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Background Information Report

Surface Water Resources

Surface Water Hydrology

Salado, Leon and Cibolo Creeks drain surface water from CSSA (Figure 9). Approximately 75 percent of CSSA is in the Salado Creek watershed, 15 percent in the Cibolo Creek watershed, and 10 percent in the Leon Creek watershed. Most of the active-use areas of CSSA are in the Leon Creek watershed, including the wastewater treatment plant, which drains into a tributary of Leon Creek at the southern boundary. All of these streams are intermittent at CSSA. The CSSA area can be characterized as hilly with stony soils and high runoff potential. Natural stream channels on CSSA generally have broad floodplains, and portions of CSSA are in the 100-year floodplain.

The Salado Creek watershed on CSSA extends in a broad swath from northwest to southeast with the Salado Creek headwaters located in adjacent Fair Oaks subdivision. Impervious cover in Fair Oaks is currently estimated at 5 to 10 percent. Drainage from Camp Bullis to the east also flows across CSSA to Salado Creek. Impervious cover for CSSA within the Salado Creek watershed is substantially less than 5 percent, with much of the area undeveloped except for dirt and gravel roads.

As shown in Figure 9, there are four ponds within the Salado Creek drainage area of CSSA, one pond in the Cibolo Creek drainage area, and one in the Leon Creek drainage area. Reservoir D is in the inner cantonment near the western boundary; three additional stock ponds are located in the outer cantonment. When it is full, reservoir D has a surface area of approximately 5 acres. It is located on a tributary of Salado Creek. The first stock pond is located on the main channel of Salado Creek in the northwest quarter of the outer cantonment and has a surface area of approximately 1 acre. The second stock pond is located along the eastern boundary of the outer cantonment and also has a surface area of approximately 1 acre. The third stock pond is located on the side of a hill just east of the northern boundary of the inner cantonment and has a surface area of approximately 1/5 acre. All of the dams exceed 6 feet in height.

Three tributaries of Cibolo Creek originating on CSSA drain the northeastern part of the outer cantonment. One stock pond with a surface area of less than 1 acre is located on the easternmost tributary. The dam exceeds 6 feet in height. The area of the Cibolo Creek watershed within CSSA is undeveloped except for dirt and gravel roads. Impervious cover in the Cibolo Creek watershed is minimal.

A tributary of Leon Creek, originating on CSSA, drains the southwest quarter of the inner cantonment. Reservoir W, in the southwest corner of the inner canton­ment, is situated on a subtributary and has a surface area of approximately 1 acre and a dam exceeding 6 feet in height. Overall, impervious cover within the Leon Creek portion of CSSA is estimated at approximately 5 percent or less, much of which is located along Tompkins Road and McElroy Drive.

In the developed areas of CSSA, rainfall runoff is conveyed to natural stream flow channels by ditches and sheet flow. CSSA has sufficient relief to allow the rapid conveyance of runoff from developed areas. In the undeveloped areas, runoff flows overland to natural channels.

Surface Water Quality

Salado Creek, from its confluence with the San Antonio River in Bexar County to Rocking Horse Lane west of Camp Bullis, is designated water quality segment 1910 of the San Antonio River basin by the Texas Water Commission (TWC), now the Texas Natural Resource Conservation Commission (TNRCC). According to the State of Texas Water Quality Inventory (TWC, 1992), segment 1910 does not meet the criteria for its designated contact recreation use because of elevated fecal coliform bacteria levels caused by urban runoff from the city of San Antonio for approximately 25 miles of its length. This document did not indicate what portion of the 44-mile segment did not meet criteria for contact recreation use, but it appears to refer to that portion of the segment which receives runoff from San Antonio downstream of CSSA. Designated uses for segment 1910 are contact recreation, high-quality aquatic habitat, public water supply, and aquifer protection. There are nine wastewater outfalls permitted to discharge a total of 0.44 million gallons per day (mgd) to this segment (TWC, 1992).

A portion of CSSA in the northeast part of the outer cantonment drains into upper Cibolo Creek, which has been designated water quality segment 1908 of the San Antonio River basin. Segment 1908 extends from the Missouri-Pacific Railroad bridge west of the city of Braken in Comal County to a point 1.5 kilometers upstream of the confluence with Champee Springs in Kendall County. Monitoring data from TWC have shown the following: elevated nutrient levels exist downstream from the city of Boerne; supersaturated dissolved oxygen levels occur from algal metabolism; and chloride, sulfate, and total dissolved solid levels outside criteria have occurred. The city of Boerne is upstream from the locations at which runoff from CSSA enters Cibolo Creek. Designated uses for segment 1908 are contact recreation, high-quality aquatic habitat, public water supply, and aquifer protection. Four outfalls are permitted to discharge a total of 1.25 mgd to this segment (TWC, 1992).

The southwest quarter of the inner cantonment drains into a tributary of Leon Creek, and effluent from the wastewater treatment plant drains into this tributary. The upper portion of Leon Creek into which CSSA drains is designated water qual­ity segment 1907. Segment 1907 extends from a point 100 meters upstream of State Highway 16 northwest of San Antonio in Bexar County to a point 9.0 kilometers upstream of Scenic Loop Road north of the city of Helotes in Bexar County. There are no water quality problems noted in this segment. Designated uses for segment 1907 are contact recreation, high-quality aquatic habitat, public water supply, and aquifer protection (TWC, 1992).

There is no current use of surface water on CSSA aside from the maintenance of water in the stock ponds.