Collection of Water and Rock Samples

Location and Description of Sampling Sites

Cave Springs (site 1), a permanent pool in Lehman Caves (site 2), a spring near upper Lehman Creek campground that discharges from glacial deposits (site 3), and Marmot Spring in the Baker Creek drainage that discharges at the contact between Prospect Mountain Quartzite and Tertiary granite (site 4) were selected for sampling in this study (fig. 2). The permanent pool in Lehman Caves was selected to obtain a water sample that was only in contact with the Pole Canyon Limestone. The caves are in the outcrop area of the Pole Canyon Limestone (fig. 2) and deeper parts of the accessible area of the cave system near the permanent pool are dry, thus the only plausible source of water in the pool is infiltration of precipitation through the Pole Canyon Limestone. The spring near upper Lehman Creek campground discharges at the end of a terminal moraine and the water has the same specific conductance as water in adjacent Lehman Creek. The discharge of the spring was in excess of 1 ft³/s when it was sampled, which doubled the flow in Lehman Creek. The volumetric flow rate was far too great and the temperature too cold for it to be ground-water flow through the Prospect Mountain Quartzite. Consequently, water discharging from the spring near upper Lehman Creek campground likely represents water from alluvial and glacial deposits upstream of Cave Springs, and water from the spring is a possible source of water to Cave Springs. Finally, the geology near Marmot Spring in the Baker Creek drainage is similar to that at Cave Springs (fig. 2).

Cave Springs was sampled at the overflow outlet of the water-collection system used to supply water to Lehman Caves Visitor Center (fig. 4A). The collection system at Cave Springs was rebuilt in 1996. A 1.5‑ft deep pool was excavated at the end of the overflow outlet. A permanent pool in Lehman Caves was sampled at the deepest part, which also was about 1.5 ft deep (fig. 4B). Similar depth pools were excavated at the overflow outlet of the spring discharging from glacial deposits near upper Lehman Creek campground and from Marmot Spring (fig. 4C and 4D).

Three rock samples were collected from outcrops between Lehman Caves Visitor Center and upper Lehman Creek campground (fig. 2). The first sample was of Pole Canyon Limestone collected from an outcrop on the south side of Lehman Creek drainage between Lehman Caves and Cave Springs (fig. 5A). The sample of Pole Canyon Limestone had been somewhat metamorphosed because of its proximity to the intruded granite. The second sample was of the Tertiary granite also collected from an outcrop on the south side of Lehman Creek drainage between where the Pole Canyon Limestone was collected and Cave Springs (fig. 5B). The third sample was of Prospect Mountain Quartzite. This sample was collected from outcrop on the south side of Lehman Creek drainage at the east end of the upper Lehman Creek campground (fig. 5C). Locations and land surface altitudes of water and rock sampling sites are summarized in table 1.

Sampling Procedures

Water for analysis of dissolved major ions plus aluminum, iron, bromide, and boron, and nutrients was collected by using a portable battery-operated peristaltic pump equipped with C‑flex tubing. The tubing was rinsed with deionized water prior to each sample collection. One end of the tubing was placed in the deepest part of a pool and water was pumped at a rate of about 1 L/min. A high volume Whatman capsule filter was attached to the other end after water had been pumped from the pool for at least 3 minutes.

All sample bottles were rinsed three times prior to collecting the sample by using either filtered or unfiltered water. Duplicate samples were collected at each site. Filtered water for dissolved cation and trace element analysis was collected in acid-rinsed 500-mL polyethylene bottles. These samples were preserved with 7.7N Ultrex nitric acid to a pH of less than 2. Filtered water for dissolved-anion analysis was collected in 250-mL polyethylene bottles. Additionally, unfiltered water was collected in 250-mL polyethylene bottles. Water for low-level nutrient analysis was collected in 125-mL polyethylene bottles. Filtered water was poured into amber bottles, whereas unfiltered water was poured into plain bottles. Water in the amber bottles was untreated, whereas water in the plain bottles was acidified to a pH less than 1 using 1 mL of 4.5 N sulfuric acid. The low-level nutrient samples were kept at or below 4^°C prior to analysis.

Unfiltered water for stable isotopes of hydrogen and oxygen was collected in 60-mL clear glass bottles. Filtered water for stable isotopes of carbon (carbon‑13/carbon‑12) was collected in 500-mL amber glass bottles and sealed with Teflon lined caps. Unfiltered water for strontium isotopes was collected in 500-mL polyethylene bottles.

Water for dissolved gas was collected in 150-mL clear glass serum bottles. The collection procedure was to place the serum bottle upside down at the bottom of the pool then slowly turn it towards the direction of flow. The bottle was filled and emptied three times prior to collecting a final sample. Once all air bubbles had been removed from the sample, a rubber stopper with needle placed to remove excess water was inserted into the open end of the bottle while the bottle was at the bottom of the pool. The needle was removed under water after the rubber stopper was in place.

Chlorofluorocarbon samples were collected in 125-mL Boston round clear-glass bottles and sealed with white plastic caps with aluminum foil liner. The dip and fill method was used to collect samples at the bottom of each pool. Each bottle was filled and emptied three times prior to collecting a sample. The foil-lined cap was placed and tightened while the bottle was at the bottom of the pool with the bottle completely filled with water. A total of five chlorofluorocarbon samples were collected at each site.

Measurements of temperature, specific conductance, pH, and dissolved oxygen were made by placing the probe for each measurement into the pool. Specific conductance and pH were calibrated to standards at the time of sampling. Dissolved oxygen was calibrated once at the beginning of sampling. Alkalinity also was determined at the time of sampling. A 50-mL sample of filtered water was titrated by using an inflection-point method with 0.16 N sulfuric acid. Bicarbonate concentrations were calculated from alkalinity.

Fresh rock samples were collected at the three sampling sites by removing weathered surfaces with a standard rock hammer. About 2 kg of rock samples were placed in yellow plastic sample bags.