
21 A. In terms of looking at whether higher order
22 terms -- whether there's any high-order serial
23 correlation structure in the values that are
24 spaced one year apart, it would be difficult to
DEPOSITION OF WILLIAM W. WALKER, JR.
879
1 identify those -- such terms with -- with only
2 12 years' worth of data. But the data that I
3 do have indicates that the serial correlation
4 coefficients from one year to the next are low
5 and are not in a range where the applicability
6 of the test should be an issue.
7 Q. On Table 2 of Exhibit 17 under your category
8 for RA values, for example, for the first
9 series there, the RA reported for Year* is
10 0.71. Could you, please, explain to me how that
11 was calculated?
12 A. That was calculated by -- starting from the raw
13 data, assigning the value to years and season
14 so that we have one value for each year and
15 season, performing the Seasonal Kendall test,
16 estimating the significance level of the
17 Seasonal Kendall test and estimating the trend
18 slope using the Seasonal Kendall slope
19 estimator, and subtracting from the seasonal
20 values the effect of the long-term trend using
21 that trend slope; so essentially removing the
22 trend from the seasonal values and subsequently
23 calculating the first-order serial correlation
24 coefficient of the remaining values.
DEPOSITION OF WILLIAM W. WALKER, JR.
880
1 Q. So you basically took a residual as against the
2 estimated Kendall slope?
3 A. That's correct.
4 Q. Let me ask you one question I missed along the
5 way, then I propose we take a break.
6 We were talking about the method you
7 used for deriving detection limits by reviewing
8 the values recorded from the lab. Would that
9 method allow you to detect a change in
10 detection limit at the time the detection limit
11 is changed by the lab?
12 A. The change in detection limit would be revealed
13 by the first observation in the data set that
14 would have an altered detection limit prior to
15 the -- compared to the prior part of the
16 record.
17 Q. So your answer is yes, it would allow you to
18 detect that change when it's made?
19 A. Only in terms of -- with -- only with respect
20 to the frame of reference of the sampling
21 dates. It can't tell you on what particular
22 date between sampling dates a change might have
23 occurred, and it can't tell you at what
24 particular date between sampling dates that
DEPOSITION OF WILLIAM W. WALKER, JR.
881
1 contain values above the detection limit. In
2 other words, the first -- the change in the
3 detection limit would be triggered by the first
4 change in the value reported as below a new
5 detection limit that had not occurred in the
6 previous part of the record.
7 MS. AHEARN: Time for a break.
8 (Short recess)
9
10 BY MS. AHEARN:
11 Q. Referring back to your RA values on Table 2,
12 Exhibit 17, Table 2 is on page 18 of that
13 exhibit.
14 For the RA value under Series A Year*,
15 is this 0.71 a month-to-month serial
16 correlation over the 12-year period?
17 MR. HARRISON: Before we go too far, is
18 Rick Burgess --
19 MR. DAVIS: You can go ahead.
20 MR. HARRISON: Okay. I didn't know if
21 he was missing.
22 A. Yes, with the trend removed.
23 Q. Is the procedure you used here deriving this
24 first order of serial correlation a procedure
DEPOSITION OF WILLIAM W. WALKER, JR.
882
1 commonly used in conjunction with the modified
2 Seasonal Kendall test?
3 MR. HARRISON: Object to form.
4 A. It's a common procedure for calculating a
5 serial correlation coefficient.
6 Q. So this procedure is a common statistical
7 procedure?
8 A. The concept of a serial correlation coefficient
9 and its calculation, yes, is a common
10 statistical procedure.
11 Q. Are you aware of any precedents for using this
12 common statistical procedure as you have
13 employed it here in conjunction with the
14 modified Seasonal Kendall test?
15 A. I'm using it here to quantify serial
16 correlation between years and between adjacent
17 months because that serial correlation bears on
18 the accuracy of the test.
19 Q. In the literature concerning the development
20 and testing of the Seasonal Kendall test, can
21 you point me to any discussions advising on the
22 use of this additional first-order serial
23 correlation?
24 A. I believe there was some discussion of that in
DEPOSITION OF WILLIAM W. WALKER, JR.
883
1 the paper by Berryman et al. in the references
2 that I supplied to the District.
3 Q. Are you aware of any applications of the
4 seasonal order of serial correlation method in
5 conjunction with the modified Seasonal Kendall
6 test to databases derived from actual
7 monitoring of other water systems?
8 A. The paper that I mentioned by Berryman may have
9 had some examples in it and some discussion of
10 applications. I don't recall.
11 Q. Table 2 in Exhibit 17 refers to S12T total
12 phosphorus data. Did you perform similar
13 first-order serial correlation calculations
14 with regard to individual S12 structures?
15 A. Yes.
16 Q. And with regard to S333 and S18?
17 A. Yes.
18 Q. Did you perform similar calculations with
19 respect to the other 19 water quality
20 constituents subject to your analysis?
21 A. Yes.
22 Q. Did you perform adjustments of your PROB2
23 values after you calculated the RA values?
24 A. Only as described in the text.
DEPOSITION OF WILLIAM W. WALKER, JR.
884
1 Q. And that would be at the top of page 19, the
2 first paragraph there?
