Construction monitoring for a master planned community

摘要

Snoqualmie Ridge is a 1340-acre master planned community being developed by Weyerhaeuser Real Estate Company (WRECO) near the city of Snoqualmie, Washington. Project planning started in the mid-1980s and construction started in November 1994. The Snoqualmie Ridge Project consists of an 18-hole TPC golf course, 2000 residential units, two business parks, a retail area, several community parks, and new municipal facilities including a water treatment plant, a police station, and a fire station. Erosion control on the Snoqualmie Ridge site is challenging due to topographic relief and on-site sensitive areas. The native soils are primarily weathered and unweathered glacial till containing 25 to 35 percent fines. The site is located on an upland plateau in the foothills of the Cascade Mountains. The project site has approximately 700 feet of vertical relief and contains five creeks, which are tributaries to the Snoqualmie River. Average annual rainfall is 70 inches. Initially, WRECO established a surface water monitoring plan to verify compliance with NPDES and the Federal Clean Water Act. This plan consisted of collecting grab samples at several locations on each stream and on the Snoqualmie River. These samples were obtained and tested for turbidity after each significant storm event (0.5" rain/24hr). In the fall of 1999, WRECO initiated an additional internal monitoring plan to more efficiently identify specific areas that were producing turbid water. A series of sample stations were selected torepresent small subbasin areas. Sampling was performed when the site received 0.5" rain in 24 hours, or at the erosion control inspector's discretion. This plan has helped to isolate and identify sources of turbid water and has aided in evaluating the performance of the BMPs. Pinpointing problem areas early and applying additional BMPs before there was a large problem was an essential part of maintaining an effective erosion control plan. A variety of standard and non-standard BMPs have been used at Snoqualmie Ridge. Straw mulch, silt fence, hydroseeding, swales and temporary sediment ponds all have been used as standard BMPs. Home construction phasing has been implemented and the driving and tracking equipment on soil is minimized during winter months. In order to reduce turbid water discharge to the on-site streams, sediment ponds that collect turbid water have been pumped into trucks and then released at an infiltration facility. The monitoring programs and additional BMP measures have been instrumental in our ability to continually improve the water quality on site.