Progress of Implementation of Nitrate TMDL for the San Lorenzo River, Santa Cruz County, California
The San Lorenzo River Total Maximum Daily Load for nitrate was the first TMDL written for a water body in the central coast region. The TMDL was first initiated in 2000, when the Central Coast Water Quality Control Board (CCWQCB) approved an amendment to the original Central Coast Basin Plan (Basin Plan). The amendment changed the Basin Plan's unrealistic nitrate concentration goal (which was so low that is was below background concentrations), to the target concentration required by a TMDL for the San Lorenzo. The CCWQCB approved the nitrate TMDL for the San Lorenzo River in September of 2000, and it was finally approved by the EPA in 2003 .
Action Taken Since TMDL Approval
Much of the implementation plan for the San Lorenzo nitrate TMDL was adopted from the existing Nitrate Management Plan (NMP), which was developed for the Basin Plan in 1995 . It was required that Santa Cruz County submit a Report on Nitrate Management Plan Implementation to the CCRWQCB in 2005, 2010, and 2020 .
In 2008, the County of Santa Cruz submitted a program status report for the Wastewater Management Plan, which included a review of the Nitrate Management Plan's progress. Implementation of the NMP was expected to reduce nitrate levels by 15-20% from 1995-2005, followed by a reduction of 10% in the next 10 years. Observed nitrate trends show that reductions are occurring slower than desired, with an 11% decrease over the past 15 years. Cen Lomons and Boulder Creek sites has experienced significant reductions of up to 60%. The report suggested that "no significant adverse impacts resulting from nitrate loading at the current level have been identified".
The following nitrate reduction measures have been directly taken from the program status report:
===Manage Wastewater Disposal for Nitrogen Reduction=== 
- Maintain the existing requirement of a one acre minimum parcel size for new development served by septic systems in the San Lorenzo Watershed (Ongoing)
- Implement improved wastewater disposal management through the San Lorenzo Wastewater Management Plan (Ongoing).
- Complete ongoing efforts to improve treatment procedures at Boulder Creek Country Club Treatment Plant to reduce nitrate discharge by using wastewater reclamation on the golf course. (The treatment process was refined and fully operational by May 1998. The improvements provide for treatment for nitrogen removal, with the possibility of wastewater reclamation on the golf course much of the year. Effluent has generally not been used for reclamation on the golf course, due to strict regulations. However, the effluent that is delivered to leachfields for disposal has significantly lower nitrogen levels. Nitrogen levels in Boulder Creek are 60% less than the levels from the mid 1990’s. )
- Maintain the new requirement for shallow leachfields for new and repaired septic systems (less than 4 feet in sandy areas, and 4-6.5 feet in other areas). (Ongoing)
- Implement enhanced technology for at least 50% nitrogen removal for septic system in sandy soils:
- Require septic systems serving new or expanded uses in sandy soils to install enhanced treatment measures which will reduce nitrogen discharge by at least 50%. (Implemented August 1995; existing systems to be upgraded at the time of major remodels (originally projected rate of 1.2% (20 systems) per year is actually 0.3%, or 5.25 systems per year over the past 12 years).)
- Encourage the use of nitrogen removal methods for any onsite disposal system which will use a nonstandard system. (Since 1995, 245 alternative systems with capability for nitrogen removal have been approved for use in the San Lorenzo Watershed: 15 sand filters, 63 Advantex Systems, and 167 FAST systems. The 61 systems installed in sandy soils will reduce the summer nitrate load from sandy areas by 6%.)
- Continue to evaluate new onsite wastewater disposal technology for nitrogen reduction to identify more cost-effective measures. Require higher levels of nitrogen removal if measures become available that are more cost-effective than sand filters. (Some new technology is becoming available, but the cost continues to be high.)
- Apply for State revolving funds and other funds to develop a funding source to assist property owners in repairing their systems to provide enhanced treatment. (Revised program is now being implemented, beginning June 2005. This could fund 100 upgrades over the next five years, although only 7 loans have been applied for in the past 2 years.)
- When more cost-effective technology and/or funding assistance becomes available, require all onsite system repairs in sandy areas to utilize enhanced treatment for nitrogen removal. (Implementation deferred, pending more inexpensive technology and documented need for further nitrogen reduction.)
Livestock Management for Nitrogen Reduction
- Continue to work with stable owners and develop a new ordinance requiring practices to reduce nitrate discharge: cover manure piles, maintain manure piles and paddock areas at least 50-100 ft from streams or drainageways, direct drainage away from paddock areas, and provide other measures as necessary to reduce discharge of nitrate, sediment, and contaminants. (Ongoing, after meetings with stable and horse owners, it was decided to pursue an approach of education, technical assistance, and voluntary compliance. A grant funded effort by the Resource Conservation District and Ecology Action got underway in 2001 and continues with new grant funds. This program has provided for 9 pilot projects implemented in the watershed, 13 area workshops, 30 site visits for technical assistance in the watershed, and significant outreach to the Horsemen’s Association and horse owners. All new or modified horse operations now prepare and implement manure management plans to reduce the runoff or percolation of nitrate)
Land Use Regulations for Nitrogen Reduction
- Maintain current density restrictions requiring 10 acres per parcel for new land divisions and other protective measures for groundwater recharge areas. (Ongoing)
- Maintain current regulations on erosion control, land clearing, and riparian corridor protection. (Ongoing)
- Do not approve new land use projects within the San Lorenzo Watershed which will increase the discharge of nitrate to groundwater or surface water by more than 15 pounds of nitrogen per acre per year from the project area. (Ongoing; a proposal to construct playing fields in the Quail Hollow area was not approved partly due to concerns over discharge of fertilizers and other chemicals.)
Ongoing Monitoring of Nitrogen Sources
- Monitor the Scotts Valley nitrate plume, and identify potential ongoing sources of nitrate. Work with the City of Scotts Valley and property owners for reduction of nitrate discharge from Scotts Valley, if feasible. (Ongoing monitoring, nitrate concentrations seems to be diminishing by 30%).
- Continue to monitor nitrate levels in surface and groundwater. Reevaluate implementation of more stringent control measures if summer nitrate levels in the River have not declined by at least 15% by 2010. (Ongoing monitoring, reevaluation in 2010).
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- CCRWQCB. 2000. Resolution No. 00-003
- CCRWQCB. 2000. Staff report for regular meeting for September 15, 2000: San Lorenzo River nitrate Total Maximum Daily Load. State of California: 1-32.
- CCRWQCB. 2000. Nitrate Total Maximum Daily Load for San Lorenzo River, Carbonera Creek, Shingle Mill Creek, and Lompico Creek. State of California: 1-44. http://www.waterboards.ca.gov/centralcoast/water_issues/programs/tmdl/docs/san_lorenzo/nitrate/slr_nitrate_tmdl_proj_rpt.pdf
- Santa Cruz County. 2008. San Lorenzo wastewater management plan: program status report 2002-2007. 1-28.
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