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Filed November 13, 2001 THOMAS N. TWAITES, PH.D., LICENSED PSYCHOLOGIST, Retired Black Dog Amphitheater Metropolitan Significance Review Q: What is your name? I hold a Doctorate (Ph.D.) from the University of Minnesota, graduating from the University of Minnesota in 1974. My major was Clinical Psychology, my minor was Neuropsychiatry, with an emphasis in Statistics and research methodology. I interned at the U.S. Veterans Administration Hospital, Minneapolis, Minnesota. I have regularly participated in numerous professional development educational courses and conferences over the years, many of them related to research and the scientific method. From 1969 to 1975, I served as Executive Vice President of Human Resource Associates, Hastings, Minnesota, a human relations and organizational development consulting firm. From 1969 to 1995, I served as a psychological consultant to the Hazelden Foundation, Center City, Minnesota. From 1969 to 1999, I served as a psychological consultant to the State of Minnesota Correctional Facility at Red Wing, Minnesota. In each of these positions, there was an element of clinical research. At Hastings State Hospital and the Minnesota Correctional Facility at Red Wing, I supervised and assisted undergraduate and graduate students in various research projects. The BAC/CARE mediation team had
repeatedly asked to have a sound study done during the summer concert season
-- one employing realistic musical content which could help everyone understand
how loud the sound might be, whether or not there would be anything to
worry about. This request was frustrated at every turn:
The BAC/CARE mediation team continued to request further testing DURING THE SUMMER CONCERT SEASON to fairly assess the acoustical impact of the amphitheater on our communities. We continued to express a need for a real-time sound source in such testing. Other participants in the mediation group had no interest in, or were unwilling to make further financial commitments for, such a purpose. BAC/CARE offered to finance additional sound testing -- without success. The property owner of the proposed amphitheater site ignored our written request to access the property for this purpose; the Rose Wild, LLC, refused to support further testing under any conditions. Thus stymied, BAC/CARE determined to undertake real-time, musical sound testing from an alternative site — on the brink of summer. Nevertheless, it seemed worthwhile to proceed with a demonstration of sound levels to help residents understand what amplified music within the legal sound limits could sound like. Advised by our BAC/CARE acoustical
consultant that data procured from testing from an alternative site would
not be equivalent to that obtained in earlier studies -- no matter how
extensive the measurements -- we scaled-down the study to a demonstration,
utilizing consumer grade instrumentation for calibration and control purposes.
We employed a professional sound company to supply and operate the amplification
equipment for the demonstration. Our goal was to simulate a real concert,
using real music, so that residents might judge impact for themselves.
At that point, no specific date for the sound demonstration had been set since it was contingent upon weather conditions; since the weather that week-end was quite variable, we only made the decision to proceed late Sunday afternoon, September 9th. The Burnsville police were notified at that point, about 4 PM, by Joe Artmann, who spoke directly with the on-duty dispatcher. A similar notification had been provided to the City of Bloomington. METROPOLITAN COUNCIL: Yes -- by a series of requests made during the mediation sessions seeking support in convincing the landowner to grant the citizens groups access to the proposed amphitheater property for the purpose of a scientific sound study. This request was made repeatedly, both orally and in writing, without success. It was assumed that the open requests made during mediation in the presence of the Metropolitan Council Mediator, Roger Williams, and Staff Members, Jim Uttley, Lynn Belgea, and Sandi Dingle, were sufficiently clear to inform the council of our intention. Finally, Rose Wild stated in writing that they do nothing to further such a sound test. Since it was clear there was no support for our proposal, we proceeded on our own, scaling the test back to a demonstration since we could not gain access to the amphitheater property. Date: Sat, 08 Sep 2001 21:36:12 -0500 From: Tom and Marion Twaites <twait001@maroon.tc.umn.edu> To: CARE supporters <care@care.com>
