Pajaro Valley Groundwater Overdraft Concerns

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A Watershed Issue examined by the ENVS 560/L Watershed Systems class at CSUMB.

Summary

PVWMA Boundaries copied from the PVWMA Revised Basin Management Plan [1]

The Pajaro Valley is an agriculturally important area of the California Central Coast. Over the past several decades, Groundwater pumping for agricultural and municipal use has led to an overdraft of the aquifer. Groundwater overdraft occurs when the pumping rate exceeds the recharge rate over an extended period of time. The situation in the Pajaro Valley is further complicated because aquifer recharge takes tens or even hundreds of years, even after mitigating steps have been taken and no further groundwater pumping occurs.[2] [3] The State of California established the Pajaro Valley Water Management Agency (PVWMA) in 1984 to manage water supply and water quality issues. [4]

Location

Highlighted Region shows Carneros Watershed copied and modified from the PVWMA Revised Basin Management Plan[1]

The Pajaro Valley lies in Central California and includes parts of City of Monterey, City of Santa Cruz, City of San Benito, and City of Santa Clara counties. The Pajaro Valley aquifer extends west into Monterey Bay and north to the Soquel-Aptos basin. It is bound to the South by Elkhorn Slough and to the East by the San Andreas fault. The watershed above this aquifer covers approximately 80,000 acres. [1] The Carneros Watershed lies along the southern boundary of the Pajaro Valley.

Resources at stake

Groundwater overdraft in a coastal region increases the risk of seawater intrusion which can adversely impact water quality. The diminished water table can also lead to increases in concentrations of dissolved solids leached into the soil by agriculture runoff. Negative effects of groundwater overdraft include:

  • Municipal drinking water supplies
  • Agricultural water supplies
  • Land subsidence [5]
  • Permanent loss of groundwater storage

A 2000 Basin Management plan by PVWMA indicates that agriculture and high septic tank density in the watershed have led to concerns that groundwater might experience high nitrate concentrations.[6] If the groundwater overdraft in the Pajaro Valley is not mitigated, parts of Monterey, Santa Cruz, Santa Clara, and San Benito counties could experience diminished freshwater resources.

Water resource control is complicated with the need to balance water supply for agriculture and municipal demand, while also preventing over-draft and water quality disturbance. Agriculture is the dominant land use in the valley, and uses 84 percent of the water, but municipal demand is growing at about 2.5 percent per year. [4] The City of Watsonville, the major urban hub in the Pajaro Valley, provides water to 66,000 customers. 90% of that water comes from groundwater, while 10% comes from stream surface water. [7] With population growth and pressure to satisfy local agricultural demand, PVWMA concluded future water shortages will disrupt the economy. PVWMA is looking into the legal right to the allocation of water from the California Aqueduct – also with its own issues with current water users. [3]

Stakeholders

The Pajaro Valley includes agricultural, developmental, municipal, and conservation activities into a water district that extends into three separate counties. Some of the major stakeholders include:

  • The Pajaro Valley Water Management Agency (PVWMA) was established in 1984 in order to manage groundwater issues in the Pajaro Valley in the region.
  • The Pajaro River Watershed Flood Prevention Authority was established in 2000 to develop and implement flood prevention strategies for the Pajaro River. Any plans for groundwater recharge will have to be coordinated through the Flood Prevention Authority. [8]
  • The counties of Monterey, Santa Clara, Santa Cruz, and San Benito all have some portion of Pajaro Valley within their borders.
  • The City of Watsonville is in the center of the Pajaro Valley and will require groundwater resources for future development. [9]
  • Potential developers in this region are subject to submitting Environmental Impact Reports that address groundwater overdraft. See Example

Laws, Policies, & Regulations

Currently in California, landowners possess the ability to pump groundwater as long as it is put to beneficial use. Assembly Bill 3030 was passed in 2002 and enables designated local agencies to form groundwater management plans. The PVWMA is the designated agency that voluntarily creates groundwater management plans for the the Pajaro Watershed. If agencies are unable to resolve local groundwater management issues, actions by local governments to enact local ordinances are necessary.[2] In 2014, the Sustainable Groundwater Management Act (SGMA) was passed by Jerry Brown as state law. SGMA requires basins such as the Pajaro Valley to reach sustainable levels by 2040. [10]

