HomeMy WebLinkAbout7285.02 Sewage Disposal Design Memo Tuscan Ridge (FNL IC 11.13.23)[68]
TECHNICAL MEMORANDUM
TO: Tuscan Ridge Associates, LLC
FROM: Ian M. Cole, PE
NexGen Engineering and Consulting LLC
PROJECT: Tuscan Ridge Planned Unit Development, Wastewater Treatment System Capacity Study
Butte County, California
DATE: November 13, 2023
1. Company Background
With a combined 40+ years of experience, the team at NexGen Engineering & Consulting LLC (NexGen)
has extensive expertise in the field of civil and environmental engineering, including the planning,
design, and construction of onsite wastewater treatment systems.
While NexGen primarily focuses on wastewater treatment solutions, the company also specializes in
land development, soils analysis, stormwater management, entitlements and due diligence, as well as
grading and drainage studies. For more information visit www.NexGenEng.com.
2. Introduction and Purpose
Tuscan Ridge Associates, LLC is proposing a Planned Unit Development (PUD) to develop the
approximately 163‐acre site referred to as Tuscan Ridge. Tuscan Ridge is located on the south side of
Skyview Road, approximately three miles west of the Town of Paradise, one‐half mile east of the Bluffs
subdivision, and four miles east of the City of Chico. The site is comprised of Assessor Parcel Numbers
(APNs) 040‐520‐104 through ‐111. It is bound by Skyway Road to the north, Paradise Rod and Gun Club
to the east, and undeveloped parcels to the south and west.
Tuscan Ridge was once occupied by the Tuscan Ridge Golf Club. In 2019 it was transformed into a
temporary base camp to provide construction staging and worker housing during the demolition and
cleanup efforts after the Paradise Camp Fire. The work included the construction of a small domestic
wastewater treatment facility (WWTF) at the southwest end of the site.
The PUD represents a mixed‐use community comprised of 165 single and multi‐family residential
homes; approximately 17.3 acres of commercial development consisting of commercial/retail space, a
gas station/convenience store and mini storage facility; a sewage dump station; and approximately 68.7
acres of recreational and open space areas.
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While the wastewater generated by the proposed development will not exceed the capacity of the
existing WWTF, upgrades are necessary in order to support the new development plan and
corresponding changes to the land uses (i.e. wastewater characteristics). This technical memorandum
provides an overview of the wastewater treatment system and processes, and an analysis of the
estimated wastewater flows generated by the proposed project.
3. Overview of Wastewater Treatment System and Processes
Wastewater Treatment Facility
The Tuscan Ridge WWTF, including the proposed upgrades, is covered under the State Water Resources
Control Board (State Water Board) General Waste Discharge Requirements for Domestic Wastewater
Treatment Systems, Order WQ 2014‐0153‐DWQ (General Order). The Waste Discharge Requirements
(WDR) permit specifies a discharge limit of 100,000 gallons per day (gpd) and requires treatment of
effluent to meet basic secondary treatment levels (including ultraviolet disinfection). The WWTF is
designed to treat and dispose of up to an average daily flow of 100,000 gpd, with a peak daily flow of
150,000 gpd. If the system operator were to ever propose an increase over the discharge limit, the
State Water Boad permit would need to be amended and approved by the Central Valley Regional
Water Quality Control Board (RWQCB).
The proposed WWTF will provide solids separation and anaerobic digestion, aerobic digestion, media
filtration, and ultraviolet light (UV) disinfection. This will be accomplished using flow equalization (EQ)
tanks, septic tanks, aerobic treatment modules, and UV disinfection units. Treated effluent will be
disposed of by evaporation and transpiration via lined evaporative ponds and a drip dispersal system. A
site plan showing the WWTF is included as Attachment 1. The treatment process is summarized in more
detail below.
The WWTF will utilize microorganisms to treat raw sewage generated by the homes and businesses
within the proposed development. The raw sewage will flow through a network of collection pipes
throughout the development which discharges into the treatment facility. In the primary treatment
phase, flow equalization (EQ) tanks will provide consistent influent flow to downstream processes by
retaining high flow fluctuations. Aeration systems within each EQ tank will prevent the raw wastewater
from becoming septic and to maintain solids in suspension. Pump systems will then deliver wastewater
in timed doses to a screener, where particles too small to be caught by the EQ tanks will be removed.