The amphitheater developer would not grant access to the site for further study of sound propagation during the summer concert season, although we have made several requests to this end. Consequently, we have been forced to simulate concert sound levels from a different site and cannot claim direct comparability to earlier studies. Depending upon weather conditions, you might hear this demonstration in Burnsville. The test demonstration will be underway between 7 pm and 10 pm. Give a listen and let us know what you heard, where, and when! One can only ask, why did the met council report NOT rely upon Mr. Watson’s report in view of the MPCA’s meteorological requirement? If amphitheater proponents now bring Mr. Watson forth in defense of their position, they must have changed their minds about him. Note that, on April 12, 2001, the consultants dismissed the relevancy of Mr. Watson’s EAW comments and predictions because "Many of Bruce Watson’s comments about weather and meteorological conditions in the area are anecdotal, granted, backed by years of experience. No one can predict the frequency and/or timing of such conditions as inversions, wind velocity or direction." The fact remains that while the MPCA-required meteorological analysis in the EAW report, no significant analysis of meteorological data was done in the Metropolitan Council report. Contrary to the consultants statement that no one can predict the frequency of inversions, wind velocity, or wind direction, anyone with the appropriate data and skill CAN predict the frequency and pattern of such conditions. This is simply a matter of probability and base rates. Probabilistic prediction is a mainstay of science: Although no given instance can be predicted with much accuracy, patterns are quite readily predicted. Scientific disciplines such as meteorology, biology, opinion research -- and even physics -- rely upon predictions made from past observations. SUBMITTED DOCUMENT
CRITIQUE AND ANALYSIS OF THE METROPOLITAN SOUND STUDY REPORT By Tom Twaites Citizens’ Alliance for Responsible Ecology INTRODUCTION Residents who have lived here for years readily provide accounts of clearly audible events far away in the valley. It is not uncommon to hear train whistles in the valley from great distances, the drone of their diesel engines, even the clicking of their wheels on tracks. Various construction and mining activities in the valley have proven to be noisy annoyances to citizens in both Bloomington and Burnsville. On some occasions, state authorities have been enlisted to remedy these problems. Thus, it was with some genuine surprise that residents on both sides of the river read the assurances from BV officials that an amphitheater located adjacent to the superfund toxic waste site, the old Freeway Landfill, would not cause noise problems. As a part of the approval process, the developer and Burnsville prepared documents attesting to its limited environmental impact, especially in the Environmental Assessment Worksheet. As part of that, a minimal sound study was conducted in January, 2000. Since the concert season would be from late spring to early autumn, the timing of this sound study seemed inappropriate. It is known that air temperature, wind, humidity, and atmospheric temperature inversions – all factors which differ from summer to winter -- play a part in limiting or enhancing sound propagation This was done in spite of the fact
that factors which play a part in limiting or enhancing sound propagation
(winds, temperature inversions, air temperature, and atmospheric humidity)
differ between summer and winter. Many residents were suspicious of this
study inasmuch as it seemed illogical to draw conclusions about summertime
sound transmission from a wintertime study. Further, since the sound used
in the EAW study was plainly intelligible to numerous residents of the
valley – anecdotes regarding the perceived sound level began to surface
immediately:
If Bloomington residents can clearly hear people speaking in conversational tones from barges on the river, trains, whistles, and clicking/clacking rails – which are further away from them than the amphitheater would be (and certainly less than 93 dB – it is reasonable to believe that they would clearly hear rock music from a closer amphitheater). As will be seen, when the initial Paoletti study for the EAW was finally released, it supported their concerns: There would be an negative impact upon the communities of Bloomington and Burnsville. Putting the best face on it, Burnsville and the developer insisted that the impact would be minimal, infrequent, and involve just a few residences. Now, having moved on to another study, the developer and the City of Burnsville seem to have chosen to ignore the findings of the original EAW It is our contention that ALL relevant facts about the transmission of sound in the Minnesota River Valley must be considered by the Metropolitan Council in considering the matter of Metropolitan Significance. These relevant facts must include
both Primary and Secondary Noise Impacts. Primary impacts have to do with
the usual decibel-related issues, noise standards, and the direct impact
of noise on human quietude, wildlife breeding and behavior, along with
other sound-connected wildlife issues. Secondary impacts are by-products
of the activities of people who are attracted by the noise of the amphitheater,
thereupon affecting the social and natural environment.
