Monitoring and the Monitoring Plan for the Sand and Gravel General Permit Gravel processing site

The sand and gravel general permit limits pollutants in discharges and requires monitoring of discharges to measure pollutant levels. The permit also requires the permittee to develop a monitoring plan and conduct representative sampling. The information below provides general guidance on what to include in the monitoring plan, goals and procedures for representative sampling, implementing the monitoring plan, reviewing the plan over time, and reporting to Ecology. The information here does not examine every aspect of permit requirements identified under Special Condition S5.B. Monitoring Plan. The permittee is responsible for reading the full text of the permit and complying with all applicable permit requirements.

Mapping Your Site

Prepare a map of the site. The map should be scaled large enough to easily identify places where water collects, production areas, stockpiles, buildings, and parking areas. At a minimum, the map should locate:

The map should also include nearby features of importance such as streams, lakes, or water supply wells. It may be necessary to develop more than one map in order to capture both onsite and offsite features of importance.

Identifying Monitoring Points

The monitoring plan must identify and provide basic information about each monitoring point. There must be sufficient monitoring points to provide representative sampling of all discharges onsite (see discussion on representative sampling below). Each monitoring point must be located on the site map and labeled. The label can be a name or number, but must be different for each monitoring point. This monitoring point label must be used on all monitoring information reported to Ecology. The label becomes the official identifier of the monitoring point.

The monitoring plan must provide the following information about each monitoring point:

Representative Sampling

The permittee is responsible for providing representative sampling of all discharges to ground and to surface water. Discharges to ground water include unlined ponds, infiltration trenches, and any place that water collects before draining into the ground. Surface water includes lakes, rivers, ponds, streams, inland waters, saltwaters, estuaries, wetlands, stormwater drainage systems, and all other surface waters and water courses within the jurisdiction of the state of Washington.

Sampling Not Required

Water contained in lined treatment ponds that are constructed in accordance with Permit Special Condition S.3.E.. Lined Impoundment Required, do not require monitoring. Only water released from the lined pond to ground or surface water requires monitoring.

Discharges to Ground Water

The permit requires pH monitoring of all discharges to ground water. Discharges of process water by concrete batch or asphalt batch plants must also be monitored for total dissolved solids. The monitoring program must be flexible enough to take into account there may not be sufficient water available for sampling on any given day. Providing alternative sampling times, perhaps based on the occurrence of rainfall events onsite, is a good way to avoid this shortcoming in a plan. "No Discharge" means there was no discharge to sample during the entire reporting period. Sampling practices must be flexible enough to take advantage of storm events when they happen.

pH Monitoring: The permittee is expected to conduct pH monitoring onsite. Most often this will require acquisition of a pH meter. The pH meter must be maintained and calibrated in accordance with operating instructions. All discharges to ground of process water, mine dewatering water, and stormwater must be monitored for pH. This does not mean that every place that water collects (e.g., every puddle) onsite must be sampled. It does mean that the reported pH values must be representative of the site.

Representative sampling is not an average of values and it is not a mixing of samples from several locations and then measuring the pH. It means the permittee must undertake a process to determine how many sampling sites are necessary to be representative of the site. Sampling is conducted at these representative sites.

To arrive at representative sampling, consider all the places that water typically collects. Take pH measurements at these locations and note what facility activities (SIC or NAICS codes) may impact the water. An analysis of the pH values and associated activities form the basis for determining the number of sample sites necessary for representative sampling of discharges to ground water. Consider:

  1. How similar are the contributing site conditions? If the different sample points are all from stockpile runoff, one sample point may be sufficient. If some sample points are located around the concrete batch plant and others around gravel stockpiles, then two sample points will likely be required.
  2. How similar are the pH measurements? If multiple samples all have a uniform pH value, then one sample point may be selected as representative. Uniform here means a variation of less that 0.5 pH units with no value in violation of the pH ground water limit.

The monitoring plan must include a description of how you determined what point or points to sample.

