ARCHIVED REPORTS XR0000960 - Laserfiche WebLink

Home Browse Search

-, field and laboratory sources of variance. As shown on Table 3 where hydrocarbon constituents have been detected over the last 4 sampling events they have generally been very close to the method detection limits (MDL) . The determination of actual concentra- tions, if they are near the MDL is difficult, Ms. Laura Kuck (lab director, Applied Analytical ) reported that the small discrepancy between the results of the two replicate analysis (MW2 and MW4 ) relates to laboratory variation. Table 4 shows the laboratory results including sample spike recovery percentage for both samples. The table shows that three separate runs were made for sample MW2. This is because the spike recovery ( 74$ ) for the first run was below the quality control minimum of 75$. there- fore two additional sample runs were made. These runs showed significantly improved spike recoveries ( 104$ and 99t) . The third run was selected as the best representation based on spike recovery and it is presented on the laboratory report. The Table 4 data gives an indication of the variation which can occur within the laboratory and which probably is an important part of the data variability noted in the quarterly sampling results. With this source of data "inconclusiveness" in mind, together with the fact that only benzene, in 1 of the 4 sample rounds collected to date, has been present above State MCL's (3.7 ppb) we believe our request for reduction of sampling require- ments to semi annual should be reconsidered. The next sampling event is scheduled for April 1991, pending the -" divisions reconsideration of the sampling frequency requirements. The monthly monitoring has shown that groundwater gradient is influenced by the tides and fluctuates in direction (Table 2) . The tidal influence is relatively clear from the data presented on Table 2. During low tide the river controlled gradient would be expected to be dominantly down river or northwesr 'the-,,,only gx�Ra�nt ''�iaterm3n�t;ion 'iirade�onrt'he�1�a5w� t�da��(�U8�320�/90)��is� "t�h�• A. tte ,gr�dient has��h$d�a �norttae`rlpy�r�conbiient��° "rSim3ar3y de'�ermna� ons made 3o"n °[iz'rt`�eart,Fth�e';:.h''��':l�r�,t`�i:aB x - J (P�4y , 90, x9/10/90, 11/30/90, 01/07/91} are in the up river or sdfi 14th,The measurements taken between the high"and '1'ow generally have a westerly component which probably reflects the swinging of the gradient from south-southeast to northwest. As requested in December 17, 1990 correspondence by Laurie A. Cotulla, the traffic box for well MW1 has been replaced and the box for well MW3 has been repaired.