A Natural History of Millbrook Marsh,
A Wetland In An Urbanizing Setting


The great number of springs on the site (Map 7) is due to the presence of the very high water table and to the geology of the area. Because of the large size of the interbedded limestones and dolomites (Chapter 4), groundwater usually occurs along joints and fractures caused by structural deformation, bedding planes, and in solution cavities caused by water. Joints in the bedrock are influential in determining the occurrence and movement of groundwater in the rock types of this area. Fracture traces are also important in the movement of the groundwater here (Clark 1965).

Several major springs exist outside of the site in the Bathgate neighborhood, on the other side of Puddintown Road. Bathgate Spring, at an elevation of 296 m (970 ft) is on the northeast side of Orchard Road and is contained in a springhouse. Another, also called Bathgate Spring, flows out of the ground on the farm at the end of Bathgate Drive. This spring is at an elevation of 305 m (1000 ft). The discharge reported in 1904 was 0.033 cms and the 1971 measurement was 0.034 cms with a water temperature of 11.0° C. Both have been used by the Lemont Water Company as a source of public water (Wood 1980). These two springs contribute the continuous streams of water which enter the site along the bend in Puddintown Road and near the tractor path. At the confluence of the two springs is an area where the water table is very high, resulting in persistent saturation. This section contains emergent and shrub wetlands located on the Farm 12 acreage. At this time, Bathgate Spring Run is one of the healthiest of the riparian-wetland areas on the site, with little or no undercutting of the streambank, and no scouring of the stream bottom. It is the only stream on site that is not affected significantly by urban stormwater surges (Figure 3-1). By far the largest spring outside of Millbrook Marsh is Thompson Spring, the source of Thompson Run.

fig2_30005.JPG (589328 bytes)
Figure 3-1 Bathgate Spring Run. July 1998.

In April 1941, B. F. Donley reported 4,192 gallons per minute, or 6.036 million gallons per day (0.247 cms) (PA Fish Commission 1941). A 1944 measurement showed a 0.237 cms discharge (Woods 1980). Historically, the output of Thompson Spring has been approximately 5 million gallons per day (0.219 cms) (Clark 1965). In 1971 a discharge of 0.170 cms was measured with the water temperature at 10.0 to 10.3° C (Woods 1980).

Another major groundwater discharge area lies within the marsh, but outside the boundary of the Millbrook Marsh Nature Center. This concentration of springs is found at the south edge of the marsh, near the west and north ends of Watkins Road and Shoferd Lane. The springs discharge through the limestone bedrock causing the ground to be consistently saturated by water with an alkaline pH level. Water testing done for the Study of Calcareous Fen Communities in Pennsylvania during the summer of 1995 showed pH levels of the water at this site in Millbrook Marsh to be 7.6, 7.5, and 7.2 (Western Pennsylvania Conservancy 1995). This alkaline groundwater supports the calcareous fen, with a unique and rare community of plant species. The PennDOT study (1980) reported a pH of 8 at 3 locations in the marsh. Other springs found throughout Millbrook include several along Thompson Run, Slab Cabin Run, and one at the east and north end of Shoferd Lane.

The percentage of the total discharge that the springs contribute to the marsh varies seasonally. In June of 1997 the flow leaving Millbrook Marsh at Slab Cabin Run equaled a total discharge of 0.608 cms (Table 3-1). About 7 percent of that, or 0.045 cms, came from the Bathgate Springs. About 0.028 cms (5 percent) originated from smaller springs throughout the site. The total from Bathgate and the smaller springs was 0.073 cms. There was a proportional shift by October. After the dry summer, the total discharge was 0.274 cms, and 21 percent of the water, 0.059 cms, was contributed by Bathgate Springs and the other unmeasured springs (Brooks et al. 1998). The amount of water contributed by springs was 80 percent of the June flow, reduced only 0.014 cms, while the total flow was only 45 percent of the June total flow, a reduction of 0.334 cms.

Table 3-1. Stream discharge data for Millbrook Marsh on June 13 and October 21, 1997

(Brooks et al. 1998, McDonnell 1960).


Discharge, cms





July 10

October 9

June 13

October 21

Thompson Run, Route 26





Slab Cabin Run, Route 26





Confluence of Bathgate Spring and tributary from Orchard Road





Other unmeasured springs





Slab Cabin Run, Puddintown Road





* Data does not include Bathgate or other small springs.

On to Stormwater