2. Partying humans attracted to areas neighboring the amphitheater -- attracted by its noise (free-loading at concerts, etc.), they end up setting fires, either accidentally or deliberately (as happened a year ago in the Burnsville portion of the refuge). 3. The amphitheater noise bringing
intruders onto residential properties while in transit to the parklands
across from the amphitheater. Vandalism and theft on private property impact
residents because the amphitheater would be an attractive nuisance.
Rose Wild and BV have accepted that the EAW study was sufficient by submitting and approving it as the basis of an EIS decision. The Metropolitan Council sound study was to supplement it, not supplant it. Therefore, statements from it should be acceptable in evidence. (If the EAW analysis is not acceptable in evidence, then the RGU’s past acceptance of it is inconsistent and casts doubt on decisions based upon it.) Most importantly, no adequate study of valley acoustics can exist in a vacuum -–it must explain all of the data. Is the proper range of data being sampled? How is it defined? To study the seasonal acoustic patterns, one must obtain representative samples of relevant information throughout the entire season in which we are interested. If we are concerned with acoustic patterns during the summer season, sample measurements must include the coolness of June, the heat of July and August, and the dry briskness of September – all qualities, along with others, which bear upon sound propagation. (Ideally, observations from several summers would provide more stable data and therefore more reliable conclusions.) On the other hand, if the goal is to study daily acoustic patterns from morning to evening, then sampling would be done on an hour-to-hour, or minute-to-minute, basis (ideally, throughout a series of days for increased reliability and validity). While the focus of the Amphitheater study is acoustical patterns throughout a concert season, the Cavanaugh study has been framed on an hour to hour basis, sampling periodically during the span of just a few days. At best, this would allow conclusions about background levels and propagation patterns during the span of a day. It says nothing about the patterns which might be expected to develop over a longer time span under varying seasonal conditions. The sampling done by Cavanaugh, et al, is not representative of a longer period of time, such as a week, a month, or a season. Thus, it is not appropriate to draw conclusions regarding an entire season. To add to the problem, the test sampling which has been done was during late autumn - the WRONG season! Thus, time-relevant sampling has not been done in this study. The only valid conclusions which can be drawn relate to diurnal acoustical patterns in late Autumn. Are the samples independent of each other? If the values in one sample are somehow dependent upon the values in another, the outcome is biased in the direction of those values. It is obvious that the evening and afternoon observations are not at all independent, thus resulting in results biased toward the non-independent measurements made during that period. The Cavanaugh study fails on this count. Has the current document incorporated past relevant data? The most immediately relevant data is found in the Black Dog EAW sound study which is barely mentioned -- and, when mentioned, it is significantly distorted. Further, the EAW measurements and analysis determined that state noise standards were exceeded at Hopkins Circle in Bloomington -- surprising Paoletti who could not explain them. The inadequacy of the sound modeling formula employed in the current Cavanaugh report is illustrated by the fact that when it is applied to the EAW sound test, it severely underestimates the actual measurements at the Hopkins Circle site. (Further, when the same formula is applied to Menge’s propagation measurements in the current Cavanaugh report, it fails dramatically by OVERESTIMATING the actual measurements. This degree of unreliability in predicting actual known, measured criteria illustrates the weakness of the Cavanaugh sound predictions and casts doubt upon any projections made in this manner. This is consistent with the presence of significant acoustical anomalies in the river valley.) Is the report and analysis consistent with established facts? No, it is not consistent with anecdotal reports of sound levels. Nor is the sound modeling is reliable when tested against actual data, such as that measured at Hopkins Circle in January EAW testing. Paoletti has misrepresented the
extent to which current Cavanaugh findings are consistent with the results
of the EAW testing. Note the stark contradiction between his current statements
and those in the EAW report:
Not only does he get the date of the study wrong, but the claim that "inaudibility" is consistent with the eaw test is completely untrue!!! If you read the EAW report, you will find that Paoletti, himself, acknowledges that, in reality, the EAW sound testing was quite audible in a number of areas in Burnsville. Further, it exceeded state standards at Hopkins Circle in Bloomington! THESE RESULTS ARE NOT CONSISTENT WITH SUBJECTIVE AND OBJECTIVE TESTS CONDUCTED ON SITE IN DECEMBER, 1999 (ACTUALLY, JAN, 2000). Read for yourself how he described the Burnsville impact in the EAW report: From the EAW report: "even though the audibility at the Bloomington
residences was `slight,’ and the audibility in Burnsville was very noticeable
at certain locations." And, "The music being played at the highest level
was clearly audible at many locations in Burnsville."
