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5.3.2 Groundwater Depth to shallow ground water beneath the property is not known. Most wells in the area are drilled to a depth of 200-300 feet. Two Tertiary aged geologic formations lie beneath the overburden: the Laguna Formation, a glacial meltwater deposit which includes the economic sand and gravel deposits present at the site; and the Mehrten Formation, a consolidated clay and sandstone. Previous drilling conducted at the site indicates that the Mehrten Formation is present below grade at the property from 0 to over 40 feet. If ground water is perched on top of the Mehrten Formation, none was detected during exploration. E Ground water within the region is withdrawn from the Mehrten Formation and the underlying Valley Springs Formation. Ground water flow direction is towards the Central Valley to the west. .t This flow can be influenced locally and regionally by surface topography, recharge and discharge areas, horizontal/vertical inconsistencies in the types and location of subsurface soil and bedrock, and proximity to pumping wells. KRC Aggregate supplements its water for processing from a well drilled to a total depth of 700 feet below the surface (bls) . There is 18 inch conductor casing extending from the surface to a depth of 39 ft. Blank 14 inch casing extends from i 40 to 255 feet bls with the interval between 255 and 315 feet bls being perforated with 1/8 inch by 3 inch holes. Blank casing also extends from 315 to 338 feet bls. The remainder is not cased. Water is withdrawn from the interval located from ' 255 to 315 feet bls. A step-drawdown aquifer test was performed on March 26; 1992 using the main production well. The test consisted of four pumping rates (steps) which were held for 45 minutes each, 'pro- ceeding from a low pumping rate of 475 gallons per minute (gpm) to successively higher rates of 690, 1000, and 1310 gpm. Water levels and corresponding drawdown measurements were recorded by a hydrogeologist throughout the test in the pumping well. Drawdown on the pumping well was about 23 . 15 feet below the original static water level (swl) after 45 minutes of pumping 1310 qpm. The original static water level was 225. 5 feet below land sur- face. It is estimated that a stable drawdown of about 25 feet would occur after one day of pumping at the maximum flow rate of j 1310 gpm. Based on the drawdown data the specific capacity of the well ranged from 59.2 gpm/ft of drawdown at 475 gpm to '56. 7 gpm/ft at a pump rate of 1310 gpm. At the highest pumpinglrate the wells efficiency is 960 of that of the low rate, which ,is very good. Water quality results for the production well can be found in Appendix 11.7. In addition to this production well, there are several other water wells on the property; however, these wells are no longer in service. Wells were identified in Tracts IV, V, and VI: Three wells were connected to windmills. The well in Tract VI formerly had an electric pump installed. Each of these wells had nearby vertical holding tanks. In addition to a holding tank, an empty i underground concrete vault near the well in Tract VI was ob- served. j k KRC Aggregate, Inc. - 3 - April 1, 1994