3 A. No.
4 Q. I'm sorry. Could you point to me where that's
5 described in the text?
6 A. It would be the second paragraph on page 19.
7 Q. I'm sorry. I misspoke. Thank you.
8 Did you adjust PROB2 values for any
9 constituent other than total phosphorus?
10 A. No. As I stated, the only adjustments that I
11 made are described in that paragraph.
12 Q. I just wanted to make sure I was clear. I
13 don't see where this paragraph specifically is
14 limited to total phosphorus. It is limited
15 specifically to total phosphorus?
16 A. Only in the case of total phosphorus did I go
17 to the trouble of making those adjustments.
18 Q. Our review of the text left off on page 9. I'm
19 really not backing up. We'll go quickly.
20 MR. HARRISON: Two steps forward and
21 four back. Okay.
22 Q. In selecting to transform your Series A and B
23 data to log scale, was that one of the
24 decisions you made during your interactive
DEPOSITION OF WILLIAM W. WALKER, JR.
885
1 sessions on the computer?
2 A. The reasons why I used the logtransform are
3 described on page 10.
4 Q. Dr. Walker, this may just be a point of
5 clarification, but we talked about your
6 interactive session on the computer. Was this
7 one of the decisions which you investigated
8 during that session?
9 A. It would be very hard to separate what I
10 learned and the impressions that I got from the
11 interactive sessions with the computer and to
12 identify specifically whether that experience
13 influenced this particular decision.
14 Q. Do you recall if you investigated
15 transformations other than the log10?
16 A. Well, as is stated in the text, the reason for
17 using the log10 was to permit expression of the
18 units of the trend in terms of percent per
19 year, which was a convenient way and less
20 awkward way than expressing it in terms of
21 milligram per liter per year or whatever.
22 Also, the important factor is that the
23 results of the analysis in terms of the
24 significance levels and the probability of a
DEPOSITION OF WILLIAM W. WALKER, JR.
886
1 trend or no trend are independent of this log
2 transformation because the procedure -- the
3 Seasonal Kendall test is based upon rankings of
4 the data.
5 Q. Okay. Did you consider any other
6 transformations?
7 A. No, I did not.
8 Q. In Series C why did you limit your samples to
9 samples collected on days with positive flow as
10 opposed to using the Series A basic data?
11 A. The samples collected on days when there was
12 positive flow reflect the concentrations and
13 loadings of materials actually entering the
14 Park on a particular sample day, and they would
15 have, I would think, greater importance in
16 terms of evaluating trends in concentrations
17 and loadings entering the Park as compared with
18 Series A including the data points when there
19 was no flow. The interpretation of those
20 particular data with respect to impact on the
21 Park is difficult because the water was not
22 moving or at least not moving into the Park.
23 Q. But the two hydrologic variables you're looking
24 at here occur outside the Park, correct?
DEPOSITION OF WILLIAM W. WALKER, JR.
887
1 A. That's correct. They reflect conditions in
2 Water Conservation Area 3A, which is the
3 immediate source of water entering the Park in
4 Shark slough.
5 Q. Could I have you refer to your Equation 1 as it
6 appears in Exhibit 7, page 4, and compare that
7 with Equation 1 on page 10 of Exhibit 17?
8 Are there any changes in this equation
9 other than those that reflect the change in
10 hydrologic variables that you used?
11 A. Yes.
12 Q. And what are those other changes?
13 A. In Exhibit 7, Equation 1, concentrations or the
14 logarithm of concentration is regressed against
15 the logarithm of flow and upstream water
16 elevation where the -- where both the flow and
17 the upstream water elevation were measured on
18 the same day that the sample for concentration
19 was collected. So there was no lagging of the
20 time factor for the hydrologic variables.
21 And in the case of Exhibit 17, the final
22 report, Equation 1, we are dealing here with --
23 instead of flow and elevation, we're dealing
24 with rainfall and elevation. That's one
DEPOSITION OF WILLIAM W. WALKER, JR.
888
1 difference. And the other difference is that
2 in this final version the antecedent periods or
3 the averaging periods for the hydrologic
4 factors, rainfall and water elevation, are
5 adjusted. They are selected by the computer
6 using stepwise regression to find the time
7 scale of rainfall -- in other words, the number
8 of days of antecedent rain or the average --
9 the number of days of averaging the antecedent
10 water elevation, which provides the highest
11 degree of correlation with concentration. And
12 those lag periods and factors are subsequently
13 used in the regression equation.
14 Q. With reference to Exhibit 7, I believe you just
15 said that you relate concentration to the
16 elevation measured on the day of the sample; is
17 that correct?
18 A. In Exhibit 7, correct.
19 Q. In the text that starts right under the
20 expression of the equation, the elevation term
21 reflects the average water surface elevation.
22 What is that average?
23 A. That average is a daily average. It's a daily
24 average over the -- over the day at which the
DEPOSITION OF WILLIAM W. WALKER, JR.
889
1 sample was collected, not a spatial average. It
2 is actually the -- the water elevation measured
3 upstream of S12C. That sentence is somewhat
4 misleading.
