Laserfiche WebLink
5.0 Summary and Conclusions <br />Listed below is a summary of Task 39 with several conclusions from the data collected through <br />Phase 4: <br />^ Autunul water level data were collected using manual measurements for a total of 101 wells, <br />85 of which are bedrock and 16 of which are alluvial. These autumn measurements will <br />complement the spring measurements collected by the DWR and allow the evaluation of <br />seasonal water level trends. <br />^ Updated well owner ilzformation, location of wells and measurement methods were <br />documented and provided to the DWP. <br />^ Analysis of seasonal trends in wells measured bi-annually revealed that local pumping or <br />other influences have affected the ability to discern seasonal trends in many of the measured <br />wells. T11e analysis identified a subset of wells measured bi-annually that appear to not be <br />affected by localized impacts and have provided a high-quality record of regional water level <br />changes at a seasonal tinge scale. <br />^ Hourly water level measurements from data loggers were downloaded from 37 alluvial and <br />5 bedrock SPDSS monitoring wells, iiz addition to t11e wells measured manually. T11e hourly <br />measurements were converted to average daily values and will be submitted to the State for <br />inclusion in HydroBase. These data provide a continuous record of water levels and reveal <br />the seasonal water level trends for eac11 well. <br />^ The continuous record of water levels at the alluvial SPDSS monitoring wells reveal seasonal <br />and annual water level trends. These contimious measurements show the variations in <br />water levels due to activities such as nearby irrigation practices and well pumping, with <br />fluctuations up to approximately 13 feet in one year. <br />^ Temporal trends at the bedrock SPDSS monitoring wells are not as apparent as those in the <br />alluvial wells because t11e bedrock wells have been monitored for only a short period. In the <br />first year of monitoring, bedrock water levels fluctuated by up to approximately 100 feet. <br />^ The continuous records of water levels show fluctuations that would not be apparent from <br />bi-annual (spring and fall) measurements. Additionally, water level trends based on bi- <br />annual measurements could be nusleading if affected by nearby irrigation and/ or pumping <br />activity. Continuous monitoring of water level provides a more complete picture of water <br />levels than bi-annual measurements. <br />^ In 83 selected alluvial wells analyzed, the annual change in alluvial water levels from spring- <br />to-spring is very similar to t11e annual change from fall-to-fall measurements. Changes in <br />fall-to-fall measurements do not provide additional insight to long-term water levels in the <br />alluvial aquifer compared to spring-to-spring measurements, but may Have value on a <br />single-year basis in evaluating aquifer response to above or below average runoff conditions <br />^ Twenty-two wells were surveyed under this Task, including 18 alluvial wells in the DWR <br />and CCWCD water level monitoring programs and the four bedrock wells selected for long- <br />term monitoring. Additional wells have been surveyed previously under Tasks 35 and 36. <br />Fifteen of the wells surveyed under this Task had existing measuring point elevations listed <br />by the DWR. The differences iiz elevations at these 15 sites range from 0.2 to 12.4 feet and <br />average 4.6 feet. Water level data from wells without surveyed measuring point elevations <br />could Have a similar range of uncertainty. These elevation differences are often large <br />compared with the low hydraulic gradients present in the study area, and consequently will <br />have a direct effect on the accuracy of groundwater flux calculations. W11ere wells are <br />SPDSS Phase 4 Task 39 Technical Memorandum-Final 22 <br />O~i20%2008 <br />