HomeMy WebLinkAbout1978-10-17; City Council; 5577-1; Encina Water Pollution Control report. ' . • W
CITY OF CARLSBAD
AGENDA BILL NO . S£* 77- ^JLo ,n A-r ffVif ^ / ' Initial:
V» — Dept.HdjEo?
DATE: October 17, 1978 - .
DEPARTMENT: _ Pub I ic Works _ _ C. Mgr.P\
Subject: CARLSBAD'S CAPACITY IN ENCINA WATER POLLUTION CONTROL' FAC I LITY
SUPPLEMENTAL REPORT #5
Statement of the Matter
In response to a City Council request, staff has reanalyzed sewage capacity
availability based on a more detailed analysis and additional information
developed since the enactment of the sewer moratorium. Exhibit I summarizes
the efforts of the reanalysis.
Exhibit
I.. Memorandum dated October 12, 1978 from Public Works Administrator
Recommendation
*"""- \
It is recommended,that City Council direct staff to prepare a resolution es-
tablishing a new EDU flow rate of 253 gallons per day per EDU and to prepare
' such other ordi nance changes as maybe required to administer available ca-
.. pacity. .
It is further recommended-that City Council accept that 640 EDUs (not to
exceed 13,751 EDUs total issued) are available and that on the advice of
Special Counsel, concurred in by the City Attorney, this capacity be retained .
by the City until the resolution of current litigation regarding claims on
capacity. Upon resolution of the litigation, the City Council should consider
an allocation system to handle equitable distribution of available capacity.
Agenda Bill #5577 - Supplement #1 Page 2
Council Action:
10-17-78 Council concurred with staff recommendation, and directed
staff to prepare the necessary documents establishing a
new EDU flow rate of 253 gallons per day per EDU, and
such changes as may be required to administer available
capaci ty.
In addition, Council accepted that 640 EDU's (not to exceed
13,751 EDU's total issued) are available and that on the
advice of Special Counsel, concurred in by the City Attorney,
this capacity be retained by the City until resolution of
current litigation regarding claims on capacity. Upon
resolution of the litigation, the Council should consider
an allocation system to handle equitable distribution of
available capacity.
MEMORANDUM
TO: City Manager
FROM: Public Works Administrator
DATE: October 12, 1978
SUBJECT: CARLSBAD'S CAPACITY IN ENCINA WATER POLLUTION CONTROL FACILITY
SUPPLEMENTAL REPORT #5
Council requested staff to report, at a minimum of six-month intervals, on
items relating to use of existing capacity, the possibility of leasing addi-
tional capacity and policy recommendations regarding our capacity at the
Encina Water Pollution Control Facility. While the last labeled supple-
mental report (number 4) was dated October, 1977, the last information up-
date and policy recommendation was a June 23, 1978 memorandum wherein the
City Council acted to establish the equivalent dwelling unit (EDU) flow
rate at 270 gallons per day per unit until such time as flow rate records
showed they were otherwise. As Council will recall, the 270 figure was
arrived at after consideration of flow rate per capita, household occu-
pancy, the figure of 280 used in planning projections, etc.
During the four months since City Council acted on the June 23, 1978 policy
memorandum, there has been considerable interest in actual, rather than es-
timated, flow rates at the Encina facility. We now have 12 months of flow
meter readings, from a meter which JAC operational personnel say is accurate,
upon which to base conclusions.
Since we first started using equivalent dwelling units as our control, we
have continually reanalyzed our techniques to improve their accuracy and
reliability. In addition, we now have the benefit of 12 months of usable
flow meter readings. Using this expanded information base, staff will make
recommendations to City Council. It should, however, be kept in mind that
our figures should be continually reanalyzed against existing flow rates,
and, as further corrections are deemed necessary, those corrections should
be made.
The following table contains information used in establishing our flow
rates: Column I shows the flows attributable by the Encina meter to Carls-
bad for the period from October, 1977 through and including September, 1978.
Column 2 shows the running total of the number of permits issued; that is,
at any one point in time these are the total number of outstanding permits
issued in the City's service area. Column 3 shows the gross EDU flow rate.