Because of errors, misstatements, and distortions, there are a number of inconsistencies. These will be discussed later. With the EAW and Cavanaugh report analyses on the table, we had to decide – just as YOU will have to decide for yourselves – the merits of these analyses. They should be evaluated in terms of: Consistency, logic, internal and external contradictions, integration, integrity, freedom from error, forthrightness, care, fair representation, scientific rigor, sampling. Unfortunately, the study has failed on several counts. It lacks scientific rigor, its language obscures reality, there are inconsistencies within it, and it is but a limited and biased sample of the conditions under which concerts would eventually transpire. It does not meet the standards of scientific inquiry. Careful evaluation of the document reveals a number of conceptual, methodological, and logical flaws. Further, there are even significant errors in the arithmetical calculations and computation of the on which conclusions are drawn. With no specific expertise, other than diligent attention to the details presented by the consultants, an educated layman can spot most of the errors and inconsistencies in this document. Unfortunately, the studies fail in most of these areas.
In one of its revisions (4/26/01) of a "final version" of the report, mistakes remained which were ultimately NEVER corrected. The report states, "all scheduled concerts will conform to the sound level limits of this report (Lmax = 103 dBA at the sound mix; and Lmax 90 dBA at the rear lawn)." (29) (Page 26) However, because of mistakes elsewhere in the report, "Lmax at the rear lawn," HAS BEEN REVISED TO BE 93 (with L1 at 90 dBA). These numbers are inconsistent WITH REVISIONS MADE ELSEWHERE (PP 23, 24, 30,31, AND 32). THEY SHOULD HAVE BEEN REVISED TOO! One table was revised twice (4/26/01,
and then again on 8/7/01) suggesting a serious failure to get things right
the first time – or even the second time! (Page 23)
2. The reports are carelessly integrated. For example, as many as three different distances are given for some residences. While this is acknowledged and described as insignificant, such a lack of coordination suggests imprecision and carelessness.
On February 27, 2001, in response
to a question by Martha Fuller about meteorologist Bruce Watson’s extensive
comments on air drainage in the EAW report, the consultants wrote:
4. At times, ambiguous and misleading phrasing is used, seemingly to minimize the amphitheater’s apparent impact. For example, Paoletti’s wording about the crowd noise: "…it is likely that at times (e.g. with the largest occupancy and downwind conditions) crowd noise will exceed the L1O and L50 noise limits."