5 Q. So in the analysis performed for the July 3
6 draft, you were using just the one gauge
7 upstream, the 12 --
8 A. S12C, the only gauge with a consistent record
9 over the entire period, correct.
10 Q. And is this average recording of -- of --
11 excuse me. Is this average the average of all
12 levels recorded from midnight to midnight on
13 the particular calendar date of a given sample?
14 A. Typically, when one deploys a stage recorder in
15 the field, the stage measurements are recorded
16 at certain time intervals. And there would be
17 some averaging process that would occur to
18 calculate the 24-hour average.
19 In other situations the water elevation
20 may be just recorded at one particular time if
21 it's done manually. I believe that these
22 measurements are made automatically and,
23 therefore, would reflect an average of a number
24 of measurements made over the day.
DEPOSITION OF WILLIAM W. WALKER, JR.
890
1 Q. Were these numbers reported to you as averages?
2 A. They were reported -- they were categorized in
3 the District's water quality database as
4 average daily values, to my recollection.
5 Q. So these aren't averages that you computed from
6 raw gauge readings?
7 A. No.
8 Q. Okay. Had you performed the stepwise multiple
9 regression for optimal values by the time you
10 had prepared the July 3 draft, Exhibit 7?
11 (The witness gave no response.)
12 Q. I mean, I recognize you've told us you had a
13 commitment to produce this document. I'm just
14 wondering, had you done the computer work,
15 performed the multiple regression, prior to
16 this time?
17 A. Are you asking me whether I did the multiple
18 regression that is reflected in Equation 1 of
19 Exhibit 17 before I wrote the first draft of
20 the report in July?
21 Q. Okay. That would be a good question.
22 A. No.
23 Q. Why did you subsequently decide to perform the
24 multiple regression?
DEPOSITION OF WILLIAM W. WALKER, JR.
891
1 A. Well, both of these equations that I have used
2 are multiple regressions.
3 Q. Let me ask my question more clearly.
4 Why didn't you select optimal values for
5 antecedent periods to employ in Equation 1 in
6 Exhibit 7?
7 MR. HARRISON: Object to form.
8 A. The concept of using variable antecedent
9 periods, which is the distinction we're making
10 here between these two drafts, I felt was
11 especially important when we brought in the
12 concept of using antecedent rainfall because
13 it's not obvious beforehand if one is trying to
14 correlate rainfall with concentration measured
15 at a certain time, there is no basis a priori
16 to specify the averaging period for the
17 rainfall. In other words, should I use the
18 rainfall on the sampling day? Should I use the
19 rainfall over the past week? Should I use the
20 rainfall over the past month? My answer to
21 those questions is I don't know.
22 So the way that I asked -- I get the
23 answer to that question is I do -- I set up the
24 programs so that they select -- they search for
DEPOSITION OF WILLIAM W. WALKER, JR.
892
1 the antecedent periods, the lengths of time
2 that provide the highest degree of correlation
3 between concentration and antecedent rainfall
4 and between concentration and antecedent water
5 elevation, and use that to adjust the
6 concentrations for hydrologic variability in my
7 Series C.
8 Q. What do you look at -- what factor or value do
9 you look at to determine which antecedent
10 period provides the highest correlation, the
11 optimal correlation?
12 A. I used a stepwise regression routine. I
13 believe the criterion that was used to select
14 the ideal or the optimal time scale was either
15 based upon something such as R2 or the
16 significance level of the regression term. I
17 don't recall precisely.
18 Q. So you may have used the P values as the
19 criterion for selecting the antecedent period?
20 A. Possibly.
21 Q. But you're not sure?
22 A. The P values in the multiple regression.
23 Q. Would you be able at this point to explain the
24 algorithm that you used? Would you be able to
DEPOSITION OF WILLIAM W. WALKER, JR.
893
1 explain that step by step?
2 A. In general terms.
3 Q. Okay.
4 A. The algorithm would involve starting with a
5 complete matrix or a table, if you will, where
6 each row would be a different sample, and for
7 each sample there would be a value for
8 concentration and there would be a value for
9 total antecedent rainfall over one day, seven
10 days, thirty days and so forth as indicated on
11 page 10. And there would also be a value for
12 antecedent water elevation averaged over one
13 day, seven days, thirty days, so forth. So
14 that would comprise a table.
15 I would then compute what is called a
16 correlation matrix or covariance matrix using
17 that table and starting with -- and then
18 address each hydrologic factor. Say if we
19 addressed rainfall, the program would search
20 for the rainfall term or the lag time one day,
21 seven days, thirty days, whatever, that was
22 most highly correlated with concentration and
23 include that in the regression equation. And
24 the next -- if -- it would be included in the
DEPOSITION OF WILLIAM W. WALKER, JR.
894
1 regression equation only if the P level for
2 that term was less than .1 -- that is, if in
3 fact there was a significant correlation
4 between rainfall for any of the time scales and
5 concentration.
6 If that procedure resulted in inclusion
7 of a rainfall term, I would then adjust the
8 concentrations by removing the portion of the
9 variability that is correlated with the
10 rainfall term and then search each of the
11 elevation terms to find the time scale that was
12 most highly correlated with elevation -- with
13 concentration. And from that exercise, I would
14 end up with an equation that had one term for
15 rainfall and one term for water elevation that
16 was correlated with concentration.
