BASIN MANAGEMENT OBJECTIVES PENTZ SUBINVENTORY UNIT

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1 BASIN MANAGEMENT OBJECTIVES PENTZ SUBINVENTORY UNIT Butte County Water Advisory Committee Member Vacant Contact Information Phone Number: Address: Description of the Pentz Sub-Inventory Unit The Pentz Sub-Inventory Unit (SIU) covers an area of about 1,900 acres in the northern portion of the East Butte Inventory Unit. It is bordered by Butte Creek to the north, the North Fork of Dry Creek to the south, foothills to the east, and Highway 99 to the west. The land uses within this SIU are non-irrigated native vegetation, pasture, and low density residential. Current groundwater use in the Pentz SIU is minimal. Management Objective It is the intent of this objective to maintain the groundwater surface elevation during the peak summer irrigation season (July and August) in all aquifer systems at a level that will assure an adequate and affordable irrigation groundwater supply, and to assure a sustainable agricultural supply of good quality water now and into the future. The management objective is also to assure an adequate groundwater supply of adequate quality from the alluvial aquifer system for all domestic users in the sub-inventory unit and to assure the water supply can be utilized without injuring groundwater quality or inducing land subsidence. Geologic Formations Identified In Sub-Inventory Unit Geologic formations in the Pentz SIU, from youngest (shallowest) to oldest (deepest), include: Modesto Formation Tuscan Unit C (Upper Tuscan) Tuscan Unit B (Lower Tuscan) Fresh Water-bearing Units. In the Sacramento Valley Region of Butte County, fresh groundwater-bearing units include, from youngest (shallowest) to oldest (deepest), the Modesto, Riverbank, Laguna, Tehama and Tuscan Formations. Those included in the Pentz SIU are: Modesto Formation Tuscan Unit C (Upper Tuscan) Tuscan Unit B (Lower Tuscan) BMO Key Wells Selected for Level Monitoring The DWR completed installation of a multi-completion monitoring well, SWN 21N02E26E003-6 in September This well was constructed as a quadruple completion well, which means the borehole contains four casings isolated in separate geologic strata, allowing for monitoring of the groundwater levels contained in the respective aquifer systems. Dedicated monitoring wells are constructed specifically for measuring groundwater levels and groundwater will not be extracted from the newly installed monitoring well. The data set is not yet sufficient for establishing BMOs for these wells. Pentz 2014 BMO 1

2 Sub- Inventory Unit Additionally, five of the monitoring wells installed by Butte County Public Works at the Neal Road Recycling and Waste Facility have been selected for inclusion in this report. These are identified as MW-4, 6, 8A, 8B, and 10. Monitoring of groundwater is a regulatory requirement for operation of the waste facility. is monitored quarterly at each of the waste facility s monitoring wells, and both level and quality measurements are taken. The monitoring wells are located within the waste facility property. A function of the monitoring wells is to calculate groundwater flow direction and velocity. The operation and monitoring of the wells located at the waste facility are under the direction of the Department of Public Works. Public Works staff will continue to provide groundwater elevation data, however, at this time BMOs have not been officially established for these wells. BMO Key Wells Selected for Quality Monitoring When the Butte County Trend Monitoring Program began, a well was sampled close to the border of the Pentz and Cherokee sub-inventory units. was measured from this well from 2002 through In 2007, a new well was located and sampled approximately 2.4 miles from the Pentz-Butte Valley well. Data is presented for both of these wells. State Well Number Annual Temperature Measurement ( o C) Pentz 21N03E29J03M Pentz-Butte 21N03E26E01M Valley Sub- Inventory Unit State Well Number Annual ph Measurement Pentz 21N03E29J03M Pentz-Butte 21N03E26E01M Valley Sub- Inventory Unit Annual Electrical Conductivity Measurement (microsiemens/cm) State Well Number Pentz 21N03E29J03M Pentz-Butte 21N03E26E01M Valley BMO Key Well(s) Selected for Land Subsidence Monitoring State Well Number 20N01E18L03M located in the Western Canal Water District. Maximum annual inelastic land subsidence shall not exceed 0.01 feet per year. Pentz 2014 BMO 2

