When it comes to communicating “best management practices” (BMPs) for sand mines, Louisiana sets the gold standard. The Louisiana Department of Environmental Quality (LDEQ) and the Concrete & Aggregate Association of Louisiana, Inc. worked together to develop BMPs. Their goals: to reduce the amount of sediment and turbidity in streams and rivers that result from sand and gravel mining and to improve water quality.
This guide represents a realistic and open approach, which I appreciated. It’s also concise, candid and clearly written. For those who don’t have time to read the entire 41-page document, a summary follows, especially of the parts that talk about sedimentation. I’ve inserted several images from the East and West Forks of the San Jacinto to contrast practices in Texas and Louisiana.
Importance of Sand and Gravel to Economy
The Introduction discusses the importance of aggregate (sand and gravel) to the Louisiana economy. Sand and gravel are essential resources for construction. In fact, they represent Louisiana’s second most valuable non-fuel natural resource.
Almost half (48%) of all the aggregate produces concrete. The second largest use (22%) is as a base material for highways, railways, runways, etc.
Types of Mining
The document then discusses different techniques of mining: dry (by excavation) and wet (by dredging). Louisiana focuses primarily on wet, which is the type of mines we have along the San Jacinto with a few exceptions.
Importance of Storm Water Management
Page 4 contains a discussion of “Non-point Source Storm Water Management.” Non-point essentially means from rain, runoff and flooding. It occurs across an entire area as opposed to a specific point, such as a leaky fuel tank. Some key quotes:
“Sand and gravel mining operations can potentially cause off-site impacts to water quality if site planning and BMPs (Best Management Practices) are not factored into every aspect of the mining operation.”
“Sand and gravel mining operations disturb land and soil…”
“Good site planning and operation can reduce the likelihood of sediments moving off of the operation…”
“The purpose of the BMP Manual is to provide information on the types of BMPs that should be utilized during every phase of the mining operation in order to prevent pollutants from leaving the mining operation.”
Dangers of Not Following BMPs
Page 5 discusses the dangers if miners do not follow best management practices.
“Siltation is considered the highest nonpoint source priority of concern in wetland areas and the second highest priority affecting lakes (1992 Report to Congress). Mining related activities have been estimated to cause 7 percent of the nation’s nonpoint source impacts to lakes and 17 percent to coastal waters. Sediments from mining operations could consist primarily of biologically inert materials which could potentially adversely affect the water body’s designated uses. Inert suspended sediments have the following detrimental impacts to the aquatic habitat:
- Sediments smother lower forms of aquatic life in the bottom of a stream. This can destroy the aquatic life in a stream because it kills the food supply. If sedimentation continues with a high concentration of suspended solids, the stream will fail to recover. Sediment deposition may also cover fish eggs and break the life cycle; thereby, destroying the fishery uses of the stream;
- A continued cloudy condition of a stream will deter its use for almost all recreational purposes;
- Directly or indirectly, it can change the characteristics of a stream channel and in many instances can limit boat usage and cause additional flooding hazards;
- In rivers that are utilized for drinking waters, silt creates an additional expense upon the water treatment and purification process for both domestic and industrial users; and
- It decreases photosynthetic action and thereby reduces the capacity of a stream to assimilate organic matter.”
Recommendations for Soil Conservation
Page 11 marks the start of the discussion about specific BMPs. The first BMP addresses soil conservation. “Sediment loads discharged to streams must be minimized, if not eliminated altogether,” they say. “There are basically two types of controls: vegetative and structural.”
Streambank BMP Recommendations
Regarding the Streambank Best Management Practice (BMP), they say: “When native vegetation is used to maintain streambanks, there are many benefits provided to the public and environment. Near the waters’ edge, herbaceous and wetland plants help filter pollutants from the water and prevent bank erosion during high flow periods. These plants also provide habitat for fish and natural predators of mosquitoes as well as increasing aesthetical appeal. Spatial balance between native trees and shrubs on the streambank provides stability and shading. Shading from trees lowers water temperature and improves water quality by conserving the oxygen in the water.”
Note the images below. The first represents the ideal and was pulled from the Louisiana BMP guide. The others are from sand mines on the West Fork of the San Jacinto and Caney Creek in Texas.