This is very misleading because it incorrectly implies a great distance. This distance is basically the hypotenuse of a right triangle (with the 90 degree vertical side representing the vertical elevation of the receptor site above the amphitheater). With the distances & elevations involved, the angle to the receptor is very shallow – often less than 1 degree. Calculation reveals that the "angular distance" is only a foot or two greater than the "map distance." 7. Both reports fail to meet accepted standards of scientific rigor. For example, in the Cavanaugh report there is a failure to report data, such as measures of data variability and margins of error – or, at least data from which such margins of error might be calculated by the reader. In addition, the consultants acknowledge that they did not even calculate some values which have a direct bearing on establishing noise impact. As an example of this, please note
that the consultants appear quite satisfied with themselves about their
approach, even boasting about a procedures which disadvantages those who
fear that the amphitheater would have an adverse noise impact. Please read
the following statements on page 2 of the report:
- "potential excessive atmosphere propagation between the amphitheater and measurement sites due to the uniqueness of the intervening Terrain." (30)
The consultants have told us that anomalous atmospheric propagation is a real factor in the Minnesota River Valley and that a major component of such propagation could the refraction of sound caused by temperature inversion layers – causing sound to be heard at greater distances than would be anticipated. This means that the effectiveness of physical barriers, berms, and fences may be reduced by noise "bouncing" back to earth behind the barrier. 8. The sampling universe from which conclusions are drawn is too narrow – in each case a limited sampling of data from a few winter days. This universe of data bears minimal acoustical resemblance to the summertime concert season. In the EAW study, Paoletti said that some noise standards violations are likely – both in terms of concert noise and crowd noise. By itself, this confirms our contention that there will be a significant impact on neighboring community of Bloomington – the point of the metropolitan significance petition and Met Council consideration. Paoletti stated that the noise standards would be exceeded under "a few extreme conditions," listing those conditions along with their frequency of occurrence. See attached table, EAW TABLE. In the EAW report, Paoletti acknowledged
that CROWD NOISE could be a substantial problem. Using measured data from
a concert in Contra Costa County, California, he stated:
"At the distance of approximately
1/2 mile, on flat unobstructed terrain, crowd noise may reach instantaneous
peaks of 60-65 dBA. The L10 and to a lesser extend the L50 could be impacted
by these discrete events, depending how often they occur. Any form of architectural
obstruction between the audience and the recipient location, would act
as a barrier and have some sound attenuating affect towards reducing the
level of crowd noise." (6)
Even more strongly, Menge – writing as a Bloomington consultant in EAW comments – concluded that there would be a massive impact on Bloomington residents. Menge said that there were demonstrable exceedances of noise standards in the data collected by Paoletti. [At] the last residence we visited at 10769 Hopkins Circle . . . the ordinance was exceeded by 2-3 dB. The ambient was exceeded by approximately 6 dB. The results at this location took us completely by surprise. We cannot account for the results at this time. (7) Since these measurements (Hopkins Circle) HAVE been documented, and thus interpreted, they must be considered in any deliberations about community impact. It appears likely that these EAW findings were the result of propagation anomalies of the kind routinely reported by Bloomington residents (caused by temperature inversions, channeling, and other acoustical phenomena – as described by Menge). Paoletti constructed a series of tables reflecting predicted sound levels at various community locations based upon his expertise and modeling. These tables indicate that there will be a number of violations of state noise standards. Mr. Paoletti generated "noise contours"
to illustrate the predicted levels of sound at various locations in the
community based on emissions from the "distributed lawn sound system."
