Shawn Oliver <br />Characterization of Groundwater System under Chico State <br />Abstract <br />Under the campus of Chico...
Field methods final project
Field methods final project
Field methods final project
Field methods final project
Field methods final project
Field methods final project
Field methods final project
Field methods final project
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Field methods final project

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Field methods final project

  1. 1. Shawn Oliver <br />Characterization of Groundwater System under Chico State <br />Abstract <br />Under the campus of Chico exists a dynamic groundwater system in interaction with Big Chico Creek. Through well excess this system was explored. Six wells were all measured for ground water level twice during two separate events. During one of these events hydraulic conductivity values were found in all but one well through data analyses of slug tests. Synthesis of data characterizes an unconfined aquifer system which is currently being recharged by Big Chico creek.<br />Contents TOC o "1-3" h z u Abstract PAGEREF _Toc293679567 h 1Introduction PAGEREF _Toc293679568 h 3Methods PAGEREF _Toc293679569 h 3Slug Test Data Collection Methods PAGEREF _Toc293679570 h 3Bower Rice Data Analysis Method (Fetter, 2004) PAGEREF _Toc293679571 h 4Well level Data Collection Methods PAGEREF _Toc293679572 h 5Results PAGEREF _Toc293679573 h 5Discussion PAGEREF _Toc293679574 h 6Works Cited PAGEREF _Toc293679575 h 7Tables and Figures PAGEREF _Toc293679576 h 8<br />Introduction<br />Ground water models are standard tools used in characterizing groundwater systems and designing policy which can have impact on a natural hydraulic system. Vulnerable unconfined aquifers which interact with an anthropogenic urban type system and stream ecological systems are home to critical water resources for both the human and natural worlds. The aquifer underneath Chico state campus is one of these critical flow systems and its monitoring provides data useful for its modeling. <br />Methods<br />Data collection involved two ground water level monitoring events using a sounder punker at a variety of Chico state monitoring wells and slug testing where drawdown was measured with time after insertion of a water slug. Slug testing data was analyzed using the Bower Rice Slug Test analysis method to find Hydraulic conductivity values for wells. Ground water level measurements yielded depth to water from well top length data on two separate occasions during the spring season. These length measurements and their change between measurement events can be referenced in table 1. Well locations were referenced from a field map used to find wells. This map was then used to create well lace marks in Google Earth to give geographic significance to wells and their measured data Figure 1. <br />Slug Test Data Collection Methods<br />Slug testing involved the measurement of well structure parameters and observation of well response to slug insertion in the form of well head change with respect to time; measurement of well head with time was recorded with a pressure transducer. This measured data was then used to estimate hydraulic conductivity within the vicinity of the well using the Bower and Rice Slug Test Method documented in fetter page 197-200. <br />Bower Rice Data Analysis Method (Fetter, 2004)<br />Uses a conceptual model a of a slug of water drawing down within a well by a rate controlled by well construction parameters, the effective area over which head is displaced and an aquifers hydraulic conductivity. With this model Hydraulic conductivity of an aquifer region can be determined if a well is present, with known dimensions and proper construction, and draw down is measured with time according to equation 1: <br />K=rcln(Re/R)2Le1tln(H0Ht)<br />Where <br />K =hydraulic Conductivity<br />Rc= radius of well casting <br />R= radius of gravel envelope<br />Re= Effective Radial Distance over witch head is dissipated <br />Le= length of well screen <br />H0= drawdown at time t=0 <br />Ht= drawdown at time t=t <br />t = time since H=H0<br />Because the variable Re is impossible to measure in the field software is used to determine this variable’s value and calculate hydraulic conductivity. Aqua solve, is able to determine this parameter through the use of equations relating Re to: well aquifer and aquifer parameters, coefficients linked to well parameters in charts and drawdown vs. time trend line analysis. <br />It should be noted that Bower Rice Method is not valid for any kind of slug test. For data to be valid testing bust be done in a well with a static water level above the well screen. Also, slugs during a test should be large and inserted as instantly as possible in order to produce data relevant data. <br />Well level Data Collection Methods <br />Well water levels were measured using a sounder plunker. A sounder plunker is a device that measures distance to water in a well in a process where circuit break is lowered into a well attached to a wire displaying length until the break comes into contact with water and sounder produces noise and length can be recorded. This data was then used with known well elevation data and well location data to find spatial and temporal aquifer head data. <br />Results<br />Studied groundwater system is dynamic and within geology showing intrinsic permeability spatial variability. <br />Hydraulic head data shown in table 2 slows, when ignoring well 10, evidence that ground water flow does not change direction during the spring. This is because wells do not change their rank of hydraulic head magnitude. This is evidence of system of constant flow direction because of property of groundwater to flow from high to low hydraulic head. Data in table 1 also shows that the water table adjacent to Little Chico creek has greater head variability because head changes calculated are greater in wells adjacent to big Chico creek. <br />Data shows that aquifer conductivity decreases logarithmically with respect to a proximity to big Chico creek south west and across the stream from Holt Hall. Conductivity measured east of Holt Hall is in conclusive other than conductivity showing to be relatively constant. Stream shape visible in Figure 1 is evidence that the wells 14, 15 and 19 penetrating into a point bar deposit. This would validate the conductivity results for the wells because decreasing clast size with respect to channel proximity is a pattern found in point bars.<br />Table 3 shows how head change is increasing among wells 14, 15 and 19. According to Darcy’s law this could mean that recharge rates have increased between measurement events. <br />Drawdown data showed well 10 to be problematic. Absence of drawdown measured by pressure transducer shows that well is clogged and unable to transmit water into aquifer. <br />Discussion <br />Head level measurement and slug testing of wells within an unconfined aquifer groundwater system underneath Chico State produced data sufficient for very basic geographic and temporal characterization of the system. Characterization of the system is as follows: Data definitively shows that groundwater system is subject to head variability and operates in geologic material with variable hydraulic properties. Data also matches what would be expected in an active alluvial groundwater system in interaction with geology undergoing active surficial processes; evidenced by what has been characterized as a point bar through geographic hydraulic conductivity value synthesis. Analysis of data also shows that stream water was recharging the unconfined aquifer during both measurement events and that this recharge rate was increasing. <br />Works Cited BIBLIOGRAPHY (n.d.).Fetter, C. W. (2004). Applied Hydrogeology (Fourth ed.). Upper Saddle River , New Jersey : Prentice Hall .<br />Tables and Figures<br />Table 1<br />well 8well 9 well 10well 14well 15well 19 K in april0.0005290.000221n/a0.012170.0010250.000997depth to water april12.463.813.355.5510.4210.8Depth to water mar12.754135.8210.6310.87well elevation199.04191.02198.13190.54195.23195.05Groundwater head Mar186.29187.02185.13184.72184.6184.18Groundwater head April186.58187.22184.78184.99184.81184.25Change in head0.290.2-0.350.270.210.07<br />Table 3rank from highest to lowest head Rank MarRank Aprilwell 9well 9well 8well 8well 10well 14well 14well 15well 15well 10well 19well 19 <br /> Table 2<br />Head differencees MarchAprilwell 14-15 0.120.18well 15-190.420.56<br />Figure 1<br />

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