Reducing Erosion through Vegetation
“Vegetation is an inexpensive and effective way to protect soil from erosion,” Louisiana says. “It also decreases erosion from flowing water by reducing its velocity. Roots hold soil and increase infiltration. Topsoil should be added where existing soils are not suitable for adequate vegetative growth.”
Vegetative controls include:
- Maintaining buffer zones between mine and river
- Sod stabilization techniques
- When installed and maintained properly, sodding can be more than 99 percent effective in reducing erosion.
- Protection of trees involves preserving and protecting selected trees that exist on the site prior to development.
- Tillage, with lime and fertilizer, to maintain adequate soil pH and nutrient content.
- Temporary seeding
- Permanent seeding
- Erosion & Sediment Control Blankets
- Surface Roughening – Creating horizontal grooves across the slope to reduce runoff velocity/erosion and aid the growth of seed.
Structural Ways to Reduce Erosion
Structural controls include:
- Diversion ridges, berms or channels of stabilized soil
- Silt fences
- Straw bale barriers
- Sediment basins with banks sloped at 2:1 or less
- Dikes – Must be well compacted and vegetated, with an outlet pipe or coarse aggregate spillway
- Riprap protection – at the outlet end of culverts or channels to reduce the depth, velocity and energy of water so that the flow will not erode the receiving stream.
- Check dams – Small dams less than 2 feet high constructed across swales or drainage ditches to reduce flow velocity and erosion.
- Aggregate stabilized site entrances – at least 50 feet long to reduce sediment tracked onto public roads. Tire washing may also be needed.
- Good housekeeping practices for fuel, debris, sediment from unstabilized areas, etc.
- Post-construction stormwater management measures
- Retention ponds
- Vegetated swales and natural depressions that filter sediments from runoff with side slopes of 4:1 or less.
Best Management Practices for Land Clearing
Regarding land clearing, Louisiana recommends:
- Disturbed areas should be temporarily stabilized or covered as soon as possible to minimize impacts on the environment.
- Only clear acreage needed for immediate use. Clearing or grubbing too much land too early in the construction phase of the mining operation will dramatically increase the potential for environmental impacts from surface water runoff and will increase the costs to control runoff.
- Allow enough undisturbed buffer at property boundaries to provides sufficient lateral support of property lines.
- A minimum 100-foot buffer zone is required adjacent to perennial streams and water bodies in the State of Louisiana.
Site Reclamation Goals and Best Management Practices
Pages 28-31 describe best practices for site reclamation. Goals include:
- Stabilization of inactive mining pit or borrow areas with herbaceous perennial plants
- Stabilizing the soil
- Preventing wind or water erosion from causing on-site or off-site damage
- Improving the aesthetic appeal
- Ability of the site to support wildlife
Best management practices include:
- Revegetation, mulching
- Grading slopes 3:1 to facilitate seeding
- Constructing diversions at tops of slopes to divert runoff away from the slope banks to a stable outlet
- Constructing aggregate lined chutes or equivalent to conduct concentrated flow of water to stable outlets
- Reclamation of abandoned roads by reshaping, recontouring, and resurfacing with topsoil and seeding for vegetative growth
- Removal of structures
- Removal of sand stockpiles
- Removal of debris
- Grading property to minimize potential impact to waterways
Education Better Than Damage Control
In the conclusion on Page 32, Louisiana states:
“One of the best ways to mitigate environmental impacts from the sand and gravel industry in Louisiana is to establish a set of voluntary best management practices for the industry to adhere. This can be accomplished by initiating good management practices, educating our operators, and taking a more proactive stance in minimizing the problems of the past that have hurt this industry’s image. We, as industry leaders, need to be actively engaged in addressing issues and taking precautions and preemptive measures. Damage control after the fact is destructive. The world is changing and we must be adaptive to these changes – good management practices in an environmentally friendly manner are synonymous with good business practice.”
I’m sure Louisiana has problems just like Texas. But I sure do like the tone of this and what they are trying to accomplish. If Texas has a similar initiative, I can’t find it.
Posted 8/19/18 by Bob Rehak
355 days since Hurricane Harvey