Laserfiche WebLink
iii iiiiiiiiniu iii <br />999 <br />MEMO <br />To: Ivtike Boulay. San own <br />From: Kent Gorham /~ <br />Subject: Seneca II-W, Permit Revision #2 (PR-02), #C-82-057 <br />Date: April 13, 1999 <br />Based on ourjoint review, I have the following comments concerning the estimated water quality <br />in Hubberson Gulch as a result of proposed expansion at the Seneca II-W mine. <br />As we discussed during ourjoint review, it appeazs that Seneca !I-W did not understand the <br />focus of question #35 (corrected to #34) of the DMG adequacy review attached to Sandy's memo <br />of March 22, 1999. Possibly, the mention of the Yampa River Basin material damage suspect <br />level of 1000 umhos/cm led to their response which primarily focused on the quality changes to <br />the Yampa River proper. Regardless, I believe the DMG question was appropriate and still <br />requires a response from SCC. <br />Please find attached DMG salinity calculations based on data collected along Hubberson Gulch <br />and SCC estimates ofpost-mining spoil spring dischazges to the gulch via sediment ponds. <br />(Attachment A) Estimated dischazge and total dissolved solids (TDS) concentrations were <br />calculated in two different methods to estimate quantity and quality at the AVF of concern. <br />First, upstream data from site WSH9 (submitted as baseline data for upstream Hubberson) was <br />combined with Seneca estimates of ground water dischazge and spoil spring discharge to <br />calculate quality and quantity downstream of the proposed expansion area. However, this <br />estimate would likely be some distance upstream of the irrigation headgate for the 26 acres of <br />irrigated pasture. Therefore, another estimate was done, combining existing data for site <br />WSH7(located at the pastures) with spoil spring dischazge estimates, producing a result which <br />may be more representative of what may occur following mining and spoil spring development. <br />As shown in the bold sections of the attachment, TDS values would range from 840-832 mg/I in <br />June, 1536-2873 mg/I in July, 2178-3444 mg/1 in August, and 2476-4366 mg/I in September, <br />depending on the method used. Dividing by .72 (TDS/EC ratio) results in a range of EC values <br />of 1109-5821 umhos/cm. All estimated values exceed the 1000 umhos/cm material damage <br />suspect level, especially during the likely imgation months of July and August, regazdless of the <br />method used. However, as irrigation water quality would directly affect any production decline <br />calculation it is important that everyone agree on any final values. <br />Given the situation, Larry believes it is important that Seneca [I respond to the original issue with <br />their own estimate of water quality at the irrigation takeout for the 26 acres along Hubberson <br />Gulch. Therefore, I have proposed the following response to SCC's response to your original <br />question #35. <br />