17 I tried alternative techniques as part
18 of the sensitivity analysis for fitting these
19 regression equations and found them to lead to
20 similar results in terms of the overall
21 significance level of the trend at S12s.
22 Q. Did you use what Snedecor and Cochran would
23 term a step-up procedure?
24 A. I used a stepwise regression equation. I guess
DEPOSITION OF WILLIAM W. WALKER, JR.
895
1 it would be termed a step-up, that's correct,
2 as opposed to a step-down.
3 Q. How many degrees of freedom did you lose when
4 you decided to use the log10 transformation?
5 A. For what purpose?
6 Q. You're asking me for what purpose you decided
7 to use the logarithmic transformation?
8 A. What are you referring to? When I used the
9 log -- you say when I used the log10
10 transformation. I used it in several instances
11 here.
12 Q. When you decided to use the log10
13 transformation for your Series A, B and C data,
14 how many degrees of freedom for application of
15 the Seasonal Kendall test did you lose?
16 MR. HARRISON: Objection, Counsel. For
17 all three combined, all three series? I just
18 want the witness to specify what his answer is
19 relating to, if he is capable of doing that
20 with that question.
21 A. In the case of Series A, B or C, I would not
22 interpret use of log10 transformation as loss
23 of any degrees of freedom.
24 Q. Some of the structures subject to your analysis
DEPOSITION OF WILLIAM W. WALKER, JR.
896
1 in Exhibit 17 are pumped structures, aren't
2 they?
3 A. I believe that S332 has a pump. I think 18C
4 may have a pump. I don't recall exactly.
5 Q. Are there any adjustments or special
6 statistical procedures that you should employ
7 to reflect the different nature of pumped
8 structures?
9 A. The flow values -- the daily flow values that I
10 have used for each of the structures would
11 reflect the combined flow through the pump plus
12 whatever might have occurred over a spillway if
13 such a structure existed at the particular
14 monitoring station. Other than reflecting the
15 total flow or the total volume released into
16 the Park on a particular day, there was nothing
17 special that needed to be done to account for
18 pumped flow as compared with released flow or
19 spilled flow.
20 Q. In terms of the factors that may impact a trend
21 in total phosphorus concentrations, are there
22 differences between pumped structures and those
23 structures that are not pumped?
24 MR. HARRISON: Object to form.
DEPOSITION OF WILLIAM W. WALKER, JR.
897
1 "Factors" is just too general. Go ahead.
2 A. The problem in your question is that when you
3 say "structures that are not pumped," that
4 could include a wide range of different type of
5 structures that could very well have some
6 distinction with pumped structures. So I can't
7 answer your question. It's way too general.
8 Q. I guess Mr. Harrison's right.
9 Are there any particular factors or
10 features of which you are aware with regard to
11 the impact of a pumped structure on total
12 phosphorus concentrations?
13 MR. HARRISON: Object to form.
14 A. Again, you would have to compare it to some
15 other scenario.
16 Q. Are you aware of any factors with regard to the
17 pumped structures you looked at compared to the
18 other structures that you looked at that didn't
19 have pumps?
20 MR. HARRISON: I object to form. Do you
21 have any of these factors in mind that you
22 might give him some specific guidance as to
23 what you're looking for?
24 MS. AHEARN: I'm wondering if the doctor
DEPOSITION OF WILLIAM W. WALKER, JR.
898
1 looked at this issue and if he identified any
2 structures that distinguished the pumped
3 structures from all other structures.
4 A. There is nothing special about the existence of
5 a pump, but there may be some distinguishing
6 characteristics between those structures with
7 pumps and those structures without pumps.
8 Q. Did you identify any such distinguishing
9 features?
10 A. Well, in the case of S332 and S18C the flow
11 releases into the Park are made from
12 essentially canal environments, canal systems,
13 and that is a different situation as compared
14 with releases through the S12s, where flow is
15 essentially released from a reservoir upstream
16 from Water Conservation Area 3A.
17 Q. Have you identified any other distinguishing
18 features?
19 A. Well, there are certainly geographic
20 differences and differences in watersheds.
21 Q. Any other distinguishing features which relate
22 to total phosphorus concentrations?
23 A. The sources of the water at the individual
24 structures would be different. There's lots of
DEPOSITION OF WILLIAM W. WALKER, JR.
899
1 distinctions from one structure to another.
2 That's my answer.
3 Q. Dr. Walker, have you performed any tests for
4 trend within the hydrologic variables you have
5 employed in Series C, both your Exhibit 7 and
6 your Exhibit 17 versions?
7 A. You're asking me if I tested for trends in the
8 hydrologic variables themselves?
9 Q. Yes.
10 A. Not to my recollection.
11 Q. If you could, please, turn to page 5 in
12 Exhibit 7. There is an Equation 2 expressed
13 mid page and then a paragraph of text under
14 that. Could you, please, read the last
15 sentence in that paragraph? It starts with
16 "More detailed analyses..." Could you read it
17 aloud, please?
18 A. More detailed analyses would be
19 needed to distinguish among alternative
20 trend shapes and to investigate causal
21 factors for those time series with
22 significant apparent trends.