Groundwater Recharge

Recharging Pajaro Valley groundwater requires both streamflow infiltration and percolation from precipitation. The University of California at Santa Cruz leads most of the projects in the Pajaro Valley that investigate the relationship between surface and groundwater interaction. The most recent research in the valley is through a grower-initiated project to help restore the aquifer using recharge ponds. According to USGS, groundwater is non-renewable in some parts of the Aromas Sands of the Pajaro Valley due to geochemical and geophysical data. [4] As early as 1943, seawater intrusion has been recognized and tied to seasonal pumping. In 1974 extensive seawater intrusion was at 100 and 200 ft., with seawater intrusion present at 300 - 600 ft. in the Aromas Sand. [4]

Addressing Overdraft Concerns

The Pajaro Valley Integrated Ground Surface water Model (PVIGSM) was created to help predict future groundwater levels and quality. PVWMA uses the PVIGSM to monitor groundwater and watershed models for the Pajaro Valley and are currently using those resources to better educate stakeholders and decision makers on possible mitigating action to remedy the issue of groundwater overdraft. Additional modeling of the Carneros watershed could prove useful in the future if the Pajaro Valley groundwater overdraft increases and extends into other watersheds. [6] The US Geologic Survey is currently operating monitoring wells in conjunction with PVWMA in order to assess the geophysical and geochemical impacts of groundwater overdraft on the aquifer. [11] Additionally, the PVWMA is conducting a project at Harkins Slough that captures storm runoff in the winter, injects that water into the aquifer, and recovers that water in the summer for distribution to growers. [12] Since 2009 PVWMA has been delivering recycled water to nearby farms for irrigation. This project is expected to meet one quarter of water needs in the valley to stop seawater intrusion and treats up to 7.7 million gallons of water per day. [13] PVWMA additionally is piloting a fallow program for farmers to leave their farms fallowed for one year receiving $1,000 per acre for the calendar year. [14]


PVWMA devoted 6.3 million dollars toward two projects in an attempt to reduce seawater intrusion. The first project would be the connection of existing pipelines to College Lake and pumping that water to farmland instead of letting it go out to the Monterey Bay. The second project is to store runoff in an underground storage basin rather than letting it discharge into the ocean. [15]

References

  1. 1.0 1.1 1.2 [PVWMA] Pajaro Valley Water Management Agency. 2006. Basin management plan documents. [30 January 2011]. Available from: : http://www.pvwma.dst.ca.us/
  2. 2.0 2.1 California Department of Water Resources. 2010. Groundwater Information Center [30 January 2011]. Available from: http://www.water.ca.gov/groundwater/index.cfm
  3. 3.0 3.1 Stephens T. 18 November 2007. UCSC hydrologist provides expert advice on Pajaro Valley's water supply. UCSC News [Internet]. [cited 31 January 2011]. Available from: http://news.ucsc.edu/2007/11/1759.html
  4. 4.0 4.1 4.2 4.3 USGS. 2003. Geohydrologic Framework of Recharge and Seawater Intrusion in the Pajaro Valley, Santa Cruz and Monterey Counties, California. [29 March 2018]. Available from: https://pubs.usgs.gov/wri/wri034096/pdf/wri034096.pdf
  5. USGS Land Subsidence Explanation
  6. 6.0 6.1 Central Coast Hydrologic Region. 20 January 2006. Pajaro valley groundwater basin. California's Groundwater Bulletin 118 [Internet]. [cited 2 February 2011]. Available from: Bulletin
  7. Watsonville Public Works and Utilities. Recycle Water & Groundwater Overdraft.
  8. Pajaro River Watershed Flood Prevention Authority
  9. City of Watsonville
  10. PVWMA Sustainable Groundwater Management
  11. USGS. August 2003. Geohydrology of Recharge and Seawater Intrusion in the Pajaro Valley, Santa Cruz and Monterey Counties, California. US Geologic Fact Sheet 044-03 [Internet]. [cited 2 February 2011]. Available from: http://pubs.usgs.gov/fs/fs-044-03/.
  12. Harkin Slough Project
  13. PVWMA Recycled Water [29 March 2018]. Available from: https://www.pvwater.org/recycled-water
  14. PVWMA Fallow Program Application. [29 March 2018] Available from: https://www.pvwater.org/images/media-room/notices/Fallow-Land-Incentive-Program-Application_FinalRev.pdf
  15. Guzman K. 2107. Santa Cruz Sentinel “Pajaro Valley water agency combats seawater intrusion with two planned projects” [29 March 2018] Available from: http://www.santacruzsentinel.com/article/NE/20170327/NEWS/170329752

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Disclaimer

This page may contain student work completed as part of assigned coursework. It may not be accurate. It does not necessary reflect the opinion or policy of CSUMB, its staff, or students.