In my opinion, the information used to obtain the gross EDU flow rate gives
a result which is less than accurate. A major reason for the inaccuracy is
because the running total of permits is based on the number issued, not the
number connected or flowing; therefore, there may be some hookups that are
not contributing flow to our sewer system at any one point in time. To ar-
rive at the true value'of flow rate per EDU, we must consider only those
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permits that are connected and flowing. There are always a number of issued
permits for facilities that are under construction, unoccupied, awaiting
sale or experiencing a seasonal fluctuation. Factors affecting the number
of non-contributing facilities are weather, season, economics and the state
of the construction market. Our review of these factors indicate that dur-
ing the period of analyses the number of permitted units actually hooked up
and flowing ranged from 84% to 88.5$ of total permits issued. The actual
percentage figure used is shown in Column 4. This percentage increased as
the period progressed because, due to the moratorium, fewer permits were
issued and the earlier issued permits were constructed and on-line. Multi-
plying the percentage factor by the total number of permits issued results,
in my opinion, in the best available estimate of actual on-line and flowing
EDUs (Column 5). When this number is divided into the recorded flow for
the corresponding month, the result is the adjusted average flow per EDU
for that month (Column 6). This adjusted figure gives us a better picture
of how actual flows may vary during the year due to use patterns. It also
eliminates variations caused by the administrative act of issuing a permit.
COLUMN
MO/YR
OCT 77
NOV 77
DEC 77
JAN 78
FEB 78
MAR 78
APR 78
MAY 78
JUN 78
JUL 78
AUG 78
SEP 78
FLOW
(MGD)
2.41 1
2. 136
2.864
3.642*
3.497*
3.249
3.574*
2.659
2.707
2.282
2.590
2.880
CONNEC-
TIONS
12,097
12,1 10
12, 138
12, 145
12,162
12, 188
12,195
12,21 1
12,429
12,521
12,551
12,724
ESTIM.
GROSS
EDU
199.3
176.4
236.0
299.9
287.5
266.6
293. 1
217.8
217.8
182.3
206.4
226.3
CONTRIB.
CONNECT.
%
84.0
84.0
84.5
84.5
84.5
85.5
85.5
85.5
86.5
87.0
88.5
89.0
ADJUSTED
CONNEC-
TIONS
10,161
10,172
10,257
10,263
10,277
10,421
10,427
10,440
10,751
10,893
1 1,108
1 1,324
ADJUSTED EDU
FLOW RATE
237.3
210.0
279.2
354.9
340.3
31 1 .8
342.8
254.7
251.8
209.5
233.2
254.3
COMMENT
DRY
DRY
WET
WET
WET
WET
WET
DRY
DRY
DRY
DRY
DRY
* EXCEEDED LEGAL PLANT CAPACITY
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Since our capacity is based on average flows, we must consider the impact
of the rainy seasons. If we use all of the information available, we get
an average EDU flow rate of 273.3 (versus our 270 as established by reso-
lution). This figure includes the months of December, January, February,
March and April when we had rains that exceeded two and one-half times
normal rainfall. This resulted in an abnormally high amount of inflow in-
to our systems. It is my recommendation that we analyze only the dry months
(October, November, May, June, July, August and September) and add a wet
weather factor to compensate for a more normal rainy season. My calcula-
tions (see Appendix "A") indicate that 230,000 gallons per day, average
daily flow, are attributable to infiltration and inflow. This amount
should be subtracted from our legally available capacity before determin-
ing our average dry weather flow rate for each EDU.
AVAILABLE CAPACITY
When City Council acted to lease capacity from the Encinitas Sanitary Dis-
trict, one of their concerns was the ability to return the capacity within
five years. While no action was taken at that time, staff suggested, and
Council considered, reserving the 75,000 gallon capacity. The Encinitas
contract calls for return of the capacity on or before September 30, 1982.
No provision is made for extension and the Encinitas Sanitary District
wouldn't negotiate to provide for it. The Phase III project schedule in-
dicates completion by mid-1982. This assumes no delays in project review
by the Federal Government, no strikes, no delays in equipment delivery, etc.
We cannot add capacity to the project or, for that matter, even receive a
grant fund offer to construct the project until the San Diego Region com-
plies with certain "Clean Air Program" requirements. Other additional
sources of capacity we considered were a rerating of existing treatment
plant facilities or the completion of Burroughs' "zero-flow" project. The
rerating is highly unlikely at this time especially since we are under
a cease-and-desist order from the Regional Water Quality Control Board.
The Burroughs project has slipped considerably and we have no confidence
when or if it wiI I occur. I believe that it would be prudent to keep the
75,000 gallons of capacity uncommitted at this time. I wiI I use only our
own capacity (3.43 MGD) in all subsequent calculations.