Taking into account the directionality of the sound system and the barrier
effects of the stage housing and totally enclosing side walls, he "produced
L10 and L50 noise contours for calm/neutral, upwind and downwind weather
conditions." (4) He considers wind speed and direction only – he does not
mention any consideration of temperature inversions. Nevertheless, he states:
Although Paoletti claims that noise
standards would not be exceeded in residential neighborhoods "except under
a few extreme conditions," Tables 1, 2 and 3 show that violations would
be quite a bit more frequent than he implies. He also acknowledges that
the "music emanating from the amphitheater may be audible under certain
conditions." See below:
Based on our noise model analysis, objective measurements and subjective evaluation of the acoustical conditions associated with the proposed Black Dog Amphitheater, it is our opinion that the Minnesota Pollution Control Agency Noise Standards would not be exceeded at either residences to the north in the City of Bloomington; or at residences to the south in the City of Burnsville when the facility is constructed except under a few extreme conditions. Refer to Tables 1, 2 and 3 for these conditions. The music emanating from the amphitheater may be audible under certain conditions, but is not expected to exceed the noise standards in most cases. (8) He further qualifies his statement by "Assuming that the proposed Black Dog Amphitheater is constructed and operated as proposed. and all of the attenuation measured listed above are employed, we believe that the Minnesota Pollution Control Agency Noise Standards would not be exceeded at either residences to the north in Bloomington; or at residences to the south in Burnsville." (8, 9) Menge continued: "Specifically, the Paoletti report predicts L10 levels of 66 dBA at the nearest Bloomington bluffs homes under downwind/temperature inversion conditions. This is a very significant 11 dB higher than the MPCA nighttime limit. This level is predicted for the worst-case condition, which is for "extremely loud" concert events (105 dBA at the mixing table'), which are predicted to be 20% of the concerts, and for "full-size" venue, where the attendance is near full capacity. Note that this analysis accounts for only sound from the sound system, and not from the audience, which is predicted to reach 60 to 65 dBA at the homes on the bluffs." (10) Menge notes that L10 levels are
predicted to be 57 dBA under "calm and neutral" atmospheric conditions,
a sound level greater than MPCA nighttime noise limits. (11) He challenges
Paoletti for minimizing the extent to which "downwind conditions" will
exist in Bloomington, reasoning that ALL winds with a southerly component
must be counted since the entire range of Bloomington bluffs is of concern.
In Menge’s opinion:
In conclusion, Menge stated, "Violations of the MPCA noise limits of up to 11 dB are expected to occur on a regular basis. We are concerned that an 11 dB reduction will be difficult to achieve without changing substantially the nature of the amphitheater's construction or operation." (17) He recommended further investigation of "enhanced sound propagation conditions (such as channeling)" since they "may occur regularly between the river and the bluffs." He said, "We believe that a test measurement program should be undertaken during several summer evenings to determine quantitatively the significance of this effect. This would assist in determining the validity of assumptions made about the effects of atmospheric conditions on sound propagation in this area with unique topography. This will be the only way to determine the true summertime sound propagation conditions that occur between the valley and bluffs, and their potential effect on sound system and crowd noise." (18) After several revisions of their final sound study report, the Metropolitan Council sound consultants have concluded that crowd noise could be a problem for Bloomington residents. (Paoletti, p 20) (20) However, both Paoletti and Menge have apparently changed their minds about the extent to which concert noise will impact Bloomington. With only minimal alteration in Paoletti’s EAW recommendations, they now state that there will be no exceedance of state noise standards in Bloomington. Menge continues to criticize the propagation measurement time-frame, reflecting that it would have been better to conduct this study during summer evenings "when concerts are expected to occur." He emphasizes that propagation-enhancing, prevailing winds from the south are more common then, and that "it is during summer evenings when temperature inversions are most likely to occur, and we expect that those atmospheric conditions are the most likely to result in the enhanced sound propagation conditions that has been described by residents of the Bloomington bluffs." (19) In view of this, he states that since "conditions were not characteristic of those expected during summer evenings" the sound propagation results "reported in this memo should be thought of as some additional information on sound propagation under the atmospheric conditions that existed at the time." (19) The consultants concluded that there might indeed be an impact upon Bloomington residences. While they minimize this impact, they state "we conclude that the community location that may be impacted sometime by the Black Dog Amphitheater, is a small group of homes, in Bloomington, on the bluff to the north and across the Minnesota River, from the proposed Black Dog Amphitheater. The potential impact at this and at other representative locations would be minimal and only on occasion with the loudest music being performed in the amphitheater, under "worst case conditions" or if the recommended acoustical controls given in this report are not followed. (25) The authors are quite vague in their comments about weather conditions and amphitheater noise propagation; more often than not, they ignore the effects of wind and temperature inversions or minimize the concern by claiming that they can regulate sound output in accordance with real-time meteorological conditions. (Since they say that wind and inversions can lead to a 10 db increase in level at distant receptors, this regulation could require a 10 db reduction in in amphitheater sound levels – i.e., frustrating the audience by cutting the volume by ½!) In general, the report fails to
