BACKGROUND
The early water system served primarily the Base Village area, having been installed by the developers (O.E. Pattison Trust). Later the Twining Water and Sanitation District was formed and service extended to other areas. Most of the water system was designed without a known Master Plan.
Around 1970 the present Phoenix Springs were located and determined to be an excellent water source. The Springs were tapped, then later adapted to assure acceptable water quality through natural filtration, (rather than construct a mechanical treatment plant). A transmission line was extended through Kachina Village, to the Phoenix Springs, located just upstream. This Spring, coupled with an excellent water right, which was obtained by the Pattisons, formed a good, reliable, base water supply source for Taos Ski Village.
During the 1990’s, it was proposed to plan and develop the Kachina Village area. At that time, the utilities had been absorbed into the incorporated Village. And the Village required that a water Master Plan be prepared for the Kachina area prior to additional development. This (practical system) Master Plan could be developed as an isolated “free body” since Kachina Village is located above other users and was known to require additional, higher, pressure zones.
Proposed redevelopment, as well as additional building in the base area – along with the lack of earlier overall planning - has resulted in the obvious need for preparation of this Plan.
For this Report, the work scope includes analysis of the existing water facilities, and prediction of future potable water requirements.
The purpose of the Master Plan is to develop designs for future (and near-future) water facilities
– all planned to integrate together into an optimum system. It is not intended that new pipelines, fire hydrants, or other water facilities be placed in the exact locations shown on the Plan. It is intended that any final design modifications should accommodate the interrelationships developed in this Plan.
WATER SUPPLY
The primary water system is the Phoenix Spring. This is now classified as a protected ground water source. The original Spring collectors were replaced with a sophisticated infiltration system when EPA established the Surface Water Treatment rule (which required complete filtration treatment for all surface water and unprotected ground water). After completion of the second collection system, particulate analysis testing (PA) demonstrated no spores. Chemical analyses confirm that this water is of excellent quality, requiring only preventative disinfection.
The firm yield of the Phoenix area springs has not been definitively established. Long term meter readings for both delivered water and overflow are not available. It is known (from original measurements) that the gallery yields over 1.0 MGD (million gallons per day), at some periods. Low period flows are not available; however, an estimate of 400 gpm (0.58 MGD), has been made by staff.
The existing collection box was originally designed as the base for a chlorination station, serving as a contact basin. This basin has been rehabilitated, but is still in poor condition. Chlorination is now applied just above the existing Red Zone tank; therefore, present customers in the Kachina Village area do not receive treated water.
The Village has two water rights which can support diversions.
A total of 10.9 AF/year of consumptive use was obtained from the O.E. Pattison Trust. This decree specifies a 95% return flow. There are no time limitations. This means the Village can divert 216 AF/yr when needed.
The San Juan Chama right provides 15.0 acre ft. of augmentation water and assumes 7.5% consumptive use. This water can only be diverted during winter months. This permitted diversion is 200 AF/yr.
To summarize, under these two rights, if properly managed, the Village can divert up to 416 AF/yr. This translates to a yearly average daily rate of 0.37 million gallons.
WATER DISTRIBUTION
The existing delivery/distribution system is illustrated on Drawing II-A. Condition of the pipelines is based on information from staff; each line has been categorized as follows:
A. Thought to be in good to excellent condition. Most of these lines are recent ductile iron pipe and are expected to have a life expectancy of more than 50 years. No significant replacement costs are expected during the next 20 years.
B. These lines are thought to be in fair condition. Most of these lines are plastic, and have experienced some break history. Replacement within the next 20 years is probable.
C. These are lines in poor condition; have multiple break or leakage history; or are known to be too small. Near-future replacement is recommended.
Because of steep topography, the system has several pressure zones. The location of existing PRV (pressure reducing valve) stations is shown on Drawing II-A. PRV stations are similarly classified, with “C” stations needing replacement. It is noted that malfunctioning PRV’s can cause pressure surges, thus increasing pipeline break frequency.
The system now has only one storage tank. This is a 250,000 gallon partially buried steel tank located off Kachina Road, just below Kachina Village. Storage at this location has four functions:
This tank, as located, does not benefit the higher Kachina Village development. Consequently, planning for Kachina Village must include another, higher tank.
The Village has periodically tested hydrants for fire flows. Drawing II-B shows the location of existing fire hydrants.
