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' 16L4EYEnvironmen1a1 Management Inc U-Haul#709-50 002-70950-02 Semi-Annual Report 12/14/00 groundwater conditions map showing the groundwater flow direction across the site The average groundwater flow direction as of June 26, 2000 was toward the northwest with an estimated hydraulic gradient of 0 0625 feet/foot(Figure 3) Other water level data collected from well casings with screened intervals below thegr oundwater level indicated that water levels in the lower casings were comparable to those in the upper and middle well casings Monitor wells used to compare water levels included MW-I, MW-IAB, MW-2, MW-2AB, MW-5, MW-SAB, MW-6, and MW-6AB These monitor wells include one lower casing and a nearby nested well (within approximately 10 feet) with middle and upper casings The middle and lower- screened casings were below the water level and the shallow casing interfaced with the water level With exception of two monitor wells MW-1 and MW-1 AB, water levels at the other wells were within approximately 0 1 feet Although water levels were comparable, most of the water levels in the lower Icasings were slightly deeper (by approximately 0 05 feet) This difference was more evident at monitor wells MW-1AB and MW-3AB where water levels between the upper (A) and middle (B) casings vaned by 0 34 feet and 1 74 feet,respectively In addition to depth to water measurements, Blaes Environmental technicians collected dissolved oxygen level measurements from each well casing using a YSI-85 dissolved oxygen meter The dissolved oxygen meter was decontaminated before and after use at each well Dissolved oxygen level measurements were also recorded on the standard field data sheet The method of dissolved oxygen measurement collection is described in Appendix B Measurements indicated that dissolved oxygen levels in groundwater ranged from 0% at monitor well MW-4 to 53 6% at monitor well MW-2 Dissolved oxygen levels above 10% were observed at monitor wells MW-2, MW-3, MW-5, MW-6 and MW-8 Other measurements were less than 10% (Table 3) 31.2 Uroundwater Sampling, June 2000 On June 28, 2000, Blaes Environmental collected 22 groundwater samples from the on-site monitoring wells Prior to sampling, Blaes Environmental purged approximately three well volumes of groundwater from the wells either by bailing or pumping Bailing was used to purge water from the upper and middle wells because purging these wells with a submersible pump may pump the wells dry Purging wells by bailing involved lowering new disposable bailers into and out of the well until approximately three well I 7