address meteorological issues in any depth. This is mystifying since the
MPCA demanded an extensive review of meteorological factors in the EAW
sound analysis as follows:
"5) The probability of temperature inversions in the river valley near the proposed facility must be investigated, and if there is a significant potential for this meteorological condition to occur, predict the effect it would have on noise levels of the most significantly affected residential receptors." (26) "The resulting "worst worst-case" concert sound levels could then be up to 10 dB higher than those shown in the "Expected Community Response" table on page 24 of the Tab 4 report." (27) In analyzing projected concert sound and ambient levels in terms of "audibility criteria," indicating those instances where concert noise would exceed certain "acceptability" levels, the consultants made major computational errors leading to a critical misrepresentation of the level of community audibility. (Metropolitan Council, Sound Study Report, Paoletti section, April, 2001, Tab 4: p. 10) my letter The effect of these miscalculations was to underestimate the predicted sound levels at each receptor site by 3 dBA. All audibility values shown in the audibility table were 3 dBA too low, giving the impression of less audibility than would be the case. These errors were acknowledged by the consultants and the calculations were subsequently corrected as follows. Expected Community Response Table as corrected – p 24
However, the above figures do not reflect a worst case condition since it gives no consideration to wind and inversion conditions. To consider the worst case effects of wind and temperature inversions, the following table has been constructed.
Since we have a clear indication of the occurrence of winds from Bruce Watson’s tabulation, the following table has been constructed to reflect the acoustic impact of winds at speeds of 4 to10 mph in the absence of an inversion.
Cavanaugh, Menge, and Paoletti have all confirmed that sound propagation may be increased by meteorological phenomena such as winds and temperature inversions: Specifically, under such conditions, the level of amphitheater sounds could increase up to 10 dBA, thus increasing the audibility of amphitheater noise. Various augmentations of sound level are reflected in the 3 small tables above. Values in the final small table have been augmented by 20 db – a reasonable degree of enhancement according to the BAC/CARE sound consultant. The Watson report states that an
in-valley
inversion condition may develop on clear to partly cloudy nights from
May through September. Inversion refers to an atmospheric condition that
can develop in the evening or nighttime hours during warm weather when
the earth begins to cool. Air near the surface, especially in sheltered
valleys is cooled at a greater rate than air aloft. This condition results
in sound rays bending towards the ground and thus may increase noise levels
at distant receptors. However, Mr. Watson states that in-valley
inversions would only weakly penetrate the top of the valley. We would
not anticipate that low-level inversions would affect noise levels at homes
on top of the ridges.
Since prevailing winds are from a southerly direction about 80% of the time, the audibility tables which show two out of three days with wind from the east (105° ) are deceptive and overemphasize that easterly wind pattern. The situation on Friday evening more accurately reflects commonly prevailing wind conditions in the Minnesota River Valley. Note that the MPCA required meteorological data for the EAW sound study. (See Environmental Assessment Worksheet, Black Dog Amphitheater, Sound Study, Bruce Watson, meteorological tables and comments, Burnsville, May, 2000) Thus, the probability of "other than east winds" is highest because of predominant wind patterns: Showing two categories for Saturday gives a misleading impression. More realistically, in fact, for other than easterly winds, Saturday eve and afternoon probably should be attributed the same background sound level as Friday Eve (because Saturday’s ambient figures are contaminated by freeway noise -- and thus higher than they would be with the more frequent pattern of winds from the south, southwest, west, or north which carry no freeway noise). When calculations are done assuming the most frequent wind patterns (from the south, southwest, or west -- carrying no freeway noise) the following figures apply: If Watson’s wind data is considered, then approximately 1 day out of 10 will have winds from the east. On those days, residences west of the freeway will experience significant freeway noise and their ambient levels will be higher than on the other 9 days. In other words, on most days, the quieter background levels found on Friday evening in this study. Consequently, the differential between L1 and L90 will be the greatest on those days – 9 out of 10 days would be in the "sometimes audible" category. A substantial portion of those days would experience an increase in concert volume because the southerly winds would carry sound from the amphitheater. See attached Letter to William Cavanaugh Same table, calculated for prevailing (80%) southerly, westerly, and northerly winds (free of Interstate 35W traffic noise), using Lmax = 93 dBA at rear of lawn as indicated in current recommendations Using Lmax = 93 dBA
Darker blue cells are "Sometimes Audible" CROWD NOISE "Based on the above and assuming
conservative losses for distance spreading, air absorption, shielding of
a portion of the crowd on the lawn by the canopy, building structure, and
nearby berms, it is estimated that the crowd only sound levels at the nearest
homes at Overlook Drive, in the City of Bloomington (represented by Site
2) could reach maximum levels of 50 to 60 dBA."