23 Q. Today do you still agree with that statement?
24 MR. HARRISON: I would caution the
DEPOSITION OF WILLIAM W. WALKER, JR.
900
1 witness to ensure that he is comfortable with
2 the context of that statement in Exhibit 7. If
3 he feels the need to read the paragraph, fine.
4 MS. AHEARN: Please, Mr. Harrison.
5 That's a lot of coaching.
6 MR. HARRISON: It's not coaching. I'm
7 not going to let you ask him whether he agrees
8 with a sentence, Counsel, taken out of context
9 if it is out of context. I'm simply cautioning
10 the witness to look at the entire paragraph
11 that it's contained in, which is something that
12 you should have certainly offered in your
13 question. There is no coaching here at all,
14 Counsel. I don't know enough to coach the
15 witness on it.
16 MS. AHEARN: If there's a context,
17 Exhibit 7 clearly provides it.
18 MR. HARRISON: It certainly does.
19 A. Well, as is stated in the sentence above the
20 one that I just read:
21 The basic objective is to determine
22 whether the underlying frequency
23 distribution of concentration (or
24 concentration at a given flow and
DEPOSITION OF WILLIAM W. WALKER, JR.
901
1 upstream surface water elevation) is
2 stable over the time period examined.
3 Q. Do you agree with the sentence that follows
4 that?
5 A. I agree that the work that has been completed
6 to date is sufficient for defining the
7 existence of trends in concentration and
8 loading at various -- under various hydrologic
9 conditions at these locations.
10 Q. Is it tough to distinguish among alternative
11 trend shapes?
12 A. The -- as is stated in this sentence and as is
13 also stated in Exhibit 17, the method that I
14 have used does not distinguish among
15 alternative trend shapes.
16 Q. Is it sufficient to investigate causal factors?
17 A. As we discussed yesterday or last week, the
18 analysis provides information on trends. It
19 provides descriptions of correlations that can
20 be used and interpreted that can -- that can be
21 helpful for formulating opinions regarding
22 causation in the system. But the trend
23 analysis itself does not quantify the causal
24 factors.
DEPOSITION OF WILLIAM W. WALKER, JR.
902
1 Q. Why was this sentence in Exhibit 7 dropped from
2 Exhibit 17?
3 A. Because I view the investigation of the causes
4 and the delineation of the causes as a separate
5 task, as a more involved task, as compared with
6 the identification of the existence of the
7 trends.
8 Q. If you would turn to page 6 in Exhibit 7, the
9 last line of the first full paragraph on that
10 page, why was that sentence dropped from
11 Exhibit 17?
12 MR. HARRISON: I'm going to object to
13 your characterization. I don't doubt that it
14 was, but I think it's more preferable to ask
15 the witness if it was. And I would just
16 caution the witness to ensure that it was
17 dropped prior to answering that question. We
18 have had no testimony on that yet.
19 MS. AHEARN: But we do have the two
20 versions of the document identified by the
21 witness.
22 MR. HARRISON: Which will speak for
23 themselves, Counsel. I mean, if you don't want
24 the documents to speak for themselves, I'm
DEPOSITION OF WILLIAM W. WALKER, JR.
903
1 simply asking you the courtesy of asking him
2 the question to lay a foundation as to whether
3 or not it was dropped. It is certainly
4 conceivable that you could have missed
5 something.
6 A. I can't give a particular reason why that
7 sentence was dropped. It was apparently an
8 editorial decision on my part.
9 Q. Did you employ any analyses using a
10 significance level of .05?
11 A. I -- there was nothing specific to any of this
12 regarding assumptions on significance levels.
13 The results are reported in terms of the P
14 levels, and one can apply whatever -- whatever
15 criterion one wishes in terms of distinguishing
16 between the presence of trend and the absence
17 of trend.
18 As described in both exhibits, a
19 two-tailed hypothesis -- that is, a hypothesis
20 of no trend -- I have used the value of .1 just
21 for convenience purposes just to summarize and
22 tabulate the results. If one is asking the
23 question of whether or not there is an
24 increasing trend in phosphorus, then it is
DEPOSITION OF WILLIAM W. WALKER, JR.
904
1 appropriate to divide that significance level
2 in half so that we are actually talking about a
3 significance level of .05 for summarizing the
4 results with respect to a null hypothesis that
5 assumes that there is no increasing trend in
6 phosphorus.
7 But, as I stated earlier, the report
8 tabulates the actual P levels or the actual
9 significance levels that come out of the
10 Seasonal Kendall test, and they can be
11 interpreted by whoever wants to interpret them.
12 Q. In your interpretations, have you ever employed
13 the .05 significance level?
14 (The witness gave no response.)
15 Q. Well, Dr. Walker, in Exhibit 17 you report the
16 existence of trends, correct?
17 A. I report the likelihood of trends.
18 Q. Okay. In coming to that conclusion from your
19 analysis, what P level did you employ?
20 A. In tabulating the results, as I stated, I used
21 a P level of .1 for a two-tailed hypothesis,
22 which is equivalent to a P level of .05 for a
23 one-tailed hypothesis.
24 Q. A little bit farther down on page 6 of
DEPOSITION OF WILLIAM W. WALKER, JR.