Next, the influent flows into a series of septic tanks that provide digestion of organic matter and
separation of floatable matter (e.g., oils and grease) and solids from the wastewater.
The secondary treatment process begins after the septic tanks where influent enters the media filter
treatment modules. These modules are specially designed to create a healthy biomat (a microscopic
layer created by the waste‐products of anaerobic bacterial activity) that operates like a living filter,
digesting waste materials as the wastewater passes through. The biomat is also responsible for
regulating the rate at which fluid moves through the system. Slowing down the liquid enables the
bacteria (both aerobic and anaerobic) the time it needs to digest the waste materials (suspended solids)
in the effluent. The end result is a self‐sustaining, self‐regulating biological ecosystem which is highly
effective at purifying effluent. After passing through the modules, the treated influent will flow through
an ultraviolet system where harmful bacteria such as E. Coli, giardia, and cryptosporidium are
deactivated by ultraviolet light. Then it will flow into pump tanks before finally being discharged via
underground pressure distribution piping to either the lined evaporative ponds or a drip dispersal
system.
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The lined evaporative ponds will be located at the south and east sides of the PUD. Effluent and
accumulated direct precipitation into the ponds will be disposed of by evaporation, enhanced using
floating fountain type aerators, and/or sprinklers spraying from the pond perimeters towards the pond
center.
The drip dispersal system will be located within the open space areas adjacent to Skyway Road. The
system will be comprised of special drip tubing that discharges the treated wastewater in small, precise
doses. The tubing will be placed at or slightly below the ground surface to make use of the most
biologically active soil zone for distribution, nutrient uptake, and evapotranspiration of the wastewater.
The drip dispersal system will be located at a distance greater than 50 feet from the existing drainage
course which runs through the open space areas and nearest property line; therefore, the system will
meet the setback requirements specified in Table 3 of the General Order. In regards to potential
impacts to groundwater, the water discharged to the ground surface is not expected to infiltrate the
underlying bedrock. If the treated wastewater does reach groundwater levels, it will have already been
treated to State standards for discharge to groundwater.
It is anticipated that the drip dispersal system will be utilized during the dry weather season (between
April and October), particularly the summer months. During the wet weather season or periods of
inclement weather, the treated wastewater will be discharged to the evaporative ponds.
To offset the areas impacted by the evaporative ponds, an equivalent sized pond mitigation area has
been defined at the eastern end of the property. This mitigation area will remain undisturbed. A site
plan showing the WWTF is included as Attachment 1.
Water Balance Analysis
A water balance analysis was performed to assess the storage capacities of the ponds for the processed
wastewater and the ability of the drip dispersal system to contain the discharge (outflow) of the
wastewater without discharging from the land application area. The analysis was submitted to the
RWQCB in response to their request for more information showing that the WWTF has the capacity to
serve the proposed development. Below is a summary of the comments received from the RWQCB on
the water balance analysis to date:
The seasonal precipitation used in the pond sizing water balance calculations shall be based
on the 100‐year return annual total precipitation distributed monthly in accordance with
average precipitation values. The calculations shall demonstrate adequate capacity to
maintain two feet of freeboard in the ponds.
Provide justification of the use of a 1.5 multiplier given the type and size of evaporators
proposed.
Use precipitation data representative of the site location.
Provide water balance calculation that utilize multiple years of average rainfall in addition to
one year of 100‐year rainfall to demonstrate adequacy of wastewater storage and disposal
system.
The water balance analysis was updated to address the above comments and resubmitted to the
RWQCB. It demonstrates that over the course of ten calendar years, the WWTF has the capacity to
capture and distribute the treated wastewater generated onsite. Once the analysis is approved, it is
anticipated that the RWQCB will issue the Notice of Applicability (NOA) for regulatory coverage under
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the General Order. The contact information for the RWQCB’s project manager assigned to this project is
as follows:
David Durette, P.E.