Paoletti suggests that there would
be additional ground attenuation due to grass, vegetation, bushes, and
leaves on trees. "In the spring and summer, when the amphitheater would
be in use, there should be substantial around cover and vegetation between
the amphitheater and the Burnsville residents."
THE CROWD: NOISE ATTENUATION Typically, the consultants note, attenuation of a sound source has been considered to occur at the rate of 6 decibels per doubling of distance. Thus a 66 decibel sound level at 300 feet distant from a source will decay to 60 decibels at 600 feet. It is contended that the crowd noise impact upon the Bloomington bluffs will be greater than represented in the Metropolitan Council report. The table below shows the crowd noise level at various distances (based on figures from the Haggard concert crowd of 2,000 described in the report). If only 1/6 of a capacity crowd (of 12,000) has line of sight to Bloomington residences, the above would be the sound level at distances noted. This indeed would be the case. The table shows the acoustical impact of southerly winds on the propagation of crowd noise as explained by the consultants. It is assumed that the effect of a 4-10 mph wind is to enhance propagation by 5 db. In the third column, figures have been increased by this amount to reflect estimated noise levels at receptor locations at the distances tabled. The fourth column shows the effect of a combined wind and temperature inversion at the distances indicated (working from the Haggard concert figures). The table indicates that under mild windy conditions, the sound level of a point source would still be in the 51 to 56 db range at a distance of over one mile (5,776 feet). These calculations confirm Paoletti’s statement that there could be a significant noise impact exceeding "the MPCA L1O and L50 noise limits for some residences on the bluff to the north of the amphitheater in the City of Bloomington." Exceeding the nighttime L10 noise
standard means that the sound level would be 55 decibels OR HIGHER for
a total of six minutes during a given hour. Exceeding the L50 nighttime
noise standard would mean the projection of a 50 decibel noise level --
OR MORE -- for a total of 30 minutes during a given hour. It should be
noted that crowd noise is a variable over which the amphitheater operator
has no significant control, unlike the electronic amplification system
for performers. A significant portion of the lawn seating audience will
have a line-of-sight exposure to the Bloomington bluffs -- and thus be
unshielded.
Dist reduce by
add 5 db add 10 db
CONCLUSIONS The Metropolitan Council Sound Study Report does not adequately document, explore, and analyze the acoustical properties of the Minnesota River valley in the area of the proposed Black Dog Amphitheater. It is far from clear that there will be no significant impact upon nearby residents. In fact, the EAW sound study found potential for violation of Minnesota noise standards. Both the EAW and the Cavanaugh studies indicate potential violations based on crowd noise. When "worst case" factors, such as wind and inversions are considered, the potential increases. Both the EAW study and the Cavanaugh
study do not meet scientific standards of sampling. Not only are they conducted
during the wrong season of the year, but they represent only a few days
of the wrong season, insufficiently sampling the range of conditions typical
of changeable Minnesota seasons.
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