3 BMO Alert Stage Definitions and Compliance Methodologies When enough years of data have been collected from the multi-completion monitoring well, the Pentz Sub-Inventory Unit will establish BMOs for those wells pursuant to the Basin Management Objective Ordinance. Future Monitoring Recommendations Efforts will be made to identify additional domestic wells that could be added to the existing monitoring well network in the sub-inventory unit to allow for development of additional management objectives for the alluvial aquifer system. Locate additional wells, either irrigation or domestic, with sufficient historical construction information to include in the water quality monitoring network, and initiate data collection in the future. Supporting Data Hydrographs depicting groundwater level measurements. Data from the Neal Road Landfill wells comes from the Third Quarter 2013 Monitoring Summary Report prepared for Butte County Department of Public Works by SCS Engineers. WSE Water Elevation (feet, above mean sea level) GSE Ground Elevation (feet, above mean sea level) QM Questionable Measurement Pentz 2014 BMO 3

4 Multi-completion Monitoring Well: 26E WSE Water Elevation (feet, above mean sea level) GSE Ground Elevation (feet, above mean sea level) Pentz 2014 BMO 4

5 WSE Water Elevation (feet, above mean sea level) GSE Ground Elevation (feet, above mean sea level) Pentz 2014 BMO 5

6 21N02E26F001 This has long been a key well highlighted in the Butte Basin Water Users annual report. 21N02E26F001M is an irrigation well located just west of Highway 99E, near the intersection of Durham-Pentz Road and Oro-Chico Highway. Within a two-mile radius of the well, groundwater is used to support agricultural production of orchard and row crops, and smallscale industrial uses associated with a beverage distribution plant. The well is a deep irrigation well with shallow casing, and a groundwater level measurement record dating back to the late-1960s. levels in this well represent a mixture of the unconfined and confined portions of the aquifer system. The groundwater levels in this well were monitored on a semi-annual basis (spring and fall) until 1991, on a monthly basis from 1991 to about 1994, and are then four times a year during March, July, August and October.. Measurements were discontinued at this location in spring The figure shows that the average seasonal fluctuation (spring to fall) in groundwater levels averages about 3 to 10 feet during years of normal precipitation and approximately 3 to 5 feet during years of drought. Long-term comparison of spring-to-spring groundwater levels shows a decline in groundwater levels during the period of , related, at least in part, to the drought. Since a groundwater elevation high of approximately 145 feet in 1985 the measured groundwater levels in this well have continued to decline. Recent groundwater level measurements indicate that the groundwater elevation in this well is approximately feet lower than the historical high in Water elevations have been monitored since 1967 at this location and the historical averages are; Spring=133 feet and Fall=126 feet. Since 1985 spring groundwater levels in this well have been declining and the spring 2008 measurement remained ten feet below historical high levels and more recent measurements continue the downward trend on the hydrograph. The long-term trend of decline observed in this well was such a point of concern it prompted the drilling of a new monitoring well to evaluate the potential causes for the decline. DWR installed a new dedicated monitoring well (21N02E26E03-6) near this existing key well in August Pentz 2014 BMO 6

7 Neal Road Landfill Monitoring Well Data: MW-4, MW-6, MW-8A, MW-8B, MW-10 Black line shows all data. Spring data are for measurements taken in March, April or May. Fall data are measurements taken in October MW ***Monitoring well dry since October 2009 until the May 2012 measurement and dry again since. Another monitoring well, 4A, was installed in MW Pentz 2014 BMO 7

8 Black line shows all data. Spring data are for measurements taken in March, April or May. Fall data are measurements taken in October. 148 MW-8A ***Monitoring well has been dry since October MW-8B Pentz 2014 BMO 8

9 Black line shows all data. Spring data are for measurements taken in March, April or May. Fall data are measurements taken in October MW ***Monitoring well was dry since October 2008 until the May 2012 measurement and then dry again since. Pentz 2014 BMO 9