905
1 Exhibit 7, the paragraph that starts "The test
2 data set includes 282 observations..." this
3 line in Exhibit 17 has the number 281.
4 MR. HARRISON: What page on 17, Counsel?
5 MS. AHEARN: Page 14.
6 Q. Can you explain the difference?
7 A. To my recollection, there was one sample that
8 was provided to us by the District that was
9 actually collected in October of 1989. We did
10 not have -- or I did not have the flow data or
11 the elevation data or the hydrologic data that
12 would correspond to that sample. And in the
13 draft analysis that is described in the
14 July 30th document, Exhibit No. 7, that sample
15 that was collected in October of 1989 I believe
16 was incorporated in the analysis in the final
17 version. Because I did not have the hydrologic
18 data for the October 1989 period, I excluded
19 that last sample and restricted the period as
20 described to December '77 through September of
21 1989, and that is the reason for the one-sample
22 decrease in the number of observations, which
23 had no significant effect on the results.
24 Q. Did you have to rerun all of the computer
DEPOSITION OF WILLIAM W. WALKER, JR.
906
1 programs?
2 A. Yes.
3 Q. What percentage of biweekly sampling values was
4 missing from the data that you obtained from
5 the District?
6 A. I don't recall.
7 Q. Was it as many as 15 percent?
8 A. I don't recall.
9 Q. Is it your understanding that 100 percent minus
10 a significance level is a confidence level?
11 A. I have seen it referred to as that, yes.
12 Q. Is that the definition you employ when you talk
13 about a confidence level?
14 A. Generally, yes.
15 Q. If you turn to page 16 in Exhibit 17, is it
16 accurate to say that the whole of the
17 correlation of hydrologic variables to
18 phosphorus concentration is less than the sum?
19 MR. HARRISON: Object to form.
20 Q. I just want to make sure I conceptualize this
21 properly as a layperson. For example, at the
22 top of page 16 you talk about regression
23 against elevation explaining 40 percent,
24 regression against antecedent rainfall
DEPOSITION OF WILLIAM W. WALKER, JR.
907
1 explaining 33.5 percent.
2 If you were to take these and other
3 hydrologic variables and figure out what
4 percentage of the phenomenon they individually
5 explain, you don't get their cumulative effect
6 by adding up those percentages, do you?
7 A. That would depend upon the particular data set
8 that you were analyzing. In some situations,
9 yes, you would get a cumulative -- you would
10 get a sum that would equal the components.
11 Q. Can you give me an example of a data set where
12 you would sum the components?
13 A. Well, you would never perform that sum. You
14 would always perform the regression analyses
15 just as I have done here.
16 Q. Can you give me the example where these
17 hydrologic variables wouldn't have that
18 overlapping effect?
19 A. In situations where the hydrologic factors such
20 as rainfall and water elevation in this example
21 are not correlated with each other. And if
22 their effects on the concentration are not
23 correlated with each other -- that is,
24 correlated between the hydrologic factors --
DEPOSITION OF WILLIAM W. WALKER, JR.
908
1 then you might approach an additive situation
2 such as you described.
3 Q. Do you have a real-world situation in mind
4 where that's the case?
5 A. That's rarely the case.
6 Q. The last sentence of this top paragraph on
7 page 16, you explained a reason for performing
8 your regressions as to generate a time series
9 of residuals which is statistically
10 independent.
11 Wouldn't it be more accurate to say that
12 this time series is uncorrelated?
13 A. Another way of describing it or stating it
14 would be to state that the objective is to
15 generate a time series of residuals which is
16 statistically uncorrelated with antecedent
17 rainfall and elevation for subsequent trend
18 testing. I don't know that stating it that way
19 is any more or less accurate than the way that
20 I have stated it using the word "independent."
21 Q. Are the residual values independent of the
22 hydrologic variables in a literal sense?
23 MR. HARRISON: Object to form.
24 A. In a statistical sense they are uncorrelated
DEPOSITION OF WILLIAM W. WALKER, JR.
909
1 and statistically independent of the hydrologic
2 factors because that is what would come out of
3 the regression analysis.
4 (Exhibit No. 39 marked for
5 identification)
6 Q. Dr. Walker, could you, please, identify
7 Exhibit 39?
8 A. These are graphs of total phosphorus
9 concentration, load and flow data from inflow
10 points to the Park.
11 Q. First I'd like to use this for illustrative
12 purposes. If we look at the first graph that
13 appears on page 1 here, you have a number of
14 data points plotted for I guess it's Period 2.
15 Those are the diamonds?
16 A. Correct.
17 Q. And then a regression line for that set of
18 data?
19 A. Correct.
20 Q. If I were to tell you that this diamond that
21 you have in the upper left-hand corner is in
22 error, in fact we have confirmed that there was
23 never any data collected on that day and you
24 should remove that from your analysis, under
DEPOSITION OF WILLIAM W. WALKER, JR.
910
1 that hypothesis -- hypothetical, excuse me, if
2 you were to make that change, would the
3 residuals for all other values for Period 2
4 change?
5 A. If you remove one data point from the graph,
6 would the other values change?
