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August 2017
7-8
City of Morgan Hill
Sewer System Master Plan
x
RM-P2
: Replace the 18-inch gravity sewer along Tennant Ave from Railroad Ave to
Monterey Road.
x
RM-P3
: Replace the 10-inch gravity sewer along La Crosse Drive / Vineyard Boulevard
from La Mar Drive to Monterey Road.
7.4 JOINT MORGAN HILL-GILROY SEWER TRUNK CAPACITY
EVALUATION
As part of this Master Plan, the Joint Morgan Hill-Gilroy Sewer Trunk (Joint Trunk) was evaluated
for capacity adequacy. The Joint Trunk has historically had capacity constraints in the portion
along California Avenue and Harding Avenue. Since the previous Master Plan, the City has
surveyed the Joint Trunk, developed additional improvement alternatives to evaluate the feasibility
of prioritizing construction, and constructed portions of a relief trunk.
The Joint Relief Trunk (Relief Trunk) was identified in the 2002 Master Plan, and subsequent
studies as a required improvement intended to mitigate existing capacity deficiencies and to
service future growth. The City has constructed Relief Trunk along California Avenue, and south
along Harding Avenue to Highland Avenue as a 30-inch parallel pipeline. The City is currently in
the process of designing the remaining 30-inch Relief Trunk from Highland Avenue to the City of
Gilroy (
Figure 7.4
).
7.5 PIPELINE CONDITION ASSESSMENT
As additional task added to the scope of the master plan, City staff requested Akel Engineering
Group to utilize existing closed-circuit television (CCTV) data to assess the condition of the
existing sewer system infrastructure. This section documents the findings and recommendations
of the condition assessment.
7.5.1
Background and Purpose
City staff have been proactively involved in the condition assessment of their pipelines, including
performing CCTV, and rating those pipelines against the NASSCO Pipeline Assessment
Certification Program (PACP). This rating system assesses pipelines based on observations from
the CCTV, and scores them from 1 to 5 based on the criticality of the observations, with 5 being
most critical. As such, City staff would like to prioritize improvement recommendations and costs
in this master plan based on the physical condition of the sewer collection system. The pipelines
that have been included in the CCTV, and which were reviewed as part of this condition
assessment, are shown graphically on
Figure 7.5
.
7.5.2
Condition Assessment Findings
The condition assessment focused on documenting major structural defects (PACP Rating 4 or 5)
and infiltration and inflow defects. Major structural defects can lead to costly pipeline failures,
while infiltration and inflow defects may contribute to sanitary sewer overflows downstream.