1992-06-12_REVISION - M1988112 (3)

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~~ - • the specific flow posh front dre tailings area to dte Rito Seco, there should be nrore sampling. 7Trerefore, M-4, A2-10 and RS-4 should be routinely smnpled until the hydrologic gradient is established artd unfit other down-gradient monitor wells are irutalled. RESPONSE: Regionally, it can be determined that the ground water gradient in the Santa Fe aquifer is generally from east to west, based on water level elevations in M-1, M- 4 and M-9. While locally it is possible that, if there were a leak in the tailings facility, some water could flow to the north towards to M-4, given the maximum head differential between the tailings pond elevation and tl+e water level elevation in M-4 (approximately 60 feet), the distance from the tailings facility to bl-4 (5,800 feet) and an aquifer permeability of 3.8 feet per day, the seepage velocity in the Santa Fe Formation is only approximately 0.1 foot per day. Given this velocity, even if the tailings facility started leaking the first day there was water in the facility, and a saturation front was immediately established, water from the tailings facility could not have reached M-4 at tl+is time. Tlrer~fore, bi-weekly sampling of M-4 and M-10 at this time would not provide the additional information identified in the comment. If the further studies related to establishing asite-specific gradient near the tailings facility indictite a gradient to the north, appropriate additional monitoring measures would be taken ?~ that time. Surface water station RS-4 monitors a dry tributary to Ritp Seco, and is monitoring a different sub-basin than what the tailings facility is Ibcated in. BMR does not believe that there is merit in bi-weekly monitoring of station RS-4 and, in any event, no samples have ever been obtained from RS-4, as it has never been observed to flow. 3. Chain of custody should begin with the commercial laboratory rhnt prepares the sarrrple containers for field sampling personr:el. 77rird party sat»pl~rs acrd vendors should supply all collection devices, sample conrainers, and rea~enrs inckrding ivaslt solutions. RESPONSE: Section 2.1.1 of the Protocol document states that "jE]mpty sample containers and laboratory water will be received in coolers. Achain-of-custody form will be received with the above-mentioned items." Therefore, the pro~col document provides that the chain-of-custody is initiated with the comtnerci 1 laboratory. While BMR agrees that the collection devices and the reagents, iYrcluding wash solutions, should be provided by the samplers, the sample contai~hers (and their associated preservatives) are provided, and should be provided, by the analytical laboratory. -2-