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August 2016
6-3
City of Morgan Hill
2015 Urban Water Management Plan
The Llagas subbasin and the Coyote Valley subarea are monitored and addressed by SCVWD.
The January 2016 Groundwater Condition Report from SCVWD notes that groundwater levels
were below the 5-year average for both the Coyote Valley subarea and the Llagas subbasin.
Additionally, groundwater pumping for 2015 was below the 5-year average for both subbasins.
Based on the South County Water Supply Planning Project dated July 2010, the Llagas Subbasin
is expected to experience a water supply shortfall in 2030 demand projections. These
groundwater projections were based on a desired groundwater elevation set forth by SCVWD.
6.2.1.2 Basin Boundaries
The City lies atop the boundary between the Llagas subbasin and the Coyote Valley subarea of
the Santa Clara subbasin, with Cochrane Road being the approximate boundary line; wells north
of Cochrane Road pump water from the Coyote Valley subarea while wells south pump from the
Llagas subbasin.
The Llagas Subbasin is 15 miles long, 3 miles wide along the northern bounds, and tapers out to
approximately 6 miles along the Pajaro River boundary. The subbasin has confined and
unconfined portions within its boundary. At approximately 74 square miles, the confined area
protrudes to the north from the Pajaro River, with a thick clay layer binding the subbasin to
approximately Church Creek. The extreme east-west portions, as well as north of Church Creek,
are generally categorized as the unconfined portion of the Llagas Subbasin
The Coyote Valley subarea is approximately 7 miles long, beginning at Metcalf Road and ending
at Cochrane Road, and is approximately 2 miles wide. The approximate surface area of the
Coyote Valley is 15 square miles. The Coyote Valley has the general characteristics of an
unconfined subbasin, with no clay confining layers, and normally drains to the Santa Clara Plain
subarea of the Santa Clara subbasin.
6.2.1.3 Groundwater Quality
Drinking water standards follow Title 22 Standards set forth by the State of California, in
conjunction with the Environmental Protection Agency, to monitor the quality of potable water.
The City currently monitors its supply wells, and the District monitors groundwater in the Santa
Clara County.
According to the SCVWD 2014 Annual Groundwater Report, the quality of the South County
groundwater, which includes the Llagas subbasin and the Coyote Valley subarea, is of generally
good quality. The District reports median nitrate levels for the Llagas and Coyote Valley
groundwater as 15.2 mg/L and 20.5 mg/L, respectively.
One of the primary contaminants of note in the City is perchlorate, as identified in the 2010
UWMP. The primary source of perchlorate contamination was identified as the Olin Chemical
Corporation highway safety flare plant. According to the SCVWD 2014 Annual Groundwater
Report, more than 167 pounds of perchlorate have been removed from the site and over 2,050 AF