ARCHIVED REPORTS XR0012691 - Laserfiche WebLink

Home Browse Search

Robert Burick Granite Construction Company October 18,1989 Page t However,on 19 July 1989 the groundwater flow beating was towards i:'ie west. Regional ground water flow in the Tracy area is generally to the north. It is believed that leakage from the underground irrigation pipe on the north side of the property probably accounted for the southward flow. However,it has been observed that the irrigation pipe is not used on a continual basis. When the pipeline is not in use,the groundwater gradient should xelurn to normal,which could account for the westward swing in the gradient in Juiy 1939. If our interpretation of groundwater gradient is correct and the leaking irrigation pipeline has influence-:the local groundwater flow,the flow directian should change during the off season (October through March). In this event,groundwater sh;)uld resume a northerly flow direction. The significance of this is that a southerly groundwater flow could move the hydrocarbons ' away from the wells during the summer and that a northerly flow direction should move the a plume back into the area of influence of the wells during the winter months. Further t? groundwater monitoring may help clarify this interpretation. U-oratory analyses of water from the monitoring wells sampled on 19 and 28 June 1989 showed ' that BTX&E and gasoline were not detected. Analytical data sheets for the three wells are enclosed. This can be interpreted as the hydrocarbons present in the groundwater in 1987 have been oxidized or have undergone biodegradation and are no longer present. Another interpretatirm is that the hydrocarbons may have migrated away from the wells and were just not detected. Further groundwater monitoring may help clarify this issue. f fes Recommendations Geolcw xcal Technics proposes the following course of action to further characterize the site and to evaluate if ground water contamination is no longer present or if migration may have 3 temporarily moved the hydrocarbons away from the monitoring well. The recommendations are: /1. To perform ground water level measurements and gradient calculations on a quarterly basis for one year. 2. To monitor ground water fur the presence of petroleum hydrocarbons on a quarterly basis for a period of one year. The three existing wells will be purged by pumping a minimum of 5 well volumes before a sample is collected. One well volume is equivalent to the amount of water contained in the well casing and in the pore spaces of the filter pack. Samples will be analyzed at a state certified lab for TPH-gasoline by method 5030 (detection limits are 0.5 mg/1)and for aromatic hydrocarbons by method 8020(detection Iimits range from 0.3 to 0.5 pg/1. 3. To submit quarterly ground water gradient calculation and lab analytical data to the regulatory agents. 4. To review the data after one year,evaluating the condition of the site and determining a future course of action. 1: