Evaluation of the South Central Region Office Well Network for the San Joaquin River Hydrogeologic Region 2015 DWR Geology and Groundwater Conference

San Joaquin River Hydrogeologic Region Subbasins include: Modesto Turlock Merced Delta-Mendota Chowchilla Madera

Exceptions Madera/Chowchilla Subbasins Oakdale ID/Stanislaus Triangle

SCRO Well Network Initiated in the 1950s Network updated through 1991 Verbal well owner permission No known previous analysis of network conducted

Previous SJRHR Well Network Designation # of wells Delta-Mendota 111 Los Banos-Grande71 Modesto-Turlock79 Oakdale ID68 Turlock ID202 Eastside WD19 Merced Bottoms86

Investigation 429 Field Data Sheet Well Completion Report

Revisions Eliminated most wells where a log containing construction information could not be located. Wells with limited construction information were retained in few instances. Some wells without construction information were retained to maintain coverage if no others available.

Limitations Age of Well Completion Reports Non-standard format Difficult to read

Limitations cont. Illegible

Limitations cont. Missing details: Location Screened intervals Cased depths

Revised SJHR Well Run Designations Designation: # of wells Delta-Mendota 69 Modesto 27 Turlock West 38 Turlock East 24 Merced 42

Delta-Mendota Delta-Mendota/Los Banos-Grande Delta-Mendota

Modesto Oakdale Irrigation District Modesto

Turlock Turlock Irrigation District Turlock West

Turlock Modesto-Turlock Turlock East

Merced Merced Bottoms Merced

CASGEM Conformity Monitoring network being updated to CASGEM monitoring entity requirements. Eliminated duplicate wells measured by monitoring entities. Intended to compliment the CASGEM monitoring entity network for the subbasin.

Goals Three wells per quarter township density. – Appropriately spaced – Representing the major aquifers Renew written permission for existing wells and receive well owner permission for expansion.

SLDMWA & DWR Well Run Delta-Mendota Groundwater Subbasin

STRGBA CASGEM & DWR Well Run Modesto Groundwater Subbasin

TGBA CASGEM & DWR Well Run Turlock Groundwater Subbasin

Merced Groundwater Subbasin MAGPI & DWR Well Run

Madera-Chowchilla Monitoring Group Madera & Chowchilla Groundwater Subbasins

San Joaquin Hydrogeologic Region Monitoring Network Subbasin # of wells Delta Mendota 236 Modesto81 Turlock 121 Merced89 Chowchilla 49 Madera 116

Region Network by Well Type CASGEM/Construction details Voluntary/Missing Details

Recognized Data Gaps Eastern margin of the Modesto, Turlock, and Merced subbasins: Thin alluvium/shallow bedrock Low population density Well clusters around artificial recharge zones (lakes, rivers)

Recognized Data Gaps Western Merced and Central Delta-Mendota subbasins: Wetlands and low lying areas Wildlife refuges, hunting clubs Sparse well coverage

Data Gap Study Reviewed Wellma database Eliminated from count: – Boring logs – Duplicates and multi- records – Test/Monitoring Wells – Cathodic Protection Wells – Sparging, vapor extraction, heat exchange, & remediation wells

Well Completion Report Count by Township

Area of Concern Corcoran Clay Large number of irrigation wells screened through the regional confining layer. Clustered in western Turlock and Modesto subbasins.

Distribution of Region Wells to Corcoran Clay

Next Phase Begin filling gap areas and updating permissions. Complete review for Tulare Lake HR and make revisions. Continuing monitoring in remote basins and expand into unmonitored basins.

Challenges Difficult to locate wells Falling water levels Dry or destroyed wells

Challenges Loss of access – Locked gates – Well houses – Wildlife Uncooperative well owners

Sustainable Groundwater Management Act (SGMA) Requires GSAs to stabilize groundwater across the groundwater basins to January 1, 2015 levels. Most likely require GSA expansion of current monitoring networks. CASGEM status unknown until regulations finalized. Monitoring network will be adjusted once GSP submitted for each basin. Possible future role as verification of groundwater level information submitted by GSAs.

Questions?