Laserfiche WebLink
`J <br /> �z <br /> Proposed Groundwater Extraction and Remediation Program <br /> The flow rate of the water (v) in a saturated, porous <br /> medium is defined by Darcy ' s Law. This law states that , <br /> under saturated conditions , the volume of water (V) flowing <br /> per unit area (A) per unit of time (T) is directly <br /> I proportional to the product of hydraulic gradient (h/L) and <br /> soil hydraulic conductivity (Ka ) , i . e . <br /> IF V/AT = v = h/t� (Ka ) <br /> EPM has , on three occasions , attempted to measure the <br /> hydraulic conductivity 'of the most shallow saturated zone.. <br /> at the site by the Auger Hole Method (using a higher <br /> capacity pump on each of these occasions) . This method <br /> requires that the groundwater table be lowered to 1/3 of <br /> its static height in a well and that the rate that <br /> groundwater subsequently refills the well be measured over <br /> known intervals of time . Even after removing 15 well <br /> volumes in approximately 6 minutes, the groundwater table <br /> in monitoring well MW-3 remained virtually unchanged. This <br /> indicated that a highly porous aquifer layer was present <br /> below the clay and silty clay deposits encountered at 9 <br /> feet bgs in the on-site soil borings previously advanced by <br /> EPM. This was confirmed when EPM reviewed logs prepared <br /> I attendant to the placement of soil borings and monitoring <br /> wells across Grant Line Road at 2360 East Street . These <br /> logs showed that sandy "silt and silty sand layers are <br /> present below 11 feet ., Such profile configurations are <br /> i common in alluvium deposits and are indicative of the <br /> presence of a semi-confined aquifer. <br /> It should be noted that< the hydraulic conductivity values : <br /> below 9 feet do not directly impact the flow rates of the <br /> lighter--than-water , non-aqueous phase liquid petroleum <br /> i hydrocarbons (LNAPLs) that are the contaminants of concern <br /> at the subject site. LNAPLs would have a horizontal flow' <br /> rate equal to the product of the hydraulic gradient and the <br /> hydraulic conductivity values exhibited by the less <br /> permeable clay and silty clay present near the top of the <br /> water table at 7-9 feet, despite the fact that groundwater <br /> below this depth appears to move at a much higher rate. <br /> This occurs because the hydraulic conductivity value for <br /> sand is in the range of- 100 ft/day, it is only about 0 . 001 <br /> ft/day to 1 . 0 ft/day for clay and silt , respectively . <br /> The direction and slope of groundwater flow were calculated <br /> : during November, 1993 and February, 1994 . Values for the ; <br /> flow direction and hydraulic gradient for both dates werei <br /> Page 6 <br />