X hits on this document

PDF document

U.S. Environmental Protection Agency, Region IX - page 3 / 97





3 / 97

is currently designed to function as a sediment basin (see Photo 0046). Prior to the January 19-22 storm event, ADOT/Fisher used small check dams in this area to filter the runoff before it entered Oak Creek. However, before the January storm event, large rocks (9-24”) were brought into the site to serve as a coffer dam. These rocks will later be used in gabion baskets to be placed elsewhere on site. According to Harris, the emergency spillway on the coffer dam functioned as designed during the January storm event. However, the void spaces between the large cobbles and boulders are too large to serve as an effective filter. We observed large amounts of fines deposited on the downstream side of the coffer dam (see Photos 0024, 0027-32). Additionally, ¾” gravel was placed in the work area to provide a more stable work surface. According to Harris, after the last pylon is set, the channel will be dug out and this material will be removed as much as possible; however it is being pressed very deeply into the creek bed and will likely be very difficult to remove.

As ADOT/Fisher installs pylons for the bridge, they must drill down into the creek bed and pump out water that is full of fine sediments. ADOT/Fisher indicated that they pump an average of 15-20,000 gpd. Disposal of this water appears to have been an issue for ADOT/Fisher. A review of the SWPPP shows that disposal of this material has occurred throughout the site, utilizing different BMPs of varying success. According to ADOT/Fisher, at one point, a contractor directly pumped the water, without filtration, into a tributary of Oak Creek without permission from ADOT/Fisher. That contractor was fired. The BMPs used immediately prior to the inspection, as well as the BMP used during the inspection, were inadequate. According to ADOT/Fisher, prior to the current BMP, ADOT/Fisher pumped the water into a pump truck, hauled it to the Chapel Staging Yard (approximately 1 mile south) and attempted to filter the water through straw wattles before discharging to a road-side ditch. However, the sediment load was too high and the wattles blew out (see Photo 0049). Additionally, the straw wattles were not effective at filtering the sediment laden water and we observed evidence of significant discharge of silty-clay soils (see Photos 0051-52, 0056-62). We traced the discharge to a tributary of Oak Creek. ADOT/Fisher attempted to install check dam BMPs along the drainage ditch but they were overtopped and blown-out. They were also using a culvert outlet, located about 150' upstream of the tributary, as a stilling basin. It was filled with sediment 2-3 feet deep and needed to be cleaned out prior to any rain or other discharge (see Photos 0059-61). We observed straw wattles placed in the drainage ditch to slow the flow of water. They were new and had been recently replaced (see Photo 0063).

The BMP in use during the inspection for this pump water discharge at the Chapel staging yard was a poorly designed settling basin (see Photos 0047, 0053, 0055, 0062, and 0064) that discharged to the sediment-laden drainage ditch described above. The basin was made of three K-rails and lined with filter-fabric wrapped sediment logs. However, the basin was over 90% full and sediment covered the sediment logs (see Photo 0055). According to Fisher, another pump delivery was scheduled for that afternoon, before the basin could be cleaned out and repaired. On February 5, 2010 (the day of the inspection) a BMP update sheet was placed in the SWPPP, describing this BMP. This could indicate that the SWPPP was not being updated in a timely fashion. As described above, this BMP is undersized and inadequate. I instructed ADOT/Fisher representatives


Document info
Document views339
Page views339
Page last viewedTue Jan 17 19:16:00 UTC 2017