PERMFILE49068 - Laserfiche WebLink

Home Browse Search

ii°'~J Mr. Alex Schatz Banks and Gesso, LLC 720 Kipling Street, Suite 117 Lakewood, Colorado 80215 Martin and Wood Water Consultants, Inc. 602 Park Point Drive, Suite 275, Goltlen, CO 80401 Phone: (303) 526-2600 . Fax: (303) 526-2624 April 13, 2006 www.martinandwood.wm Re: Western Slope Aggregates, Inc. Silt Mine Modeling Project Number 680.1 d.,T As requested dt~g l~~hone conversation we have carried out additional modeling simulations for the propose Western Slope Aggregates Inc., Silt gravel mine using the model constructed for our~t3wicWf~®¢lstkaE~itd as per the report dated March 27, 2006. The subject simulations incorpor°~i~1~al~'e mine dewatering discharge to rechazge the defined jurisdictional wetland aeeas as per the site map prepared by Banks and Gesso dated December 28, 2005. To carry out the various model runs made, we started with the first phase of proposed mining, referred to as Pit I. Using the dewatering dischazge as per the prior model runs for this pit, we routed this discharge to the two wetlands areas delineated between the Phase I and Phase III pits. In the model the wetlands covered an area that comprised 100 model cells. The recharge water was evenly distributed over these 100 cells and the model was run to generate comparisons in the level of drawdown observed in the wetlands areas and to determine if the recharge had any impact on the level of dewatering required (required flows out of the pit) and the induced leakage from the river. The results of the model runs for Pit I are presented on the attached Figures 1 and 2, depicting the drawdown contours from the pit dewatering with and without the rechazge. Note that there is in the figures an apparent slight mis-registration of the defined pit area on the base map and the cells representing the pit dewatering as depicted in green. This is an artifact of the overlay process and does not represent any problem in the relative locations of the various modeled features. It can readily be observed in the figures that the recharge does limit the drawdown in the wetland vicinity significantly, especially for the westernmost of the two wetland areas between Pit I and Pit III. What is noteworthy, however, is that the recharge could not avoid fairly significant drawdowns in the azea of the easternmost of the two wetland areas, located adjacent to the northwestern comer of Pit I. Here it is observed that a very steep gradient is established but that there remains predicted drawdowns in excess of 5-feet. A comparison of the dewatering with recharge to that without the recharge reveals that the situation has significantly improved overall, however. Without the recharge, there aze predicted drawdowns ranging up to I S-feet in the southern portion of the westernmost wetland area, and as much as 9- feet at the north end. It maybe possible to adjust the recharge water application rates by specific