Total Dissolved Solids Monitoring (TDS): The permit requires that process water from concrete batch plants and asphalt batch plants be collected in lined ponds. All discharges of process water from the lined pond to ground must be monitored for TDS. Samples should not typically be taken directly from the lined pond. If possible, take a sample of the wastewater discharge after any additional treatment such as pH adjustment and just before it contacts ground.

Oil Sheen: The permit also requires a visual inspection for oil sheen. When water is present, there should be daily visual inspection in areas of the facility where employees and equipment are present. In portions of the facility where personnel and equipment are not active, visual inspections should be consistent with the frequency of personnel entering that area, but not less than once a month when water is present.

Discharges to Surface Water

All discharges to surface water require monitoring. While representative sampling in discharges to ground emphasized finding representative sampling points, representative sampling in surface water discharges emphasizes identification of the most appropriate time to sample (see below). Monitoring parameters include pH, turbidity, total suspended solids (process water and mine dewatering water), temperature (summer months only), oil sheen, and total dissolved solids (concrete batch process water only).

Parameters such as temperature and turbidity can vary considerably over the duration of a discharge and from one discharge event to another. Monitoring frequency can be increased (e.g., weekly, daily, continuous) to capture a complete picture of this variation or you can identify the values you are most interested in and schedule monitoring to increase the odds of measuring those values. Monitoring frequency in the sand and gravel general permit relies in part on conducting sampling at the most appropriate time.

Turbidity and TSS: Sampling should be conducted when discharge turbidity and suspended solids are likely to be greatest.

Temperature: Sampling should be conducted when discharge temperature is likely to be highest.

pH: Maximum and minimum values are of interest.

Oil Sheen: Visual examination.

TDS: Sampling should be conducted to capture the highest values.

Permit limits for pollutants in discharges are set to protect the environment. The permittee implements best management practices and treatment to assure that wastewater discharges will comply with permit limits. Monitoring is conducted to demonstrate how successful the BMPs and treatment are. In order for monitoring to make the demonstration, however, the samples must be taken when the potential for system failure is greatest. This is similar to proving that concrete meets the specified strength requirements. A representative cylinder of concrete is subjected to a cylinder compression strength test, compressed until it fails, demonstrating the strength of the concrete. The trick for monitoring is determining the best time to take a sample that will best test the effectiveness of BMPs and treatment.

Representative sampling for process water and mine dewatering water discharges should not present a difficult problem. These discharges can be easily anticipated, characteristics of discharge known, and sampling scheduled to capture a representative sample.

Discharges that result from stormwater, however, are less predictable and subject to significant variability both in quantity and quality of the discharge. Storm intensity, volume, and duration, as well as site conditions (e.g., saturation of soils, antecedent storms, increased activity, and unexpected erosion) can markedly influence the quantity and quality of stormwater. Therefore, it is recommended the permittee visually inspect the discharge during several major storm events (those 0.5 inches or more of rain in 24 hours). Pay attention to how the discharge quality (e.g., turbidity, temperature) varies over the duration of storms. Use these observations to determine the best time to obtain a representative sample and include the observations and sampling strategy in the site monitoring plan.

Laboratory Analysis

The permittee must follow accepted procedures for handling and shipping samples. If an accredited lab is used for analysis they can assist in this. They will typically provide the sampling containers and shipping materials. The permittee should make them aware of when they must submit their report to Ecology.

Discharge Monitoring Report

The permit requires that monitoring data be reported to Ecology once a quarter using the discharge monitoring report developed by Ecology. Reports must be received by Ecology no later than January 15 (October, November, December), April 15 (January, February, March), July 15 (April, May, June), and October 15 (July, August, September), for each reporting period or partial reporting period of coverage. All concrete and asphalt batch plants and all active mine sites must submit the report. (Note: All mine sites are considered active unless Ecology has received notification of inactive status.) Even if there were no discharges during the reporting period, the permittee must still file the report. Failure to report is a violation of permit conditions and can result in an enforcement action.

Periodic Plan Review

The permit requires a review of the monitoring plan on at least an annual basis. Conditions can change over time and sampling must remain representative. Periodic pH readings around the site, observations of site conditions and the visual quality of discharges are important. Even when there is no need to alter the monitoring plan, that decision and the date should be recorded in the monitoring plan.