Senior Water Resource Control Engineer
Central Valley Regional Water Board
Office: (530) 224‐3208
Email: david.durette@waterboards.ca.gov
Project Reference No: WDID 5A04NC00068
Sewage Dump Station
The sewage dump station will be constructed within the northeastern commercial area of the project.
The dump station will receive domestic wastes and domestic wastewater primarily from the holding
tanks of septage pumper trucks originating from Paradise, California and the greater Butte County area
subject to the daily maximum limit of 10,000 gpd, as set forth below. However, in the event that there
is available capacity, the system may receive wastewater from travel trailers, recreational vehicles, or
other similar mobile vehicles.
The sewage dump station will include a series of septic and clarification tanks that will allow for both
septage detention and liquid waste discharge to the treatment system. The tanks will be sized as
follows. A 40,000‐gallon solids holding tank will be installed to accept the raw sewage. It will then
digest the solid waste, fill and overflow through commercial effluent filters into a 20,000‐gallon
clarification tank that will eventually allow the pretreated waste to flow by gravity towards the
treatment plant. These tanks are sized to accept peak flow while providing a retention time of three to
four days for separation of solids from the liquid. The long retention time will minimize cleaning
frequency and provide the sewage more time to digest and thus reduce the load on the treatment
system.
Solid levels will be monitored monthly, while wastewater will be monitored in real time via telemetry
and an alarm system. The system operator will be notified via the real‐time monitoring system and
when solid levels reach seventy‐five percent (75%) of capacity and tanks will be pumped when solid
levels reach ninety percent (90%) solid capacity. Once the solid levels reach 90%, the system shall not
accept any further wastewater until the tanks are pumped. The septage wastes (solids) that are
pumped from the tanks will be hauled away and disposed of at a local sewage treatment facility. The
nearest local sewage treatment facility is in Lincoln, California.
Operations and Maintenance
Although the sewage dump station’s basic function is straightforward, operating a successful station
involves properly executing many different tasks. Some tasks are routine and easily understood, while
others occur infrequently and might be difficult to conduct properly without step‐by‐step directions. To
help ensure proper operations, prior to commencement of operations, the dump station shall have a
written Operations and Maintenance Plan (OMP), which will be reviewed by the County, that includes
the following elements:
Facility operating schedule, including days of the week, hours each day, and holidays, including
conditions upon which wastewater from travel trailers, recreational vehicles and similar mobile
vehicles will be accepted at the facility.
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Staffing plan that lists duties by job title, minimum staffing levels, and typical work schedules.
Description of acceptable and unacceptable wastes, and procedures for diverting restricted
waste before and after unloading.
Operating methods for each component of the facility, including waste‐screening methods,
onsite and offsite litter cleanup, and wastewater collection system operations.
Description of maintenance procedures for each component, including the building, mobile
equipment, utilities, and landscaping.
Employee training.
Safety rules and regulations.
Recordkeeping procedures.
Contingency plans in the event of transfer vehicle or equipment failure, or if the disposal site is
unavailable.
4. Estimated Wastewater Flows
Wastewater will be generated from the residential and commercial land uses proposed at the Tuscan
Ridge development, including the single‐ and multi‐family residences, office and retail spaces, and
sewage dump station. The wastewater will consist of domestic waste generated from flush toilets,
sinks, dishwashers, washing machines, bathtubs and showers.
Residential
Wastewater design flows for each residential connection or equivalent dwelling unit (EDU) are
estimated to be either 350 gpd/EDU or 450 gpd/EDU depending on whether the parcel includes an
accessory dwelling unit (ADU). 350 gpd/EDU is based on an average bedroom count of 3.5, while 450
gpd/EDU includes an additional bedroom. The total number of bedrooms is then multiplied by an
assumed unit flow factor of 100 gpd/bedroom. The 100 gpd/bedroom figure is based on the 2002
United States Environmental Protection Agency (EPA) Onsite Wastewater Treatment System Manual,
taking into account the use of water conserving plumbing fixtures and the fact that this is a large
community system and not an individual system.
