6.3.3. Results of the Vipava Area 6.3.3.1. The Second Tracing Experiment in Spring 1994 (H. BEHRENS, R. BENISCHKE, W. KÄSS, M. ZUPAN) From the individual sampling stations at the Vipava springs the samples have been delivered in different packages (Tab. 6.5). After analysis of a first series of samples some promising results showed a steep but smooth increase of the concentrations. So it could be expected for the first moment that this was a beginning of a rather classical breakthrough curve. But in the samples of the following series the pattern of breakthrough was quite different and brought concentrations for all sampling stations that could be interpreted in many different ways (influence of biological, chemical or photochemical decay, hydrological events, analytical errors and so on). The most likely interpretation is, that the samples have been influenced by some decay or adsorption processes. During evaluation and comparison of the results from the different outlets it became apparent, that a component separation based on the data of the artificial tracer would lead to unreliable results, especially for those, where the concentration values of Vipava 4/8 (the total runoff) were higher then those of the individual springs. This is impossible, because any mixing can result at the best in the same concentration as it can be observed in the springs (Fig. 6.20). The breakthrough-curve shows in the beginning a normal increase and is not influenced by secondary discharge peaks, also the discharge peak at approx. 500 h after injection had no influence on the concentration. The strong discharge pulse on 19th of May caused a new concentration peak, showing that the tracer which remained obviously in the system until that time has been washed out. From this time on only a decrease in concentration could be observed until the end of the sampling program. The shape of the first concentration peak cannot be explained by special hydraulic influences from subsystems of the Vipava aquifer, because there is no indication in the discharge curve. Irregular changes or fluctuations in the time-concentration graph a short time after the main peak and a significant concentration dropdown (approx. 300 h after injection) may be a hint on other than hydraulic influences. Possible explanations will be given later in this section. With exception of station Vipava 4/8 no other spring was equipped for continuous recording of discharge or stage, only Vipava 4/6 and Vipava 4/7 were measured at a bridge of their joint runoff channel about 100 m downstream of the outlets. This was a pity insofar that there was no other possibility to compare the tracer breakthrough curves at the springs with their individual discharge. Before the tracing experiment it was known from hydro-chemical analyses and conductivity measurements that the most northern spring T I 2D 18 16 1>t 12 10 \ g v 1 6 k \ 4 1 o A 0 ^---- /u 2m 4D «D 8CD 1he I" r s 8 L 4 2 O \ \ J 1 1 ^ an 4D eoo 11mn^li(ecllcn aoD 120 Fig. 6.25: Second experiment, April 1994: Breakthrough curve of Uranine at Vipava 4/5 (Pod Skalo). KÄSS (ref. to chapter 8.1.) could be irregular adsorption at the walls in the sample flasks, or it is a combined influence of both adsorption and biodegra-dation. Summarising the characteristic data from all breakthrough-curves it can be said that the first arrival and therefore the maximum flow velocity is quite similar for all stations (Tab. 6.14). The data for peak concentration and the flow velocity calculated for the concentration peak are very influenced by the above mentioned irregularities in the concentrations; they depend on the degree of possible degradation effects. Despite these influences the calculated recovery for Vipava 4/8 (the only station where discharge data were available) is rather high. But a recovery of about 74 % means that approx. 25 % remained in the system until the end of the sampling program. But taking into account, that the measured concentration values are the result from unknown effects mentioned above, the total recovery could also be nearly 90 or 100 %. Attempts to separate runoff components only by the uranine data failed. Corresponding concentration values could not be compared in the strong mathematical sense and for separating the discharge of Vipava 4/6 and Vipava 4/7 from Vipava 4/8 was not possible by means of the uranine data, because there was no sampling station at the gauging section for Vipava 4/6 and 4/7. Tab. 6.14: Summary of tracer data from all sampling stations. Injection Start Injection End Hor. Distance Vert. Difference 1994.04.16/12:45 1994.04.16/ 12:50 12990 365 Tracer: Amount (gross;kg): Reference (net;kg): Amount (net;kg): Uranine 7.000000 0.004228 6.995772 Spring Date/Time Flow time after inj. start (h) Flow velocit y(m/h) Conc. (mg/m^) Std. Conc. (m-=) Load (mg/s) Vipava 4/1 (Pri Kapelici) 1. Arrival 1994.04.19 14:00 73.25 177.3 0013 0.186 Peak 1994.04.23 10:00 165.25 78.6 0.939 13.429 Vipava 4/2 (Pod Lipo) 1. Aiiival 1994.04.19 15:00 74.25 174.9 0013 0.187 Peak 1994.04.23 11:00 166.25 78.1 1.305 18.654 Vipava 4/3,(Perhavčeva Klet) 1. Arrival 1994.04.19 11:00 7025 184.9 0.008 0.119 Peak 1994.04.20 09:00 92.25 1408 1.467 20.975 Vipava 4/4 (Vipavska Jama) 1. Arrival 1994.04.19 14:30 73.75 176.1 0.065 0.929 Peak 1994.04.22 08:00 139.25 93.3 1.512 21.614 Vipava 4/5 (Pod Skalo) 1. Arrival 1994.04.19 14:30 73.75 176.1 0.048 0.686 Peak 1994.04.22 08:00 13925 93.3 1.258 17.986 Vipava 4/6 (Pod Farovžem A) 1. Arrival 1994.04.19 14:30 73.75 176.1 0054 0.771 Peak 1994.04.22 08:00 139.25 93.3 1.219 17.429 Vipava 4/7 (Pod Farovžem B) 1. Arrival 1994.04.1911:00 70.25 184.9 0.001 0.014 Peak 1994.04.19 21:00 80.25 161.9 0.074 1.059 Vipava 4/8 1. Arrival 1994.04.19 10:00 69.25 187.6 0.005 0.067 0091 Peak 1994.04.20 20:00 103.25 125.8 1.455 20.796 13.963 Load - peak conc. 1994.04.20 20:00 13.963 Peak load at: 1994.04.20 18:00 14.121 Recovery until: 1994.07.28 09:00 5.14 kg Recovery until: 1994.07.28 09:00 73.46 %