This drawing summarizes the approximate delivery capability (based on fire hydrant flow tests) and coverage area for each hydrant. For this comparison, the tested deliveries have been compared to design fire flow rates (as stated in Section III). These comparisons are probably optimistic: by convention, design fire flow rates are in addition to the average rate for a maximum demand day – and it is not likely that the hydrant tests were performed during peak days.
It can be seen that fire protection is now significantly weak at the Base area and in the Kachina Village area.
Design Criteria for water Master planning generally involves three characteristics: water quality; water quantity (delivery rate); and system reliability.
The water supply must meet all EPA/New Mexico requirements. Taos Ski Valley is very fortunate to have a water source which achieves required water quality naturally – without treatment. Only preventative disinfection treatment is necessary under present State/EPA regulations.
Water demands vary diurnally and seasonally. The critical period for design of source of supply system is the maximum day (probably average of 3 consecutive peak days).
For a community the size of Taos Ski Valley, fire protection demands dominate distribution system design. The conventional design peak rate consists of the design fire flow plus the average demand rate for a peak day.
Based on typical practice for similar communities, and discussions with TSV staff, the following design fire flows are recommended:
Water demands at Taos Ski Valley are essentially all for inside potable use. The water rights decrees assume 95% and 92.5% return flows so that water usage and wastewater flows should be similar. In the past, distribution leakage has exerted excessive water demands; however, for master planning purposes, it can be assumed that replacement of lines will reduce leakage to minimal amounts.
To estimate future design water demands, the EQR (Equivalent Residential Unit) is convenient to use as a common denominator. The peak day demand for a typical, small, single family residence is estimated at 300 gallons.
Review of Village records result in the following approximations:
Recommended Design Flows
Probable build out of TSV 1500 EQR
Design Peak Day Use 450,000 gpd
The above design flows are thought to be in the right range – but not reliable. A part of the Plan would be to monitor customers and future water usage to more accurately establish design criteria. (Using proposed new flow meters).
System reliability is measured by outage frequency and duration of outage. All water lines required for service inevitably require repairs, and eventually, replacement.
Service reliability is provided by line “looping”, that is each major group of customers is fed by two lines, from two directions. Typical designs require that, any group of more than, say, 15 residential customers, must have two supply points. Designers may increase this number of customers because of cost involved – particularly in mountainous areas.
Water storage is considered a supply source. From a reliability standpoint, the volume should be adequate to furnish water during a source outage or transmission problems; typically this can be from four hours to two days, depending on the system.
GENERAL
Improvement projects are typically completed in three phases:
The Master Plan is the first step of Preliminary design. It is intended to describe an optimum overall system, with all elements interrelated. Once the Master Plan is accepted, for any future improvement, then, the Preliminary Design can be limited to the specific element(s) proposed
(e.g. a waterline replacement, storage tank, or pressure reducing station).
Future Master Plan updating may be necessary if:
At this time, it is believed that the Phoenix Springs (with normal system storage) will prove adequate for build out of Taos Ski Valley. However, yield and usage history records are inadequate to conclusively verify this opinion. As a key part of the Master Plan, it is recommended that:
This Master Plan primarily addresses the distribution system. Significant distribution system deficiencies use:
General reliability-related practice is that any group of customers (say 15-25 dwelling units) should have two supply sources (i.e. a “looped” system). At Taos Ski Valley, the entire Base Village is connected to the source of supply (Red Zone Tank) but only one pipe is available at several locations.
Drawings IV-A, Sheets 1, 2, and 3 illustrate the proposed Master Plan.
Total system storage for the Village in the range of 500,000 to 700,000 gallons can be justified. The components are:
Fire Protection – 2000 gpm for 3 hours – 3600,000 gal.
Peaking Storage: approximately 35% of 500,000gal = 175,000 gal.
Reliability – one high days use (2 days with conservation) – approximately 500,000 gal. Note: Fire and supply reliability problems are not expected to occur simultaneously, so that total storage, using the above values, should be in the range of 700,000 gallons.
Because of the nature of the supply/distribution pipe system, a new tank, protecting the Base Village area, is proposed. This tank, coupled with the proposed Blue Zone Tank above Kachina Village, should provide reasonable protection. At the proposed sizes, a total of 750,000 gallons would be available.
It is not within the scope of this Master Plan to prioritize the long-term improvement program. The improvements scheduled will be based on development rates and funds available. However, near-future needs (early priority improvements) are:
Those denoted as Condition “C” on Drawing II-A, should be replaced as soon as practical. During pipeline replacements, new fire hydrants should be located as needed to provide proper coverage.