Hanson Aggregates West Concord Rock Quarry Facility Design

Client: Hanson Aggregates, Mid-Pacific Region

Location: Clayton and San Luis Obispo, California

Period of Performance: June - December 2004

Scope of Services: Clayton Quarry is an active open pit aggregate quarry on the north side of Mt Diablo near Clayton, California. Due to on site activities and the exposure of materials to storm water, TSS concentrations in runoff from the facility has been measured up to 90,000 mg/L. To comply with NPDES II regulations, the client required implementation of engineered sediment removal structures and source control BMPs in accordance with their SWPPP.

Storm Water Detention Ponds: ADH Designed and supervised construction of two storm water detention ponds to reduce TSS concentrations from storm water from the Primary Quarry (P1) and the Exit Road (P3) with drainage areas of approximately 11 and 5 acres, respectively. The detention ponds were designed in accordance with Caltrans BMP specifications to handle 10-year 24-hour storms with a detention time of 72-hours-for vector control. The actual constructed detention ponds were less elaborate than the proposed design (shown below).

Erosion Control BMPs: Based upon onsite field assessments, ADH selected sediment erosion control (BMP) features, determined optimal locations and supervised the installation of the features along the facilities´ roadways, which included excelsior matting, fiber rolls, water bars, and drainage rock fill used in drainage channels.

Results: TSS concentrations from a BMP postconstruction self-monitored storm event were as follows:

• P1 was measured at 42 mg/L, reduced from as great as 84,000 mg/L
• P3 was measured at 1700 mg/L, reduced from as great as 48,000 mg/L
• Two locations along the facilities´ roadways were measured at 250 and 1300 mg/L, reduced from as great as 74,000 and 27,000 mg/L, respectively.

Storm Water BMP Plan Review: ADH reviewed and revised Hanson's San Luis Obispo concrete facility's Augmented Stormwater BMPs Plan. The Plan addresses the potential impacts to surface water associated with the concrete ingredients as indicated by TSS, specific conductance, and pH.