7 Q. The residuals.
8 A. Offhand I can't -- I don't understand how
9 removing one data point can change anything --
10 any of the other data points on the graph.
11 Q. Well, you've plotted concentration against flow
12 here, right? We're talking about actual
13 measurements?
14 A. Correct.
15 Q. And then the distance from each plotted point
16 from the regression line would be the residual?
17 A. Correct.
18 Q. If you remove this data point that I have
19 identified as being spurious, will your
20 regression line change? Will the slope of your
21 regression line change?
22 A. If you repeat the regression?
23 Q. Do whatever recalculations you feel are
24 appropriate.
DEPOSITION OF WILLIAM W. WALKER, JR.
911
1 MR. HARRISON: Object to form.
2 A. I don't know what you're asking, so I don't
3 know what's appropriate. I can't see why
4 removing one data point is going to change
5 other data points.
6 Q. Let me try and rephrase it one more time
7 because I think I just had a hard time
8 communicating this thought to you.
9 If we were to remove this spurious data
10 point and you were then to refit the regression
11 line to the corrected data set, would the
12 residuals calculated from that new regression
13 line change, the regression value associated
14 with each particular data point which I'm not
15 changing that are plotted on this graph?
16 A. Well, if you had a hypothetical sample such as
17 that and you hypothetically removed it and you
18 hypothetically fit a new regression line, then
19 there would be -- there may be some effect on
20 the residuals from the other data points,
21 that's correct.
22 Q. So in my hypothetical the residuals of the
23 values in Period 2 are statistically
24 interdependent with the erroneous data value
DEPOSITION OF WILLIAM W. WALKER, JR.
912
1 point -- if I change that, I change the rest?
2 A. The regression line would not necessarily
3 change upon removing a particular data point.
4 Q. Well, in my hypothetical here when I'm going to
5 remove this --
6 A. Well, I don't understand what -- what the point
7 of a hypothetical removal of a hypothetical
8 data point is.
9 Q. Just to try and discuss a concept. That's
10 okay. Let's get back to specifics.
11 Why did you generate Exhibit 39?
12 MR. HARRISON: I don't believe that's
13 been established. Maybe it has. I can't
14 remember hearing him identify it. Maybe that's
15 my problem.
16 Q. You have identified this as being a document
17 you produced, correct?
18 A. I don't think I've identified that for the
19 record.
20 Q. Is this your handwriting on it?
21 A. Yes, it is.
22 Q. Is this a document you produced?
23 A. Yes.
24 Q. Okay. Why?
DEPOSITION OF WILLIAM W. WALKER, JR.
913
1 A. This was a sort of an exploratory or
2 supplementary analysis that I did just to
3 examine the relationships between
4 concentration, flow and load, phosphorus load,
5 at each structure for different time periods.
6 Q. At what time did you perform this analysis?
7 A. I don't recall. It would have been probably in
8 1990 sometime.
9 Q. Did you generate Exhibit 39 in conjunction with
10 the analyses which are the basis for
11 Exhibit 17?
12 A. I generated this exhibit using the same data
13 that are used in Exhibit 17, but I wouldn't say
14 that I generated it in conjunction with that
15 exhibit.
16 Q. Did you rely on Exhibit 39 for purposes of
17 performing the analyses reflected in
18 Exhibit 17?
19 A. Well, the results shown in Exhibit 39 are
20 generally consistent with those found and
21 described in Exhibit 17 in that they support or
22 suggest the presence of higher phosphorus
23 concentrations at a given flow and higher
24 phosphorus loadings at a given flow at these
DEPOSITION OF WILLIAM W. WALKER, JR.
914
1 structures when one compares the early part of
2 the record which I identify in Exhibit 39 as
3 Period 1, the first five years of data, and the
4 remaining portion of the record identified as
5 Period 2. In other words, the -- excuse me,
6 the phosphorus concentrations were higher in
7 Period 2 as compared with Period 1.
8 Q. On each page here in Exhibit 39 do these
9 reflect separate regression analyses, for
10 example, where you would fit the regression
11 line to the concentration data and then perform
12 a separate calculation for load?
13 A. During each period a separate regression is fit
14 between concentration and flow or between load
15 and flow.
16 Q. Are you aware that the regression equation for
17 load could have been derived exactly from those
18 for concentration?
19 A. Well, they're essentially the same thing,
20 that's correct.
21 Q. The reference here to "Method: 6 REG-3," what
22 does that mean?
23 A. That essentially identifies a particular method
24 for representing the relationship between
DEPOSITION OF WILLIAM W. WALKER, JR.
915
1 concentration and flow, and that particular
2 method is to regress concentration against
3 flow.
4 Q. The concentration values that you have plotted
5 here, are those flow-weighted?
6 A. These are individual sample values, and on
7 page 1 here we're looking at data from S12T,
8 which is the composite cross session for S12A,
9 B and C.
10 Q. On page 2, the bottom graph, what does the
11 reference "Method: 7 MULTI" refer to?
12 A. That would refer to an alternative way of
13 representing the concentration or load versus
14 flow relationship. But in this example I
15 believe that the way I applied that alternative
16 method, it would be essentially the same as
17 simply regressing concentration against flow
18 for each of the two time periods.
