The permit sets a pH limit for ground water discharges and limits turbidity, total suspended solids, and pH in surface water discharges. The permit also limits total dissolved solids in discharges of process water from concrete batch operations. New permittees may be required to monitor the temperature of discharges to surface water during the summer months.
pH extremes are toxic to fish and unsuitable for ground water used as a drinking water source. The data demonstrate that within the activities covered under this permit, both high and low pH extremes do occur on occasion. All discharges will require monitoring for pH except stormwater discharges from Construction Sand and Gravel and Industrial Sand facilities. Discharges to surface water or ground water must be within the range of pH 6.5 to 8.5.
Turbidity of water is related to the amount of suspended and colloidal matter contained in the water. It reduces the clarity and penetration of light. Turbidity is an indirect measure of total suspended solids. Because turbidity is a known and common pollutant in discharges associated with the industries covered under this general permit, all surface water dischargers are required to monitor for turbidity. The permit requires monitoring for turbidity twice a month for both process water and stormwater discharges to surface water. The turbidity limit is 50 NTU (nephelometric turbidity units) as maximum daily and monthly average.
Total Suspended Solids (TSS) include organic and inorganic materials present in wastewater from sand, cement, and fines as a result of water used to sort and wash materials. These materials include sand, silt, and clay. Stormwater may also contain significant levels of TSS. These solids may settle out rapidly or be suspended in water for a time. While in suspension, TSS increases the turbidity of the water, reduces light penetration and impairs the photosynthetic activity of aquatic plants, thereby contributing to oxygen depletion. TSS can kill fish and shellfish through abrasive injury or clogging of gills and respiratory passages. Excessive TSS can destroy aquatic habitats by coating the bottom with sediment. Because TSS is a known and common pollutant in discharges associated with the industries covered under this general permit, all discharges to surface water of process water and mine dewatering water are required to monitor for TSS. Except for construction and industrial sand facilities, the average monthly value cannot exceed 40 mg/liter. Industrial sand facilities cannot exceed an average quarterly value of 25 mg/liter.
Total Dissolved Solids (TDS) are a gross measure of the amount of soluble pollutants in the wastewater. TDS can be detrimental to aquatic organisms in fresh water systems and unless significant and immediate dilution is available, it may cause unacceptable degradation. TDS can also contaminate ground water and violate drinking water standards. Because the data suggest that discharges from concrete batch plants can have elevated levels of TDS, these facilities will be required to monitor their process water discharges for TDS. The permit includes a discharge limit of 500 mg/liter TDS.
Temperature increases and decreases for process water, mine dewatering water, and stormwater are primarily a result of ambient air temperature and solar influences. Processing by the facilities covered under this permit does not typically transfer significant thermal energy. Temperature increases from sand and gravel facilities have not been identified as a significant environmental concern but there are more than 300 rivers in the state that are listed for water quality temperature excursions as a result of high temperatures. The temperature of discharges to surface water during the warm weather months are therefore a concern. The previous permit required monitoring of temperature for all discharges to surface water during the warm weather months. This monitoring showed no discharge of concern, however, new discharges may be required to conduct temperature studies.
Good site management is critical to the control of contamination of stormwater. Stormwater quickly picks up pollutants from improperly stored materials, spills, and erosion. Coverage for toxic materials, site grading, channeling of stormwater, preventative maintenance, and employee training are required by the permit. The permit requires source control consistent with Ecology's Stormwater Management Manual for industrial activities such as fueling, loading and unloading liquid materials, and outside storage of raw materials. A spill plan must be in place to implement spill prevention and response. The permit also requires ongoing inspection to assure that site management is having the desired effect.
- Process Wastewater
Process wastewater is any water that is used for or results from the production, clean-up, or use of any raw material, intermediate product, finished product, byproduct, or waste product. The term shall also mean any waste water used in or results from the slurry transport of mined material, air emissions control, or processing exclusive of mining.
Stormwater is that portion of precipitation that does not naturally percolate into the ground or evaporate but flows via overland flow, channels, or pipes into surface water channels, impoundments, or constructed infiltration facility. The existing Sand & Gravel General Permit references three types of stormwater.
- Type 1 Stormwater is stormwater from any portions of the permitted site where no industrial activities have occurred or from a site or area within a permitted site that has been reclaimed and the reclamation bond (if any) has been released.
- Type 2 Stormwater means stormwater from: 1) portions of a site where mining has temporarily or permanently ceased; or 2) from portions of a site with exposed soils in areas cleared in preparation for mining or other industrial activity.
- Type 3 Stormwater is stormwater from (1) industrial plant yards; (2) immediate access roads and rail lines used or traveled by carriers of raw materials, manufactured products, waste material, or by-products used or created by the facility; (3) material handling sites; (4) sites used for the storage and maintenance of material handling equipment; (5) sites used for residual treatment, storage, or disposal; (6) shipping and receiving areas: (7) storage areas for raw materials or intermediate and finished products at active sites; or (8) areas where industrial activity has taken place in the past and significant materials remain and are exposed to stormwater.
- Mine Dewatering Water
Mine dewatering water is any water that is impounded or that collects in the mine and is pumped, drained, or otherwise removed from the mine through the efforts of the mine operator. It also includes wet pit overflows caused solely by direct rainfall and ground water seepage. However, if process water is added to mine dewatering water or a mine is used for treatment of process generated wastewater, discharge of this commingled water shall be deemed discharge of process water.
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