WORK PLANS - Laserfiche WebLink

Home Browse Search

Ms, Luci '17hater 2 - 9 March 2006 during the fourth quarter of 2005. During the second quarter of 2005, MW-1 had a slightly higher groundwater elevation (Figure 313) than upgradient MW-4. The groundwater downgradient flow directions between MW-1 and MW-4 are reported as reversed for these two quarters,towards the east for the second quarter2005 and to the west for fourth quarter 2005. If you take MW-1 entirely out of the equation during the second, third, and fourth quarters of 2005,the groundwater downgradient direction of flow is exclusively towards the southwest from MW-4 to MW-2 and MW-3,which would be the expected result. If this is the actual groundwater downgradient direction of flow(towards the southwest minus MW-1),then the lateral extent of the groundwater plume appears to be defined. However, the third quarter of 2005 groundwater elevation map(Figure 3C) is also enigmatic, as the upgradient well (MW-4) is exactly one foot higher than the nearest well (MW-1),resulting in a relatively steep gradient of 0.07 ft/ft from MW-4 to MWA,which decreases to an order of magnitude less gradient 0.006 ft/ft between MWA, MW-2, and MW-3. The third quarter 2005 groundwater downgradient direction of flow remains consistently southwest across the property for all wells. The unusual groundwater gradient changes in the northeastern quarter of the property (one half to an order of magnitude greater than the remainder of the property to the south), combined with the groundwater downgradient direction of flow, which varies over 180 degrees for three consecutive quarters of sampling: a) Do not appear to be representative of known Lodi regional groundwater gradients and direction of flow(southeast to southwest), and b) Is not representative of any other nearby sites monitoring wells gradient(groundwater direction of flow was southeasterly at 0.006 to 0.007 ft/ft over several blocks during the fourth quarter of 2005 along the 100 block of Cherokee St). Furthermore, MW-1 (Enclosed Figure 3 cross-section from Monitoring Well Installation and Quarterly Monitoring Report received 20 June 2005)was: • constructed in 1985 with a 35-foot well screen,the bottom of which is drawn as intersecting the Iowest three feet of a highly permeable sand zone; most likely has a typical filter pack, constructed 2-foot above well screen and which appears to extend upward into another highly permeable sand zone above the well screen. That sand zone may act as a conduit in the boring logs (moist soil reported at all depths in the boring logs)and convey perched or recharge water down through the contaminated soil reported at 35 and 40 ft bgs into the shallow aquifer; • has 15 feet of well screen exposure into the vadose zone; and may have questionable construction of the annular space sanitary seal. Figure 2 also shows the former tank pit(containing MW-1) is less than 15 feet from an existing house to the west of the site, All of the above data and figures show evidence of water table mounding at MW-1 during the second-and fourth quarters of 2005, in that the water level is equal to or nearly equal the upgradient monitoring well(MW-4), or up to a foot higher at MW-4 during the third quarter of 2005. Besides possible faulty well construction for either MW-I or MW-4, other possible explanations include: a) A highly permeable backfill exists in the tank pit, coupled with either