The NCWC&ID #4 provides water service to developed lands from the North boundary of Mustang Island State Park to the Corpus Christi ship channel, including Harbor Island. By agreement with the City of Corpus Christi, responsibility for providing water from the North boundary of Mustang Island State Park to the South rests with the City of Corpus Christi; however, this contract contains the following provision:
“Should there be a shortage in the basic supply of water which requires the restriction or curtailing of any consumer of water within the city limits of Corpus Christi that coincide with such restriction or limitation within Corpus Christi, the District will limit and restrict all of its customers, both direct and indirect through resale to the same extent.”
Presently, there are two water systems that provide water to the Island. From the North, treated water is purchased from the San Patricio Municipal Water District (SPMWD) which is re-pumped at the Beasley PS in the City of Aransas Pass. it is then transmitted through an 8-inch and a 12-inch line on Harbor Island to the Corpus Christi Ship Channel, and a 20-inch line carries the water under the ship channel to the Ferry Landing PS in the City of Port Aransas. SPMWD’s contractual agreement with NCWC&ID#4 presently states that the maximum daily supply is 1.2 MG. In the South, the Island obtains water from the City of Corpus Christi by a 24-inch line from the Flour Bluff area which is re-pumped at the Sanddollar PS and transmitted through a 20-inch line to the Mustang Island PS. A 20-inch line and a 16-inch line carry the water to the NCWC&ID #4 system at the North end of Mustang Island State Park.
The water supply from the North is accomplished by an agreement with the SPMWD. The SPMWD purchases treated and untreated water from the City of Corpus Christi, which in tum obtains its supply from the Lake Corpus Christi/Choke Canyon Reservoir System along with an intake from the Mary Rhodes Pipeline.
The contract provision indicated above regarding restriction applies to the supply from the SPMWD as well. In addition to the main transmission for water supply indicated above, the District has the following facilities:
A. STORAGE AND PUMPING
The elevated and ground storage tanks perform different functions; however they both aim to decrease the impact of the demand fluctuations. The distribution system provides water to the elevated storage tanks that serves three purposes:
- Equalization of peak demands to maintain a fairly constant pumping rate.
- Provide pressure maintenance and system surge protection.
- Reserve capacity for fire protection and emergency conditions.
In addition to meeting the TCEQ elevated storage criteria, sufficient storage should be provided to meet four hours of fire flow demand in excess of 3,500 gpm with no pumping according to Insurance Services Organization (ISO). The current system has an elevated storage capacity of 1.00 MG, therefore the system is adequate and meets the maximum fire flow demand with no pumping (3 ,500 gpm multiply by 60 minutes/ hour multiply by 4 hours equals 840,000 gallons). Refer to Table’s IV-2 and IV-3 for a comparison of the TCEQ minimum standard requirements to the District’s available storage and pumping capacity.
Ground storage tanks are located at the pump stations and generally serve two functions:
- Equalizing the different rates of supply and pumping into the system.
- Reserve for emergency conditions.
Ground storage must contain sufficient capacity to supply the difference between average and maximum demands. In addition to meeting the TCEQ storage criteria, sufficient ground storage should provide a minimum of 50% of the Maximum Day Demand (MD). In year 2007, the District’s ground storage capacity provided 80% of the maximum day demand (2.70 MG ground storage capacity divided by 3.371 MGD peak day demand); therefore the system meets and exceeds the minimum capacity needed.
The existing NCWC&ID #4 water distribution system is served by two elevated storage tanks, six ground storage tanks, and three pump stations. The total existing available storage capacity is provided in the following table:
TABLE III-1: Summary of Existing Water Storage
|Mid-Island Elevated Tank (Mustang Island)||500,000|
|Port Aransas Elevated Tank (Eskridge Rd. & Glover Rd.)||500,000|
|Mustand Island Pump Station (South end of the Primary Service Boundary)||1,500,000 & 100,000|
|Ferry Landing Pump Station (Port Street)||1,000,000 & 200,000|
|Beasley Street Pump Station (Beasley Ave., Aransas Pass)||200,000 & 40,000|
The storage tank and pump station locations and capacities are described in the following:
1. ELEVATED STORAGE
The District has the following two elevated storage tanks:
Mid-Island Elevated Tank: 500,000 gallons.
Located West of S.H. 361 along Mustang Island
Overflow Elev. El. 126.5
Base Elev.: El.5
Port Aransas Elevated Tank: 500,000 gallons.