19 Q. On the third page of Exhibit 39, what does
20 "Method: 2 Q WTD C" refer to?
21 A. That means essentially instead of correlating
22 concentration against flow for this particular
23 station, that correlation was not significant.
24 So "2 Q WTD C" is just -- in that situation we
DEPOSITION OF WILLIAM W. WALKER, JR.
916
1 are representing the concentration as merely
2 the flow-weighted average concentration for the
3 entire data set for the entire time period.
4 Q. Are these graphs on the log scale?
5 A. That's correct.
6 Q. Is that true for each page of Exhibit 39? If
7 you could just point out any graphs that aren't
8 on the log scale.
9 A. I believe they're all on log scales.
10 Q. How did you determine how to split your
11 Period 1 and Period 2?
12 A. Period 1 was essentially the first five years
13 of data that we had used in the ONRW
14 discussions and have used in developing the
15 interim standards for the federal remedy to the
16 lawsuit as a baseline period for developing
17 standards.
18 Q. How about for Taylor slough and the Coastal
19 Basin? How did you decide where to cut the
20 data there?
21 A. I believe I attempted to cut the data set
22 approximately in half.
23 Q. Were you surprised when you saw a decreasing
24 trend in nitrogen?
DEPOSITION OF WILLIAM W. WALKER, JR.
917
1 A. I did not anticipate a decrease in the trend in
2 nitrogen.
3 Q. On page 17, paragraph numbered 3, you state
4 that increases in nutrient concentrations have
5 been observed. By "nutrient concentrations"
6 there, do you include both phosphorus and
7 nitrogen?
8 A. At least with reference to that particular
9 report by Worth, 1988, I don't recall whether
10 his work documents such changes in nitrogen,
11 but I know that I was at least referring to
12 phosphorus. Whether I was also including
13 nitrogen as part of that, I don't recall.
14 Q. Does leaching from plant detritus, increased
15 peat mineralization and concentration by
16 evaporation as a general matter commonly lead
17 to increased nitrogen concentrations?
18 MR. HARRISON: I object to form.
19 A. Not necessarily.
20 Q. Does it in some instances and not others?
21 A. It would depend upon the relative magnitudes of
22 the nitrogen sources and sinks in a particular
23 environment.
24 Q. In the Everglades does the leaching of plant
DEPOSITION OF WILLIAM W. WALKER, JR.
918
1 detritus lead to increases in nitrogen
2 concentrations?
3 MR. HARRISON: Increases --
4 A. It is very hard to generalize about that on
5 nitrogen.
6 Q. In Water Conservation Area 2A during the water
7 level drawdown, do you know whether the
8 phenomenon you report here in this Paragraph 3
9 increased nitrogen concentrations?
10 A. I don't recall specifically.
11 Q. Does the term "hydroperiod" have a specific
12 meaning for you?
13 A. It has a general meaning.
14 Q. And what does that term mean to you?
15 A. It would mean that portion of the year at which
16 there is standing water at a given location.
17 Q. Have you ever heard the term "hydroperiod" used
18 to refer to the combined pattern of timing,
19 duration and volume of water at a given
20 location?
21 A. Well, I suppose that the term may have
22 different meanings for different people but --
23 Q. Do you know how the term is usually used in the
24 context of the Everglades?
DEPOSITION OF WILLIAM W. WALKER, JR.
919
1 MR. HARRISON: Object to form. Usually
2 by whom?
3 Q. Do you know how the term is usually used among
4 scientists who have studied the Everglades?
5 A. I have given the definition that I would
6 normally ascribe to the term. I don't know.
7 Other people may have other versions of that
8 definition.
9 Q. Dr. Walker, rather early in Exhibit 17 you make
10 the case for the modified -- the second version
11 of the Seasonal Kendall test because it
12 accounts for serial correlation.
13 Why did you continue your analysis and
14 report your analysis for both versions, that
15 with and without serial correlation?
16 A. Well, first of all, because there were some
17 differences of opinion within the statistical
18 community as we discussed regarding, for
19 example, Mr. Loftis' opinion regarding the fact
20 that this version of the test using serial
21 correlation is too conservative and would,
22 therefore, miss trends and should not be used,
23 I felt that reporting both versions of the test
24 would provide as complete a picture as possible
DEPOSITION OF WILLIAM W. WALKER, JR.
920
1 regarding the probability of trends.
2 And the other important factor is that
3 the version of the test that accounts for
4 serial correlation is -- has been shown to be
5 conservative -- that is, to be probable of
6 missing trends, especially in time series that
7 are less than ten years in length. And two of
8 the time series that I'm examining here, S18C
9 and S332, have durations on the order of six
10 years.
11 So the trend magnitudes estimated by the
12 second test -- not the trend magnitude but the
13 significance levels may be overestimated by the
14 test in those examples.
15 Q. In formulating your opinions concerning the
16 South Florida litigation, will you be relying
17 on both versions of the Seasonal Kendall test?
18 MR. HARRISON: Object to the form of the
19 question.
20 A. I will be relying on all the information and
21 all the analyses that I have conducted. That
22 will include both versions of the Seasonal
23 Kendall test.
24 Q. Is that true also for your tre
