Laserfiche WebLink
<br />in an estimated average of 4.6 X 10.11 g-Ag mrl. equivaleOl to 46 ppt by wdghl. Of course. these <br />calculations unrealistically assume that 100 perct.'nl of the t..'"tllincd silver ended up in the <br />mountain sno....-pack. <br /> <br />The only source known to the authors. which estimatcd the percentage of releasc..'ti Ag in <br />the seasonal snowpack. was the article by Super and Heimbach (1983). They estimatcd that <br />about 40.70 pcrccnt of the total silver emitted during hours of target snowfall wa, in the seasonal <br />target snowpack of the BRE. However. \'alues were reduced to 14-18 percenl when all hours of <br />seeding were considered. I.acking other infonnation. a 15 perceOl valut' was applied in the <br />current study to the 7Q ppt estimate from Michigan Creek. The result is an average of 12 ppl. <br />similar to the higher values found in Table 2 except for Michigan Creek Of course. the BRE used <br />high elevation gcncrators demonstrated to routinely target the orographic doud zone. There were <br />no doubt other significant differences between the BRE and thc 0\),/8 project. such as dcciding <br />when to st.-eO. <br /> <br />\"bile the above calculations are of the type referred to as "ballpark" or "back of the <br />envelope" they do suggest one possible problem with the own project. It is certainly plausible <br />that the low Ag values generally found in the target area snowpack were largely the result of <br />relatively low Agl release rates for the large target area.. Yet. one might expect that favonlbJc <br />target locations would have Ag contcnts at least a few multiples of the approximately 5 ppt <br />background. But only 13enhoud Summit had as much as three times background. and onl~ <br />"1ichigan Cn.'ck was many times b'Teater As \\ill now be discussed funher. frequcnt trapping of <br />Agl released from relatively low elevations is known to be a problem. as is likely mistargeting as <br />indicated by the Rock) Mountain NP snow sample. assuming it was not contaminated. Tmppt.-d <br />Agl might be transported from the mountain valleys during windy periods betwl..'Cn stonns. In <br />the abscnce of cloud or snowfall. thcre would be little expectation that much of this Agl would <br />be deposited on the sno.....pack. l.ow-Ievel transport of the Ag.1 in unintended directions is another <br />possibility as shown by Rcynolds et 81. (198Q) and Warburton et a!. (1995a). In thl: lattcr study <br />AgI somctimes contaminated control sites during southt:r1y now C3.Sl:S" A major Colorado <br />experiment which had seeding agent tnll'lsport problems is discussed in the following section <br /> <br />The purpose of this limited study was to examine thl: occurrence and amount of silvcr <br />deposition in the target ~a snowpack in order to provide a first tcst of targl:ting success by" the <br />operational program" It had been proposed to track the Agl during storm periods using an <br />instrumented van equipped v.ith an acoustical ice nucleus counter. This approach would have <br />allowed physical tl..'Sting of whcther Agl releases were being tr.msporll.-d thmugh mountain <br />passes. which are the paths of least resistance over burners. were being trapped within valley's <br />containing Agl generators for cxtcndl..-d periods. or were being transportl..-d in unintended <br />directions. A similar approach was successfully used in Utah. which revealed fn.-quent low-level <br />trapping of high AgJ concentrations in mountain \"alleys (Super IQQ9a). However. funding was <br />not available for such an approach in the OWB project. Any study of wind pattcms in the likely <br />shallow layers of Agl transport \\"as also beyond the scope of this project. IlowC'vl:r. a fcw prior <br />Colorado studies will no\\ be cited which address the Agl transport is.'iue. <br /> <br />,- <br />-, <br />