Atlantic Richfield Company
Butte, Montana

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Base Flow

What you should know

Base flow is the general condition of the stream and other surface water bodies absent of effects from runoff conditions from storms or snowmelt events.

Golden Triangle (area where Metro Storm Drain meets Blacktail creek) before stream bank restoration

Golden Triangle after stream bank restoration

Base flow is the general condition of the stream and other surface water bodies absent of effects from runoff conditions from storms or snowmelt events. Base flow conditions represent the flow of a stream on a regular basis (over approximately 90% of the time).

At the BPSOU site, base flow data conditions are also a main compliance media for groundwater at the site for certain Contaminants of Concern (COCs) including arsenic, cadmium, copper, mercury, lead and zinc. Concentrations for these COCs are typically expressed in micrograms per liter (ug/L). Concentrations are also measured as for both the dissolved (Dis) and total recoverable (TR) forms of a sample.

Below are links to several charts showing COC concentrations at several base flow stations in both Blacktail Creek and Silver Bow Creek. These charts show compliance ratios of each COC versus the stream monitoring locations. A compliance ratio is the ratio of the concentration of the COC to the applicable compliance standard. The compliance standards are functions of total hardness (mg/l, CaCO3) at the time of sampling which are defined by Circular DEQ-7.

For further information, visit our Reports and Publications page to download related documents.