There will be a total of 165 residential parcels. It is assumed that 82 (just less than 50 percent) of these
parcels will also contain an ADU. The total estimated wastewater flow for the 83 residential parcels
without ADU’s and the 82 parcels with ADU’s is 29,050 gpd and 36,900 gpd, respectively. Therefore, the
total wastewater flow from all the residential parcels is approximately 65,950 gpd.
Commercial
The assumed unit flow factor for the commercial area is 1,200 gpd/acre. This is based on the Vallecitos
Water District 2018 Water, Wastewater, and Recycled Water Master Plan dated October 4, 2018, and
prepared by Black and Veatch.
The project proposes to develop 17.3 acres for commercial uses. This equates to a total estimated
wastewater flow of 20,760 gpd.
It should be noted that water usage and wastewater flow are not correlated given that potable water
will be used for irrigation and other outside uses that does not end up as part of the wastewater flow.
The percentage can range widely from 50 percent to more than 90 percent, depending on such things as
the amount of irrigation uses and the time of year.
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Gas Station/Convenience Store
The gas station/convenience store is anticipated to generate 500 gpd/service bay. This unit factor was
obtained from the Butte County On‐Site Wastewater Systems Ordinance dated March 16, 2010.
Assuming six service bays, the resulting wastewater flow from the gas station/convenience store is
estimated to be 3,000 gpd.
Mini Storage
The mini storage facility will contain a one‐bedroom managers unit. Based on the 100 gpd/bedroom
unit flow factor identified previously, the mini storage facility will generate approximate 100 gpd of
wastewater.
Sewage Dump Station
The recommended wastewater unit flow factor for the sewage dump station is 700 gpd/vehicle. This is
based on the lowest capacity septage pumper of 1,000‐gallons and applying a 0.7 reduction factor. The
reduction factor assumes that 30 percent of the volume is solid matter that will remain in the dump
station septic tank, while the remaining 70 percent is wastewater that will pass through to the WWTF.
It is anticipated that an average of 5 to 10 vehicles will use the sewage dump station daily. The dump
station will be primarily utilized, and priority will be given to septage pumpers. As such and given that
septage pumpers dump substantially more sewage than an RV, it is conservatively assumed that all 5 to
10 of the vehicles using the dump station each day will be septage pumpers. Therefore, the estimated
wastewater flow for the sewage dump station is 3,500 gpd to 7,000 gpd. It is important to note that the
total amount of daily discharges at the sewage dump station will be subject to the daily maximum limit
of the wastewater treatment system.
As itemized in Table 1 below, the total wastewater flow for the project is estimated to be 96,810 gpd.
Table 1. Wastewater Flow Estimates
Facility Factor Flow Rate Estimated Flow (gpd)
Residential (Primary Dwelling) 165 units 350 gpd/unit1 57,750
Residential (Accessory dwelling) 82 units 100 gpd/unit1 8,200
Commercial 17.3 acres 1,200 gpd/acres2 20,760
Gas Station/Convenience Store 6 bays 500 gpd/bay3 3,000
Mini Storage 1 unit 100 gpd/unit1 100 gpd
Sanitary Sewage Disposal Station 10 vehicles 700 gpd/vehicle4 7,000
Total Flow 96,810
1 Based on EPA Onsite Wastewater Treatment System Manual.
2 Per Vallecitos Water District 2018 Water, Wastewater, and Recycled Water Master Plan.
3 Per Butte County On‐Site Wastewater Systems Ordinance.
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5. References
County of Butte, March 16, 2010. On‐Site Wastewater Systems Ordinance – Bute County Code Chapter
19. Available at: https://www.buttecounty.net/Portals/21/Env_Health/Wastewater/Ordinance.pdf
Vallecitos Water District, 2018. 2018 Water, Wastewater, and Recycled Water Master Plan.
Available at:
https://www.vwd.org/home/showpublisheddocument/10656/636752049380230000
US EPA, 2002, Onsite Wastewater Treatment Systems Manual, EPA/625/R‐00/008.
Attachment 1 – WWTF Site Plan
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1043 NICHOLS DR SUITE 200ROCKLIN, CA 95765 866.269.09991LEGENDWWTF SITE PLANTUSCAN RIDGE DEVELOPMENTAPN'S 040-520-100 AND 042-520-103