From our capacity of 3.43 MGD we must subtract the 0.23 MGD assigned to
handle wet weather flows. The balance, 3,200,000 gallons, is available to
handle the flow from all our connections. The existing connections (12,724)
can be expected to flow at an average dry weather flow of 3,000,319 gallons
per day. This must be subtracted from the 3.2 MGD. We also have a balance
of 48,750± (dry weather) gallons per day additional capacity committed to
the balance of the Plaza Camino Real Shopping Center expansion. This also
must be subtracted from our balance.
3,200,000 - (3,000,319 + 48,750) = 150,930
Dividing 150,930 by 235.8 gives 640 EDUs of capacity available. To deter-
mine total EDUs we must add existing permits (12,724) to those that may be
made available (640) and add the shopping center's capacity estimated to be
207 (48,750 ^ 235.8). This gives an EDU total of 13,751 (12,724 + 640 + 207),
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EDU VALUE DETERMINATION
It must be kept in mind that the 230,000 gallons per day allotted for wet
weather flow must be shared by all connections in determining a usable EDU
figure. If it is equally allotted to each of the 13,751 EDUs determined
to be available it equals 16.7+ gallons per EDU (230,000 gallons t 13,751
EDUs). This figure must be added to the 235.8 dry weather flow figure to
obtain the average daily flow per EDU.
235.8 + 16.7+ - 252.5+ gallons per day per EDU (use 253)
Acceptance by the City Council of the figures used in this report will ne-
cessitate changes in two areas: (I) A new resolution would have to be
adopted modifying the flow rate per EDU; and (2) the ordinances which es-
tablish flow rates on a square footage basis, or otherwise, in our Municipal
Code, would have to be modified.
RECOMMENDATION
It is recommended that City Council direct staff to prepare a resolution
establishing a new EDU flow rate at 253 gallons per day per EDU and to pre-
pare such other ordinance changes as may be required to administer available
capacity.
It is further recommended that City Council accept that 640 EDUs (not to
exceed 13,751 EDUs total issued) are available and that on the advice of
Special Counsel, concurred in by the City Attorney, this capacity be re-
tained by the City until the resolution of current litigation regarding
claims on capacity. Upon resolution of the litigation, the City Council
should consider an allocation system to handle equitable distribution of
available capacity.
Ronald A. Beckman, P.E.
Public Works Administrator
RAB:VEB
Attachment: Appendix "A"
APPENDIX "A1
Brown & Caldwell, in their 1976 report on Carlsbad's sewer system, indi-
cated that our flow from infiltration was approximately 100 gallons per
acre per day for the existing sewered area. Our sewered area is approxi-
mately 5,000 acres. This equates to approximately 500,000 gallons per day
for each of the four months of our normal wet weather season. This figure
must be augmented by an undetermined amount to compensate for peak flow into
the system caused by inflow. This is the situation when our streets are
flooded by momentary peaks in wet weather causing water to infiltrate through
manhole covers and the like into our sewer system.
Another technical method of determining infiltration and inflow considers
the length and size of underground pipe. This method uses a factor of 500
gallons per day per inch-mile of sewer (two miles of eight-inch diameter
sewer equals 16 inch-miles; one mile of 16-inch diameter sewer equals 16
inch-miles). In addition, a factor should be added for each manhole. Normal
manhole factors in textbooks use from 500 to 5,000 gallons per day per man-
hole. This allows for deteriorated condition, the use of brick manholes and
for a high groundwater table. Since our system is relatively new, uses pre-
cast concrete to a large extent and, for the most part, is we I I above the
groundwater table, I propose to use a factor of 100 gallons per day per man-
hole. Our sewer system has approximately 750 inch-miles of sewer line
(70± miles of eight-inch through 39-inch line) and I700± manholes.
(750 x 500) + (1700 x 100) = 375,000 + 170,000 = 545,000 gallons per day
Since we must account for deterioration of the system, I propose to use a
safety factor of 25%.
I.25 x 545,000 = 681,250
This is the additional flow per day that can be expected during the rainy
season and for a short period thereafter. To equate this additional wet
weather flow, which lasts on the average of four months per year, to an
average daily flow figure for the entire year, we take one-third (four
months wet weather divided by 12 months per year); therefore,
681,250 t 3 = 227,083 (use 230,000)
This amount of capacity is used for wet weather flow and, therefore, must
be subtracted from our total available capacity.
3.43 MGD - .23 MGD = 3.2 MGD available capacity