Assessment of Groundwater Quality in the Borrego Valley
The quality of water in the Borrego Valley is a concern because of the basin's reliance on groundwater for agricultural, recreational, and municipal supply. Groundwater quality can be affected by land-use activities occurring at or near land surface. These activities include irrigation of vegetated landscapes and the use of septic systems to dispose of wastewater. Groundwater quality can also be affected by declining water levels, as there is the potential to change the distribution of flow from underlying aquifers to wells. Historic and current water-quality data was used to determine which constituents had relatively high concentrations compared to water-quality thresholds and if these constituent concentrations were changing in response to declining water levels. Age-dating isotopes (tritium and carbon-14) were analyzed to determine if modern groundwater recharge is occurring in the Borrego Valley. Major findings of groundwater-quality portion of this study are the following:
- Historic water-quality data showed that in the upper aquifer, total dissolved solids (TDS) and nitrate as N exceeded their respective water-quality thresholds of 500 mg/L (secondary recommended CA-MCL) and 10 mg/L. Currently, the source of this nitrate is unknown.
- TDS and sulfate were the only constituents that showed increasing concentrations with simultaneous declines in water levels.
- TDS and nitrate concentrations were generally highest in the upper aquifer and in the northern portion of the Borrego Valley, where agricultural activities are primarily concentrated.
- age-dating isotopes indicated that very little groundwater recharge is occurring under current climatic conditions and that the vast majority of natural recharge is occurring adjacent to the mountain fronts.
BoundariesBorrego Valley Groundwater Basin
Borrego Water District
Groundwater Model Active Cells
Site Cluster, and number of wells in the cluster
Water-quality ClassesChemical/Physical Water Quality Indicators
Volatile Organic Compounds
Water-quality data displayed in the site popups show only the most recent sample for the water quality constituent class selected. If there is not a value shown for a constituent that means that the constituent was not analyzed for in that sample. However, that constituent may have been analyzed for in earlier samples, so the user should check the downloadable Excel workbooks found on the "Datasets" page.
Water-quality data can be downloaded in an Excel format from this website. The Excel workbooks contain current and historical water-quality data for groundwater samples collected in the Borrego Valley and spring samples collected in pertinent watersheds. The workbooks are categorized by constituent class. These classes are:
- Chemical and physical water quality indicators
- Inorganic and nutrient constituents
- Isotopic tracers
- Other organic compounds
- Pharmaceutical constituents
- Pesticide and pesticide degradates
- Radiological constituents
- Volatile organic compounds
There are three sources for the water-quality data presented on this website: Borrego Water District (BWD), State Water Resources Control Board Division of Drinking Water (DDW) and U.S. Geological Survey (USGS)
- BWD water-quality data — Sample dates range from 1917 to 2007. Some of the more recent BWD data is also reported in the DDW database. Data that is reported in both the BWD and DDW database will only be listed as being sourced from DDW. Some non-detects in the BWD database are shown as zero "0" or "ND" instead of less than values "<" (for example <0.5, assuming 0.5 is the detection limit). Less than values, zeroes and ND indicate that a constituent was not detected. Constituent classes contributed from the BWD database are chemical and physical water quality indicators, inorganic and nutrient constituents and radiological constituents. Data from the BWD database is reported as it was received; no quality control checks or manipulation of values have been done.
- DDW water-quality data — Sample dates range from 1985 to 2010. Some non-detects in the DDW database are shown as zero "0" instead of less than values "<" (for example <0.5, assuming 0.5 is the detection limit). This indicates that the analyzing laboratory has decided to report data below the State detection limit. Both less than values and zeroes indicate that a constituent was not detected. Data from the DDW database is reported as it was received with the exception of the removal of three VOC detections that were indicated as false positives. No other quality control checks or manipulation of values have been made to prepare the data for this website.
- USGS water-quality data — Sample dates range from 1980 to 2013. Non-detections in the USGS database are indicated by less than values "<." USGS data reported on this website has generally undergone quality control checks. Quality control checks include collection of blank and replicate data and analysis of cation and anion balances.
Water-quality Data Displayed in Dialogue Boxes
Data displayed in the dialogue boxes show only the most recent sample for the water quality class/constituent selected.
If there is not a value shown for a constituent that means that the constituent was not analyzed for in that sample. However, that constituent may have been analyzed for in earlier samples, so the user should check the downloadable Excel workbooks.
Sites with Scanned water-quality data
Well and spring sites in the study area that had water-quality data in a hard copy format were scanned and formatted as Adobe Portable Format Documents (PDFs). Scanned water-quality data can be reviewed and (or) downloaded by clicking the site of interest on the interactive map.