Located at intersection of Eskridge & Glover Rd.
Overflow Elev.: El. 126.0
Base Elev.: El. 5
The combined elevated storage capacity for the District is 1,000,000 gallons.
2. GROUND STORAGE
The District has the following six ground storage tanks:
- Beasley Ground Storage Tanks – 200,000 gallons and 40,000 gallons. These are located at the Beasley Street Pump Station in the City of Aransas Pass.
- Mustang Island Ground Storage Tanks – 1,500,000 gallons and 100,000 gallons. These two tanks are located at the Mustang Island Pump Station at the south end of the District’s primary service boundary.
- Ferry Landing Ground Storage Tanks – 1,000,000 gallons and 200,000 gallons. These are located at the Port Street Pump Station within the city of Port Aransas near the ferry landing.
Due to pump location and piping, only 1,500,000 gallons are available at the Mustang Island PS and the storage at the Beasley Street PS is used only to maintain pressure on the pumps. Considering that the ground storage tanks will not be completely emptied during normal operation, the combined storage capacity for the District is 1,000,000 gallons of elevated storage and 2,700,000 gallons of ground storage.
3. WATER PUMP STATIONS
The Beasley Pump Station and associated storage tanks located on Beasley Street in Aransas Pass, approximately seven miles west of Port Aransas, store water received from the SPMWD and pump it to the Ferry Landing Pump Station in Port Aransas through an 8-inch, 12-inch, and 20-inch transmission lines. The pump station is equipped with four pumps that run independently of one another; two pumps are 20 Hp jockey pumps with a capacity of 400 gpm each and two pumps have 60 Hp motors with a capacity of 1200 gpm each. According to District personnel, the normal operating pressure is 55 psi and the average pumping capacity is 1.30 MGD with one 60 Hp pump in operation. According to the Harbor Island Water Study model and as discussed in Chapter VII, the maximum pumping capacity at the Beasley PS, with an operating pressure of 65 psi, is 1.55 MGD.
The Ferry Landing Pump Station and associated storage tanks located at Port Street and Cotter Avenue in Port Aransas, store water received from Beasley PS in Aransas Pass. The pump station is equipped with three pumps used to pump water to the Port Aransas Elevated Tank and provide service to the distribution system. Two are equipped with a 50 Hp motor with a capacity of 800 gpm each maintaining an average operating pressure of 50 psi, and one is equipped with a 20 Hp motor with a capacity of 400 gpm. The maximum pumping capacity at the Ferry Landing PS is approximately 2.88 MGD according to District personnel.
The Mustang Island Pump Station and associated storage tanks located approximately 11 miles south of the city of Port Aransas on Mustang Island store water received from the City of Corpus Christi. The water is then pumped to Port Aransas through a 12-inch, 14-inch, 16-inch, and 18-inch transmission lines. The pump station is equipped with two pumps that run independently of one another; two pumps have a 200 Hp motor with a capacity of 2,070 gpm each maintaining an average operating pressure of 70 psi. The maximum pumping capacity of the Mustang Island Pump Station is approximately 3.60 MGD according to District personnel.
The NCWCID #4 no longer operates or maintains any water wells. The locations of the pump stations and storage tanks are illustrated on Figure III-1.
B. WATER DISTRIBUTION
The District owns and operates the water distribution system which supplies water to the customers of Port Aransas, Mustang Island, and Harbor Island. In order to maintain and operate the distribution system, the District has seventeen employees and ten certified operators; one of which has “B” certification, three of which have “C” certification licenses and six have “D” certification licenses. In the year 2007, the distribution system served approximately 19,364 customers during the peak season with a system of pipelines ranging in diameter from 2 inches to 20 inches. The existing distribution system is shown on the NCWC&ID#4 Master Utility Maps attached to this report.
The distribution system is designed and should be sustained to provide a minimum operating pressure of 45 psi during normal conditions and a minimum of 20 psi during extreme operating conditions, such as during a fire flow demand. According to TCEQ, the minimum normal pressure allowed is 35 psi. Pressures above 80 psi should be limited and no greater than 120 psi due to potential harmful affect on the system and higher operating costs. Maximum allowable velocities in the piping should be limited to 8 FPS. Refer to Table’s IV-2 and IV-3 for a comparison of the existing system and the TCEQ requirements.